WO2017033790A1 - 無線通信システムおよび無線通信方法 - Google Patents
無線通信システムおよび無線通信方法 Download PDFInfo
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- WO2017033790A1 WO2017033790A1 PCT/JP2016/073839 JP2016073839W WO2017033790A1 WO 2017033790 A1 WO2017033790 A1 WO 2017033790A1 JP 2016073839 W JP2016073839 W JP 2016073839W WO 2017033790 A1 WO2017033790 A1 WO 2017033790A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W28/00—Network traffic management; Network resource management
- H04W28/16—Central resource management; Negotiation of resources or communication parameters, e.g. negotiating bandwidth or QoS [Quality of Service]
- H04W28/18—Negotiating wireless communication parameters
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W48/00—Access restriction; Network selection; Access point selection
- H04W48/02—Access restriction performed under specific conditions
- H04W48/06—Access restriction performed under specific conditions based on traffic conditions
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/18—TPC being performed according to specific parameters
- H04W52/24—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters
- H04W52/243—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters taking into account interferences
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- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W72/00—Local resource management
- H04W72/50—Allocation or scheduling criteria for wireless resources
- H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
- H04W72/541—Allocation or scheduling criteria for wireless resources based on quality criteria using the level of interference
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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
- H04W74/0808—Non-scheduled access, e.g. ALOHA using carrier sensing, e.g. carrier sense multiple access [CSMA]
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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
- H04W74/0808—Non-scheduled access, e.g. ALOHA using carrier sensing, e.g. carrier sense multiple access [CSMA]
- H04W74/0816—Non-scheduled access, e.g. ALOHA using carrier sensing, e.g. carrier sense multiple access [CSMA] with collision avoidance
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
- H04L1/0002—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate
- H04L1/0003—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate by switching between different modulation schemes
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- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W84/00—Network topologies
- H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
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- H04W84/12—WLAN [Wireless Local Area Networks]
Definitions
- the present invention relates to a wireless communication system and a wireless communication method for improving throughput reduction caused by CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) control of each communication station in a dense environment of a wireless LAN (Local Area Network). .
- CSMA / CA Carrier Sense Multiple Access with Collision Avoidance
- the IEEE802.11 standard wireless LAN includes an IEEE802.11b / g / n standard wireless LAN using a 2.4 GHz band and an IEEE802.11a / n / ac standard wireless LAN using a 5 GHz band.
- BSS Basic Service Set
- a plurality of BSSs use the same channel.
- the throughput of the BSS and the entire system is reduced due to the influence of interference between BSSs using the same channel. Therefore, in the wireless LAN, autonomous distributed access control that uses CSMA / CA control to transmit data only when a channel is free due to carrier sense is used.
- a CCA (Clear Channel Assessment) threshold value for determining idle or busy of the channel usage status using the received signal strength RSSI is set.
- DSC Dynamic Sensitivity Control
- FIG. 8 (a) shows a state in which each AP is included in the carrier sense range according to the CCA thresholds of AP1 and AP2.
- STA1 of BSS1 and STA2 of BSS2 are each outside the other carrier sense range, BSS1 can transmit from AP1 to STA1 during transmission from AP2 to STA2.
- AP1 determines that the channel state is busy and waits for transmission to STA1. This is the exposed terminal problem. Therefore, as shown in FIG. 8 (b) IV, if DS1 controls the CCA threshold value and narrows the corresponding carrier sense range by DSC, AP1 can be transmitted even when AP2 is transmitting, and the system throughput is improved. To do.
- AP1 can be transmitted by dynamic CCA threshold control
- BSS identification is performed in the preamble portion of the wireless LAN frame, and the wireless LAN frame of the own BSS is distinguished from other wireless signals.
- FIG. 9 (a) IV when the wireless LAN frame transmitted from the STA 1-2 of the own BSS 1 is detected in AP1, the wireless LAN frame is received and the transmission is waited.
- DS1 controls the CCA threshold to enable transmission from AP1 to STA1-1.
- the method for determining the CCA threshold is not specifically established in the situation of an exposed terminal or in the situation of receiving a wireless LAN frame whose BSS identifier does not match. Therefore, when the CCA threshold is not controlled to an appropriate value, the throughput may be deteriorated even if dynamic control is performed. For example, if the control is performed so that the CCA threshold is excessively increased, transmission starts even though high interference power is received, and transmission eventually fails.
- MCS Modulation and Coding Scheme
- SINR Signal to Interference and Noise power Ratio
- the present invention selects an optimal CCA threshold and MCS when the CCA threshold can be dynamically controlled by DSC technology, and efficiently acquires transmission opportunities in a wireless LAN dense environment, thereby improving system throughput. It is an object to provide a system and a wireless communication method.
- the transmitting terminal determines the CCA threshold according to the interference power value of the BSS considered as an interference source, calculates the SINR at the destination terminal according to the interference power value, and the SINR And a control means for determining MCS, which is a combination of a modulation scheme and a coding rate, and performing access control by CSMA / CA.
- control means of the transmitting terminal is configured to determine the MCS by assuming the SINR at the destination terminal using the interference power value observed at the transmitting terminal.
- the control means of the transmitting terminal determines the MCS, determines the minimum SINR of the destination terminal corresponding to the determined MCS, and is acceptable for achieving the minimum SINR at the destination terminal
- the CCA threshold is determined by estimating the distance between the transmitting terminal and the interference source.
- the destination terminal includes means for notifying the transmission terminal of interference power information including an interference power value observed by itself, and the control means of the transmission terminal includes the interference power notified from the destination terminal.
- This is a configuration for predicting the SINR at the destination terminal using the value and determining the MCS.
- the control means of the transmitting terminal sets initial values of the MCS and the CCA threshold, and sequentially updates the MCS and the CCA threshold according to the interference situation obtained by observation at regular intervals. It is the structure to perform.
- the control means of the transmitting terminal calculates the average SINR from the interference situation observed by the destination terminal at regular time intervals, updates the MCS from the average SINR, and the percentage of busy time observed by the transmitting terminal at regular time intervals Is calculated, and the CCA threshold is changed according to the calculation result of the evaluation function.
- the control means of the transmitting terminal detects the BSS identifier included in the received frame, and excludes it as busy time if it matches the BSS identifier of its own BSS.
- the transmitting terminal determines a CCA threshold according to the interference power value of the BSS considered as an interference source, calculates the SINR at the destination terminal according to the interference power value, and A step of determining MCS which is a combination of a modulation scheme and a coding rate corresponding to SINR, and setting the determined CCA threshold and MCS to perform access control by CSMA / CA.
- the present invention can dynamically control the CCA threshold according to the interference power value and can select the MCS according to the SINR at the destination terminal, it can efficiently acquire a transmission opportunity in a wireless LAN dense environment, Throughput can be improved.
- FIG. It is a figure which shows the structural example of the radio
- FIG. It is a flowchart which shows the example of a process sequence of the determination method 3 of a CCA threshold value and MCS. It is a flowchart which shows the example of a process sequence of the determination method 4 of a CCA threshold value and MCS.
- FIG. 1 shows a configuration example of a wireless communication system of the present invention.
- AP1 and STA1-1 and STA1-2 constitute BSS1
- AP2 and STA2-1 constitute BSS2.
- a dashed circle centered on AP1 indicates a carrier sense range corresponding to the CCA threshold of AP1.
- AP1 and STA1-1 are subject to interference from AP2 and STA2-1 of BSS2 in communication, and AP1 sets the CCA threshold and MCS. Indicates the situation to be determined. That is, the transmission terminal is AP1, the destination terminal is STA1-1, and AP2 and STA2-1 are included in the carrier sense range according to the CCA threshold before control of AP1. Therefore, an interference signal accompanying communication between AP2 and STA2-1 is detected in AP1, and transmission is disabled by CSAM / CA control.
- the dotted arrows in the figure indicate interference signals.
- the CCA threshold value and MCS determination method 1 in the transmission terminal determines the CCA threshold value from the interference power information observed at the transmission terminal, assumes that the interference status between the transmission terminal and the destination terminal is equivalent, and determines the destination from the interference power information of the transmission terminal. This is a procedure for determining the MCS assuming the SINR at the time of reception by the terminal.
- FIG. 2 shows a processing procedure example of CCA threshold and MCS determination method 1.
- AP1 shown in FIG. 1 is a transmission terminal and STA1-1 is a destination terminal.
- the transmitting terminal AP1 observes beacon power values of all BSSs other than its own BSS as interference power (S11).
- the transmitting terminal AP1 also observes the received power value Ps of the frame transmitted from the destination terminal STA1-1 and uses it for calculation of SINR assumed in the STA1-1 described later.
- the transmission terminal STA1-1 when STA1-1 is a transmission terminal and AP1 is a destination terminal, the transmission terminal STA1-1 observes the beacon power values of all BSSs including its own BSS, and uses the beacon power values of other BSSs as interference power.
- the received power value Ps of the beacon of the own BSS transmitted from the destination terminal AP1 is used for the SINR calculation assumed in the destination terminal AP1.
- the transmitting terminal AP1 calculates the sum ⁇ Pobss of the BSS beacon power values considered as interference sources among the beacon power values of all the BSSs observed in step S11, and determines the CCA threshold so as to exceed the value. (S12).
- AP1 and AP2 can be transmitted simultaneously in the example shown in FIG.
- the transmitting terminal AP1 selects a BSS to be considered as an interference source based on the beacon power value.
- the transmitting terminal AP1 has a large interference power that limits the number of BSSs or cannot cope with even a low MCS.
- the BCA that is present may be excluded so that the CCA threshold does not increase more than necessary.
- SINR Ps / ⁇ Pobss
- Ps is the received power value of the frame transmitted from the destination terminal STA1-1
- ⁇ Pobss is the sum of the BSS beacon power values considered as interference sources.
- the transmitting terminal AP1 determines the optimum MCS from the SINR of the destination terminal STA1-1 assumed in step S13 (S14). For example, the relationship between the optimum MCS and SINR value is tabulated in advance, and the optimum MCS is selected from the SINR. Alternatively, the relationship of BER (Bit Error Rate) or PER (Packet Error Rate) with respect to SINR of each MCS is tabulated in advance, and the BER value or PER value predicted from SINR is lower than a preset threshold value. The largest MCS is selected.
- steps S12 to S14 CCA threshold control and transmission power control (TPC) are linked at the transmission terminal, and for example, when the transmission power is decreased when the CCA threshold is increased, the observed reception power value Ps is adjusted. Then, the SINR assumed at the destination terminal may be corrected, and the MCS corresponding to the SINR may be determined.
- TPC transmission power control
- the transmission terminal may change the process in step S13 as follows.
- the transmitting terminal obtains the current optimum MCS based on the link quality information, and further calculates the current SINR assumed by the destination terminal.
- the transmitting terminal may calculate the expected SINR at the time of reception at the destination terminal based on the assumed current SINR and the interference power information observed by itself in steps S11 and S12.
- the CCA threshold value and MCS determination method 2 in the transmitting terminal determines the MCS first, determines the minimum SINR below a certain BER and PER value at the destination terminal from the determined MCS, and interferes with the transmitting terminal that can tolerate the minimum SINR. This is a procedure for determining the CCA threshold by estimating the distance of the source.
- FIG. 3 shows a processing procedure example of CCA threshold value and MCS determination method 2.
- TX shown in FIG. 4 is described as a transmission terminal, and RX is described as a destination terminal.
- the determination method 2 first, the MCS of the transmission terminal TX is determined (S21). Next, the minimum SINR required for the destination terminal RX to receive with the determined MCS is calculated (S22). Next, the CCA threshold of the transmission terminal TX is determined by estimating the distance between the transmission terminal TX and the interference source from the interference power that can be allowed for the destination terminal RX to achieve the minimum SINR (S23).
- step S23 the process of step S23 is as follows in FIG.
- the transmission terminal TX estimates the distance D from the destination terminal RX from the received power value of the frame transmitted from the destination terminal RX.
- the distance D ′ between the interference source and the destination terminal RX is estimated from the interference power that can be allowed to achieve the minimum SINR calculated in step S22.
- a CCA threshold corresponding to the carrier sense range corresponding to the distance D + D ′ between the transmission terminal TX and the interference source is determined.
- the processing for calculating the SINR of the destination terminal RX may be changed as follows. Assuming that the interference power of the destination terminal RX is the same as the interference power of the transmission terminal TX, the CNR threshold is determined by calculating the SINR assumed by the destination terminal RX based on the interference power observed by the transmission terminal TX. Good. Alternatively, interference power observed at the destination terminal RX may be fed back to the transmission terminal TX, and the transmission terminal TX may calculate the SINR assumed at the destination terminal RX to determine the CCA threshold.
- the interference power observed at the destination terminal RX is adjusted to adjust the interference power.
- the CNR threshold corresponding to the SINR may be determined by correcting the assumed SINR.
- the CCA threshold and MCS determination method 3 at the transmitting terminal determines the CCA threshold from the interference power information observed at the transmitting terminal, predicts the SINR at the time of reception of the destination terminal from the interference power information observed at the destination terminal, and calculates the MCS. It is a procedure to decide.
- FIG. 5 shows a processing procedure example of the CCA threshold and MCS determination method 3.
- AP1 shown in FIG. 1 is a transmission terminal and STA1-1 is a destination terminal.
- the destination terminal STA1-1 observes the beacon power value of all BSSs as interference power, and sums ⁇ Pobss and BSSID information of the BSS beacon power values considered as interference sources and the beacon received from the transmitting terminal AP1.
- the received power value Ps is reported to the transmitting terminal AP1 as interference power information (S31).
- the destination terminal STA1-1 selects a BSS to be considered as an interference source based on the interference power information.
- the destination terminal STA1-1 limits the number of BSSs or has a large interference power that cannot be handled even with a low MCS. BSSs that have become may be excluded.
- the destination terminal STA1-1 may respond the observation result in response to the interference power information collection request from the transmission terminal AP1, for example, the beacon interval period or the observation result at regular intervals of an integral multiple thereof. You may report it.
- the transmitting terminal AP1 that has received the report from the destination terminal STA1-1 observes the beacon power value of the BSS that is considered as the interference source reported in the total BSS or interference power information as interference power (S32).
- the transmitting terminal AP1 calculates the sum ⁇ Pobss of the BSS beacon power values considered as the interference sources observed in step S32, and determines the CCA threshold so as to exceed the value (S33).
- SINR Ps / ⁇ Pobss Since Ps and ⁇ Pobss used for SINR prediction are beacon power values observed at the destination terminal STA1-1, they are more accurate than SINR assumed from the beacon power values observed at the transmission terminal AP1 as in the determination method 1. SINR can be calculated.
- the transmitting terminal AP1 determines the optimum MCS from the predicted SINR of the destination terminal STA1-1 (S35). For example, the relationship between the optimum MCS and SINR value is tabulated in advance, and the optimum MCS is selected from the SINR. Alternatively, the relationship of BER or PER with respect to SINR of each MCS is tabulated in advance, and the largest MCS is selected from among MCSs in which the BER value or PER value predicted from SINR falls below a preset threshold value.
- the received power value of the destination terminal observed and reported in step S31 PNR may be adjusted to predict SINR, and MCS corresponding to SINR may be determined.
- the transmission terminal may change the process in step S34 as follows.
- the transmitting terminal obtains the current optimum MCS based on the link quality information, and further calculates the current SINR assumed by the destination terminal.
- the transmitting terminal may predict the SINR at the time of reception of the destination terminal based on the assumed current SINR and the interference power information of the destination terminal observed and reported in step S31.
- the CCA threshold and MCS determination method 4 at the transmitting terminal sets initial values of the MCS and the CCA threshold at the transmitting terminal, calculates an evaluation function from the interference state observed at regular intervals, selects the MCS, and sequentially updates the CCA threshold. It is a procedure to perform.
- FIG. 6 shows a processing procedure example of CCA threshold value and MCS determination method 4.
- AP1 shown in FIG. 1 is a transmission terminal and STA1-1 is a destination terminal.
- the initial values of the MCS and CCA thresholds are set at the transmitting terminal AP1 (S41), the destination terminal STA1-1 observes the interference situation at regular intervals t1 (S42), and the average SINR of the data frame is calculated.
- the optimum MCS is determined from the average SINR (S44). For example, the relationship between the optimum MCS and SINR value is tabulated in advance, and the optimum MCS is selected from the SINR. Alternatively, the relationship of BER or PER with respect to SINR of each MCS is tabulated in advance, and the largest MCS is selected from among MCSs in which the BER value or PER value predicted from SINR falls below a preset threshold value.
- the transmitting terminal AP1 observes the busy time and the data frame time at a constant time t2 (S45), and calculates an evaluation function f (p) for CCA threshold evaluation (S46).
- an evaluation function f (p) is shown.
- f (p) L F / (T B + T BO + T F ) L F : Average number of bits in one frame T B : Average busy time observed until transmission of one frame, except for busy period due to own BSS signal (BSS identifier of own BSS and BSS threshold in frame match) T BO : Average of DIFS + backoff time required until one frame transmission TF : Average data frame time length of one frame p: CCA threshold
- the CCA threshold is changed in the same direction as the previous time (S48). Change in the opposite direction to the previous time (S49). Since there is no previous evaluation value for the evaluation of the initial values of the MCS and CCA threshold values, the CCA threshold value is changed to an arbitrary direction, for example.
- the number of determinations based on the above evaluation function is incremented (S50), and the processing from step S42 is repeated until the specified number of times is reached (S51).
- FIG. 7 shows a configuration example of the wireless communication apparatus of the present invention.
- the transmission terminal and the destination terminal have a common configuration.
- the wireless communication unit 11 transmits and receives wireless signals via the antenna 12.
- the information recording unit 13 and the information management unit 14 receive the received power value of the frame transmitted from the destination terminal, the received power value of the frame transmitted from the terminal that may cause interference with other BSS, the transmitted power value of the wireless LAN terminal, and the antenna gain. Records and manages numerical values necessary for calculating an expected SINR such as a value.
- an optimum MCS with respect to SINR when MCS is determined using Goodput or PER data is provided as a table.
- the busy time when the busy time is measured is recorded and managed.
- the calculation unit 15 calculates an assumed value or predicted value of SINR or calculates an evaluation function from information recorded and managed by the information recording unit 13 and the information management unit 14.
- the time management unit 16 measures busy time caused by signals other than the received signal of the own BSS.
- the control unit 17 performs information input and output processing according to the processing for each step of each of the determination methods 1 to 4 described above.
- a function such as notification of interference power information collection timing is added.
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Abstract
Description
図1において、AP1とSTA1-1,STA1-2はBSS1を構成し、AP2とSTA2-1はBSS2を構成する。AP1を中心とする破線の円は、AP1のCCA閾値に応じたキャリアセンス範囲を示す。
送信端末におけるCCA閾値およびMCSの決定方法1は、送信端末で観測する干渉電力情報からCCA閾値を決定し、送信端末と宛先端末の干渉状況を同等と想定し、送信端末の干渉電力情報から宛先端末の受信時のSINRを想定してMCSを決定する手順である。
図2において、送信端末AP1は、干渉電力として自BSS以外の全BSSのビーコン電力値を観測する(S11)。このとき送信端末AP1は、宛先端末STA1-1から送信されたフレームの受信電力値Ps も併せて観測し、後述するSTA1-1で想定されるSINRの計算に用いる。ただし、STA1-1を送信端末とし、AP1を宛先端末とした場合は、送信端末STA1-1は自BSSを含む全BSSのビーコン電力値を観測し、他BSSのビーコン電力値を干渉電力とし、宛先端末AP1から送信された自BSSのビーコンの受信電力値Ps を宛先端末AP1で想定するSINRの計算に用いる。
SINR=Ps /ΣPobss
ここで、Ps は、宛先端末STA1-1から送信されたフレームの受信電力値であり、ΣPobssは、干渉源として考慮するBSSのビーコン電力値の総和である。
送信端末におけるCCA閾値およびMCSの決定方法2は、先にMCSを決定し、決定したMCSから宛先端末で一定のBER,PER値を下回る最小SINRを決定し、最小SINRを許容できる送信端末と干渉源の距離を推定してCCA閾値を決定する手順である。
図3において、決定方法2では、まず送信端末TXのMCSを決定する(S21)。次に、決定したMCSで宛先端末RXが受信するために必要となる最小SINRを算出する(S22)。次に、宛先端末RXが最小SINRを達成するために許容できる干渉電力から、送信端末TXと干渉源の距離を推定して送信端末TXのCCA閾値を決定する(S23)。
SINRmin =Pt-Pi+Gt-Gi+L(D) -L(D')
なお、Pt=Pi、Gt=Giと仮定すると、
SINRmin =L(D)-L(D')
となる。
送信端末におけるCCA閾値およびMCSの決定方法3は、送信端末で観測する干渉電力情報からCCA閾値を決定し、宛先端末で観測する干渉電力情報から宛先端末の受信時のSINRを予測してMCSを決定する手順である。
図5において、宛先端末STA1-1は、干渉電力として全BSSのビーコン電力値を観測し、干渉源として考慮するBSSのビーコン電力値の総和ΣPobssおよびBSSID情報と、送信端末AP1から受信したビーコンの受信電力値Ps を干渉電力情報として送信端末AP1へ報告する(S31)。なお、宛先端末STA1-1は、干渉電力情報をもとに干渉源として考慮するBSSを選定することになるが、例えばBSSの数を制限したり、低MCSでも対応できないような大きな干渉電力となっているBSSを除外してもよい。また、宛先端末STA1-1は、送信端末AP1からの干渉電力情報収集要求に応じて観測した結果を応答してもよいし、例えばビーコンインターバル期間またはその整数倍の一定期間ごとに観測した結果を報告してもよい。
SINR=Ps /ΣPobss
なお、SINRの予測に用いるPs ,ΣPobssは、宛先端末STA1-1で観測したビーコン電力値であるので、決定方法1のように送信端末AP1で観測したビーコン電力値から想定されるSINRより正確なSINRを算出することができる。
送信端末におけるCCA閾値およびMCSの決定方法4は、送信端末でMCSとCCA閾値の初期値を設定し、一定時間ごとに観測する干渉状況から評価関数を計算し、MCS選定とCCA閾値の逐次更新を行う手順である。
図6において、送信端末AP1でMCSとCCA閾値の初期値を設定し(S41)、宛先端末STA1-1で干渉状況を一定時間t1ごとに観測し(S42)、データフレームの平均SINRを計算し(S43)、平均SINRから最適なMCSを決定する(S44)。例えば、予め最適MCSとSINR値の関係をテーブル化しておき、SINRから最適なMCSを選択する。あるいは、予め各MCSのSINRに対するBERまたはPERの関係をテーブル化しておき、SINRから予測されるBER値またはPER値が事前に設定された閾値を下回るMCSの中で最大のMCSを選択する。
LF :1フレームの平均ビット数
TB :1フレーム送信までに観測した平均ビジー時間、ただし、自BSS信号(自BSSのBSS識別子とフレーム内のBSS閾値が一致)によるビジー期間は除く
TBO:1フレーム送信までに必要なDIFS+バックオフ時間の平均
TF :1フレームの平均データフレーム時間長
p :CCA閾値
図7において、無線通信部11は、アンテナ12を介して無線信号を送受信する。情報記録部13および情報管理部14は、宛先端末から送信されるフレームの受信電力値、他BSSの干渉となりうる端末から送信されるフレームの受信電力値、無線LAN端末の送信電力値とアンテナゲイン値など予想されるSINRを算出するときに必要な数値を記録、管理する。また、Goodput やPERデータを用いてMCSを決定する場合のSINRに対する最適MCSをテーブルとしてもつ。さらに、ビジー時間を計測する場合のビジー時間も記録し、管理する。
時間管理部16は、自BSSの受信信号以外の信号に起因するビジー時間を計測する。
STA 無線端末
11 無線通信部
12 アンテナ
13 情報記録部
14 情報管理部
15 計算部
16 時間管理部
17 制御部
Claims (8)
- CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance)によるアクセス制御により送信端末から宛先端末に送信するBSS(Basic Service Set)が隣接して複数存在し、同一チャネルを使用する各BSS間で干渉電力値を考慮したCCA閾値を制御して無線通信を行う無線通信システムにおいて、
前記送信端末は、干渉源として考慮するBSSの前記干渉電力値に応じて前記CCA閾値を決定するとともに、前記干渉電力値に応じて前記宛先端末におけるSINR(Signal to Interference and Noise power Ratio)を算出し、当該SINRに対応して変調方式と符号化率の組み合わせであるMCS(Modulation and Coding Scheme)を決定し、前記CSMA/CAによるアクセス制御を行う制御手段を備えた
ことを特徴とする無線通信システム。 - 請求項1に記載の無線通信システムにおいて、
前記送信端末の制御手段は、前記送信端末で観測される前記干渉電力値を用いて前記宛先端末における前記SINRを想定し、前記MCSを決定する構成である
ことを特徴とする無線通信システム。 - 請求項1に記載の無線通信システムにおいて、
前記送信端末の制御手段は、前記MCSを決定し、決定したMCSに対応する前記宛先端末の最小SINRを決定し、前記宛先端末で当該最小SINRを達成するために許容できる前記送信端末と干渉源の距離を推定して前記CCA閾値を決定する構成である
ことを特徴とする無線通信システム。 - 請求項1に記載の無線通信システムにおいて、
前記宛先端末は、自ら観測する干渉電力値を含む干渉電力情報を前記送信端末に通知する手段を備え、
前記送信端末の制御手段は、前記宛先端末から通知された前記干渉電力値を用いて前記宛先端末における前記SINRを予測し、前記MCSを決定する構成である
ことを特徴とする無線通信システム。 - 請求項1に記載の無線通信システムにおいて、
前記送信端末の制御手段は、前記MCSと前記CCA閾値の初期値を設定し、一定時間ごとに観測して得られる干渉状況に応じて前記MCSと前記CCA閾値の逐次更新を行う構成である
ことを特徴とする無線通信システム。 - 請求項5に記載の無線通信システムにおいて、
前記送信端末の制御手段は、前記宛先端末が一定時間ごとに観測した前記干渉状況から平均SINRを計算し、当該平均SINRから前記MCSの更新を行うとともに、前記送信端末が一定時間ごとに観測したビジー時間の割合を示す評価関数を計算し、当該評価関数の計算結果に応じて前記CCA閾値を変更する構成である
ことを特徴とする無線通信システム。 - 請求項6に記載の無線通信システムにおいて、
前記送信端末の制御手段は、受信フレームに含まれるBSS識別子を検出し、自BSSのBSS識別子と一致した場合は、前記ビジー時間として除外する構成である
ことを特徴とする無線通信システム。 - CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance)によるアクセス制御により送信端末から宛先端末に送信するBSS(Basic Service Set)が隣接して複数存在し、同一チャネルを使用する各BSS間で干渉電力値を考慮したCCA閾値を制御して無線通信を行う無線通信方法において、
前記送信端末は、
干渉源として考慮するBSSの前記干渉電力値に応じて前記CCA閾値を決定するステップと、
前記干渉電力値に応じて前記宛先端末におけるSINR(Signal to Interference and Noise power Ratio)を算出し、当該SINRに対応して変調方式と符号化率の組み合わせであるMCS(Modulation and Coding Scheme)を決定するステップと
を有し、前記決定したCCA閾値とMCSを設定して前記CSMA/CAによるアクセス制御を行う
ことを特徴とする無線通信方法。
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