CN105163395A - Wireless local area network access control method based on radio-on-fiber wireless system - Google Patents

Wireless local area network access control method based on radio-on-fiber wireless system Download PDF

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Publication number
CN105163395A
CN105163395A CN201510400133.2A CN201510400133A CN105163395A CN 105163395 A CN105163395 A CN 105163395A CN 201510400133 A CN201510400133 A CN 201510400133A CN 105163395 A CN105163395 A CN 105163395A
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poll
field
frame
data
base station
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CN201510400133.2A
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CN105163395B (en
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官铮
钱文华
张学杰
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Yunnan Youbei Communication Technology Co ltd
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Yunnan University YNU
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W74/00—Wireless channel access, e.g. scheduled or random access
    • H04W74/04—Scheduled or contention-free access
    • H04W74/06—Scheduled or contention-free access using polling
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2575—Radio-over-fibre, e.g. radio frequency signal modulated onto an optical carrier
    • H04B10/25752—Optical arrangements for wireless networks
    • H04B10/25753—Distribution optical network, e.g. between a base station and a plurality of remote units

Abstract

The invention discloses a wireless local area network access control method based on a radio-on-fiber wireless system. The method takes the IEEE802.11PCF technology as a core to improve the channel utilization rate and avoid idle polling, users having data sending requests are marked in an active state, and users without data sending requests are marked in a dormant state; a polling table is updated according to user states by a base station in a competition period after the end of each no-competition period, the polling table only comprises the active users; retransmission time delay design is taken into consideration in an overweight retransmission mechanism during fiber leading in. The method is advantaged in that the polling table is updated by the center base station according to the user states, polling requests are sent to the active users only, and thereby free station polling is avoided.

Description

A kind of wireless local network access control method based on radio over fibre system
Technical field
The invention belongs to areas of information technology, relate to a kind of wireless local network access control method based on radio over fibre system.
Background technology
Light-carried wireless distributing antenna system (RadiooverFiber-DistributedAntennaSystems, RoF-DSA) in, portable antenna unit (Remoteantennaunits, RAUs) by Fiber connection to the centralized control unit based on base station equipment.With broadcasting in light-carried wireless distributing antenna system (RoF-DAS), the centralized control unit based on single base station connects many RAUs, thus improves base station for the coverage of indoor wireless networks and bandwidth availability ratio.In this system up-link, the user terminal in different RAUs coverage needs by competition sharing base and transmission medium.For the standard that RoF network MAC layer agreement is still ununified at present, research mainly concentrates on and improves the relevant parameters such as its response time to offset the time delay of optical fiber introducing thus to make it be applicable to optical fiber radio system to the MAC protocol of traditional wireless communication standard as Wi-Fi, WiMAX.IEEE802.11 is that the medium education of WLAN (wireless local area network) provides 3 kinds of elementary tactics: basic distributed coordination (DCF, DistributedCoordinationFunction), DCF (DCFinRTS/CTS) and the point with request/reply coordinate (PCF, PointCoordinationFunction) control mode.But, standard traffic distance in WLAN (wireless local area network) between user and base station access point is less than 100 meters, comparatively speaking, in actual RoF-DAS, access point covers larger communication range, and the decay of signal makes traditional distributed Carrier Sense Multiple access/conflict avoidance (CSMA/CA) validity reduce.The impact (Chinacommunication, 2013 (1): 81-92) of extra time delay on throughput introduced by some access control mode Shen Xi analytic demonstration optical fiber based on booking-mechanism; LiJianqiang etc. propose a kind of access control optimisation strategy based on IEEE802.11, PCF access way is adopted to solve hidden terminal problem, and according to Optical Fiber Transmission distance increase in the PIFS cycle optical fiber introduce time of delay improve throughput (Chinacommunication, 2014 (5): 37-48), but, the method also makes the waiting-timeout time consumed during base station poll free time website increase, and during low load, channel utilization reduces.
Summary of the invention
The object of the present invention is to provide a kind of wireless local network access control method based on radio over fibre system, solve existing method and the waiting-timeout time consumed during base station poll free time website is increased, the problem that during low load, channel utilization reduces.
The technical solution adopted in the present invention is carried out according to following steps:
Step 1: definition frame form
Frame CTS, Frame Data, acknowledgement frame ACK are removed in request transmission frame RTS, transmission;
Request transmission frame RTS, when adding polling list polling table for active user to base station requests, comprise FrameControl, Src, Dest, Serv_type, FCS field, wherein FrameControl field is control field, 2 bytes, wherein Type part b 7b 6b 5b 4=1011, Subtype part b 3b 2=01, Src field 2 byte, indicates sender address, and Dest field 2 byte, indicates recipient address, and Serv_type field 2 byte remains for prioritization in advance, without priority area timesharing Serv_type=0x00; When sending polling beacon for base station to active user, FrameControl field Type part b in CF-Poll 7b 6b 5b 4=0110, Subtype part b 3b 2=10, Src field 2 byte, indicates sender address, and Dest field 2 byte, indicates recipient address, and Poll_squ field 2 byte is used for showing request object poll sequence number, without priority area timesharing Serv_type=0x00; FCS field is the ITU-TCRC check digit of 16bit;
Send and remove frame CTS: send poll order lastest imformation for base station to user, comprise FrameControl, Src, Dest, Poll_squ, FCS field, wherein FrameControl field is control field, 2 bytes, wherein Type part b 7b 6b 5b 4=1100, Subtype part b 3b 2=01, Src field 2 byte, indicates sender address, and Dest field 2 byte, indicates recipient address, and Poll_squ field 2 byte receives the poll sequence number of user in epicycle CFP for indicating; FCS field is the ITU-TCRC check digit of 16bit;
Frame Data: authorized user and cognitive user mail to the data of base station, comprise FrameControl, Src, Dest, Dsn, I_last, Data, FCS field, wherein Src, Dest, FCS Field Definition is identical with RTS, Dsn field 1 byte, indicate current data sequence number, I_last field 1 byte, indicate whether current data packet is last data in buffering area, I_last=FF represents, I_last=0x00 represents in buffering area to also have remaining data; DATA field is data message, variable-length; FrameControl field Type part b in Date+CF-ACK 7b 6b 5b 4=0001, Subtype part b 3b 2frameControl field Typeb in=10, Date 7b 6b 5b 4=0000, Subtype part b 3b 2=10;
ACK acknowledgement frame: for confirming data receiver and request of data when base station sends to active user, comprise FrameControl, Src, Dest, Dsn, S next, FCS field, wherein Src, Dest, FCS Field Definition is identical with RTS, Dsn field 2 byte, indicates and applies for next Frame sequence number of receiving; As the I_last=0x00 received, Dsn=Dsn+1, FrameControl field Type part b 7b 6b 5b 4=1101, Subtype part b 3b 2=01; As the I_last=0xFF received, FrameControl field Typeb in CF-Poll+ACK frame is replied in base station 7b 6b 5b 4=0111, Subtype part b 3b 2=10, Dsn=0x00; S nEXTfield 2 byte, is marked as next request object poll sequence number, works as S nEXT=0x00 shows that in polling list polling table, all STA had accepted base station poll all, and FrameControl field Typeb in CF-End+ACK is replied in base station 7b 6b 5b 4=1111, Subtype part b 3b 2=10; Active user sends to the ACK of base station for confirming that polling list polling table lastest imformation correctly receives, and comprise FrameControl, Src, Dest, Dsn, Poll_squ, FCS field, wherein Src, Dest, FCS Field Definition is identical with RTS; FrameControl field Type part b 7b 6b 5b 4=1101, Subtype part b 3b 2=01, Dsn=0x00, Poll_squ field 2 byte, for indicating STA poll sequence number; FCS field is the ITU-TCRC check digit of 16bit;
Step 2: based on the polling multi-access Access Control Policy of User Status
(1) contention free period
Base station sends beacon mark CFP and starts, T sIFSbehind interval base station to active user according to polling list polling table order to active user request msg, carry out roll-call access process, wherein SIFS is with reference to IEEE802.11, T sIFS=28 μ s;
When in the Frame that base station receives during I_last=FF, by arranging Dsn=0, S in the ACK frame of replying next=Poll_squ+1, represents the polling request to active user next in polling list polling table; When base station completes in polling list polling table after the reception of last user data, by arranging Dsn=0x00, S in the ACK replied next=0x00 marks CFP to be terminated;
During CFP, active user continues to intercept channel, when in the RTS frame receiving base station transmission, Poll_squ equals active user's poll sequence number, or receives Dsn=0x00 in ACK and S nextwhen equaling active user's poll sequence number, behind SIFS interval, active user sends data to base station; Transfer of data adopts Retransmission timeout mechanism, and sender is T after transmission information frame pIFS_delaytime-out does not receive ACK and confirms then to carry out data re-transmission, T pIFS_delayconsider that propagation delay time introduced by optical fiber, be calculated as follows:
T PIFS_delay＝T PIFS+2×fiberlength×5μs/km
Wherein, T pIFSwith reference to IEEE802.11 value T pIFS=78 μ s;
Active user completes all data in buffer memory and enters resting state stopping channel sense after sending, and is waken up and again intercepts channel after new data arrives; When applying for adding polling list polling table during CP after reception CF-End+ACK frame;
(2) phase is competed
After base station sends CF-End+ACK, system enters the CP stage; During CP, active user adopts RTS/CTS
The application of DCF mechanism obtains the poll qualification of next round; Active user applies for poll sequence number by RTS frame to base station; After base station correctly receives, in CTS frame, Poll_squ field indicates user's poll sequence number; User correctly receives rear reply ACK frame acknowledgment; Adopt Retransmission timeout mechanism during CP, after information frame sends, timing is more than T dIFS_delaydo not receive reply then to start to retransmit, T dIFS_delayconsider that optical fiber is introduced time delay and calculated according to the following formula:
T DIFS_delay＝T DIFS+2×fiberlength×5μs/km
Wherein T dIFSwith reference to IEEE802.11 value T dIFS=128 μ s.
Further,
1) base station end control algolithm:
Step 1: Initialize installation Poll_squ=0x01;
Step 2: send Beacon mark CFP and start;
Step 2: send polling request CF-Poll;
Step 3: if T pIFS_delaytime-out does not receive data and then returns step 2; If correctly receive data, reply ACK acknowledgement frame; In the Data frame of reception during I_last=0xFF, reply ACK+CF_Poll, wherein Poll_squ=Poll_squ+1, Dsn=0; In the Data frame of reception during I_last=0x00, reply Poll_squ=Poll_squ, Dsn=Dsn+1 in ACK;
Step 4: receive the Data frame that Poll_squ is last user in polling list polling table, until I_last=0xFF detected, sends ACK+CF_End mark CFP and terminates;
Step 5: intercept channel, receives the RTS from active user, distributes Poll_squ; T dFIStime-out does not receive RTS, returns step 1;
Step 6: reply CTS and inform user's poll sequence number Poll_squ;
Step 7: receive the ACK frame from Poll_squ user; T dFIS_delaytime-out does not receive ACK and then retransmits, and returns step 6;
Step 8: intercept channel, T after correct reception ACK dFIS_delaytime-out does not receive RTS, returns step 1;
2) user side control algolithm:
Step 1: data arrive, and STA is waken up and enters active state;
Step 2: intercept channel, after receiving CF_end frame, the application of interval SIFS transmission RTS frame adds polling list polling table;
Step 3: accept the CTS frame from base station, record Poll_squ sequence number, replys ACK and confirms;
Step 4: intercept channel, receives CF_Poll or the ACK+CF_Poll signal from base station, starts to send data;
Step 5: data send and terminate, and enter resting state; Return step 1.
The invention has the beneficial effects as follows relative in known RoF-DAS Access Control Technique, the present invention is based on IEEE802.11 point coordination access control mode and a kind of dynamic polling connection control method based on User Status cognition is provided, the access user not having data to send in the method enters resting state, center base station upgrades polling list polling table according to User Status, only send polling request to active user, thus avoid idle website poll.
Accompanying drawing explanation
Fig. 1 is an example communication system, can implement disclosed one or more execution modes in this communication system;
Fig. 2 is the four class medium education information frame forms that can use in communication system shown in Fig. 1;
Fig. 3 be can in four category information frame structures shown in Fig. 2 FrameControl field format;
Fig. 4 is that an example user is at the flow chart implementing disclosed scheme access scheme;
Fig. 5 is that an exemplary base is at the flow chart implementing open scheme polling dispatching scheme;
Fig. 6 is the embodiment of the method adopting WLAN (wireless local area network) access control of the present invention in the distributing antenna system of light-carried wireless shown in Fig. 1.
Embodiment
Below in conjunction with embodiment, the present invention is described in detail.
The method for core with IEEE802.11PCF technology, to improve channel utilization and to avoid the free time to be polled as object, will have the user of data sending request to be labeled as active state, not have the user of data sending request to be labeled as resting state; Base station is terminated rear according to User Status renewal polling list polling table each contention free period (ContentionFreePeriod, CFP), only include active user in polling list polling table.
The present invention completes according to the following steps:
1. definition frame form
The media access control method that inventing provides comprises four class frames: frame (CTS), Frame (Data), acknowledgement frame (ACK) are removed in request transmission frame (RTS), transmission.
FrameControl Field Definition in four class frame structures is identical with IEEE802.11, wherein uses Type and Subtype field to indicate packet type.FCS field is the ITU-TCRC check digit of 16bit.
Request transmission frame RTS: when adding polling list polling table for active user to base station requests, comprise FrameControl, Src, Dest, Serv_type, FCS field.Wherein FrameControl field is control field, 2 bytes, wherein Typeb 7b 6b 5b 4=1011, Subtype part b 3b 2=01; Src field 2 byte, indicates sender address; Dest field 2 byte, indicates recipient address; Serv_type field 2 byte remains for prioritization in advance, without priority area timesharing Serv_type=0x00; When sending polling beacon for base station to active user, FrameControl field Typeb in CF-Poll 7b 6b 5b 4=0110, Subtype part b 3b 2=10; Src field 2 byte, indicates sender address; Dest field 2 byte, indicates recipient address; Poll_squ field 2 byte is used for showing request object poll sequence number, without priority area timesharing Serv_type=0x00; FCS field is the ITU-TCRC check digit of 16bit.
Send and remove frame CTS: send poll order lastest imformation for base station to user, comprise FrameControl, Src, Dest, Poll_squ, FCS field.Wherein FrameControl field is control field, 2 bytes, wherein Typeb 7b 6b 5b 4=1100, Subtype part b 3b 2=01; Src field 2 byte, indicates sender address; Dest field 2 byte, indicates recipient address; Poll_squ field 2 byte receives the poll sequence number of user in epicycle CFP for indicating; FCS field is the ITU-TCRC check digit of 16bit.
Frame DATA: authorized user and cognitive user mail to the data of base station, comprises FrameControl, Src, Dest, Dsn, I_last, Data, FCS field.Wherein Src, Dest, FCS Field Definition is identical with RTS, Dsn field 1 byte, indicate current data sequence number, I_last field 1 byte, indicate whether current data packet is last data in buffering area, I_last=FF represents, I_last=0x00 represents in buffering area to also have remaining data; DATA field is data message, variable-length; FrameControl field Typeb in Date+CF-ACK 7b 6b 5b 4=0001, Subtype part b 3b 2frameControl field Typeb in=10, Date 7b 6b 5b 4=0000, Subtype part b 3b 2=10.
ACK acknowledgement frame: for confirming data receiver and request of data when base station sends to active user, comprise FrameControl, Src, Dest, Dsn, S next, FCS field, wherein Src, Dest, FCS Field Definition is identical with RTS, Dsn field 2 byte, indicates and applies for next packet sequence number of receiving; As the I_last=0x00 received, FrameControl field Typeb in Dsn=Dsn+1, ACK 7b 6b 5b 4=1101, Subtype part b 3b 2=01; As the I_last=FF received, FrameControl field Typeb in Dsn=0x00, CF-Poll+ACK 7b 6b 5b 4=0111, Subtype part b 3b 2=10; S nEXTfield 2 byte, is marked as next request object poll sequence number, works as S nEXT=0x00 shows that in polling list polling table, all STA had accepted base station poll all, now FrameControl field Typeb in CF-End+ACK 7b 6b 5b 4=1111, Subtype part b 3b 2=10; Active user sends to the ACK of base station for confirming that polling list polling table lastest imformation correctly receives, and comprise FrameControl, Src, Dest, Dsn, Poll_squ, FCS field, wherein Src, Dest, FCS Field Definition is identical with RTS; FrameControl field Typeb 7b 6b 5b 4=1101, Subtype part b 3b 2=01; Dsn=0x00, Poll_squ field 2 byte, for indicating STA poll sequence number; FCS field is the ITU-TCRC check digit of 16bit.
2. based on the polling multi-access Access Control Policy of User Status
Be made up of contention free period (ContentionFreePeriod, CFP) and competition phase (ContentionPeriod, CP) based on IEEE802.11PCF superframe.
Base station sends beacon mark CFP and starts, T sIFSbehind interval base station to active user according to polling list polling table order to active user request msg, carry out roll-call access process, wherein SIFS is with reference to IEEE802.11, T sIFS=28 μ s.When in the Frame that base station receives during I_last=FF, by arranging Dsn=0, S in the ACK frame of replying next=Poll_squ+1, represents the polling request to active user next in polling list polling table; When base station completes in polling list polling table after the reception of last user data, by arranging Dsn=0x00, S in the ACK replied next=0x00 marks CFP to be terminated.
During CFP, active user continues to intercept channel, when in the RTS frame receiving base station transmission, Poll_squ equals active user's poll sequence number, or receives Dsn=0x00 in ACK and S nextwhen equaling active user's poll sequence number, behind SIFS interval, active user sends data to base station; In data transmission procedure, if user is T after transmission Date frame pIFS_delaytime-out does not receive ACK acknowledgement frame and then carries out data re-transmission.T pIFS_delayconsider that propagation delay time introduced by optical fiber, be calculated as follows:
T PIFS_delay＝T PIFS+2×fiberlength×5μs/km
Wherein, T pIFSwith reference to IEEE802.11 value T pIFS=78 μ s.Fiberlength is fiber lengths.
Active user completes all data in buffer memory and enters resting state after sending and stop channel sense, is waken up, starts to intercept channel after new data arrives, and after receiving the ACK frame that mark CFP terminates, during CP subsequently, application adds polling list polling table.
CFP terminates rear system and enters the CP stage.During CP, active user adopts the application of RTS/CTSDCF mechanism to obtain the poll qualification of next round.Active user applies for poll sequence number by RTS frame to base station; After base station correctly receives, in CTS frame, Poll_squ field indicates user's poll sequence number; User correctly receives rear reply ACK frame acknowledgment; Base station starts timing after sending CTS, and timing is more than T dIFS_delaydo not receive ACK acknowledgement frame then to start to retransmit, T dIFS_delayconsider that optical fiber is introduced time delay and calculated according to the following formula:
T DIFS_delay＝T DIFS+2×fiberlength×5μs/km
Wherein T dIFSwith reference to IEEE802.11 value T dIFS=128 μ s.
3. base station AP control algolithm:
Step 1: Initialize installation Poll_squ=0x01;
Step 2: send Beacon mark CFP and start;
Step 3: send polling request CF-Poll;
Step 4: if T pIFS_delaytime-out does not receive data and then returns step 2; If correctly receive data, reply ACK acknowledgement frame.In the Data frame of reception during I_last=0xFF, reply ACK+CF_Poll, wherein Poll_squ=Poll_squ+1, Dsn=0.In the Data frame of reception during I_last=0x00, reply Poll_squ=Poll_squ, Dsn=Dsn+1 in ACK.
Step 5: receive the Data frame that Poll_squ is last user in polling list polling table, until I_last=0xFF detected, sends ACK+CF_End mark CFP and terminates.
Step 6: intercept channel, receives the RTS from active user, distributes Poll_squ; T dFIStime-out does not receive RTS, returns step 1;
Step 7: reply CTS and inform user's poll sequence number Poll_squ;
Step 8: receive the ACK frame from Poll_squ user; T dFIS_delaytime-out does not receive ACK and then retransmits, and returns step 6;
Step 9: intercept channel, T after correct reception ACK dFIS_delaytime-out does not receive RTS, returns step 1.
4. user STA control algolithm:
Step 1: data arrive, and STA is waken up and enters active state;
Step 2: intercept channel, after receiving CF_end frame, the application of interval SIFS transmission RTS frame adds polling list polling table;
Step 3: accept the CTS frame from base station, record Poll_squ sequence number, replys ACK and confirms;
Step 4: intercept channel, receives CF_Poll or the ACK+CF_Poll signal from base station, starts to send data;
Step 5: data send and terminate, and enter resting state; Return step 1.
Fig. 1 is an example communication system, can implement disclosed one or more execution modes in this communication system; Fig. 2 is the four class medium education information frame forms that can use in communication system shown in Fig. 1.Fig. 3 be can in four category information frame structures shown in Fig. 2 FrameControl field format.Fig. 4 is that an example user is at the flow chart implementing disclosed scheme access scheme.Fig. 5 is that an exemplary base is at the flow chart implementing open scheme polling dispatching scheme.Fig. 6 is the embodiment of the method adopting WLAN (wireless local area network) access control of the present invention in the distributing antenna system of light-carried wireless shown in Fig. 1.Table 1 is Type and Subtype part assignment explanation in mac frame FrameControl field of the present invention.
Table 1
The present invention will be described to enumerate specific embodiment below.
The present embodiment is depicted as a roll-call access cycle in access control process.Light-carried wireless distributing antenna system in embodiment has 1 base station BS and 3 wireless access terminal user STA.In the present embodiment CFP start time, STA1 and STA2 is because there is data sending request to be in active state, STA1 and STA2 is added polling list polling table by the renewal that base station had completed polling list polling table within a upper competition phase.Then in current polling cycle, media access control flow journey is as follows:
T0: base station sends Beacon and indicates that contention free period starts;
T1: interval T sIFSrear base station sends the request of CF-Poll data access to STA1;
T2:STA1 receives the CF-Poll frame from base station, interval T sIFSsend CF-ACK and Date frame to base station afterwards, and in the end mark I_last=0xFF in a Date frame and represent DTD;
T3: base station receives the Data frame being marked with I_last=0xFF from STA1, interval T sIFSrear transmission ACK+CF-Poll, mark Poll-squ=STA2 is incidentally to the data request information of STA2;
T4: have data to arrive and wake dormant user IdelSTA up, start to intercept channel after entering active state;
T5:STA1 data buffer area is empty, and correct reception proceeds to resting state from after the ACK+CF-Poll frame of base station;
T6:STA2 receives the ACK-CF-Poll frame from base station, interval T sIFSsend CF-ACK and Date frame to base station afterwards, and in the end mark I_last=0xFF in a Date frame and represent DTD;
T7: have data to arrive and wake the STA1 being in resting state up, start to intercept channel after entering active state;
T8:STA2 in the end marks I_last=0xFF in a Date frame and represents DTD;
T9: base station receives the Data frame being marked with I_last=0xFF from STA2, detects in polling list polling table and needs access, interval T without residue STA sIFSrear transmission ACK+CF-end frame, mark S next=0x00 incidentally represents that contention free period terminates;
T10: the STA of active state listen to ACK+CF-end after enter contention access state, adopt RTS/CTS mode of operation to send the polling sequence of a polling request application new round to base station;
T11: base station upgrades polling list polling table, and complete the distribution of new round polling sequence, contention access periods terminates; Send Beacon and represent that the next round uncontested data access phase starts.
Advantage of the present invention:
1, in the error retransmission treatment mechanism accessing application and data transfer phase, consider that transmission delay design T introduced by optical fiber dFIS_delayand T dFIS_delaybe more suitable for RoF – DAS system;
2, send demand according to user data and carry out User Status differentiation;
3, countlessly enter resting state according to sending the user of demand, active user participates in the competition polling sequence;
4, base station upgrades polling list polling table according to User Status in competing cycle, avoids the free time in polling cycle to access, and improves network throughput;
5, utilize piggy mechanism to achieve the parallel processing of transfer of data and request of data, reduce data awaiting transmission time delay.
The above is only to better embodiment of the present invention, not any pro forma restriction is done to the present invention, every any simple modification done above execution mode according to technical spirit of the present invention, equivalent variations and modification, all belong in the scope of technical solution of the present invention.

Claims (2)

1., based on a wireless local network access control method for radio over fibre system, it is characterized in that carrying out according to following steps:
Step 1: definition frame form
Frame CTS, Frame Data, acknowledgement frame ACK are removed in request transmission frame RTS, transmission;
Request transmission frame RTS, when adding polling list polling table for active user to base station requests, comprise FrameControl, Src, Dest, Serv_type, FCS field, wherein FrameControl field is control field, 2 bytes, wherein Type part b 7b 6b 5b 4=1011, Subtype part b 3b 2=01, Src field 2 byte, indicates sender address, and Dest field 2 byte, indicates recipient address, and Serv_type field 2 byte remains for prioritization in advance, without priority area timesharing Serv_type=0x00; When sending polling beacon for base station to active user, FrameControl field Type part b in CF-Poll 7b 6b 5b 4=0110, Subtype part b 3b 2=10, Src field 2 byte, indicates sender address, and Dest field 2 byte, indicates recipient address, and Poll_squ field 2 byte is used for showing request object poll sequence number, without priority area timesharing Serv_type=0x00; FCS field is the ITU-TCRC check digit of 16bit;
Send and remove frame CTS: send poll order lastest imformation for base station to user, comprise FrameControl, Src, Dest, Poll_squ, FCS field, wherein FrameControl field is control field, 2 bytes, wherein Type part b 7b 6b 5b 4=1100, Subtype part b 3b 2=01, Src field 2 byte, indicates sender address, and Dest field 2 byte, indicates recipient address, and Poll_squ field 2 byte receives the poll sequence number of user in epicycle CFP for indicating; FCS field is the ITU-TCRC check digit of 16bit;
Frame Data: authorized user and cognitive user mail to the data of base station, comprise FrameControl, Src, Dest, Dsn, I_last, Data, FCS field, wherein Src, Dest, FCS Field Definition is identical with RTS, Dsn field 1 byte, indicate current data sequence number, I_last field 1 byte, indicate whether current data packet is last data in buffering area, I_last=FF represents, I_last=0x00 represents in buffering area to also have remaining data; DATA field is data message, variable-length; FrameControl field Type part b in Date+CF-ACK 7b 6b 5b 4=0001, Subtype part b 3b 2frameControl field Typeb in=10, Date 7b 6b 5b 4=0000, Subtype part b 3b 2=10;
ACK acknowledgement frame: for confirming data receiver and request of data when base station sends to active user, comprise FrameControl, Src, Dest, Dsn, S next, FCS field, wherein Src, Dest, FCS Field Definition is identical with RTS, Dsn field 2 byte, indicates and applies for next Frame sequence number of receiving; As the I_last=0x00 received, Dsn=Dsn+1, FrameControl field Type part b 7b 6b 5b 4=1101, Subtype part b 3b 2=01; As the I_last=0xFF received, FrameControl field Typeb in CF-Poll+ACK frame is replied in base station 7b 6b 5b 4=0111, Subtype part b 3b 2=10, Dsn=0x00; S nEXTfield 2 byte, is marked as next request object poll sequence number, works as S nEXT=0x00 shows that in polling list polling table, all STA had accepted base station poll all, and FrameControl field Typeb in CF-End+ACK is replied in base station 7b 6b 5b 4=1111, Subtype part b 3b 2=10; Active user sends to the ACK of base station for confirming that polling list polling table lastest imformation correctly receives, and comprise FrameControl, Src, Dest, Dsn, Poll_squ, FCS field, wherein Src, Dest, FCS Field Definition is identical with RTS; FrameControl field Type part b 7b 6b 5b 4=1101, Subtype part b 3b 2=01, Dsn=0x00, Poll_squ field 2 byte, for indicating STA poll sequence number; FCS field is the ITU-TCRC check digit of 16bit;
Step 2: based on the polling multi-access Access Control Policy of User Status
1) contention free period
Base station sends beacon mark CFP and starts, T sIFSbehind interval base station to active user according to polling list polling table order to active user request msg, carry out roll-call access process, wherein SIFS is with reference to IEEE802.11, T sIFS=28 μ s;
When in the Frame that base station receives during I_last=FF, by arranging Dsn=0, S in the ACK frame of replying next=Poll_squ+1, represents the polling request to active user next in polling list polling table; When base station completes in polling list polling table after the reception of last user data, by arranging Dsn=0x00, S in the ACK replied next=0x00 marks CFP to be terminated;
During CFP, active user continues to intercept channel, when in the RTS frame receiving base station transmission, Poll_squ equals active user's poll sequence number, or receives Dsn=0x00 in ACK and S nextwhen equaling active user's poll sequence number, behind SIFS interval, active user sends data to base station; Transfer of data adopts Retransmission timeout mechanism, and sender is T after transmission information frame pIFS_delaytime-out does not receive ACK and confirms then to carry out data re-transmission, T pIFS_delayconsider that propagation delay time introduced by optical fiber, be calculated as follows:
T PIFS_delay＝T PIFS+2×fiberlength×5μs/km
Wherein, T pIFSwith reference to IEEE802.11 value T pIFS=78 μ s;
Active user completes all data in buffer memory and enters resting state stopping channel sense after sending, and is waken up and again intercepts channel after new data arrives; When applying for adding polling list polling table during CP after reception CF-End+ACK frame;
2) phase is competed
After base station sends CF-End+ACK, system enters the CP stage; During CP, active user adopts RTS/CTS
The application of DCF mechanism obtains the poll qualification of next round; Active user applies for poll sequence number by RTS frame to base station; After base station correctly receives, in CTS frame, Poll_squ field indicates user's poll sequence number; User correctly receives rear reply ACK frame acknowledgment; Adopt Retransmission timeout mechanism during CP, after information frame sends, timing is more than T dIFS_delaydo not receive reply then to start to retransmit, T dIFS_delayconsider that optical fiber is introduced time delay and calculated according to the following formula:
T DIFS_delay＝T DIFS+2×fiberlength×5μs/km
Wherein T dIFSwith reference to IEEE802.11 value T dIFS=128 μ s.
2., according to the wireless local network access control method based on radio over fibre system a kind of described in claim 1, it is characterized in that:
1) base station end control algolithm:
Step 1: Initialize installation Poll_squ=0x01;
Step 2: send Beacon mark CFP and start;
Step 3: send polling request CF-Poll;
Step 4: if T pIFS_delaytime-out does not receive data and then returns step 2; If correctly receive data, reply ACK acknowledgement frame; In the Data frame of reception during I_last=0xFF, reply ACK+CF_Poll, wherein Poll_squ=Poll_squ+1, Dsn=0; In the Data frame of reception during I_last=0x00, reply Poll_squ=Poll_squ, Dsn=Dsn+1 in ACK;
Step 5: receive the Data frame that Poll_squ is last user in polling list polling table, until I_last=0xFF detected, sends ACK+CF_End mark CFP and terminates;
Step 6: intercept channel, receives the RTS from active user, distributes Poll_squ; T dFIStime-out does not receive RTS, returns step 1;
Step 7: reply CTS and inform user's poll sequence number Poll_squ;
Step 8: receive the ACK frame from Poll_squ user; T dFIS_delaytime-out does not receive ACK and then retransmits, and returns step 6;
Step 9: intercept channel, T after correct reception ACK dFIS_delaytime-out does not receive RTS, returns step 1;
2) user side control algolithm:
Step 1: data arrive, and STA is waken up and enters active state;
Step 2: intercept channel, after receiving CF_end frame, the application of interval SIFS transmission RTS frame adds polling list polling table;
Step 3: accept the CTS frame from base station, record Poll_squ sequence number, replys ACK and confirms;
Step 4: intercept channel, receives CF_Poll or the ACK+CF_Poll signal from base station, starts to send data;
Step 5: data send and terminate, and enter resting state; Return step 1.
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