JP6505590B2 - Wireless communication system, wireless communication method, central control station apparatus and wireless station apparatus - Google Patents

Description

  The present invention relates to a wireless communication system, and a centralized control station device that improves the reduction in throughput caused by control of Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) of each communication station in a dense area of a wireless LAN (Local Area Network). And a radio station apparatus.

  In recent years, base station apparatuses (APs) based on the IEEE802.11a standard, the IEEE802.11g standard, etc. are widely spread as high-speed wireless access systems using the 2.4 GHz band or the 5 GHz band. Wireless LAN systems based on these standards use Orthogonal Frequency Division Multiplexing (OFDM) modulation, which is a technology to stabilize characteristics in multipath fading environments, and use transmission rates of up to 54 Mbps. Is realized (Non-Patent Document 1).

  However, the transmission rate described above is a transmission rate on the physical layer, not a data throughput effective for the user. In fact, since the transmission efficiency in the MAC (Medium Access Control) layer is about 50 to 70%, the throughput is about 30 Mbps as the upper limit value.

  On the other hand, the communication speed of the wired LAN is also rising with the spread of FTTH (Fiber to the home). Therefore, it is assumed that further speeding up of the transmission rate is required also in the wireless LAN in the future. Although various spatial signal processing techniques such as MIMO and multi-user MIMO have been studied for the purpose of increasing the throughput of the wireless section, the communication frequency band has been expanded as another method. In IEEE802.11a and IEEE802.11g, a 20 MHz wide frequency band is defined as a channel, and communication is performed using one communication channel selected in advance. In IEEE802.11 n, continuous 20 MHz wide channels are used. It is possible to perform communication using a 40 MHz wide frequency band by bundling two. Furthermore, IEEE802.11ac can communicate using an 80 MHz wide frequency band using four 20 MHz wide channels, and including options, it can be used up to 160 MHz wide at one time. Thus, expansion of the channel band used when performing wireless LAN communication is in progress (Non-Patent Document 2).

  As described above, the maximum frequency band of the channel used for communication is expanded eight times from IEEE 802.11a to IEEE 802.11 ac. However, no significant expansion has been permitted for the entire frequency band that can be used for wireless LAN communication. That is, with the spread of wireless LANs, frequency resources are becoming insufficient, and in dense environments of wireless LANs where there are more BSS (Basic Service Set) in a certain area than the number of available channels, the distance between each other When two or more BSSs close to one another use the same channel, an Overlapping BSS (BSS) environment arises where the BSSs overlap. At this time, depending on the channel selected by the base station, the throughput may be reduced due to the influence of interference of packet signals from other base stations whose communication areas overlap each other, and the throughput efficiency of the entire system may be reduced.

  Therefore, in the wireless LAN, using CSMA / CA, the transmitting station checks carrier availability by carrier sense, and autonomous distributed access control is used where data transmission is started only when the channel is availability. There is.

Specifically, the communication station from which the transmission request has been made first performs carrier sensing for a predetermined sensing period (DIFS: Distributed Inter-Frame Space) to monitor the state of the wireless medium,
If there is no transmission signal from another communication station during this time, 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 a channel can transmit data to other communication stations in the same BSS, and 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 AP performs carrier sense on all channels for a predetermined period, selects a channel with the smallest interference power, and transmits / receives data to / from a subordinate terminal apparatus on 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 Clear Channel Assessment (CCA) threshold is set to determine the channel usage status using received signal strength indicator (RSSI). For example, in the IEEE 802.11 standard, two CCA thresholds are defined. One is a CCA threshold (hereinafter referred to as a CCA-SD (Signal Detection) threshold) when the preamble of the wireless LAN signal can be detected in the received signal received in the carrier sense, and the other is a carrier This is a CCA threshold (hereinafter, referred to as a CCA-ED (Energy Detection) threshold) when the preamble of the wireless LAN signal can not be detected in the received signal received in the sense. For example, in the IEEE 802.11a standard, the CCA-SD threshold is set to -82 dBm. The CCA-ED threshold is set to -62 dBm.

  If the RSSI is equal to or higher than the CCA-SD threshold and carrier frequency detection detects a preamble of a wireless LAN signal, it is determined that the channel is busy (communication is not possible). Also, even if the preamble of the wireless LAN signal can not be detected by the carrier sense, if the RSSI is equal to or higher than the CCA-ED threshold, it is regarded as an interference wave from the neighboring BSS or other systems and the channel is determined to be busy (communication not possible). . Otherwise, it is determined that the channel is idle (communicable).

IEEE, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Enhancements for Higher Throughput," IEEE 802.11n-2009, Oct. 2009. IEEE 802.11ac Draft Standard, D7.0, Sept. 2013. Morikura Masahiro, Kubota ed., "802.11 High-speed Wireless LAN Textbook" Revised 3rd Edition, Impress R & D, March 2008

In wireless LAN, since access control is performed by CSMA / CA, when the number of competing wireless LAN base stations and terminal stations increases, interference signals increase between BSSs, and there is a probability of becoming busy when carrier sensing is performed. It becomes larger, transmission opportunities decrease and throughput decreases. Therefore, as a method for increasing the transmission opportunity, carrier sense threshold (for example, CCA
It is conceivable to set -SD) to a high value to reduce the probability of the channel becoming busy. However, when one BSS sets the carrier sense threshold to a high value to increase the transmission opportunity, interference signals to other BSSs may increase, causing reception errors and reducing the throughput of the entire system.

  In particular, when transmitting from the terminal station to the base station, it is necessary to set the carrier sense threshold carefully. When a terminal station exists at the end of a communication area formed with the base station as a center, the influence of interference given to the adjacent BSS becomes large when the terminal station transmits. On the other hand, when the terminal station exists near the center of the communication area, the influence of interference on the adjacent BSSs is reduced. The terminal stations are often randomly arranged in the communication area, so the influence varies depending on the arrangement relationship of the terminal stations, and it is necessary to set a carrier sense threshold in consideration of the influence of the interference.

  Also, since the carrier sense threshold is set to a high value, if signals from other stations in the BSS to which the own station belongs are not detected, the state becomes the same as a hidden terminal and a collision occurs in the BSS, thereby improving throughput. I can not expect.

  Also, when the reception power value of the interference signal received by the receiving station from the neighboring BSS exceeds the reception sensitivity threshold due to the increase of interference signal between BSSs, preamble detection and demodulation processing of the wireless LAN signal is also performed for the interference signal. Is done. If the desired signal arrives during the demodulation process of the interference signal, the desired signal can not be demodulated due to the collision. Also in this case, it is necessary to carefully set the reception sensitivity threshold in consideration of the throughput in the BSS to which the own station belongs and the throughput of the entire system including interference to other stations as described above.

  The present invention provides a wireless communication system, centralized control station apparatus and wireless station apparatus capable of improving throughput by controlling carrier sense threshold and reception sensitivity threshold in BSS based on wireless environment information of each BSS. The purpose is

In the first invention, a plurality of BSSs in which a base station and a plurality of terminal stations communicate with each other by a CSMA / CA access control adjacently exist, and a carrier sense threshold considering interference power values between BSSs using the same channel In a wireless communication system that performs wireless communication after performing control, when there are BSSs to be controlled by the central control station and BSSs not to be controlled among the BSSs, the central control station is controlled from the BSSs to be controlled to the wireless environment Information is collected, and based on the wireless environment information, the interfered power value from the BSS not controlled in the BSS to be controlled is less than the predetermined reception sensitivity threshold of the limit level at which the signal can be detected , and controlled BSS which the interference power value from the BSS of the controlled object other than the own BSS in BSS is less than the upper limit value of a predetermined reception sensitivity threshold or more and the carrier sense threshold Comprises means for selecting as the BSS for controlling the carrier sensing threshold value.

  In the wireless communication system of the first invention, when the central control station sets one of the BSSs for controlling the carrier sense threshold as a first BSS and the other as a second BSS, the central control station When the interference power value to the BSS is less than the interference reference value in the second BSS, and the interfered power value from the second BSS to the first BSS is less than the upper limit value of the carrier sense threshold, The carrier sense threshold set in one BSS includes means for calculating in a range above the interfered power value and less than the upper limit value of the carrier sense threshold.

  Furthermore, in calculating the carrier sense threshold of the first BSS, the central control station in the wireless communication system according to the first aspect of the invention determines, as the second BSS, the received power value with the first BSS. A means is provided for selecting an object to evaluate the given interference power value and the interfered power value.

  Furthermore, the central control station in the wireless communication system according to the first invention sets the reception sensitivity threshold to be set to the first BSS in a range exceeding the value of the interfered power from the second BSS and below the carrier sense threshold. Means are provided.

In the second invention, a plurality of BSSs in which a base station and a plurality of terminal stations communicate with each other by a CSMA / CA access control are adjacent to each other, and a carrier sense threshold considering interference power values between BSSs using the same channel In the wireless communication method of performing wireless communication after performing control, when there are BSSs to be controlled by the central control station and BSSs not to be controlled among the BSSs, the central control station is controlled from the BSSs to be controlled to the wireless environment Information is collected, and based on the wireless environment information, the interfered power value from the BSS not controlled in the BSS to be controlled is less than the predetermined reception sensitivity threshold of the limit level at which the signal can be detected , and controlled the BSS which the interference power value from the BSS of the controlled object other than the own BSS in BSS is less than the upper limit value of a predetermined reception sensitivity threshold or more and the carrier sensing threshold value, Comprising the step of selecting as the BSS for controlling the Yariasensu threshold.

  In the wireless communication method of the second invention, when the central control station sets one of the BSSs that controls the carrier sense threshold as a first BSS and the other as a second BSS, the central control station When the interference power value to the BSS is less than the interference reference value in the second BSS, and the interfered power value from the second BSS to the first BSS is less than the upper limit value of the carrier sense threshold, A step of calculating as a carrier sense threshold set to one BSS in a range exceeding the interfered power value and less than the upper limit value of the carrier sense threshold is included.

  Further, in calculating the carrier sense threshold of the first BSS, the central control station in the wireless communication method according to the second aspect of the invention determines, as the second BSS, the received power value with the first BSS. Selecting an object to evaluate the given interference power value and the interfered power value.

  Furthermore, in the wireless communication method of the second invention, the central control station sets as a reception sensitivity threshold to be set to the first BSS in a range exceeding the value of the interfered power from the second BSS and below the carrier sense threshold. Have steps.

  In the third invention, a plurality of BSSs in which a base station and a plurality of terminal stations communicate with each other by a CSMA / CA access control are adjacent to each other, and a carrier sense threshold considering interference power values between BSSs using the same channel It is a centralized control station apparatus used in a wireless communication system which performs wireless communication after performing control, and each means constituting the centralized control station of the first invention, and a carrier sense threshold and a reception sensitivity threshold calculated by each means. And a means for notifying a base station and a terminal station that constitute a BSS to be controlled.

  In the fourth invention, a plurality of BSSs in which a base station and a plurality of terminal stations communicate with each other by a CSMA / CA access control are adjacent to each other, and a carrier sense threshold considering interference power values between BSSs using the same channel A radio station apparatus that is used in a radio communication system that performs radio communication after performing control and that includes a base station forming each BSS and a plurality of terminal stations, and that communicates with the central control station apparatus of the third invention And means for performing access control by setting the carrier sense threshold and the reception sensitivity threshold notified from the central control station.

  According to the present invention, in an environment in which BSSs performing access control by CSMA / CA are concentrated, the centralized control station centrally controls the carrier sense threshold and the reception sensitivity threshold of the BSS to be controlled, thereby providing an interfered power value and Throughput can be improved while considering the interference power value.

It is a figure which shows the Example structure of the radio | wireless communications system of this invention. FIG. 2 is a diagram showing an example of configuration of a base station 10, a terminal station 20 and a central control station 40. It is a flowchart which shows the outline | summary of the process sequence of the central control station. It is a flowchart which shows the example of a setting procedure of the control terminal station 20 'in the central control station 40. FIG. It is a flowchart which shows the example of a calculation procedure of the carrier sense threshold value of control terminal station 20 '. It is a flowchart which shows the example of a production | generation procedure of an interference evaluation BSS group. It is a flowchart which shows the example of a setting procedure of the receiving sensitivity threshold value of control terminal station 20 '.

FIG. 1 shows the configuration of an embodiment of a wireless communication system of the present invention.
In FIG. 1, there are A (A is an integer of 2 or more) base stations (AP) 10-1 to 10-A, and B (B is an integer of 1 or more) terminals to which the base station 10-1 belongs And wirelessly communicate with the stations (STA) 20-1-1 to 20-1-B, and similarly, the base station 10-A communicates with the belonging terminal station (STA) 20-A-1 to 20-AB. Perform wireless communication. Here, the number of terminal stations 20 belonging to each base station is B, but the number of terminal stations belonging to each base station does not necessarily have to be the same number of B. The base stations 10-1 to 10-A are connected to the central control station 40 via the network 30. A circle centered on base stations 10-1 to 10-A schematically indicates a carrier sense range corresponding to the size of a carrier sense threshold described later, and solid arrows indicate base stations and terminal stations belonging to them. Communication signals between them, dashed arrows indicate interference signals from adjacent BSSs. Also, a base station (AP) and a terminal station (STA) forming a BSS are collectively referred to as a wireless station.

FIG. 2 shows a configuration example of the base station 10, the terminal station 20 and the central control station 40.
In FIG. 2, the base station 10 includes an antenna element 11, a wireless communication unit 12, an information storage unit 13, and a network communication unit 14.

  The antenna element 11 transmits and receives a radio signal to and from the terminal station 20. The wireless communication unit 12 demodulates the wireless signal received by the antenna element 11 into a baseband signal, performs signal reception processing such as error correction and decoding to a data signal sequence, and outputs the signal to the network communication unit 14. Further, the wireless communication unit 12 acquires wireless environment information such as the RSSI of the wireless signal received by the antenna element 11, stores communication performance information and communication status information of the base station 10 in the information storage unit 13, and CSMA / CA control is performed according to the carrier sense threshold and the reception sensitivity threshold notified from 40. The wireless communication unit 12 also receives transmission data from the network communication unit 14 to the terminal station 20, performs signal transmission processing such as error correction coding, converts it into a baseband signal, modulates it into a wireless signal, and transmits it to an antenna. Transmit from the element 11.

  The network communication unit 14 outputs the transmission data and control signal received from the central control station 40 via the network 30 to the wireless communication unit 12. In addition, the network communication unit 14 transmits the data signal sequence output from the wireless communication unit 12 and the wireless environment information, communication performance information, and communication status information read from the information storage unit 13 to the central control station 40 via the network 30. Do.

The terminal station 20 includes an antenna element 21, a wireless communication unit 22, and an information storage unit 23.
The antenna element 21 transmits and receives radio signals to and from the base station 10. The wireless communication unit 22 demodulates the wireless signal received by the antenna element 21 into a baseband signal, and performs signal reception processing such as error correction and decoding into a data signal sequence. Further, the wireless communication unit 22 acquires wireless environment information such as the RSSI of the wireless signal received by the antenna element 21, stores communication performance information and communication status information of the terminal station 20 in the information storage unit 23, and 40 performs CSMA / CA control in accordance with the carrier sense threshold and the reception sensitivity threshold notified via the base station 10. Also, the wireless communication unit 22 inputs transmission data to the base station 10, performs signal transmission processing such as error correction coding, converts it into a baseband signal, modulates it into a wireless signal, and transmits it from the antenna element 21. .

  The central control station 40 includes a network communication unit 41, a carrier sense threshold / reception sensitivity threshold calculation unit 42, and a wireless information database 43.

  The network communication unit 41 communicates with the base station 10 via the network 30, transmits a control signal for acquiring radio environment information, communication performance information, and communication status information from the base station 10, and acquires each information. The signal is then output to the carrier sense threshold / reception sensitivity threshold calculator 42. Also, the network communication unit 41 transmits the notification information of the carrier sense threshold and the reception sensitivity threshold calculated by the carrier sense threshold / reception sensitivity threshold calculation unit 42 to the base station 10 via the network 30.

  The carrier sense threshold / reception sensitivity threshold calculation unit 42 generates a control signal for acquiring wireless environment information, communication performance information, and communication status information from the base station 10, and the base station via the network communication unit 41 via the network 30. 10, each information acquired by the network communication unit 41 is input and written to the wireless information database 43. Further, the carrier sense threshold / reception sensitivity threshold calculation unit 42 calculates the carrier sense threshold and reception sensitivity threshold of the terminal station 20 based on each information read from the wireless information database 43 and writes the result in the wireless information database 43. The network communication unit 41 notifies the base station 10 via the network 30, and notifies the terminal station 20 to which the base station 10 belongs.

  The wireless information database 43 stores wireless environment information, communication performance information, and communication status information of the base station 10. Further, the wireless information database 43 receives the read request from the carrier sense threshold / reception sensitivity threshold calculation unit 42, and returns the corresponding information.

(Processing procedure of central control station 40)
FIG. 3 shows an outline of the processing procedure of the central control station 40 of the wireless communication system of the present invention.
In FIG. 3, the central control station 40 collects radio environment information from the base station 10 and the terminal station 20 under its control (step S1). For example, the central control station instructs the subordinate base station 10 and the terminal station 20 to collect the radio environment information, and the base station 10 and the terminal station 20 that have received the instruction each acquire radio environment information around the own station, The base station 10 notifies the central control station 40 via the network 30, and the terminal station 20 notifies the central control station 40 via the connected base station 10 and the network 30. Here, the wireless environment information is information indicating a wireless communication environment obtained by the base station 10 or the terminal station 20 collecting wireless signals for a predetermined time, and, for example, RSSI of signals received from nearby wireless LAN stations. And ID unique to the transmission source such as a MAC (Media Access Control) address, interference power values from devices using the same frequency band other than the surrounding wireless LAN system, and the like. Also, the terminal station 20 may use its own location information obtained using GPS (Global Positioning System) or RSSI values from neighboring base stations as information about the own station, or may use its own location information obtained using an acceleration sensor or the like. It is also possible to acquire the moving speed etc. and add it to the wireless environment information collected by the own station.

Furthermore, the central control station 40 may acquire communication performance information and communication state information of the base station 10 and the terminal station 20.
The communication performance information is information indicating the performance when the base station 10 and the terminal station 20 perform wireless communication, and, like the wireless environment information, the communication performance information of the base station 10 is acquired from the base station 10 via the network 30 The communication performance information of the terminal station 20 is acquired via the connection destination base station 10 and the network 30. As communication performance information, for example, the number of antennas (maximum number of antennas used when transmitting or receiving), configurable bandwidth transmission power, type of error correction code (FEC), MCS (Modulation and coding scheme), transmission stream The number, the short GI (Guard interval) setting availability, the type of transmission diversity, the availability of transmission beamforming and its weight, the availability of multi-user MIMO, the availability of A-MSDU / A-MPDU, etc. may be mentioned.

The communication status information is the use ratio of all or all of the parameter values used within a certain period of time from the communication performance information in the base station 10 or the terminal station 20. As an example, there is the following information in communication performed by the base station 10 within a certain period of time.
• 100% when one transmitting antenna is used.
• 100% when one receiving antenna is used.
・ 23% of communication using 80 MHz bandwidth, 62% of communication using 40 MHz, and 15% of communication using 20 MHz.
The transmission power setting value is 10% at 14 dBm and 90% at 17 dBBm.
The error correction code is 80% when it is a convolutional code and 20% when it is an LDPC (Low Density Pality Check) code.
・ The MCS index is 9 at 10%, 8 at 10%, 7 at 10%, 6 at 12%,
(Omitted), 1 is 8%.
The number of transmission streams is 90% when 1 and 10% when 2.
・ There is no 100% short GI.
-There is no 100% transmission diversity.
・ Multi-user MIMO is not performed 100%.
・ The number of A-MPDU aggregation is 1 in 50%, 2 in 15%, 3 in 10
%, (Abbreviated below).

  Next, the central control station 40 extracts a terminal station to which carrier sense threshold control is applied from the subordinate terminal stations 20 based on the wireless environment information, and sets it in the control terminal station 20 '(step S2). In the following description, among the base stations and terminal stations constituting each BSS, the control procedure of the carrier sense threshold and the reception sensitivity threshold will be described by taking the terminal station as an example.

  Among the terminal stations 20, the control terminal station 20 'excludes terminal stations that do not have the function of changing the carrier sense threshold. In addition, when there is another wireless LAN station that performs wireless communication on the same frequency channel as the terminal station 20 and does not control the carrier sense threshold (is unable to) in the vicinity of the terminal station 20, the transmission opportunity If carrier sense threshold control is applied to the terminal station 20 in order to increase the channel frequency, interference will be unilaterally given to other wireless LAN stations, and it will be difficult to make fair time segregation with other wireless LAN systems. To avoid that, such terminals are also excluded from the control terminal. In addition, in an isolated state where there are only wireless LAN stations in the same cell in the periphery, the effect of improving the throughput by carrier sense threshold control of the terminal station 20 can not be expected, and such terminals are also excluded from the control terminal station. .

Next, the central control station 40 calculates an interference evaluation BSS group for each of the carrier sense threshold control terminals 20 ′ based on the radio environment information (step S3).
The interference evaluation BSS group is a set of BSSs that perform interference evaluation and interference evaluation when calculating the carrier sense threshold in each of the control terminal stations 20 ′, and the control terminal station 20 ′ and the centralized control station 40 It can be determined by the RSSI value with the BSS under control. Here, as a method of calculating the RSSI value between the BSS and the terminal station, either the average value or the weighted combined value of each RSSI value in the base station and the terminal station belonging to the BSS is used, or the RSSI value in the base station is used. Or the maximum value among the RSSI values of the base station or the terminal station.

Next, the central control station 40 calculates the carrier sense threshold of each of the control terminal stations 20 ′ based on the wireless environment information (step S4).
The carrier sense threshold of the control terminal station 20 'is increased from the initial set value, which is the lowest carrier sense threshold that can be set by the terminal station, in order to increase the transmission opportunity. It is necessary to avoid that the signal from the destination base station and other terminals in the same BSS can not be detected. That is, if the carrier sense threshold of the control terminal station 20 'is set to a value higher than the reception power value from the connection destination base station or another terminal station in the same BSS, the connection destination base station or another terminal station transmits In the midst of doing so, the channel misinterprets as idle and starts transmission, causing a signal collision and reducing throughput. Therefore, the central control station 40 sets the upper limit value of the carrier sense threshold in the control terminal station 20 'based on the wireless environment information, and controls the carrier sense threshold of the control terminal station 20' in the range below the upper limit value. There is a need.

  Also, setting the carrier sense threshold to a high value in order to increase the transmission opportunity of the control terminal station 20 'causes an increase in the interference to other BSSs due to the increase of the transmission opportunity of the control terminal station 20'. Therefore, it is necessary to adjust the carrier sense threshold appropriately in consideration of interference (interference interference) with the BSS to which the control terminal station 20 'belongs and other BSSs.

  Next, the central control station 40 calculates the reception sensitivity threshold of each of the control terminal stations 20 'based on the radio environment information and the carrier sense threshold calculated in the previous stage (step S5).

  Next, the central control station 40 notifies the control terminal station 20 'of the newly calculated carrier sense threshold and reception sensitivity threshold (step S6), and ends the processing. The control terminal station 20 'notified from the central control station 40 updates its own carrier sense threshold and reception sensitivity threshold.

(S2: setting of control terminal station 20 'in central control station 40)
FIG. 4 shows an example of a setting procedure of the control terminal station 20 'in the central control station 40.
In FIG. 4, the central control station 40 selects one undetermined terminal station from the terminal stations 20 to be controlled, and sets it as a determination target terminal station 20p (step S21).

  Next, based on the communication performance information of the determination target terminal station 20p, it is determined whether the determination target terminal station 20p can change the setting of the carrier sense threshold (step S22). Here, when the setting change is possible, next, based on the MAC address information of the control target base station and the terminal station of the central control station 40 and the wireless environment information in the determination target terminal station 20p, the determination target terminal station 20p At step S23, it is determined whether the interfered power value from the radio station not controlled by the central control station 40 is less than the threshold (step S23). As the interference power value used here, the maximum interference power value from a plurality of radio stations not to be controlled, the average interference power value, etc. can be used. Further, as the threshold value, for example, the minimum reception sensitivity value of the wireless LAN or a value obtained by adding a margin to the value can be set.

If the interference power value from the radio station not to be controlled is less than the threshold, the terminal station 20p to be judged based on the MAC address information of the base station and terminal station to be controlled and the radio environment information in the terminal station 20p to be judged. It is determined whether the interfered power value from the base station to be controlled by the central control station 40 and the terminal station other than the BSS to which B belongs is less than the threshold (step S24). For example, in FIG. 1, when the terminal station 20-p to be determined is a terminal station 20-1-1 belonging to the base station 10-1, interference from the base stations 10-2 and 10-3 and the terminal stations belonging respectively Determine the power value. As the interference power value used here, the maximum value or the average value of the interference power from the base station to be controlled and the terminal station can be used. Also, as the threshold value, for example, the maximum carrier sense threshold that can be set in the wireless LAN, the maximum value that can be set according to the performance of the wireless device, or a value obtained by adding a margin to that value can be set.

  If the interference power value from the base station or terminal station to be controlled is less than the threshold, the terminal station 20p to be determined is set as the control terminal station 20 '(step S25).

  On the other hand, a terminal station determined that the setting change of the carrier sense threshold can not be made in step S22, a terminal station in which the interfered power value from a wireless station not controlled is determined to be equal to or more than the threshold in step S23, a control target in step S24. A terminal station whose interference power value from the base station or terminal station is determined to be equal to or higher than the threshold is not set as a control terminal station because raising the carrier sense threshold to increase transmission opportunities does not contribute to throughput improvement.

  Then, the processing of steps S21 to S25 is performed until all the terminal stations have been determined (step S26), and the central control station 40 narrows the control terminal station 20 'out of the terminal stations 20 to be controlled and then performs processing. Finish.

(S4: Calculation of carrier sense threshold of control terminal station 20 ')
FIG. 5 shows an example of the procedure for calculating the carrier sense threshold of the control terminal station 20 '.

  In FIG. 5, the central control station 40 calculates the upper limit value of the carrier sense threshold of each control terminal station 20 'based on the wireless environment information (step S31). Here, the upper limit value is the minimum value among the received power values (RSSI values) from the terminal station 20 excluding the own station in the own BSS and the connection destination base station 10 in each control terminal station 20 ', or The margin is set to the value.

  Next, based on the wireless environment information, one control terminal station 20 'whose carrier sense threshold value is not calculated is selected, and is set as a calculation target control station 20's (step S32). As selection criteria of the calculation target control station 20's, for example, the RSSI value from the connection destination base station is large, or the number of BSSs in the interference evaluation BSS group is large or small, or between the interference evaluation BSS group and the BSS It is conceivable that the interference power value is small.

  The centralized control station 40 selects one BSS among the BSSs included in the interference evaluation BSS group of the calculation target control station 20's that has not yet been determined and the interference power value from the calculation target control station 20's is the smallest (step S33). ).

  Next, in the BSS where the interference power value from the calculation target control station 20's is the smallest, it is determined whether the interference power value is less than or equal to the interference reference value (step S34). The interference reference value in this case can be set as a value that can be received from any terminal station included in the BSS even if it receives interference from the calculation target control station 20's, for example, and a base station included in the selected BSS And, the maximum value or the average value of the RSSI values from the calculation target control station 20's at the terminal station can be calculated as a weighted combined value. Therefore, if the minimum value of the interference power value in the interference evaluation BSS exceeds the interference reference value, control of the carrier sense threshold of the calculation target control station 20's is not performed, and selection of the next calculation target control station is started ( Step S38 → S32).

  On the other hand, if the interference power value to the BSS selected by the calculation target control station 20's is equal to or less than the interference reference value, the interfered power value from the BSS is less than the upper limit of the carrier sense threshold of the calculation target control station 20's. It is determined (step S35). Here, if the interfered power value from the BSS is equal to or higher than the upper limit (S35: No), it is useless to raise the carrier sense threshold of the calculation target control station 20's, so the carrier sense threshold of the calculation target control station 20's The control is not performed, and selection of the next calculation target control station is started (steps S38 and S32).

  On the other hand, if the interfered power value is less than the upper limit value of the carrier sense threshold value, the carrier sense threshold value of the calculation target control station 20's is updated to a value exceeding the interfered power value from the BSS selected in the range not exceeding the upper limit value. (Step S36).

  Next, it is determined whether or not updating of the carrier sense threshold has been determined for all interference evaluation BSSs in the calculation target control station 20's (step S37), and if there is an undetermined BSS, the process returns to step S33. The determinations of S34 and S35 are performed. If all interference evaluation BSSs have been determined, or if "No" in the determinations in steps S34 and S35, it is determined whether the carrier sense threshold of all control terminal stations 20 'has been calculated ( Step S38) If there is an uncalculated control terminal station 20 ', the process returns to step S32 to select the next control target control station 20's, and when it is calculated, the process ends.

  Through the above process, while the control terminal station 20 'suppresses the interference power to the surrounding BSSs to a certain level or less, the carrier sense threshold of the control terminal station 20' is increased to increase the transmission opportunity and improve the throughput. it can. Further, even in the terminal station 20 which has not performed carrier sense threshold value control, the transmission time occupied by the control terminal station 20 'in the same BSS is shortened, and the transmission time of the own station can be increased. it can.

(S3: Generation of interference evaluation BSS group)
In step S3 of FIG. 3, an interference evaluation BSS group is generated when calculating the carrier sense threshold of the control terminal station 20 ', and calculation of the carrier sense threshold is performed for each interference evaluation BSS group.

  Hereinafter, a method of generating an interference evaluation BSS group will be described. The interference evaluation BSS group is obtained by dividing the BSS including the control terminal into one or more groups as a unit to which carrier sense threshold control is applied, and is set based on the interference power value between the interference evaluation BSSs. . With the BSSs in the interference evaluation BSS group, simultaneous setting can not be performed simultaneously between the BSSs by the CSMA / CA by the setting initial value of the carrier sense threshold in the terminal station, and the communication opportunity is lowered, and the carrier of the terminal station By increasing communication opportunities by sense thresholds, BSSs that have opportunities to obtain an improvement in throughput are selected to generate an interference evaluation BSS group.

FIG. 6 shows an example of a procedure for generating an interference evaluation BSS group.
6, first, the central control station 40 based on the radio environment information, and respectively, less than the minimum threshold P _L, or maximum threshold P _H or the interference power value between any two BSS from all BSS The interference power value between BSSs is excluded (step S41). Minimum threshold P _L, the interference power value between BSS is small, is already possible simultaneous communication between BSS, increasing effect of the applied even communicate opportunities carrier sensing threshold controlled by the control target terminal station of the centralized control station 40 In order to remove from the processing the interference power value between BSSs that can not be obtained, P _L is given by, for example, the initial value of the carrier sense threshold at the terminal station. Also, P _H has a high interference power value between BSS, can not be carried out simultaneous communication between BSS be applied carrier sensing threshold controlled by the control target terminal station of the centralized control station 40, the effect of increasing communication opportunities obtained In order to remove the inter-BSS interference power value that can not be processed, P _H is given by, for example, the maximum value of the carrier sense threshold in the terminal station.

Next, the smallest interference power value is selected between the two BSSs, and the two BSSα and BSSβ are selected (step S42). Next, it is determined whether or not both BSSα and BSSβ belong to the interference evaluation BSS group (step S43). If they both belong, the process proceeds to step S52, and at least one BSS belongs to the interference evaluation BSS group If not, it is determined whether or not one of BSSα and BSSβ belongs to the interference evaluation BSS group based on the wireless environment information (step S44).

Here, when one of BSSα and BSSβ belongs to the interference evaluation BSS group, here, the average between the BSSs in the interference evaluation BSS group j to which BSSα belongs and the BSSβ not belonging to BSS group j. An interference power value is calculated (step S45). Then, the calculated average interference power value determines whether less than the threshold value P _B (step S46). Here, if the threshold value P _B or the process proceeds to step S52, if it is less than the threshold value P _B, less than or BSS number included in the interference evaluation BSS group j is the limit BSS number of possible belong to interference evaluation BSS group threshold It is determined whether or not it is (step S47). Here, if it is equal to or more than the threshold value, the process proceeds to step S52, and if less than the threshold value, BSS is added to the interference evaluation BSS group j (step S48), and the process proceeds to step S52.

If neither BSSα nor BSSβ belongs to the interference evaluation BSS group in step S44, it is determined whether the average interference power value between BSSα and BSSβ is less than the threshold value P _B (step S49). Here, the process proceeds to step S52 if the threshold value P _B above, if it is less than the threshold value P _B BSSarufa, generating a new interference evaluation BSS group i in BSSbeta (step S50). Then, i is set to i + 1 (step S51), and the process proceeds to step S52.

  In step S52, it is determined whether or not the interference power value between any two BSSs among all the interference evaluation BSSs has already been determined, and if not determined, the process returns to step S42, and if all have been determined End the process.

(S5: setting of reception sensitivity threshold of control terminal station 20 ')
FIG. 7 shows an example of a setting procedure of the reception sensitivity threshold of the control terminal station 20 '.
In FIG. 7, the central control station 40 selects one of the control terminal stations 20 'whose carrier sense threshold has been updated according to the calculation procedure shown in FIG. 't (step S61).

  Next, based on the communication performance information of the setting target terminal station 20't, it is determined whether the setting target terminal station 20't can change the setting of the reception sensitivity threshold (step S62). Here, if the setting change is possible, it is determined whether the reception sensitivity threshold is smaller than the carrier sense threshold (S63). When the reception sensitivity threshold is smaller than the carrier sense threshold, whether or not to detect one or more interference power values from control target BSSs other than the own BSS, between the reception sensitivity threshold and the carrier sense threshold (CCA-SD) Is determined (S64). If there is an interference power value between the reception sensitivity threshold and the carrier sense threshold (CCA-SD), the reception sensitivity threshold of the setting target terminal 20 't exceeds the interference power value and is less than or equal to the carrier sense threshold. It sets to (S65).

  Next, the processing of steps S61 to S65 is performed until all control terminal stations 20 'have been set (step S66), and the reception sensitivity threshold setting processing is performed for all control terminal stations 20'.

  In addition, if it is possible to obtain the transmission power setting value at the time of transmitting a signal at the base station of another wireless LAN system in the vicinity, the number of transmission antennas, the presence or absence of transmission beamforming, etc. An increase or decrease in the amount of interference due to power control can be estimated, which is effective for setting a carrier sense threshold. For example, if there is a base station transmitting at half the maximum transmission power (50% value), the measured RSSI value of the signal received from that base station will be measured from the measured RSSI value when transmitted at the maximum transmission power. Since it is also expected to increase by 3 dB, the carrier sense threshold can be set in consideration of the 3 dB.

In addition, since there is a risk that communication quality may be affected by sudden interference signals inside and outside the system, it is also effective to set the setting margin of the carrier sense threshold by M (M> 0) dB. Further, the radio environment information such as the RSSI value and the packet error rate (PER) so far is stored in the radio information database 43 of the central control station in association with at least one of the communication performance information and the communication state information. Thus, the optimum carrier sense threshold setting can be empirically grasped. In addition, when wireless environment information such as an RSSI value is newly obtained by storing it in the centralized control station as a carrier sense threshold table, an optimum carrier sense threshold is extracted from the carrier sense threshold table for that value. Can be set.

10 base stations (AP)
11 antenna element 12 wireless communication unit 13 information storage unit 14 network communication unit 20 terminal station (STA)
Reference Signs List 21 wireless communication unit 22 information storage unit 30 network 40 central control station 41 network communication unit 42 carrier sense threshold / reception sensitivity threshold calculation unit 43 wireless information database

Claims (10)

There are multiple Basic Service Sets (BSSs) in which a base station and multiple terminal stations communicate with each other by access control based on Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA), and interference occurs between BSSs using the same channel. In a wireless communication system that performs wireless communication after performing carrier sense threshold control considering power values,
When there are BSSs to be controlled by the central control station and BSSs not to be controlled among the BSSs,
The centralized control station collects radio environment information from the BSS to be controlled, and based on the radio environment information, an interference power value from the BSS not to be controlled in the BSS to be controlled can detect a signal. It is less than the predetermined reception sensitivity threshold of the limit level , and the interfered power value from the BSSs of the control object other than the own BSS in the BSS to be controlled is not less than the predetermined reception sensitivity threshold and less than the upper limit of the carrier sense threshold. A wireless communication system, comprising: means for selecting a BSS as a BSS to control the carrier sense threshold. In the wireless communication system according to claim 1,
When the central control station sets one of the BSSs controlling the carrier sense threshold as a first BSS and the other as a second BSS, an interference power value from the first BSS to the second BSS Is less than or equal to the interference reference value in the second BSS, and the carrier power to be set to the first BSS when the interfered power value from the second BSS to the first BSS is less than the upper limit value of the carrier sense threshold A wireless communication system comprising: means for calculating as a sense threshold value in a range above the interfered power value and less than the upper limit value of the carrier sense threshold value. In the wireless communication system according to claim 2,
When the centralized control station calculates the carrier sense threshold of the first BSS, the interference power value and the interference power value are determined as the second BSS according to the received power value with the first BSS. A wireless communication system comprising: means for selecting an object to evaluate an interfered power value. In the wireless communication system according to claim 2,
The centralized control station is characterized by comprising means for setting, as a reception sensitivity threshold to be set to the first BSS, a range exceeding the value of the interfered power from the second BSS and not more than the carrier sense threshold. Wireless communication system. There are multiple Basic Service Sets (BSSs) in which a base station and multiple terminal stations communicate with each other by access control based on Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA), and interference occurs between BSSs using the same channel. In a wireless communication method for performing wireless communication after performing carrier sense threshold control in consideration of a power value,
When there are BSSs to be controlled by the central control station and BSSs not to be controlled among the BSSs,
The centralized control station collects radio environment information from the BSS to be controlled, and based on the radio environment information, an interference power value from the BSS not to be controlled in the BSS to be controlled can detect a signal. It is less than the predetermined reception sensitivity threshold of the limit level , and the interfered power value from the BSSs of the control object other than the own BSS in the BSS to be controlled is not less than the predetermined reception sensitivity threshold and less than the upper limit of the carrier sense threshold. A wireless communication method, comprising the steps of: selecting a BSS as a BSS to control the carrier sense threshold. In the wireless communication method according to claim 5,
When the central control station sets one of the BSSs controlling the carrier sense threshold as a first BSS and the other as a second BSS, an interference power value from the first BSS to the second BSS Is less than or equal to the interference reference value in the second BSS, and the carrier power to be set to the first BSS when the interfered power value from the second BSS to the first BSS is less than the upper limit value of the carrier sense threshold A wireless communication method comprising: calculating as a sense threshold in a range above the interfered power value and less than the upper limit of the carrier sense threshold. In the wireless communication method according to claim 6,
When the centralized control station calculates the carrier sense threshold of the first BSS, the interference power value and the interference power value are determined as the second BSS according to the received power value with the first BSS. A wireless communication method comprising the steps of: selecting an object to evaluate an interfered power value. In the wireless communication method according to claim 6,
The centralized control station has a step of setting as a reception sensitivity threshold to be set to the first BSS in a range exceeding an interfered power value from the second BSS and not more than the carrier sense threshold.
Wireless communication method characterized in that There are multiple Basic Service Sets (BSSs) in which a base station and multiple terminal stations communicate with each other by access control based on Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA), and interference occurs between BSSs using the same channel. A centralized control station apparatus used in a wireless communication system that performs wireless communication after performing carrier sense threshold control in consideration of a power value,
Each means according to claims 1 to 4;
A central control station apparatus comprising: a base station that constitutes the BSS to be controlled, and means for notifying a terminal station of the carrier sense threshold and the reception sensitivity threshold calculated by each of the means. There are multiple Basic Service Sets (BSSs) in which a base station and multiple terminal stations communicate with each other by access control based on Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA), and interference occurs between BSSs using the same channel. A radio station apparatus including: the base station forming each BSS and a plurality of terminal stations, which is used in a radio communication system that performs radio communication after performing carrier sense threshold control in consideration of a power value,
A means for communicating with the central control station apparatus according to claim 9;
And a means for setting the carrier sense threshold value notified from the central control station and the reception sensitivity threshold value to perform the access control.

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