CN102413582B - Method for accessing 802.11 wireless network channel under centralized control - Google Patents

Abstract

The invention relates to a centrally controlled 802.11 wireless network channel access method. On the premise of retaining the competition mechanism, this method changes the way of channel access through "random fallback" into the way of centralized control by the wireless controller (AP), and optimizes the following problems in the channel access process: ( 1) The waiting time for random backoff of the station (STA) is removed, and different inter-frame interval durations (IFS) are uniformly replaced with short inter-frame interval interval durations (SIFS), which reduces the delay between frame transmissions and improves channel performance. The utilization rate greatly increases the throughput of the system; (3) when multiple sites compete for the channel at the same time, the occurrence of collision is avoided, the access delay of the site is reduced, and the packet loss rate of the site is reduced; (4) The use of the channel availability assessment (CCA) by the station is improved, and the energy consumption of the station is reduced.

Description

A method for centrally controlled 802.11 wireless network channel access

technical field

The invention is a centrally controlled 802.11 wireless network channel access method, which belongs to the intersection field of computer network and wireless communication.

Background technique

With the development of wireless communication technology, people's working environment has changed from fixed to flexible, and wireless local area networks have been widely used in various fields.

802.11 is one of the most mainstream wireless LAN technologies at present. It is an international standard formulated by the Institute of Electrical and Electronics Engineers (IEEE) to regulate the physical layer (PHY) and media access control layer (MAC) of wireless LAN. The 802.11 series standards currently provide two MAC access mechanisms, namely distributed coordination function (DCF, Distributed Coordination Function) and centralized coordination function (PCF, Point Coordination Function), among which distributed coordination function is currently the most widely used MAC access mechanism. The distributed coordination function does not use any central control, but allows each station to use the distributed access method of the carrier sense/collision avoidance (CSMA/CA) mechanism, so that each station can obtain the access right of the channel through free competition . When each station intends to access, it needs to first conduct a channel availability assessment (CCA) by listening to the medium for a fixed duration (DCF inter-frame space, DIFS). If the state of the medium is idle, the station considers its Can own the media and start a frame exchange. If the medium is busy, the station waits for the deadline to become idle, delays the DIFS duration, and further waits for a random backoff period. If the medium remains idle during the DIFS post-delay and backoff periods, then the station considers it can own the medium and can start a frame exchange.

The DCF mechanism stipulates that all stations must perform CCA before accessing the medium, and when the medium becomes idle, it needs to delay the DIFS duration, and then wait for a fallback period. In addition, if multiple sites access and collide at the same time, all sites need to adopt a fallback mechanism, and expand the value range [0, CW] (contention window, CW) of the random fallback time length in the next access , so as to reduce the probability of collision again. Therefore, when the number of sites increases and the traffic increases, the DCF mechanism is difficult to solve the problem of frequent collisions and increasing back-off periods, resulting in increased site access delays and decreased channel utilization.

Contents of the invention

Technical goal: The purpose of the present invention is to provide an improved method for centrally controlling 802.11 channel access in order to overcome the above-mentioned shortcomings in the prior art. This method uses the wireless controller (AP) to centrally manage and control the access of the channel, under the premise of ensuring competition, removes the random back-off free competition of the station (STA), and unifies the different inter-frame interval time (IFS) Replaced by short frame interval (SIFS), which reduces the delay between frame transmissions and improves the efficiency of channel utilization, especially when multiple sites compete for channels at the same time, avoiding collisions, optimizing site access, and making sites The use of channel availability assessment (CCA) is eliminated, and the energy consumption of the site is reduced.

Conditions of use: In a method for centrally controlling 802.11 wireless network channel access of the present invention, when the following conditions occur, the AP and the station enable the method:

1) When the station wants to perform continuous frame exchange, or transmit more than one transmission opportunity (TXOP), after the station completes the first frame exchange, or after a TXOP, the AP and the station enable this method;

2) In a basic service set (BSS), if more than one active station wants to exchange frames at the same time, the AP and the station enable this method.

In order to achieve the above-mentioned purpose, the present invention adopts the following technical scheme: in the method for a kind of central control type 802.11 wireless network channel access of the present invention, AP will set up a station information competition arrangement list, prepare to use the station of channel to send to AP The random number in a specific interval is used as its own competition information, and the AP organizes the stations to perform channel access by recording and arranging these competition information.

A central control type 802.11 wireless network channel access method, including the following working process:

1) After the beacon (Beacon) frame broadcast periodically, the AP sets an access slot with a length of DCF frame interval (DIFS), and all newly joined stations can send to AP sends access request;

2) After the AP broadcasts the beacon frame, it continuously monitors the channel under its jurisdiction for DIFS duration to determine whether there is a newly added station requesting access;

3) After receiving the beacon (Beacon) frame, the newly joined station does not perform channel availability assessment (CCA) on the medium. After the SIFS time slot, it directly sends an access request (RTS) frame to the AP to try to access the channel. Access is the initial access of a newly joined site;

4) After the AP detects the RTS frame, it replies an improved clear to send (eCTS) frame to the newly joined station to inform the corresponding station that it can use the channel in the next time slot;

5) The newly joined station exchanges data with the AP after accessing the channel, and maintains the next communication with the AP by exchanging data frames with random numbers;

6) The AP records the random number in the competition ranking table, and then determines the next station using the channel according to the competition ranking table, sends an eCTS frame, informs the station to use the channel in the next time slot, and confirms (ACK) the previous station's Random number, at the same time, AP updates the competition ranking table;

7) The corresponding station exchanges data with the AP, and maintains the next communication with the AP by exchanging data frames with random numbers until the transmission of all data is completed, thereby ending the communication and exiting the competition ranking table.

In the above-mentioned centrally controlled 802.11 wireless channel access method, in the step (1), the periodic broadcast of the beacon (Beacon) is specifically: the interval length of the AP's periodic broadcast of the beacon (Beacon) is 20~ 1000ms, the default value is 100ms.

In the above-mentioned 802.11 wireless channel access method controlled by the center, the improved clear to send (eCTS) frame in the step (4) is specifically: this frame is a newly defined frame of this method, and it acts on the connection between the AP and the STA. During the period, the eCTS frame is sent by the AP to the station to inform the next station that can use the channel to access, to confirm (CRT field) whether the random number sent by the previous station is correctly received by the AP, and to confirm (ACK) the previous station The transmitted data frame.

In the above-mentioned 802.11 wireless channel access method controlled by the center, in the step (2), it is judged whether there is a newly added station requesting access, and the following steps are followed successively: After the request to send (RTS) frame of the newly joined station, an improved clear to send (eCTS) frame is sent, and the newly joined station is given priority to carry out the next data frame exchange with a random number; If there is no incoming request, it will continue to exchange frames with the stations in the ranking list according to the order of the competition ranking list.

In the above-mentioned 802.11 wireless channel access method controlled by the center, in the step (3), the newly joined station sends an access request (RTS) frame to the AP to try to initially access the channel, and the following steps are followed in turn: if the station receives When the eCTS frame corresponding to itself sent by the AP is received, the access channel is successful, and the newly joined station exchanges data frames with random numbers for the first time with the AP; if the station does not receive the eCTS frame corresponding to itself, then access If the channel fails, the station selects a random backoff number from the interval [0, CW], and delays the corresponding number of beacons, and then requests access, and the station repeats step (3) until the access is completed.

In the above-mentioned 802.11 wireless channel access method controlled by the center, the interval [0, CW] specifically refers to: the initial value of the contention window parameter CW is set to 3, which is effectively doubled each time the access is unsuccessful until 15, (that is, 3, 7, 15) and keep this value unless it is reset, and the CW is reset after the new station successfully accesses.

In the above-mentioned 802.11 wireless channel access method controlled by the center, the data frame exchange with random numbers in the step (5) is specifically: when the station performs data exchange each time, in the data frame (or the last one in a TXOP) data frame) and send a random number within the contention window interval [0, CWmax] as the contention information for obtaining the right to use the channel next time.

In the above centrally controlled 802.11 wireless channel access method, the interval [0, CWmax] specifically means: the interval is a fixed interval, and the value of CWmax is 1023. The random number selected by the station preparing to access the medium from the contention window interval is only used to determine the position of the station in the competition list.

In the above-mentioned 802.11 wireless channel access method controlled by the center, in the step (6), the AP updates the contention arrangement list, and the specific method is: after the AP selects the next station using the channel, it uses the rest of the contention arrangement list Subtract the random number corresponding to the station from the random number to complete the update.

In the above-mentioned 802.11 wireless channel access method controlled by the center, after the step (7), if the AP does not receive the random number after the frame exchange of the stations ends, the information of the stations in the contention list is cleared.

Beneficial effects: the 802.11 wireless channel access method controlled by the center is adopted. During the process of STA accessing the channel, competition is guaranteed, and the waiting time slot for STA random backoff is eliminated, and different frame interval durations ( IFS) is uniformly replaced by Short Frame Interval (SIFS), which reduces the delay between frame transmissions and improves the efficiency of channel utilization, especially when multiple sites compete for channels at the same time, avoiding collisions and optimizing STA access. At the same time, the STA is exempt from the use of channel availability assessment (CCA), reducing energy consumption of the station.

Description of drawings

Fig. 1 is the frame structure diagram of the eCTS (improved access frame) of the central control type 802.11 wireless channel centralized access method of the present invention, wherein the CRT field is used to confirm the random number of the last station, and the RA field is the next The address of the station that is allowed to access the channel, the RA (ACK) field is used to confirm the last data frame;

Fig. 2 is a schematic diagram of the central control type 802.11 wireless channel centralized access method of the present invention in which stations compete for access rights. The new access STA1 first completes a data transmission and then sends a random backoff number, and the remaining STAs are ranked according to the competition in the AP. The channel access rights are obtained sequentially in the list order, and a random backoff number is sent after the data frame;

Fig. 3 is a schematic diagram of the use of TXOP in which stations compete for access rights in the central control type 802.11 wireless channel centralized access method of the present invention. STA1 has completed the transmission of required data in one TXOP, and STA2 has not completed the required data transmission in one TXOP. For data transmission, a random backoff number is sent after the last data frame in the TXOP;

4 is a schematic diagram of the block data exchange sequence of the central control type 802.11 wireless channel centralized access method of the present invention. STA1 performs a data burst without collision detection in the first TXOP. If the block transmission needs to span multiple TXOPs, Then the STA sends a random backoff number after the last data frame;

Fig. 5 is a flow chart of the central control type 802.11 wireless channel centralized access method of the present invention.

Detailed ways

In order to understand the technical content of the present invention more clearly, the following examples are given in detail.

Please refer to FIG. 1 and FIG. 4 , which are a flow chart of a frame exchange sequence and implementation manner of a centrally controlled 802.11 wireless network access method provided by the present invention.

Assumed application example: an 802.11-based wireless network, all STAs have been associated with APs, and all STAs are in the same BSS set, the network has just been initialized, and the contention list of APs is empty. Its specific implementation is described as follows:

1) AP checks whether the competition ranking list is empty;

2) The AP periodically (100ms) sends beacons, then waits for the DIFS period, and listens to whether there is an RTS frame sent from the STA to be accessed within this period;

3) A station (STA1) is about to initiate communication, STA1 does not perform CCA detection on the channel, but directly sends an RTS frame to the AP:

4) After the AP receives the RTS frame sent from STA1, after the SIFS period, the AP sends an eCTS (STA1) frame to allow STA1 to perform frame exchange;

5) After STA1 receives the eCTS frame, it knows that it has obtained the channel access right, waits for the SIFS period, and starts frame exchange. After the first (TXOP) data frame exchange is completed, there is still data to be sent, so in the last data frame Send a random backoff number (eg, 317) after the frame;

6) The AP receives the data frame and the number of backoffs from STA1, and establishes a competition ranking table;

7) Since only STA1 is currently in the AP's current competition list, the AP sends an eCTS (STA1) frame after an interval of SIFS to confirm the last data frame and the random backoff number of STA1, and inform STA1 to allow the next channel access;

8) The AP ensures that the beacon is sent periodically while communicating with STA1;

9) After a certain period of time, STA2, STA3, ..., STAn (n=2, 3, ..., 1024) also start data exchange respectively;

10) Stations such as STA2 use the initial access method to access the channel after the AP broadcasts the beacon, and send a random backoff number to the AP after completing the first data exchange with the AP, and join the AP's competition list;

11) The AP selects the STA with the smallest number of back-offs for the next channel access according to the competition arrangement table, and updates the competition arrangement table after sending the eCTS frame until STA1, STA2, ..., STAn(n = 1, 2, ..., 1024) all data transmission is completed, the contention list of the AP is empty, and step (1) is repeated.

Adopting a centrally controlled 802.11 wireless network access method of the invention, the wireless STA no longer needs to perform CCA detection on the medium before accessing the channel, but only needs to listen to the eCTS frame to determine whether to obtain channel access Right, the waiting DIFS slot after the medium is idle is also reduced to SIFS. In addition, this method changes the nature of the random backoff number, which not only removes the physical time waiting, but also retains the competition mechanism. At the same time, due to the establishment of the competition arrangement table, collisions are completely avoided.

In this specification, the invention has been described with reference to specific embodiments thereof. However, it is obvious that various modifications and changes can be made without departing from the spirit and scope of the invention. Accordingly, the specification and drawings are to be regarded as illustrative rather than restrictive.

Claims (2)

1. the method that 802.11 radio network information channels that center controls access, 802.11 described wireless networks comprise wireless access point AP and some wireless site STA, and described cut-in method comprises the following steps:

1) AP periodically sends beacon frame, then waits for the distributed frame spacing duration DIFS period, and intercepts the access request RTS frame whether having and send from STA to be accessed in section at this moment;

2) new site STA1 prepares initiating communication, and STA1 does not carry out channel available assessments CCA to channel and detects, but sends RTS frame to AP after waiting for the short frame pitch duration SIFS period after beacon frame;

3) after AP receives the RTS frame sent from STA1, preferentially give the chance of a new access website data frames exchange, through the SIFS period, AP sends modified model and allows to send eCTS frame, allows STA1 to carry out data frames exchange;

4), after STA1 receives eCTS frame, learn and oneself obtain channel access power, after waiting for the SIFS period, start data frames exchange, after completing first transmission opportunity TXOP data frames exchange, if still have outgoing data, then in the end carry random back number in a Frame;

5) AP receives Frame from STA1 and random back number, is joined by STA1 in competition permutation table;

6) AP selects to have in competition permutation table the exchanges data that the minimum STA of random back number carries out next time, after the interval SIFS period, send eCTS frame, a upper Frame carrying random back number is confirmed, and inform that selected STA carries out data frames exchange, the SIFS period is waited for after being received eCTS by the STA selected, complete a TXOP data frames exchange, if still have outgoing data, in the end carry random back number in a Frame, AP upgrades competition permutation table after receiving random back number, send until all STA in competition permutation table all complete data, the competition permutation table of AP is empty, repeat step 1),

7) after some periods, STA2, STA3, ..., STAn performs step 1 respectively as new site according to the mode of STA1)-5) realize the exchange of first run Frame, after this when not having new site to add, according to step 6) and mode carry out the exchange of subsequent data frame, wherein, n represents the STA number in network.

2. the method that 802.11 radio network information channels that a kind of center according to claim 1 controls access, it is characterized in that, STA is only when accessing channel first, send RTS and carry out access channel request, STA only, after receiving the eCTS frame of informing and oneself allowing to access channel, just sends Frame, if fail to receive corresponding eCTS frame, then adopt the mode of rollback, wait for that next access slot sends RTS frame again and asks; STA, except obtaining in the period except channel access power, does not carry out channel competition.