CN101801109A - Medium access control system and medium access control method in wireless packet network - Google Patents
Medium access control system and medium access control method in wireless packet network Download PDFInfo
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Abstract
The invention discloses a medium access control system and a medium access control method in a wireless packet network, which mainly aim to solve the problem of the incapacity of an exposed terminal in concurrent communication in the prior art. The system comprises a medium access control module, a received signal resolving module, an antenna, a radio frequency front end, a digital-to-analogue converter, a modulation/coding module, a physical layer frame forming module, an analogue-to-digital converter, an MAC frame extraction module and a physical channel management module, wherein the medium access control module judges whether a channel is idle or not and whether a terminal is the exposed terminal or not in transmission, and if the channel is idle and the terminal is the exposed terminal, transmits an RTS frame and presets expected ACK frame detection according to a known frame; the received signal resolving module executes the expected frame detection, judges whether an ACK is received or not and executes expected frame removal to suppress inter-frame interference; and the MAC layer frame extraction module extracts an MAC layer frame from signals after the expected frame removal. The system and the method have the advantages of simple implementation, high communication concurrence, high network capacity and compatibility with a conventional IEEE 802.11 standard, and can be used for realizing a large-scale wireless self-organizing communication network.
Description
Technical field
The present invention relates to field of wireless communications networks, relate in particular to a kind of by data link layer and collaborative radio packet network medium access control system and the method that realizes of physical layer, be used for solving wireless ad hoc network exposed terminal problem, improve communication concurrency and network capacity.
Background technology
Along with popularizing of development of wireless communication devices and wireless communications application, the ad-hoc wireless packet network that constitutes by equal Wireless Telecom Equipment, and the wireless sensor network of contact physical environment and computing environment obtains application more and more widely.In this network that is known as wireless Ad hoc, the medium access control protocol determines the actual performance and the level of resources utilization of network to a great extent.
In the wireless Ad hoc network, the widely used carrier sense of medium access control layer (Carrier Sensing) technology locks into hidden terminal problem and exposed terminal problem.Become the distributed collaboration mechanism of stipulating in IEEE 802.11 agreements of standard (DCF), adopt to have sent request/transmission affirmation (RTS/CTS) frame and the control rule of shaking hands and solve the problems referred to above.This method has remedied the deficiency that physical carrier is intercepted to a certain extent by introducing virtual carrier sensing in wireless network communication and network allocation vector, can solve hidden terminal problem.But this method fails effectively to solve exposed terminal problem.
As shown in Figure 1, terminal D listens to the RTS control frame that A sends, and can listen to the carrier signal of A when sending data, thereby is suppressed, and can not send data to terminal F.But D sends the session that in fact can't disturb between A and the B to F.In this case, D is called the exposed terminal of session AB, and the communication that exposed terminal causes suppresses to be called exposed terminal problem.
For improving the throughput of wireless Ad hoc network, improving RTS/CTS control signaling, improving concurrent communication density both at home and abroad, promptly many researchs have been carried out in the space reuse degree aspect.These research work are based on 802.11 handshake mechanisms, by appropriate change control signaling and controlling mechanism, manage to discern and allow can not cause interference hide and/or exposed terminal is initiated concurrent session.According to the processing mode of disturbing between control frame and the concurrent Frame, these methods can be divided three classes:
1. cancellation method for avoiding control frame interfering data frame, is removed some control frames in agreement.For example, the MACA abrogation of agreement physics monitoring, so directly avoid producing exposed terminal problem, simultaneously receiving terminal no longer sends confirmation of receipt frame ACK, has avoided the interference of ACK to ongoing Data Receiving.The major defect of these class methods is the mis-behaves on the upper strata (as TCP) that causes of the disappearance of ACK, and is not suitable for wireless network, and these class methods also can worsen hidden terminal problem.
2. same footwork promptly manages to make concurrent session to finish simultaneously, and receiving terminal sends the Data Receiving that ACK just can not disturb another session like this, for example to improvement agreement MACA-P and the CTMAC agreement of MACA.It is too complicated to be with the disadvantage of footwork that signaling is shaken hands, and for realize concurrent session synchronously, terminal is waits for too long when sending.
3. evade method, promptly by the control signaling mutual information, only from network, choose the exposed terminal or the communication of concealed terminal execution concurrence that can not cause the phase mutual interference, the type of for example keeping forging ahead MAC agreement and bag are intercepted multichannel access/conflict and are avoided (PSMA/CA) technology.The essence of these class methods is to have strengthened the condition that allows concurrent communication to take place, and shortcoming is fully to realize concurrent communication and spatial reuse.
Summary of the invention
The objective of the invention is to avoid the shortcoming of above-mentioned prior art, on the basis of existing IEEE 802.11 standards, a kind of radio packet network medium access control system and method are proposed, collaborative by data link layer in the wireless communication terminal and physical layer, expected frame in the achieve frame receiving course detects and eliminates, solve exposed terminal problem, improve the message capacity of cordless communication network.
Technical scheme of the present invention is achieved in that
One, term explanation
The MAC layer: medium access control layer, in the network hierarchy structure of ISO regulation, be responsible for the sublayer that physical medium is obtained and used in the link layer;
Frame: link layer and physical layer protocol unit;
Grouping: corresponding with frame, claim the above level agreement unit of link layer to be grouping;
Frame: the link layer protocol unit of carrying user data business tine;
Control frame: carrier signaling information is used to realize the mac-layer protocol unit of tasks such as control and management;
RTS/CTS/ACK: three kinds of control frames that are used to realize 802.11 wireless network medium access control Handshake Protocols, correspond to respectively and send claim frame, send permission frame and confirmation of receipt frame, control frame has fixing frame length and frame format;
Terminal: with the wireless device of Peer formation wireless network, terminal room sends or receives data/control frame mutually by Radio Link;
Session or communication: claim a Frame transmitting-receiving of terminal room to be session.If A sends Frame to B, then be referred to as the AB session;
Exposed terminal: because carrier sense, being in the adjacent end that sends in the terminal signaling coverage can not initiation session.If the session that this adjacent end is initiated can not disturbed original session, then this adjacent end promptly becomes exposed terminal.Exposed terminal can cause unnecessary concurrent communication loss;
Sending duration field: in frame, have special field to send the required time in order to clearly to write down the Frame that will carry out.Utilize this field value corresponding and current time, terminal can be expected the transmitting time of the follow-up frame of this session (for example ACK);
Physical carrier is intercepted: terminal receiver is judged channel according to the actual reception signal power, and whether the busy physical carrier that is called is intercepted;
Virtual carrier sensing in wireless network communication: the sending duration field of terminal from the frame that the adjacent end that receives is sent, can judge adjacent end and in a period of time, whether receive (perhaps sending) data, this mode of intercepting is called virtual carrier sensing in wireless network communication; Virtual carrier sensing in wireless network communication is realized the not busy condition managing of channel busy by the NAV timer;
NAV timer: NAV is the abbreviation of English network allocation vector.Terminal is provided with transmission and/or receives the NAV timer according to type field in the frame and sending duration field after listening to control frame.If send the NAV timer just in timing, representing has data to send in the adjacent end of this terminal; Receive the NAV timer just in timing, have data to receive in the expression adjacent end;
Expected frame: refer to the content of terminal, can dope the frame that certain particular moment after current time will occur in advance according to the control frame that had before listened to;
Expected frame detects: the wireless signal that terminal receives can regard as signal that one or more transmission terminals send after wireless channel is propagated with the stack of noise signal, therefrom detect and judge that the operation whether expected frame exists is called the expected frame detection;
Expected frame is eliminated: exist in case judge expected frame, receiver can be according to the copy of a known content frame and an expected frame signal that receives of channel estimating parameter generation, and it is deducted from the wireless signal that receives, thereby residual signal can correctly be received, and this operation is called expected frame and eliminates.
Two, radio packet network medium access control system of the present invention, comprise: medium inserts molded of control, received signal parsing module, antenna, RF front-end module, analog to digital converter, digital to analog converter, mac layer frame extraction module, physical layer frame formation module, modulation/coding module and physical channel administration module, wherein:
Described medium access control module comprises:
The upper-layer protocol interface is used for receiving packet from upper-layer protocol, it is assembled into to send to behind the mac layer frame send collaborative unit, and collects the mac layer frame that receives from receive collaborative unit, and the packet of extracting wherein sends to upper-layer protocol;
Frame sends collaborative unit, be used for instruction according to medium access control protocol and other functional unit, the necessary controlling mechanism of shaking hands when realizing the mac layer frame transmission, the control frame transmitting element sends suitable control frame and Frame at reasonable time, and detects and eliminate unit setting or expected frame detection according to the RTS content frame indication expected frame of sending;
The frame transmitting element is used for sending the physical layer frame formation module of mac layer frame to the outside under the control of the collaborative unit of frame transmission, the collaborative unit of frame reception;
Receive collaborative unit, be used for instruction according to medium access control protocol and other functional unit, the necessary controlling mechanism of shaking hands when realizing that mac layer frame sends determines that according to the frame type that receives sending to the frame transmitting element after the type of response frame and the content in time sends;
The frame receiving element, be used for after outside mac layer frame extraction module receives mac layer frame, in time submitting to the collaborative unit of reception, type and sending duration field notification channel administrative unit according to the frame that receives more relocate the receiving and send the NAV timer, and detect and eliminate the unit setting or carry out the expected frame detection according to RTS frame that receives and CTS frame indication expected frame;
The channel management unit is used to receive indications such as, signal power level initial from the received signal of the RF front-end module of outside, and from the NAV timer update instruction of frame receiving element, realizes the condition managing of channel;
Keep out of the way administrative unit, be used for keeping out of the way sending to carry out when unsuccessful, notice sends collaborative unit and sends respective frame once more when keeping out of the way the timer timing and stop;
Expected frame detects and eliminates control unit, be used for according to the indication that sends collaborative unit and receiving element, the content and the time of advent of the ACK frame that will occur according to the RTS frame of current transmission or the current RTS/CTS frame expection that receives, the outside received signal parsing module of notice and control is carried out expected frame and is detected and eliminate, and the result is fed back to frame sends collaborative unit or frame receiving element.
Described received signal parsing module comprises:
The digital signal buffer is used to receive and the digital medium-frequency signal of buffer memory after analog-to-digital conversion, and offers expected frame detecting unit, expected frame elimination unit and demodulator/decoder unit use respectively according to different demands;
The expected frame detecting unit is used for the instruction according to external medium access control module, detects specific expected frame from the digital signal sequences that receives, and the result is returned to external medium access control module;
Expected frame is eliminated the unit, is used for the instruction according to external medium access control module or expected frame cancellation module, eliminate corresponding expected frame signal from the digital signal sequences that receives, and the signal that will eliminate after the expected frame sends to demodulator/decoder unit;
Demodulator/decoder unit is used to receive the digital medium-frequency signal from digital signal buffer or expected frame elimination unit, and it is carried out the demodulate/decode operation, therefrom obtains digital baseband signal and sends to outside mac layer frame extraction module.
Three, radio packet network medium connection control method of the present invention comprises the steps:
(1) when terminal has Frame to send, whether have by the transmission of carrier sense inhibition specified data frame according to current, if this terminal is not suppressed, belong to the exposed terminal inhibition but perhaps be suppressed, then send RTS, and wait for receiving terminal response CTS; Otherwise execution is kept out of the way, and sends RTS until terminal;
(2) after receiving terminal is received RTS,, then respond CTS and wait for receiving data frames if be not suppressed; Otherwise do not respond;
(3) adjacent end is provided with respectively and receives and send the NAV timer, to determine oneself to belong to which kind of state according to the type and the sending duration field of the frame that listens to;
(4) if terminal can expect that certain moment in future an ACK frame will occur by complete and accurate according to type, address and the duration field of the frame that has just sent out or received, then be arranged on the moment that expection ACK frame occurs, carry out expected frame and detect and eliminate, otherwise do not need to be provided with expected frame;
(5) terminal is after receiving wireless signal, if received signal and the expected frame time-interleaving that is provided with in advance, then according to frame zero-time, frame preamble sequence and frame delimiting sequence and the content frame field of expecting, adopt the sequence correlation method to carry out the detection of expected frame, detect precise time and the channel parameter estimation that obtains according to expected frame, produce a received signal copy after the transmission of expected frame channel, this expected frame copy is eliminated from received signal, and expected frame signal afterwards carries out demodulating and decoding and frame extracts to eliminating;
(6) send terminal and receive CTS, shake hands successfully, expection ACK frame is set receives, and send Frame, wait for receiving ACK;
(7) after receiving terminal successfully receives Frame, send the ACK frame acknowledgment, otherwise take defeat;
(8) send terminal and successfully receive the ACK frame, data send successfully; Otherwise send failure, return step (1).
The present invention has increased the expected frame detection and has eliminated function by described medium access control module and received signal parsing module, when making terminal equipment become exposed terminal, also can send RTS frame and Frame; The present invention adopts expected frame to detect, and makes terminal also can correctly receive the ACK frame of expection under situation about being interfered; The present invention adopts expected frame to eliminate, and can eliminate from received signal producing the expection ACK frame that disturbs, and residual signal can correctly be received.The present invention supports the medium connection control method of concurrent communication to compare with existing three classes, can not only increase wireless communication concurrency and network capacity, and can avoid the caused upper-layer protocol mis-behave of these methods, send waits for too long, agreement is too complicated, the abundant shortcoming of multiplexing and incompatible 802.11 standards in implementation space.
Description of drawings
Fig. 1 is hiding and the exposed terminal schematic diagram in the wireless network;
Fig. 2 is a system architecture diagram of the present invention;
Fig. 3 is the medium access control modular structure schematic diagram in the system of the present invention;
Fig. 4 is the received signal parsing module structural representation in the system of the present invention;
Fig. 5 is a medium access control general flow chart of the present invention;
Fig. 6 is according to RTS and CTS expection ACK frame schematic diagram in the medium access control of the present invention;
Fig. 7 is that expected frame of the present invention detects sub-process figure;
Fig. 8 is that expected frame of the present invention is eliminated sub-process figure.
Embodiment
For making the object of the invention, technical scheme and advantage clearer, below with reference to the accompanying drawing embodiment that develops simultaneously, the present invention is further described in detail.
With reference to Fig. 2, radio terminal system of the present invention comprises: medium access control module 10, received signal parsing module 20, analog to digital converter 30, mac layer frame extraction module 40, physical layer frame form module 50, modulation/coding module 60, digital to analog converter 70, RF front-end module 80, physical layer channel administration module 90 and antenna.Wherein:
Medium access control module 10, physical layer frame formation module 50, modulation/coding module 60, digital to analog converter 70 are connected the composition data sendaisle with RF front-end module 80 is unidirectional successively; RF front-end module 80, analog to digital converter 30, received signal parsing module 20, mac layer frame extraction module 40 and 10 unidirectional successively connections of medium access control module, composition data receive path.RF front-end module 80 and physical channel administration module 90 two-way transmitting control and the notification messages of being connected; Physical channel administration module 90 and 10 unidirectional connections of medium access control module are to this medium access control module notification channel state; Medium access control module 10 and 20 two-way connections of received signal parsing module are transmitted received signal and are resolved required control command and relevant information; RF front-end module 80 receives and sends wireless signal with two-way connection of antenna.
When medium access control module 10 sends Frame, at first the upper layer data packet group is dressed up mac layer frame and issued physical layer frame formation module 50, form the required field of interpolation physical layer transmission in the module in this physical layer frame, comprise targeting sequencing and frame alignment sequence, constitute physical layer frame; Then physical layer frame is passed to modulation/coding module 60; Modulation/coding module 60 is carried out coding, spread spectrum and modulation functions, changes physical layer frame into be adapted at transmitting in the wireless channel digital intermediate frequency signal, and passes to digital to analog converter 70 and be converted to analog intermediate frequency signal; Digital to analog converter 70 is passed to RF front-end module 80 with this signal under the cooperation of physical channel administration module 90, change rf wireless signal into through behind frequency conversion, filtering and the amplifieroperation; At last rf wireless signal is sent by antenna.
When RF front-end module 80 receives faint wireless high-frequency signal from antenna, through after amplification, filtering and the frequency conversion, change wireless intermediate-freuqncy signal into, send analog to digital converter 30 to, should wireless intermediate-freuqncy signal be converted to digital intermediate frequency signal; Simultaneously, RF front-end module 80 is notified to physical channel administration module 90 with the beginning and ending time and the watt level information of detected radio frequency signal; This physical channel administration module changes beginning and ending time and watt level information into physical carrier intercepts message, and conveys to medium access control module 10; Digital intermediate frequency signal after analog-to-digital conversion passes to received signal parsing module 20 by analog to digital converter 30; Received signal parsing module 20 carries out expected frame detection, expected frame elimination and demodulate/decode to digital intermediate frequency signal under the control of medium access control module 10, and the intermediate object program of necessity is notified to medium access control module 10; Signal behind received signal parsing module 20 demodulating and decodings sends to mac layer frame extraction module 40, therefrom extracts MAC layer data frame or control frame, submits to medium access control module 10.
With reference to Fig. 3, medium access control module of the present invention comprises: upper-layer protocol interface 101, the collaborative unit 102 of transmission, frame transmitting element 103, reception are worked in coordination with unit 104, frame receiving element 105, channel management unit 106, keep out of the way administrative unit 107 and expected frame detection and are eliminated control unit 108.Wherein upper-layer protocol interface 101 unidirectional being connected to send collaborative unit 102, send the collaborative unit 102 unidirectional frame transmitting elements 103 that are connected to, the 103 unidirectional physical layer frames that are connected to module-external form module 50, form the sendaisle from the Frame of upper-layer protocol.Frame receiving element 105 and outside 40 unidirectional connections of mac layer frame extraction module, and the unidirectional collaborative unit 104 of reception that is connected to, the unidirectional upper-layer protocol interface 101 that is connected in the collaborative unit of this reception constitutes the Frame receive path of going to upper-layer protocol.Receive collaborative unit 104 and 103 unidirectional connections of frame transmitting element, notify 103 to send the control corresponding frame according to the frame type that receives.Keep out of the way unidirectional being connected to of administrative unit 107 and send collaborative unit 102 and channel management unit 106, carry out according to back off algorithm and keep out of the way and change channel status management information.The frame receiving element 105 unidirectional channel management unit 106 that are connected to are provided with corresponding NAV timer in 106 according to send continuing duration field and type in the frame that receives.Channel management unit 106 simultaneously with 90 unidirectional connections of physical channel administration module of outside, receive physical carrier intercepted result from this physical channel administration module.Expected frame detects and eliminates control unit 108 and 90 unidirectional connections of physical channel administration module, receives received signal beginning and ending time, signal strength signal intensity and channel estimating parameter message from this physical channel administration module; Expected frame detects with elimination control unit 108 and works in coordination with unit 102 and 105 two-way connections of frame receiving element with received signal parsing module 20, transmission respectively simultaneously, control received signal parsing module is carried out and is detected and eliminate and receive the result who carries out, reception detects and the elimination request from sending the expected frame of working in coordination with unit and frame receiving element, and execution result is returned to collaborative unit of transmission and frame receiving element.
With reference to Fig. 4, received signal parsing module of the present invention comprises: digital signal buffer memory 201, expected frame detecting unit 202, expected frame are eliminated unit 203 and demodulator/decoder unit 204, wherein digital signal buffer 201 and outside 30 unidirectional connections of analog-to-digital conversion module receive and the digital medium-frequency signal of buffer memory after conversion; The digital signal buffer is eliminated unit 203 and 204 unidirectional connections of demodulator/decoder unit with expected frame detecting unit 202, expected frame respectively simultaneously, the digital signal that transmission need detect or eliminate eliminates the unit for expected frame detecting unit and expected frame, and transmission can directly be carried out the digital medium-frequency signal of demodulate/decode and give demodulator/decoder unit.Demodulator/decoder unit 204 is eliminated unidirectional connection the between the unit 203 with expected frame, receives the digital medium-frequency signal after expected frame is eliminated; Data after the demodulate/decode are issued outside mac layer frame extraction module 40, are used to extract complete mac layer frame; Simultaneously, demodulator/decoder unit 204 and expected frame are eliminated 203 two-way connections of unit, and this demodulator/decoder unit 204 detects and eliminates 108 unidirectional connections of control unit with expected frame in the medium access control module 10, all in order to the elimination of auxiliary realization expected frame.Expection in expected frame detecting unit 202 and the external medium access control module 10 detects and eliminates 108 two-way connections of control unit, receives expected frame and detects request and also can return testing result and relevant information; Expected frame is eliminated two-way connection the between unit 203 and the expected frame detecting unit 202, is used for carrying out the expected frame elimination earlier when unsuccessful and detecting directly detecting; Expected frame eliminate unit 203 simultaneously with external medium access control module 10 in expection detect and eliminate 108 unidirectional connections of control unit, accept to eliminate and ask from 108 expected frame.
With reference to Fig. 5, radio packet network medium connection control method implementation method of the present invention comprises the steps:
Step 1, terminal are received the packet from the upper strata, and it is assembled into MAC layer data frame, and according to its destination address, the corresponding RTS frame of generations such as data length is ready for sending.
Step 2, sending current whether being intercepted with virtual carrier sensing in wireless network communication by physical carrier of terminal judges self suppresses, if terminal physics and virtual carrier sensing in wireless network communication result all show the channel spare time, though perhaps physical carrier is intercepted to busy still virtual carrier sensing in wireless network communication and found that this terminal belongs to exposed terminal, then execution in step 3; Otherwise execution is kept out of the way, and sends RTS until terminal.
Step 3 sends terminal and sends RTS, and waits for the CTS that receives from the purpose terminal.
Step 4 after receiving terminal is received RTS, if judge and can receive according to carrier sense, then responds CTS and waits for receiving data frames; Otherwise do not respond.
Step 5 with reception and transmission terminal neighboring terminals, according to the type and the sending duration field of the frame that listens to, is provided with or renewal reception NAV timer or transmission NAV timer.
Step 6, if terminal can expect that certain moment in future an ACK frame will occur by complete and accurate according to type, address and the duration field of the known frame that just sends out or receive, then be arranged on the moment that expection ACK frame occurs, carry out expected frame and detect and eliminate, otherwise do not need to be provided with expected frame;
With reference to Fig. 6, wherein obtain to expect that according to given frame the concrete condition of ACK frame time of occurrence and content frame is divided into following three kinds of situations:
First kind of situation is: if the RTS frame has just been sent or received to terminal, expect that then the destination address of ACK frame is the source address of RTS frame; The time of occurrence of expection ACK frame: T=t+D-t
Sfs-t
ACK, wherein t is the current time, D
RTSBe the sending duration in the RTS frame, t
SfsBe the shortest frame period, t
ACKFor the ACK frame transmits required time;
Second kind of situation is: if the frame that terminal receives is CTS, expect that then the destination address of ACK frame is the destination address of CTS frame; The time of occurrence of expection ACK frame: T=t+D-t
Sfs-t
ACK, wherein t is the current time, D
CTSBe the sending duration in the CTS frame, t
SfsBe the shortest frame period, t
ACKFor the ACK frame transmits required time;
The third situation is: if the frame that terminal receives is the frame of other types, do not carry out the expected frame setting;
In above first kind and second kind of situation, the frame control word in the expection ACK frame is the known fixed form, and the sending duration field is 0, and Frame Check Sequence recomputates according to the content of frame control word, sending duration and destination address field (DAF).
Step 7, terminal is after receiving wireless signal, if received signal and the expected frame time-interleaving that is provided with in advance, then according to frame zero-time, frame preamble sequence and the frame delimiting sequence of expecting, and the content frame field, adopt the sequence correlation method to carry out the detection of expected frame.
With reference to Fig. 7, being implemented as follows of this step:
7.1 the expected frame detecting unit receives the intermediate frequency wireless signal after digitlization, and the initial moment of the expected frame that presets and frame format content information;
7.2, in expected frame near the initial moment, with known frame preamble sequence and the received signal multiplication mutually that slides, near the expected frame original position, what multiply each other if slide is long-pending obviously greater than the product after before this position and this position, then thinks the significant correlation peak value to occur, execution in step 7.3; Otherwise think not have expected frame, detect failure, return expected frame and detect failed message;
7.3, definite position from the relevant peaks indication, according to the parameter of channel estimating to the calculating of multiplying each other of sliding of complete expected frame, if from then on the slip phase product that begins of position is before this position and the product after this position, think that then expected frame detects successfully, return expected frame and detect success message, detect and eliminate control unit to expected frame by information such as definite original position of frame that detects acquisition and channel parameter estimation; Otherwise execution in step 7.4;
7.4, send targeting sequencing relevant peaks accurate location, channel and transmitter parameter Estimation, expected frame format content to expected frame elimination unit requests trial elimination;
7.5 if expected frame is eliminated successfully, then expection detects successfully, returns expected frame detection success message, targeting sequencing relevant peaks accurate location and channel parameter estimation information and detects and eliminate control unit to expected frame; Otherwise expected frame detects failure, returns expected frame and detects failed message.
Step 8, detect precise time and the channel parameter estimation that obtains according to expected frame, produce a received signal copy after the transmission of expected frame channel, this expected frame copy is eliminated from received signal, and expected frame signal afterwards carries out demodulating and decoding and frame extracts to eliminating.
With reference to Fig. 8, being implemented as follows of this step:
8.1 expected frame is eliminated the unit and is received necessary information, comprises that expected frame eliminates request, need therefrom eliminate the definite original position of wireless digital signal, expected frame, expected frame format content, channel estimating parameter and the transmitter estimated parameter of expected frame;
8.2, according to the physical layer frame structure of stipulating in the format content of expected frame and 802.11 standards, add targeting sequencing and frame alignment sequence, assemble out complete physical layer frame;
8.3, according in 802.11 standards to the modulation coding method of physical layer specifies, physical layer frame is pursued bits of encoded and modulation, obtain encoded and the modulation after digital signal sequences;
8.4, according to channel and transmitter estimated parameter, increasing distortion to frequency, phase place and the amplitude of the digital signal behind modulation and the coding, resulting digital signal sequences is the expected frame signal copy after the channel transmission;
8.5, carry out the digital signal of expected frame elimination from needs, from the definite position that the targeting sequencing relevant peaks occurs, deduct the expected frame signal copy of generation, and the surplus signal of institute is submitted to the demodulating and decoding unit;
8.6 the demodulating and decoding unit carries out the demodulation sign indicating number to residual signal, and the bit sequence after the demodulation sign indicating number is submitted to the mac layer frame extraction module;
8.7, the mac layer frame extraction module carries out mac layer frame to the bit sequence that receives and delimits, and use the check polynomial of stipulating in 802.11 standards that this frame is carried out cyclic redundancy check (CRC), if the verification that obtains with frame in consistent, then expected frame is eliminated successfully, and the mac layer frame that obtains is submitted to medium access control module; Otherwise execution in step 8.8;
8.8, select whether to attempt again, if number of retries does not surpass the upper limit, then adjust channel and transmitter estimated parameter, generate new expected frame signal copy, execution in step 8.5; Otherwise, return the elimination failed message, expected frame is eliminated and is stopped.
Step 9 sends terminal and receives CTS, shakes hands successfully, expection ACK frame is set receives, and send Frame, waits for receiving ACK; Otherwise after keeping out of the way, execution re-executes step 1.
After step 10, receiving terminal successfully receive Frame, send the ACK frame acknowledgment, otherwise take defeat.
Step 11 sends terminal and successfully receives the ACK frame, and data send successfully; Otherwise send failure, return step 1 after execution is kept out of the way.
Claims (6)
1. radio packet network medium access control system, comprise: medium inserts molded of control, received signal parsing module, antenna, RF front-end module, analog to digital converter, digital to analog converter, mac layer frame extraction module, physical layer frame formation module, modulation/coding module and physical channel administration module, it is characterized in that:
Described medium access control module comprises:
The upper-layer protocol interface is used for receiving packet from upper-layer protocol, it is assembled into to send to behind the mac layer frame send collaborative unit, and collects the mac layer frame that receives from receive collaborative unit, and the packet of extracting wherein sends to upper-layer protocol;
Frame sends collaborative unit, be used for instruction according to medium access control protocol and other functional unit, the necessary controlling mechanism of shaking hands when realizing the mac layer frame transmission, the control frame transmitting element sends suitable control frame and Frame at reasonable time, and detects and eliminate unit setting or expected frame detection according to the RTS content frame indication expected frame of sending;
The frame transmitting element is used for sending the physical layer frame formation module of mac layer frame to the outside under the control of the collaborative unit of frame transmission, the collaborative unit of frame reception;
Receive collaborative unit, be used for instruction according to medium access control protocol and other functional unit, the necessary controlling mechanism of shaking hands when realizing that mac layer frame sends determines that according to the frame type that receives sending to the frame transmitting element after the type of response frame and the content in time sends;
The frame receiving element, be used for after outside mac layer frame extraction module receives mac layer frame, in time submitting to the collaborative unit of reception, type and sending duration field notification channel administrative unit according to the frame that receives more relocate the receiving and send the NAV timer, and detect and eliminate the unit setting or carry out the expected frame detection according to RTS frame that receives and CTS frame indication expected frame;
The channel management unit is used to receive initial, the signal power level indication of received signal from the RF front-end module of outside, and from the NAV timer update instruction of frame receiving element, realizes the channel status management;
Keep out of the way administrative unit, be used for keeping out of the way sending to carry out when unsuccessful, notice sends collaborative unit and sends respective frame once more when keeping out of the way the timer timing and stop;
Expected frame detects and eliminates control unit, be used for according to the indication that sends collaborative unit and receiving element, the content and the time of advent of the ACK frame that will occur according to the RTS frame of current transmission or the current RTS/CTS frame expection that receives, the outside received signal parsing module of notice and control is carried out expected frame and is detected and eliminate, and the result is fed back to frame sends collaborative unit or frame receiving element.
Described received signal parsing module comprises:
The digital signal buffer is used to receive and the digital medium-frequency signal of buffer memory after analog-to-digital conversion, and offers expected frame detecting unit, expected frame elimination unit and demodulator/decoder unit use respectively according to different demands;
The expected frame detecting unit is used for the instruction according to external medium access control module, detects specific expected frame from the digital signal sequences that receives, and the result is returned to external medium access control module;
Expected frame is eliminated the unit, is used for the instruction according to external medium access control module or expected frame cancellation module, eliminate corresponding expected frame signal from the digital signal sequences that receives, and the signal that will eliminate after the expected frame sends to demodulator/decoder unit;
Demodulator/decoder unit is used to receive the digital medium-frequency signal from digital signal buffer or expected frame elimination unit, and it is carried out the demodulate/decode operation, therefrom obtains digital baseband signal and sends to outside mac layer frame extraction module.
2. a radio packet network medium connection control method comprises the steps:
(1) when terminal has Frame to send, whether have by the transmission of carrier sense inhibition specified data frame according to current, if this terminal is not suppressed, belong to the exposed terminal inhibition but perhaps be suppressed, then send RTS, and wait for receiving terminal response CTS; Otherwise execution is kept out of the way, and sends RTS until terminal;
(2) after receiving terminal is received RTS,, then respond CTS and wait for receiving data frames if be not suppressed; Otherwise do not respond;
(3) adjacent end is provided with respectively and receives and send the NAV timer, to determine oneself to belong to which kind of state according to the type and the sending duration field of the frame that listens to;
(4) if terminal can expect that certain moment in future an ACK frame will occur by complete and accurate according to type, address and the duration field of the frame that has just sent out or received, then be arranged on the moment that expection ACK frame occurs, carry out expected frame and detect and eliminate, otherwise do not need to be provided with expected frame;
(5) terminal is after receiving wireless signal, if received signal and the expected frame time-interleaving that is provided with in advance, then according to frame zero-time, frame preamble sequence and frame delimiting sequence and the content frame field of expecting, adopt the sequence correlation method to carry out the detection of expected frame, detect precise time and the channel parameter estimation that obtains according to expected frame, produce a received signal copy after the transmission of expected frame channel, this expected frame copy is eliminated from received signal, and expected frame signal afterwards carries out demodulating and decoding and frame extracts to eliminating;
(6) send terminal and receive CTS, shake hands successfully, expection ACK frame is set receives, and send Frame, wait for receiving ACK;
(7) after receiving terminal successfully receives Frame, send the ACK frame acknowledgment, otherwise take defeat;
(8) send terminal and successfully receive the ACK frame, data send successfully; Otherwise send failure, return step (1).
3. radio packet network medium connection control method according to claim 2, wherein step (4) is described according to the ACK frame of given frame expection certain moment in future with appearance, is divided into three kinds of situations:
First kind of situation is: if the RTS frame has just been sent or received to terminal, expect that then the destination address of ACK frame is the source address of RTS frame, field expeced time among the ACK is 0, the time of occurrence of expection ACK frame: T=t+D-t
Sfs-t
ACK, wherein t is the current time, D is the sending duration in the RTS frame, t
SfsBe the shortest frame period, t
ACKFor the ACK frame transmits required time;
Second kind of situation is: if the frame that terminal receives is CTS, expect that then the destination address of ACK frame is the destination address of CTS frame, field expeced time among the ACK is 0, the time of occurrence of expection ACK frame: T=t+D-t
Sfs-t
ACK, wherein t is the current time, D is the sending duration in the CTS frame, t
SfsBe the shortest frame period, t
ACKFor the ACK frame transmits required time;
The third situation is: if the frame that terminal receives is the frame of other types, do not carry out the expected frame setting.
4. radio packet network medium connection control method according to claim 2, wherein step (5) is described according to frame zero-time, frame preamble sequence and frame delimiting sequence and the content frame field of expecting, adopt the sequence correlation method to carry out the detection of expected frame, comprise the steps:
(4a) the expected frame detecting unit receives the intermediate frequency wireless signal after digitlization, and the initial moment of the expected frame that presets and frame format content information;
(4b) in expected frame near the initial moment, with known frame preamble sequence and the received signal multiplication mutually that slides, if in the error allowed band, near the expected frame original position, what slip was multiplied each other is long-pending obviously greater than the product after before this position and this position, then think and significant correlation peak value, execution in step 4c occur; Otherwise think not have expected frame, detect failure;
(4c) from the definite position of relevant peaks indication, according to the parameter of channel estimating to the calculating of multiplying each other of sliding of complete expected frame, if what the slip that begins in this position was multiplied each other amasss before this position and the product after this position, think that then expected frame detects successfully; Otherwise execution in step 4d;
(4d) send targeting sequencing relevant peaks accurate location, channel and transmitter parameter Estimation, expected frame format content to the elimination of expected frame elimination unit requests;
(4e) if expected frame is eliminated successfully, then expection detects successfully; Otherwise expected frame detects failure.
5. radio packet network medium connection control method according to claim 2, described precise time and the channel parameter estimation that detect to obtain according to expected frame of step (5) wherein, produce a received signal copy after the transmission of expected frame channel, carry out as follows:
(5a) expected frame is eliminated the unit and is received the request of elimination, and the definite original position of wireless digital signal, expected frame, channel and transmitter estimated parameter and these necessary informations of expected frame format content that need therefrom eliminate expected frame;
(5b) according to the physical layer frame structure of stipulating in the format content of expected frame and 802.11 standards, add targeting sequencing and frame alignment sequence, assemble out complete physical layer frame;
(5c), physical layer frame is pursued bits of encoded and modulation, obtain encoded and modulation digital signal sequences afterwards according to the modulation coding method of physical layer specifies;
(5d) according to channel and transmitter estimated parameter, increase distortion to frequency, phase place and the amplitude of the digital signal behind modulation and the coding, resulting digital signal sequences is the expected frame signal copy after the channel transmission.
6. radio packet network medium connection control method according to claim 2, wherein step (6) is described eliminates the expected frame copy from received signal, and expected frame signal afterwards carries out demodulating and decoding and frame extracts to eliminating, and carries out as follows:
(6a) carry out the digital signal of expected frame elimination from needs, the definite position that occurs according to the targeting sequencing relevant peaks begins, and deducts the expected frame signal copy of generation, and the surplus signal of institute is submitted to the demodulating and decoding unit;
(6b) the demodulating and decoding unit carries out the demodulation sign indicating number to residual signal, and the bit sequence after the demodulation sign indicating number is submitted to the mac layer frame extraction module;
(6c) the mac frame extraction module carries out the mac layer frame demarcation to the bit sequence that receives, and use the check polynomial of stipulating in 802.11 standards that this frame is carried out cyclic redundancy check (CRC), if the verification that obtains is with consistent with the Frame Check Sequence in the frame, then expected frame is eliminated successfully, and the mac layer frame that obtains is submitted to medium access control module; Otherwise carry out 6d;
(6d) select whether to attempt again,, then adjust channel and transmitter estimated parameter, generate new expected frame signal copy, carry out 6a if number of retries does not surpass the upper limit; Otherwise, return the elimination failed message, expected frame is eliminated and is stopped.
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