WO2018082133A1 - 一种基于小数退避的信道接入方法 - Google Patents

一种基于小数退避的信道接入方法 Download PDF

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WO2018082133A1
WO2018082133A1 PCT/CN2016/106907 CN2016106907W WO2018082133A1 WO 2018082133 A1 WO2018082133 A1 WO 2018082133A1 CN 2016106907 W CN2016106907 W CN 2016106907W WO 2018082133 A1 WO2018082133 A1 WO 2018082133A1
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backoff
cca
channel
source node
value
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PCT/CN2016/106907
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English (en)
French (fr)
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李波
杨懋
杨博
闫中江
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西北工业大学
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W74/00—Wireless channel access
    • H04W74/08—Non-scheduled access, e.g. ALOHA
    • H04W74/0833—Random access procedures, e.g. with 4-step access
    • H04W74/0841—Random access procedures, e.g. with 4-step access with collision treatment
    • H04W74/085—Random access procedures, e.g. with 4-step access with collision treatment collision avoidance

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  • the present invention relates to the field of communication technologies, and in particular, to a backoff mechanism.
  • the IEEE 802.11 standard employs a mechanism called Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA).
  • CSMA/CA Carrier Sense Multiple Access with Collision Avoidance
  • a node determines whether a channel is idle by performing carrier sensing. After the channel is idle, the node starts to perform the Binary Exponential Backoff process. If the channel becomes busy during the backoff process, it needs to wait for a period of time until the channel becomes idle again, and then resumes the evacuation until the backoff. Data can be sent after the end to reduce the probability of collision of data transmission.
  • 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 collision, it does not wait for the channel to become idle immediately after transmitting the data, but delays a random time (or called backoff) and then resends the data. After each collision, the average waiting time of the node 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], and CW represents the value of the competition window.
  • m CW min when the conflict occurs, the backoff order m is increased by one.
  • the value of the backoff counter is decremented by one each time it is detected that the channel is idle for one slot.
  • the node can send data.
  • the node's perception of channel quality is coarser. That is to say, the result of node-to-channel sensing includes only two cases: the channel is "busy” or the channel is "free”. If the channel is "busy”, that is, if the interference level of the channel exceeds the CCA (Clear Channel Assessment) threshold, the backoff process will be suspended; if the channel is "idle", the channel interference is detected. The level is lower than the CCA threshold, expressed as CCA th , and its backoff process will advance at the same pace, that is, whenever the channel is idle for one slot time, the node's backoff counter value is decremented by one.
  • CCA Cross Channel Assessment
  • the CCA threshold is set too low, the number of nodes that consider the channel to be "busy” too much will restrict the possibility of parallel transmission and reduce the channel resource utilization; if the CCA threshold is set too high , will result in too many nodes that consider the channel to be "free” at the same time, thus increasing the probability of collision.
  • the present invention provides a fractional backoff mechanism, which can improve the access priority of a link with a high data rate and a small interference range, that is, increase the backoff speed of the link, and reduce the data rate.
  • the access priority of a link with a large interference range reduces the backoff speed of the link, thereby improving the area throughput performance of the network.
  • Step 1 When the source node S sends data to the destination node D, the source node S queries the CCA range that it maintains at this time, that is, [-82dBm, CCA th ], and the CCA th refers to the CCA threshold value, that is, the CCA range. Upper limit value, and CCA th >-82dBm, after which, proceed 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 hangs and continues to detect the signal energy I on the channel; Otherwise, go to step 3;
  • Step 3 the source node S estimates the signal to interference and noise ratio SINR e , according to the mapping of the value of SINR e in the rate and the signal-to-noise ratio segmentation curve Rate-SINR, obtain the corresponding data transmission rate R, and proceeds to step 4;
  • Step 4 the source node S calculates the backoff speed ⁇ BK in the current time slot according to the data transmission rate R, and proceeds to step 5;
  • Step 5 After the time slot ends, the source node S subtracts the current backoff counter value from ⁇ BK , and then determines whether the backoff counter value after subtracting ⁇ BK is less than or equal to 0. If yes, 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 is fed back by the destination node D during data transmission between the previous time slot and the source node S.
  • Pr is the destination node D receiving the received power of the request transmission frame RTS transmitted by the source node S, and SINR th indicating the signal to noise ratio corresponding to the maximum available modulation and coding scheme.
  • the source node S calculates an equivalent data rate.
  • A represents the interference area of the link, that is, the union of the area of the interference area of the transmitting node S and the area of the interference area of the receiving node D;
  • the source node S calculates the backoff speed ⁇ BK in the current slot, where R * represents the area throughput, and the corresponding backoff speed is
  • the invention has the beneficial effects that a finer backoff mode is realized by accelerating the backoff speed of a node that contributes a large amount to the regional throughput, thereby further refining the relative priority when the user competes for the channel, and achieving a better Collision avoidance and more efficient channel resource utilization; simple implementation, compatible with IEEE 802.11 standard protocol, and applicable to both single-channel and multi-channel environments; in addition, the present invention can be implemented in firmware of a network card At the same time, it can also be implemented in the driver; the invention estimates the interference state of the receiving end through the transmitting end, so that the backoff is more accurate, thereby greatly improving the regional throughput.
  • FIGS. 1 and 2 are diagrams of Embodiment 1 of the present invention.
  • FIG. 3 is a diagram of Embodiment 2 of the present invention.
  • FIG. 4 is a diagram of Embodiment 3 of the present invention.
  • FIG. 5 is a diagram of Embodiment 4 of the present invention.
  • FIG. 6 is a diagram of Embodiment 5 of the present invention.
  • FIG. 7 is a diagram showing Embodiment 6 of the present invention.
  • Figure 8 is a diagram showing an eighth embodiment of the present invention.
  • Figure 9 is a diagram showing the ninth embodiment of the present invention.
  • Figure 10 is a schematic diagram of simulation results of the present invention.
  • AP-access point Access Point RTS-Request access Request-To-Send, CTS-Allow Clear-To-Send, ACK-Acknowledgement, SIFS-Short Interframe Space, CH-channel Channel, BSS-Basic Service Set.
  • the drawbacks of the traditional binary backoff mechanism for coarse-grained sensing of channel quality are overcome, so that the back-off process is organically combined with the actual state of the network, thereby achieving a more elaborate backoff.
  • the present invention is easy to implement and is compatible with the IEEE 802.11 standard protocol. The simulation results show that this patent can greatly improve the regional throughput of the network.
  • the present invention is a flexible backoff mechanism applied in a wireless network, and aims to overcome the disadvantages of the traditional binary backoff mechanism for coarse-grained sensing of channel quality, so that the back-off process is organically combined with the actual state of the network, thereby achieving finer Treatment and increase the regional throughput of the network.
  • the implementation process of this patent will be described in detail below with reference to eight embodiments.
  • Step 1 When the source node S sends data to the destination node D, S queries the CCA range that it maintains at this time, that is, [-82dBm, CCA th ], and CCA th refers to the CCA threshold, which is the upper limit of the CCA range. Value, and CCA th >-82dBm, after which, 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, the backoff process of S hangs and returns to step 2 to continue listening; otherwise, That is, the condition I ⁇ CCA th is satisfied, and the process proceeds to step 3;
  • Step 3 S estimated Signal to Interference with Noise Ratio (SINR), denoted as SINR e , and then S according to the SINR e lookup table to obtain the corresponding data transmission rate R, after which, proceeds to step 4;
  • SINR Signal to Interference with Noise Ratio
  • Step 4 S according to the data transmission rate R, calculate the backoff speed ⁇ BK in this time slot, and then proceeds to step 5;
  • Step 5 After the end of this time slot, S subtracts ⁇ BK from its current backoff counter value, and then judges whether the backoff counter value after subtracting ⁇ BK is less than or equal to 0. If yes, S accesses the channel and transmits data. Otherwise, go to step 2 to continue the backoff process.
  • the embodiment side re-described the fractional backoff process in a single channel environment.
  • a cell Station, STA
  • AP access point
  • S and D perform a fractional backoff procedure on the channel (CH). After the backoff is successful, S sends data to the D on the CH.
  • CH channel
  • Step 1 When the source node S sends data to the destination node D, S queries the CCA range that it maintains at this time;
  • Step 1.1 S queries the CCA threshold CCA th that it maintains at this time.
  • the CCA th may be unique to the entire network, or may be fed back by D during the last data transmission with S (when D receives After RTS, the received power of the RTS frame is Pr, then
  • SINR th represents a threshold value of the signal to noise ratio, that is, a signal to noise ratio corresponding to the maximum available modulation and coding mode, and the value may be given in advance. Then the value of CCA th maintained by each transmitting node may be different. After that, proceed to step 1.2;
  • 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 hangs; otherwise, it proceeds to step 3. Specific steps are as follows:
  • Step 2.1 S detects the signal energy (ie, the interference strength) on the channel in each time slot, denoted as I. After that, proceed to step 2.2;
  • Step 2.2 If the condition I ⁇ CCA th is satisfied, the backoff process of S hangs until the channel becomes idle (ie, the condition I ⁇ CCA th is satisfied) and the duration of the distributed inter-frame Spacing ( DISFS ) is maintained. After that, S proceeds to step 1 to restart the execution of the backoff process. After that, go to step 3;
  • Step 3 S SINR estimate SINR e, and obtain the corresponding data transmission rate R according SINR e, then, proceeds to step 4. Specific steps are as follows:
  • Step 3.2 According to the segmentation curve of Rate-SINR, S obtains the corresponding data transmission rate R by mapping the value of SINR e , and then proceeds to step 4;
  • Step 4 S calculates the backoff speed ⁇ BK in this time slot, and then proceeds to step 5. Specific steps are as follows:
  • Step 4.1 According to the formula S calculates the equivalent data rate R e .
  • A represents the interference area of the link, that is, the union of the interference area (area) of the transmitting node S and the interference area (area) of the receiving node D.
  • Characterize the impact of links on regional throughput The larger, the greater the contribution of the link to the regional throughput of the network.
  • d represents a distance between the S and D.
  • Step 4.2 According to the formula S calculates the backoff speed ⁇ BK in this time slot, that is, the greater the contribution of the link to the regional throughput of the network, then the backoff speed ⁇ BK is larger.
  • R * represents a value of the regional throughput
  • the corresponding retreat speed is For example, in the IEEE802.11a standard, the maximum transmission rate is 54 Mbps, and when the S and D positions coincide, the union of the interference areas is the smallest, denoted as A * , then the area throughput obtained at this time The amount is the largest, recorded as Corresponding The value can be 2, and then S can calculate the value of ⁇ BK .
  • ⁇ BK 1. After that, go to step 5;
  • Step 5 When the end of the time slot, the current S their backoff counter value minus ⁇ BK, S further determined by subtracting the value of ⁇ BK backoff counter is less than or equal to 0, and if yes, S an access channel and transmit data Otherwise, go to step 2 to continue the backoff process.
  • Specific steps are as follows:
  • Step 5.2 S determines whether the current backoff count value CW is less than or equal to zero. If the condition cw ⁇ 0 is satisfied, the S accesses the channel and transmits data by means of 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 records the received power Pr carried in the CTS frame sent by D. If cw>0, then S proceeds to step 2 to continue the fractional backoff process.
  • a four-way handshake ie, RTS-CTS-DATA-ACK
  • the second embodiment focuses on the fractional backoff process after the backoff condition is introduced in a single channel environment.
  • the back-off conditions are introduced to limit node access that contributes too little to the throughput performance of the network area, thereby alleviating network conflicts and improving network area throughput performance.
  • the cell includes two sites, namely, 'S' and 'E', wherein S is relatively close to the AP, and E is far from the AP.
  • the specific operation process of the second embodiment will be exemplified below.
  • Steps 1 to 4 Steps 1 to 4 in the first embodiment, through steps 1 to 4, S and E respectively calculate respective retraction speeds, expressed as ⁇ BK and ⁇ ' BK , and then proceeds to step 5 ;
  • Step 5 At the end of the respective time slots, S and E judge whether or not each of the backoff conditions is satisfied. If the backoff condition is not met, S and E do not retreat in this time slot; otherwise, the current backoff counter value is subtracted from ⁇ BK , and then S and E determine whether the current backoff count value is 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 5.3 S determines whether the current value of cw is less than or equal to zero. If cw ⁇ 0, then S accesses the channel and transmits data. In this process, D records the received power of the RTS received by S and carries it in the CTS frame and feeds it back to S, and then records the received power Pr carried in the CTS frame sent by D. If cw>0, then S proceeds to step 2 to continue the fractional backoff process. Similarly, E also performs the same operations as S.
  • the third embodiment focuses on the AP in the single-channel environment, and the AP adjusts the backoff weight ⁇ , 0 ⁇ 1, in the fractional backoff process according to the number of STAs in the current cell.
  • the AP dynamically adjusts the backoff weight ⁇ of all STAs according to the change of the number of STAs in the network, thereby improving network performance. If the number of STAs in the cell is small, the AP can adjust the value of the a large value, which can speed up the STA's backoff speed and improve resource utilization, thereby improving the area throughput performance.
  • the AP can appropriately adjust the value of the small alpha to make the backoff speed of all STAs finer, thereby alleviating network conflicts.
  • STAs in the cell there are 2 STAs in the cell, respectively A and B; and in Figure 4(b), there are 4 STAs in the cell, which are A, B, C, and E, respectively.
  • the specific operation of the third embodiment will be exemplified below.
  • Step 1 When the source node S sends data to the destination node D, S queries the CCA range that it maintains at this time;
  • Step 1.1 The AP adjusts the value of the backoff weight ⁇ of all STAs according to the number of STAs in the current cell.
  • Step 1.2 The AP seizes the channel usage right. For example, after waiting for the channel to be idle for a PCF Inter-Frame Space (PIFS), the AP sends a Beacon frame and notifies all STAs in the cell of the adjusted backoff weight ⁇ . By performing steps 1.1 to 1.2, the AP can adjust the backoff weight ⁇ of all STAs in the current cell according to the number of STAs in the current cell. After that, proceed to step 1.3;
  • PIFS PCF Inter-Frame Space
  • Step 1.3 S queries the CCA threshold CCA th that it maintains at this time.
  • the CCA th may be unique to the entire network, or may be fed back by D during the last data transmission with S, then each transmission The value of CCA th maintained by the node may be different. After that, proceed to step 1.4;
  • Step 2 to Step 4 Steps 2 to 4 in the same manner as in the first embodiment.
  • Step 5 All STAs in the cell adjust their respective backoff values according to the value of ⁇ , and determine whether the current backoff count value is less than or equal to zero. If yes, access the channel and transmit data; otherwise, go to step 2 to continue the backoff process. Specific steps are as follows:
  • Step 5.2 Assuming that the backoff counter value of the current STA i is cw i , then after the time slot ends, STA i subtracts its current backoff counter. which is After that, proceed to step 6.3;
  • Step 5.3 STA i determines whether its current backoff count value cw i is less than or equal to zero. 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 received by the S and reports it to the STA i through the CTS frame, and the STA i records the received power Pr carried in the CTS frame sent by the AP. If cw i >0, STA i proceeds to step 1 to continue the fractional backoff process.
  • Embodiment 4 focuses on the fact that in a single channel environment, the AP combines the interference situation of the STAs in the current cell, and adjusts the CCA threshold CCA th .
  • the AP adjusts the CCA th to improve the channel access priority of STAs that contribute a lot to the regional throughput (because the greater the interference received by the link, the lower the data rate, then the network area The smaller the contribution of throughput, the higher the throughput performance of the network area.
  • FIG. 5 there are four STAs in the cell, which are A, B, C, and E, respectively. Among them, A and B are in the OBSS region at the edge of the cell, and the interference intensity I is large, while the interference intensity I received by C and E is small.
  • the specific operation of the fourth embodiment will be exemplified below.
  • Step 1 The AP adjusts the CCA threshold CCA th according to the interference situation of the STA in the current cell. Furthermore, the STAs in the cell obtain their own CCA interval [-82dBm, CCA th ] according to CCA th . After that, go to step 2. Specific steps are as follows:
  • the AP adjusts the CCA threshold of all STAs in the cell according to the interference value of each STA. For example, the CCA threshold CCA th is reduced from -62 dBm to -70 dBm. After that, proceed to step 1.2;
  • Step 1.2 The AP occupies the channel usage right. For example, the AP waits for the channel to be idle for one PIFS duration, and then sends the beacon frame, and the adjusted CCA th is notified to all STAs in the cell. After that, proceed to step 1.3;
  • Step 1.3 STA i sets its own CCA threshold interval according to the adjusted CCA th , that is, [-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 hangs; otherwise, it proceeds 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, proceed to step 2.2;
  • Step 2.2 If the condition I i ⁇ CCA th is satisfied in the time slot, the backoff procedure of STA i hangs until the channel becomes idle (ie, the condition I i ⁇ CCA th is satisfied) and the duration of the DIFS is maintained, the STA i turns The retreat process is restarted in step 1; otherwise, the process proceeds to step 3; therefore, in the present embodiment, only the site C and the site E in the cell can continue the fractional backoff process.
  • Step 3 to Step 5 Steps 3 to 5 in the same manner as in the first embodiment.
  • STA i carries the measured interference value I i through the RTS frame and sends it to D, and D records the interference value I i carried in the RTS frame.
  • Embodiment 5 focuses on the description that in a single channel environment, a transmitting node (such as a STA) adjusts its own CCA threshold CCA th according to feedback from a destination node (such as an AP).
  • the AP improves the channel access performance of the network area by feeding back CCA th to improve the channel access priority of STAs that contribute more to the area throughput.
  • FIG 6 there are two STAs in the cell, which are A and B respectively. Among them, A is in the OBSS area at the edge of the cell, and the received interference intensity I is large, and B is in the vicinity of the AP, and the received interference intensity I is small.
  • Steps 1 to 4 Steps 1 to 4 in the first embodiment, in which the stations A and B query the CCA threshold (ie, CCA th ) that the AP last feedback in the CTS.
  • the maintained CCA range that is, [-82dBm, CCA th ], if the CCA th value of the AP feedback (such as the first backoff process) has not been received before, the default CCA th value of the whole network, such as -62dBm, is directly adopted.
  • Step 5 After the end of this time slot, stations A and B subtract their respective backoff counter values from their respective backoff values (eg with And determining whether the current backoff count value is less than or equal to 0. If yes, the station A or B accesses the channel and transmits data, and the AP feeds back the appropriate CCA th in the process; otherwise, proceeds to step 2 to continue the backoff. process. Specific steps are as follows:
  • Step 5.1 Assume that the current backoff counters of stations A and B are cw A and cw B respectively . When the time slot ends, stations A and B subtract their own backoff counters from the backoff value (for example). with ), then there is After that, proceed to step 5.2;
  • Step 5.2 Sites A and B determine whether their current backoff count value is less than or equal to zero. For example, if station A first retreats, that is, if condition cw A ⁇ 0 is satisfied, station A accesses the channel and transmits an RTS frame. After that, proceed to step 5.3;
  • Step 5.4 The AP calculates CCA th and puts it into the CTS frame for transmission. After that, proceed to step 5.5;
  • Step 5.5 A station in accordance with the received CTS frame, TH CCA obtained feedback value AP, and set their CCA CCA range according to the value TH [-82dBm, CCA th]. After that, proceed to step 5.6;
  • the sixth embodiment focuses on the AP in the single-channel environment, and the AP adjusts the backoff weight ⁇ , 0 ⁇ 1 of each STA or group of STAs according to the interference situation of all the STAs in the current cell. Fair access between the two. As shown in Figure 7, there are three STAs in the cell, which are A, B, and C. A is located in the OBSS area at the edge of the cell, and the AP wants to increase the access opportunity of the edge A.
  • the specific operation of the sixth embodiment will be exemplified below.
  • Step 1 When the source node S sends data to the destination node D, S queries the CCA range that it maintains at this time;
  • Step 1.2 AP STA i suffered The interference value I i, the disturbance to the appropriate access rights to a large value sites, such as edge enhance cell site A access weight beta] A, while appropriately reducing interference suffered
  • Step 1.3 The AP uses the channel usage right. For example, the AP waits for the channel idle PIFS duration to send a beacon frame, and informs the adjusted STA i of the backoff weight ⁇ i (including ⁇ A , ⁇ B , and ⁇ C ) into the cell. All STAs. Then, the process proceeds to step 2; by performing steps 1.1 to 1.3, the AP can adjust the access weight ⁇ , 0 ⁇ 1 of each STA or group of STAs according to the interference situation of all STAs in the cell. After that, go to step 1.4.
  • Step 1.4 S queries the CCA threshold CCA th that it maintains at this time.
  • the CCA th may be unique to the entire network, or may be fed back by D during the last data transmission with S, then each transmission The value of CCA th maintained by the node may be different. After that, proceed to step 1.2;
  • Step 5 STA i adjusts its own backoff value according to the value of ⁇ i and performs fractional backoff. Further, it is determined whether the current backoff count value is less than or equal to 0. If yes, the channel is accessed and the data is transmitted; otherwise, the process proceeds to step 2 to continue the backoff process. Specific steps are as follows:
  • Step 5.1 STA i adjusts its own backoff value. Hypothesis The current backoff value of STA i , then the adjusted backoff value is After that, proceed to step 5.2;
  • Step 5.2 to Step 5.3 Step 5.2 to Step 5.3 in the same manner as in the third embodiment.
  • the seventh embodiment focuses on the AP in combination with the number and distribution of STAs in the current cell in a single-channel environment, and adjusts the backoff weights ⁇ and ⁇ of the STAs to ensure the throughput performance of the network area. Access fairness between STAs. As shown in Figure 7, there are three STAs in the cell, which are A, B, and C. Where A is located in the OBSS area at the edge of the cell.
  • the AP appropriately increases the access weight ⁇ A of the edge site A , and reduces the access weights ⁇ B and ⁇ C of the B and C.
  • Step 1 When the source node S sends data to the destination node D, S queries the CCA range that it maintains at this time;
  • Step 1.2 The AP preempts the channel usage right. For example, the AP waits for the channel idle PIFS duration to send a beacon frame, and informs the adjusted backoff weights ⁇ and ⁇ (including: ⁇ A , ⁇ B , and ⁇ C ) of all stations. All STAs in the cell. After that, the process proceeds to step 1.3. By performing steps 1.1 to 1.2, the AP completes the adjustment of the backoff weights ⁇ and ⁇ of the STA. After that, proceed to step 1.3;
  • Steps 1.3 to 1.4 Steps 1.3 to 1.4 in the same manner as in the third embodiment. After that, go to step 2;
  • Step 5 STA i adjusts its own backoff value according to ⁇ and ⁇ i and performs fractional backoff. Further, it is determined whether the current backoff count value is less than or equal to 0. If yes, the channel is accessed and the data is transmitted; otherwise, the process proceeds to step 1 to continue the backoff process. Specific steps are as follows:
  • Step 5.1 STA i adjusts its own backoff value. Hypothesis The current backoff value of STA i , then the adjusted backoff value is After that, proceed to step 5.2;
  • Step 5.2 to Step 5.3 Step 5.2 to Step 5.3 in the same manner as in the third embodiment.
  • Embodiment 8 focuses on the fractional backoff process in a multi-channel environment.
  • a cell 'S' is included in the cell, and the distance between S and the AP (ie, 'D') is d.
  • CH k is the primary channel and the remaining channels are the secondary channels.
  • S and D perform fractional backoff through the primary channel (CH 1 ), and data transmission is performed through K channels after successful backoff, as shown in FIG. 8(b).
  • the specific operation of the seventh embodiment will be exemplified below.
  • Step 1 Same as step 1 in the first embodiment. After that, go to step 2.
  • Step 2 In each time slot, S detects the signal energy on each channel, which is recorded as 1 ⁇ k ⁇ K. If the conditions are met Then the backoff process of S hangs; 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 I.e. interference strength S and D for data transmission on the channel CH k are subjected during. After that, proceed to step 2.2;
  • Step 2.2 If the condition is met in the current time slot Then the backoff process of S hangs until the channel becomes idle (ie, the condition is met) After maintaining the DIFS duration, S proceeds to step 1 to restart the execution of 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 Estimating the signal to interference noise ratio of the channel CH k SINR e, k.
  • Pr is the last received transmission power of the Request-to-send (RTS) frame sent by S during the transmission of S and D.
  • Step 3.2 S maps the values of SINR e, k according to the Rate-SINR segmentation curve to obtain a corresponding data transmission rate R k . After that, go to step 4;
  • Step 4 S calculates the backoff speed ⁇ 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 R e in a multi-channel environment, where A represents the interference region (area) of the link, that is, the union of the interference region of S and the interference region of D, and R k represents the kth (1 ⁇ k ⁇ K) the corresponding data transmission rate on the channel, K represents the total number of channels in the network, Characterizing the average data transmission rate of a link in a multi-channel environment, thus Characterize the impact of links on regional throughput. The larger, the greater the contribution of the link to the regional throughput of the network.
  • d is the distance between S and D.
  • Step 4.2 S according to the formula The backoff speed ⁇ BK in this time slot is calculated, that is, the greater the contribution of the link to the regional throughput of the network, the greater the backoff speed ⁇ BK . After that, go to step 5;
  • Step 5 After the end of this time slot, S subtracts ⁇ BK from its current backoff counter value. S further determines whether the current backoff count value is less than or equal to 0. If yes, S accesses and transmits data through K channels; otherwise, proceeds to step 2 to continue the backoff process. Specific steps are as follows:
  • Step 5.2 S determines whether the current backoff count value cw is less than or equal to zero. If the condition cw ⁇ 0 is satisfied, the S accesses the channel and transmits data through the K channels, and the AP returns an acknowledgement (ACK) on the K channels, respectively. After the end of the transmission process, S records the received power Pr recorded in the CTS frame sent by D; otherwise, S proceeds to step 2 to continue the backoff process.
  • cw current backoff count value
  • Embodiment 9 focuses on the fractional backoff process in the case of introducing a backoff condition in a multi-channel environment.
  • the introduction of the backoff condition is mainly 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.
  • two sites ie, 'S' and 'E'
  • S is closer to the AP
  • E is farther from the AP.
  • the specific operation of the ninth embodiment will be exemplified below.
  • Steps 1 to 4 Steps 1 to 4 in the same manner as in the eighth embodiment.
  • S and E respectively calculate the backoff speeds ⁇ BK and ⁇ ' BK in the respective time slots, and then proceeds to step 5;
  • Step 5 At the end of the respective time slots, S and E determine whether the respective backoff conditions are met on the primary channel (such as CH 1 ). If not, the backoff is not performed in this time slot; otherwise, the current backoff is performed. The counter value is subtracted from ⁇ BK , and then S and E determine whether the current backoff count value is less than or equal to 0. If yes, S accesses and transmits data through K channels; otherwise, proceeds to step 2 to continue the backoff process. . Specific steps are as follows:
  • Step 5.3 S and E determine whether each of the current backoff count values (i.e., cw and cw') is less than or equal to zero. If so, the channel is accessed and transmitted through K channels, and the AP then replies to the ACK acknowledgement frame on the K channels. After the end of the transmission process, S records the received power Pr recorded in the CTS frame sent by D; otherwise, S proceeds to step 2 to continue the backoff process. At the same time, E also performs the same operation.
  • the current backoff count values i.e., cw and cw'
  • the regional throughput of the network is statistically compared in the simulation and compared to the IEEE 802.11 DCF (ie baseline version) using a binary exponential backoff method.

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Abstract

本发明提供了一种基于小数退避的信道接入方法，通过加快对区域吞吐量贡献较大的节点的退避速度，实现了更精细的退避方式，从而进一步细化分解了用户竞争信道时的相对优先级，实现了更好的冲突回避以及更为高效的信道资源利用率；实现简单，能与IEEE 802.11标准协议相兼容，且可同时应用于单信道和多信道的环境下；另外，本发明可通过在网卡的固件中实现，同时也可以实现在驱动程序中；本发明通过发送端预估接收端的干扰状况，使得退避更加准确，从而大幅度提升了区域吞吐量。

Description

一种基于小数退避的信道接入方法
本申请要求于2016年11月07日提交中国专利局、申请号为201610976702.2、发明名称为“一种基于小数退避的信道接入方法”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本发明涉及通信技术领域，尤其是一种退避机制。
背景技术
为了减少无线网络中的碰撞，IEEE 802.11标准采用了一种叫做载波侦听多址接入/避免冲撞协议(Carrier Sense Multiple Access with Collision Avoidance，CSMA/CA)的机制。在CSMA/CA机制中，节点通过执行载波侦听来判断信道是否空闲。当信道空闲后，节点开始进行执行二进制指数退避(Binary Exponential Backoff)过程，若在退避过程中信道变忙，则需要随机等待一段时间，直到信道再次变为空闲后再开始继续进行退避，直至退避结束后才能发送数据，以减小数据传输的冲突概率。其中，CSMA/CA机制中所使用的二进制指数退避算法是减小网络冲突的关键所在。所谓二进制指数退避，是指当节点遇到冲突时，不是等待信道变为空闲后立即发送数据，而是推迟一个随机的时间后(或称为退避)再重新发送数据。在每一次冲突之后，节点的平均等待的时间也将加倍。即：每个节点均维持一个退避计数器，而这个退避计数器的值从[0,CW]中随机选取，CW代表竞争窗的取值，其初始值为最小竞争窗CWmin，并且有CW＝2mCWmin，当发生冲突后，退避阶数m加一。每当侦听到信道空闲一个时隙(slot)的时间后，退避计数器的值减一。当退避计数器减为0时，节点就可以发送数据了。但是，在目前的二进制退避过程中，节点对信道质量的感知粒度较粗。也就是说，节点对信道感知的结果仅包括两种情况：信道为“忙”，或者信道为“闲”。若信道为“忙”，即检测到信道的干扰水平超过了CCA(Clear Channel Assessment，信道空闲评估)门限，其退避过程将被挂起；而若信道为“闲”，即检测到信道的干扰水平低于了CCA门限，表示为CCAth，其退避过程将以相同的步伐推进，即每当信道空闲了一个时隙时间，节点的退避计数器值减1。
在下一代无线局域网(Wireless Local Area Networks，WLAN)中，将面临高密集部署场景以及爆炸式增长的业务需求，因此如何大幅度地提升区域吞吐量(即单位面积内的吞吐量)已成为一个有待解决的棘手问题。如果在下一代WLAN中延用传统的二元退避思路，若一些关键参数(如CCA门限)设置不合理，将难以与网络的实际状况相适配并难以实现对信道资源的充分利用，从而抑制区域吞吐量性能。比如，若CCA门限值设置过低，则将导致同时认为信道为“忙”的节点数过多，从而制约了并行传输的可能性，降低信道资源利用率；若CCA门限值设置过高，则将导致同时认为信道为“闲”的节点数过多，从而增大了冲突概率。
发明内容
为了克服现有技术的不足，本发明提供一种小数退避机制，能够提升数据速率高、干扰范围小的链路的接入优先权，即增加该链路的退避速度，同时削减数据速率低、干扰范围大的链路的接入优先权，即降低该链路的退避速度，从而提升网络的区域吞吐量性能。
本发明解决其技术问题所采用的技术方案包括以下步骤：
步骤1，当源节点S给目的节点D发送数据，源节点S查询此时自己所维持的CCA范围，即[-82dBm,CCAth]，CCAth是指CCA门限值，也就是CCA范围的上限值，且CCAth>-82dBm，之后，转入步骤2；
步骤2，在每一个时隙内，源节点S实时检测信道上的信号能量I，若满足条件I≥CCAth，则源节点S的退避过程挂起，并继续检测信道上的信号能量I；否则，转入步骤3；
步骤3，源节点S估算信干噪比SINRe，根据SINRe的取值在速率和信干噪比的分段曲线Rate-SINR中的映射，获得对应的数据传输速率R，转入步骤4；
步骤4，源节点S根据数据传输速率R计算出本时隙内的退避速度ωBK，转入步骤5；
步骤5：当本时隙结束后，源节点S将自己当前的退避计数器值减去ωBK，再判断减去ωBK后的退避计数器值是否小于或等于0，若是，则源节点S接入信道并传输数据；否则，转入步骤2继续进行退避过程。
所述的CCAth提前设定，或由目的节点D在上一时隙与源节点S进行数据传输过程中反馈得到，
Figure PCTCN2016106907-appb-000001
其中，Pr为目的节点D接收到源节点S发送的请求发送帧RTS的接收功率，SINRth表示最大可以采用的调制编码方式所对应的信噪比。
所述的步骤3中，信干噪比SINRe＝Pr-I；如果当前时隙是第一个传输时隙，则ωBK＝1，然后直接转入步骤5。
所述的步骤4中，源节点S计算等效数据速率
Figure PCTCN2016106907-appb-000002
其中，A表示链路的干扰面积，即发送节点S的干扰区域面积与接收节点D的干扰区域面积的并集；根据公式
Figure PCTCN2016106907-appb-000003
源节点S计算出本时隙内的退避速度ωBK，其中，R*代表区域吞吐量，与之所对应的退避速度为
Figure PCTCN2016106907-appb-000004
本发明的有益效果是：通过加快对区域吞吐量贡献较大的节点的退避速度，实现了更精细的退避方式，从而进一步细化分解了用户竞争信道时的相对优先级，实现了更好的冲突回避以及更为高效的信道资源利用率；实现简单，能与IEEE 802.11标准协议相兼容，且可同时应用于单信道和多信道的环境下；另外，本发明可通过在网卡的固件中实现，同时也可以实现在驱动程序中；本发明通过发送端预估接收端的干扰状况，使得退避更加准确，从而大幅度提升了区域吞吐量。
附图说明
图1和图2是本发明实施例一的图示；
图3是本发明实施例二的图示；
图4是本发明实施例三的图示；
图5是本发明实施例四的图示；
图6是本发明实施例五的图示；
图7是本发明实施例六、实施例七的图示；
图8是本发明实施例八的图示；
图9是本发明实施例九的图示；
图10是本发明的仿真结果示意图；
图中，AP-接入点Access Point，RTS-请求接入Request-To-Send，CTS-允许发送Clear-To-Send，ACK-确认Acknowledgement，SIFS-短帧间间隔Short Interframe Space，CH-信道Channel，BSS-基本服务集Basic Service Set。
具体实施方式
下面结合附图和实施例对本发明进一步说明，本发明包括但不仅限于下述实施例。
在该机制中，克服了传统的二元退避机制对信道质量的粗粒度感知的弊端，使得退避过程与网络的实际状况有机结合，从而实现更为精细的退避。另外，本发明实现容易，并能与IEEE 802.11标准协议相兼容。仿真结果表明，本专利可大幅度提升网络的区域吞吐量。
本发明是应用于无线网络中的一种灵活的退避机制，旨在克服传统二元退避机制对信道质量的粗粒度感知的弊端，使得退避过程与网络的实际状况有机结合，从而实现更为精细的退避，并提升网络的区域吞吐量。下面结合八个实施例对本专利的实现过程进行详细介绍。
本发明的详细步骤如下：
步骤1：当源节点S给目的节点D发送数据，S查询此时自己所维持的CCA范围，即[-82dBm,CCAth]，CCAth是指CCA门限值，也就是CCA范围的上限值，且CCAth>-82dBm，之后，转入步骤2；
步骤2：在每一个时隙内，S实时检测信道上的信号能量，记为I，若满足条件I≥CCAth，则S的退避过程挂起，并返回步骤2中继续侦听；否则，即满足条件I<CCAth，转入步骤3；
步骤3：S估算信干噪比(Signal To Interference with Noise Ratio，SINR)，记为SINRe，进而S根据SINRe查表得到对应的数据传输速率R，之后，转入步骤4；
步骤4：S根据数据传输速率R，计算出本时隙内的退避速度ωBK，之后，转入步骤5；
步骤5：当本时隙结束后，S将自己当前的退避计数器值减去ωBK，再判断减去ωBK后的退避计数器值是否小于或等于0，若是，则S接入信道并传输数据；否则，转入步骤2继续进行退避过程。
实施例一
实施例一侧重描述在单信道环境下的小数退避过程。如图1所示，小区中包括一个站点(Station，STA)‘S’，且S与接入点(Access Point，AP)‘D’之间的距离为d。在图2中，S与D在信道(CH)上进行小数退避过程。当退避成功后，S给D在CH上进行数据传输。以下将举例说明实施例一的具体操作过程。
步骤1：当源节点S给目的节点D发送数据，S查询此时自己所维持的CCA范围；
步骤1.1：S查询此时自己所维持的CCA门限值CCAth，该CCAth可以是全网唯一的，也可以由D在上一次与S进行数据传输过程中所反馈得到(当D收到RTS后，记RTS帧的接收功率为Pr，则
Figure PCTCN2016106907-appb-000005
其中，SINRth表示信噪比的门限值，即最大可以采用的调制编码方式所对应的信噪比，其取值可以提前给定。那么每个发送节点维持的CCAth取值可能不同。之后，转入步骤1.2；
步骤1.2：S将所查询到的CCAth设置为自己的CCA区间的上限，进而得到自己的CCA区间。比如，CCAth＝-62dBm，那么S的CCA区间为[-82dBm,-62dBm]。之后，转入步骤2。
步骤2：在每一个时隙内，S实时检测信道上的信号能量，并记为I。若满足条件I≥CCAth，则S的退避过程挂起；否则，转入步骤3。具体步骤如下：
步骤2.1：S在每个时隙内检测信道上的信号能量(即干扰强度)，记为I。之后，转入步骤2.2；
步骤2.2：若满足条件I≥CCAth，则S的退避过程挂起，直至信道变为空闲(即满足条件I<CCAth)且维持DIFS(Distributed Inter-frame Spacing，分布式帧间间隙)时长后，S转入步骤1中重新开始执行退避过程。之后，转入步骤3；
步骤3：S估算信干噪比SINRe，并根据SINRe得到对应的数据传输速率R，之后，转入步骤4。具体步骤如下：
步骤3.1：S通过公式SINRe(dB)＝Pr-I来估算信干噪比SINRe，其中，Pr为上一次在S与D的传输过程中D接收到S所发送的请求发送(Request-to-send，RTS)帧的接收功率值，S可以通过读取来自D回复的允许发送(Clear-to-send，CTS)帧所携带的Pr取值。如果本次传输是第一次传输，那么S尚未获得Pr的取值，则此次退避直接采用传统的二进制指数退避方式(即ωBK＝1)，然后转入步骤5；否则，转入步骤3.2；
步骤3.2：根据Rate-SINR的分段曲线，S通过将SINRe的取值进行映射，获得对应的数据传输速率R，之后，转入步骤4；
步骤4：S计算出本时隙内的退避速度ωBK，之后，转入步骤5。具体步骤如下：
步骤4.1：根据公式
Figure PCTCN2016106907-appb-000006
S计算等效数据速率Re。其中，A表示链路的干扰面积，即发送节点S的干扰区域(面积)与接收节点D的干扰区域(面积)的并集，
Figure PCTCN2016106907-appb-000007
表征链路对区域吞吐量的影响，
Figure PCTCN2016106907-appb-000008
越大，则表示该链路对网络的区域吞吐量的贡献越大。在本实施例中令
Figure PCTCN2016106907-appb-000009
来刻画等效数据速率Re，其中，d表示S与D之间的距离。之后，转入步骤4.2；
步骤4.2：根据公式
Figure PCTCN2016106907-appb-000010
S计算出本时隙内的退避速度ωBK，即链路对网络的区域吞吐量的贡献越大，那么其退避速度ωBK就越大。其中，R*代表区域吞吐量的一个取值，与之所对应的退避速度为
Figure PCTCN2016106907-appb-000011
例如，在IEEE802.11a标准中，最大的传输速率为54Mbps，而当S与D位置重合时，两者干扰面积的并集是最小的，记为A*，那么，此时所获得的区域吞吐量为最大，记为
Figure PCTCN2016106907-appb-000012
与之对应的
Figure PCTCN2016106907-appb-000013
可取值为2，进而，S就可以计算出ωBK的取值。而对于传统的二进制指数退避算法，ωBK＝1。之后，转入步骤5；
步骤5：当本时隙结束后，S将自己当前的退避计数器值减去ωBK，S进而判断减去ωBK的退避计数器值是否小于或等于0，若是，则S接入信道并传输数据；否则，转入步骤2继续进行退避过程。具体步骤如下：
步骤5.1：假设S当前的退避计数器的取值为cw，那么当本时隙结束后，S将自己当前的退避计数器减去ωBK，即cw＝cw-ωBK。之后，转入步骤5.2；
步骤5.2：S判断自己当前的退避计数值CW是否小于或等于0。若满足条件cw≤0，则S接入信道并采用四次握手的方式(即RTS-CTS-DATA-ACK)传输数据。在该过程中，D将接收到S所发送的RTS帧的接收功率记录下来并通过CTS帧反馈给S，进而S记录下D所发送的CTS帧中所携带的接收功率Pr。若cw>0，则S转入步骤2继续进行小数退避过程。
实施例二
实施例二侧重描述在单信道环境下，引入退避条件后的小数退避过程。在该实施例中，通过引入退避条件来限制那些对网络区域吞吐量性能贡献太小的节点接入，从而缓解网络冲突，提升网络区域吞吐量性能。如 图3所示，小区中包括两个站点即‘S’和‘E’，其中，S与AP距离较近，而E与AP距离较远。以下将举例说明实施例二的具体操作过程。
步骤1～步骤4：同实施例一中的步骤1～步骤4，通过步骤1～4，S和E分别计算出各自的退避速度，表示为ωBK和ω'BK，之后，转入步骤5；
步骤5：在各自的时隙结束时，S和E判断各自是否满足退避条件。若不满足退避条件，则S和E在本时隙内不进行退避；否则，将自己当前的退避计数器值减去ωBK，进而，S和E判断各自当前的退避计数值是否小于或等于0，若是，则接入信道并传输数据；否则，转入步骤2继续进行退避过程。具体步骤如下：
步骤5.1：假设
Figure PCTCN2016106907-appb-000014
为退避门限值，取
Figure PCTCN2016106907-appb-000015
当本时隙结束时，S判断是否满足退避条件
Figure PCTCN2016106907-appb-000016
若满足退避条件，则正常进行退避过程，否则，S在本时隙内不进行退避，即ωBK＝0。之后，转入步骤5.2；与此同时，E也执行相同的操作。在本实施例中，假设S和E在步骤4中计算出的退避值分别为ωBK＝1.2、ω'BK＝0.6，由于
Figure PCTCN2016106907-appb-000017
且
Figure PCTCN2016106907-appb-000018
因而S在本时隙内正常退避而E在本时隙内无法退避，即ω'BK＝0。
步骤5.2：假设S当前的退避计数器值为cw，E当前的退避计数器值为cw'。那么当本时隙结束后，S将自己当前的退避计数器减去ωBK，即cw＝cw-ωBK，与此同时，E也进行相同的操作，E将自己当前的退避计数器减去ω'BK，即cw'＝cw'-ω'BK，因而cw'的取值不变。之后，转入步骤5.3；
步骤5.3：S判断当前的cw取值是否小于或等于0。若cw≤0，则S接入信道并传输数据。在该过程中，D将接收到S所发送的RTS的接收功率记录下来并携带在CTS帧中反馈给S，进而S记录下D所发送的CTS帧中所携带的接收功率Pr。若cw>0，则S转入步骤2继续进行小数退避过程。同理，E也进行与S相同的操作。
实施例三
实施例三侧重描述在单信道环境下，AP根据当前本小区中的STA数量来调整小数退避过程中的退避权值α，0<α≤1。在该实施例中，AP根据网络中STA个数的变化，动态调整所有STA的退避权值α，从而提升网络性能。若本小区内的STA数量较少，则AP可适当调大α的取值，这样可以加快STA的退避速度，提升资源利用率，从而提升区域吞吐量性能。若本小区内的STA数量过多，则AP可适当调小α的取值，使所有STA的退避速度更加精细，从而缓解网络冲突。在图4(a)中，小区内有2个STA，分别为 A和B；而在图4(b)中，小区内有4个STA，分别为A、B、C和E。以下将举例说明实施例三的具体操作过程。
步骤1：当源节点S给目的节点D发送数据，S查询此时自己所维持的CCA范围；
步骤1.1：AP根据当前小区中STA数量，调整所有STA的退避权值α的取值。在图4(a)中，小区有2个STA，则AP适当调大α的取值，以加快STA的退避速度，从而更加充分地利用信道资源。比如，取α＝1.0；而在图4(b)中，小区有4个STA，则AP适当降低α的取值，以降低STA的退避速度，从而缓解网络冲突。比如，取α＝0.5。之后，转入步骤5.2；
步骤1.2：AP通过抢占信道使用权。比如，AP等待信道空闲一个优先帧间距时长(PCF Inter-Frame Space，PIFS)后，发送Beacon帧，将所调整后的退避权值α告知小区内的所有STA。通过执行步骤1.1～步骤1.2，AP就可根据当前本小区内的STA数量，来调整本小区内所有STA的退避权值α。之后，转入步骤1.3；
步骤1.3：S查询此时自己所维持的CCA门限值CCAth，该CCAth可以是全网唯一的，也可以由D在上一次与S进行数据传输过程中所反馈得到，那么每个发送节点维持的CCAth取值可能不同。之后，转入步骤1.4；
步骤1.4：S将所查询到的CCAth设置为自己的CCA区间的上限，进而得到自己的CCA区间。比如，CCAth＝-62dBm，那么S的CCA区间为[-82dBm,-62dBm]。之后，转入步骤2。
步骤2～步骤4：同实施例一中的步骤2～步骤4。通过步骤2～4，小区内的所有STA计算出各自时隙内的退避速度，分别为
Figure PCTCN2016106907-appb-000019
i＝A,B,C,E，之后，转入步骤5；
步骤5：小区内所有STA根据α的取值调整各自的退避值，并判断自己当前的退避计数值是否小于或等于0。若是，则接入信道并传输数据；否则，转入步骤2继续进行退避过程。具体步骤如下：
步骤5.1：小区内所有STA调整自己的退避值。假设
Figure PCTCN2016106907-appb-000020
为小区内标号为i的STA(表示为STAi，i＝A,B,C,E)的当前退避值，那么调整后的退避值为
Figure PCTCN2016106907-appb-000021
之后，转入步骤5.2；
步骤5.2：假设当前STAi的退避计数器值为cwi，那么当本时隙结束后，STAi将自己当前的退避计数器减去
Figure PCTCN2016106907-appb-000022
即
Figure PCTCN2016106907-appb-000023
之后，转入步骤6.3；
步骤5.3：STAi判断自己当前的退避计数值cwi是否小于或等于0。若满 足cwi≤0，则STAi接入信道并传输数据。在该过程中，AP将接收到S所发送的RTS的接收功率记录下来并通过CTS帧反馈给STAi，进而STAi记录下AP所发送的CTS帧中所携带的接收功率Pr。若cwi>0，则STAi转入步骤1，继续进行小数退避过程。
实施例四
实施例四侧重描述在单信道环境下，AP结合当前本小区中的STA所受到的干扰情况，调整CCA门限值CCAth。在本实施中，AP通过调整CCAth，来提升那些对区域吞吐量贡献较大的STA的信道接入优先权(因为链路所受到的干扰越大，其数据速率越低，那么对网络区域吞吐量的贡献就越小)，从而提升网络区域吞吐量性能。如图5所示，小区内有4个STA，分别为A、B、C和E。其中，A和B处于本小区边缘的OBSS区域内，受到的干扰强度I较大，而C和E受到的干扰强度I较小。以下将举例说明实施例四的具体操作过程。
步骤1：AP根据当前小区内STA所受的干扰情况，调整CCA的门限值CCAth。进而，小区内的STA根据CCAth得到自己的CCA区间[-82dBm,CCAth]。之后，转入步骤2。具体步骤如下：
步骤1.1：AP获知当前小区内STA的干扰情况，记为Ii，i＝A,B,C,E，为了获得Ii，AP可以通过与STAi(表示小区内标号为i的STA)上一次的传输过程中，记录下STAi所发送的RTS帧中携带的干扰值，比如，IA＝-65dBm，IB＝-63dBm，IC＝-80dBm，IE＝-85dBm，而且此时小区内的CCA门限为CCAth＝-62dBm，进而，AP根据各个STA的干扰值，调整小区内所有STA的CCA门限值。比如，将CCA门限值CCAth从-62dBm降低至-70dBm。之后，转入步骤1.2；
步骤1.2：AP通过抢占信道使用权，比如，AP等待信道空闲一个PIFS时长后发送信标帧，将调整后的CCAth告知小区内的所有STA。之后，转入步骤1.3；
步骤1.3：STAi根据调整后的CCAth，设置自己的CCA门限区间，即[-82dBm,-70dBm]。之后，转入步骤2；
步骤2：在每一个时隙内，STAi检测信道上的信号能量，记为Ii。若满足条件Ii≥CCAth，则STAi的退避过程挂起；否则，转入步骤3。具体步骤如下：
步骤2.1：STAi在每个时隙内检测信道上的信号能量，记为Ii。之后，转入步骤2.2；
步骤2.2：若在该时隙内满足条件Ii≥CCAth，则STAi的退避过程挂起，直至信道变为空闲(即满足条件Ii<CCAth)且维持DIFS时长后，STAi转入步骤1中重新开始执行退避过程；否则，转入步骤3；因此，在本实施例中，小区内只有站点C和站点E可以继续进行小数退避过程。
步骤3～步骤5：同实施例一中的步骤3～步骤5。其中，在步骤5.2中，STAi将所测出的干扰值Ii通过RTS帧携带并发送给D，进而D记录下RTS帧中所携带的干扰取值Ii。
实施例五
实施例五侧重描述在单信道环境下，发送节点(如STA)根据目的节点(如AP)的反馈，来调整自己的CCA门限值CCAth。在本实施中，AP通过反馈CCAth，来提升那些对区域吞吐量贡献较大的STA的信道接入优先权，从而提升网络区域吞吐量性能。如图6所示，小区内有2个STA，分别为A和B。其中，A处于本小区边缘的OBSS区域内，受到的干扰强度I较大，而B处于AP的附近，所受到的干扰强度I较小。以下将举例说明实施例五的具体操作过程。
步骤1～步骤4：同实施例一中的步骤1～步骤4，其中，在步骤1中站点A和B根据AP上一次在CTS中反馈的CCA门限(即CCAth)来查询此时自己所维持的CCA范围，即[-82dBm,CCAth]，如果此前没有收到AP反馈的CCAth值(比如首次退避过程)，则直接采用一个全网默认的CCAth值，比如-62dBm。
步骤5：当本时隙结束后，站点A和B将自己当前的退避计数器值减去各自的退避值(如
Figure PCTCN2016106907-appb-000024
和
Figure PCTCN2016106907-appb-000025
)，进而判断自己当前的退避计数值是否小于或等于0，若是，则站点A或B接入信道并传输数据，在此过程中AP反馈合适的CCAth；否则，转入步骤2继续进行退避过程。具体步骤如下：
步骤5.1：假设站点A和B当前的退避计数器的取值分别为cwA和cwB，当本时隙结束后，站点A和B将自己当前的退避计数器减去退避值(比如
Figure PCTCN2016106907-appb-000026
和
Figure PCTCN2016106907-appb-000027
)，那么有
Figure PCTCN2016106907-appb-000028
之后，转入步骤5.2；
步骤5.2：站点A和B判断自己当前的退避计数值是否小于或等于0。比如，站点A先退避完成，即满足条件cwA≤0，则站点A接入信道并发送 RTS帧。之后，转入步骤5.3；
步骤5.3：AP收到站点A发送的RTS帧后，记录下所接收到RTS的功率为Pr，进而，D根据公式CCAth＝Pr-Margin计算出CCAth，其中Margin代表一个AP所期望或最优的SINR值。之后，转入步骤5.4；
步骤5.4：AP计算出CCAth，并将其放入CTS帧发送出去。之后，转入步骤5.5；
步骤5.5：站点A根据收到的CTS帧，得出AP反馈的CCAth值，并根据CCAth的取值设置自己的CCA范围为[-82dBm,CCAth]。之后，转入步骤5.6；
步骤5.6：站点A给AP发送DATA，AP在收到DATA并等待SIFS之后，回复ACK。(注：AP也可通过接收到DATA后，根据公式CCAth＝Pr-Margin计算出CCAth并通过ACK来反馈CCAth的取值。)
实施例六
实施例六侧重描述在单信道环境下，AP根据当前本小区中所有STA所受到的干扰情况，调整每一个或每一群STA的退避权值β，0<β≤1，从而在保障小区内STA之间的接入公平性。如图7所示，本小区内有3个STA，分别为A、B和C。其中，A位于本小区边缘的OBSS区域内，而AP希望提升边缘A的接入机会。以下将举例说明实施例六的具体操作过程。
步骤1：当源节点S给目的节点D发送数据，S查询此时自己所维持的CCA范围；
步骤1.1：AP获知当前小区内STA的干扰情况，记为Ii，i＝A,B,C,E。为了获得Ii，AP可以通过上一次与STAi的传输过程中，记录下STAi所发送的RTS帧中携带的干扰值。比如，IA＝-65dBm，IB＝-63dBm，IC＝-80dBm，IE＝-85dBm。之后，转入步骤1.2；
步骤1.2：AP根据STAi所受的干扰值Ii，来适当所受干扰较大的站点的接入权值，比如提升小区边缘站点A的接入权值βA，同时适当降低所受干扰较小的站点的接入权值，比如降低站点B和站点C的接入权值βB和βC，从而提升边缘站点A的接入优先级。比如，经过AP的调整后，βA＝0.8，βB＝βC＝0.4。之后，转入步骤1.3；
步骤1.3：AP通过抢占信道使用权，比如，AP等待信道空闲PIFS时长后发送信标帧，将调整后的STAi的退避权值βi(包括βA、βB和βC)告知小区内的所有STA。之后，转入步骤2；通过执行步骤1.1～步骤1.3，AP就可根 据小区内所有STA的干扰情况，调节每一个或每一群STA的接入权值β，0<β≤1。之后，转入步骤1.4。
步骤1.4：S查询此时自己所维持的CCA门限值CCAth，该CCAth可以是全网唯一的，也可以由D在上一次与S进行数据传输过程中所反馈得到，那么每个发送节点维持的CCAth取值可能不同。之后，转入步骤1.2；
步骤1.5：S将所查询到的CCAth设置为自己的CCA区间的上限，进而得到自己的CCA区间。比如，CCAth＝-62dBm，那么S的CCA区间为[-82dBm,-62dBm]。之后，转入步骤2。
步骤2～步骤4：同实施例一中的步骤2～步骤4，通过步骤2～步骤4，STAi分别计算出各自时隙内的退避速度
Figure PCTCN2016106907-appb-000029
i＝A,B,C，之后，转入步骤5；
步骤5：STAi根据βi值调整自己的退避值并进行小数退避。进而判断自己当前的退避计数值是否小于或等于0，若是，则接入信道并传输数据；否则，转入步骤2继续进行退避过程。具体步骤如下：
步骤5.1：STAi调整自己的退避值。假设
Figure PCTCN2016106907-appb-000030
为STAi的当前退避值，那么调整后的退避值为
Figure PCTCN2016106907-appb-000031
之后，转入步骤5.2；
步骤5.2～步骤5.3：同实施例三中的步骤5.2～步骤5.3。
实施例七
实施例七侧重描述在单信道环境下，AP结合当前本小区中的STA的数量与分布情况，同时调整STA的退避权值α和β，从而在提升网络区域吞吐量性能的前提下保障小区内STA之间的接入公平性。如图7所示，本小区内有3个STA，分别为A、B和C。其中，A位于本小区边缘的OBSS区域内。AP根据当前小区中STA数量，调整所有STA的退避权值α的取值。比如，为了提升信道资源利用率，则AP可选取较大的α，比如，取α＝0.9。同时，AP为了保障小区边缘站点A的接入公平性，适当提高边缘站点A的接入权值βA，同时降低B和C的接入权值βB和βC。比如，经过调整后的β取值分别为：βA＝0.8，βB＝βC＝0.4。以下将举例说明实施例七的具体操作过程。
步骤1：当源节点S给目的节点D发送数据，S查询此时自己所维持的CCA范围；
步骤1.1：AP根据当前小区中STA数量，调整所有STA的退避权值α的取值。比如，本小区中只有3个STA，为了提升信道资源利用率，则AP可选取较大的α，比如，取α＝0.9。同时，AP为了保障小区边缘站点A的 接入公平性，适当提高边缘站点A的接入权值βA，同时降低B和C的接入权值βB和βC。比如，经过调整后的β取值分别为：βA＝0.8，βB＝βC＝0.4。之后，转入步骤1.2；
步骤1.2：AP通过抢占信道使用权，比如，AP等待信道空闲PIFS时长后发送信标帧，将调整后的所有站点的退避权值α和β(包括：βA、βB和βC)告知小区内的所有STA。之后，转入步骤1.3；通过执行步骤1.1～步骤1.2，AP就完成了对STA的退避权值α和β的调节。之后，转入步骤1.3；
步骤1.3～步骤1.4：同实施例三中的步骤1.3～步骤1.4。之后，转入步骤2；
步骤2～步骤4：同实施例一中的步骤2～步骤4，通过步骤2～步骤4，本小区内的STAi分别计算出各自时隙内的退避速度
Figure PCTCN2016106907-appb-000032
i＝A,B,C，之后，转入步骤5；
步骤5：STAi根据α和βi调整自己的退避值并进行小数退避。进而判断自己当前的退避计数值是否小于或等于0，若是，则接入信道并传输数据；否则，转入步骤1继续进行退避过程。具体步骤如下：
步骤5.1：STAi调整自己的退避值。假设
Figure PCTCN2016106907-appb-000033
为STAi的当前退避值，那么调整后的退避值为之后，转入步骤5.2；
步骤5.2～步骤5.3：同实施例三中的步骤5.2～步骤5.3。
实施例八
实施例八侧重描述在多信道环境下的小数退避过程。如图8(a)所示，小区中包括一个站点‘S’，且S与AP(即‘D’)之间的距离为d。此外，网络中共有K个信道，表示为CHk,1≤k≤K。其中，CH1为主信道，其余信道为从信道。S与D通过主信道(CH1)进行小数退避，退避成功后通过K个信道进行数据传输，如图8(b)所示。以下将举例说明实施例七的具体操作过程。
步骤1：同实施例一中的步骤1。之后，转入步骤2。
步骤2：在每一个时隙内，S检测每个信道上的信号能量，分别记为
Figure PCTCN2016106907-appb-000035
1≤k≤K。若满足条件
Figure PCTCN2016106907-appb-000036
则S的退避过程挂起；否则，转入步骤3。具体步骤如下：
步骤2.1：S在每个时隙内检测每个信道上的信号能量
Figure PCTCN2016106907-appb-000037
即S与D在信道CHk上的数据传输过程中所受到的干扰强度。之后，转入步骤2.2；
步骤2.2：若在当前时隙内满足条件
Figure PCTCN2016106907-appb-000038
则S的退避过程挂起,直至信道变为空闲(即满足条件
Figure PCTCN2016106907-appb-000039
)且维持DIFS时长后，S转入步骤1中重新开始执行退避过程。否则，转入步骤3；
步骤3：S估算信道CHk的信干噪比(Signal To Interference with Noise Ratio，SINR)，并记为SINRe,k，进而S获得每个信道上所对应的数据传输速率Rk。之后，转入步骤4。具体步骤如下：
步骤3.1：S通过公式
Figure PCTCN2016106907-appb-000040
来估算信道CHk上的信干噪比SINRe,k。其中，Pr为上一次在S与D的传输过程中，D接收到S发送的请求发送(Request-to-send，RTS)帧的接收功率。可以通过读取来自D回复的允许发送(Clear-to-send，CTS)帧获得Pr的取值。如果本次传输是第一次传输，那么S尚未获得Pr的取值，则此次退避直接采用传统的二进制指数退避方式(即ωBK＝1)，然后转入步骤5；否则，转入步骤3.2；
步骤3.2：S根据Rate-SINR分段曲线，将SINRe,k的取值进行映射来获得对应的数据传输速率Rk。之后，转入步骤4；
步骤4：S计算出本时隙内的退避速度ωBK。之后，转入步骤5。具体步骤如下：
步骤4.1：S根据公式
Figure PCTCN2016106907-appb-000041
计算多信道环境下的等效数据速率Re，其中，A表示链路的干扰区域(面积)，即S的干扰区域和D的干扰区域的并集，Rk表示第k(1≤k≤K)个信道上所对应的数据传输速率，K表示网络中的总信道个数，
Figure PCTCN2016106907-appb-000042
表征多信道环境下链路的平均数据传输速率，因而
Figure PCTCN2016106907-appb-000043
表征链路对区域吞吐量的影响。
Figure PCTCN2016106907-appb-000044
越大，则表示该链路对网络的区域吞吐量的贡献越大。为了简单，在本实施例中也可令
Figure PCTCN2016106907-appb-000045
来刻画等效数据速率Re，其中，d为S与D之间的距离。之后，转入步骤4.2；
步骤4.2：S根据公式
Figure PCTCN2016106907-appb-000046
计算出本时隙内的退避速度ωBK，也就是说，该链路对网络的区域吞吐量的贡献越大，那么退避速度ωBK就越大。之后，转入步骤5；
步骤5：当本时隙结束后，S将自己当前的退避计数器值减去ωBK。S进而判断自己当前的退避计数值是否小于或等于0，若是，则S接入并通过K个信道来传输数据；否则，转入步骤2继续进行退避过程。具体步骤如下：
步骤5.1：假设S当前的退避计数器值为cw，那么当本时隙结束后，S将自己当前的退避计数器减去ωBK，即cw＝cw-ωBK。之后，转入步骤5.2；
步骤5.2：S判断自己当前的退避计数值cw是否小于或等于0。若满足条件cw≤0，则S接入信道并通过K个信道来传输数据，进而AP分别在K个信道上回复确认帧(Acknowledgement，ACK)。待本次传输过程结束后，S记录下D所发送的CTS帧中所记录的接收功率Pr；否则，S转入步骤2继续进行退避过程。
实施例九
实施例九侧重描述在多信道环境下，引入退避条件情况下的小数退避过程。引入退避条件主要是为了限制那些对网络区域吞吐量性能贡献太小的节点接入，从而缓解网络冲突，提升网络区域吞吐量性能。如图9所示，小区中包括两个站点(即‘S’和‘E’)，其中，S与AP距离较近，而E与AP距离较远。以下将举例说明实施例九的具体操作过程。
步骤1～步骤4：同实施例八中的步骤1～步骤4。通过步骤1～步骤4，S和E分别计算出各自时隙内的退避速度ωBK和ω'BK，之后，转入步骤5；c
步骤5：在各自的时隙结束时，S和E判断各自在主信道(如CH1)上是否满足退避条件，若不满足，则在本时隙不进行退避；否则，将自己当前的退避计数器值减去ωBK，进而，S和E判断各自当前的退避计数值是否小于或等于0，若是，则S接入并通过K个信道来传输数据；否则，转入步骤2继续进行退避过程。具体步骤如下：
步骤5.1：当本时隙结束时，S判断是否满足主信道上的退避条件。假设
Figure PCTCN2016106907-appb-000047
为退避门限值，比如，
Figure PCTCN2016106907-appb-000048
若满足退避条件
Figure PCTCN2016106907-appb-000049
则可正常在主信道上进行小数退避过程，否则，S在本时隙内不进行退避(即ωBK＝0)。之后，转入步骤5.2；与此同时，E也进行相同的操作。在本实施例中，假设S和E在步骤4中计算出的退避值分别为ωBK＝1.2和ω'BK＝0.6，由于
Figure PCTCN2016106907-appb-000050
且
Figure PCTCN2016106907-appb-000051
因此，经过退避条件的判断后，S在本时隙内可通过主信道进行正常的小数退避，而E在本时隙内无法退避，即ω'BK＝0。
步骤5.2：假设S当前的退避计数器值为cw，E当前的退避计数器值为cw'，那么当本时隙结束后，S将自己当前的退避计数器减去ωBK，即cw＝cw-ωBK。 与此同时，发送E也进行相同的操作，即E将自己当前的退避计数器减去ω'BK，有cw'＝cw'-ω'BK＝cw'。之后，转入步骤5.3；
步骤5.3：S与E判断各自当前的退避计数值(即cw和cw')是否小于或等于0。若是，则接入信道并通过K个信道来传输数据，进而AP分别在K个信道上回复ACK确认帧。待本次传输过程结束后，S记录下D所发送的CTS帧中所记录的接收功率Pr；否则，S转入步骤2继续进行退避过程。同时，E也执行相同的操作。
仿真中统计了网络的区域吞吐量，并与采用二进制指数退避方法的IEEE 802.11DCF(即基线版本)进行了对比。仿真场景设置如下：每个小区各包含5个上行STA、5个下行STA；所有STA均为饱和业务，且业务类型是视频流业务；CCA门限值为CCAth＝-62dBm。即，CCA范围是[-82dBm,-62dBm]。通过仿真结果图10可以看出，本发明的区域吞吐量性能远高于IEEE 802.11DCF，并且随着小区个数的增加，本发明所获得的区域吞吐量性能增益越明显。

Claims (4)

  1. 一种基于小数退避的信道接入方法，其特征在于包括下述步骤：
    步骤1，当源节点S给目的节点D发送数据，源节点S查询此时自己所维持的CCA范围，即[-82dBm,CCAth]，CCAth是指CCA门限值，也就是CCA范围的上限值，且CCAth>-82dBm，之后，转入步骤2；
    步骤2，在每一个时隙内，源节点S实时检测信道上的信号能量I，若满足条件I≥CCAth，则源节点S的退避过程挂起，并继续检测信道上的信号能量I；否则，转入步骤3；
    步骤3，源节点S估算信干噪比SINRe，根据SINRe的取值在速率和信干噪比的分段曲线Rate-SINR中的映射，获得对应的数据传输速率R，转入步骤4；
    步骤4，源节点S根据数据传输速率R计算出本时隙内的退避速度ωBK，转入步骤5；
    步骤5：当本时隙结束后，源节点S将自己当前的退避计数器值减去ωBK，再判断减去ωBK后的退避计数器值是否小于或等于0，若是，则源节点S接入信道并传输数据；否则，转入步骤2继续进行退避过程。
  2. 根据权利要求1所述的基于小数退避的信道接入方法，其特征在于：所述的CCAth提前设定，或由目的节点D在上一时隙与源节点S进行数据传输过程中反馈得到，
    Figure PCTCN2016106907-appb-100001
    其中，Pr为目的节点D接收到源节点S发送的请求发送帧RTS的接收功率，SINRth表示最大可以采用的调制编码方式所对应的信噪比。
  3. 根据权利要求1所述的基于小数退避的信道接入方法，其特征在于：所述的步骤3中，信干噪比SINRe＝Pr-I；如果当前时隙是第一个传输时隙，则ωBK＝1，然后直接转入步骤5。
  4. 根据权利要求1所述的基于小数退避的信道接入方法，其特征在于：所述的步骤4中，源节点S计算等效数据速率
    Figure PCTCN2016106907-appb-100002
    其中，A表示链路的干扰面积，即发送节点S的干扰区域面积与接收节点D的干扰区域面积的并集；根据公式
    Figure PCTCN2016106907-appb-100003
    源节点S计算出本时隙内的退避速度ωBK，其中，R*代表区域吞吐量，与之所对应的退避速度为
    Figure PCTCN2016106907-appb-100004
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