CN106572499A - Chanel access method based on decimal backoff - Google Patents

Abstract

The present invention provides a channel access method based on decimal backoff, which realizes a more refined backoff mode by accelerating the backoff speed of nodes that contribute greatly to the area throughput, thereby further refining and decomposing the relative Priority, to achieve better conflict avoidance and more efficient channel resource utilization; easy to implement, compatible with IEEE 802.11 standard protocol, and can be applied to single-channel and multi-channel environments; in addition, the present invention It can be implemented in the firmware of the network card, and can also be implemented in the driver program; the invention estimates the interference status of the receiving end by the sending end, making the backoff more accurate, thereby greatly improving the area throughput.

Description

A Channel Access Method Based on Decimal Backoff

technical field

The present invention relates to the technical field of communication, in particular to a backoff mechanism.

Background technique

In order to reduce collisions in wireless networks, the IEEE 802.11 standard adopts a mechanism called Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). In the CSMA/CA mechanism, a node judges whether the channel is idle by performing carrier sense. When the channel is idle, the node starts to perform the binary exponential backoff (Binary Exponential Backoff) process. If the channel becomes busy during the backoff process, it needs to wait for a random period of time until the channel becomes idle again before continuing to backoff until the backoff Data can only be sent after the end to reduce the collision probability of data transmission. Among them, the binary exponential backoff algorithm used in the CSMA/CA mechanism is the key to reducing network conflicts. The so-called binary exponential backoff means that when a node encounters a conflict, it does not wait for the channel to become idle to send data immediately, but delays a random time (or backoff) before resending data. After each collision, the average waiting time of nodes will also be doubled. That is: each node maintains a backoff counter, and the value of this backoff counter is randomly selected from [0, CW], CW represents the value of the contention window, and its initial value is the minimum contention window CW _min , and CW=2 ^m CW _min , when a conflict occurs, the backoff order m increases by one. Whenever it is detected that the channel is idle for one slot, the value of the backoff counter is decremented by one. When the backoff counter is reduced to 0, the node can send data. However, in the current binary backoff process, nodes perceive the channel quality at a coarser granularity. That is to say, the result of the node's perception of the channel only includes two situations: the channel is "busy" or the channel is "idle". If the channel is "busy", that is, the interference level of the detected channel exceeds the CCA (Clear Channel Assessment, channel idle assessment) threshold, the backoff process will be suspended; and if the channel is "idle", that is, the interference of the channel is detected If the level is lower than the CCA threshold, expressed as CCA _th , its backoff process will advance at the same pace, that is, every time the channel is idle for a time slot, the backoff counter value of the node will be decremented by 1.

In the next generation of wireless local area networks (Wireless Local Area Networks, WLAN), it will face high-density deployment scenarios and explosive growth of business requirements, so how to greatly improve the regional throughput (that is, the throughput per unit area) has become a Difficult problems to be solved. If the traditional binary backoff approach is used in the next-generation WLAN, if some key parameters (such as the CCA threshold) are set unreasonably, it will be difficult to adapt to the actual situation of the network and make full use of channel resources, thereby inhibiting the area Throughput performance. For example, if the CCA threshold is set too low, it will lead to too many nodes that think the channel is "busy" at the same time, thus restricting the possibility of parallel transmission and reducing the utilization of channel resources; if the CCA threshold is set too high , it will lead to too many nodes that think the channel is "idle" at the same time, thus increasing the probability of collision.

Contents of the invention

In order to overcome the deficiencies of the prior art, the present invention provides a decimal back-off mechanism, which can increase the access priority of links with high data rates and small interference ranges, that is, increase the back-off speed of the links, and at the same time reduce the The access priority of the link with a large interference range is to reduce the back-off speed of the link, thereby improving the area throughput performance of the network.

The technical solution adopted by the present invention to solve its technical problems comprises the following steps:

Step 1, when the source node S sends data to the destination node D, the source node S queries the CCA range maintained by itself at this time, that is, [-82dBm, CCA _th ], and CCA _th refers to the CCA threshold value, that is, the CCA range Upper limit value, and CCA _th >-82dBm, after that, go to step 2;

Step 2. In each time slot, the source node S detects the signal energy I on the channel in real time. If the condition I≥CCA _th is satisfied, the backoff process of the source node S is suspended and continues to detect the signal energy I on the channel; Otherwise, go to step 3;

Step 3, the source node S estimates the SINR _e , and obtains the corresponding data transmission rate R according to the mapping of the value of SINR _e in the segmented curve Rate-SINR of the rate and SINR, and proceeds to step 4;

Step 4, the source node S calculates the backoff speed ω _BK in this time slot according to the data transmission rate R, and turns to step 5;

Step 5: When the time slot ends, the source node S subtracts ω _BK from its current backoff counter value, and then judges whether the backoff counter value after subtracting ω _BK is less than or equal to 0, and if so, the source node S accesses channel and transmit data; otherwise, go to step 2 to continue the backoff process.

The CCA _th is set in advance, or obtained by feedback from the destination node D during data transmission with the source node S in the last time slot, Wherein, Pr is the receiving power of the request to send frame RTS sent by the source node S received by the destination node D, and SINR _th represents the signal-to-noise ratio corresponding to the maximum modulation and coding method that can be adopted.

In the step 3, SINR _e =Pr-I; if the current time slot is the first transmission time slot, then ω _BK =1, and then go directly to step 5.

In step 4, the source node S calculates the equivalent data rate Among them, A represents the interference area of the link, that is, the union of the interference area area of the sending node S and the interference area area of the receiving node D; according to the formula The source node S calculates the back-off speed ω _BK in this time slot, where R ^* represents the area throughput, and the corresponding back-off speed is

The beneficial effects of the present invention are: by accelerating the back-off speed of nodes that contribute more to the regional throughput, a more refined back-off mode is realized, thereby further refining and decomposing the relative priority of users when they compete for channels, and achieving better Conflict avoidance and more efficient channel resource utilization; simple implementation, compatible with IEEE 802.11 standard protocol, and can be applied to single-channel and multi-channel environments; in addition, the present invention can be implemented in the firmware of the network card , and can also be implemented in the driver program; the invention makes the backoff more accurate by predicting the interference situation of the receiving end by the sending end, thereby greatly improving the area throughput.

Description of drawings

Fig. 1 is the diagram of embodiment one of the present invention;

Fig. 2 is the illustration of the second embodiment of the present invention;

FIG. 3 is a diagram of Embodiment 3 of the present invention;

FIG. 4 is a diagram of Embodiment 4 of the present invention;

FIG. 5 is a diagram of Embodiment 5 of the present invention;

Figure 6 is a diagram of Embodiment 6 and Embodiment 7 of the present invention;

FIG. 7 is a diagram of Embodiment 8 of the present invention;

FIG. 8 is a diagram of Embodiment 9 of the present invention;

Fig. 9 is a schematic diagram of simulation results of the present invention;

In the figure, AP-access point Access Point, RTS-request access Request-To-Send, CTS-permit to send Clear-To-Send, ACK-confirmation Acknowledgment, SIFS-Short Interframe Space, CH-channel Channel, BSS-Basic Service Set Basic Service Set.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and embodiments, and the present invention includes but not limited to the following embodiments.

In this mechanism, the shortcomings of the coarse-grained perception of channel quality in the traditional binary backoff mechanism are overcome, and the backoff process is organically combined with the actual situation of the network, thereby realizing more fine-grained backoff. In addition, the invention is easy to implement and compatible with IEEE 802.11 standard protocol. Simulation results show that this patent can greatly improve the regional throughput of the network.

The present invention is a flexible back-off mechanism applied in wireless networks, aiming to overcome the disadvantages of coarse-grained perception of channel quality in the traditional binary back-off mechanism, so that the back-off process can be organically combined with the actual situation of the network, thereby achieving a more refined backoff and improve the regional throughput of the network. The implementation process of this patent will be introduced in detail below in combination with eight embodiments.

Detailed steps of the present invention are as follows:

Step 1: When the source node S sends data to the destination node D, S queries the CCA range maintained by itself at this time, that is, [-82dBm, CCA _th ], and CCA _th refers to the CCA threshold value, which is the upper limit of the CCA range value, and CCA _th >-82dBm, after that, go to step 2;

Step 2: In each time slot, S detects the signal energy on the channel in real time, denoted as I, if the condition I≥CCA _th is satisfied, then the backoff process of S is suspended, and returns to step 2 to continue listening; otherwise, That is, if the condition I<CCA _th is satisfied, go to step 3;

Step 3: S estimates the SINR (Signal To Interference with Noise Ratio, SINR), which is recorded as SINR _e , and then S obtains the corresponding data transmission rate R according to the SINR _e table lookup, and then turns to step 4;

Step 4: S calculates the back-off speed ω _BK in this time slot according to the data transmission rate R, and then proceeds to step 5;

Step 5: When the current time slot ends, S subtracts ω _BK from its current backoff counter value, and then judges whether the backoff counter value after subtracting ω _BK is less than or equal to 0. If so, S accesses the channel and transmits data ; Otherwise, go to step 2 to continue the backoff process.

Embodiment one

The embodiment side focuses on describing the fractional backoff process in a single channel environment. As shown in Figure 1(a), the cell includes a station (Station, STA) 'S', and the distance between S and the access point (Access Point, AP) 'D' is d. In Figure 1(b), S and D perform a fractional backoff process on the channel (CH). After the backoff succeeds, S transmits data to D on the CH. The following will illustrate the specific operation process of the first embodiment.

Step 1: When the source node S sends data to the destination node D, S queries the CCA range it maintains at this time;

Step 1.1: S queries the CCA threshold value CCA _th maintained by itself at this time. The CCA _th can be unique in the whole network, or it can be obtained by D's feedback during the last data transmission with S (when D receives After RTS, record the received power of the RTS frame as Pr, then Wherein, SINR _th represents the threshold value of the signal-to-noise ratio, that is, the signal-to-noise ratio corresponding to the maximum modulation and coding mode that can be adopted, and its value can be given in advance. Then the value of CCA _th maintained by each sending node may be different. After that, go to step 1.2;

Step 1.2: S sets the queried CCA _th as the upper limit of its own CCA interval, and then obtains its own CCA interval. For example, CCA _th =-62dBm, then the CCA interval of S is [-82dBm, -62dBm]. After that, go to step 2.

Step 2: In each time slot, S detects the signal energy on the channel in real time, and records it as I. If the condition I≥CCA _th is satisfied, the backoff process of S is suspended; otherwise, go to step 3. Specific steps are as follows:

Step 2.1: S detects the signal energy (i.e. interference intensity) on the channel in each time slot, denoted as I. After that, go to step 2.2;

Step 2.2: If the condition I≥CCA _th is satisfied, the backoff process of S is suspended until the channel becomes idle (that is, the condition I<CCA _th is satisfied) and the DIFS (Distributed Inter-frame Spacing, distributed inter-frame gap) duration is maintained After that, S turns to step 1 and restarts the backoff process. After that, go to step 3;

Step 3: S estimates the signal-to-interference and noise ratio SINR _e , and obtains the corresponding data transmission rate R according to the SINR _e , and then proceeds to step 4. Specific steps are as follows:

Step 3.1: S uses the formula SINR _e (dB)=Pr-I to estimate the signal-to-interference and noise ratio SINR _e , where Pr is the request sent by D received by S during the transmission process between S and D last time (Request- The received power value of the to-send (RTS) frame, S can read the Pr value carried by the Clear-to-send (CTS) frame replied from D. If this transmission is the first transmission, and S has not yet obtained the value of Pr, then the traditional binary exponential backoff method is directly adopted for this backoff (that is, ω _BK = 1), and then go to step 5; otherwise, go to step 3.2;

Step 3.2: According to the segmented curve of Rate-SINR, S obtains the corresponding data transmission rate R by mapping the value of SINR _e , and then turns to step 4;

Step 4: S calculates the back-off speed ω _BK in this time slot, and then goes to step 5. Specific steps are as follows:

Step 4.1: According to the formula S calculates the equivalent data rate _Re . Among them, A represents the interference area of the link, that is, the union of the interference area (area) of the sending node S and the interference area (area) of the receiving node D, To characterize the link's impact on area throughput, The larger the value, the greater the contribution of the link to the regional throughput of the network. In this example let To characterize the equivalent data rate _Re , where d represents the distance between S and D. After that, go to step 4.2;

Step 4.2: According to the formula S calculates the back-off speed ω _BK in this time slot, that is, the greater the link's contribution to the regional throughput of the network, the greater its back-off speed ω _BK . Among them, R ^* represents a value of regional throughput, and the corresponding backoff speed is For example, in the IEEE 802.11a standard, the maximum transmission rate is 54Mbps, and when the positions of S and D coincide, the union of the two interference areas is the smallest, which is recorded as A ^* , then the area throughput obtained at this time The amount is the largest, denoted as Corresponding The possible value is 2, and then, S can calculate the value of ω _BK . For the traditional binary exponential backoff algorithm, ω _BK =1. After that, go to step 5;

Step 5: When the time slot ends, S subtracts ω _BK from its current backoff counter value, and S then judges whether the backoff counter value minus ω _BK is less than or equal to 0. If so, S accesses the channel and transmits data ; Otherwise, go to step 2 to continue the backoff process. Specific steps are as follows:

Step 5.1: Assuming that the current backoff counter of S is cw, then when the current time slot ends, S subtracts ω _BK from its current backoff counter, that is, cw=cw-ω _BK . After that, go to step 5.2;

Step 5.2: S judges whether its current backoff count value CW is less than or equal to 0. If the condition cw≤0 is satisfied, then S accesses the channel and transmits data in a four-way handshake (ie, RTS-CTS-DATA-ACK). In this process, D records the received power of the RTS frame sent by S and feeds it back to S through the CTS frame, and then S records the received power Pr carried in the CTS frame sent by D. If cw>0, then S goes to step 2 to continue the decimal backoff process.

Embodiment two

The second embodiment focuses on describing the fractional backoff process after the backoff condition is introduced in a single channel environment. In this embodiment, a backoff condition is introduced to limit the access of nodes that contribute too little to the throughput performance of the network area, thereby alleviating network conflicts and improving the throughput performance of the network area. As shown in Figure 2, the cell includes two stations, 'S' and 'E', where S is closer to the AP, and E is farther away from the AP. The following will illustrate the specific operation process of the second embodiment.

Step 1-Step 4: Same as Step 1-Step 4 in Embodiment 1, through Steps 1-4, S and E respectively calculate their respective retreat speeds, expressed as ω _BK and ω' _BK , after that, turn to Step 5 ;

Step 5: At the end of their respective time slots, S and E judge whether they meet the backoff condition. If the backoff condition is not satisfied, S and E will not backoff in this time slot; otherwise, subtract ω _BK from their current backoff counter value, and then, S and E judge whether their current backoff counter value is less than or equal to 0 , if yes, then access the channel and transmit data; otherwise, go to step 2 to continue the backoff process. Specific steps are as follows:

Step 5.1: Assumptions is the back-off threshold, take When the time slot ends, S judges whether the backoff condition is satisfied If the back-off condition is satisfied, the back-off process is performed normally, otherwise, S does not perform back-off in this time slot, that is, ω _BK =0. After that, go to step 5.2; at the same time, E also performs the same operation. In this embodiment, it is assumed that the backoff values calculated by S and E in step 4 are ω _BK =1.2, ω' _BK =0.6, respectively, because and Therefore, S normally backs off in this time slot and E cannot back off in this time slot, that is, ω' _BK =0.

Step 5.2: Assume that the current backoff counter value of S is cw, and the current backoff counter value of E is cw'. Then when this time slot ends, S subtracts ω _BK from its current backoff counter, that is, cw=cw-ω _BK , and at the same time, E also performs the same operation, and E subtracts ω' from its current backoff counter _BK , that is, cw'=cw'-ω' _BK , so the value of cw' remains unchanged. After that, go to step 5.3;

Step 5.3: S judges whether the current value of cw is less than or equal to 0. If cw≤0, S accesses the channel and transmits data. In this process, D records the received power of the RTS sent by S and carries it in the CTS frame and feeds it back to S, and then S records the received power Pr carried in the CTS frame sent by D. If cw>0, then S goes to step 2 to continue the decimal backoff process. Similarly, E also performs the same operation as S.

Embodiment Three

Embodiment 3 focuses on describing that in a single channel environment, the AP adjusts the backoff weight α in the fractional backoff process according to the number of STAs in the current cell, where 0<α≦1. In this embodiment, the AP dynamically adjusts back-off weights α of all STAs according to changes in the number of STAs in the network, thereby improving network performance. If the number of STAs in the cell is small, the AP can appropriately increase the value of α, which can speed up the backoff speed of STAs, improve resource utilization, and improve the area throughput performance. If there are too many STAs in the cell, the AP can appropriately reduce the value of α to make the backoff speed of all STAs more precise, thereby alleviating network conflicts. In Figure 3(a), there are 2 STAs in the cell, named A and B; while in Figure 3(b), there are 4 STAs in the cell, named A, B, C, and E. The following will illustrate the specific operation process of the third embodiment.

Step 1: When the source node S sends data to the destination node D, S queries the CCA range it maintains at this time;

Step 1.1: The AP adjusts the back-off weight α of all STAs according to the number of STAs in the current cell. In Figure 3(a), there are 2 STAs in the cell, and the AP appropriately increases the value of α to speed up the backoff speed of the STAs, thereby more fully utilizing channel resources. For example, take α=1.0; and in Figure 3(b), there are 4 STAs in the cell, then the AP appropriately reduces the value of α to reduce the backoff speed of STAs, thereby alleviating network conflicts. For example, take α=0.5. After that, go to step 5.2;

Step 1.2: The AP preempts the right to use the channel. For example, after the AP waits for the channel to be idle for a PCF Inter-Frame Space (PIFS), it sends a Beacon frame and informs all STAs in the cell of the adjusted backoff weight α. By performing steps 1.1 to 1.2, the AP can adjust the back-off weight α of all STAs in the cell according to the number of STAs in the cell. After that, go to step 1.3;

Step 1.3: S queries the CCA threshold value CCA _th maintained by itself at this time. The CCA _th can be unique in the whole network, or can be obtained by feedback from D in the last data transmission process with S. Then each sending The CCA _th values maintained by nodes may be different. After that, go to step 1.4;

Step 1.4: S sets the queried CCA _th as the upper limit of its own CCA interval, and then obtains its own CCA interval. For example, CCA _th =-62dBm, then the CCA interval of S is [-82dBm, -62dBm]. After that, go to step 2.

Step 2-Step 4: Same as Step 2-Step 4 in Embodiment 1. Through steps 2 to 4, all STAs in the cell calculate the backoff speed in their respective time slots, which are respectively i=A, B, C, E, after that, turn to step 5;

Step 5: All STAs in the cell adjust their backoff values according to the value of α, and judge whether their current backoff counts are less than or equal to 0. If yes, access the channel and transmit data; otherwise, go to step 2 to continue the backoff process. Specific steps are as follows:

Step 5.1: All STAs in the cell adjust their backoff values. suppose is the current backoff value of the STA labeled i in the cell (represented as STA _i , i=A, B, C, E), then the adjusted backoff value is After that, go to step 5.2;

Step 5.2: Assume that the current backoff counter value of STA _i is cw _i , then when the current time slot ends, STA _i subtracts its current backoff counter from which is After that, go to step 6.3;

Step 5.3: STA _i judges whether its current backoff count value cw _i is less than or equal to 0. If cw _i ≤0 is satisfied, STA _i accesses the channel and transmits data. In this process, the AP records the received power of the RTS sent by S and feeds it back to STA _i through the CTS frame, and then STA _i records the received power Pr carried in the CTS frame sent by the AP. If cw _i >0, STA _i goes to step 1 and continues the decimal backoff process.

Embodiment four

Embodiment 4 focuses on describing that in a single-channel environment, the AP adjusts the CCA threshold value CCA _th in consideration of the interference received by the STAs in the current cell. In this implementation, the AP adjusts the CCA _th to increase the channel access priority of those STAs that contribute more to the area throughput (because the greater the interference on the link, the lower the data rate, the lower the network area The contribution of throughput is smaller), thereby improving the throughput performance of the network area. As shown in Figure 4, there are four STAs in the cell, namely A, B, C and E. Among them, A and B are located in the OBSS area at the edge of the cell, and the interference intensity I received is relatively large, while the interference intensity I received by C and E is relatively small. The following will illustrate the specific operation process of the fourth embodiment.

Step 1: The AP adjusts the CCA threshold value CCA _th according to the interference situation of the STAs in the current cell. Furthermore, the STAs in the cell obtain their own CCA range [-82dBm, CCA _th ] according to the CCA _th . After that, go to step 2. Specific steps are as follows:

Step 1.1: AP learns the interference situation of STAs in the current cell, denoted as I _i , i=A, B, C, E, in order to obtain I _i , the AP can communicate with STA _i (representing the STA labeled i in the cell) During one transmission, record the interference value carried in the RTS frame sent by STA _i , for example, I _A =-65dBm, I _B =-63dBm, I _C =-80dBm, I _E =-85dBm, and at this time The CCA threshold in the cell is CCA _th =-62dBm, and then, the AP adjusts the CCA thresholds of all STAs in the cell according to the interference value of each STA. For example, reduce the CCA threshold CCA _th from -62dBm to -70dBm. After that, go to step 1.2;

Step 1.2: The AP preempts the right to use the channel, for example, the AP waits for the channel to be idle for a PIFS period before sending a beacon frame, and informs all STAs in the cell of the adjusted CCA _th . After that, go to step 1.3;

Step 1.3: STA _i sets its own CCA threshold interval according to the adjusted CCA _th , namely [-82dBm, -70dBm]. After that, go to step 2;

Step 2: In each time slot, STA _i detects the signal energy on the channel, denoted as I _i . If the condition I _i ≥ CCA _th is satisfied, the backoff process of STA _i is suspended; otherwise, go to step 3. Specific steps are as follows:

Step 2.1: STA _i detects the signal energy on the channel in each time slot, denoted as I _i . After that, go to step 2.2;

Step 2.2: If the condition I _i ≥ CCA _th is satisfied in this time slot, the backoff process of STA _i is suspended until the channel becomes idle (that is, the condition I _i <CCA _th is met) and after the DIFS duration is maintained, STA _i turns to Enter step 1 to restart the back-off process; otherwise, go to step 3; therefore, in this embodiment, only site C and site E in the cell can continue to perform the fractional back-off process.

Step 3-Step 5: Same as Step 3-Step 5 in Embodiment 1. Wherein, in step 5.2, STA _i carries the measured interference value I _i through the RTS frame and sends it to D, and then D records the interference value I _i carried in the RTS frame.

Embodiment five

Embodiment 5 focuses on describing that in a single channel environment, the sending node (such as STA) adjusts its own CCA threshold value CCA _th according to the feedback from the destination node (such as AP). In this implementation, the AP feeds back the CCA _th to increase the channel access priority of those STAs that contribute more to the area throughput, thereby improving the network area throughput performance. As shown in Figure 5, there are two STAs in the cell, namely A and B. Among them, A is located in the OBSS area at the edge of the cell, and the interference intensity I received is relatively large, while B is near the AP, and the interference intensity I received is relatively small. The following will illustrate the specific operation process of the fifth embodiment.

Steps 1 to 4: Same as Steps 1 to 4 in Embodiment 1, wherein, in Step 1, stations A and B query the CCA threshold (that is, CCA _th ) fed back by the AP in the CTS last time. The maintained CCA range, that is, [-82dBm, CCA _th ], if the CCA _th value fed back by the AP has not been received before (such as the first back-off process), a default CCA _th value of the entire network, such as -62dBm, will be used directly.

Step 5: When the time slot ends, stations A and B subtract their current backoff counter values from their respective backoff values (such as with ), and then judge whether the current backoff count value of oneself is less than or equal to 0, if so, then station A or B accesses the channel and transmits data, and AP feeds back a suitable CCA _th in the process; otherwise, go to step 2 and continue backoff process. Specific steps are as follows:

Step 5.1: Assume that the values of the current backoff counters of stations A and B are cw _A and cw _B respectively. When the current time slot ends, stations A and B will subtract the backoff value from their current backoff counters (such as with ), then there are After that, go to step 5.2;

Step 5.2: Stations A and B determine whether their current backoff counts are less than or equal to 0. For example, station A completes the backoff first, that is, satisfies the condition cw _A ≤ 0, then station A accesses the channel and sends an RTS frame. After that, go to step 5.3;

Step 5.3: After AP receives the RTS frame sent by station A, it records the power of the received RTS as Pr, and then, D calculates CCA _th according to the formula CCA _th =Pr-Margin, where Margin represents an AP's expected or maximum Excellent SINR value. After that, go to step 5.4;

Step 5.4: AP calculates CCA _th , puts it into CTS frame and sends it out. After that, go to step 5.5;

Step 5.5: Station A obtains the CCA _th value fed back by the AP according to the received CTS frame, and sets its own CCA range to [-82dBm, CCA _th ] according to the value of CCA _th . After that, go to step 5.6;

Step 5.6: Station A sends DATA to AP, and AP replies ACK after receiving DATA and waiting for SIFS. (Note: AP can also calculate CCA _th according to the formula CCA _th = Pr-Margin after receiving DATA and feed back the value of CCA _th through ACK.)

Embodiment six

Embodiment 6 focuses on the description that in a single-channel environment, the AP adjusts the backoff weight β of each or each group of STAs according to the interference received by all STAs in the current cell, 0<β≤1, so that STAs in the guaranteed cell Access fairness between. As shown in Figure 6, there are three STAs in the cell, namely A, B and C. Among them, A is located in the OBSS area at the edge of the cell, and the AP hopes to increase the access opportunity of A at the edge. The following will illustrate the specific operation process of the sixth embodiment.

Step 1: When the source node S sends data to the destination node D, S queries the CCA range it maintains at this time;

Step 1.1: The AP learns the interference situation of STAs in the current cell, denoted as I _i , i=A, B, C, E. In order to obtain I _i , the AP may record the interference value carried in the RTS frame sent by the STA _{i during the last transmission process with the STA i .} For example, I _A =-65dBm, I _B =-63dBm, I _C =-80dBm, I _E =-85dBm. After that, go to step 1.2;

Step 1.2: According to the interference value I _i suffered by STA _i , the AP appropriately adjusts the access weight of the station that suffers from greater interference, such as increasing the access weight β _A of the cell edge station A, while appropriately reducing the interference The access weights of smaller sites, such as reducing the access weights β _B and β _C of sites B and C, so as to increase the access priority of edge site A. For example, after AP adjustment, β _A =0.8, β _B =β _C =0.4. After that, go to step 1.3;

Step 1.3: AP preempts the right to use the channel, for example, the AP waits for the channel to be idle for PIFS before sending a beacon frame, and informs the adjusted backoff weight β _i (including β _A , β _B and β _C ) of STA _i in the cell All STAs. Afterwards, turn to step 2; by performing steps 1.1 to 1.3, the AP can adjust the access weight β of each or each group of STAs according to the interference of all STAs in the cell, 0<β≤1. After that, go to step 1.4.

Step 1.4: S queries the CCA threshold value CCA _th maintained by itself at this time. The CCA _th can be unique in the whole network, or can be obtained by feedback from D in the last data transmission process with S. Then each sending The CCA _th values maintained by nodes may be different. After that, go to step 1.2;

Step 1.5: S sets the queried CCA _th as the upper limit of its own CCA interval, and then obtains its own CCA interval. For example, CCA _th =-62dBm, then the CCA interval of S is [-82dBm, -62dBm]. After that, go to step 2.

Step 2-Step 4: Same as Step 2-Step 4 in Embodiment 1, through Step 2-Step 4, STA _i respectively calculates the back-off speed in each time slot i=A, B, C, after that, turn to step 5;

Step 5: STA _i adjusts its own backoff value according to the value of β _i and performs decimal backoff. Then judge whether the current backoff count value is less than or equal to 0, if so, access the channel and transmit data; otherwise, go to step 2 to continue the backoff process. Specific steps are as follows:

Step 5.1: STA _i adjusts its backoff value. suppose is the current backoff value of STA _i , then the adjusted backoff value is After that, go to step 5.2;

Step 5.2 to Step 5.3: Same as Step 5.2 to Step 5.3 in Embodiment 3.

Embodiment seven

Embodiment 7 focuses on the description that in a single-channel environment, the AP adjusts the back-off weights α and β of the STAs while considering the number and distribution of STAs in the current cell, so as to ensure the throughput performance in the cell under the premise of improving the throughput performance of the network area. Access fairness among STAs. As shown in Figure 6, there are three STAs in the cell, namely A, B and C. Wherein, A is located in the OBSS area at the edge of the cell. The AP adjusts the backoff weight α of all STAs according to the number of STAs in the current cell. For example, in order to improve the utilization rate of channel resources, the AP may select a larger α, for example, α=0.9. At the same time, in order to ensure the access fairness of the cell edge site A, the AP appropriately increases the access weight β A of the edge site _A , while reducing the access weights β _B and β _C of B and C. For example, the adjusted values of β are: β _A =0.8, β _B =β _C =0.4. The following will illustrate the specific operation process of the seventh embodiment.

Step 1: When the source node S sends data to the destination node D, S queries the CCA range it maintains at this time;

Step 1.1: The AP adjusts the back-off weight α of all STAs according to the number of STAs in the current cell. For example, there are only 3 STAs in the cell, and in order to improve channel resource utilization, the AP may select a larger α, for example, α=0.9. At the same time, in order to ensure the access fairness of the cell edge site A, the AP appropriately increases the access weight β A of the edge site _A , while reducing the access weights β _B and β _C of B and C. For example, the adjusted values of β are: β _A =0.8, β _B =β _C =0.4. After that, go to step 1.2;

Step 1.2: The AP preempts the right to use the channel, for example, the AP sends a beacon frame after waiting for the channel to be idle for PIFS, and informs the adjusted backoff weights α and β (including: β _A , β _B and β _C ) of all stations All STAs in the cell. Afterwards, turn to step 1.3; by executing steps 1.1 to 1.2, the AP completes the adjustment of the STA's backoff weights α and β. After that, go to step 1.3;

Step 1.3 to Step 1.4: Same as Step 1.3 to Step 1.4 in Embodiment 3. After that, go to step 2;

Step 2 to Step 4: Same as Step 2 to Step 4 in Embodiment 1, through Step 2 to Step 4, STA _i in the cell respectively calculates the backoff speed in each time slot i=A, B, C, after that, turn to step 5;

Step 5: STA _i adjusts its own backoff value according to α and β _i and performs decimal backoff. Then judge whether the current backoff count value is less than or equal to 0, if so, access the channel and transmit data; otherwise, go to step 1 to continue the backoff process. Specific steps are as follows:

Step 5.1: STA _i adjusts its backoff value. suppose is the current backoff value of STA _i , then the adjusted backoff value is After that, go to step 5.2;

Step 5.2 to Step 5.3: Same as Step 5.2 to Step 5.3 in Embodiment 3.

Embodiment eight

Embodiment 8 focuses on describing the fractional backoff process in a multi-channel environment. As shown in Fig. 7(a), the cell includes a station 'S', and the distance between S and the AP (ie 'D') is d. In addition, there are K channels in the network, denoted as CH _k , 1≤k≤K. Among them, CH ₁ is the main channel, and other channels are slave channels. S and D perform fractional backoff through the main channel (CH ₁ ), and perform data transmission through K channels after successful backoff, as shown in Figure 7(b). The following will illustrate the specific operation process of the seventh embodiment.

Step 1: Same as Step 1 in Example 1. After that, go to step 2.

Step 2: In each time slot, S detects the signal energy on each channel, which is denoted as 1≤k≤K. If the conditions are met Then the backoff process of S is suspended; otherwise, go to step 3. Specific steps are as follows:

Step 2.1: S detects the signal energy on each channel in each time slot That is, the intensity of interference suffered by S and D during data transmission on the channel CH _k . After that, go to step 2.2;

Step 2.2: If the condition is met in the current time slot Then the backoff process of S is suspended until the channel becomes idle (that is, the condition ) and maintain the DIFS duration, S turns to step 1 and restarts the backoff process. Otherwise, go to step 3;

Step 3: S estimates the Signal To Interference with Noise Ratio (SINR) of the channel CH _k , and records it as SINR _e,k , and then S obtains the corresponding data transmission rate R _k on each channel. After that, go to step 4. Specific steps are as follows:

Step 3.1: S through the formula to estimate the SINR _{e,k on the channel CH k .} Wherein, Pr is the received power of the Request-to-send (RTS) frame sent by S when D received the last transmission process between S and D. The value of Pr can be obtained by reading the Clear-to-send (CTS) frame replied by D. If this transmission is the first transmission, and S has not yet obtained the value of Pr, then the traditional binary exponential backoff method is directly adopted for this backoff (that is, ω _BK = 1), and then go to step 5; otherwise, go to step 3.2;

Step 3.2: S maps the values of SINR _e,k according to the Rate-SINR segmentation curve to obtain the corresponding data transmission rate R _k . After that, go to step 4;

Step 4: S calculates the back-off speed ω _BK in this time slot. After that, go to step 5. Specific steps are as follows:

Step 4.1: S according to the formula Calculate the equivalent data rate _Re in a multi-channel environment, where A represents the interference area (area) of the link, that is, the union of the interference area of S and the interference area of D, and R _k represents the kth (1≤k≤ K) the corresponding data transmission rate on the channels, K represents the total number of channels in the network, Characterizes the average data transmission rate of a link in a multi-channel environment, thus Characterize the link's impact on area throughput. The larger the value, the greater the contribution of the link to the regional throughput of the network. For simplicity, in this embodiment can also make To characterize the equivalent data rate _Re , where d is the distance between S and D. After that, go to step 4.2;

Step 4.2: S according to the formula Calculate the back-off speed ω _BK in this time slot, that is, the greater the contribution of the link to the regional throughput of the network, the greater the back-off speed ω _BK . After that, go to step 5;

Step 5: When the time slot ends, S subtracts ω _BK from its current backoff counter value. S then judges whether its current backoff count is less than or equal to 0, if so, then S accesses and transmits data through K channels; otherwise, goes to step 2 to continue the backoff process. Specific steps are as follows:

Step 5.1: Assuming that the current backoff counter value of S is cw, then when the current time slot ends, S subtracts ω _BK from its current backoff counter, that is, cw=cw-ω _BK . After that, go to step 5.2;

Step 5.2: S judges whether its current backoff count value cw is less than or equal to 0. If the condition cw≤0 is satisfied, S accesses the channel and transmits data through K channels, and then the AP replies with acknowledgment frames (Acknowledgment, ACK) on the K channels respectively. After this transmission process ends, S records the received power Pr recorded in the CTS frame sent by D; otherwise, S goes to step 2 to continue the backoff process.

Embodiment nine

Embodiment 9 focuses on describing the fractional backoff process when a backoff condition is introduced in a multi-channel environment. The main purpose of introducing the backoff condition is to limit the access of nodes that contribute too little to the throughput performance of the network area, thereby alleviating network conflicts and improving the throughput performance of the network area. As shown in Figure 8, the cell includes two stations (namely 'S' and 'E'), where S is closer to the AP, and E is farther away from the AP. The following will illustrate the specific operation process of the ninth embodiment.

Step 1-Step 4: Same as Step 1-Step 4 in Embodiment 8. Through steps 1 to 4, S and E respectively calculate the back-off speed ω _BK and ω' _BK in their respective time slots, and then turn to step 5; c

Step 5: At the end of their respective time slots, S and E judge whether they meet the backoff conditions on the main channel (such as CH ₁ ), if not, do not back off in this time slot; otherwise, set their current backoff conditions to Subtract ω _BK from the counter value, and then, S and E judge whether their current backoff count value is less than or equal to 0, if so, then S accesses and transmits data through K channels; otherwise, go to step 2 to continue the backoff process . Specific steps are as follows:

Step 5.1: When the time slot ends, S judges whether the backoff condition on the main channel is satisfied. suppose is the backoff threshold, for example, If the backoff condition is met Then the fractional backoff process can be normally performed on the main channel, otherwise, S does not perform backoff in this time slot (ie ω _BK =0). After that, turn to step 5.2; at the same time, E also performs the same operation. In this embodiment, it is assumed that the backoff values of S and E calculated in step 4 are ω _BK =1.2 and ω' _BK =0.6, respectively, because and Therefore, after the backoff condition is judged, S can perform normal fractional backoff through the main channel in this time slot, but E cannot back off in this time slot, that is, ω' _BK =0.

Step 5.2: Assuming that the current backoff counter value of S is cw, and the current backoff counter value of E is cw', then when this time slot ends, S subtracts ω _BK from its current backoff counter, that is, cw=cw-ω _BK . At the same time, the sender E also performs the same operation, that is, E subtracts ω' _BK from its current backoff counter, so that cw'=cw'-ω' _BK =cw'. After that, go to step 5.3;

Step 5.3: S and E determine whether their respective current backoff count values (ie cw and cw') are less than or equal to 0. If yes, the channel is accessed and data is transmitted through K channels, and then the AP replies with ACK confirmation frames on the K channels respectively. After this transmission process ends, S records the received power Pr recorded in the CTS frame sent by D; otherwise, S goes to step 2 to continue the backoff process. At the same time, E also performs the same operation.

In the simulation, the area throughput of the network is counted, and compared with IEEE802.11DCF (ie, the baseline version) using the binary exponential backoff method. The simulation scenario is set as follows: each cell contains 5 uplink STAs and 5 downlink STAs; all STAs are saturated services, and the service type is video streaming services; the CCA threshold value is CCA _th = -62dBm. That is, the CCA range is [-82dBm, -62dBm]. From the simulation results shown in Figure 9, it can be seen that the area throughput performance of the present invention is much higher than that of IEEE 802.11 DCF, and as the number of cells increases, the area throughput performance gain obtained by the present invention is more obvious.

Claims (4)

1. A channel access method based on decimal backoff, characterized in that it comprises the following steps: Step 1, when the source node S sends data to the destination node D, the source node S queries the CCA range maintained by itself at this time, that is, [-82dBm,CCA _th ], CCA _th refers to the CCA threshold value, that is, the CCA range Upper limit value, and CCA _th >-82dBm, after that, go to step 2; Step 2. In each time slot, the source node S detects the signal energy I on the channel in real time. If the condition I≥CCA _th is satisfied, the backoff process of the source node S is suspended and continues to detect the signal energy I on the channel; Otherwise, go to step 3; Step 3, the source node S estimates the SINR _e , and obtains the corresponding data transmission rate R according to the mapping of the value of SINR _e in the segmented curve Rate-SINR of the rate and SINR, and proceeds to step 4; Step 4, the source node S calculates the backoff speed ω _BK in this time slot according to the data transmission rate R, and turns to step 5; Step 5: When the time slot ends, the source node S subtracts ω _BK from its current backoff counter value, and then judges whether the backoff counter value after subtracting ω _BK is less than or equal to 0, and if so, the source node S accesses channel and transmit data; otherwise, go to step 2 to continue the backoff process. 2. The channel access method based on decimal backoff according to claim 1, characterized in that: said CCA _th is set in advance, or fed back by destination node D during data transmission with source node S in the last time slot get, Wherein, Pr is the receiving power of the request to send frame RTS sent by the source node S received by the destination node D, and SINR _th represents the signal-to-noise ratio corresponding to the maximum modulation and coding method that can be adopted. 3. The channel access method based on decimal backoff according to claim 1, characterized in that: in the step 3, SINR _e =Pr-I; if the current time slot is the first transmission gap, then ω _BK = 1, and then go directly to step 5. 4. The channel access method based on decimal backoff according to claim 1, characterized in that: in the step 4, the source node S calculates the equivalent data rate Wherein, A represents the interference area of the link, i.e. the union of the interference area area of the sending node S and the interference area area of the receiving node D; according to the formula ω B _K : The source node S calculates the back-off speed ω _BK in this time slot, where R ^* represents the area throughput, and the corresponding back-off speed is