CN102571801A - High speed media access control and direct link protocol - Google Patents
High speed media access control and direct link protocol Download PDFInfo
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- CN102571801A CN102571801A CN2012100148758A CN201210014875A CN102571801A CN 102571801 A CN102571801 A CN 102571801A CN 2012100148758 A CN2012100148758 A CN 2012100148758A CN 201210014875 A CN201210014875 A CN 201210014875A CN 102571801 A CN102571801 A CN 102571801A
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Abstract
The present invention discloses a technology used for MAC processing in order to effectively utilize a high-throughput system and to be compatible with various traditional systems. In one aspect, data frames are formed, the data frames comprise a common portion, the common portion is used for transmission in a format capable of being received by various stations such as access point and remote station. The data frames also comprise a special portion, the special portion is formatted and used for the transmission of a specific remote station. In another aspect, the common portion is unguided and the special portion is guided. In a third aspect, access point response data indication performs scheduling on distribution, the data indication is contained in the common portion of the data frames transmitted from one remote station to another station. In a fourth aspect, a first station transmits a reference to a second station, and the second station performs measurement on the reference and generates a feedback according to the measurement.
Description
The application be submitted on October 15th, 2004, application number is 200480037333.6, name is called dividing an application of ' high speed media access control and direct link agreement '.
Priority request according to 35U.S.C § 119
Present patent application requires the priority of following U.S. temporary patent application, and these U.S. temporary patent applications comprise:
The exercise question of submitting on October 15th, 2003 is the provisional application No.60/511 of " Method and Apparatus forProviding Interoperability and Backward Compatibility in WirelessCommunication Systems (in wireless communication system, being used to provide the method and apparatus of interoperability and backwards compatibility) ", 750;
The exercise question that on October 15th, 2003 submitted to is the provisional application No.60/511 of " Method; Apparatus; and Systemfor Medium Access Control in a High Performance Wireless LANEnvironment (methods, devices and systems that in the high performance radio local area network environment, are used for the medium access control) ", 904;
The exercise question that on October 21st, 2003 submitted to is the provisional application No.60/513 of " Peer-to-Peer Connections inMIMO WLAN System (equity in the MIMO wireless lan system connects) ", 239;
The exercise question that on December 1st, 2003 submitted to is the provisional application No.60/526 of " Method; Apparatus; and Systemfor Sub-Network Protocol Stack for Very High Speed Wireless LAN (methods, devices and systems that are used for the Subnetwork protocol stack of ultrahigh speed WLAN) ", 347;
The exercise question of submitting on December 1st, 2003 is the provisional application No.60/526 of " Method and Apparatus forMultiplexing Protocol data Units in a High Performance Wireless LANEnvironment (method and apparatus that in the high performance radio local area network environment, is used for multiplexing protocol data units) ", 356;
The exercise question that on December 23rd, 2003 submitted to is the provisional application No.60/532 of " Wireless CommunicationsMedium Access Control (MAC) Enhancements (wireless communication media access control enhancing) ", 791;
The exercise question that on February 18th, 2004 submitted to is the provisional application No.60/545 of " Adaptive Coordination Function (ACF) (self adaptation coordination function) ", 963;
The exercise question of submitting on June 2nd, 2004 is the provisional application No.60/576 of " Method and Apparatus for RobustWireless Network (method and apparatus that is used for the robust wireless network) ", 545;
The exercise question of submitting on July 8th, 2004 is the provisional application No.60/586 of " Method and Apparatus forDistribution Communication Resources Among Multiple Users (method and apparatus that is used for allocate communications resource between a plurality of users) ", 841; And
The exercise question that on August 11st, 2004 submitted to is the provisional application No.60/600 of " Method, Apparatus, and Systemfor Wireless Communications (being used for method of wireless communication, device and system) ", 960;
All these provisional application have transferred the application's assignee, thereby clearly it are incorporated herein by reference.
Technical field
The present invention relates generally to communication, more specifically, relate to the medium access control.
Background technology
Widespread deployment wireless communication system, so that the various types of communications such as voice-and-data to be provided.Typical radio data system or network are the access that a plurality of users provide one or more shared resources.A system can use multiple multi-access technology, like frequency division multiplexing (FDM), Time Division Multiplexing, code division multiplexing (CDM) etc.
Example wireless network comprises the data system based on honeycomb.Below be some such examples: (1) " TIA/EIA-95-B Mobile Station-Base Station CompatibilityStandard for Dual-Mode Wideband Spread Spectrum Cellular System (the TIA/EIA-95-B travelling carriage-base station compatible standard that is used for dual mode wideband spread spectrum cellular) " (IS-95 standard); (2) standard that provides by " 3rd Generation Partnership Project (third generation cooperative programme) " association (3GPP) by name, this standard is incorporated in (W-CDMA standard) in the group file that comprises file Nos.3G TS 25.211,3G TS 25.212,3G TS 25.213 and 3G TS 25.214; (3) standard that provides by " 3rd GenerationPartnership Project 2 (third generation cooperative programme 2) " association (3GPP2) by name, this standard is incorporated in " TR-45.5 Physical Layer Standard for cdma2000Spread Spectrum Systems (the TR-45.5 physical layer standard that is used for the cdma2000 spread spectrum system) " (IS-2000 standard); And (4) meet high data rate (HDR) system of TIA/EIA/IS-856 standard (IS-856 standard).
Other example of wireless system comprises the wireless lan (wlan) such as IEEE 802.11 standards (i.e. 802.11 (a) and (b) or (g)).Improvement on these networks can comprise that many inputs majority of OFDM (OFDM) modulation technique goes out (MIMO) WLAN and realizes through employing.Proposed IEEE 802.11 (e), improved on some shortcomings with former 802.11 standards.
Along with the progress of wireless system design, can utilize higher data rate.Higher data rate has been opened and has been comprised that voice, video, rapid data transmit and the possibility of the ADVANCED APPLICATIONS of various other application.Yet various application can have for they data transmission different requirement separately.Polytype data can have time-delay and throughput requirement, perhaps need some service quality (QoS) to guarantee.If there is not resource management, the capacity of system possibly reduce, and system may not move efficiently.
Medium access control (MAC) agreement is often used in distributing shared communication resource between a plurality of users.The MAC agreement usually will be more high-rise be carried out interface with the physical layer that is used to transmit and receive data.In order from data rate increases, to be benefited, must design the MAC agreement to utilize shared resource efficiently.Usually, also the interoperability with optional or conventional communications standards is kept in expectation.Therefore, need utilize the MAC of high throughput systems to handle in this area efficiently.Also need this MAC to handle in this area and keep backward compatibility with various types of legacy systems.
Summary of the invention
For efficiently utilize high throughput systems and with various types of legacy system backward compatibility, embodiment disclosed herein has proposed the demand that MAC handles.On the one hand, the composition data frame, this Frame comprises public part, and this public part is used for transmitting with the form that the various stations such as access point and distant station can receive.Frame also comprises private part, and this private part is formatd, and is used for the transmission of particular remote station.In another aspect, access point response data indication is dispatched distribution, and this data indication is included in from a distant station and sends to the public part of Frame of another distant station.
In another aspect, first stop will be with reference to sending to second station, and second station is to feeding back with reference to measuring and generating in view of the above.Under situation about receiving from the feedback at second station, first stop sends to second station according to feedback with data.Various others have also been proposed.
The accompanying drawing summary
Fig. 1 is the exemplary embodiment that comprises the system of high speed WLAN;
Fig. 2 has provided the exemplary embodiment of Wireless Telecom Equipment, can be access point or user terminal with this wireless communications device configurations;
Fig. 3 has provided 802.11 frame pitch parameters;
Fig. 4 has provided an exemplary physical layer (PHY) span line, is used for explaining that using DIFS to add back off time according to DCF inserts;
Fig. 5 has provided an exemplary physical layer (PHY) span line, is used for explanation and before ACK, uses SIFS, and it has than the higher priority of DIFS access;
Fig. 6 shows big packet fragmentation is become little fragment, and the latter has the SIFS that is associated;
Fig. 7 has provided an exemplary physical layer (PHY) span line, is used to explain that every frame all has the TXOP of affirmation;
Fig. 8 shows has the TXOP that piece is confirmed;
Fig. 9 has provided an exemplary physical layer (PHY) span line, is used to explain the poll TXOP that uses HCCA;
Figure 10 is the exemplary embodiment of TXOP, and it comprises a plurality of continuous transmission that has no the gap;
Figure 11 is the exemplary embodiment of TXOP, is used for explanation and reduces required preamble transmissions amount;
An exemplary embodiment of the method that Figure 12 shows various aspects integrated, it comprise gather lead code, deletion such as SIFS the gap and insert GIF as required;
Figure 13 has provided an exemplary physical layer (PHY) span line, is used for explanation and gathers poll frame and corresponding TXOP;
Figure 14 has provided an illustrative methods that is used to gather poll frame;
Figure 15 has provided an exemplary mac frame;
Figure 16 has provided an exemplary MAC PDU;
Figure 17 has provided an exemplary point to point link;
Figure 18 shows the physical layer bursts of a prior art;
Figure 19 has provided an exemplary physical layer bursts, and it can be used for point to point link;
Figure 20 has provided an exemplary embodiment of mac frame, and it comprises optional self-organizing section;
Figure 21 has provided an exemplary physical layer bursts;
Figure 22 shows an exemplary point-to-point data transmission method;
Figure 23 has provided an exemplary point to point link method;
Figure 24 has provided and has been used for connecting the illustrative methods that Rate Feedback is provided at point-to-point;
The point-to-point of being managed that Figure 25 shows between two stations and the access point connects;
The point-to-point that Figure 26 shows based on competition (or self-organizing) connects;
Figure 27 has provided an exemplary mac frame, is used to explain the point to point link of being managed between the station;
Figure 28 shows and on identical Frequency Distribution, supports tradition and novel station;
Figure 29 shows tradition and new media access control is combined;
Figure 30 has provided a kind of illustrative methods of getting transmission opportunity;
Figure 31 has provided a kind of illustrative methods of sharing single FA with a plurality of BSS;
Figure 32 shows the overlapping BSS that uses single FA;
Figure 33 provided with traditional B SS interoperability in carry out a kind of illustrative methods of high speed point to point link;
Figure 34 shows the point to point link that uses the MIMO technology, and it competes access on traditional B SS;
Figure 35 shows one or more mac frames (fragment) is encapsulated in the aggregate frame;
Figure 36 shows a traditional M AC frame;
Figure 37 shows an exemplary decompressed frame;
Figure 38 has provided an exemplary condensed frame;
Figure 39 has provided another exemplary condensed frame;
Figure 40 has provided an exemplary polymerization stem;
Figure 41 has provided an exemplary embodiment of the scheduling access period frame (SCAP) that in ACF, uses;
How Figure 42 shows SCAP and HCCA and EDCA is combined use;
Figure 43 shows beacon interval, comprises a plurality of SCAP, has inserted the access period based on competition therebetween;
Figure 44 shows the low delay operation of adopting a large amount of MIMO STA;
Figure 45 has provided an exemplary SCHED message;
Figure 46 has provided an exemplary power management field;
Figure 47 has provided an exemplary MAP field;
Figure 48 has provided and has been used for the exemplary SCHED control frame that TXOP distributes;
Figure 49 shows a traditional 802.11PPDU;
Figure 50 has provided an exemplary MIMO PPDU who is used for transfer of data;
Figure 51 has provided an exemplary SCHED PPDU;
Figure 52 has provided an exemplary FRACH PPDU; And
Figure 53 show can with another embodiment of the method for legacy system interoperability.
Embodiment
The very high bit rate physical layer of combining wireless LAN (perhaps, using the similar application of emerging transmission technology) discloses the exemplary embodiment of supporting efficient operation.This example WLAN supports to surpass the bit rate of 100Mbp (MBPS) in the 20MHz bandwidth.
Various exemplary embodiments have kept the simplicity and the robustness of the distributed collaboration operation of traditional wlan system, can in 802.11 (a-e), find the example of these traditional wlan systems.Can realize the advantage of various embodiment, keep backward compatibility simultaneously with these legacy systems.(should be noted in the discussion above that in the explanation below, is exemplary legacy system with 802.11 system descriptions.Those skilled in the art will find that these improve same and other system and operating such.)
A kind of exemplary WLAN can comprise the Subnetwork protocol stack.The Subnetwork protocol stack can be supported the physical layer transmission mechanism of high data rate, high bandwidth usually, including, but not limited to: based on the mechanism of OFDM modulation; The single-carrier modulated technology; Use system's (multiple-input and multiple-output (MIMO) system comprises the single output of many inputs (MISO) system) of a plurality of emissions and a plurality of reception antennas, be used for the very operation of high bandwidth efficiency; Thereby a plurality of antenna and space multiplexing technique of transmitting and receiving are combined in the identical time interval and to receive the system of data to a plurality of user terminal to transmit data or from a plurality of user terminals; Employing code division multiple access (CDMA) technology realizes a plurality of users system for transmitting simultaneously.Other example comprises single many outputs of input (SIMO) and the single output of single input (SISO) system.
One or more exemplary embodiment given here is launched to introduce to the wireless data communication system environment.Though preferably in this environment, use, also can different embodiments of the invention be applied to different environment or configuration.Generally, processor, integrated circuit or the discrete logic of various systems described herein available software control are realized.Data, instruction, order, information, signal, symbol and the chip that runs through the application preferably makes up with voltage, electric current, electromagnetic wave, magnetic field or particle, light field or particle or its to be represented.In addition, the module shown in every width of cloth block diagram can be represented the step of hardware or method.Under the situation that does not depart from protection range of the present invention, the step of method can be exchanged." exemplary " used herein speech means " as example, illustration or explanation ".Here any embodiment that is described to " exemplary " should not be interpreted as than other embodiment more preferably or have more advantage.
Fig. 1 is an exemplary embodiment of system 100, and it comprises an access point (AP) 104, is connected to one or more user terminals (UT) 106A-N.Consistent with 802.11 terms, in this article, AP and UT also are called as the station, or STA.AP and UT communicate via wireless lan (wlan) 120.In this exemplary embodiment, WLAN120 is a high speed MIMO ofdm system.But WLAN 120 also can be any WLAN.Access point 104 communicates with any amount of external equipment or process via network 102.Network 102 can be the Internet, Intranet or any other wired, wireless or optical-fiber network.Connect 110 physical layer signal is sent to access point 104 from network.Equipment or process can be connected to network 102, perhaps, and as the UT on the WLAN 120 (or via with its be connected).The example of the equipment that can be connected with network 102 or WLAN 120 comprises: phone; PDA(Personal Digital Assistant); Various types of computers (terminal of laptop computer, PC, work station, any kind); Video equipment is like camera, video camera, network camera; And, the data equipment of any other type.Process can comprise sound, video, data communication etc.Various data flow possibly have different transmission demand, and these can be met through using different service quality (QoS) technology.
System 100 can use a centralized AP 104 to dispose.In an exemplary embodiment, all UT 106 communicate with this AP.In another embodiment, can between two UT, carry out direct point to point link, and need not the modification system, this is conspicuous to those skilled in the art, will describe its example below.Access can be managed by AP, or (that is, based on what compete) of self-organizing, will be elaborated to this below.
In one embodiment, AP 104 provides Ethernet to adapt to.In this case, except that AP, can also dispose an ip router, with the connection (not showing its details here) that is provided to network 102.Ethernet frame can pass through the WLAN subnet, transmission (below will specify) between router and UT106.It is the known technology in this area that Ethernet adapts to being connected.
In another embodiment, AP 104 provides IP to adapt to.In this case, for the set that connects UT (not showing its details), AP serves as a gateway router.In this case, AP 104 can be routed to UT 106 with IP datagram, and, the IP datagram from UT 106 is carried out route.It is the known technology in this area that IP adapts to being connected.
Fig. 2 has provided an exemplary embodiment of Wireless Telecom Equipment, and this Wireless Telecom Equipment can be configured to access point 104 or user terminal 106.Fig. 2 shows the configuration of access point 104.Transceiver 210 is connecting reception and transmission signal on 110 according to the physical layer requirement of network 102.From or the data sent out to equipment that is connected with network 102 or application be passed to mac processor 220.These data are called as stream 260 here.Stream possibly have different characteristic, and, based on the type of the application that is associated with this stream, possibly need different processing.For example, video or speech can be called as low delay stream (video has higher throughput than speech usually and requires).A lot of data are used time-delay not too responsive, require (that is, losing of some groupings can be tolerated in speech, but file transfer can't stand losing of grouping usually) but possibly have higher data integrity.
In one exemplary embodiment, adaptation layer (ADAP) and data link control layer (DLC) are carried out in mac processor 220.Physical layer (PHY) is carried out on WLAN transceiver 240.One skilled in the art will appreciate that and under arbitrary configuration, to carry out cutting apart of various functions.Mac processor 220 can be carried out a part of or whole of physical layer process.The WLAN transceiver can comprise a processor, is used to carry out MAC and handles or its part.Can adopt any amount of processor, specialized hardware or its combination.
Except storage is used to carry out the instruction and data of function described here, memory 255 also can be used to store the data that are associated with individual queue.
WLAN transceiver 240 can be the transceiver of any kind.In an exemplary embodiment, WLAN transceiver 240 is OFDM transceivers, and it can utilize MIMO or the work of MISO interface.To those skilled in the art, OFDM, MIMO and MISO are known.The U.S. Patent application No.10/650 common co-pending that is entitled as " FREQUENCY-INDEPENDENT SPATIAL-PROCESSING FORWIDEBAND MISO AND MIMO SYSTEMS (the frequency separate space that is used for broadband MISO and mimo system is handled) " that on August 27th, 2003 submitted to; In 295; Described OFDM, MIMO and the MISO transceiver of various exemplary, this application has transferred assignee of the present invention.Other embodiment can comprise SIMO or SISO system.
Shown WLAN transceiver 240 is connected with antenna 250A-N.In various embodiment, can support any amount of antenna.Antenna 250 can be used on WLAN 120, send and receive signal.
WLAN transceiver 240 can comprise with one or more antennas 250 in each spatial processor that is connected.This spatial processor can be handled the data that each antenna will send independently, perhaps, the signal that receives on all antennas is carried out Combined Treatment.The example of independent process can be based on channel estimating, feedback, channel switch (channelinversion) or multiple other technologies as known in the art from UT.This processing is to use one of any execution in the multiple spatial processing technique.A plurality of such transceivers can use wave beam formation, beam steering (beam steering), characteristic guiding (eigen-steering) or other space technologies, improve and send out to the throughput of a given user terminal with from the throughput of a given user terminal.In an exemplary embodiment of wherein sending the OFDM symbol, this spatial processor can comprise a plurality of subspaces processor, is used for handling each OFDM subchannel or drawer (bin).
In one exemplary embodiment, this AP can have N antenna, and an exemplary UT can have M antenna.Therefore, the MxN paths is arranged between the antenna of this AP and this UT.In the art, the various space technologies of using said mulitpath to improve throughput all are known.In a kind of space-time emission diversity (STTD) system (here, also be called as " divide collection "), the transmission data are formatd and encode, then, go out through all antenna transmission as individual traffic.Use M transmitting antenna and N reception antenna, can form MIN (M, N) individual independent channel.Spatial reuse utilizes these independent pathways, and can on these independent pathways, send different data, thereby improves transmission rate.
The various technology that are used to learn and adapt to the characteristic of channel between AP and the UT are known.Can send unique pilot signal from each transmitting antenna.Receive and measure these pilot signals at each reception antenna place.Then, can the channel condition information feedback be returned to transmitter, for use in transmission.Can carry out the feature decomposition of measured channel matrix, to confirm the channel characteristics pattern.Another kind avoids in receiver, carrying out the technology of the feature decomposition of channel matrix, uses the characteristic guiding of pilot signal and data, comes the spatial manipulation in the simplified receiver.
Therefore, according to current channel status, the transmission for each user terminal in system can provide different data rates.Particularly, the concrete link between AP and each UT has more high-performance than multicast link or broadcasting link, and multicast link or broadcasting link can be shared from AP to above UT.Further the example of this respect is elaborated below.Use which kind of spatial manipulation based on the physical link between AP and each UT, WLAN transceiver 240 can be confirmed supported speed.This information can feedback through connecting 280, handles to be used for MAC.
The quantity of antenna can be disposed according to the demand data of UT and size and form factor.For example, because its high bandwidth requirement, the high definition video display can comprise for example four antennas; And PDA has two antennas just can satisfy.An exemplary access point can have four antennas.
Can dispose user terminal 106 through the mode similar with access point shown in Figure 2 104.Not to let stream 260 be connected to the LAN transceiver (although UT can comprise such transceiver; Be wired or wireless); Stream 260 normally from UT be attached thereto one or more application that the equipment that connects works or handle receive, or be delivered to UT or be attached thereto the one or more application or the processing of working on the equipment that connects.The high level that is connected with AP 104 or UT 106 can be an any kind.Layer described herein only is illustrative.
Traditional 802.11MAC
As stated, in order to keep compatible, can adopt various embodiment described herein with legacy system.IEEE 802.11 (e) function is gathered (with 802.11 standards maintenance backward compatibility early) and is comprised the various functions that will sum up in this joint, and in the function of introducing in the standard morning.For the detailed description of these functions, please refer to corresponding IEEE 802.11 standards.
802.11 basic MAC comprise distributed coordination function (DCF) and the some collaboration feature (PCF) of avoiding (CSMA/CA) based on carrier sense multiple/conflict.DCF can insert medium under the situation that does not have central authorities' control.In AP, use PCF, thereby centralized control is provided.For fear of conflict, DCF and PCF utilize the various gaps between the transmission continuously.Transmission is called as frame, and the gap between the frame then is called as frame pitch (IFS).Frame can be user data frame, control frame or management frames.
The type of frame pitch duration according to the insertion gap changes.Fig. 3 shows 802.11 frame pitch parameters: short frame pitch (SIFS), some frame pitch (PIFS) and DCF frame pitch (DIFS).Note that SIFS＜PIFS＜DIFS.Therefore, compare, be positioned at the transmission afterwards of shorter duration and will have higher priority with before attempting access channel, waiting for the transmission of long period.
According to carrier sense (CSMA) function of CSMA/CA, when at least one DIFS detected channel for the free time in the duration, stand (STA) can obtain the access right of channel.(employed here term " STA " can refer to an access any station of WLAN, and can comprise access point and user terminal).For fear of conflict, except that DIFS, each STA also waits for a back off time (backoff) of selecting at random, then could access channel.STA with longer back off time will be noted that when high priority STA begins on channel, to send, and has therefore avoided conflicting mutually with this STA.(STA of each wait can reduce it with its corresponding back off time and listen to the time quantum of waiting for before other transmission on this channel, thereby keeps its relative priority).Therefore, avoid (CA) function according to the conflict of this agreement, STA keeps out of the way a random time section between [0, CW], and wherein selecting CW at first is CWmin, increases factor 2 when conflicting, till maximum CWmax at every turn.
Fig. 4 has provided an exemplary physical layer (PHY) span line 400, is used for explaining that how to use DIFS to add back off time according to DCF inserts.Existing transmission 410 busy channels.In this example, when transmission 410 stopped, the more access of high priority did not appear, so, after DIFS and the back off time that is associated, begin new transmission 420.In the discussion below, suppose that the STA that carries out transmission 420 has obtained this transmission opportunity through competition in this case, to be used for transmission.
Only expecting that a specific STA makes current transmission in the frame sequence of response, using SIFS.For example, when sending an affirmation (ACK) in response to the Frame of receiving, can receive that data send this ACK after adding SIFS immediately.Other transfer sequence also can use SIFS between frame., a request during SIFS, can follow a clear to send (CTS) frame after sending (RTS) frame, then, transmission data during SIFS that can be after CTS, after this, the SIFS after data can follow an ACK.As stated, these frame sequences all are interspersed with SIFS.The SIFS duration can be used for: (a) detect the energy on the channel, and judge whether energy exhausts (that is channel clear); (b) if having time previous message is decoded and judge whether the ACK frame shows that transmission is received by correct; And (c) STA lets transceiver switch to emission and switch to reception from emission from reception if having time.
Fig. 5 has provided an exemplary physical layer (PHY) span line 500, is used for explaining how before ACK, to use SIFS, and it inserts than DIFS has higher priority.An existing transmission 510 takies this channel.In this example, when transmission 510 stops,, transmission 510 followed ACK 520 when finishing a back SIFS.Note that ACK 520 began at the expiration at DIFS, so any other STA that attempts to win transmission opportunity can be not successful.In this example, ACK 520 the more access of high priority do not occur after finishing, so, after DIFS and the back off time that is associated, begin new transmission 530, if any.
RTS/CTS frame sequence (except flow control function is provided) can be used to improve the protection to data frame transfer.RTS and CTS comprise the duration information of subsequent data frame and ACK and any middle SIFS.Listen to the STA of RTS or CTS and on their network allocation vector (NAV), mark the shared duration, and in this duration, medium are regarded as busy.Usually, utilize RTS/CTS, the frame longer than designated length can be protected, and short frame is sent out away under the unprotect situation.
PCF can be used to make AP that the centralized control of channel is provided.Detecting medium when PIFS is the free time in the duration, AP can obtain the control to these medium.PIFS is shorter than DIFS, so have higher priority than DIFS.Compare with DCF, in case AP has obtained the access right to channel, it just can provide uncompetitive access chance to other STA, thereby improves MAC efficient.PCF note that SIFS has higher priority than PIFS, so must wait for, till all SIFS EOSs before control channel.
In case AP uses PIFS to obtain the access right to medium, it just can establish a uncontended periods (CFP), and in this cycle, AP can provide the poll formula to insert to the STA that is associated.Uncompetitive poll frame (CF-Poll), or be simply referred to as poll frame is sent by AP, its followed be from receiving the transmission of poll STA to AP.Equally, STA must wait for the SIFS duration after CF-Poll, although receive poll STA needn't wait for DIFS or any back off time.802.11 (e) introduced various enhancings, comprise the enhancing of polling mechanism, will combine Fig. 9 that such example is described in further detail below.
The beacon that AP sends is established the duration of CFP.This is similar to and uses RTS or CTS to prevent that competition from inserting.But this beacon can't be heard in some terminal, but its transmission may cause interference to the transmission of being dispatched by AP, so hidden terminal problem still can occur.Further protection can be realized through using CTS-to-self in each terminal that in CFP, begins to transmit.
ACK and CF-Poll can be included in the frame, and can be included in Frame, thereby improve MAC efficient.Note that SIFS＜PIFS＜DIFS relation provides a kind of certainty priority mechanism for channel inserts.In DCF, it is probabilistic that the competition between the STA inserts based on avoidance mechanism.
802.11 early stage standards have also been stipulated big packet fragmentation is become less fragment.An advantage of this segmentation is: the mistake in fragment needs less re-transmission than the mistake in the bigger grouping.Segmentation shortcoming is in these standards: for the transmission of affirmation type, need send an ACK for each fragment, wherein, additional SIFS is corresponding to additional ACK transmission and fragments for transport.Fig. 6 shows this point.This exemplary physical layer (PHY) span line 600 has provided N section and the corresponding transmission of confirming thereof.An existing transmission 610 is sent out away.When transmission 610 finished, a STA waited for DIFS 620 and back off time 630, to obtain the access right to channel.The one STA sends N fragment 640A-640N to the 2nd STA, and the delay of the individual corresponding SIFS 650A-650N of N must arranged respectively thereafter.The 2nd STA sends N acknowledgement frame 660A-660N.Between each fragment, a STA must wait for SIFS, so, there be N-1 SIFS 670A-670N-1.Therefore, compare with a SIFS with a grouping of transmission, an ACK, the grouping through segmentation needs the identical transmitted in packets time, but N ACK and 2N-1 SIFS are arranged.
802.11 (e) standard has been added enhancement function so that improve 802.11 (a) and (b) with (g) in former MAC.802.11 (g) with (a) all be ofdm system, they are very similar, but work in different frequency bands.The various functions of the low speed MAC agreement such as 802.11 (b) pass on to forward has the more system of high bit rate, thereby has introduced poor efficiency, and the back will be elaborated to this.
In 802.11 (e), DCF has obtained enhancing, strengthens distributed channel access (EDCA) so be called as.It is to have introduced arbitration frame spacing (AIFS) that the main service quality (QoS) of EDCA strengthens.AIFS [i] is associated with the type of service (TC) that identifies with numbering i.AP can use with other STA can different AIFS [i] value of employed AIFS [i] value.AIFS [i] value of having only AP to use to equate with PIFS.In other cases, AIFS [i] is more than or equal to DIFS.Under the default situation,, select to equal the AIFS of DIFS for " speech " and " video " type of service.If AIFS is bigger, then is indicated as type of service " best endeavors " and " background " and has selected lower priority.
The size of competition window also is the function of TC.The limit priority type allows to be provided with CW=1,, does not have back off time that is.For other TC, different contention window size provides probabilistic relative priority level, postpones to guarantee but can not be used for reaching.
802.11 (e) introduced transmission opportunity (TXOP).In order to improve MAC efficient, when STA inserts when getting access to medium through EDCA or through the poll formula in HCCA, STA can send more than one frame.These one or more frames are called as TXOP.In the media, the maximum length of TXOP depends on type of service, and is confirmed by AP.In addition, for the TXOP that receives poll, AP indicates the allowance duration of TXOP.During TXOP, STA can send a series of frame, is embroidered with SIFS and ACK from purpose side therebetween.Except waiting for that DIFS adds the back off time to each frame, the STA that has won a TXOP can know that it can occupy this channel to be used for subsequent transmission.
During TXOP, can be (just as the same in 802.11MAC early) of every frame from the ACK of purpose side, perhaps, can use piece ACK at once or that postpone, be described below.In addition, for specific Business Stream,, allow the strategy of no ACK like broadcasting or multicast.
Fig. 7 has provided an exemplary physical layer (PHY) span line 700, is used to explain the TXOP that has by frame acknowledgment.An existing transmission 710 is sent out away.After transmission 710 and wait for that if any, STA gets TXOP 790 after DIFS 720 and the back off time 730.TXOP 790 comprises N frame 740A-740N, each frame followed N corresponding SIFS 750A-750N.The STA that receives makes response with N corresponding ACK760A-760N.ACK 760 a followed N-1 SIFS 770A-770N-1.Should be noted in the discussion above that each frame 740 comprises lead code 770, and stem and grouping 780.The exemplary embodiment that specifies below can be reduced to the transmission time amount that lead code is reserved greatly.
Fig. 8 shows has the TXOP 810 that piece is confirmed.TXOP 810 can win through competition or poll.TXOP 810 comprises N frame 820A-820N, each frame followed N corresponding SIFS 830A-830N.After the transmission of frame 820 and SIFS 830, send a piece ACK request 840.The STA that receives will ask to make response in a certain moment in future to this piece ACK.This piece ACK can perhaps can postpone immediately following after the frame piece end of transmission, to allow the software processes of receiver.
The exemplary embodiment that specifies below can significantly reduce the transmission time amount (in this example, being SIFS) between the frame.In some embodiments, there is no need delay continuously between the transmission (being frame).
Should be noted in the discussion above that in 802.11 (a) and other standards for specific transformat, defined a kind of signal extension (Signal Extension), its end at every frame increases additional delay.Although be not included in technically in the definition of SIFS, each embodiment of following detailed description also can remove signal extension.
Piece ACK function can be raised the efficiency.In an example; STA can send and corresponding maximum 64 the MAC service data units of 1024 frames (SDU) (each can also be divided into 16 fragments); And purpose side STA can provide single response in the end of frame piece, to show the ACK state of this 1024 frame.Generally, when speed was high, MAC SDU can not carry out segmentation, and for low delay, before need the piece ACK from purpose side, can send and was less than 64 MAC SDU.In this case, in order to send M frame, total time reduces to M frame+M SIFS+ piece ACK from M frame+M SIFS+M ACK+M-1 SIFS.The embodiment that specifies below further improves the efficient of piece ACK.
802.11 the direct link agreement of (e) introducing (DLP) makes STA can frame directly be transmitted to another the purpose side STA (by identical AP control) that is in the set of basic (BSS).AP can provide the TXOP of poll for this direct frame transmission between the STA.Before introducing this function, in poll formula access procedure, from the purpose side of the frame that receives poll STA AP always, AP is transmitted to purpose side STA with these frames.Frame through eliminating double bounce is transmitted, and medium efficient is improved.The embodiment of following further explain increases tangible efficient for the DLP transmission.
802.11 (e) also introduced in-dash computer F, be called as and mix collaboration feature (HCF).Channel in HCF control inserts in (HCCA), and AP is access channel at any time, thereby sets up controlled access phase (CAP), and this is similar with CFP, and any time that is used in the competitive stage provides transmission opportunity, rather than only immediately following behind beacon.AP inserts medium then not having to wait for PIFS under the situation of back off time.
Fig. 9 has provided an exemplary physical layer (PHY) span line 800, is used to explain the TXOP that ask that uses HCCA.In this example, AP competes this poll.An existing transmission 910 is sent out away.After transmission 910, AP waits for PIFS, sends the poll frame 920 that points to a STA then.Other STA that should be noted in the discussion above that this channel of competition must wait for DIFS at least, and this can not occur owing to the poll frame 920 that sends, and is as shown in the figure.The STA that is ask sends the TXOP940 that is ask after poll frame 920 and SIFS 930.AP can continue poll, waits for PIFS respectively being ask between TXOP 940 and the poll frame 920.In another kind of situation, AP can wait for PIFS from transmitting 910, thereby establishes CAP.AP can send one or more poll frames during CAP.
MAC improves
As stated, the various poor efficiency functions of former MAC also pass in the version later on.For example, the very long lead code that designs for 11Mbps and 64Mbps can cause poor efficiency.Along with the increase of speed, Medium Access Control (MAC) Protocol Data Unit (MPDU) constantly dwindles, so, make various frame pitch and/or lead code keep the constant corresponding reduction that just means channel utilization.For example, the length of high data rate MIMO MPDU transmission possibly have only several microseconds, and by contrast, 802.11 (g) have the lead code of 72 μ s.Eliminate or the reduction delay,, will improve throughput and channel utilization like SIFS, signal extension and/or lead code.
Figure 10 is the exemplary embodiment of TXOP 1010, and it comprises a plurality of continuous transmission frames, and has no the gap.TXOP 1010 comprises N frame 1020A-1020N, and they are (required SIFS among this and the TXOP 810 shown in Figure 8 are compared) of transmission in an orderly manner under having no the situation in gap.The quantity of the frame among this TXOP only is subject to the buffer and the decoding capability of receiver.When STA sends successive frame together with piece ACK in TXOP 1010, needn't insert the SIFS duration, because between successive frame, do not have other STA need obtain access right to medium.Behind N frame, add an optional piece ACK request 1030.The business of some type possibly not need to confirm.Be right after after TXOP, can make response, perhaps, can send after a while a piece ACK request.The expansion of frame 1020 undesired signals.Any embodiment that TXOP 1010 can be used for describing in detail here is as long as wherein need TXOP.
Shown in figure 10, when sending all frames, between the successive frame of TXOP, needn't send SIFS by same STA.In 802.11 (e), these gaps have been kept, so that limit complexity requirement at the receiver place.In 802.11 (e) standard, the SIFS period of 10 μ s and the ofdm signal of 6 μ s expand to receiver 16 μ s altogether are provided, and are used to handle the frame of receiving (comprising the demodulation sign indicating number).But if PHY speed is very big, this 16 μ s can lower efficiency significantly.In some embodiments, handle, handle even if 16 μ s also are not enough to accomplish through introducing MIMO.And in this exemplary embodiment,, do not need SIFS and ofdm signal expansion (using the direct link agreement) from a STA to AP or to the continuous transmission of another STA.Therefore,, then can carry out these functions after the end of transmission, simultaneously these medium are used for additional transmitted stream if a receiver needs additional period to be used for processing of MIMO receiver and channel-decoding (for example: Turbo/ convolution/LDPC decodes).After a while, can send an acknowledgement frame, (for example, use piece ACK) as stated.
Because the different propagation delays between the STA; Different STA between transmission can use the protection period separately; The receiver place that is transmitted in continuously from different STA clashes (Figure 10 does not show, but will make further detailed description in the back) on these medium to avoid.In one exemplary embodiment, (4 μ s) all working environment for 802.11 all is enough the protection period of an OFDM symbol.Need not use the protection period to separate (shown in figure 10) from the transmission of same STA STA to various objectives side.Also with further explain, these protection periods can be called as protection frequency band frame pitch (GIFS) below.
Do not use SIFS and/or signal extension; Through using ARQ mechanism (rollback N or repetition selectively) based on window; The required receiver processing time (for example, being used for MIMO processing and decoding) can be provided, and these technology are known to those skilled in the art.Stop-and-wait (stop-and-wait) the MAC layer ACK of tradition 802.11 has been enhanced to the mechanism of window type in 802.11 (e), reach 1024 frames and piece ACK at most, in this example.The preferred ARQ mechanism of introducing based on normal window, but not the self-organizing piece ACK of design mechanism among 802.11 (e).
The maximized window that is allowed depends on receiver processing complexity and buffering.Transmitter can according to transmitter-receiver between accessible peak value PHY speed, send enough data and fill up receiver window.For example,, receiver possibly can't get caught up in PHY speed, so receiver possibly need the output of storage soft (soft) decoder, till they can be decoded because handling.Therefore, the buffer requirement of physical layer process can be used to confirm the maximized window that allows during peak value PHY speed.
In one exemplary embodiment, receiver can be announced it and can under the situation that its physical layer buffer is overflowed, the maximum with a specific PHY rate processing allow PHY piece size.Perhaps, receiver also can be announced it and can under the situation that its physical layer buffer is overflowed, the maximum with maximum PHY rate processing allow PHY piece size.When PHY speed is low, can under the situation that does not have buffer to overflow, handle long piece size.The maximum of announcing during according to maximum PHY speed allows PHY piece size, and the maximum that transmitter can use known formula to calculate for specific PHY speed allows PHY piece size.
If the maximum PHY piece size of announcement is a static parameter; Be another receiver parameters handling physical layer buffer and the receiver time quantum before being ready to receive next PHY burst then, this receiver parameters is known at the transmitter place and also is known at the scheduler place.Perhaps, according to the situation that takies of physical layer buffer, the maximum PHY piece size of being announced can dynamically change.
The receiver processing delay can be used to confirm that ARQ come and go (round-trip) postpones, and the latter can be used to the delay that definite UR arrives.Therefore, in order to support the low delay service, can limit the PHY piece size of permission.
Figure 11 has provided the exemplary embodiment of TXOP 1110, is used to the preamble transmissions amount of explaining that reduction is required.TXOP 1110 comprises lead code 1120, followed be N transmission 1130A-1130N continuously.Can add an optional piece ACK request 1140.In this example, transmission 1130 comprises a stem and a grouping.TXOP 1110 is compared with the TXOP 790 of Fig. 7, and except that stem with dividing into groups, each frame 740 also comprises a lead code.For the transmission data of same amount, through sending single lead code, required preamble transmissions only is a lead code, rather than N lead code.
Therefore, lead code 1120 can exclude from continuous transmission.Receiver can use initial preamble 1120 to obtain signal and obtain with the fine frequency that is used for OFDM.Compare with current OFDM lead code, for the MIMO transmission, initial preamble 1120 can be expanded, so that receiver can the estimation space channel.But, the lead code that the subsequent frame in the same TXOP can not need add.Pilot tone in the OFDM symbol is enough to carry out signal trace usually.In another embodiment, additional symbol (being similar to lead code) can interlock on TXOP 1110 intercycle property ground.But, can obviously reduce total lead code expense.Can only just send lead code where necessary, and the time quantum based on since the last lead code of sending, having passed can send lead code differently.
Should be noted in the discussion above that TXOP 1110 also can combine with the function of legacy system.For example, piece ACK is optional.Also can support the ACK of higher frequency.Even so, less clearance like GIFS, can be replaced long SIFS and (add signal extension, if you are using).Continuous transmission 1130 can also comprise a plurality of sections of bigger grouping, as stated.The stem that should also be noted that the continuous transmission 1130 of mailing to same recipient STA can be compressed.Also will specify an example of compressed header below.
Figure 12 has provided an exemplary embodiment of method 1200, and it is combined with above-mentioned each side, comprises gathering lead code, remove the gap such as SIFS and inserting GIF as required.This flow process starts from frame 1210, wherein, uses any technology of describing in detail here, and a STA has won a TXOP.In frame 1220, as required, send a lead code.Equally, existing lead code can is longer than or be shorter than to this lead code, and can change according to various parameters (for example, the time that since last transmission lead code, has passed), so that recipient STA can estimate the MIMO space channel.In frame 1230, STA sends one or more groupings (perhaps, more generally, the continuous transmission of any kind) to purpose side.Not should be noted in the discussion above that and need send additional lead code.In other embodiments, also can send one or more additional lead codes, perhaps, as required, can insert the symbol of similar lead code.In frame 1240, STA sends signal to an additional recipient STA side alternatively.In this case, insert GIFS as required, and, can one or more continuous transmission be sent to additional recipient STA.Then, flow process can finish.In other embodiments, STA can continue to send signal to plural STA, and inserts required GIFS and/or the lead code of estimated performance grade.
Therefore, as stated,, can further improve MAC efficient, much or all protect the period thereby save through the transmission from a STA to a plurality of purpose side STA is gathered into continuous transmission, and, the lead code expense reduced.For a plurality of continuous transmission, can use single lead code (perhaps, pilot transmission) from same STA STA to various objectives side.
Gather through poll frame, can obtain extra high efficiency.In one exemplary embodiment, can a plurality of poll frames be aggregated in the control channel, will describe its example in detail below.In an example, AP can send signal to a plurality of purpose side STA, comprising the polling message that is used for distribution T XOP.By contrast, in 802.11 (e), the CF-Poll from AP is arranged before each TXOP, SIFS follows after this CF-Poll.When a plurality of such CF-Poll message being gathered into single control channel message (in the exemplary embodiment that is discussed in more detail below, being referred to as SCHED message) when being used for distributing a plurality of TXOP, can raise the efficiency.In a common embodiment, section can be distributed to poll frame and the corresponding TXOP thereof after gathering any time.Describe an exemplary embodiment below in conjunction with Figure 15, and this paper also comprises other examples.
In order further to raise the efficiency, can use the speed structure of layering that control channel (being SCHED) message is encoded.Correspondingly, the polling message that mails to any STA can be encoded according to the channel quality between AP and the STA.The order of transmission of polling message needs not to be the order of the distribution T XOP of institute, but can be ranked according to the coding robustness.
Figure 13 has provided an exemplary physical layer (PHY) span line 1300, is used for explanation and gathers poll frame and corresponding TXOP thereof.Gathering poll frame 1310 is sent out away.Can use the control channel structure of describing in detail here, perhaps, can use various other technologies, send these poll frames, to those skilled in the art, these are conspicuous.In this example,, gathering directly transmission forward link TXOP 1320 of poll frame 1310 backs in order between poll frame and any forward link TXOP, not use frame pitch.After forward link TXOP1320, send various reverse link TXOP 1330A-1330N, wherein can insert GIFS 1340 as required.Should be noted in the discussion above that when when a STA transmits in order, needn't comprise GIFS (be similar to for the forward link transmissions that sends to different STA from AP and do not need GIFS).In this example, reverse link TXOP comprises the TXOP (for example, use DLP) of STA to STA (that is point-to-point).Order of transmission shown in should be noted in the discussion above that is illustrative.Forward direction and reverse link TXOP (comprising the point-to-point transmission) can exchange, and perhaps, intert mutually.The number of gaps that some configuration is eliminated possibly be different from the number of gaps that other configurations are eliminated.Through the application's disclosure, those skilled in the art can design multiple interchangeable embodiment at an easy rate.
Figure 14 shows an exemplary embodiment of the method 1400 that is used to gather poll frame.Flow process starts from frame 1410, wherein, with channel resource allocation in one or more TXOP.Can use any scheduling feature, make this TXOP Decision of Allocation.In frame 1420, coming the poll frame of distribution T XOP to gather according to this assignment information.In frame 1430,, this is gathered poll frame send to one or more STA (that is, in the exemplary embodiment that is discussed in more detail below, the CTRLJ section of SCHED message) through one or more control channels.In an interchangeable embodiment, can use any message delivery techniques, send and gather poll frame.In frame 1440, STA gathers the poll assignment information in the poll frame according to this, sends TXOP.Then, flow process can finish.This method can combine the poll frame that gathers of any length to use at interval, gathers poll frame and can comprise all or part of of system's beacon interval.As stated, gathering poll can be used for based on the access of competition or traditional poll off and on.In one exemplary embodiment, can periodically perhaps,,, repeat method 1400 like system load or transfer of data requirement according to other parameters.
Below in conjunction with Figure 15 and 16, describe an exemplary embodiment of MAC agreement in detail, with the explanation various aspects.Submit to simultaneously with the application, exercise question is the U.S. Patent application XX/XXX common co-pending of " WIRELESS LANPROTOCOL STACK (protocol of wireless local area network stack) "; XXX, XX/XXX; XXX and XX/XXX; Among the XXX (file number is respectively 030428,030433 and 030436) this MAC agreement has been described in further detail, these three pieces of assignees that application has transferred the application.
An exemplary TDD mac frame interval 1500 has been shown among Figure 15.Term " the TDD mac frame at interval " used in this occasion refers to a period of time, wherein, has defined the various span lines of following detailed description.TDD mac frame interval 1500 is different from the term " frame " of general use, so that describe the transmission in 802.11 systems.In 802.11 terms, TDD mac frame interval 1500 is similar to the sub-fraction of beacon interval or beacon interval.The parameter of describing in detail in conjunction with Figure 15 and 16 only is illustrative.Some of the use parts of describing or whole and various parameter value, those of ordinary skills can make this example be adapted to multiple other embodiment at an easy rate.MAC function 1500 is distributed between following transmission channel section: broadcasting, control, forward business and reverse traffic (being called as downlink phase and uplink phase respectively) and access at random.
In this exemplary embodiment, TDD mac frame interval 1500 is time division duplex (TDD) in 2 milliseconds the time interval, is divided into five transmission channel section 1510-1550, and is as shown in the figure.In other embodiments, can use other order and different frame sizes.The duration of the dispensing section on the TDD mac frame interval 1500 can be quantized into a certain mini-bus time interval.
The downlink phase section of the comprising 1510-1530 of frame 1500.The uplink phase section of comprising 1540-1550.Section 1560 next TDD mac frame of expression beginnings at interval.Further describe another embodiment that comprises the point-to-point transmission below.
Broadcast channel (BCH) and beacon 1510 are sent by AP.The first of BCH 510 comprises the common physical layer expense, like pilot signal, comprises that sequential and frequency obtain pilot signal.In an exemplary embodiment, beacon comprises 2 short OFDM symbols, is used for frequency and the time obtains by UT, and the back is 8 short OFDM symbols of public MIMO pilot tone, is used to estimate channel by UT.
The second portion of BCH 1510 is a data division.The BCH data division has defined the distribution of TDDMAC frame period about transmission channel section CCH 1520, F-TCH 1530, R-TCH 1540 and RCH 1550, and has defined the composition of CCH about subchannel.In this example, BCH 1510 has defined the coverage of WLAN 120, so, under available robust data transmission mode, send.The length of whole BCH is fixed.In an exemplary embodiment, BCH has defined the coverage of MIMO-WLAN, and, under space-time emission diversity (STTD) pattern, use the binary phase shift keying (BPSK) of 1/4 rate coding to send.In this example, the length of BCH is fixed as 10 short OFDM symbols.In other embodiments, can use other different signaling technologys.
The control channel (CCH) 1520 that is sent by AP has defined the combination of TDD mac frame remainder at interval, and shows how to use and gather poll frame.CCH 1520 sends in a plurality of subchannels with very strong transmission mode, and each subchannel has different data rates.First subchannel is the most strong, and expection can be decoded by all UT.In an exemplary embodiment, the BPSK of 1/4 rate coding is used for a CCH subchannel.Also provide other robustnesss to reduce the subchannel of (efficient rising).In one exemplary embodiment, use maximum three additional subchannels.Each UT decodes to all subchannels in order as possible, till the decoding failure.CCH transmission channel section in each frame has length variable, and this length depends on the quantity of CCH message in each subchannel.The reverse link affirmation information of access burst at random is on the most strong (first) subchannel of CCH, to transmit.
CCH comprises the assignment information of physical layer bursts on forward direction and reverse link (be similar to gather poll frame in TXOP).Assignment information is used in forward direction or reverse link transmitting data.Usually, the physical layer bursts assignment information comprises: (a) MAC ID; (b) value is represented time started (in F-TCH or R-TCH) of dispensing section in this frame; (c) length of dispensing section; (d) length of special-purpose physical layer overhead; (e) transmission mode; (f) be used for the coding and the modulation scheme of physical layer bursts.
The assignment information of last other exemplary types of CCH comprises: be used to transmit the assignment information from the dedicated pilot of UT on the reverse link; Be used on the reverse link transmit from the buffer of UT and the assignment information of link-state information.The reservation unused portion of all right definition frame of CCH.These unused portions of this frame can be used for carrying out noise floor (and interference) by UT to be estimated, and, measure the adjacent system beacon.
RACH (RCH) the 1550th, reverse chain channel, UT can send access burst at random through it.For each frame, in BCH, specify the variable-length of RCH.
Forward traffic channel (F-TCH) 1530 comprises one or more physical layer bursts that send from AP 104.The specific MAC ID that each burst target directing shows in the CCH assignment information.Each burst comprises special-purpose physical layer overhead, for example, and the pilot signal (if any) and the MAC PDU that send according to the transmission mode that shows in the CCH assignment information and coding and modulation scheme.F-TCH has length variable.In an exemplary embodiment, special-purpose physical layer overhead can comprise the MIMO pilot tone of a special use.Figure 16 has provided an exemplary MAC PDU in detail.
Reverse chain channel (R-TCH) 1540 comprises the physical layer bursts transmission from one or more UT 106.Each burst is to be sent by one that shows in the CCH assignment information specific UT.Each burst can comprise a dedicated pilot lead code (if any) and MAC PDU who sends according to the transmission mode that shows in the CCH assignment information and coding and modulation scheme.R-TCH has length variable.
In this exemplary embodiment, F-TCH 530, R-TCH 540 or the two can the multiplexing or CDMAs of usage space, transmit when realizing with MAC PDU that different UT are associated.A field that comprises the MAC ID (that is, the transmit leg on the up link, or the expection recipient on the down link) that is associated with MAC PDU can be included in the MACPDU stem.All addressing uncertain problems that this can possibly occur when solving the multiplexing or CDMA of usage space.In other embodiments, during strictly based on time division technique, do not need MAC ID in the MAC PDU stem when multiplexing, because addressing information is included in the CCH message, CCH message has been distributed to a concrete MAC ID with the special period of TDD mac frame at interval.Can adopt spatial reuse, code division multiplexing, time division multiplexing and any other technological combination known in the art.
Figure 16 shows an exemplary MAC PDU 1660 from a grouping 1610, and in this example, it can be IP datagram or ethernet segment.Described exemplary fields type and size are illustrative.One skilled in the art will recognize that in protection scope of the present invention various other sizes, type and configuration also can be imagined and obtain.
As shown in the figure, segmentation is carried out in packet 1610 in adaptation layer.One of in each these section 1620 of adaptation sublayer PDU 1630 carryings.In this example, packet 1610 is divided into N section 1620A-N.Adapt to sublayer PDU 1630 and comprise load 1634, load 1634 comprises corresponding section 1620.Type field 1632 (being a byte in this example) appends to and adapts among the sublayer PDU 1630.
Logical links (LL) stem 1642 (being 4 bytes in this example) is added in the load 1644, and load 1644 comprises adaptation layer PDU 1630.The exemplary information of LL stem 1642 comprises flow identifier, control information and sequence number.To stem 1642 and load 1644, calculate CRC 1646, and affix it, to form logical links sublayer PDU (LL PDU) 1640.Logic link control (LLC) and Radio Link control (RLC) PDU can form through similar fashion.LL PDU 1640 and LLC PDU and RLC PDU are placed on (for example, high QoS formation, best endeavors formation or control messages formation) in the formation, to be used by the MUX functional section.
In this example, the communication resource on the shared medium is distributed in a series of TDD mac frames interval by the MAC agreement.Among other embodiment that will describe in detail below, the TDD mac frame of these types at interval can insert various other MAC functional sections, comprise based on competition or poll, and comprise that the access protocol and the legacy system that use other types carry out alternately.As stated, scheduler can confirm in each TDD mac frame interval, to distribute to the size (being similar to the TXOP that gathers poll) of the physical layer bursts of one or more MAC ID.Should be noted in the discussion above that not to be that each MAC ID that has data to send can both be assigned to the interior at interval space of any specific T DD mac frame.In protection scope of the present invention, can use any access control or scheduling scheme.When carrying out the branch timing to MAC ID, the corresponding MUX functional section of this MAC ID will constitute MAC PDU 1660, and it comprises one or more MUXPDU 1650, so that be included in this TDD mac frame interval.One or more MUX PDU 1660 to one or more MAC ID that distributed will be included in (that is, TDD mac frame interval 1500 has combined Figure 15 to be described in detail above) in the TDDMAC frame period.
In one exemplary embodiment, an aspect makes it possible to send a part MPDU1650, thereby in MAC PDU 1660, realizes efficient packing.In this example, all part MPDU 1650 remaining byte of not sending in preceding once transmission can be included, and by part MPDU 1664 signs.In present frame, these bytes 1664 will be sent at all new PDU 1666 (that is, LL PDU or control PDU) before.Stem 1662 (being 2 bytes in this example) comprises the MUX pointer, and it points to the beginning of first new MPDU (in this example, being MPDU 1666A) that will send in the present frame.Stem 1662 also comprises MAC Address.
Therefore, this exemplary MAC PDU 1660 shows a transmission (perhaps, being frame by 802.11 terms), and it can send to another STA from a STA, comprises the data division from the one or more streams that point to this purpose side STA.Through using part MUX PDU alternatively, can realize efficient packing.What in CCH, comprise gathers the time that shows in the poll frame, and each MAC PDU can send in a TXOP (using 802.11 terms).
The exemplary embodiment of describing in detail among Figure 15 and 16 has been listed various aspects, comprise through from each STA (comprising AP) thus send physical layer bursts in an orderly manner and gather poll frame, reduce preamble transmissions and eliminate the gap.These aspects also are applicable to any MAC agreement, comprise 802.11 systems.Further provide other embodiment below, other various technology are described, these technology can realize the high efficiency of MAC, and, support the point-to-point transmission, and can get up with existing legacy protocol or systems incorporate and/or cooperate.
As stated, the various embodiment that describe in detail here can adopt channel estimating and strict rate controlled.Through the unnecessary transmission on the medium is minimized, can improve MAC efficient, still, in some cases, inadequate rate controlled feedback will reduce overall throughput.Therefore,, enough chances can be provided for channel estimating and feedback, so that the maximization of the transmission rate under all MIMO patterns, thereby prevent that because the throughput that insufficient channel estimating caused reduces, the throughput reduction can be offset any MAC efficient to be increased.Therefore, MAC embodiment that can design example property, so that enough preamble transmissions chances to be provided, and, let receiver have an opportunity the rate controlled feedback to be provided to transmitter, above this is introduced, below also with further explain.
In an example, AP periodically inserts MIMO pilot tone (every at least TP millisecond, wherein, TP can be fixing or variable parameter) in its transmission.Each STA can begin it with a MIMO pilot tone and ask TXOP, and this MIMO pilot tone can be used for estimating channel by other STA and AP.For the transmission of using direct link agreement (below with further explain) to mail to AP or another STA, the MIMO pilot tone can be the reference signal (steered reference) that is directed to, so that the receiver that helps to simplify among the purpose side STA is handled.
AP can offer an opportunity to purpose side STA, so that let it that ACK is provided feedback.Purpose side STA also can use these feedback chances, and the rate controlled feedback of available MIMO pattern is provided to transmit leg STA.Such rate controlled feedback does not define in 802.11 traditional systems, comprises 802.11 (e).Introduce the total amount (to every kind of MIMO pattern) that MIMO can improve rate control information.In some cases,, can replenish these through strict rate controlled feedback for improved effect is being maximized aspect the MAC efficient.
Here by the agency of and be storage level (backlog) information and the scheduling of STA on the other hand below with further explain.Each STA can begin its TXOP with a lead code, the request duration of next TXOP of followed.This information purpose is pointed to AP.AP collects next request TXOP for information about from a plurality of different STA, and, for next TDD mac frame at interval, confirm TXOP duration distribution condition in the media.AP can use different priority or QoS rule, how to confirm shared medium, and perhaps, it can use very simple rule, according to request from STA, and proportional ground shared medium.Can also adopt any other dispatching technique.Next TDD mac frame TXOP dispensing section at interval is in the back control channel message from AP, to distribute.
The access point of appointment
In embodiment described herein, network can be supported real access point or not have the operation under the situation of real access point.When having real AP, for example, it can be connected to wired wide pipeline and connect (that is, cable, optical fiber, DSL or T1/T3, Ethernet) or home entertainment server.In this case, this real AP can be the information source and the stay of two nights of most of data that equipment room flows in the network.
When not having real AP, the distributed coordination function (DCF) of 802.11b/g/a or the technology such as enhanced distributed channel access of 802.11e still can be used in a plurality of stations, communicate each other, these technology are described above.Below also with further explain be, when the needs additional resource, adopt centralized scheduling scheme, can use medium more efficiently.For example, this network architecture possibly occur in the family, and wherein, a lot of distinct devices (that is, DVD-TV, CD-Amp-Speaker etc.) need communicate each other.In this case, these network stations specify a station to serve as AP automatically.Should be noted in the discussion above that to be described below that self adaptation coordination function (ACF) can be used through specifying access point, and can be at centralized scheduling, insert at random, adopt under the situation of self-organizing communication or its combination in any.
Some non-AP equipment but not every non-AP equipment has the MAC ability of enhancing is so be suitable for working as specifying AP.Should be noted in the discussion above that not all equipment all need be designed with the AP MAC ability of specifying.When QoS (for example, secure time-delay), high-throughput and/when efficient was very important, an equipment in the network must can support to specify the operation of AP.
This means, specify the ability of AP to be associated with the equipment that possesses high ability usually, for example, have one or more attributes, like line power (line power), a large amount of antenna and/or transmit, or the high-throughput requirement.(below the additive factor that is used to select to specify AP will be described in further detail).Therefore, low side devices like low side camera or phone, need not possess the ability of specifying AP, and high-end equipment like high-end video source or high definition video display, can possess the ability of specifying AP.
In not having the network of AP, the AP of appointment is bringing into play the effect of real AP, and can have or can not have function still less.In various embodiments, the AP of appointment can carry out following function: (a) establish network set of basic (BSS) ID; (b) through sending beacon and broadcast channel (BCH) network configuration information (medium before next BCH of BCH definition are synthetic), the network sequential is set; (c) use forward control channel (FCCH), the transmission at the station in the network is dispatched, thereby management connects; (d) management related (association); (e) for providing, QoS stream admits control; And/or (f) various other functions.Specify AP can realize complicated scheduler, perhaps, the dispatching algorithm of any kind.Can adopt simple scheduler, its example is described in further detail below.
Below in conjunction with point to point link, describe improved physical layer convergence protocol (plcp) stem in detail, this also is applicable to specifies AP.In one embodiment, the PLCP stem of all transmission is sent with the master data speed that can be stood by all (AP that comprises appointment) decodes.The data reserve amount that comprises the place, station that is associated with certain priority or stream from the PLCP stem of the transmission at a plurality of stations.Perhaps, it comprises a duration request for a back launching opportunity of certain priority or stream.
Through " spying upon (snooping) ", the AP of appointment can confirm storage level or the transmission opportunity duration by these station requests in the PLCP stem of all station transmission.Based on load, conflict or other congested indexs, the AP of appointment can confirm to distribute to (distributed access) based on EDCA to portion of time, portion of time is distributed to uncompetitive poll (centralized) insert.The AP of appointment can move a basic scheduler, and it distributes and the proportional bandwidth of request, and in uncontended periods, it is dispatched.The scheduler that strengthens also is fine, but is not necessary.The transmission of process scheduling is by specifying AP at the enterprising announcement that works of CCH (control channel).
The AP of appointment need not transmit (echo) to another station (that is, serving as springboard) with the transmission at a station, but this function is also permitted.Real AP possesses transfer capability.
When selecting to specify access point, can create a kind of hierarchical system, confirm that which equipment should serve as access point.Admissible example factors comprises following when selecting to specify access point: (a) user's configuration (over-ride); (b) higher preference grade; (c) safe class; (d) ability: line power; (e) ability: antenna amount; (f) ability: maximum transmission power; (g) based on the additional consideration (break a tie) of other factors: medium access control (MAC) address; (h) first equipment of start; (i) any other factor.
In fact, the AP of appointment preferably is positioned at the center, and has best total Rx SNR CDF (that is, can under the situation of good SNR, receive all stations).Usually, the antenna that station has is many more, and receiving sensitivity is just good more.In addition, the AP of appointment can have higher transmitting power, thereby makes the AP of this appointment to be listened to by a large amount of stations.When adding the station and/or station when moving, can assess these attributes, and utilize them, so that network can dynamically reconfigure.
If network configuration has the AP of a real AP or an appointment, then can support point-to-point to connect.Next joint will be described point-to-point in detail and connect.In one embodiment, can support two types point-to-point to connect: the point-to-point of (a) being managed connects, and wherein, AP dispatches the transmission that participate at each station; (b) connection of self-organizing, wherein, AP do not participate in the standing management and the scheduling of transmission.
The AP of appointment can set mac frame at interval, and when frame begins pilot signal transmitted.Broadcasting and control channel can be specified the duration of having distributed in the frame that lets the station send.Asked the station (for AP, these requests are known) that transmission distributes concerning point-to-point for those, AP can provide the dispensing section that has passed through scheduling.AP can announce these dispensing sections in control channel, for example, and in each mac frame.
AP can also be included in A-TCH (self-organizing) section in this mac frame (below will be elaborated to this).Whether exist A-TCH in BCH and FCCH, to indicate in the mac frame.In A-TCH, stand and to use the CSMA/CA process to carry out point to point link.Can revise the CSMA/CA process of IEEE WLAN standard 802.11, to get rid of the requirement of ACK at once.Rob when accounting for channel when a station, a MAC-PDU (protocol Data Unit) can be sent in this station, and it comprises a plurality of LLC-PDU.One stands in the maximum duration that can take among the A-TCH and in BCH, provides.For LLC, can window size be confirmed to postpone to hold consultation with maximum according to required application delay through confirming.Specify improved mac frame below in conjunction with Figure 20, it has the A-TCH section, can be used for the real AP and the AP of appointment.
In one embodiment, (unsteered) MIMO pilot tone that is not directed to can make all stations learn they self and dispatching station between channel.In some cases, this is useful.In addition, the AP of appointment can use the MIMO pilot tone that is not directed to, so that carry out the demodulation of channel estimating and PCCH, can therefrom derive dispensing section then.In case the AP of appointment receives all requested dispensing sections in the frame of a special MAC, then it can be dispatched them to follow-up mac frame.Should be noted in the discussion above that rate control information needn't be included among the FCCH.
In one embodiment, scheduler can be carried out following operation: at first, for next mac frame, scheduler is collected all requested dispensing sections, and calculates total quilt request dispensing section (Total Requested).The second, scheduler calculates the total available resources (Total Available) that can distribute to F-TCH and R-TCH.The 3rd, if Total Requested, then uses the factor of being confirmed by Total Available/Total Requested greater than TotalAvailable, all requested dispensing sections are carried out convergent-divergent.The 4th, for less than dispensing section behind any convergent-divergent of 12 OFDM symbols, these dispensing sections are increased to 12 OFDM symbols (like this in this exemplary embodiment, but other embodiment can use different parameters).The 5th, for the dispensing section of gained is provided in F-TCH+R-TCH,, begin from maximum through reducing all dispensing sections in a looping fashion greater than 12 OFDM symbols, next symbol can provide any extra OFDM symbol and/or guard time.
An example can be explained the foregoing description.Consider following request for allocation: 20,40,12,48.So, Total Requested=120.Suppose Total Available=90.Suppose that more required guard time is 0.2 OFDM symbol.Therefore, of the 3rd top operation, the dispensing section behind the convergent-divergent is: 15,30,9,36.The 4th operation as top is said, and dispensing section 9 is increased to 12.According to the 5th operation, with amended dispensing section and guard time addition, the total allocation section is 93.8.This means that dispensing section will reduce by 4 symbols.From the beginning of maximum, once remove a symbol, thereby confirm that final dispensing section is 14,29,12,34.(that is, 89 symbols and 0.8 symbol that is used for guard time) altogether
In one exemplary embodiment, when having appointment AP, it can be set up the beacon of BSS and the network sequential is set.A plurality of equipment are associated with the AP of this appointment.When needing a QoS to be connected with two equipment of specifying AP to be associated, for example, have the HDTV link of low delay and high-throughput requirement, so, they provide operational indicator to this appointment AP, so that admit control.This appointment AP can admit or refuse this connection request.
If the medium utilance is enough low, then can use CSMA/CA, reserve the whole duration of medium between beacon, be used for the EDCA operation.If EDCA operation operation is smooth and easy, for example, do not have excessive conflict, keep out of the way and postpone, then this appointment AP needn't provide coordination function.
The AP of appointment can continue to keep watch on the medium utilance through the PLCP stem of monitoring station transmission.According to observation to medium, and storage level or the request of launching opportunity duration, specify AP can determine when the dissatisfied required QoS that permits stream of EDCA operation.For example, it can observation station the storage level and the trend of the duration of being asked of report, and, itself and desired value are compared based on the stream of permitting.
When specifying AP to confirm under distributed access situation, not satisfy required QoS, it can convert the operation on the medium to the operation with poll and scheduling.The latter provides and has more deterministic time-delay and higher throughput efficiency.To describe the example of this operation below in detail.
Therefore, from the transmission opportunity request of dispatching station with will ask and permit QoS and flow and carry out comparison, can convert scheduling (centralized) operation adaptively to through observation medium utilance, conflict, congested and observation from EDCA (distributed access mechanism).
As previously mentioned, in any embodiment that the application describes in detail, wherein described access point, it will be appreciated by those skilled in the art that this embodiment can adapt to and real access point arranged or specifying under the situation of access point and work.Just as that kind that specifies, can adopt and/or select one to specify access point here, this specifies access point can be according to any agreement work, comprises the agreement do not mentioned among the application or any combination of various protocols.
Point-to-point transmission and direct link agreement (DLP)
As stated, point-to-point (or abbreviate as " some point ") transmission makes a STA directly send data to another STA, and needn't send the data to AP earlier.Here the various aspects of describing in detail go for the point-to-point transmission.In one embodiment, can revise direct link agreement (DLP), be described below.Figure 17 shows an exemplary point to point link in the system 100.System 100 in this example is similar to system shown in Figure 1 100, and it can (this example, show the transmission between UT 106A and the UT 106B) from a UT to another UT and realize directly transmission through revising.UT 106 can pass through WLAN 120, directly communicates with AP 104, will be described in greater detail here.
In various exemplary embodiments, can support two types some point to connect: the some point of (a) being managed connects, and wherein, AP dispatches the transmission that each STA participates in; (b) the some point of self-organizing connects, and wherein, AP does not participate in the management or the scheduling of STA transmission.Embodiment can comprise a kind of of these two kinds of connections or the two.In one exemplary embodiment, the signal that sends can comprise: a part, and it comprises the public information that can be received by one or more stations (also possibly comprise access point); And, carried out format specially so that by an information of some receiving station reception.Public information can be used for scheduling (for example, shown in figure 25), perhaps is used for competition by various neighbours station and keeps out of the way (for example, shown in figure 26).
The closed loop rate control that the various exemplary embodiment introduction point points of describing in detail below connect.Can adopt this rate controlled, make full use of available high data rate.
For ease of explanation, do not specify various functions (that is, confirming) in the exemplary embodiment.It will be recognized by those skilled in the art that function disclosed herein can combine, thereby in various embodiment, form the set or the subclass of any amount.
Figure 18 shows the physical layer bursts 1800 of prior art.Can send lead code 1810 earlier, physical layer convergence protocol (plcp) stem 1820 of followed.802.11 traditional system definitions a kind of PLCP stem, comprise speed type and modulation format, be used for as data symbol 1830 and the data of transmission.
Figure 19 has provided an exemplary physical layer bursts 1900, and it can be used for a some transmission.The same as Figure 18, lead code 1810 is includable with PLCP stem 1820, followed be that the some point that is marked as P2P 1940 transmits.P2P 1940 can comprise the MIMO pilot tone of being used by recipient UT 1910.MIMO Rate Feedback 1920 is also includable, so that used in the transmission in future that sends back to transmit leg UT by recipient UT.Rate Feedback can generate in response to last transmission from the receiving station to the dispatching station.Then, data symbol 1930 can send according to selected rates and the modulation format that a point connects.Should be noted in the discussion above that physical layer bursts, like PHY burst 1900, the some point that can be used for the AP management connects, and the transmission of the some point of self-organizing.The Rate Feedback embodiment of following detailed description exemplary.Other embodiment that also comprise the physical layer transmission burst that comprises these aspects below.
In an exemplary embodiment, AP sets the TDD mac frame at interval.Can use broadcasting and control channel to indicate the duration of having distributed in the TDD mac frame interval.For the STA (is known for AP) that has asked some transmission dispensing section, AP can provide the dispensing section through scheduling, and in each TDD mac frame interval, in control channel, announces them.Top Figure 15 has provided an exemplary system.
Figure 20 shows a TDD mac frame exemplary embodiment of 2000 at interval, and it comprises an optional self-organizing section, is identified as A-TCH 2010.The TDD mac frame can comprise in 2000 at interval with above the identical part of numbering described in conjunction with Figure 15.Can show among BCH510 and/or the CCH 520 in the TDD mac frame interval 2000 and whether have A-TCH 2010.During A-TCH 2010, STA can use any competition process, carries out point to point link.For example, can use 802.11 technology, like the SIFS of top detailed description, DIFS, back off time etc.Also can use QoS technology, like those (that is AIFS) technology, of introducing among 802.11 (e).Can also use various other schemes based on competition.
In one exemplary embodiment, the CSMA/CA process that is used to compete for example, has been carried out the process of definition in 802.11, can revise as follows.Do not need ACK at once.When robbing when accounting for channel, a STA can send and comprise that a plurality of PDU are (that is, LLC-PDU) at interior Medium Access Control (MAC) Protocol Data Unit (MAC-PDU).Can show STA shared maximum duration in A-TCH among the BCH.When hope during, can consult window size and confirm to postpone according to required application delay with maximum through the transmission confirmed.
In this example, F-TCH 530 is TDD mac frame parts at interval, is used for the transmission from AP to STA.In A-TCH 2010, can use the competition technology to carry out the point to point link between the STA.In R-TCH 540, can carry out the scheduling point to point link between the STA.In these three sections any one can be made as sky.
Figure 21 has provided an exemplary physical layer bursts 2100, also is called as " PHY burst ".PHY burst 2100 can be used for dispatching point point and connects, and for example during R-TCH 540, or during the connection of the self-organizing such as A-TCH 2010, has combined Figure 20 that this is described in detail above.PHY burst 2100 comprises the MIMO pilot tone 2110 that is not directed to, reciprocity CCCH (PCCH) 2120 and one or more data symbols 2130.The MIMO pilot tone 2110 that is not directed to can receive at place, one or more station, and, can be by receiving station with the respective channel of estimating between dispatching station and the receiving station for referencial use.This exemplary PCCH comprises fields: (a) purpose side MAC-ID; (b) for next TDD mac frame request for allocation of transmitting continuous time of expection at interval; (c) transmission rate designator is used to indicate current data transmission packets form; (d) (that is, CCH) subchannel is used to receive any dispensing section from AP to control channel; (e) CRC.PCCH 2120 and the MIMO pilot tone 2110 that is not directed to are common segment, so can be received by various monitoring stations (comprising access point).Can in PCCH, insert request for allocation, so that realize that in the TDD in future mac frame interval the point point of being managed connects.Such PHY burst can be included in the self-organizing connection, and, still can in following TDD mac frame interval, connect by the point-to-point of request scheduling.In this exemplary embodiment, the MIMO pilot tone that is not directed to is 8 OFDM symbols (among other embodiment that specify below, less symbol just is enough to realize channel estimating), and PCCH is two OFDM symbols.In common segment (comprising the MIMO pilot tone 2110 and PCCH 2120 that are not directed to) afterwards, use spatial reuse and/or the higher modulation form confirmed by each STA in the some connection, send one or more data symbols 2130.The rate control information that embeds in the data division of this part of transmission according to transmission is encoded.Therefore, the part of PHY burst 2100 can be received by a plurality of peripheries station, and actual data have been passed through special finishing, so that station or AP that high efficiency of transmission connects to one or more specific points.Data 2130 can be sent as that kind that access point distributed, and perhaps, send (that is, based on the CSMA/CA process of competition) according to the self-organizing connection.
An exemplary embodiment of PHY burst comprises a lead code, is made up of 8 OFDM symbols of the MIMO reference that is not directed to.Equity CCCH (PCCH) MAC-PDU stem is included in 2 follow-up OFDM symbols, has used the STTD pattern, encodes with R=1/2BPSK.MAC-ID is 12 bits.The request for allocation that also comprises one 8 bit is so that by receiving (therefore, largest request is 256 short OFDM symbols) in the expected duration of AP in next TDD mac frame interval.TX speed is 16 bits, is used for identifying the speed that current group is used.FCCH subchannel preference is two bits, and corresponding to the preference between maximum four subchannel, based on this, AP makes any suitable distribution.CRC is 10 bits.Any amount of other fields and/or field size can be included among other PHY bursts embodiment.
In this example, spatial reuse that each STA during remaining MAC-PDU transmission use is connected by a point confirms and the modulation of Geng Gao.This part of this transmission is that the rate control information that embeds in the data division according to transmission is encoded.
Figure 22 has provided the illustrative methods 2200 of some point data transmission.In frame 2210, flow process begins, and wherein, the MIMO pilot tone that is not directed to is sent at a station.In frame 2220, but the information of together decode is sent at this station.For example, the MIMO pilot tone 2110 that is not directed to and PCCH 2120 as managed be connected in an example of the request mechanism of distributing, AP or other control stations need and can decode to the signal section that comprises this request.Those skilled in the art can recognize to also have other countless request mechanisms, be used on shared channel, a some connection being dispatched.In frame 2230, according to the transformat that consults, data are sent to another station from a station.In this example, the data that are directed to are with sending according to the determined speed of measurement result and the parameter of the MIMO pilot tone 2110 that is not directed to.Those skilled in the art can recognize to also have multiple other means to can be used to be sent as specific some channel and the data of special finishing.
Figure 23 shows a kind of illustrative methods 2300 of point to point link.This illustrative methods 2300 has provided many aspects, and the part of these aspects can be used in any specific embodiment.In decision block 2310, flow process begins.In decision block 2310,, then get into decision block 2320 if there are data will carry out the STA-STA transmission.If no, then get into frame 2370, carry out the communication of any other type, comprise other access styles, if any.After getting into frame 2360, flow process can be returned decision block 2310 and carry out repetition, and perhaps, flow process can finish.
In decision block 2320, if there are the STA-STA data to transmit, then judge this some point connect be the scheduling type or self-organizing.If this transmission is the scheduling type, then get into frame 2330, and the dispensing section of a TXOP is won in request.Should be noted in the discussion above that in the TDD mac frame part of access at random at interval, can send request for allocation, as stated, perhaps, it can be included in the self-organizing transmission.In case make distribution, so, in frame 2350, just can send a STA-STA physical burst.In one exemplary embodiment, method 2200 can be used for one type of STA-STA PHY burst.
In decision block 2320, do not connect if do not hope the some point of scheduling type, then get in the frame 2340, so that the competition access right.For example, can use at interval 2010 sections of 2000 A-TCH of TDD mac frame.After winning access right, get into frame 2350, and send a STA-STA PHY burst, as stated through competition success.
Get into decision block 2360 from frame 2350, wherein, flow process can repeat, and as stated, perhaps, can stop.
Figure 24 shows a kind of illustrative methods 2400 that Rate Feedback is provided, and is used for a point and connects.The figure shows various transmission with can be by other steps of two station STA1 and STA2 execution.STA1 sends a pilot tone that is not directed to 2410 to STA2.STA2 when receiving the pilot tone 2410 be not directed to, measured channel 2420.In one exemplary embodiment, but STA 2 confirms the supporting rate that transmits on the measured channels.This speed is confirmed that the result as Rate Feedback 2430, sends to STA 1.In various other embodiment, can transmit other parameters, so that in STA 1, make the Rate Feedback decision-making.In 2440, STA 1 receives the dispensing section through scheduling, perhaps, and contention transmission opportunities, for example, in A-TCH.In case won transmission opportunity, in 2450, STA 1 just with according to Rate Feedback 2430 determined speed and modulation formats, sends data to STA2.
Can method shown in Figure 24 be promoted the use of among the various embodiment, this is conspicuous to those skilled in the art.Integrated point velocity feedback and more otherwise examples will be described in further detail below.
The point point of being managed that method 2500 among Figure 25 shows between two station STA 1 and STA 2 and access point (AP) connects.In 2505, STA 1 sends the pilot tone that is not directed to, and request for allocation.Also can will be explained below according to sending data than dispensing section early and previous Rate Feedback.In addition, according to from connected by management point point or coming free STA 1 or the Rate Feedback of the self-organizing communication that STA 2 initiates, can send any such data.STA 2 can receive pilot tone and the transmission requests (can be received by various other stations in this zone) that is not directed to access point.
Access point is received transmission requests, and a kind of according in the multiple dispatching algorithm, determines when and whether make the distribution that is used for point to point link.STA 2 measured channel, in 2505, the pilot tone that is not directed to is sent out away, so but STA 2 can confirm to carry out with STA 1 supporting rate of point to point link simultaneously.Alternatively, STA 2 also can receive Rate Feedback and/or data from STA 1 according to preceding once transmission.
In this example, access point has confirmed that will be directed against the transmission of being asked provides allocative decision.In 2515, a dispensing section is transferred to STA 1 from access point.In this example, the last dispensing section of R-TCH540 is in control channel (like above-mentioned CCH 520), to transmit.Equally, in 2520,, make the allocative decision on the R-TCH to STA 2.In 2525, STA 1 receives the dispensing section from access point.In 2530, STA 2 receives the dispensing section from access point.
In 2535, according to dispensing section 2520, STA 2 transmission rates feedback.Alternatively, can comprise the aforesaid request that is used for the transmission of scheduling type, and, any data that will send according to last request.As stated, the Rate Feedback of transmission is selected according to channel measurement 2510.2535 PHY burst also can comprise the pilot tone that is not directed to.In 2540, the channel that STA 1 measures from STA2 receives feedback, and can receive optional data.
In 2545, according to dispensing section 2515, STA 1 sends data according to the Rate Feedback information of receiving.In addition,, can make request, and, Rate Feedback is provided according to the channel measurement result in 2540 for the dispensing section in future.Data are to send according to the concrete channel measurement result that click-through is believed.In 2550, STA 2 receives data, and, any Rate Feedback of sending alternatively.STA2 also can measured channel, so that Rate Feedback is provided for following transmission.
Should be noted in the discussion above that transmission 2535 and 2545 all can be received by access point, is that the part that is not directed to can be received, as stated at least.Therefore, for any request that comprises, access point can provide the additional allocation section that is used for following transmission, respectively by dispensing section 2555 that mails to STA 1 and STA 2 and 2560 expressions.In 2565 and 2570, STA 1 and STA2 receive dispensing section separately.Then, this flow process ad infinitum repeats, wherein, the access on the access point management shared medium, STA 1 and STA2 directly send the click-through letter each other according to supported selected speed and modulation format on the some channel.Note that in other embodiments, also can carry out self-organizing click-through letter, also carry out the click-through of being managed shown in figure 25 simultaneously and believe.
Figure 26 shows (that is self-organizing) the some point connection based on competition.STA 1 and STA2 communicate each other.Other STA also can be in the range of receiving, and can insert shared channel.In 2610, the STA 1 that has data will send to STA 2 keeps watch on shared channel, and the competition access right.In case won transmission opportunity, just a PHY burst 2615 is sent to STA 2, PHY burst 2615 also possibly received by other STA.In 2620, other STA that keep watch on shared channel possibly receive the transmission from STA 1, and the old friend avoids in the road inserting this channel.For example, above-described PCCH can be included in the transmission 2615.In 2630, STA 2 measures channel according to the pilot tone that is not directed to, and the return on the competition shared channel inserts.STA2 also can send data as required.Notice that the competition time can change.For example, in traditional 802.11 systems, after SIFS, can return an ACK.Because SIFS priority is the highest, so STA 2 can make response under the situation of not losing channel.Other embodiment can reduce delay, and can high priority be provided for return data.
In 2635, STA 2 is to STA 1 transmission rate feedback and optional data.In 2640, STA 1 receiving velocity feedback is competed the access right to shared channel again, and in 2645, according to the Rate Feedback of receiving, sends signal to STA 2.In 2640, STA 1 all right measured channel, so that be provided for the Rate Feedback of following transmission to STA2, and can receive any optional data that sends out by STA 2.In 2650, speed and modulation format that STA 2 confirms according to measured channel conditions receive transfer of data 2645.STA2 also can feed back by receiving velocity, to be used for returning a transmission to STA 1.STA 2 also can measured channel, so that following Rate Feedback to be provided.Therefore, get back in 2635, let STA2 return Rate Feedback and data, this flow process can repeat.
Therefore, self-organizing communication can be carried out through the competition access right in two stations two-wayly.Transmission through using Rate Feedback and special finishing to mail to receiving station makes a some connection itself very efficient.But when using the public receiving unit (like PCCH) of PHY burst, so, shown in 2620, other STA can visit this information, and on channel, cause interference in the known holding time of avoiding in PCCH, showing.Shown in figure 25, before step shown in Figure 26, click-through letter that managed or self-organizing can be initiated transfer of data, and, can be used for proceeding subsequently the click-through letter.Therefore, can use any combination of the click-through letter of scheduling type and self-organizing.
Figure 27 has provided an exemplary TDD mac frame interval 2700, is used to explain that the management point point that receives between the station is communicated by letter.In this example, F-TCH and A-TCH duration all are set as 0.Beacon/BCH 510 and CCH 520 transmissions the same as before.The beginning of beacon/BCH 560 expression next frames.CCH 520 indicates the dispensing section that is used for the click-through letter.According to these dispensing sections, during the burst that has distributed 2710, STA 1 sends signal to STA 2.Note that STA 2 distributes the sections of obtaining 2730, is used for STA 1 is made response in identical TDD mac frame interval.Can comprise above-mentioned various compositions in the burst of arbitrary specific some point PHY layer, like Rate Feedback, pilot tone that ask, be directed to and/or that be not directed to, data that be directed to and/or that be not directed to.In dispensing section 2720, STA 3 sends signal to STA 4.In dispensing section 2740, STA 4 sends signal to STA 3 in a similar manner.Can comprise various other rl transmission among the R-TCH, comprise that non-some point connects.Further provide in detail below these and otherwise additional exemplary embodiment are described.
Note that in Figure 27, as required, can dispatch at interval the protection between the section.A major issue about click-through letter is, generally, be unknown path delay between two STA.To this, a kind of processing method is, lets each STA keep its transmitting time to fix, thereby makes they and the clock synchronised ground arrival AP of AP.In this case, AP can provide guard time at the two ends of each point-to-point dispensing section, to compensate the unknown path delay between two STA in the communication.Under many circumstances, Cyclic Prefix will be enough, and needn't adjust in STA reception place.Then, STA must confirm their time deviations separately, so that know the transmission that when receives other STA.The STA receiver possibly kept two receive clocks: one is used for AP frame sequential, and another is used for a point and connects.
As top various embodiment were described, receiver can obtain confirming and channel feedback in its dispensing section, and feed back to transmitter.Even if total Business Stream is unidirectional, receiver also can send reference and request, to obtain dispensing section.The AP scheduler is guaranteed for feedback enough resources to be provided.
Carry out interoperability with tradition station and access point
Just as that kind that specifies here, described various embodiment provide the improvement with respect to legacy system.But because legacy system extensively existed already, a system preferably can keep backward compatibility with existing legacy system and/or legacy user terminals.Term used herein " novel " is used for distinguishing mutually with traditional system.Novel system can be integrated with one or more aspects or the characteristic of describing in detail here.An exemplary novel system is the MIMO ofdm system of describing below in conjunction with Figure 35-52.In addition, being used to of describing in detail below makes the aspect of novel system and legacy system interoperability also be applicable to the system that other wait to develop, and no matter whether comprise any particular refinement of detailed description here in this system.
In an exemplary embodiment, through using different Frequency Distribution (FA), can keep backward compatibility, thereby a novel system is worked on the FA different with the legacy user with other system.Therefore, novel system can be searched for the available FA that works above that.Dynamic frequency selects (DFS) algorithm to can be implemented in this New WLAN, to realize this function.Preferably adopt the AP of multicarrier.
The traditional STA that attempts to insert WLAN can adopt two kinds of scan methods: active scan and drive sweep.Under the situation of drive sweep, through the scanning work frequency band, STA obtains near the tabulation of the feasible set of basic (BSS) it.Under the situation of active scan, STA sends a query messages, with the response of request from other STA among the BSS.
How to confirm to add which BSS for STA, traditional standard is kept silent, and still, in case make a decision, just can attempt carrying out association.If unsuccessful, STA will move through its BSS tabulation, till success.When a traditional STA can't understand the beacon message that is sent, this STA can not attempt to be associated with a New WLAN.But as a kind of method of on single FA, keeping single WLAN type, a novel AP (and UT) can ignore the request from traditional STA.
Another kind of technology is, lets new A P or New type of S TA use effectively tradition (that is, 802.11) message delivery techniques, refuses the request of any traditional STA.If a legacy system is supported this message delivery techniques, then can redirect message be provided for this STA of tradition.
Be to support the frequency spectrum that two types STA need add with the obvious drawback that is associated of on different FA, working.A benefit is to be convenient to manage different WLAN, and to keep like functions such as QoS.But; Just as that kind of describing in detail among the application, for the high data rate that novel system is supported, traditional CSMA MAC agreement (as; Those agreements of describing in detail in tradition 802.11 standards) efficient inadequately usually, like the mimo system embodiment that describes in detail here.Therefore, preferably adopt the mode of operation of backward compatibility, so that novel MAC coexists on identical FA with traditional M AC.Several exemplary embodiments are described below, and wherein, tradition can be shared identical FA with novel system.
Figure 28 shows method 2800, be used on identical Frequency Distribution supporting tradition and novel station the two.In this example,, suppose BSS work (that is, between a plurality of overlapping BSS less than cooperate) for ease of explanation isolatedly.Flow process starts from the frame 2810, uses traditional signaling to establish a uncontended periods.
Be the several illustrated examples that are used for traditional 802.11 systems below, wherein, New WLAN AP can use built-in hook in traditional 802.11 standards, reserves by the special-purpose time of novel station.In addition,, can use any amount of other signaling technologys, establish a uncontended periods for various types of legacy systems.
A kind of technology is under the PCF/HCF pattern, to establish uncontended periods (CFP).AP can establish a beacon interval, and in this beacon interval, announces a uncontended periods, and wherein, it can provide service for novel and traditional STA under poll pattern.This makes duration of the CFP that all traditional STA are arranged to its network allocation vector (NAV) to be announced that network allocation vector is the counter that is used for following the tracks of CFP.So, in CFP, receive that traditional STA of this beacon must not use channel, only if by the AP poll.
Another kind of technology is through RTS/CTS and duration/id field, establishes CFP and NAV is set.In this case, this new A P can send a specific RTS with reservation address (RA), shows that to all New type of S TA this AP is reserving this channel.Traditional STA resolves to this RA field and points to a specific STA, and does not make response.Novel STA makes response with a specific CTS, thereby, remove BSS in the time period that in the duration/id field of CTS/RTS message pair, provides.At this point, channel can freely be used in novel station in the reservation duration, and not conflict.
In frame 2820, the traditional STA that has received the signal that is used to establish uncontended periods waits for, till being finished by poll or uncontended periods.Like this, access point has become distribution of work shared medium uses for novel MAC agreement.In frame 2830, new STA can insert according to this agreement.Any set or the subclass of the aspect that specifies here may be used in a kind of so novel MAC agreement.For example, can adopt the forward direction and the rl transmission of scheduling type, and, the transmission of the some point managed, self-organizing or based on the communication (comprising a point) of competition, perhaps, the combination in any of above-mentioned transmission.In frame 2840, use any in the multiple signal type, finish novel access period, signal type can change according to the legacy system that is adopted.In this exemplary embodiment, send a uncontended periods end signal.In another embodiment, in uncontended periods, also can poll tradition STA.Such access can perhaps, can intert therein after novel access.
In frame 2850, if stipulated a competing cycle for legacy system, then all STA can compete access right.The legacy system that in uncontended periods, can not communicate like this, the request of just can sending and/or attempt to send signal.In decision block 2860, this flow process can be able to continue through turning back to frame 2810, perhaps, also can stop.
Figure 29 shows the combination of tradition and new media access control.On novel agreement 2930, provided traditional MAC agreement 2910, when the two combines when this, just formed a MAC agreement, like the MAC agreement 2950 after the combination.In this example, for purpose of explanation, 802.11 traditional signaling message have been used.It will be recognized by those skilled in the art that technology disclosed herein also is applicable to any and any novel MAC agreement in the multiple legacy system, comprises the combination of function disclosed herein.
Traditional M AC agreement 2910 comprises beacon 2902, and it identifies beacon interval.Traditional beacon interval comprises uncontended periods 2904, followed be competing cycle 2906.Various contention free-poll frame 2908A-N can produce in uncontended periods 2904.Uncontended periods 2904 stops by means of uncontended periods end 2910.In 802.11 exemplary embodiments, each beacon 2902 was sent out away in target beacon transmitting time (TBTT) time.Novel MAC agreement 2930 comprises mac frame 2932A-N.
Note that in CFP 2904 traditional STA should not disturb any New WLAN transmission.AP can be in CFP any traditional STA of poll, thereby in this section, allow to carry out mixed mode operations.In addition, AP can reserve entire CF P 2904 for novel use, and when beacon interval finishes, pushes all traditional businesses to competing cycle (CP) 2906.
These exemplary 802.11 traditional standards need CP 2906 to look is enough to support two exchanges between the conventional terminal.So, can adopt beacon, but this can cause the time jitter (time jitter) in the system.If necessary, in order to reduce shake, can shorten CFP at interval, thereby keep fixing beacon interval.Can be provided for establishing the timer of CFP and CP, so that CFP (that is, about 1.024 seconds) is longer than CP (that is, less than 10 milliseconds).But if AP poll conventional terminal during CFP, then the duration of their transmission possibly be unknown, and possibly cause extra time jitter.Therefore, in the time of on traditional STA being contained in identical FA, must be noted that the QoS that keeps New type of S TA.802.11 traditional standards are synchronized to 1.024 milliseconds time quantum (TU).In this example, adopt the mac frame duration of 2TU or 2.048 milliseconds, novel MAC can be designed to legacy system synchronous.
In some embodiments, preferably guarantee to make novel mac frame synchronous.That is to say that the mac frame clock of system can be continuous, and when sending, this mac frame border starts from the integral multiple of 2.048 milliseconds of frame periods.Like this, be easy to keep the sleep pattern of STA.
Novel transmission need be not compatible with conventional transmission.Stem, lead code etc. can be distinctive for novel system, and their example runs through among the application to be described in detail.Tradition STA can attempt its decoding, but can't correctly decode.Traditional STA under the sleep pattern can not be affected usually.
Figure 30 shows the method 3000 that obtains transmission opportunity.Method 3000 can be as the frame 2830 in the exemplary embodiment of method 2800, as stated.This flow process starts from decision block 3010, wherein, access can be the scheduling type, perhaps is non-scheduling type.It will be recognized by those skilled in the art,, in any specific embodiment, can support in these two kinds of access styles one or both of though this example shows two types access.In decision block 3010, if expect the access of non-scheduling type, then get into frame 3040, thus the competition access right.Can use any amount of access technology based on competition.In case obtained transmission opportunity (TXOP), then in frame 3050, sent according to this transmission opportunity.Then, flow process can finish.
In frame 3010,, insert with request if the access of expectation scheduling type then gets into frame 3020.This access request can be made on RACH during the self-organizing competition, perhaps, uses any other technology disclosed herein.In frame 3030, after this access request goes through, will receive a dispensing section.Get in the frame 3050,, send TXOP according to the dispensing section of receiving.
In some cases, preferably use overlapping traditional B SS, in identical Frequency Distribution, between new A P and the BSS that is associated thereof, realize interoperability.Traditional B SS can be operated under DCF or the PCF/HCF pattern, so between novel B SS and the traditional B SS possibly not be to reach synchronously.
If traditional B SS is operated under PCF or the HCF pattern, then new A P can attempt to be synchronized to TBTT.If this is possible, then new A P can use various mechanism in competing cycle, to occupy channel, its example has been made description above, so that be operated in the overlapping BSS zone.If traditional B SS is operated under the DCF, then new A P also can attempt to occupy channel, and announces a CFP, to remove channel.
Under some occasion, some among the traditional B SS or whole STA possibly can not receive new A P transmission.In this case, these traditional STA may disturb the operation of New WLAN.For fear of this interference, the operation based on CSMA can be given tacit consent in novel station, and relies on the transmission (the following Figure 33-34 that also will combine describes in further detail it) of some point.
Figure 31 shows a kind of exemplary method 3100, so that a plurality of BSS shares single FA.In frame 3110, traditional access point sends a beacon.The novel access point of sharing identical frequency assignments can be synchronized to the TBTT (optional) that is associated with this beacon.In frame 3120, if traditional uncontended periods stipulate according to this beacon, then carry out it.In case uncontended periods (if any) finishes, then all STA just can compete access right in the competing cycle of regulation.In frame 3130, novel access point is competed access right in competing cycle.In frame 3140, New type of S TA can insert shared medium in novel access point has been competed time of access right.Access style between this novel access periods can comprise to be described in detail aspect any one here.Can use multiple technologies, to the time quantum of traditional this access point channel reservation of STA indication like top detailed description.In frame 3150, in case this end cycle, then traditional STA just can compete.In decision block 3160, this flow process can continue through turning back in the frame 3110, perhaps, can finish.
Figure 32 shows the overlapping BSS that uses single FA.Legacy system 3210 sends beacon 3205 (3205A and 3205B have been shown among the figure, have been used to explain the TBTT and total beacon interval of legacy system).Beacon 3205A identifies uncontended periods 3210 and competing cycle 3215.In uncontended periods 3210, can carry out traditional contention free-poll frame 3220A-N, followed be the end indicator 3225 of uncontended periods.
Station monitoring channel in the New WLAN 3240 receives beacon 3205, and gains control of oneself and do not insert medium, till the chance of competition access right is arrived.In this example, chance the earliest is in uncontended periods.After PIFS 3230, novel access point sends a classical signals 3245 to the tradition station, with the time quantum of indication with busy channel.Multiple symbol can be used to carry out this function, and their example is described in detail in the above.Can adopt various other signals, this depends on expectation and which legacy system realization interoperability.Traditional STA in the range of receiving of classical signals 3245 can avoid access channel, till novel access period 3250 finishes.Cycle 3250 comprises one or more TDD mac frames 3260 (in this example, being 3260A-N) at interval.TDD mac frame interval 3260 can be an any kind, and its example comprises one or more aspects of describing in detail here.
In an exemplary embodiment, new A P is busy channel (that is, in per 40 milliseconds, 20 milliseconds of new A P busy channels) in the interval of fixed length.New A P can keep a timer, guaranteeing its only busy channel in expected duration, thereby guarantees the fairness of Channel Sharing.In seizing the process of channel, new A P can use any signaling technology.For example, can send CTS/RTS or conventional beacon, announce new CFP.
In novel interval 3250, exemplary TDD mac frame at interval can be as giving a definition: at first, send a beacon and add F-CCH, with indicate will be in current mac frame the UT on the polling list.Behind F-CCH, broadcast one section MIMO pilot tone, so that STA obtains mimo channel and the accurate tolerance result who forms mimo channel.In one exemplary embodiment, each antenna can be realized fabulous performance with 2 short OFDM symbols.This means that the F-TCH in the initial mac frame comprises 8 MIMO frequency pilot signs substantially.The R-TCH part of first mac frame can so be constructed: so that the STA on the polling list sends MIMO pilot tone and the rate indicator (being used for down link) that is not directed to AP, and confirm.In this example, at this point, all terminals on the polling list prepare in next TDD mac frame interval, to be operated under the normal consistency type mode.After this, under the coordination of AP, use any technology disclosed herein, the TDD mac frame after the TDD mac frame interval can be used for swap data at interval.
As stated, under specific circumstances (for example, when among the traditional B SS some or when all STA can not receive new A P transmission), novel station acquiescence is based on the operation of CSMA, and relies on the transmission of some point.At this moment, above-described connection/close circulation possibly not have advantage, perhaps, or even impossible.In these cases, a point operation can be given tacit consent in novel station.
Figure 33 has provided a kind of illustrative methods 3300, and it uses various technology disclosed herein, carries out high speed click-through letter, simultaneously with traditional B SS interoperability.Flow process starts from frame 3310, wherein, has data will issue the STA competition access right of the 2nd STA.In frame 3320, successfully compete access right after, classical signals is used at this station, those signals as described above, cleaning medium.In frame 3330, a STA sends a request (with pilot tone) to the 2nd STA.The 2nd STA can be according to the pilot tone of being sent, measured channel.The 2nd STA sends to a STA with channel feedback.Therefore, in frame 3340, first stop is received the have channel feedback response of (for example, Rate Feedback).In frame 3350, according to this feedback, a STA sends pilot tone and the data that are directed to second station.In frame 3360, the 2nd STA can send to a STA and confirm, and can send follow-up Rate Feedback, to be used for other transmission.The classical signals that is used for clearing up medium makes: use any high speed technology and with respect to the improvement of legacy system, like those technology disclosed herein, carry out frame 3330 to 3360.In protection scope of the present invention,, just can use any some point MAC agreement in case STA has cleared up medium.Flow process is returned frame 3310 and can be able to continue, and shown in decision block 3370, perhaps, flow process can finish.
In one exemplary embodiment, adopt the some dot pattern, seize channel and work according to the traditional rule of CSMA.In this example, do not adopt PCF and HCF, and a centralized network architecture needn't be arranged.When a New type of S TA hopes and another New type of S TA (or AP) when communicating that this STA seizes channel.First transmission comprises enough MIMO pilot tones, adds the message that a certain request connects.Can adopt CTS and RTS to come cut-back region and set aside some time.Requesting party STA message must comprise STA BSS ID, STA MAC ID and target STAMAC ID (if knowing).Response should comprise the BSSID of response party STA.Like this, these STA just can judge whether they need carry out the receiver correction of emission guiding (transmitsteering) vector, if used guiding (steering).Note that and in this example, do not use the emission guiding, but done advantage like this, if STA has used the appointment AP that coordinates BSS and calibrated.
Shown in figure 33, response can comprise MIMO pilot tone (if adopt, being directed to), adds the speed indication.In case should exchange occur, just can on each link, lead.But,, then initiate the transmission that first between the STA of this connection be directed to and can comprise the MIMO pilot signal that is directed to, so that the receiver of response party STA can be proofreaied and correct the phase difference value between the different B SS if these STA belong to different BSS.
In this exemplary embodiment, in case initial exchange has taken place, just can lead.These exchanges should be followed the SIFS interval between down link and the ul transmissions.Owing to calculate the potential processing delay of the characteristic vector that is used for leading, this possibly need STA to use least mean-square error (MMSE) to handle, rather than characteristic vector is handled.In case calculate guiding vector, STA just can begin at transmitting party use characteristic vector, and the recipient can continue to adopt MMSE to handle, and separates and changes towards the optimal spatial matched filter.Periodic feedback between two STA helps to follow the tracks of and rate controlled.Can add SIFS at interval, so that let STA keep control to channel.
Figure 34 shows the click-through letter, and it uses the MIMO technology, on traditional B SS, competes access right (that is, not managed).In this example, initiator 106A competes access right on channel.Successfully rob when accounting for channel when it, send MIMO pilot tone 3405, the back and then asks 3410 again.This message can comprise the MAC ID of BSS ID, initiator STA and the MAC ID of target STA, if known words.Other signalings like CTS and RTS, can be used to further clear up channel.Response party STA 106B sends the pilot tone 3420 that is directed to, and followed is confirmed and Rate Feedback 3425.The pilot tone 3420 that is directed to is sent when the SIFS 3415 that asks after 3410.In this exemplary embodiment, traditional access point is 802.11 access points, and SIFS has limit priority, and therefore, response station 106B keeps the control to channel.The various transmission that Figure 34 describes in detail can phase mutual edge distance SIFS and send, thereby keeps the control to channel, till the click-through letter finishes.
In one exemplary embodiment, can confirm the maximum duration of channel occupancy.Pilot tone that is directed to 3430 after Rate Feedback 3425 and data 3435 send to response station STA 106B according to this Rate Feedback from initiator STA 106A.After data 3435, response party STA 106B sends pilot tone 3440 and affirmation and the rate controlled 3445 that is directed to.As response, initiator 106A sends the pilot tone 3450 that is directed to, and the back is data 3455 then.
This flow process can ad infinitum continue, and perhaps reaches channel at most and inserts the maximum time that is allowed, and this depends on deployment cycle.Though do not show that in Figure 34 response party STA also can send data, and initiator also can transmission rate control.These data segments can combine with those sections shown in Figure 34, so that maximizing efficiency (that is, SIFS needn't be inserted between these transmission).
When two or more BSS were overlapping, preferably adopting can be with the mechanism of cooperation mode shared channel.Provide several kinds of exemplary mechanism and the exemplary operational process that is associated with it below.These mechanism can combine use.
First kind of exemplary mechanism is that dynamic frequency is selected (DFS).Before establishing a BSS, WLAN need search for this wireless medium and confirm best Frequency Distribution (FA), so that establish the operation of BSS.In the process of search for candidate FA, AP also can create neighbor list so that be redirected and AP between switch.In addition, WLAN can carry out mac frame sequential and neighbours BSS (below will further specify) synchronously.Can use DFS to distribute BSS, synchronisation requirement minimizes between BSS thereby make.
Second kind of exemplary mechanism is synchronous between BSS.In the DFS process, AP can obtain the sequential of neighbours BSS.Usually, preferably make all BSS (in one embodiment, on single FA, perhaps, in another embodiment, striding across a plurality of FA) synchronous, so that carry out switching between BSS.But, adopt this mechanism, on identical FA, work at least and synchronous its mac frame of approximating those BSS.In addition, if be total to channel BSS overlapping (that is, AP can listen to the other side each other), then newly arrived AP can exist situation to inform the AP of original establishment it, and formulates Resource Sharing Protocol as follows.
The third exemplary mechanism is Resource Sharing Protocol.Overlapping BSS shared channel coequally on same FA.Mac frame is replaced between BSS according to certain predetermined way, thereby realize this point.Like this, the business among each BSS just can be used channel, and can not emit the risk of being disturbed by other BSS.Shared can be implemented between all overlapping BSS like this.For example, under the overlapping situation of 2 BSS, an AP uses the mac frame of even-numbered, and another AP uses the mac frame of odd-numbered.Under the overlapping situation of three BSS, share and to use 3 to realize as mould.Other embodiment can adopt the shared mechanism of any kind.Control field in the BCH Overhead Message can show the type that whether can carry out resource-sharing and shared cycle.In this example, the sequential of all STA is adjusted to the suitable shared cycle among the BSS.In this example, under the overlapping situation of BSS, time-delay will increase.
The 4th kind of exemplary mechanism is auxiliary synchronous again of STA.This situation may occur: two BSS can't hear the other side each other, but a new STA in the overlapping region can hear they two.This STA can confirm the sequential of these two BSS, and this is reported to them.In addition, this STA can confirm time deviation, and indicate which AP should its frame sequential of slippage and slippage what.This information must propagate into all BSS that are connected with this AP, and they all must rebulid the frame sequential, to realize synchronously.Can in BCH, announcing synchronously again of frame.Can this algorithm be applied to handle more how unconscious overlapping BSS.
Describe in detail below and can be used for above-mentioned one or more machine-processed example process.
AP can realize synchronously when powering up or in other fixed times.Through near the system search in all FA, can confirm system sequence.For ease of synchronously, one group of orthogonal code can be used for assisting to distinguish different AP.For example, AP has the known beacon of repetition in each mac frame.These beacons can use Walsh sequence (for example, length is 16) to cover.Therefore, the equipment such as AP or STA can be carried out the pilot frequency intensity measuring (PSM) of local AP, to confirm overlapping BSS.With further explain, the movable STA that is associated with an AP can send echo below, to assist synchronously.These echoes can use and corresponding sequential of AP overlay code (cover) and soverlay technique (covering).Therefore, when overlapping but these BSS AP separately of BSS can't detect the signal from the other side, the STA echo can be received by neighbor AP, thus provide its AP for information about and neighbor AP can be synchronous signal.Note that the overlay code that on different FA, can reuse quadrature.
Can be based on the set of undetected Walsh overlay code, the selection (that is, selecting a not detected Walsh overlay code on neighbor AP) of Walsh overlay code is accomplished on certainty ground.If all overlay codes all exist, then can reuse by new AP with the corresponding sign indicating number of the most weak received signal level (RSL).Otherwise, in one embodiment, can select to make the maximized sign indicating number in working point (see also the reusable structuring power of self adaptation avoidance mechanism, also will be elaborated below) of AP to this.
In this example, by interlaced with each other the coming of frame counter of each AP transmission.The interlace mode that is adopted is corresponding to Walsh overlay code label.Therefore, AP0 uses Walsh sign indicating number 0.When AP0 frame counter=j, APj uses Walsh overlay code j, and its frame counter equals 0.
When powering up or will carry out the synchronous any time, AP monitors neighbor AP beacon and/or STA echo.If do not detect the neighbours system, then AP establishes its time reference.This can be arbitrarily, and is perhaps relevant with GPS, or any other local time reference.If detect individual system, then correspondingly establish local sequential.If AP detects two or more systems that do with the different time lineman, then AP can carry out with the system with peak signal synchronously.If these system works are on identical Frequency Distribution (FA), then AP can attempt to be associated with more weak AP, thereby informs that it is operated near other AP on the independent clock.This new AP attempts synchronous two required time deviations in AP district are informed more weak AP.More weak then district AP can adjust its sequential.For a plurality of neighbor AP, this can repeat.With the synchronous sequence of two or more systems, new AP can establish its sequential.If all neighbor AP all can not be synchronized to single sequential (no matter being what reason), then this new AP can be synchronized to any one neighbor AP.
AP can carry out dynamic frequency and select when powering up.As stated; Generally; Preferably can select to make the overlapping minimum of BSS through DFS; Thereby make the quantity and any delay or the throughput reduction related that need synchronous BSS minimize (that is, compare the BSS that must share these medium with one or more neighbours BSS, the BSS that on a FA, can insert whole medium is more efficient) with this locking phase.Synchronously, new AP can select to have the FA (that is, when measuring neighbor AP, or during echo) of minimum RSL.AP can periodically inquire STA, so that carry out the AP pilot measurement.Equally, AP can dispatch silence period, to assess the AP place by the level of interference that STA was caused from other districts (being neighbor bss S).If this RSL grade is excessive, then AP can attempt seeking another FA in non-dispatching cycle, and/or the braking power compensation policy, was described below.
As stated, can organize AP according to the pilot tone overlay code.In this example, it is 16 Walsh sequence overlay code that each AP can use length.Can use the sign indicating number of a different length arbitrarily.The pilot tone overlay code is used for the symbol at a super frame period internal modulation beacon.In this example, super frame period equals 32 milliseconds (that is 16 continuous N AC frame beacons).Then, STA can be in superframe interval integration coherently, with the pilot power of confirming to be associated with a specific AP.As stated, AP can select its Walsh sign indicating number from undetected a plurality of available Walsh sign indicating numbers.If detect all sign indicating numbers (on identical FA), then AP can be according to from the most by force they are ranked to the most weak inferior ordered pair.AP can reuse and the most weak detected corresponding Walsh sign indicating number of Walsh sign indicating number.
For ease of the identification neighbor AP, STA can be used for sending echo, to identify their corresponding AP.Therefore, as stated, an AP who does not detect neighbor AP may detect corresponding STA echo, thereby identifies this AP and sequential thereof.Each AP can send configuration information in its beacon, and each STA can serve as repeater, so that resend AP configuration information and sequential to the neighbor AP of any reception.
When the order of receiving from AP, movable STA need send a predetermined pattern, so that be operated in the existence that near AP on the identical FA detects this neighbours system.A kind of simple method is, a definition observation interval (for example, between FCH and RCH) in mac frame, and it is not used for any business by AP.The duration of observation interval can be defined as long enough, to handle maximum different propagation delays between the STA that STA that this AP is associated and neighbor AP be associated (for example, 160 chips, perhaps, 2 OFDM symbols).For example, use STA that the AP of Walsh overlay code j is associated can be in its mac frame counter=0 o'clock to send echo.On this echo coding have the neighbor AP of making detect existence and with adjacent AP district in the STA information necessary that coexists efficiently.
Can adopt the reusable structuring power back-off of self adaptation (backoff).When system is crowded must near another AP, reuse to each FA the time, it is machine-processed preferably to apply a kind of structurized power back-off, so that the terminal in two districts is all with maximal efficiency work.When detecting when crowded, can use power control, improve the efficient of system.That is to say, be not whenever all to send with total power, and AP can use a kind of structurized power back-off mechanism of mac frame counter synchronisation with them.
For example, suppose that two AP are operated on the identical FA.In case these AP detect this situation, they will work out known power back-off strategy.For example, two AP use a kind of compensation mechanism, and it makes: total power Ptot on mac frame 0, and Ptot on mac frame 1 (15/16) ..., Ptot/16 on mac frame 15.Because AP is synchronous and their frame counter interlocks, so, there is not the AP district to use total power simultaneously.This target is the compensation model that selection makes the STAs in each AP district work with highest-possible throughput.
The used compensation model of specific AP can be the function of detected degree of disturbance.In this example, a specific AP can use maximum 16 known compensation models.AP can transmit used compensation model in BCH and in the echo that the STA that is associated by AP sends.
Walton etc. make, exercise question is the United States Patent (USP) 6 of " Method and apparatus for controllingtransmissions of a communications systems (being used to control the method and apparatus of communication system transmits) "; 493; Describe a kind of exemplary compensation mechanism in 331 in detail, this patent has transferred assignee of the present invention.
Figure 53 shows another exemplary embodiment that can carry out the technology of interoperability with legacy system.An exemplary mac frame 1500 has been shown among the figure, has combined Figure 15 that it is specified above.Also introduce a kind of time slot pattern, wherein, defined slot time 5310.Slot time 5310 comprises MIMO pilot interval 5315 and time slot gap 5320.As shown in the figure, inserted pilot tone 5315, to reserve this channel, make it avoid influence according to other stations (comprising AP) of the rule work such as EDCA.Improved mac frame 5330 consists essentially of mac frame 1500, has wherein inserted pilot tone 5315, so that keep the control to medium.Figure 53 is illustrative, and to those skilled in the art, this is conspicuous.The time slot pattern can combine with the mac frame of any kind, describes its various examples here in detail.
In this example, for ease of explanation, the mac frame of supposing traditional 802.11 systems use is 1.204 milliseconds a integral multiple.Mac frame can be made as 2.048 milliseconds, so that synchronously.At target beacon transmitting time (TBTT), the announcement CFP duration is so that STA is provided with its NAV.During CFP, the STA among the BSS should not send signal, only if by poll.Alternatively, as previously mentioned, AP also can send RTS, and lets STA respond an identical CTS, with further cleaning BSS.This CTS can be the synchronous transmission from all STA.In this example, always start from 2.048 milliseconds of borders through guaranteeing mac frame, can eliminate shake.Like this, even if under the situation that TBTT shortens, also between adjacent/overlapping BSS, hold time synchronously.Above-described various other technologies can combine with the technology that describes below.In case reserved medium for amended mac frame 5330; Just can use any techniques available; Adopt the time slot pattern to keep the right of possession corporeal right, disturb the transmission that received scheduling to prevent traditional STA, thereby the throughput that reduces novel system potentially increases (promptly medium; Use mechanism shown in Figure 15 or Figure 53, other mechanism of perhaps describing in detail here).
In this example, new A P follows the CSMA rule and seizes channel.But before this, it should or listen to beacon, and perhaps other STA attempt to determine whether to exist another BSS.But,, do not need synchronously in order to realize fair resource-sharing.
In case detect neighbours BSS, this new A P just can seize channel through sending its beacon.In order to stop (lock out) other users, this new A P sends has the pilot tone of a certain frequency, thereby prevents that other STA from using this channel (that is, not having idling cycle to be longer than PIFS=25usec).
This new A P can be provided with one can make it at the timer of confirming to take in the fair fixedly duration this channel.Like this can be roughly synchronous with the beacon period of traditional AP, perhaps asynchronous (that is, per 200 milliseconds in 100 milliseconds).
This new A P can seize channel by any point in the interval that it allowed, and this can be postponed by the traditional B session service user.If there is not business to serve, this new A P can abandon channel before its time expires.When this new A P occupied channel, it was restricted to a just time period with its use.In addition, the sequential of this new A P establishment can be consistent with original mac frame sequential.That is to say that novel beacon appears on 2.048 milliseconds of borders of new A P clock.Like this, New type of S TA can judge whether HTAP has occupied channel through observing these specific intervals, thereby keeps synchronously.
This new A P can announce its frame parameter in beacon.The part of frame parameter can comprise the pilot interval spacing, is used to represent the frequency of pilot transmission in this mac frame.Note that this new A P can dispatch STA, so that its transmission is overlapping with periodic burst pilot.In this case, the overlapping STA of dispensing section knows this point, and in this cycle, ignores pilot tone.Other STA do not know this point, therefore use a threshold supervision device, confirm what whether pilot tone sent in predetermined distance.
This situation: STA may occur and originally will send pilot signal by the moment that AP sends, perhaps, AP sends the pilot signal that is directed to and arrives STA in this interval.Worsen its channel estimating in order to prevent other STA from using these pilot signals, the AP pilot signal can be used and the public guide frequency Walsh overlay code Walsh overlay code of quadrature mutually.Can adopt the structure that is used to distribute the Walsh overlay code.For example; When STA uses different Walsh overlay codes with AP; The Walsh space can comprise 2N overlay code; The overlay code of N is wherein reserved for AP, and other overlay code is to reserve for the STA that is associated with a specific AP, and the overlay code that this specific AP uses is related with the Walsh overlay code of corresponding AP in a known way.
When this new A P when STA sends assignment information, its this STA of expectation sends to it in predetermined distance.This STA possibly not receive this assignment information, and in this case, PIFS is longer than at the interval that channel possibly not be used.In order to prevent this situation, AP can detect channel in t＜SIFS, and judges whether it is occupied.If unoccupied, then AP can seize channel immediately through sending the pilot tone of corresponding phasing.
Can novel channel allocation section time slot be changed into the interval (16 microsecond) of SIFS.Like this, channel occupancy just can be protected, thereby refuses the legacy user in new exclusive in the cycle.
Must be designed to support interoperability to RCH, this is because the duration of RCH possibly surpass 16usec.If In a particular embodiment this RCH can not be provided at an easy rate, so, when novel MAC does not have the channel control (, coexistence under traditional mode), can distribute this RCH to be operated under the traditional mode.Through allowing any time (that is, wait for 4 microseconds, and send 8 microseconds) of STA after pilot transmission to send the request of access, F-RCH can be provided, shown in Figure 53.
Exemplary embodiment: the 802.11MIMO WLAN of enhancing
The exemplary embodiment of describing in detail is below explained above-mentioned various aspects and other aspects.In this example, show the enhancing 802.11WLAN that uses MIMO.To describe various MAC in detail and strengthen, and, be used in corresponding data and message transferring structure on MAC layer and the physical layer.It will be recognized by those skilled in the art, only disclose the part of WLAN characteristic, and they can make content disclosed herein be applicable to 802.11 legacy system interoperability, and, with the interoperability of various other systems.
The exemplary embodiment of describing in detail below is characterised in that: can with traditional 802.11a, 802.11g STA interoperability, and, can with the ultimate criterion interoperability of 802.11e draft and expection.This exemplary embodiment comprises MIMO OFDMAP, and so name is in order to distinguish mutually with traditional AP.Also will specify below, because backwards compatibility, traditional STA can be associated with MIMO OFDM AP.But MIMO OFDM AP can refuse the association request from traditional STA clearly, if necessary.The DFS process can be directed to the AP (can be traditional AP or another MIMO OFDMAP) that another supports traditional operation to unaccepted STA.
MIMO OFDM STA can be associated with the 802.11a that does not wherein have AP or 802.11g BSS or Independent B SS (IBSS).Therefore, for this operation, a such STA will realize all indispensable functions of 802.11a, 802.11g and 802.11e expection final version.
In BSS or IBSS, when tradition is shared identical RF channel with MIMO OFDM STA, support various functions.The MIMO OFDM PHY spectral mask and the existing 802.11a that are advised, the spectral mask of 802.11g is compatible, thereby, can not introduce additional adjacent-channel interference to traditional STA.The signal field backward compatibility of extended signal field in the PLCP stem (following detailed description) and tradition 802.11.In the legacy signal field not the rate value of usefulness be configured to define new PPDU type (below will specify).Adaptive cooperation function (ACF) (below will specify) can make the medium between tradition and the MIMO OFDM STA realize sharing arbitrarily.802.11e the cycle of EDCA, 802.11e CAP and SCAP (following introduction) can be inserted any beacon interval arbitrarily, this is confirmed by the AP scheduler.
As stated, need realize the high data rate that MIMO WLAN physical layer is supported effectively with high-performance MAC.Describe the various attributes of this exemplary MAC embodiment below in detail.Be the attribute of certain exemplary below:
The self adaptation of PHY speed and transmission mode effectively utilizes the capacity of MIM0 channel.
The low delay service of PHY provides low end-to-end delay, to solve high-throughput (for example, multimedia) demands of applications.When low load, adopt MAC technology, perhaps, when the heavy duty system, use centralized or distributed scheduling, can realize the low delay operation based on competition.Low delay has a lot of benefits.For example, low delay can be realized quick self-adapted, thereby makes the physical layer data rate maximization.Low delay can be realized cheap MAC by enough minibuffer devices, and needn't stop ARQ.Use for multimedia and high-throughput, low delay also makes end-to-end delay minimize.
Another attribute is high MAC efficient and low competition expense.In the MAC based on competition, when data rate was high, time that useful transmission takies shortened, and incremental portion that should the time is wasted in expense, conflict and the idling cycle.Through scheduling, and, through a plurality of high layer packets (for example, IP datagram) are aggregated in the single mac frame, can reduce the time of waste in the media.Also aggregate frame be can form, thereby lead code and training expense minimized.
The high data rate that PHY supports can realize that the QoS that simplifies handles.
The exemplary MAC that specifies below strengthen can with the mode of 802.11g with 802.11a maintenance backward compatibility, solve above-mentioned performance standard.In addition, as stated, the support of the function that comprises among the draft standard 802.11e and improvement comprise following function, like TXOP and direct link agreement (DLP), and, optional piece affirmation mechanism.
In order to describe following embodiment,, use new term for some notions of top introduction.The mapping table of new terminology is as shown in table 1:
Table 1, term mapping table
Frame aggregation flexibly
In this example, frame aggregation flexibly is easy to realize.Figure 35 shows encapsulation one or more mac frames (or segment) in an aggregate frame.Frame aggregation can be encapsulated in one or more mac frames (or segment) 3510 in the aggregate frame 3520, wherein can add header compressedly, will be elaborated to this below.Polymerization mac frame 3520 forms PSDU 3530, can be used as a PPDU and sends.Aggregate frame 3520 can containing type be the frame (or segment) 3510 after the encapsulation of data, management or control.When the needs privacy, can encrypt the frame load.The mac frame stem of encrypted frame is " being under the plaintext state (in the clear) " transmission.
The frame aggregation of aforesaid this MAC level can be transferred to identical recipient STA with frame under the situation that does not have IFS or BIFS (the burst frame spacing is below with further explain).In some applications, preferably can make AP not have under the situation of IFS that a plurality of frames or aggregate frame are sent to a plurality of recipient STA.Through using the SCHED frame, can realize this point, also will discuss below to this.The time started of a plurality of TXOP of SCHED frame definition.When AP carries out back-to-back (back-to-back) when transmission to a plurality of recipient STA, can be without lead code and IFS.This is called as the PPDU polymerization, to be different from the frame aggregation of MAC layer.
It is lead code that an exemplary polymerization mac frame transmission (being PPDU) begins the place; Be that MIMO OFDM PLCP stem (comprises signal field then; This signal field can comprise signal 1 and 2 two fields of signal), the back is a MIMO OFDM training symbol (if any) again.Below in conjunction with the exemplary PPDU form of Figure 49-52 further explain.The polymerization mac frame neatly polymerization to send to frame or the segment after one or more encapsulation of identical recipient STA.(the SCHED message of following detailed description allow will TXOP carry out polymerization) from AP to a plurality of recipient STA.For the quantity of polymerisable frame and segment, not restriction.Full-size for the aggregate frame of establishing through consultation can have restriction.Usually, first frame in the aggregate frame possibly be the segment of creating for efficient package with last frame.When the Frame after a plurality of encapsulation was included in the aggregate frame, the MAC stem and the QoS Frame of data can compress, and are described below.
Through using frame aggregation flexibly, transmit leg MAC can reduce PHY and PLCP expense and idling cycle as possible.Can frame be carried out polymerization, with elimination frame pitch and PLCP stem, and frame segmentation flexibly to take the free space among the TXOP fully, realizes this point.In a kind of exemplary techniques, based on current data rate with distributed or based on duration of TXOP of competition, the calculating of MAC elder generation will offer the byte number of PHY.Then, can be with the packing of the mac frame after the complete sum segmentation, to take whole TXOP.
If a complete frame can not be contained in the remaining space among the TXOP, then MAC can carry out segmentation with next frame, to take remainder bytes as much as possible among the TXOP.For package efficiently, can carry out any segmentation to frame.In one exemplary embodiment, this any segmentation will receive the restriction of maximum 16 segments of every frame.In other embodiments, can not need should limit.The residue segment of mac frame can be sent in follow-up TXOP.In follow-up TXOP, MAC can give the not segment of the frame of complete transmission higher priority, if expectation.
The polymerization stem (being 2 bytes in this example) that specifies below is inserted into the MAC stem of each encapsulated frame (or segment), and encapsulated frame (or segment) is inserted in the aggregate frame.Length field in the polymerization stem representes to encapsulate the length (unit is a byte) of back mac frame, and is used for from aggregate frame, extracting frame (and segment) by receiver.The size (quantity of OFDM symbol) of the PPDU size field regulation MIMO OFDM PPDU transmission in the signal field of being advised, and the length of the mac frame after each encapsulation is indicated by the polymerization stem.
Encapsulated frame header compressed
Figure 36 shows a traditional M AC frame 3600, and it comprises MAC stem 3660, followed be frame entity 3650 (can comprise a variable number N byte) and frame check symbol (FCS) 3655 (in this example, being 4 bytes).This prior art mac frame form has carried out detailed description in 802.11e.MAC stem 3660 comprises: frame control field 3610 (2 bytes), duration/id field 3615 (2 bytes), sequential control field 3635 (2 bytes) and QoS control field 3645 (2 bytes).In addition, also comprise four address fields: address 1 3620, address 2 3625, address 3 3630 and address 43640 (each all is 6 bytes).Also can these addresses be called TA, RA, SA and DA respectively.TA is a transmitter station address, and RA is the destination address, and SA is a source station address, and DA is the address, point of destination.
When comprising a plurality of encapsulation of data frame in the aggregate frame, can the MAC stem and the QoS Frame of data be compressed.For example, Figure 37-39 shows the MAC stem after the exemplary compression that is used for the QoS Frame.Note that FCS calculates according to the MAC stem after the compression and (encryption or unencrypted) load.
Shown in Figure 37-39, when with MIMO data PPDU (type 0000) transmit frame, in the MAC of mac frame 3600 stem 3660, introduce a polymerization header field, thereby create the mac frame after the encapsulation, promptly 3705,3805 or 3905.The MAC stem comprises the polymerization header field, is called as the MAC stem (promptly 3700,3800 or 3900) of expansion.Can be aggregated to the management after one or more encapsulation, control and/or Frame (comprising the QoS data) in the mac frame after the polymerization.When using data-privacy, can encrypt data load or QoS Frame.
For each frame (or segment) that is inserted in the aggregate frame (being respectively 3705,3805 or 3905), insert polymerization stem 3710.Header compressed polymerization stem type field by following detailed description indicates.The frame stem and the QoS Frame of data can compress, to eliminate redundant field.The aggregate frame 3705 that provides among Figure 37 shows a kind of unpressed frame, and it comprises all four addresses and duration/id fields.
After sending a unpressed aggregate frame, other aggregate frame just needn't identify dispatching station and destination address, because they are identical.Therefore, can omit address 1 3620 and address 2 3625.For the subsequent frame in the aggregate frame, needn't comprise duration/id field 3615.Duration is used to set NAV.Duration/id field is determined on a case-by-case basis.In polling message, it comprises inserts ID (AID).In other message, identical field indicates the duration that is used to set NAV.Corresponding frame 3805 has been shown among Figure 38.
When source address and address, point of destination comprise identical information, further compression can be provided.In this case, address 3 3630 also can be omitted with address 4 3640, thereby obtains frame shown in Figure 39 3905.
When field was removed, in order to decompress, the respective field of last stem (after decompression) was inserted in the receiver auto polymerization in the future frame.In this example, first frame in aggregate frame always is to use unpressed stem.The deciphering of load need be from some fields of MAC stem, these fields maybe be for ease of header compressed and be removed.After the decompression of frame stem, can offer decryption engine to these fields.Length field is used for extracting frame (and segment) from aggregate frame by receiver.Length field indicates the length (unit is a byte) of the frame with compressed header.
After extracting, remove the polymerization header field.Then, the frame after decompressing is delivered to decryption engine.In decrypting process, the field in (after the decompression) MAC stem need be carried out the message integrity checking.
Figure 40 has provided an exemplary polymerization stem 3710.For the one or more frames that in MIMO data PPDU, send (encryption, or unencrypted), be that each frame (or segment) stem is added the polymerization stem.This polymerization stem comprise one 2 bit polymerization stem type field 4010 (be used for expression whether adopted header compressed, and which kind of type) and the length field 4030 of one 12 bit.Type 00 frame does not adopt header compressed.Type 01 frame has been removed duration/ID, address 1 and address 2 fields.Class1 0 frame has the removal field identical with type 01 frame, has removed address 3 and address 4 fields in addition.Length field 4030 in the polymerization stem indicates the length of the frame with compressed header, and unit is a byte.2 bits 4020 are reserved.Summed up polymerization stem type in the table 2.
Table 2, polymerization stem type
In this exemplary embodiment, all management frames that encapsulate in the aggregate frame and control frame adopt unpressed frame stem, and its polymerization stem type is 00.Following management frames can be encapsulated in the aggregate frame with Frame: association request, associated response, association request, associated response, probe requests thereby, probe response, disassociation, authentication and releasing authentication again again.Following control frame can be encapsulated in the aggregate frame with Frame: BlockAck and BlockAckRequest.In other embodiments, can encapsulate the frame of any kind.
The adaptive cooperation function
Adaptive cooperation function (ACF) is the extended version of HCCA and EDCA, and it can realize flexibly, the operation of efficient, low delay scheduling, the operation of the high data rate that is suitable for being supported by MIMO PHY.Figure 41 has provided an exemplary embodiment of the scheduling access period frame (SCAP) that in ACF, uses.Use SCHED message 4120, AP can dispatch one or more AP-STA, STA-AP or STA-STA TXOP simultaneously in the cycle of scheduling access period 4130 by name.These transmission through scheduling are identified as the transmission 4140 of scheduled.SCHED message 4120 has replaced traditional HCCA poll frame of top detailed description.In this exemplary embodiment, the maximum permissible value of SCAP is 4 milliseconds.
For ease of explanation, Figure 41 has provided exemplary scheduled transmissions 4140, and it comprises that AP transmits 4146 to AP transmission 4144 and STA to STA to STA transmission 4142, STA.In this example, AP sends 4142A to STA B, then, sends 4142B to STA D, sends 4142C to STA G again.Note that between these TXOP and needn't introduce the gap, because for each transmission, information source (AP) is identical.When information source changes, show gap between the TXOP (below exemplary gap clearance is described in further detail).In this example, transmit after 4142 to STA at AP, STA C sends 4144A to AP, and then, behind a gap, STA G sends 4144B to AP, and through a gap, STAE sends 4144C to AP again.Then, a point-to-point TXOP 4146 is dispatched.In this case, STA E is information source (sending to STA F), so, if STA E transmitting power is constant, then need not introduce the gap, otherwise, the BIFS gap can be used.Can other STA be dispatched to the STA transmission, but in this example, do not show these.According to any order, can dispatch any combination of TXOP.The order of shown TXOP type just for purpose of explanation.In order to reduce required gap number, preferably can dispatch TXOP, still, this is not necessarily.
When only having MIMO STA, the NAV of SCAP can set (following also the SCHED frame can be described in further detail) through the duration field in the SCHED frame.Alternatively, if hope to avoid the protection of traditional STA influence, AP also can be provided with CTS-to-Self4110 before SCHED frame 4120, thereby was the SCAP establishment NAV at all STA places among the BSS.
In this embodiment, MIMO STA observes the SCAP border.Last STA that in SCAP, sends must stop its TXOP in the duration of PIFS at least before SCAP finishes.MIMO STA also observes the TXOP border through scheduling, and before the TXOP that is distributed finishes, accomplishes its transmission.Like this, the follow-up STA that is scheduled just can begin its TXOP under for idle situation needn't detecting channel.
Can show in the ACF ability item allowed in the SCAP based on scheduling or based on the maximum length of the TXOP of competition.In this embodiment, the length of SCAP does not change in a beacon interval.This length may be displayed in the ACF ability item.An exemplary ACF item comprises: SCAP length (10 bit), maximum SCAP TXOP length (10 bit), protection IFS (GIFS) duration (4 bit) and FRACH response (4 bit).SCAP length is represented the length of SCAP in the current beacon interval.This field is that unit encodes with 4 μ s.Maximum SCAP TXOP length representes that the maximum in the SCAP allows TXOP length.This field is that unit encodes with 4 μ s.The GIFS duration is the continuous protection interval between the STA TXOP that dispatches of passing through.This field is that unit encodes with 800ns.The FRACH response is that unit representes with SCAP.AP must use FRACH PPDU, through in FRACH RESPONSE SCAP, to STA the TXOP through scheduling being provided, response is made in the request of receiving.
Figure 42 has provided an example that SCAP and HCCA and EDCA is combined use.In any beacon interval (4210A-C representes with beacon), AP fully can be flexibly, will intert with 802.11e CAP, MIMOOFDM SCAP based on the access duration of EDCA competition adaptively and be in the same place.
Therefore, use ACF, AP can be as working in HCCA, and still, it can also be the SCAP assignment period.For example, AP can be as using CFP and CP in PCF, as in HCCA for polling operation distributes CAP, perhaps, can distribute SCAP for scheduling operation.Shown in figure 42, in a beacon interval, AP can use any combination based on the cycle of access (EDCA) 4220A-F, CAP 4230A-F and the SCAP 4100A-I of competition.(for the sake of simplicity, the example among Figure 42 does not show any CFP.) AP is based on its dispatching algorithm and observed result that medium are taken thereof, the ratio of the medium that adjustment is taken by dissimilar access mechanisms.Can adopt any dispatching technique.AP confirms whether the QoS stream of being admitted is satisfied with, and can use other observed results, comprises that the medium of measuring take situation, adjust.
HCCA and related CAP thereof have been described above.Provided an illustrative CAP 4230 among Figure 42.AP TXOP 4232 followed be poll frame 4234A.HCCATXOP 4236A follows in poll frame 4234A back.Send another poll frame 4234B, its followed be another corresponding HCCATXOP 4236B.
EDCA has been described above.Provided an illustrative EDCA 4220 among Figure 42.Show various EDCATXOP 4222A-C.Omitted CFP in this example.
The form that SCAP 4100 shown in figure 42 can adopt Figure 41 to describe in detail comprises optional CTS-to-Self4110, SCHED 4120 and scheduling access period 4130.
AP uses 802.11 business transferring Indication message (DTIM) message, and the indication scheduling operation is described below.DTIM comprises the bitmap that inserts ID (AID), and another STA among this AP or the BSS has laid in data for it.Use DTIM, notify all STA that possess the MIMO ability after beacon, to keep wake-up states.In the BSS that traditional and MIMO STA exist,, dispatch traditional STA earlier immediately following after beacon.After conventional transmission, send SCHED message immediately, it shows the composition of dispatching access period.The STA that possesses the MIMO ability that in the particular schedule access period, is not scheduled can sleep in remaining SCAP, wakes up then and monitors follow-up SCHED message.
Adopt ACF, can realize various other operator schemes.Figure 43 shows an exemplary operation, and wherein, each beacon interval comprises a plurality of SCAP 4100, wherein is interspersed with the access period 4220 based on competition.Under this pattern, shared medium wherein, is dispatched MIMO QoS stream during SCAP liberally, and the non-QoS stream of MIMO uses competing cycle with traditional STA (if existence) simultaneously.The cycle of inserting is realized the low delay service to MIMO and traditional STA.
As stated, in SCAP, before the SCHED message CTS-to-Self can be arranged, be used to be protected from the influence of traditional STA.If there is not traditional STA, then do not need CTS-to-Self (or other traditional cleaning signals).Beacon 4210 can be set a long CFP, avoids the influence of any arrival tradition STA to protect all SCAP.CP when beacon interval finishes makes newly arrived traditional STA can insert medium.
Use exemplary operation shown in Figure 44, under the situation that a large amount of MIMO STA are arranged, can realize the optimization of low delay operation.In this example, suppose that traditional STA (if any) only needs Limited resources.AP sends a beacon, thereby sets up long CFP 4410 and short CP 4420.Beacon 4210 followed be any broadcast/multi broadcast message that is used for traditional STA.Then, lean against privately SCAP 4100 is dispatched.This operator scheme can realize the power management optimized, because STA need periodically wake up in order to listen to SCHED message, and, if be not scheduled among the current SCAP, then can sleep at interval at SCAP.
FRACH that comprises in the scheduling access period 4130 through SCAP 4100 or MIMO EDCA cycle, provide to be used for inserting of MIMO STA based on protected competition.In CP 4420, traditional STA can carry out the access based on competition to medium.
After the transmission of SCHED frame, can dispatch continuous scheduling type transmission from AP.The SCHED frame can send with lead code.The follow-up AP transmission that is scheduled can be sent under the situation of lead code not having.(can send the designator that is used to represent whether to comprise lead code).An exemplary PLCP lead code is described in further detail below.In this exemplary embodiment, the STA that is scheduled is transmitted under the situation of lead code and begins.
Mistake is recovered
Recover in order to receive the mistake from SCHED, AP can use various processes.For example, if a STA can't decode to a SCHED message, then it can not utilize its TXOP.If the TXOP that is scheduled did not begin in the time started of being distributed, send during then through the PIFS after not beginning with scheduling TXOP, AP can start recovery.AP can use the not scheduling TXOP cycle of usefulness, as a CAP.In this CAP, AP can send signal, perhaps STA of poll to one or more STA.Poll frame can mail to STA or another STA that has lost the TXOP that is scheduled.Before next was scheduled TXOP, this CAP finished.
When the TXOP that is scheduled finishes too early, also can use identical process.Send during through the PIFS after last end of transmission in the TXOP that is scheduled, AP can begin to recover.AP can use the cycle of not using of the TXOP that is scheduled, as CAP, as stated.
Shielded competition
As stated, SCAP also can comprise: be exclusively used in the part of FRACH transmission and/or the part that MIMO STA can use the EDCA process therein.These access periods based on competition can be protected by the NAV that sets for SCAP.
Shielded competition allows STA indication TXOP request, so that in scheduling, assist AP, thus replenish the low delay scheduling operation.In cycle, MIMOOFDM STA can use the access (avoiding and traditional STA competition) based on EDCA to come transmit frame at shielded EDCA.Use conventional art, STA can indicate the TXOP duration to ask or buffer state in the MAC stem in the 802.11e QoS control field.But FRACH provides a kind of more efficient means of identical function.In cycle, STA can use the competition of the Aloha formula of gapization at FRACH, access channel in the FRACH of fixed dimension time slot.FRACH PPDU can comprise that the TXOP duration asks.
In this exemplary embodiment, MIMO PLCP stem is used in the transmission of MIMO frame, will be elaborated to this below.Exist under the situation of non-MIMO STA; Because traditional 802.11b, 802.11a and 802.11g STA can only decode to signal 1 field (below will combine Figure 50 to be described in detail) of MIMO PLCP stem; So the MIMO frame must send having under the situation of protection.When traditional and MIMO STA exist, use the STA of EDCA access procedure can use traditional RTS/CTS sequence, protect.Tradition RTS/CTS refers to and uses traditional lead code, PLCP stem and mac frame form to transmit the RTS/CTS frame.
The protection mechanism that the MIMO transmission also can use 802.11e HCCA to provide.Therefore, use control access period (CAP), the transmission from AP to STA, the polled transmission of from STA to AP or from STA to another STA, (using the direct link agreement) can be protected.
AP also can use traditional CTS-to-Self, and protection MIMO scheduling access period (SCAP) is avoided the influence of traditional STA.
When an AP confirms that all STA that exist among the BSS can both decode to MIMO PLCP stem, indicate this point in its MIMO ability item in beacon.Such BSS is called as MIMO BSS.
In MIMO BSS, under EDCA and HCCA, according to the aging rule of MIMO OFDM training symbol, MIMO PLCP stem and MIMO OFDM training symbol are used in the frame transmission.MIMO PLCP is used in transmission among the MIMO BSS.
The frame pitch that reduces
Describe the various technology that are generally used for reducing frame pitch above in detail.Here provide the example of the frame pitch in this exemplary embodiment of several reductions.For scheduled transmission, the time started of TXOP indicates in SCHED message.The accurate time started that transmitting party STA can indicate in SCHED message, begin its scheduling TXOP, and needn't confirm that medium are idle.As stated, during SCAP, continuous scheduling AP transmission is not have to send under the situation of minimum IFS.
In this exemplary embodiment, the continuous STA transmission (from different STA) that is scheduled is under the situation of IFS at least one protection IFS (GIFS), to send.The default value of GIFS is 800ns.Can select bigger value, the value of the burst IFS (BIFS) of definition below reaching at most.The value of GIFS can indicate in ACF ability item, as stated.Other embodiment can adopt any value of GIFS and BIFS.
Continuous N IMO OFDM PPDU transmission (TXOP burst) from identical STA is separated with BIFS.In the time of in being operated in the 2.4GHz frequency band, BIFS equals 10 μ s, and MIMO OFDM PPDU does not comprise the ofdm signal expansion of 6 μ s.In the time of in being operated in the 5GHz frequency band, BIFS is 10 μ s.In another embodiment, BIFS can be made as big or smaller value, comprises 0.For recipient STA automatic gain control (AGC) can be changed, when the transmitting power of transmitting party STA changes, can use gap greater than 0 between transmission.
Need not be to use MIMO OFDMPPDU to send from the frame of response at once of recipient STA.On the contrary, they are to use conventional P PDU to send, that is, and and clause 19 in the 2.4GHz frequency band or the clause 17 in the 5GHz frequency band.Provide several examples below, explain how tradition and MIMO OFDM PPDU are multiplexed on the medium.
At first, consider a traditional RTS/CTS, its followed MIMO OFDM PPDU burst.This transfer sequence is following: traditional RTS-SIFS-traditional CT S-SIFS-MIMOOFDM PPDU-BIFS-MIMO OFDM PPDU.In 2.4GHz, traditional RTS or CTS PPDU use the ofdm signal expansion, and SIFS is 10 μ s.In 5GHz, do not have the OFDM expansion, but SIFS is 16 μ s.
Secondly, consider an EDCA TXOP who uses MIMO OFDM PPDU.This transfer sequence is following: MIMO OFDM PPDU-BIFS-traditional B lockAckRequest-SIFS-ACK.For suitable access style (AC), use the EDCA process, obtain EDCA TXOP.As stated, the access style of EDCA definition can use different parameters to each AC, like AIFS [AC], CWmin [AC] and CWmax [AC].Traditional BlockAckRequest sends under the situation that signal extension or 16 μ s SIFS are arranged.If send in the aggregate frame of BlockAckRequest in MIMO OFDM PPDU, then do not have ACK.
The 3rd, consider the continuous TXOP that is scheduled.Transfer sequence is following: STA A MIMOOFDM PPDU-GIFS-STA B MIMO OFDM PPDU.If the maximum that the PPDU transfer ratio is distributed allows the TXOP time short, so, after STA A MIMO OFDMPPDU transmission, possibly have one period free time.
As stated, the decoding and the demodulation of coding OFDM transmission have been forced extra processing demands at recipient STA place.In order to solve this point, 802.11a and 802.11g allow recipient STA that the additional time was arranged before must sending ACK.In 802.11a, the SIFS time is made as 16 μ s.In 802.11g, the SIFS time is made as 10 μ s, but has introduced additional 6 μ s ofdm signals expansion.
According to identical logic, because the decoding of MIMO OFDM transmission and demodulation meeting cause more processing burden, so, can design an embodiment who improves SIFS or ofdm signal expansion, this can further lower efficiency.In this exemplary embodiment, through piece ACK and the delay block affirmation mechanism of expansion 802.11e,, needn't need ACK at once for all MIMO OFDM transmission.SIFS or signal extension do not increase, and have also eliminated signal extension, and for a lot of situation, the required frame spacing between the transmission has obtained reducing or eliminating continuously, thereby raises the efficiency.
SCHED message
Figure 45 shows SCHED message, combines Figure 41 it to be introduced above, also will do further detailed description to it below.SCHED message 4120 is polling messages more than, in the duration of scheduling access period (SCAP), distributes one or more AP-STA, STA-AP and STA-STA TXOP.Use SCHED message, can reduce poll and competition expense, and, unnecessary IFS eliminated.
This exemplary MAC stem 4510 comprises: frame control 4535 (2 bytes), duration 4540 (2 bytes), BSSID 4545 (6 bytes), power management 4550 (2 bytes) and MAP 4555 (3 bytes).The bit 13-0 of duration field 4540 indicates the length of SCAP, and unit is a microsecond.Duration field 4540 is used in the duration of SCAP, setting NAV by the STA that can carry out MIMO OFDM transmission.When having traditional STA among the BSS, AP can use other means, protects SCAP, for example, and traditional CTS-to-Self.In this exemplary embodiment, the maximum of SCAP is 4 milliseconds.BSSID field 4545 sign AP.
The SCHED counting is a field (being 6 bits in this example) that when each SCHED transmits, all increases progressively.The SCHED counting resets when each beacon sends.The SCHED counting can be used for various purposes.For example, the electricity-saving function that uses the SCHED counting is described below.
The used transmitted power level of transmitting power field 4630 expression AP.In this exemplary embodiment, this 4 bit field is encoded as follows: on behalf of transmitted power level, the channel that indicates in the item of information for beacon, this value be lower than the quantity of the 4dB stride of maximum transmit power level (unit is dBm).
The received power level of received power field 4640 expression AP place's expectations.In this exemplary embodiment, this 4 bit field is encoded as follows: on behalf of received power level, this value be higher than the minimum receiver sensitivity level (quantity of 4dB stride 82dBm).Based on the received power level at STA place, STA can calculate its transmitted power level as follows: STA transmitting power (dBm)=AP transmitting power (dBm)+AP received power (dBm)-STA received power (dBm).
In this exemplary embodiment, in the STA-STA transmission course that is scheduled, control section is sent with the launching electrical level that can decode at AP and recipient STA place.From the power control report of AP, or the power management field in the SCHED frame 4550, make STA can confirm can be at the AP place to the control section required transmitted power level of decoding.Combine Figure 22 to describe this general aspect above.For the STA-STA transmission that is scheduled, when the required power of decoding at the AP place is different from the power of decoding required at recipient STA place, send PPDU with the higher person in these two power levels.
Whether the MAP field 4555 shown in Figure 47 exists access period and the duration thereof based on protected competition during being illustrated in SCAP.MAP field 4555 comprises: FRACH counting 4710, FRACH skew 4720 and EDCA skew 4730.This exemplary FRACH counting 4710 (4 bits) are in the squint quantity (10 bits) of the FRACH time slot that 4720 places begin to dispatch of FRACH.Each FRACH time slot is 28 μ s.If the FRACH count value is 0, then representing does not have the FRACH cycle in the current scheduling access period.EDCA skew 4730 is the beginnings in protected EDCA cycle.This exemplary EDCA skew 4730 is 10 bits.FRACH skew 4720 all is that the beginning of transmitting from the SCHED frame is a unit with 4 μ s with EDCA skew 4730.
Figure 48 shows and is used for the SCHED control frame that TXOP distributes.Among 4530 sections of CTRL0 4515, CTRL1 4520, CTRL2 4525 and the CTRL3 each all has length variable, and each comprises 0 or a plurality of assignment item (being respectively 4820,4840,4860 and 4880).Each CTRLJ section is added with FCS (being respectively 4830,4850,4870 and 4890) and 6 tail bits (not shown)s of one 16 bit.For CTRL0 section 4515, FCS calculates (so, in Figure 48, show, before the MAC stem is added on CTRL0 4515) to MAC stem 4510 with all CTRL0 assignment item 4820.In this exemplary embodiment, even do not comprise assignment item in the CTRL0 section, also comprise the FCS 4830 of CTRL04515.
That kind of just describing in detail as this paper, AP sends the assignment information of the AP-STA, STA-AP and the STA-STA transmission that are used for the SCHED frame.Assignment item to different STA is sent in the CTRLJ section, is represented by the STA in the SCHED speed field of the PLCP stem of its transmission.Note that CTRL0 to CTRL3 corresponding to the robustness of successively decreasing.Each STA begins the PLCP stem of SCHED PPDU is decoded.Signal field indicates the existence and the length thereof of CTRL0 among the SCHED PPDU, CTRL1, CTRL2 and CTRL3 section.When the STA receiver begins MAC stem and CTRL0 section are decoded, each assignment item is decoded till FCS, it can't stop through the CTRLJ section place of checking at FCS with continued decode CTRL1, CTRL2 and CTRL3.
As shown in table 3, defined five kinds of assignment item.Can several assignment item be bundled in each CTRLJ section.Each assignment item indicates the maximum permission length that transmit leg STA inserts ID (AID), recipient STAAID, the time started of the TXOP that is scheduled and the TXOP that is scheduled.
Table 3, assignment item type
In continuous transmission, can eliminate lead code from AP.If AP does not send lead code for scheduling type AP transmission, then exist bit to be made as 0 lead code.For example, the benefit of eliminating lead code is, when AP has low bandwidth to a plurality of STA, low delay stream, for example, in having a plurality of BSS that transmit speeches (VoIP) stream through IP.Therefore, the SCHED frame can be realized the polymerization (that is, above-mentioned PPDU polymerization) of the transmission from AP to a plurality of recipient STA.The frame that above-mentioned frame aggregation allows to mail to a recipient STA carries out polymerization.
The beginning offset field is the integral multiple of 4 μ s, is that the time started from SCHED message lead code obtains.AID is the access ID of the STA that distributed.
For all the assignment item types except that the STA-STA transmission of being scheduled, TXOP duration field is that the be scheduled maximum of TXOP allows length, is the integral multiple of 4 μ s.The actual PPDU size of the PPDU that is sent shows (below with further explain) in signal 1 field of PPDU.
For the STA-STA that is scheduled transmission (assignment item type 011 and 100), maximum PPDU size field also is the maximum permission length of TXOP of being scheduled, and is the integral multiple of 4 μ s, still, also can use other rules.In this exemplary embodiment, for the STA-STA transmission that is scheduled, TXOP only comprises a PPDU.Recipient STA uses the maximum PPDU size that shows in the assignment item, confirms the quantity (because the PPDU size field is replaced by the request field in the signal 1, specifying below in conjunction with Figure 51) of OFDM symbol among the PPDU.Have the standard protection OFDM symbol of (GI) at interval if STA-STA stream uses, then will the be scheduled PPDU size of TXOP of recipient STA is set a maximum PPDU size that shows in distributing for.Have the OFDM symbol that shortens GI if STA-STA stream uses, then recipient STA confirms the PPDU size through maximum PPDU size field being amplified with factor 1 0/9 and rounding up.Transmit leg STA can send and compare the short PPDU of maximum PPDU size that is distributed.The PPDU size is the length of mac frame after receiver provides polymerization not.The length of encapsulated frame is included in the polymerization stem of each mac frame.
Transmitting party and recipient STA are included in the assignment item, can make the not predetermined STA power saving of sending or receiving in SCAP.The SCHED count area of introducing above recalling.The maximum that each assignment information of being dispatched by SCHED message indicates transmit leg STAAID, recipient STA AID, the time started of the TXOP that is scheduled and the TXOP that is scheduled allows length.SCHED counting increases progressively when each SCHED transmission, and when each beacon transmissions, resets.STA can indicate power-save operation to AP, thereby concrete SCHED count value is provided, and during this period, they can be assigned to the emission that is scheduled or be received TXOP by AP.Then, under the situation of suitable SCHED counting, STA can periodically wake up, and just listens attentively to SCHED message.
The PPDU form
Figure 49 shows traditional 802.11PPDU 4970, and it comprises PLCP lead code 4975 (12 OFSM symbols), PLCP stem 4910, the afterbody 4950 of elongated PSDU 4945,6 bits and elongated filling information 4955.The part 4960 of PPDU 4970 comprises: signal field (1 OFDM symbol), send with speed=1/2 with BPSK; Elongated data field 4985 sends with modulation format that indicates in the signal 4980 and speed.PLCP stem 4910 comprises the service field 4940 (be included in the data 4985, send according to this form) of signal 4980 and 16 bits.Signal field 4980 comprises: speed 4915 (4 bit), reserved field 4920 (1 bit), length 4925 (12 bit), parity bit 4930 and afterbody 4935 (6 bit).
Extended signal field (below will describe in detail) in this exemplary PLCP stem keeps backward compatibility with the signal field 4980 of tradition 802.11.The not usefulness value of the speed field 4915 in traditional signal field 4980 is set, to define new PPDU type (following detailed description).
Introduced multiple new PPDU type.In order to keep backward compatibility with traditional STA, the speed field in the signal field of PLCP stem is revised as speed/type field.Speed be not designated as the PPDU type with value.Whether PPDU type also expression signal field extension specification signal 2 exists and length.The new value of speed/type field defines in table 4.For traditional STA, these values of speed/type field define.Therefore, traditional STA can abandon the decoding to PPDU after signal 1 field successfully being decoded and find the undefined value in the speed field.
Perhaps, can the reserved bit in the legacy signal field be made as 1, mail to the MIMO OFDM transmission of a New type of S TA with expression.Recipient STA can ignore reserved bit, and continues to attempt signal field and remaining transmission are decoded.
Receiver can be confirmed the length of signal 2 fields based on the PPDU type.FRACHPPDU has only occurred once in the specified portions of SCAP, and only need be decoded by AP.
Table 4, MIMO PPDU type
Figure 50 shows the MIMO PPDU form 5000 that is used for transfer of data.PPDU 5000 is called as PPDU type 0000.PPDU 5000 comprises: PLCP lead code 5010, signal 1 5020 (1 OFDM symbol), signal 25040 (1 OFDM symbol), training symbol 5060 (0,2,3 or 4 symbol) and elongated data field 5080.In this exemplary embodiment, PLCP lead code 5010 (if existence) is 16 μ s.Send signal 1 5020 and signal 2 5040 with PPDU control section speed and modulation format.Data 5080 comprise: service 5082 (16 bits); Feedback 5084 (16 bits); Elongated PSDU5086; Afterbody 5088 (each stream has 6 bits) wherein, is used different convolution chnnel codings to each stream; Elongated filling information 5090.Send data 5080 with PPDU control section speed and modulation format.
The MIMO PLCP stem of PPDU type 0000 comprises: signal (comprise signal 1 5020 with signal 2 5040), service 5082 and feed back 5084 fields.Compare with traditional 802.11, service field is constant, and is with this data segment speed and form transmission.
The ES field is represented preferred guidance method.In this exemplary embodiment, when the set of ES bit, select characteristic vector guiding (ES), otherwise, spatial spread (SS) selected.
Data rate vector feedback (DRVF) field provides feedback to the peer station, but about the supporting rate on maximum four spatial models.
Clear and definite Rate Feedback makes the station can be fast and maximize its transmission rate exactly, thereby improves system effectiveness greatly.The feedback of low delay is desirable.But the feedback chance needs not to be synchronous.Can obtain transmission opportunity through any way, for example, based on (being EDCA) of competition, (being HCF) or (being ACF) mode of scheduling of poll.Therefore, can between transmission opportunity and Rate Feedback, transmit the variable time amount.Based on the age of Rate Feedback, transmitter can be used avoidance mechanism, to confirm transmission rate.
For the MPTS from STAA to STA B, PPDU data segment rate adaptation depends on the feedback that provided to STA A by STA B (front is described, for example, referring to Figure 24).For ES or SS operator scheme, whenever STA B when STAA receives the MIMOOFDM training symbol, it all will estimate attainable data rate on each spatial flow.Any subsequent transmission stream from STA B to STA A, STA B is included in this estimated value in the DRVF field of feedback 5084.The DRVF field is sent with data segment 5080 speed.
When STAB sends signal, the DRVF that STAA receives from STAB based on it confirms to use which kind of transmission rate, also can adopt avoidance mechanism to consider time-delay in case of necessity.Signal field (following detailed description) comprises the DRV field 5046 of 13 bits, so that recipient STAB can decode to the frame that sends from STA A.DRV 5046 sends with control section speed.
The DRVF field is encoded, and it comprises: STR field (4 bit), R2 field (3 field), R3 field (3 bit) and R4 field (3 bit).The STR field representes to flow 1 speed.With this code field is the STR value shown in the table 5.R2 representes to flow 1 STR value and flows the difference between 2 the STR value.R2 value " 111 " expression stream 2 turn-offs.R3 representes to flow 2 STR value and flows the difference between 3 the STR value.R3 value " 111 " expression stream 3 turn-offs.If R2=" 111 " then is made as R3 " 111 ".R4 representes to flow 3 STR value and flows the difference between 4 the STR value.R4 value " 111 " expression stream 4 turn-offs.If R3=" 111 " then is made as R4 " 111 ".
When ES=0, promptly during spatial spread, the another kind of DRVF coding as follows: the speed (4 bit) of fluxion amount (2 bit), each stream.The speed field of each stream is encoded as above-mentioned STR value.Remaining 7 bits keep.
Table 5, STR coding
Except DRVF, STAB also provides the power Control and Feedback to transmit leg STAA.This feedback is included in the power control field, and also sends with data segment speed.This field is 2 bits, and expression increases power or reduction power or keep power constant.Resulting transmitted power level is designated as the data segment transmitted power level.
Table 6 shows exemplary power control word segment value.Other embodiment can adopt the power control field of different sizes, and other power adjustment.
Table 6, power control word segment value
| The power control field | Implication |
| 00 | No change |
| 01 | Power is increased |
| 10 | Power is reduced 1dB |
| 11 | Keep |
For entire PP DU, transmitted power level remains unchanged.When data segment transmitted power level and open loop STA transmitting power (that is, AP is to the above-mentioned transmission required power level of decoding) not simultaneously, are sent PPDU with the maximum in these two power levels.That is to say that the PPDU transmitted power level is the maximum in open loop STA transmitting power (dBm) and the data segment transmitting power (dBm).
In this exemplary embodiment, in first frame of any frame turnaround sequence, the power control field is made as " 00 ".In follow-up frame, its expression increases or reduces power according to the step-length of 1dB.Recipient STA will use this feedback information in all subsequent frame transmission of mailing to this STA.
PPDU size/request 5026 has two effects, and this depends on transmission mode.In STA transmission and all AP transmission based on competition, this field is represented the PPDU size.Under first kind of pattern, bit 1 expression PPDU has used the OFDM symbol of expansion, and bit 2 expression PPDU use has the OFDM symbol that shortens GI, and bit 3-12 representes the quantity of OFDM symbol.
In the non-AP STA transmission that is scheduled, the 5026 expression requests of PPDU size/request field.Under second kind of pattern, bit 1-2 representes SCHED speed.The SCHED field of SCHED rate representation numbering the highest (0,1,2 or 3) can be used to send a dispensing section to STA.Between the training symbol transmission period from AP, each non-AP STA estimates that it can receive the speed of SCHED frame transmission steadily from AP.In the follow-up scheduled transmission from STA, the maximum rate of permission is included in the SCHED speed field.This field is decoded by AP.AP uses this information, the follow-up TXOP of STA dispatched, and definite CTRLJ (0,1,2 or 3), to be used for sending these dispensing sections to STA.
Under second kind of pattern, bit 3-4 representes qos field, the part of its sign TC 0 or 1 request (be 1/3rd multiple) (that is, 0%, 33%, 67%, 100%).Bit 5-12 representes the request length (in this exemplary embodiment, being the integral multiple of 16 μ s) of TXOP.
Whether signal 2 fields 5040 exist and length is indicated by the speed/type field in the signal 1 5,020 5022.Signal 2 fields 5040 are to send with control section speed and form.Signal 2 5040 comprises: reservation bit 5042, training type 5044 (3 bit), data rate vector (DRV) 5046 (13 bit), parity bit 5048 and afterbody 5050 (6 bit).The training type field of 3 bits indicates the length and the form of MIMO OFDM training symbol.Bit 1-2 representes the quantity (0,2,3 or 4 OFDM symbol) of MIMO OFDM training symbol 5060.Bit 3 is training type fields: 0 expression SS, 1 expression ES.DRV5046 provides the speed of maximum four spatial models.DRV 5046 is identical with the coded system that DRVF adopts (to be included in the feedback 5084, as stated).Signal 2 fields 5040 are carried out verification through 1 parity bit 5048, end up being 6 bit tail 5050 that are used for convolution coder.
Figure 51 shows SCHED PPDU 5100 (speed/type=0010).SCHEDPPDU 5100 comprises: PLCP lead code 5110, signal 1 5120 (1 OFDM symbol), signal 2 5140 (1 OFDM symbol), training symbol 5160 (0,2,3 or 4 symbol) and elongated SCHED frame 5180.In this embodiment, when PLCP lead code 5110 exists, be 16 μ s.Signal 1 5020 is to send with PPDU control section speed and modulation format with signal 2 5040.SCHED frame 5180 can comprise the above-mentioned various speed that combine ACF to describe.
The segment length of the SCHED PPDU that CTRL2 size 5146 the following flank speeds of expression (being 18Mbps in this example) are sent.In this example, this value is to encode with the integral multiple of 4 μ s.The CTRL2 size is " 0 " expression: do not have corresponding CTRL2 section among the SCHED PPDU.5148 expressions of CTRL3 size are with the segment length of the SCHED PPDU of flank speed (being 24Mbps in this example) transmission.In this example, this value is to encode with the integral multiple of 4 μ s.The CTRL2 size is " 0 " expression: do not have corresponding CTRL3 section among the SCHED PPDU.
Figure 52 shows FRACH PPDU 5200 (speed/type=0100).FRACHPPDU 5200 comprises: PLCP lead code 5210, signal 1 5220 (1 OFDM symbol) and signal 2 5240 (2 OFDM symbols).In this exemplary embodiment, PLCP lead code 5210 (when existing) is 16 μ s.Signal 1 5220 is to send with PPDU control section speed and modulation format with signal 2 5240.During the FRACH in MIMO scheduling access period, STA sends FRACH PPDU 5200.The FRACH cycle is established by AP, so be known (as stated) for it.
In this exemplary embodiment, STA can use the Aloha of time slotization to come access channel, and in FRACH, sends a request message.If successfully received by AP, then AP provides a TXOP through scheduling to requesting party STA in the one scheduling access period of back.The FRACH timeslot number of current scheduling access period indicates N_FRACH in SCHED message.
STA can also keep a variable B_FRACH.After the transmission on the FRACH, if STA receives the TXOP assignment information from AP, its B_FRACH that resets then.If STA does not receive the TXOP assignment information from AP in the SCHED of predetermined quantity (FRACH_RESPONSE) transmission, then B_FRACH is increased by 1, reach maximum 7 at most.Parameter F RACH_RESPONSE is included in the ACF item of beacon.In any FRACH, STA is (N_FRACH) at probability
-1* 2
-B_FRACHSituation under choose a FRACH time slot.
If AP does not dispatch any FRACH cycle, then MIMO STA can use the EDCA rule, is at war with in the protected competing cycle in SCAP.
It will be appreciated by those skilled in the art that and to use multiple different technologies and method representation information and signal.For example, data, instruction, order, information, signal, bit, symbol and the chip of mentioning in the description on run through can with voltage, electric current, electromagnetic wave, magnetic field or particle, light field or particle, or above-mentioned combination in any represent.
Those skilled in the art also can understand, combine here various exemplary box, module, circuit and algorithm steps that the disclosed embodiments describe all can electronic hardware, computer software or the combination of the two realize.In order to be clearly shown that the interchangeability between the hardware and software, more than various exemplary assembly, frame, module, circuit and steps are all carried out description generally with its functional form.This functional be to realize or realize depending on the design constraint that certain applications and whole system are applied with software with hardware.Those skilled in the art can realize described functional to each certain applications in many ways, and still the result of this realization should not be construed as and causes deviating from scope of the present invention.
Utilize general processor, digital signal processor (DSP), application-specific integrated circuit (ASIC) (ASIC), field programmable gate array (FPGA) or other programmable logical devices, discrete gate or transistor logic, discrete hardware components or the combination in any among them, can realize or carry out various exemplary logic diagram, module and the circuit that combine embodiment disclosed herein to describe.General processor possibly be a microprocessor, but in another kind of situation, this processor possibly be processor, controller, microcontroller or the state machine of any routine.Processor also possibly be implemented as the combination of computing equipment, for example, and the combination of DSP and microprocessor, a plurality of microprocessor, one or more microprocessor or any other this kind structure that combines the DSP core more.
In conjunction with the step of described method of embodiment disclosed herein or algorithm can directly be presented as hardware, the two combination of the software module carried out by processor or this.Software module possibly be present in the storage media of RAM memory, flash memory, ROM memory, eprom memory, eeprom memory, register, hard disk, mobile disk, CD-ROM or any other form well known in the art.The coupling of a kind of exemplary storage medium and processor, thus make processor can be from this storage media read message, and can be to this storage media write information.In the replacement instance, storage media is the part of processor.Processor and storage media possibly be present among the ASIC.This ASIC possibly be present in the subscriber station.In a replacement instance, the discrete assembly that processor and storage media can be used as in the subscriber station exists.
The title that comprises among this paper is used for reference and helps each joint of location.These titles are not to want to be limited in the protection range of described notion thereafter.These notions go in full.
Provide the foregoing description of said disclosed embodiment can make those skilled in the art can realize or use the present invention.To those skilled in the art, the various modifications of these embodiment are conspicuous, and the general principles of definition here also can be applied to other embodiment on the basis that does not depart from the scope of the present invention with purport.Therefore, the embodiment that the present invention is not limited to illustrate here, but consistent with the widest scope that meets principle disclosed herein and novel feature.
Claims (8)
1. method comprises:
Frame is transferred to second station from first stop, and said frame comprises:
Public part is according to being transmitted by first form that one or more the 3rd stations receive; And
Private part can be transmitted by second form that said second station receives according to selected.
2. method as claimed in claim 1, wherein said public part comprises the reference that is not directed to.
3. method as claimed in claim 1, wherein said second form comprise said private part are led.
4. method as claimed in claim 1, wherein first comprises the data indication that is used for transmission in the future.
5. method as claimed in claim 4, wherein said second station receive said data indication.
6. method as claimed in claim 4, wherein said data indication is a request for allocation.
7. method as claimed in claim 4, wherein said one or more the 3rd stations comprise access point, and wherein said access point:
Being received in said first stop indicates to the said data in the said public part of second station transmission;
Responding said data indication dispatches distribution; And
Said distribution is transferred to said first stop.
8. method as claimed in claim 7, the wherein said distribution of transmission in gathering poll.
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| BRPI0415426A (en) | 2006-12-05 |
| CN102612076B (en) | 2015-07-01 |
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| BRPI0415422A (en) | 2006-12-05 |
| CN102571801B (en) | 2015-09-09 |
| TWI385993B (en) | 2013-02-11 |
| TWI384793B (en) | 2013-02-01 |
| CN102612076A (en) | 2012-07-25 |
| TW200536306A (en) | 2005-11-01 |
| TWI383302B (en) | 2013-01-21 |
| CN101860925A (en) | 2010-10-13 |
| TWI380633B (en) | 2012-12-21 |
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