JP2020188437A - Radio communication system and radio communication method - Google Patents

Abstract

To balance loads on radio base stations in an event of the occurrence of sudden traffic or the like in a specific case by using radio environment information around a radio base station transmitting data, and information on the traffic and reception throughput of a destination communication station in an environment in which radio base stations using a shared radio frequency band are densely deployed.SOLUTION: A radio base station has a plurality of antennas for radio communication, and includes: environmental information acquisition means for acquiring peripheral radio environmental information, traffic destined to a user terminal, and throughput information on the user terminal; and parameter setting means for selecting antennas for which connection with the user terminal is permitted or antennas for which not permitted based on the information collected by the environmental information acquisition means.SELECTED DRAWING: Figure 2

Description

The present invention is a wireless communication system and a wireless communication method for improving a decrease in throughput due to CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) control of each wireless communication station in a dense environment of a wireless LAN (Local Area Network). Regarding.

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 IEEE802.11a / 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 5 MHz intervals between 2400 MHz and 2483.5 MHz. However, when using a plurality of channels in the same place, if the channels are used so that the spectra do not overlap in order 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 a 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 at 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 reduced as the number of wireless communication stations that try to transmit information increases.

On the other hand, in wired LAN, high-speed lines of 100 Mbps to 1 Gbps class have been 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 even in wireless LANs, further speeding up of transmission speed is required.

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. 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.

In addition, the IEEE 802.11ac standard, which was standardized in 2013, expands the channel bandwidth to 80 MHz and 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.

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 wireless base station.

The channel, bandwidth and other parameter settings used in the own cell and other parameters that can be handled by the own radio base station are the Probe for the Beacon frame that is transmitted regularly and the Probe Request frame that is 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 communication stations in the vicinity.

In a radio base station, there are four methods for selecting and setting frequency channels, bandwidths, and other parameters.
(1) How to use 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

In addition, the number of channels that can be used simultaneously at the same location is 3, for a 2.4 GHz band wireless LAN, and 2, 4, 9, or 19 for a 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 1).

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 19 channels at 20 MHz, 9 channels, 4 channels, and 2 channels. 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 wireless LAN, autonomous decentralized access control is used in which CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) is used to transmit data only when a channel is free due to carrier sense.

Specifically, the wireless communication 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 wireless medium, and during this period, other wireless communication stations. If there is no transmission signal by, random backoff is performed. The radio communication station continues to perform carrier sense during the random backoff period, but also obtains the right to use the channel when there is no transmission signal from another radio communication station during this period. Transmission / reception by another wireless communication station is determined by whether or not a signal larger than a preset carrier sense threshold value is received. The radio communication station that has obtained the right to use the channel can transmit data to other radio communication stations in the same BSS and receive data from those radio communication 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, select an appropriate channel, and select a transmission power value and carrier sense threshold that enable simultaneous transmission and reception.

Since the channel selection method for wireless base stations is not defined by the IEEE802.11 standard, each vendor adopts its own method, but the most common channel selection method is the channel with the least interference power. There is a method of selecting autonomously and decentralized. The radio base station carriers sense all channels for a certain period of time, selects the channel with the smallest interference power, and transmits / receives data to / from the subordinate terminal device on the selected channel. The interference power is the level of a signal received from a neighboring BSS or another system.

The IEEE802.11 standard stipulates the procedure for changing channels when the radio conditions around the BSS change, but basically, except for forced migration due to radar detection, etc., the channel once selected is reselected. Not. That is, in the current wireless LAN, the channel is not optimized according to the change in the wireless condition.

In addition, the IEEE 802.11 standard stipulates the maximum transmission output value of signals to be transmitted in accordance with the Radio Law established in each country. The carrier sense threshold is defined as -82 dBm when the detection signal is a wireless LAN signal, and -62 dBm in other cases.

In this way, the maximum transmission power value and carrier sense threshold are specified, but when multiple wireless communication stations transmit and receive on the same channel, the optimum value according to changes in wireless conditions is specified. Not.

Masahiro Morikura, supervised by Shuji Kubota, "802.11 High Speed Wireless LAN Textbook" Revised 3rd Edition, Impress R & D, March 2008.

Of the above-mentioned frequency channel, bandwidth and other parameter selection and setting methods (1) to (4), the cheapest radio base station uses the default parameters set by the manufacturer in (1) as they are. I often do it. However, in an environment where multiple wireless base stations of the same manufacturer are installed nearby, all wireless base stations use the same frequency channel and transmission power value, causing interference between wireless base stations. There is a problem that the communication quality deteriorates.

In a relatively small network such as a general household, it is conceivable that the user who operates the wireless LAN in (2) sets appropriate parameters. However, although various parameters can be set in an environment without external interference sources, it is appropriate for users or administrators in environments where wireless LAN is used around urban areas and apartment buildings, or in medium-sized and large-scale networks. It is difficult to set various parameters.

A radio base station capable of autonomous distributed operation can autonomously select a parameter value based on the radio environment information detected by each radio base station at startup in (3). However, the appropriate parameter values differ depending on the order in which the radio base stations are activated.

In addition, when environmental changes such as changes in the number of active wireless base stations, changes in the wireless terminal devices under each wireless base station, and changes in the amount of data transmitted by the wireless devices in each cell occur. Since the channel used, the transmission power value used, the carrier sense threshold used, and the attenuation value used are not optimized, there is a problem that a difference occurs between the throughputs of each cell and the throughput deteriorates in the entire system.

In the present invention, in an environment where radio base stations using a shared radio frequency band are densely packed, the radio environment information around the radio base station that transmits data and the traffic amount and reception throughput information at the destination communication station are used. It is an object of the present invention to provide a wireless communication system and a wireless communication method capable of distributing the load of a wireless base station when a sudden traffic occurs in a specific case.

The first invention is a wireless communication system including a plurality of wireless base stations that perform wireless communication on a shared wireless frequency band. The wireless base station has a plurality of antennas for wireless communication and provides peripheral wireless environment information. And a parameter that selects an antenna that allows or does not allow connection with the user terminal based on the traffic to the user terminal, the environmental information acquisition means that acquires the throughput information of the user terminal, and the information collected by the environmental information acquisition means. It has a setting means.

In the wireless communication system of the first invention, the parameter setting means connects to the user terminal so as to minimize the difference, standard deviation, or degree of unfairness between the throughputs of the wireless base stations. It is a configuration to select the antenna that allows or does not allow.

In the wireless communication system of the first invention, the parameter setting means is an antenna that allows connection with a user terminal so that the degree of congestion varies according to the degree of traffic congestion of each antenna of each radio base station. It is a configuration to select antennas that are not allowed.

A second invention is a wireless communication method in which a plurality of wireless base stations perform wireless communication on a shared wireless frequency band, wherein the environmental information acquisition means of the wireless base station has a plurality of antennas for wireless communication and is in the vicinity. The wireless environment information, traffic addressed to the user terminal, and throughput information of the user terminal are acquired, and the parameter setting means of the wireless base station is an antenna that permits connection with the user terminal based on the information collected by the environment information acquisition means. Select antennas that are not allowed.

In the wireless communication method of the second invention, the parameter setting means connects to the user terminal so as to minimize the difference, standard deviation, or degree of unfairness between the throughputs of the wireless base stations. Select antennas that allow or do not allow.

In the wireless communication method of the second invention, the parameter setting means is an antenna that allows connection with a user terminal so that the degree of congestion varies according to the degree of traffic congestion of each antenna of each wireless base station. Select antennas that are not allowed.

The present invention has an effect of reducing congestion of radio channels in a specific place in an environment where radio base stations using a shared radio frequency band are densely packed. Therefore, the access right when the radio base station transmits data ( The waiting time until the channel usage right) is acquired is shortened. Therefore, the throughput of the receiving wireless base station is improved, and the effect of improving the communication quality of the application used and the perceived quality of the user can be obtained.

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 wireless base station of the wireless communication system of this invention. It is a flowchart which shows the processing procedure example of the wireless base station of the wireless communication system of this invention. It is a figure which shows an example of the selection process of ON / OFF of an antenna.

FIG. 1 shows a configuration example of the wireless communication system of the present invention.
In FIG. 1, the radio base stations AP1 to AP5 perform wireless communication with one or more belonging radio terminal stations (user terminals) by using a plurality of antennas distributed and arranged in the shared radio frequency band. The AP1 wirelessly communicates with the belonging wireless terminal stations STA11 to STA13 via the antennas ANTs 13, 14 and 12, respectively. The AP2 wirelessly communicates with the belonging wireless terminal station STA21 via the antenna ANT23. The AP3 wirelessly communicates with the belonging wireless terminal station STA31 via the antenna ANT32. The AP4 wirelessly communicates with the belonging wireless terminal stations STA41 to STA42 via the antennas ANT43 and 42. The AP5 wirelessly communicates with the belonging wireless terminal station STA51 via the antenna ANT53.

FIG. 2 shows a configuration example of a wireless base station of the wireless communication system of the present invention.
In FIG. 2, the wireless base station is composed of a plurality of distributed antennas ANTs 11 to 14, a wireless communication unit 11 that transmits / receives data to / from a destination wireless terminal station via those antennas, and peripheral wireless environment information. Using the wireless environment information acquisition unit 12 that performs scanning and acquires wireless environment information such as usage parameters of surrounding wireless base stations and information on the amount of traffic and reception throughput at the destination wireless terminal station, and the acquired wireless environment information. Access right by carrier sense, parameter calculation unit 13 that selects antennas that allow or do not allow user connection in the wireless base station, parameter setting unit 14 that sets ON / OFF of each antenna according to the calculated antenna selection information. It is composed of the access right acquisition unit 15 for acquiring the above.

FIG. 3 shows an example of a processing procedure of a wireless base station of the wireless communication system of the present invention.
In FIG. 3, when this procedure is started, the wireless environment information acquisition unit 12 of the wireless base station acquires wireless environment information such as usage parameters of peripheral wireless communication stations (S11), and traffic to each wireless station. The amount and received throughput information is acquired (S12). Next, the parameter calculation unit 13 uses each acquired information to select antennas that allow user connection and antennas that do not allow user connection in the radio base station (S13). Next, the parameter setting unit 14 sets ON / OFF of each antenna according to the antenna selection information calculated by the parameter calculation unit 13 (S14), and starts operation.

In this selection, for example, using the Back pressure algorithm for the probability determination process model, the packet discard rate corresponding to the radio channel congestion degree is applied as the "state", and the combination of antenna ON / OFF is applied as the "action" to the reward function. , ON / OFF of each antenna is switched in order, and the combination of ON / OFF of the antenna that maximizes the reward function (minimum packet discard rate) is selected. This allows the difference, standard deviation, or degree of unfairness between each radio base station throughput to be minimized.

FIG. 4 shows an example of the ON / OFF selection process of the antenna.
In FIG. 4, each radio base station AP1 to AP3 is provided with six antennas, □ indicates an antenna OFF state, and ■ indicates an antenna ON state.

(1) is a normal state, and each radio base station AP1 to AP3 has two antennas turned on, and in this state, the traffic in the vicinity of the turned-on antenna is evenly accommodated.

In (2), traffic is concentrated in the area A surrounded by the broken line circle, but since the only antenna turned on in that area A is the radio base station AP1, the radio base station AP1 is in a high load state. .. In such a state, in step S13 of FIG. 3, the Back pressure algorithm is used to optimize the ON / OFF combination of the antenna in each radio base station.

In (3), as a result of optimizing the combination of ON / OFF of the antenna, the antenna covering the area A is turned on in each radio base station AP1 to AP3, and the traffic of the area A is distributed by each radio base station. , The high load state of the radio base station AP1 can be eliminated.

AP wireless base station STA wireless terminal station 11 Wireless communication unit 12 Wireless environment information acquisition unit 13 Parameter calculation unit 14 Parameter setting unit 15 Access right acquisition unit

Claims (6)

In a wireless communication system equipped with a plurality of wireless base stations that perform wireless communication on a shared radio frequency band,
The radio base station
An environment information acquisition means that has multiple antennas for wireless communication and acquires peripheral wireless environment information, traffic addressed to the user terminal, and throughput information of the user terminal.
A wireless communication system provided with a parameter setting means for selecting an antenna that allows connection with the user terminal or an antenna that does not allow connection with the user terminal based on the information collected by the environment information acquisition means. In the wireless communication system according to claim 1,
The parameter setting means has antennas that allow or disallow connection with the user terminal so as to minimize the difference, standard deviation, or degree of inequity between radio base station throughputs. A wireless communication system characterized in that it has a configuration for selecting antennas. In the wireless communication system according to claim 1,
The parameter setting means is configured to select antennas that allow connection with the user terminal or antennas that do not allow connection with the user terminal so that the variation in the degree of congestion is reduced according to the degree of traffic congestion of each antenna of each radio base station. A wireless communication system characterized by being present. In a wireless communication method in which multiple wireless base stations perform wireless communication on a shared radio frequency band,
The environment information acquisition means of the wireless base station has a plurality of antennas for wireless communication, and acquires peripheral wireless environment information, traffic addressed to the user terminal, and throughput information of the user terminal.
A wireless communication method, wherein the parameter setting means of the wireless base station selects an antenna that permits or does not allow connection with the user terminal based on the information collected by the environmental information acquisition means. In the wireless communication method according to claim 4,
The parameter setting means is an antenna that allows or does not allow connection with the user terminal so as to minimize the difference, standard deviation, or degree of unfairness between the throughputs of each radio base station. A wireless communication method characterized by sorting out. In the wireless communication method according to claim 4,
The parameter setting means selects antennas that allow connection with the user terminal or antennas that do not allow connection with the user terminal so that the variation in the degree of congestion is reduced according to the degree of traffic congestion of each antenna of each radio base station. A characteristic wireless communication method.

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