JP7022965B2 - Wireless communication system, wireless communication method and wireless base station - Google Patents

Description

The present invention provides a wireless communication system, a wireless communication method, and a wireless communication method for improving the decrease in throughput caused by CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) control of each wireless station in a dense environment of a wireless LAN (Local Area Network). Regarding wireless base stations.

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

In the wireless LAN of the IEEE802.11b standard and the IEEE802.11g standard, 13 channels are prepared at 5MHz intervals between 2400MHz and 2483.5MHz. However, when using a plurality of channels in the same place, if the channels are used so that the spectra do not overlap to avoid interference, a maximum of 3 channels, and in some cases up to 4 channels can be used at the same time.

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

The maximum transmission speed of wireless LAN is 11 Mbps in the case of the IEEE802.11b standard, and 54 Mbps in the case of the IEEE802.11a standard and the IEEE802.11g standard. However, the transmission speed here is the transmission speed on the physical layer. Actually, the transmission efficiency in the MAC (Medium Access Control) layer is about 50 to 70%, so the upper limit of the actual throughput is about 5 Mbps in the IEEE802.11b standard, and 30 Mbps in the IEEE802.11a standard and the IEEE802.11g standard. Degree. Further, the transmission speed is further lowered as the number of radio stations that try to transmit information increases.

On the other hand, for wired LAN, high-speed lines of 100 Mbps to 1 Gbps class will be provided due to the spread of FTTH (Fiber to the home) using optical fiber in each home, including the 100Base-T interface of Ethernet (registered trademark). It has become widespread, and there is a demand for even higher transmission speeds in wireless LANs.

Therefore, in the IEEE 802.11n standard, which was standardized in 2009, the channel bandwidth, which was previously fixed at 20 MHz, has been expanded to a maximum of 40 MHz, and the spatial multiplex transmission technology (MIMO: Multiple input multiple output) technology has been expanded. The introduction was decided. By applying all the functions specified in the IEEE802.11n standard for transmission and reception, it is possible to achieve a maximum communication speed of 600 Mbps at the physical layer.

Furthermore, in the IEEE802.11ac standard, which was standardized in 2013, the channel bandwidth can be expanded to 80 MHz or up to 160 MHz (or 80 + 80 MHz), and multi-access using Space Division Multiple Access (SDMA). It has been decided to introduce a user MIMO (MU-MIMO) transmission method. By applying all the functions specified in the IEEE802.11ac standard for transmission and reception, it is possible to achieve a maximum communication speed of approximately 6.9 Gbps at the physical layer.

In addition, the IEEE802.11ax standard currently being formulated is expected to specify OFDMA (Orthogonal Frequency Division Multiple Access) that can transmit and receive frames by dividing the above 20MHz, 40MHz, 80MHz, 160MHz, and 80 + 80MHz channels into fine subchannels. Is. When OFDMA is used, the channel is divided into small subchannels, and simultaneous transmission by a plurality of radio stations is possible for each resource unit. Further, the IEEE802.11ax standard is expected to specify a function of increasing communication opportunities while suppressing interference from other peripheral cells by controlling a carrier sense threshold (CCA threshold) (Non-Patent Document 1).

Since the IEEE802.11 standard wireless LAN operates in the 2.4 GHz band or the 5 GHz band, which does not require a license, the IEEE802.11 standard wireless base station is used when forming a wireless LAN cell (BSS: Basic Service Set). In addition, one frequency channel is selected and operated from the frequency channels that can be supported by the own radio base station.

The channels used in the own cell, the bandwidth and other parameter settings, and other parameters that can be handled by the own wireless base station are the Beacon frames that are transmitted periodically and the Probe Request frames that are received from the wireless terminal. The cell is operated by describing it in the response frame or the like, transmitting the frame on the frequency channel whose operation has been decided, and notifying the subordinate wireless terminal and other wireless stations in the vicinity.

In a radio base station, there are four methods for selecting and setting frequency channels, bandwidths, and other parameters.
(1) A method of using the default parameter values set by the manufacturer of the wireless base station as they are.
(2) How to use the value manually set by the user who operates the wireless base station
(3) A method of autonomously selecting and setting parameter values based on the wireless environment information detected by each wireless base station at its own station at startup.
(4) How to set the parameter value determined by the centralized control station such as a wireless LAN controller

The number of channels that can be used simultaneously at the same location is 3, 4 for 2.4 GHz band wireless LAN, 2, 4, 9 or 19 channels for 5 GHz band wireless LAN, depending on the channel bandwidth used for communication. Therefore, when actually introducing a wireless LAN, it is necessary for the wireless base station to select a channel to be used in its own BSS (Non-Patent Document 2).

When the channel bandwidth is widened to 40 MHz, 80 MHz, 160 MHz or 80 + 80 MHz, the number of channels that can be used simultaneously at the same location in the 5 GHz band is 9 channels, 4 channels, and 2 channels instead of 19 channels at 20 MHz. Less. That is, as the channel bandwidth increases, the number of available channels decreases.

In a dense environment of a wireless LAN where the number of BSS is larger than the number of available channels, a plurality of BSS will use the same channel (OBSS: Overlapping BSS). Therefore, in the wireless LAN, autonomous decentralized access control is used in which data is transmitted only when the channel is free due to carrier sense by using CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance).

Specifically, the radio station in which the transmission request is generated first performs carrier sense for a predetermined sensing period (DIFS: Distributed Inter-Frame Space) to monitor the state of the radio medium, and during this period, transmission by another radio station is performed. If no signal is present, a random backoff is performed. The radio station continues to perform carrier sense during the random backoff period, during which time it gains the right to use the channel if there is no transmission signal from another radio station. Transmission / reception by another radio station is determined by whether or not a signal larger than a preset carrier sense threshold value is received. A radio station that has obtained the right to use a channel can transmit data to other radio stations in the same BSS and receive data from those radio stations. When such CSMA / CA control is performed, in a dense environment of a wireless LAN using the same channel, the frequency of the channel becoming busy due to carrier sense increases, so that the throughput decreases. Therefore, it is important to monitor the surrounding environment and appropriately select the channel to be used, transmission power value, carrier sense threshold, attenuation value, OFDMA resource unit, accommodation traffic amount, and simultaneous transmission according to environmental information. become.

Since the selection method of the above parameters such as channel selection in the radio base station is not defined by the IEEE802.11 standard, each vendor adopts its own method.

JP-A-2017-224949

Robert Stacey, “Specification Framework for TGax,” 2016. Masahiro Morikura, supervised by Shuji Kubota, "802.11 High Speed Wireless LAN Textbook" Revised 3rd Edition, Impress R & D, March 2008.

The high-efficiency wireless LAN standard (IEEE802.11ax) stipulates a simultaneous transmission function by multiple wireless terminal stations using OFDMA and a function to increase communication opportunities while suppressing interference from other cells in the vicinity by CCA threshold control. Is expected.

In the era of IEEE802.11ax, in order to make the best use of these OFDMA and CCA threshold control effects, appropriate selection of wireless terminal stations that perform simultaneous transmission and appropriate CCA threshold values used by each wireless terminal station are appropriate. The settings are important.

The present invention increases the opportunity for simultaneous transmission of a plurality of wireless terminal stations by optimizing the grouping of wireless terminal stations that perform simultaneous transmission by OFDMA and the CCA threshold set for the wireless terminal stations of each group, and the throughput. It is an object of the present invention to provide a radio communication system, a radio communication method, and a radio base station that enable improvement and reduction of delay time.

The first invention is a wireless communication system in which a plurality of wireless terminal stations belonging to the own cell of the wireless base station simultaneously transmit using OFDMA on a shared radio frequency band, in which the wireless base station has a plurality of members belonging to the own cell. Generated by the wireless environment information acquisition unit that acquires the wireless environment information of the wireless terminal station, the wireless terminal station grouping unit that groups multiple wireless terminal stations belonging to the own cell based on the wireless environment information, and the wireless terminal station grouping unit. A scheduling unit that adjusts the transmission opportunity of each group and a parameter control unit that calculates and sets the parameters required for simultaneous transmission according to the wireless environment information for each group generated by the wireless terminal station grouping unit. The wireless environment information acquisition unit is configured to acquire the RSSI value indicating the signal strength between the wireless base station and the wireless terminal station, and the parameter control unit is configured to acquire the RSSI value indicating the signal strength between the wireless base station and the wireless terminal station, and the parameter control unit is configured to acquire the RSSI value indicating the signal strength between the wireless base station and the wireless terminal station. The configuration is such that the CCA threshold of the group corresponding to the minimum RSSI value is calculated and the same CCA threshold is set for a plurality of wireless terminal stations of the same group. The configuration is such that simultaneous transmission is performed using the parameters set by the parameter control unit at the transmission opportunity adjusted in.

The wireless terminal station grouping unit may be configured to distribute a plurality of wireless terminal stations having close RSSI values to the same group, up to the number of wireless terminal stations capable of simultaneous transmission.

The scheduling unit may be configured to schedule access rights that give transmission opportunities to each group in a predetermined order.

The second invention is a wireless communication method in which a plurality of wireless terminal stations belonging to the own cell of the wireless base station simultaneously transmit using OFDMA on a shared radio frequency band, in which the wireless base station has a plurality of wireless base stations belonging to the own cell. Generated by a wireless environment information acquisition step for acquiring wireless environment information of a wireless terminal station, a wireless terminal station grouping step for grouping multiple wireless terminal stations belonging to the own cell based on the wireless environment information, and a wireless terminal station grouping step. A scheduling step that adjusts the transmission opportunity of each group and a parameter control step that calculates and sets the parameters required for simultaneous transmission according to the wireless environment information for each group generated by the wireless terminal station grouping step. In the wireless environment information acquisition step, the process of acquiring the RSSI value indicating the signal strength between the wireless base station and the wireless terminal station is performed, and in the parameter control step, a plurality of wireless terminal stations of the same group are used as parameters. The CCA threshold of the group corresponding to the minimum RSSI value is calculated from among them, the process of setting the same CCA threshold for multiple wireless terminal stations of the same group is performed, and the multiple wireless terminal stations of each group are scheduled. Simultaneous transmission is performed using the parameters set in the parameter control step at the transmission opportunity adjusted in the step.

In the wireless communication method of the second invention, in the wireless terminal station grouping step , a process of distributing a plurality of wireless terminal stations having close RSSI values to the same group is performed up to the number of wireless terminal stations capable of simultaneous transmission. In the scheduling step , the process of scheduling the access right that gives each group a transmission opportunity in a predetermined order is performed.

The third invention is a radio base station of a radio communication system in which a plurality of radio terminal stations belonging to the own cell of the radio base station simultaneously transmit using OFDMA on a shared radio frequency band, and a plurality of radios belonging to the own cell. Generated by the wireless environment information acquisition unit that acquires the wireless environment information of the terminal station, the wireless terminal station grouping unit that groups multiple wireless terminal stations belonging to the own cell based on the wireless environment information, and the wireless terminal station grouping unit. It is equipped with a scheduling unit that adjusts the transmission opportunity of each group and a parameter control unit that calculates and sets the parameters required for simultaneous transmission according to the wireless environment information for each group generated by the wireless terminal station grouping unit. The wireless environment information acquisition unit is configured to acquire the RSSI value indicating the signal strength between the wireless base station and the wireless terminal station, and the parameter control unit is configured to acquire the RSSI value indicating the signal strength between the wireless base station and the wireless terminal station, and the parameter control unit is among a plurality of wireless terminal stations in the same group as parameters. The CCA threshold of the group corresponding to the minimum RSSI value is calculated from, and the same CCA threshold is set for a plurality of wireless terminal stations of the same group. Scheduled for a plurality of wireless terminal stations of each group. The configuration is such that simultaneous transmission is performed using the parameters set by the parameter control unit at the transmission opportunity adjusted by the unit.

In the present invention, in an environment where wireless base stations and wireless terminal stations using a shared radio frequency band are densely packed, wireless terminal stations capable of simultaneous transmission by OFDMA are grouped and a CCA threshold is set for each group. , The opportunity for simultaneous transmission at wireless terminal stations increases, and throughput improves. In addition, since the transmission opportunity increases, the access time of the wireless terminal station is shortened, and the effect of shortening the traffic delay time can be expected.

It is a figure which shows the structural example of the wireless communication system of this invention. It is a figure which shows the configuration example of the radio base station AP and the radio terminal station STA. It is a flowchart which shows the processing procedure example of a radio base station AP. It is a figure which shows the example of scheduling of a wireless terminal station STA. It is a figure which shows the computer simulation result which shows the effect by this invention.

FIG. 1 shows a configuration example of the wireless communication system of the present invention.
In FIG. 1, the radio base station AP groups radio terminal stations STA1 to STA6, and sets access right scheduling and CCA threshold values that give transmission opportunities for each group. The radio terminal station STA of each group performs set scheduling and access control based on the CCA threshold value, and simultaneously transmits using OFDMA on the shared radio frequency band. Hereinafter, a method of grouping the radio terminal station STA in the radio base station AP, a method of scheduling, and a method of setting the CCA threshold value will be described.

FIG. 2 shows a configuration example of a radio base station AP and a radio terminal station STA.
In FIG. 2, the wireless base station AP is a wireless communication unit 11 that transmits / receives data to / from the wireless terminal station STA, and a wireless environment information acquisition unit that acquires wireless environment information (RSSI or SINR) of the wireless terminal station STA belonging to the own cell. 12, the wireless terminal station grouping unit 13 that groups the wireless terminal stations STA belonging to the own cell based on the wireless environment information, the scheduling unit 14 that adjusts the transmission opportunity for each group, and appropriate parameters for each group ( It is composed of a parameter control unit 15 that calculates and sets a CCA threshold) and an access right acquisition unit 16 that acquires an access right by carrier sense.

The wireless terminal station STA has a wireless communication unit 21 that transmits / receives data to / from the wireless base station AP, a wireless base station notification information holding unit 22 that holds grouping information, scheduling information, and parameters notified from the wireless base station AP, and a unit thereof. It is composed of an access right acquisition unit 23 that acquires an access right by carrier sense using parameters, and a transmission control unit 24 that performs simultaneous transmission using OFDMA according to the grouping and scheduling thereof.

FIG. 3 shows an example of the processing procedure of the radio base station AP.
In FIG. 3, the radio environment information acquisition unit 12 of the radio base station AP has an RSSI value indicating the signal strength between the radio base station AP and the radio terminal station STA as the radio environment information of the radio terminal station STA belonging to the own cell. (S1).

Next, the wireless terminal station grouping unit 13 groups the wireless terminal stations STA belonging to the own cell based on the RSSI value (S2). First, as the upper limit of the number of STAs belonging to the group, the number of units that can be simultaneously transmitted by OFDMA is set. Next, STAs having close RSSI values are distributed to the same group, up to the number of units that can be transmitted simultaneously. That is, the RSSI value of the STA of the same group is within a predetermined range, and the predetermined range of the RSSI value is different for each group. In the example shown in FIG. 1, group 1 is STA1, STA2, group 2 is STA3, STA4, and group 3 is STA5, STA6. Here, the RSSI values become smaller in the order of groups 1, 2, and 3, but the RSSI values of the STAs to be simultaneously transmitted in each group are close to each other within a predetermined range.

Next, the scheduling unit 14 performs scheduling for adjusting transmission opportunities for each group (S3). For example, as shown by an arrow in FIG. 4, transmission opportunities are given in the order of groups 1, 2, and 3, so that transmission opportunities are equalized among the groups.

Next, the parameter control unit 15 calculates and sets a CCA threshold value that is inversely proportional to the RSSI value of the wireless terminal station STA belonging to the group, for example, corresponding to the minimum value of the RSSI value, as a parameter for each group (S4). The signal reception sensitivity can be changed by adjusting the CCA threshold value. For example, if the CCA threshold is set to −75 dBm, only signals of −75 dBm or higher will be received. In the present invention, the same CCA threshold value is set for all wireless terminal station STAs belonging to each group.

Here, since the radio base station AP needs to normally receive the signals from all the radio terminal station STAs belonging to each group, the CCA threshold value to be set is the RSSI value between AP and STA in the group. Matches the radio terminal station STA with the smallest, that is, the radio terminal station STA with the weakest received signal level.

Multiple wireless terminal station STAs in each group perform access control using the CCA threshold value calculated and notified by the wireless base station in the order of scheduling set for each group, and when the transmission right is acquired, OFDMA Simultaneously transmit using.

FIG. 5 shows a computer simulation result showing the effect of the present invention.
In FIG. 5, the horizontal axis is the density of the radio base station AP, and the vertical axis is the throughput of the entire wireless communication system. A1 is a case where grouping and CCA threshold control are not performed, A2 is a case where random grouping and CCA threshold control for each group are performed, and A3 is a case where grouping and CCA threshold control for each group are performed according to the present invention.

In the case of A3, the wireless terminal station STAs having almost the same RSSI value are grouped, and the group closer to the wireless base station AP (larger RSSI value) increases the CCA threshold value, so that the parameter setting makes it easier to transmit at the same time. It is possible to improve the throughput and reduce the delay time. On the other hand, in the case of A2, since the grouping is random, even if the CCA threshold control is performed for each group, the effect of improving the throughput by simultaneous transmission is small.

11 Wireless communication unit 12 Wireless environment information acquisition unit 13 Wireless terminal station grouping unit 14 Scheduling unit 15 Parameter control unit 16 Access right acquisition unit 21 Wireless communication unit 22 Wireless base station notification information retention unit 23 Access right acquisition unit 24 Transmission control unit

Claims (6)

In a wireless communication system in which multiple wireless terminal stations belonging to the own cell of a wireless base station simultaneously transmit using OFDMA (Orthogonal Frequency Division Multiple Access) on a shared wireless frequency band.
The radio base station is
A wireless environment information acquisition unit that acquires wireless environment information of a plurality of wireless terminal stations belonging to the own cell, and
A wireless terminal station grouping unit that groups a plurality of wireless terminal stations belonging to the own cell based on the wireless environment information.
A scheduling unit that adjusts the transmission opportunity of each group generated by the wireless terminal station grouping unit,
Each group generated by the wireless terminal station grouping unit is provided with a parameter control unit that calculates and sets the parameters required for the simultaneous transmission according to the wireless environment information.
The wireless environment information acquisition unit is configured to acquire an RSSI value indicating a signal strength between the wireless base station and the wireless terminal station.
As the parameter, the parameter control unit calculates the CCA threshold value of the group corresponding to the minimum RSSI value from the plurality of wireless terminal stations of the same group, and the same CCA is used for the plurality of wireless terminal stations of the same group. It is a configuration that sets a threshold value.
The plurality of wireless terminal stations of each group are configured to perform the simultaneous transmission using the parameters set by the parameter control unit at the transmission opportunity adjusted by the scheduling unit. system. In the wireless communication system according to claim 1 ,
The wireless terminal station grouping unit is a wireless communication system characterized in that a plurality of wireless terminal stations having close RSSI values are distributed to the same group, up to the number of wireless terminal stations capable of simultaneous transmission. .. In the wireless communication system according to claim 1,
The scheduling unit is a wireless communication system characterized in that it is configured to schedule access rights that give the transmission opportunity to each group in a predetermined order. In a wireless communication method in which multiple wireless terminal stations belonging to the own cell of a wireless base station simultaneously transmit using OFDMA (Orthogonal Frequency Division Multiple Access) on a shared wireless frequency band.
The radio base station is
A wireless environment information acquisition step for acquiring wireless environment information of a plurality of wireless terminal stations belonging to the own cell, and
A wireless terminal station grouping step for grouping a plurality of wireless terminal stations belonging to the own cell based on the wireless environment information,
A scheduling step that adjusts the transmission opportunity of each group generated in the wireless terminal grouping step, and
A parameter control step for calculating and setting the parameters required for the simultaneous transmission according to the wireless environment information is executed for each group generated in the wireless terminal station grouping step.
In the wireless environment information acquisition step, a process of acquiring an RSSI value indicating a signal strength between the wireless base station and the wireless terminal station is performed.
In the parameter control step, as the parameter, the CCA threshold value of the group corresponding to the minimum RSSI value is calculated from the plurality of wireless terminal stations of the same group, and the same CCA is applied to the plurality of wireless terminal stations of the same group. Perform the process of setting the threshold value
A wireless communication method, wherein a plurality of wireless terminal stations in each group perform the simultaneous transmission using the parameters set in the parameter control step at the transmission opportunity adjusted in the scheduling step. In the wireless communication method according to claim 4 ,
In the wireless terminal station grouping step , a process of distributing a plurality of wireless terminal stations having close RSSI values to the same group is performed up to the number of wireless terminal stations capable of simultaneous transmission.
In the scheduling step , a process of scheduling access rights that give the transmission opportunity to each group in a predetermined order is performed .
A wireless communication method characterized by that. In a radio base station of a radio communication system in which multiple radio terminal stations belonging to the own cell of the radio base station simultaneously transmit using OFDMA (Orthogonal Frequency Division Multiple Access) on the shared radio frequency band.
A wireless environment information acquisition unit that acquires wireless environment information of a plurality of wireless terminal stations belonging to the own cell, and
A wireless terminal station grouping unit that groups a plurality of wireless terminal stations belonging to the own cell based on the wireless environment information.
A scheduling unit that adjusts the transmission opportunity of each group generated by the wireless terminal station grouping unit,
Each group generated by the wireless terminal station grouping unit is provided with a parameter control unit that calculates and sets the parameters required for the simultaneous transmission according to the wireless environment information.
The wireless environment information acquisition unit is configured to acquire an RSSI value indicating a signal strength between the wireless base station and the wireless terminal station.
As the parameter, the parameter control unit calculates the CCA threshold value of the group corresponding to the minimum RSSI value from the plurality of wireless terminal stations of the same group, and the same CCA is used for the plurality of wireless terminal stations of the same group. It is a configuration that sets a threshold value.
The feature is that the plurality of wireless terminal stations of each group are allowed to perform the simultaneous transmission using the parameters set by the parameter control unit at the transmission opportunity adjusted by the scheduling unit. Radio base station to do.

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