JP6552994B2 - Wireless communication system, wireless communication method and central control station - Google Patents

Description

  The present invention relates to a wireless communication system, a wireless communication method, and a wireless communication system that improve a reduction in throughput caused by CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) control of each communication station in a dense environment of a wireless local area network (LAN). The central control station.

  In recent years, with the spread of portable and high-performance wireless terminals such as laptop computers and smartphones, wireless LANs based on the IEEE 802.11 standard have been widely used not only in businesses and public spaces, but also in general homes. The IEEE802.11 standard wireless LAN includes an IEEE802.11b / g / n standard wireless LAN using the 2.4 GHz band and an IEEE802.11a / n / ac standard wireless LAN using the 5 GHz band.

  In the wireless LAN of IEEE802.11b standard or IEEE802.11g standard, 13 channels are prepared at intervals of 5 MHz between 2400 MHz and 2483.5 MHz. However, when using multiple channels at the same place, it is possible to simultaneously use up to three channels or even up to four channels at the same time by using channels so that spectra do not overlap to avoid interference.

  In the wireless LAN of IEEE802.11a standard, in Japan, a total of 19 channels of 8 channels and 11 channels that do not overlap each other are defined between 5170 MHz and 5330 MHz and between 5490 MHz and 5710 MHz. In the IEEE 802.11a standard, the bandwidth per channel is fixed at 20 MHz.

  The maximum transmission rate of the wireless LAN is 11 Mbps in the case of the IEEE 802.11b standard, and 54 Mbps in the case of the IEEE 802.11a standard and the IEEE 802.11g standard. However, the transmission rate here is the transmission rate on the physical layer. Actually, since the transmission efficiency at the MAC (Medium Access Control) layer is about 50 to 70%, the upper limit of the actual throughput is about 5 Mbps in the IEEE 802.11b standard, and 30 Mbps in the IEEE 802.11a standard or the IEEE 802.11g standard Degree. In addition, the transmission rate further decreases as the number of communication stations that attempt to transmit information increases.

  On the other hand, in wired LANs, the introduction of Ethernet (registered trademark) 100Base-T interface and the spread of FTTH (Fiber to the home) using optical fiber in each home has led to the provision of high-speed lines of 100 Mbps to 1 Gbps. It is widespread, and further increase in transmission speed is required even in wireless LAN.

  Therefore, in the IEEE 802.11n standard, which was standardized in 2009, the channel bandwidth, which has been fixed at 20 MHz, is expanded to 40 MHz at the maximum, and in addition, MIMO (Multiple input multiple output) technology The introduction was decided. If transmission and reception are performed by applying all the functions defined in the IEEE802.11n standard, it is possible to realize a communication speed of up to 600 Mbps in the physical layer.

  Furthermore, the IEEE 802.11ac standard, which has been standardized in 2013, extends the channel bandwidth to 80 MHz and up to 160 MHz, and multi-user MIMO (MU) using Space Division Multiple Access (SDMA). The introduction of a transmission method has been decided (for example, see Non-Patent Document 1). When transmission and reception are performed by applying all the functions defined in the IEEE 802.11ac standard, the physical layer can realize a communication speed of up to about 6.9 Gbps.

  However, when the channel bandwidth is widened to 40 MHz, 80 MHz, and 160 MHz in the IEEE802.11ac standard, the number of channels that can be used simultaneously in the same place in the 5 GHz band is 19 channels with a channel bandwidth of 20 MHz. There are fewer channels and 2 channels. That is, as the channel bandwidth increases, the number of usable channels decreases.

  Thus, depending on the channel bandwidth used for communication, the number of channels that can be used simultaneously at the same location is three in the 2.4 GHz band wireless LAN, and two, four, nine, or 19 channels in the 5 GHz band wireless LAN. Therefore, when actually introducing a wireless LAN, it is necessary for the wireless base station (access point (AP)) to select a channel to be used in its own cell (BSS: Basic Service Set).

  Here, in a dense environment of a wireless LAN where the number of BSSs is larger than the number of usable channels, a plurality of BSSs use the same channel (OBSS: Overlapping BSS). In that case, the interference between BSSs using the same channel will reduce the throughput of the BSS and the entire system. Therefore, in the wireless LAN, autonomous distributed access control is used, which uses CSMA / CA to transmit data only when the channel is open due to carrier sense.

  Specifically, the communication station that has generated a transmission request first performs carrier sense for a predetermined sensing period (DIFS: Distributed Inter-Frame Space) to monitor the state of the wireless medium, and during this time, transmission by another communication station is performed. If no signal is present, random backoff is performed. The communication station continues to perform carrier sensing during the random backoff period, but during this time, if there is no transmission signal from another communication station, it acquires the channel Opportunity (TXOP). A communication station (TXOP Holder) that has obtained the right to use the channel can transmit data to other communication stations in the same BSS and can receive data from those communication stations. When performing such CSMA / CA control, in a dense LAN environment using the same channel, the frequency of the channel becoming busy due to carrier sense increases, so the transmission opportunity (the opportunity to obtain the right to use the channel) decreases. And throughput will be reduced. Therefore, it is important to monitor the surrounding environment and select an appropriate channel.

  Although the channel selection method in the wireless base station is not defined in the IEEE 802.11 standard, each vendor adopts a unique method, but the channel with the least interference power is the most common channel selection method. There is a method to select in an autonomous distributed manner. The radio base station performs carrier sensing for all channels for a certain period, selects a channel with the smallest interference power, and transmits / receives data to / from a terminal device under the selected channel. The interference power is a level of a signal received from a neighboring BSS or another system, and can be measured by, for example, a received signal strength indicator (RSSI).

  Here, when carrier sense is performed in the radio base station, a CCA (Clear Channel Assessment) threshold is set that determines the channel usage status using received signal strength indicator (RSSI). For example, in the IEEE 802.11 standard, two CCA thresholds are defined as shown in FIG. One is a CCA-SD (Signal Detection) threshold used when the radio base station AP1 can detect a preamble of a radio frame received by carrier sensing and received, and the other is that the AP1 performs carrier sensing and receives It is a CCA-ED (Energy Detection) threshold used when a preamble of a radio frame can not be detected. In the IEEE 802.11a standard, the CCA-SD threshold is set to -82 dBm and the CCA-ED threshold is set to -62 dBm.

Hereinafter, the CCA-ED threshold (−62 dBm) is referred to as threshold 1, and the CCA-SD threshold (−82 dBm) is referred to as threshold 2. Also, according to the RSSI in AP1, the area for AP1 is defined as follows.
Near region: RSSI ≧ threshold 1
Middle region: threshold 1> RSSI ≧ threshold 2
Far region: RSSI <threshold 2

  AP1 can detect the preamble of the wireless frame by carrier sense, and if RSSI ≧ threshold 2 (near region and middle region), it is determined that the channel is busy (communication not possible) because it is a wireless frame of own / other BSS And wait for transmission. Also, even if the preamble of the radio frame can not be detected by carrier sense, if RSSI1threshold 1 (near-field), it is regarded as an interference wave from another system and the channel is determined to be busy (communication not possible) and transmission standby To do. In other cases, the channel is determined to be idle (communication enabled), and transmission starts if a transmission frame occurs.

Specification Framework for TGax, November 2015.

  In the IEEE802.11 standard, when the radio base station AP1 can detect the preamble of the radio frame and threshold value 1> RSSI ≧ threshold value 2 (intermediate region), the channel is determined to be busy and is in transmission standby. There are two cases shown in FIG. 7 as the situation. The first case is when the AP1 receives a radio frame from the wireless station STA1 in its own BSS, and in this case it is necessary to wait for transmission and continue reception. The second case is when AP1 receives a wireless frame of AP3 other than its own BSS. In this case, AP1 does not necessarily have to wait for transmission, but rather stops receiving (demodulating) the wireless frame of AP3. In some cases, throughput can be improved by enabling transmission.

  In order to cope with the second case, it is determined whether the wireless frame to be received is the own BSS or other than the own BSS, and if it is a wireless frame other than the own BSS, reception (demodulation processing) is canceled and simultaneous transmission is performed. Techniques for improving throughput by performing the above are being studied. Furthermore, in order to determine whether a radio frame is the own BSS or other than the own BSS, a method using a BSS identifier stored in a preamble portion of the radio frame is being studied.

  This BSS identifier is stored in a PLCP (Physical Layer Convergence Protocol) preamble portion of a radio frame and used for identifying a BSS, unlike a unique BSSID (a MAC address of a base station) in a MAC header of a conventional frame format. It is an identifier. FIG. 8 (1) shows the frame format of the conventional standard (802.11a / 11n / 11ac), and FIG. 8 (2) shows the frame format of the new standard assumed in the present invention. The PLCP preamble stores information for detecting and synchronizing frame signals, in which BSS identifiers of several bits or less are stored. The PLCP header stores information such as the transmission rate and the time to transmit the data part. The MAC header stores a source / destination address, a BSSID, a sequence number, a fragment number, and the like. The payload is the data body part.

  In this way, if the BSS identifier is stored in the most advanced PLCP preamble of the frame, the reception process of the PLCP preamble quickly determines whether the received radio frame is the own BSS or other than the own BSS. For example, control can be performed such that reception is continued as it is, and reception (demodulation processing) is stopped and transmission is possible for a radio frame other than its own BSS.

FIG. 9 shows a reception process procedure of a radio frame using a BSS identifier.
In FIG. 9, the wireless station performs carrier sense to receive a wireless frame, and performs processing to detect the RSSI and the BSS identifier of the preamble (S51), and the RSSI of the wireless frame is "threshold 1> RSSI ≧ threshold 2" It is determined whether or not it is a radio frame from the intermediate area (S52). Here, if the RSSI of the radio frame is RSSI ≧ threshold 1 (near region), reception is continued regardless of the BSS identifier and it is determined that the channel is busy (S52: No, S53: Yes, S54), RSSI <threshold If it is 2 (far area), the reception is stopped regardless of the BSS identifier and channel idle is made (S52: No, S53: No, S55). On the other hand, if threshold 1> RSSI ≧ threshold 2 (intermediate region) (S52: Yes), it is determined whether or not the BSS identifier of the radio frame matches the BSS identifier of the own BSS (S56).

  If the BSS identifier of the radio frame matches the own BSS, the reception is continued and the channel is busy and the transmission is waited (S54). On the other hand, if the BSS identifier of the wireless frame does not match the own BSS, the reception is stopped, the wireless frame is discarded, and transmission as channel idle is enabled (S57). This means that a radio frame with a BSS identifier different from that of its own BSS is regarded as an interference frame from other BSSs, so that the reception (demodulation processing) of its useless radio frame is canceled and its own BSS can transmit a radio frame. Throughput is expected to improve.

  Here, in a BSS dense environment, it is assumed that existing radio base stations set BSS identifiers autonomously and distributedly. On the other hand, the assumed BSS identifier is a few bits or less, and if there is a wireless base station of the type of the BSS identifier or more, there will be a wireless base station using a common BSS identifier. In that case, when the wireless frame is received, the BSS identifier matches the own BSS although the wireless frame is from another BSS in step S56 of FIG. If so, a phenomenon occurs in which reception is continued and transmission is waited for (S54). The reception continuation and the transmission standby are up to the MAC header of the radio frame, and at that time, it is determined that the radio frame is from another BSS, and is discarded and transmission is possible.

  However, if it is determined that the radio frame of another BSS is received at the time of detection of the preamble, and reception is stopped and transmission is enabled thereby, it is possible to save time for demodulation to the MAC header and to improve the throughput improvement effect. For this purpose, although it is necessary to assign different BSS identifiers to all radio base stations in the BSS dense environment, this may not be possible because the BSS identifiers are limited. That is, although it is necessary to assign a common BSS identifier to some of the wireless base stations, the assignment method may significantly reduce the throughput of the wireless base station's BSS and the entire system, and thus the throughput requirement may be required. Accordingly, it is necessary to assign an optimal BSS identifier.

  The present invention can optimize the assignment of BSS identifiers to each wireless base station according to the RSSI-based positional relationship of wireless base stations to promote simultaneous transmission and improve throughput in a BSS dense environment. An object of the present invention is to provide a wireless communication system and a wireless communication method.

  In the first invention, there are a plurality of adjacent BSSs composed of a plurality of radio stations that transmit and receive radio frames using a predetermined channel, and the radio stations of each BSS perform radio communication by access control by CSMA / CA. In the wireless communication system that performs the wireless communication, a plurality of wireless stations are connected, and wireless environment information including mutual received signal strength (RSSI) of the plurality of wireless stations is acquired, and a BSS to which each wireless station belongs according to the RSSI. When assigning a BSS identifier used for identification to each wireless station, a concentration that preferentially assigns different BSS identifiers to two wireless stations that are in a relationship of threshold 1> RSSI ≧ threshold 2 and belong to different BSSs A control station, wherein the radio station stores a BSS identifier assigned by the central control station in a preamble of a radio frame and transmits the means; When the preamble can be detected from the received signal by carrier sense of SMA / CA, the magnitude relationship between received signal strength (RSSI) of the received signal and threshold 1 and threshold 2 is determined, and threshold 1> RSSI ≧ threshold 2 In some cases, it is determined whether or not the preamble BSS identifier matches the BSS identifier assigned to the own BSS. If the BSS identifier matches, the reception is continued and the channel is busy. Means.

  In the wireless communication system according to the first aspect of the present invention, the central control station is configured such that the BSS identifier of one specific wireless station and the BSS identifiers of other wireless stations among the wireless stations in the relationship of threshold 1> RSSI ≧ threshold 2. Assign differently.

  In the wireless communication system of the first invention, the centralized control station has a different BSS identifier type with respect to the number of wireless stations to be controlled, and is different from each other for each wireless station having a relationship of threshold 1> RSSI ≧ threshold 2. When a BSS identifier cannot be assigned, a utility function indicating the throughput of the entire system according to the BSS identifier assignment pattern assigned to each radio station is calculated, and the BSS identifier assignment pattern that maximizes the utility function is selected. A BSS identifier is assigned to each wireless station.

  In the wireless communication system according to the first aspect of the invention, among the wireless stations having the relationship of threshold 1> RSSI ≧ threshold 2, the utility function has interference between wireless stations having the same BSS identifier and wireless stations with different BSS identifiers. The throughput of each wireless station is calculated assuming that there is no interference, and the total throughput of each wireless station is calculated as the throughput of the entire system.

  In the second invention, there are a plurality of adjacent BSSs composed of a plurality of radio stations that transmit and receive radio frames using a predetermined channel, and the radio stations of each BSS perform radio communication by access control by CSMA / CA. In the wireless communication method for performing the above, a centralized control station connected to a plurality of wireless stations acquires wireless environment information including mutual received signal strengths (RSSI) of the plurality of wireless stations, and each wireless station according to the RSSI When assigning a BSS identifier used to identify a BSS to which each belongs, to each wireless station, different BSS identifiers for two wireless stations belonging to different BSSs that have a relationship of threshold 1> RSSI ≧ threshold 2. The wireless station performs priority assignment processing, and the wireless station stores the BSS identifier assigned from the centralized control station in the preamble of the wireless frame and transmits it. When the preamble can be detected from the received signal by the carrier sense of A / CA, the magnitude relationship between received signal strength (RSSI) of the received signal and threshold 1 and threshold 2 is determined, and threshold 1> RSSIRSSIthreshold 2 If there is a match, it is determined whether or not the BSS identifier of the preamble matches the BSS identifier assigned to the own BSS. If there is a match, the reception is continued and channel busy is determined. The process is performed.

  In the wireless communication method according to the second aspect of the present invention, the central control station is configured such that the BSS identifier of one specific wireless station and the BSS identifiers of the other wireless stations out of the wireless stations in the relationship of threshold 1> RSSI ≧ threshold 2. Assign differently.

  In the wireless communication method of the second invention, the central control station has a different BSS identifier type with respect to the number of wireless stations to be controlled, and is different from each other for each wireless station having a relationship of threshold 1> RSSI ≧ threshold 2. When a BSS identifier cannot be assigned, a utility function indicating the throughput of the entire system according to the BSS identifier assignment pattern assigned to each radio station is calculated, and the BSS identifier assignment pattern that maximizes the utility function is selected. A BSS identifier is assigned to each wireless station.

  In the wireless communication method according to the second aspect of the invention, among the wireless stations having the relationship of threshold 1> RSSI ≧ threshold 2, the utility function has interference between wireless stations having the same BSS identifier and wireless stations with different BSS identifiers. The throughput of each wireless station is calculated assuming that there is no interference, and the total throughput of each wireless station is calculated as the throughput of the entire system.

  The present invention can realize optimal assignment of BSS identifiers considering the throughput of the entire system or a specific BSS even when the same BSS identifier is assigned to a plurality of wireless base stations in an intermediate area.

It is a figure which shows the structural example of the radio | wireless communications system of this invention. 6 is a flowchart illustrating an example of a procedure for assigning a BSS identifier in the first embodiment. It is a figure explaining the physical relationship of AP1-AP4. It is a figure which shows the example of calculation of the utility function in step S3, S4. 12 is a flowchart illustrating an example of a procedure for assigning a BSS identifier in the second embodiment. It is a figure which shows the calculation example ((alpha) = 0.9, (beta) = 0.1) of the utility function in step S13, S14. It is a figure which shows the example of control of a CCA threshold value. It is a figure which shows a frame format. It is a flowchart which shows the reception processing procedure of the radio | wireless frame using a BSS identifier.

FIG. 1 shows a configuration example of a wireless communication system of the present invention.
In FIG. 1, AP1 to AP4 are radio base stations of BSSs different from one another, and perform radio communication with their subordinate radio terminals (not shown) using common frequency channels. The AP 1 to AP 4 are connected to the central control station 6 via the network 5. AP1 to AP4 notify the central control station 6 of radio environment information such as BSSID of each AP detected by carrier sense, RSSI between APs, and RSSI with each AP in a subordinate radio terminal. The central control station 6 grasps the mutual positional relationship based on the wireless environment information notified from the AP1 to AP4, and assigns a BSS identifier to each AP.

  Here, the BSS identifier A or B is assigned to the four AP1 to AP4, but in general, for example, a limited type represented by several bits for several tens of APs to be controlled. Will be assigned a BSS identifier. Therefore, since the same BSS identifier is assigned to a plurality of APs, the present invention realizes an optimal assignment of BSS identifiers considering the throughput of the entire system or a specific BSS.

  In FIG. 1, the positional relationship on the basis of the RSSI between AP1 and AP2-AP4 is shown. With respect to AP1, AP2 is in the near region of RSSI 閾 値 threshold 1, AP3 is in the middle region of threshold 1> RSSI ≧ threshold 2, and AP4 is in the far region of RSSI <threshold 2.

  Here, when the BSS identifier A is assigned to AP1, the central control station 6 selects the BSS identifier A or B assigned to AP2 to AP4, respectively. If the BSS identifier A is assigned to the AP3 in the middle area, as described above, the AP1 determines that the signal of the AP3 is the signal of the own BSS, causing the problem of useless reception continuation. Therefore, it is desirable to assign a BSS identifier B different from AP1 to AP3 in the intermediate area with respect to AP1. As a result, AP1 determines that the signal of AP3 is a radio frame of another BSS at the time of detection of the preamble, cancels reception, discards the radio frame, enables simultaneous transmission with AP3, and improves throughput.

  On the other hand, since AP2 in the near area has an interference level with AP1 equal to or higher than threshold 1, AP1 cannot perform simultaneous transmission regardless of the BSS identifier of AP2. Further, since the AP4 in the far region has an interference level with the AP1 less than the threshold 2, the AP1 can perform simultaneous transmission regardless of the BSS identifier of the AP4. Therefore, the BSS identifiers of AP2 and AP4 do not need to be positively assigned a BSS identifier B different from AP1 as in the intermediate region AP3. Rather, it may be desirable that the BSS identifiers of AP2 and AP4 are BSS identifiers different from AP3, that is, the same BSS identifier A as AP1 depending on the mutual positional relationship with AP3. Therefore, with regard to BSS identifiers assigned to a plurality of APs, there is an optimal BSS identifier assignment method according to their positional relationship.

Example 1
FIG. 2 shows an example of an assignment procedure of BSS identifiers in the first embodiment.
In FIG. 2, a BSS identifier list indicating the assignment pattern of BSS identifiers is created for the radio base stations AP1 to APn (n is an integer of 2 or more) to be controlled (S1). Here, it is assumed that k types of assignable BSS identifiers (k is an integer of 2 or more and less than n) can not be used to assign different BSS identifiers to n APs. At this time, the assignment patterns of the BSS identifiers of AP1 to APn are k ⁿ ways. Next, one allocation pattern j is selected from the BSS identifier list, and a BSS identifier corresponding to the allocation pattern j is allocated to AP1 to APn (S2). Next, the throughput at each AP is calculated based on the relationship between the RSSI of AP1 to APn and the BSS identifier allocated to each (S3).

Here, the throughput T (i) of APi (i is 1 to n) depends on the number N (i) of APs that interfere with APi, where Tmax is the maximum throughput of APi.
T (i) = Tmax / (1 + N (i))
Is calculated. Note that the AP number N (i) that interferes with APi can be estimated as the sum of the number of APs in the near area as seen from APi and the number of APs to which the same BSS identifier is assigned in the intermediate area and APi.

  The AP number N (i) that interferes with APi may include an AP that does not have a control function according to the BSS identifier or an AP in the near area as viewed from the wireless terminal that belongs to APi. Furthermore, the throughput T (i) of APi may be divided by the number of wireless terminals belonging to APi and replaced with the throughput per one wireless terminal belonging. Further, as the throughput T (i) of APi, a value obtained by measuring the downlink throughput or the uplink throughput when a BSS identifier corresponding to the allocation pattern j is allocated to each AP may be used, or a value estimated as described above. The one with the smaller measured throughput may be selected.

  Next, the sum total of the throughputs T (1) to T (n) of AP1 to APn is calculated and set as the utility function Φ (j) in the BSS identifier allocation pattern j (S4). Next, the processes of S2 to S4 are repeated until the utility function に 対 す る is obtained for all allocation patterns of the BSS identifier list (S5), and thereafter the allocation pattern of the BSS identifier for which the utility function 最大 is maximum is determined, and the BSS The identifier is set to AP1 to APn, and the process ends (S6).

  Hereinafter, an example of assigning a BSS identifier that maximizes the utility function Φ when assigning the BSS identifiers A and B to the four AP1 to AP4 will be described with reference to FIGS. 3 and 4.

FIG. 3 shows the positional relationship of AP1 to AP4.
In FIG. 3, the threshold 1 and the threshold 2 are shown by dotted lines and broken lines with respect to AP1 to AP4. AP1, AP2 and AP4 are in an intermediate area relationship with each other, and AP2, AP3 and AP4 are in an intermediate area relationship with each other. AP1 and AP3 are in a far-field relationship. The APs in the middle area are connected by a solid line.

FIG. 4 shows an example of calculation of the utility function in steps S3 and S4.
In FIG. 4, BSS identifiers assigned to AP1 to AP4 shown in FIG. That is, if ● is BSS identifier A, ○ will be BSS identifier B, and vice versa. It should be noted that in the calculation of the throughput in each AP, since the APs having an intermediate area relationship interfere with each other when the BSS identifiers are the same and do not interfere with each other when different, assignment is performed even if the correspondence between ● and 逆 is reversed. The patterns are treated the same, and the assignment pattern based on AP1 is 2 ^4-1 = 8 patterns.

  A case where the APs are in the intermediate region and the BSS identifiers are the same is connected by a solid line, and a case where the APs are in the intermediate region and the BSS identifiers are different is connected by the dotted line. That is, APs connected by solid lines (● and ●, ○ and ○) have a relationship of interference, and APs connected by dotted lines (● and ○) have a relationship of not interfering with each other.

  Based on the above, throughputs T (1) to T (n) of AP1 to AP4 in allocation pattern 1 are 1/3, 1/4, 1/3, 1/4, and the utility function ((1) is 7 / 6 (≈1.17). Here, Tmax = 1. Similarly, the utility functions ((2) to ((8) of allocation patterns 2 to 8 are 7/3 (≒ 2.33), 2, 7/3 (≒ 2.33), 2, 2, 3, 2 and are allocated The utility function Φ (7) of pattern 7 becomes the maximum value. Therefore, the optimum BSS identifier allocation pattern in AP1 to AP4 is (A, B, A, B) or (B, A, B, A).

  Here, when priority is given to the throughput of AP1, BSS identifiers different from AP1 are assigned to AP2 and AP4 in the intermediate area as seen from AP1, and the assignment pattern 7 or the assignment pattern 8 in which the throughput of AP1 is 1 is obtained. . However, the BSS identifier for the AP3 in the far region as seen from the AP1 may be arbitrary, but when comparing the utility functions Φ (7) and Φ (8) considering the throughput from the AP2 to AP4, Φ (7)> Φ (8 Allocation pattern 7 is optimal because

  Similarly, when priority is given to the throughput of AP2, the allocation pattern 2 in which the throughput of AP2 becomes 1 is obtained. When it is desired to prioritize the throughput of AP3, the allocation patterns 3 and 7 in which the throughput of AP3 is 1 are obtained. When the utility functions Φ (3) and Φ (7) are compared, Φ (3) <Φ ( 7) Therefore, allocation pattern 7 is optimal. When priority is given to the throughput of the AP 4, an allocation pattern 4 in which the throughput of the AP 4 is 1 is obtained.

  Alternatively, a plurality of APs may be divided into two or more groups, the sum of normalized throughputs calculated for each group may be calculated as a utility function, and the optimal assignment pattern may be determined using the utility function. When calculating the utility function, the priority between groups can be adjusted by weighting the normalized throughput for each group. Hereinafter, an example of an assignment procedure of BSS identifiers when a plurality of APs are divided into two groups will be described as a second embodiment.

(Example 2)
FIG. 5 shows an example of an assignment procedure of the BSS identifier in the second embodiment.
In FIG. 5, a BSS identifier list indicating the assignment pattern of BSS identifiers is created for the radio base stations AP1 to APn (n is an integer of 2 or more) to be controlled (S11). At this time, AP1 to APn are divided into two groups G1 and G2 according to a predetermined standard. Next, one allocation pattern j is selected from the BSS identifier list, and a BSS identifier corresponding to the allocation pattern j is allocated to AP1 to APn (S12). Next, the throughput in each AP is calculated based on the relationship between the RSSI of AP1 to APn and the BSS identifier allocated to each (S13). Up to this point is the same as in the first embodiment.

Next, the throughputs of the APs belonging to the groups G1 and G2 are normalized (for example, averaged), and the normalized throughputs T (G1) and T (G2) of each group are multiplied by weighting coefficients α and β, respectively. The sum is calculated, and it is set as the utility function ((j) in the assignment pattern j of the BSS identifier (S14).
Φ (j) = α · T (G1) + β · T (G2)
Next, the processes of S12 to S14 are repeated until the utility function に 対 す る for all allocation patterns of the BSS identifier list is obtained (S15), and thereafter the allocation pattern of the BSS identifier for which the utility function 最大 is maximum is determined, and the BSS The identifiers are set to AP1 to APn and the process is ended (S16).

FIG. 6 shows an example of calculation of the utility function in steps S13 and S14.
In FIG. 6, similarly to FIG. 4, BSS identifiers assigned to AP1 to AP4 are indicated by .circle-solid. A case where the APs are in the intermediate region and the BSS identifiers are the same is connected by a solid line, and a case where the APs are in the intermediate region and the BSS identifiers are different is connected by the dotted line. That is, the APs connected by solid lines (● and ●, ○ and)) are in a relation of interference, and the APs connected by dotted lines are in a relation not to interfere with each other (● and)).

  Here, AP1 is a group G1, AP2 to AP4 is a group G2, and weighting coefficients corresponding to the respective groups are .alpha. = 0.9 and .beta. = 0.1.

Based on the above, the throughputs T (1) to T (n) of AP1 to AP4 in allocation pattern 1 are 1/3, 1/4, 1/3, 1/4. Here, Tmax = 1. The normalized throughput T (G1) of AP1 of group G1 is 1/3, and the normalized throughput T (G2) of AP2 to AP4 of group G2 is
(1/4 + 1/3 + 1/4) / 3 = 5/18
It becomes. Therefore, the utility function ((1) is Φ (1) = 0.9 · 1/3 + 0.1 · 5/18 = 0.33
It becomes.

Similarly, in the allocation patterns 2 to 8, the utility functions Φ (2) to Φ (8) using the normalized throughputs T (G1) and T (G2) of the groups G1 and G2 are 0.51, 0.35, 0.51, 0.5, 0.5,
It becomes 0.97, 0.93, and the utility function ((7) of the allocation pattern 7 becomes the maximum value. Therefore, the optimum BSS identifier assignment pattern in AP1 of group G1 and AP2 to AP4 of group G2 is A and (B, A, B) or B and (A, B, A).

1, 2, 3, 4 Radio base station (AP)
5 Network 6 Central control station

Claims (8)

A plurality of BSSs (Basic Service Set) composed of a plurality of radio stations that transmit and receive radio frames using a predetermined channel exist adjacent to each other, and each BSS radio station has a CSMA / CA (Carrier Sense Multiple Access with Collision). In a wireless communication system that performs wireless communication by access control by Avoidance),
A BSS that is connected to the plurality of radio stations, acquires radio environment information including mutual received signal strength (RSSI) of the plurality of radio stations, and is used to identify the BSS to which each radio station belongs according to the RSSI When assigning an identifier to each wireless station, there is provided a centralized control station that preferentially assigns different BSS identifiers to two wireless stations that are in a relationship of threshold 1> RSSI ≧ threshold 2 and belong to different BSSs,
The radio station is
A means for storing the BSS identifier assigned by the central control station in the preamble of the radio frame and transmitting it;
When the preamble can be detected from the received signal based on the CSMA / CA carrier sense, the magnitude relationship between the received signal strength (RSSI) of the received signal and the threshold value 1 and the threshold value 2 is determined, and threshold value 1> RSSI If 閾 値 threshold 2, it is determined whether or not the BSS identifier of the preamble matches the BSS identifier assigned to the own BSS. If they match, the reception is continued and channel busy is determined. And a means for stopping and channel idle. In the wireless communication system according to claim 1,
The central control station assigns the BSS identifier of one specific wireless station and the BSS identifiers of other wireless stations to be different from each other among the wireless stations having the relationship of threshold 1> RSSI ≧ threshold 2. A wireless communication system. In the wireless communication system according to claim 1,
The centralized control station has insufficient BSS identifier types for the number of radio stations to be controlled, and cannot assign different BSS identifiers to the respective radio stations in the relationship of threshold value 1> RSSI ≧ threshold value 2. Then, the utility function indicating the throughput of the entire system according to the assignment pattern of the BSS identifiers assigned to each wireless station is calculated, the assignment pattern of the BSS identifier with the largest utility function is selected, and the BSS identifiers are selected for each wireless station. A wireless communication system characterized in that In the wireless communication system according to claim 3,
The utility function assumes that there is interference between radio stations having the same BSS identifier among radio stations in the relationship of threshold value 1> RSSI ≧ threshold value 2, and that radio stations having different BSS identifiers are considered to have no interference. And calculating the throughput of each of the plurality of wireless stations as the throughput of the entire system. A plurality of BSSs (Basic Service Set) composed of a plurality of radio stations that transmit and receive radio frames using a predetermined channel exist adjacent to each other, and each BSS radio station has a CSMA / CA (Carrier Sense Multiple Access with Collision). In a wireless communication method for performing wireless communication by access control by Avoidance,
The central control station connected to the plurality of radio stations acquires radio environment information including mutual received signal strengths (RSSI) of the plurality of radio stations, and the BSS to which each radio station belongs according to the RSSI. A process of prioritizing different BSS identifiers with respect to two wireless stations belonging to different BSSs with a relationship of threshold 1> RSSI ≧ threshold 2 when assigning the BSS identifiers used for identification to each wireless station And
The radio station is
Storing the BSS identifier assigned by the central control station in a preamble of the radio frame and transmitting the preamble;
When the preamble can be detected from the received signal by the carrier sense of the CSMA / CA, the magnitude relationship between the received signal strength (RSSI) of the received signal and the threshold 1 and the threshold 2 is determined, threshold 1> RSSI If 閾 値 threshold 2, it is determined whether or not the BSS identifier of the preamble matches the BSS identifier assigned to the own BSS. If they match, the reception is continued and channel busy is determined. A wireless communication method characterized by performing processing of stopping and channel idle. The wireless communication method according to claim 5, wherein
The central control station assigns the BSS identifier of one specific wireless station and the BSS identifiers of other wireless stations to be different from each other among the wireless stations having the relationship of threshold 1> RSSI ≧ threshold 2. A wireless communication method. In the wireless communication method according to claim 5,
The centralized control station has insufficient BSS identifier types for the number of radio stations to be controlled, and cannot assign different BSS identifiers to the respective radio stations in the relationship of threshold value 1> RSSI ≧ threshold value 2. Then, the utility function indicating the throughput of the entire system according to the assignment pattern of the BSS identifiers assigned to each wireless station is calculated, the assignment pattern of the BSS identifier with the largest utility function is selected, and the BSS identifiers are selected for each wireless station. Assigning a wireless communication method. In the wireless communication method according to claim 7,
Among the wireless stations having the relationship of threshold 1> RSSI ≧ threshold 2, the utility function is considered as interference between wireless stations having the same BSS identifier and wireless stations with different BSS identifiers as no interference. And calculating the total throughput of each wireless station as the throughput of the entire system.

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