ES2356947T3 - MAC PROTOCOL FOR MULTICANAL WIRELESS LOCAL AREA NETWORKS OF CENTRALIZED CONTROL. - Google Patents

Abstract

Wireless communication method, the method comprising: providing a plurality of code channels, cch (cch1, cch2, cch3, cch4), on a single frequency channel; assign at least one period (204, 205) free of CFP contention in at least one of the code channels (cch1, cch2, cch3, cch4); the procedure being characterized in that it also comprises assigning at least one CP containment period in other code channels that begins simultaneously with the CFP.

Description

Wireless communication bandwidth has increased significantly with advances in channel modulation techniques, making the wireless medium a viable alternative to cable and fiber optic solutions. As such, the use of wireless connectivity in data and voice communications continues to increase. 5 These devices include mobile phones, laptops in wireless networks (for example, wireless local area networks (WLAN), stationary computers in wireless networks, portable phone devices, to name just a few).

Each wireless network includes a series of layers and sub-layers. The media access control sublayer (MAC) and the physical layer (PHY) are two of these layers. The MAC layer is the bottom of two sub-layers of the 10 data link layer in the Open Systems Interconnect Stack (OSI). The MAC layer provides coordination among many users that require simultaneous access to the same wireless medium.

The MAC layer protocol includes a series of rules that govern access to the broadcast media that users share within the network. As is known, several different multiple access technologies (often called MAC protocols) have been defined to work within the protocols that govern the MAC layer. 15 These include, but are not limited to, multiple carrier division access (CDMA), multiple carrier detection access (CSMA), multiple frequency division access (FDMA) and multiple time division access (TDMA).

As is known, in a WLAN that has a centralized MAC protocol, and among other functions, an access point (AP) provides control over the allocation of access to the system through other wireless stations (STA) that access the WLAN. The control of the WLAN by the AP serves to reduce collisions of communication packets 20 between STA and the AP and between the STAs themselves. By proper control of access to the environment, collisions are avoided, reducing lost packets, and increasing WLAN performance.

As is known, many WLANs include multi-channel (or multi-carrier) MAC (MC-MAC). Although MC-MACs allow greater access to the medium by the STAs, the demands on the AP are further increased by the need to provide control over more channels. In known WLANs, this may result in an increase in "overload" or system needs, both of which may have a negative impact on the complexity of the system and the cost of its implementation.

According to a representative embodiment, a wireless communication method includes: providing a plurality of code channels (cch) in a single frequency channel; assign at least one containment free period (CFP) in at least one of the code channels; and assign at least one containment period (CP) on other channels of code that begins simultaneously with the CFP.

According to another representative embodiment, a wireless network includes: a plurality of wireless stations (STA); an operational access point (AP) for granting access to a wireless medium to the STAs; a superframe having a plurality of code channels (cch) in a single frequency channel; at least one containment free period (CFP) in at least one of the code channels; and at least one containment period (CP) in another channel of code that begins simultaneously with the CFP.

The invention is better understood from the following detailed description when read with the figures of the attached drawing. It is emphasized that the various features are not necessarily scale drawings. In fact, the dimensions can be arbitrarily increased or decreased for a clearer explanation.

Figure 1 is a simplified schematic diagram of a WLAN according to a representative embodiment. 40

Figure 2 is a conceptual view of a superframe structure with containment periods (CP) and containment free periods (CFP) according to a representative embodiment.

Fig. 3 is a conceptual view of a request to send application frame format (RTSapp) according to a representative embodiment.

Figure 4 is a conceptual view of a ready-to-send accumulation frame (CTScum) according to a representative embodiment.

Figure 5 is a conceptual view of a time diagram according to an example embodiment.

In the following detailed description, for purposes of explanation and not limitation, exemplary embodiments are set forth that disclose specific details so that the exemplary embodiments are fully understood. However, it will be apparent to one skilled in the art who has benefited from the present description that other embodiments that depart from the specific details disclosed herein. In addition, descriptions of well-known devices, procedures, systems and protocols may be omitted so as not to complicate the description of the present invention. However, such devices, procedures,

systems and protocols that are within the scope of one skilled in the art can be used according to the example embodiments. Finally, whenever possible, similar reference numbers refer to similar characteristics.

It is noted that in the illustrative embodiments described herein, the network may be a wireless network with a centralized architecture. The wireless network includes wireless stations (STA) with modulation 5 and updated (more recent) frame formats as well as legacy STAs. Illustratively, the network may be one that operates under the IEEE 802.11 standard (inheritance) and includes one or more wireless stations that have a MAC layer in accordance with the IEEE 802.11n standard or any of its descendants. As will be appreciated from a summary of the present description, the MC-MACs of the illustrative embodiments are CDMA based systems. However, the present teachings are not limited to MAC layers governed by the IEEE 802.11 standard and application 10 of the teachings is contemplated in other networks / protocols. This includes, but is not limited to: cellular networks; wireless local area networks (WLAN); time division multiple access protocol (TDMA); CSMA; CSMA with collision avoidance (CSMA / CA); and multiple frequency division access (FDMA). It is noted that these protocols are merely illustrative and that protocols other than those specifically mentioned can be used without departing from the exemplary embodiments. In addition, the exemplary embodiments are applicable to a variety of centralized networks 15 that include STAs operating under updated modulation and frame formats as well as inherited STAs.

Fig. 1 is a schematic diagram of a wireless network 100 according to an example embodiment. The wireless network 100 includes a centralized MAC layer within an AP 102 (CENTRAL COMPUTER), which illustratively operates according to one of the plurality of illustrative protocols indicated above. The AP 101 serves 20 a series of first STA 101 (wireless devices) according to the chosen protocol. Illustratively, network 100 is a WLAN, a wide area network (WAN) or mobile phone network, and STA 102 (devices) are computers, mobile phones, digital personal assistants (PDAs) or a similar device that normally It operates on these networks. As indicated by the bi-directional arrows, the devices 101 can communicate bilaterally; and AP 102 and devices 101 can communicate bilaterally. 25

It is noted that according to certain MAC layer protocols, communication from one STA device to another STA is not direct; rather, such communications pass through the central computer 102, which then transmits the communications (using known planning procedures) to the correct receiving device 101.

It is also noted that although only some STA 101 are shown, this is simply to simplify the explanation. Of course, many other devices 101 can be used. Finally, it is noted that the devices 30 101 are not necessarily the same. In fact, a plethora of different devices that operate under the protocol (s) chosen within the network 100 can be used.

Figure 2 is a timeline 200 according to the exemplary embodiment and illustrates the basic features of the time division in WLAN according to a representative embodiment. Timeline 200 is best understood when considered in conjunction with the illustrative embodiments of Figure 1. The interval shown, which begins with the transmission of a beacon 201 and whose duration is equal to the transmission time of the target beacon (TBTT ), is defined as superframe 201 and constitutes the basic element of the centralized mode.

The superframe of Figure 2 illustrates the bandwidth allocation of a frequency channel. Naturally, the principles are usefully applied to a plurality of frequency channels, which are controlled by the AP 102 and the MC-MAC of the WLAN 100. Only one channel is explained in detail to avoid complicating the description of the embodiments. illustrative The channel is divided into subchannels in time and code, and the subchannels are called code channels (cch), which are indicated in Figure 2. The time division of the code channels provides CP and CFP. During the CP, the operation of the network follows the rules of C-DCF, described in G. Orfanos, J. Habetha, L Liu, “MC-CDMA based IEEE 802.11 wireless LAN,” Proc. IEEE MASCOTS 2004, October 2004; and during the CFPs the AP 102 has control over the network as provided by the 802.11a / e standard. Four. Five

As will be appreciated, during CPs, STA 101s essentially have unrestricted access to a subchannel or code channel (cch); and during a CFP, cch access is assigned by the AP 102. The division of available resources is done in both the time and code domain, according to the broadcast information contained in the beacon. Notably, the assigned band of an example is illustrated in Figure 2, in which the CP is operated in channel 3 of code (cch) and cch 4 for 60% of the superframe duration. fifty

At selected intervals the AP 102 of the network 100 (centralized) transmits the beacon. As is known, the period between beacons 202 is often called a superframe. The beacons are received within the scope of network 100. In an example embodiment, STA 101 requests service within network 100. For example, STA 101 can operate under the 802.11 protocol. Such a protocol is often called the “listen before speaking” protocol. As such, request-to-send (RTS) and ready-to-send (CTS) exchanges may occur between STA 101 and AP 55 after receiving the beacon. As can be seen, this process continues while one or more of the devices remain within the reach of the central computer 101. At the end of a first superframe interval, another beacon is transmitted indicating the start of a second superframe interval.

The AP 102 transmits the (first) beacon during the beacon period 202 immediately after its initialization, and signals indicates the operating characteristics of the networks. In addition to the information contained in the IEEE 802.11a beacon, the AP 102 indicates the duration of the CFPs 204 for each cch as shown in Figure 2. A different allocation of CFP / CP of this type between the cchs adds flexibility to network. STAs, which initiate a new connection, can use the CP for their first transmissions, thus reducing their delay until they are granted resources for the CFP. Additionally, STAs with better effort or lower load traffic can operate in CP continuously. It should be noted that the total duration of the CFP depends on the network traffic and can be adjusted by the AP, for each cch, in each superframe.

At the end of the beacon period, and after completing a safety interval (not shown), the AP 102 performs a transmission of CTS 203 accumulation (CTScum). In a representative embodiment, the transmission of 10 CTScum 203 provides all CTS commands to all STA 101 of network 100. For this purpose, each STA 101 transmits one or more RTS to AP 102. The CTScum 203 is transmitted in all the cch, and contains information for the next transmissions during the CFP in each cch, thereby providing access concessions to the media to the STAs that require it. Each access grant (CFP) contains the corresponding transmitter and receiver addresses that establish a connection. Alternatively, the access grant contains connection identifiers.

Illustratively, an extra byte CTScum signals the periodic repetition of access concessions indicated above until the end of the superframe, in order to reduce the overhead. As such, each STA 102 is informed of the CFPs in each cch. Each STA 101 acquires the subchannel and time allocated to access the medium from this broadcast. Beneficially, the CTScum 203 reduces the overhead of the MC-MAC and improves the quality of service (QoS) as a result.

After finishing the CTScum 203, each cch is in a respective CFP 205. The CFP 205 requires operation under the IEEE 802.11x standard or under the teachings of the IEEE publication referred to above, incorporated above. During this period, the AP 102 maintains control of the medium, having been granted access to it during the beacon period 202 or the CTScum 203. The AP 102 also indicates the duration of the 25 CFP 205 for each cch.

After completion of the CFP 205, the respective cchs enter one of a CP or CFP under the period 206 of the superframe 201. During this part of the superframe 201, some of the cch are restricted with respect to the access of CFP by the STA 101, while some allow unrestricted access to the channel by STA 101. After the end of period 206, the next superframe begins with the next beacon period as shown in Figure 2.

It is worth explaining some general observations. First, the order of period 205 of CFP and period 206 is merely illustrative. Notably, the order of time of these periods can be reversed with respect to that shown in Figure 2. In addition, AP 102 disseminates the allocation of periods 205 and 206, and particularly the number, identity and synchronism of the cch that are controlled respectively ( CP) and that allow unrestricted access (CFP) within the period 206. The AP 102 determines the needs based on the RTS packets received from the STA 101 during the previous superframe and allocates the access accordingly in an attempt to satisfy requests and provide adequate QoS, among other known benefits.

As one skilled in the art who has benefited from the present description will appreciate, the allocation of CFP / CP between cch in period 206 adds flexibility to network 100. For example, STA 101, which initiates a new connection between themselves and the AP 102 and each other, can use the CP for their first transmissions, thus reducing their delay until they are granted resources for the CFP. Additionally, STA 101 with better effort or lower load traffic can operate in CP continuously. It should be noted that the total duration of the CFP depends on the network traffic and can be adjusted by the AP 102, for each cch, in each superframe.

According to illustrative embodiments, the division of channel bandwidth into many parallel cch allows the operation of centralized and decentralized mode in parallel, which is very important for supporting different traffic characteristics in a network. In systems with variable spreading factor (SF), a cch could be reserved for signaling and transmissions during the CP, where the spreading factor will define its capacity. Such a channel is useful for at least the following reasons:

1. Since any STA 101 can use this cch to send an access request for CFP at any time, the access delay is reduced.

2. Collisions and unpredictable beacon delays can be more easily avoided by the operation of CP and CFP on the same channel, since the separation of two transmission periods takes place in the code domain, instead of the time division duplex procedure (TDM) usual for IEEE 802.11a / e.

3. STA 101 with a need for high quality of service (QoS) (for example, STAs used in emergency or medical applications) can transmit throughout the time in CFP, and transmission delays can be guaranteed.

Additionally, the present teachings also contemplate the division of available resources between CP and CFP in both time and code domain, according to the dissemination information contained in the beacon. The CP position in the code domain and its duration may vary in each superframe. In addition, signaling to the AP or any other network control entity, or to the peer receiver, the amount of data to be sent, by transmitting an RTSapp frame. The RTSapp frame contains either the amount of data to be transmitted or a request 5 for transmissions according to a traffic class. In addition, the signaling of forward link traffic, uplink, downlink to be transmitted during the CFP in a control frame (eg CTScum). This frame contains information for the next transmissions during the CFP in each cch, the so-called access concessions. Each media access grant contains the corresponding transmitter and receiver addresses that establish a connection. 10

Alternatively, the access grant contains connection identifiers. An extra CTScum of bytes signals the periodic repetition of access concessions indicated above until the end of the superframe. In addition, for the final connections, the AP can plan in the CTScum frame the transmissions in all jumps within its control area, reducing the delay and the number of attempts to access the medium in multi-hop connections. In addition, header compression can be achieved, if during the association each MAC entity achieves a unique ID through the AP. The MAC entities can then be distinguished by the given ID and the AP MAC address. The hardware devices using the procedures described above are also disclosed.

Figure 3 is a conceptual view of a request to send an application frame format (RTSapp) according to a representative embodiment. STAs request CFP resources for transmission by sending the RTSapp frame to the AP. This frame is sent during a CP, following the C-DCF access rules, and contains either the amount of data to be transmitted, or a request for transmissions according to a traffic class. The latter defines a transmission rate, which guides the AP to plan transmissions appropriately for this MS. Additional details of this can be found in S. Heier. Leistungsbewertung der UMTS Funkschnittstelle. Dissertation, Aachen University, 2003, ISBN 3-86073-167-9). In addition, a maximum tolerable delay can be provided according to, for example, the IEEE 802.11e / D9 standard: "Wireless LAN Medium Access Control (MAC) and 25 physical layer (PHY) specifications: Medium Access Control (MAC) Enhancements for Quality of Service (QoS), Technical Specification, IEEE LAN / MAN Standard Committee. IEEE, August 2004 ”.

Figure 4 is a conceptual view of a ready-to-send accumulation frame (CTScum) according to a representative embodiment. The beacon transmission is followed, after a safety interval of, for example, a slot, of the transmission of the ready-to-send accumulation frame (CTScum). As previously indicated, and 30 as the beacons, the CTScum is transmitted in all cch, and contains information for the next transmissions during the CFP in each cch, the so-called access concessions. Each access grant contains the corresponding transmitter and receiver addresses that establish a connection. Alternatively, the access grant contains connection identifiers. An extra byte CTScum signals the periodic repetition of access concessions indicated above until the end of the superframe, in order to reduce the overhead. 35

In order to further reduce the overload, the present teachings contemplate steering compression in centralized mode. For this purpose, the STA 101, after association with the AP 102, acquire a single address of one byte in length, which is used as their identifier, instead of the addresses of 6 bytes in length of the standard. One byte is sufficient to support 255 STAs in a subnet, and together with the subnet identifier, they provide a different address to each STA. In addition, the number of MAC addresses, necessary for explicit differentiation between STAs, can be reduced to a minimum of three (4) bytes, which constitute the source, destination and subnet address. Additional details can be found in IEEE 802.11 Wireless LAN Medium Access Control (MAC) and physical layer (PHY) specifications: Wireless LAN Medium Access Control (MAC) and physical layer (PHY) specifications, Technical Specification, IEEE LAN / MAN Standard Committee. IEEE, July 1999; and Wireless LAN Medium Access Control (MAC) and physical layer (PHY) specifications: Wireless LAN Medium Access Control (MAC) 45 and physical layer (PHY) specifications, Technical Specification, IEEE LAN / MAN Standard Committee. IEEE, July 1999. Descriptions of the indicated IEEE specifications are specifically incorporated herein by reference.

According to the access concessions, the STAs initiate transmissions in the cch in the predefined order. The correct reception of a data packet with an acknowledgment frame (ACK), transmitted after a short time between frames (SIFS) of time, is acknowledged. As the SIFS is mainly defined by the response time of the transmitter, the same interval separates the ACK from the next data frame, in order to allow consecutive transmissions of data packets from the same MS. An example is given in Figure 5.

As shown in Figure 5, the CFP ends after a superframe duration of 40% in two cch. The operation of CP in cch 2 and cch 4 is then allowed. According to the announcement of TBTT in the last beacon frame, the AP begins the beacon transmission, after detecting that the channel is free for a gap of space between frames of the point coordination function (PIFS). In order to avoid collisions with the beacon, the resource concessions for CFPs consider the TBTT, and the STAs operating in the CP, which received the previous beacon, must refrain from transmissions when the TBTT approaches.

In view of this description it is noted that the various procedures and devices described herein can be implemented in hardware and software. In addition, the various procedures and parameters are included by way of example only and not in a limiting sense. In view of this description, those skilled in the art can implement the various example devices and procedures by determining their own techniques and the equipment necessary to perform these techniques, remaining within the scope of the appended claims.

Claims (13)

1. Wireless communication method, the method comprising: providing a plurality of code channels, cch (cch1, cch2, cch3, cch4), on a single frequency channel; assign at least one period (204, 205) free of CFP contention in at least one of the code channels (cch1, cch2, cch3, cch4); the procedure being characterized in that it also comprises assigning at least a 5 CP containment period in other code channels that begins simultaneously with the CFP.

2. A method according to claim 1, further comprising providing a plurality of containment periods in respective code channels that begin simultaneously.

3. Method according to claim 2, further comprising providing a CTScum (203) ready to send accumulation after a beacon period. 10

4. The method according to claim 1, wherein the actions of providing and assigning are carried out in a superframe (201).

5. A method according to claim 1, further comprising: signaling to an AP access point a quantity of data to be transmitted by a wireless STA station, the amount of data to be transmitted, or a request for transmissions according to a class of traffic. fifteen

6. The method according to claim 5, wherein the signaling further comprises the transmission of an RTSapp frame.

7. A method according to claim 1, further comprising: the signaling of traffic to be transmitted during the CFP in a control frame.

8. The method of claim 7, wherein the frame includes information for upcoming transmissions 20 during the CFP in each of the code channels.

A method according to claim 8, further comprising providing addresses of the corresponding transmitter and receiver that establish a connection.

10. Method according to claim 8, further comprising connection identifiers.

11. Wireless network (100), comprising: a plurality of STA wireless stations (101); an operational AP access point (102) 25 for granting access to a wireless medium to the STAs according to a superframe (201) having a plurality of code channels, cch, (cch1, cch2, cch3, cch4) in a channel of single frequency; at least one period (204, 205) free of CFP contention in at least one of the code channels; the network being characterized because the superframe also comprises at least one CP containment period in another code channel that begins simultaneously with the CFP. 30

12. The wireless network according to claim 11, wherein the superframe further comprises a plurality of containment periods in respective code channels that begin simultaneously.

13. Wireless network according to claim 11, wherein the superframe further comprises a CTScum ready to send accumulation after a beacon period.