JP7209292B2 - Wireless communication system and wireless communication method - Google Patents

Description

The present invention provides a wireless communication system and a wireless communication method that improve throughput degradation caused by CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) control of each wireless communication station in a dense wireless LAN (Local Area Network) environment. Regarding.

In recent years, due to the spread of portable and high-performance wireless terminals such as notebook computers and smart phones, wireless LANs conforming to the IEEE802.11 standard have come to be widely used not only in companies and public spaces but also in ordinary homes. IEEE802.11 standard wireless LAN includes IEEE802.11b/g/n standard wireless LAN using 2.4 GHz band and IEEE802.11a/n/ac standard wireless LAN using 5 GHz band.

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

In the wireless LAN of the IEEE802.11a standard, in Japan, a total of 19 channels, 8 channels and 11 channels that do not overlap each other, are defined between 5170 MHz and 5330 MHz and between 5490 MHz and 5710 MHz. Note that the IEEE802.11a standard fixes the bandwidth per channel to 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. In reality, the MAC (Medium Access Control) layer has a transmission efficiency of about 50 to 70%, so the upper limit of the actual throughput is about 5 Mbps for the IEEE802.11b standard, and 30 Mbps for the IEEE802.11a and IEEE802.11g standards. degree. Also, the transmission rate is further reduced as the number of wireless communication stations attempting to transmit information increases.

On the other hand, in wired LAN, the spread of FTTH (Fiber to the home) using optical fiber, including the 100Base-T interface of Ethernet (registered trademark), has led to the provision of high-speed lines of the 100 Mbps to 1 Gbps class. It is widely used, and wireless LAN is also required to have a higher transmission speed.

For this reason, the IEEE802.11n standard, which was completed in 2009, expands the channel bandwidth from the fixed 20MHz to a maximum of 40MHz, and also introduces spatial multiplexing transmission technology (MIMO: Multiple input multiple output) technology. decided to introduce. If all the functions specified in the IEEE802.11n standard are applied for transmission and reception, a maximum communication speed of 600 Mbps can be achieved in the physical layer.

Furthermore, the IEEE802.11ac standard, which was standardized in 2013, expands the channel bandwidth to 80 MHz or a maximum of 160 MHz (or 80 + 80 MHz), and multi-channel communication using Space Division Multiple Access (SDMA). It has been decided to introduce a user MIMO (MU-MIMO) transmission method. If all the functions specified in the IEEE802.11ac standard are applied for transmission and reception, a maximum communication speed of approximately 6.9 Gbps can be achieved in the physical layer.

IEEE802.11 standard wireless LAN operates in the unlicensed frequency band of 2.4 GHz band or 5 GHz band. First, it selects and operates one frequency channel from the frequency channels that can be handled by its own radio base station.

The channel, bandwidth, and other parameter settings used in the own cell and other parameters that can be handled by the own wireless base station are the Beacon frames that are periodically transmitted and the Probe Request frame received from the wireless terminal. The cell is operated by describing it in a response frame or the like, transmitting the frame on the frequency channel for which operation has been decided, and notifying the radio terminals under its control and other surrounding radio communication stations.

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

Also, 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 a wireless base station to select a channel to be used within its own BSS (Non-Patent Document 1).

When the channel bandwidth is widened to 40MHz, 80MHz, 160MHz or 80 + 80MHz, the number of channels that can be used simultaneously in the same location in the 5GHz band is 19 channels with a channel bandwidth of 20MHz, but 9 channels, 4 channels, and 2 channels. less. That is, as the channel bandwidth increases, the number of available channels will decrease.

In a wireless LAN dense environment where there are more BSSs than available channels, multiple BSSs will use the same channel (OBSS: Overlapping BSS). Therefore, in wireless LANs, CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) is used to perform autonomous decentralized access control in which data is transmitted only when a channel is available due to carrier sense.

Specifically, a wireless communication station that has issued a transmission request first performs carrier sensing for a predetermined sensing period (DIFS: Distributed Inter-Frame Space) to monitor the state of the wireless medium. Random backoff is performed if there is no transmitted signal by . The radio communication station continues to perform carrier sensing during the random backoff period, but obtains the right to use the channel if there is no transmission signal from another radio communication station during this period. Note that transmission/reception by other wireless communication stations is determined by whether or not a signal greater than a preset carrier sense threshold is received. A radio station that gains access to the channel can transmit data to and receive data from other radio stations within the same BSS. When such CSMA/CA control is performed, in a dense environment of a wireless LAN using the same channel, carrier sense increases the frequency of busy channels, resulting in a decrease in throughput. Therefore, it is important to monitor the surrounding environment, select an appropriate channel, and select a transmission power value and a carrier sense threshold that enable simultaneous transmission and reception.

Since the IEEE802.11 standard does not define the channel selection method for wireless base stations, each vendor has adopted its own method. There is a method of autonomous decentralized selection of A radio base station carries out carrier sensing on all channels for a certain period of time, selects a channel with the lowest interference power, and transmits and receives data to and from a terminal device under its control on the selected channel. The interference power is the level of signals received from neighboring BSSs and other systems.

The IEEE802.11 standard stipulates channel change procedures when the radio conditions around the BSS change. not That is, in the current wireless LAN, channel optimization according to changes in wireless conditions is not performed.

Patent Literature 1 shows a method of selecting a channel to be used by a wireless base station so as to avoid throughput degradation due to the effects of hidden terminals and exposed terminals in a wireless LAN dense environment. For example, by not selecting the channel used by the adjacent wireless base station and the next adjacent wireless base station as the channel used by the own station, it is possible to avoid local drop in throughput even in a dense wireless LAN environment.

In addition, the IEEE802.11 standard defines the maximum transmission output value of signals to be transmitted in accordance with the Radio Law defined in each country. The carrier sense threshold is specified to be -82 dBm when the detection signal is a wireless LAN signal, and -62 dBm otherwise.

In this way, the maximum values of the transmission power value and the carrier sense threshold are specified. not (Non-Patent Document 2).

Patent document 2 shows a method of simultaneously adjusting a transmission power value and a carrier sense threshold by adjusting an attenuation value of an attenuator of a wireless communication station. For example, if the attenuation value of the attenuator is increased by a [dB], the transmission power value of the wireless communication station is decreased by a [dB] and the received power value is also decreased by a [dB], so the carrier sense threshold is increased by a [dB]. be equivalent to At this time, by lowering the transmission power value by a [dB], the SINR at the destination wireless communication station deteriorates and the throughput decreases. On the other hand, if the carrier sense threshold is increased by a [dB], the number of wireless communication stations in the vicinity decreases, making it easier to obtain access rights and increasing the throughput. Therefore, the adjustment amount of the transmission power value and the carrier sense threshold has an optimum value that does not significantly decrease the SINR while maximizing the throughput. , that is, a method for calculating the correction value a of the attenuator.

JP 2017-224948 A JP 2017-224949 A

Masahiro Morikura, Shuji Kubota, "802.11 High Speed Wireless LAN Textbook" Revised 3rd Edition, Impress R&D, March 2008. Robert Stacey, “Specification Framework for TGax,” January 28, 2016.

Among the methods (1) to (4) for selecting and setting the frequency channel, bandwidth, and other parameters described above, particularly inexpensive wireless base stations use the default parameters set by the manufacturer in (1) as they are. often do. However, in an environment where multiple wireless base stations from 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 is degraded.

In a relatively small-scale network such as a general home, it is conceivable that (2) the user who operates the wireless LAN sets appropriate parameters. However, although it is possible to set various parameters in an environment where there are no sources of external interference, in environments where wireless LANs are used around, such as urban areas and apartment buildings, or in medium- or large-scale networks, users or administrators may parameter setting is difficult.

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

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

The present invention uses information on the radio environment around a radio communication station that performs data transmission and the signal power to interference power ratio (SINR) at the destination communication station in an environment where radio communication stations that use a shared radio frequency band are concentrated. It is therefore an object of the present invention to provide a radio communication system and a radio communication method capable of calculating the frequency channel to be used for data transmission, the optimum transmission power value, and the carrier sense threshold adjustment amount.

A first invention is a radio communication system having a plurality of radio communication stations that perform radio communication on a shared radio frequency band, in which the radio communication stations provide surrounding radio environment information and signal power versus interference power at a destination radio communication station. Throughput of a destination wireless communication station according to a wireless environment information acquiring means for acquiring information of a ratio SINR, an SINR at the target wireless communication station, and the number of surrounding wireless communication stations using a shared wireless frequency band detected by the own station and parameter calculation/setting means for simultaneously calculating and setting a transmission power value and an adjustment amount of a carrier sense threshold.

In the wireless communication system of the first invention, the wireless environment information acquiring means includes, as surrounding wireless environment information, operating frequency channels, transmission power values and carrier sense thresholds in all adjacent wireless communication stations within two hops, and destination wireless communication It is a configuration for collecting SINR at a station.

In the radio communication system of the first invention, the parameter calculation/setting means calculates the frequency channel of the own station that maximizes a predetermined gain function based on the radio environment information collected by the radio environment information acquisition means, and the transmission power. In this configuration, the value and the adjustment amount of the carrier sense threshold are calculated and set at the same time.

The gain function in the wireless communication system of the first invention is
u3 _i =(1−w)·u1 _i (a _Ni ,c _Ni )+w·u2 _i (a _Si ,c _Si )
where c is the operating frequency channel, a is the transmission power value and carrier sense threshold adjustment amount, and _u1 is a gain function based on information a _Ni and c _Ni of all adjacent radio base stations Ni including the own station. , u2 are gain functions based on the information a _Si and c _Si of adjacent radio base stations _Si within two hops including the own station, and w is a weighting factor.

A second invention is a radio communication method in which a plurality of radio communication stations perform radio communication on a shared radio frequency band, in which the radio communication stations transmit surrounding radio environment information and a signal power to interference power ratio SINR at a destination radio communication station. , the SINR of the destination wireless communication station, and the number of surrounding wireless communication stations using the shared wireless frequency band detected by the own station, the throughput of the destination wireless communication station is maximized. and a parameter calculation/setting step for simultaneously calculating and setting the transmission power value and the carrier sense threshold adjustment amount.

In the wireless communication method according to the second aspect of the invention, the wireless environment information obtaining step includes operating frequency channels, transmission power values, and carrier sense thresholds in all adjacent wireless communication stations within two hops, and destination wireless communication as the surrounding wireless environment information. Collect the SINR at the station.

In the radio communication method of the second invention, the parameter calculation/setting step includes, based on the radio environment information collected by the radio environment information acquisition step, the frequency channel of the own station that maximizes a predetermined gain function and the transmission power value and carrier sense threshold adjustment amount are calculated and set at the same time.

The gain function in the wireless communication method of the second invention is
u3 _i =(1−w)·u1 _i (a _Ni ,c _Ni )+w·u2 _i (a _Si ,c _Si )
where c is the operating frequency channel, a is the transmission power value and carrier sense threshold adjustment amount, and _u1 is a gain function based on information a _Ni and c _Ni of all adjacent radio base stations Ni including the own station. , u2 are gain functions based on the information a _Si and c _Si of adjacent radio base stations _Si within two hops including the own station, and w is a weighting factor.

In an environment where wireless communication stations using a shared radio frequency band are concentrated, the present invention has the effect of reducing interference from and received from wireless communication stations. Waiting time until acquisition of (channel usage right) is shortened. Therefore, the throughput of the receiving wireless communication station is improved, and the effect of improving the communication quality of the application used and the user's experience quality is obtained.

1 is a diagram showing a configuration example of a wireless communication system of the present invention; FIG. It is a figure which compares the conventional radio|wireless communications system and the radio|wireless communications system of this invention. 1 is a diagram showing a configuration example of a radio communication station of a radio communication system according to the present invention; FIG. 4 is a flow chart showing an example of a processing procedure of a radio communication station of the radio communication system of the present invention; 4 is a flow chart showing an example of an environment information notification procedure in a radio base station of the radio communication system of the present invention; 4 is a flow chart showing an example of a parameter calculation procedure in a radio communication station of the radio communication system of the present invention; FIG. 10 is a diagram showing Effect 1 of the present invention by comparing average throughputs; FIG. 10 is a diagram showing effect 2 of the present invention by comparing the number of wireless communication stations in an exposed state;

FIG. 1 shows a configuration example of a wireless communication system of the present invention.
In FIG. 1, radio base stations AP1 to AP5 perform radio communication with respective radio terminal stations to which they belong in a shared radio frequency band. AP1 performs wireless communication with the wireless terminal stations STA11 to STA13 to which it belongs, AP2 performs wireless communication with the wireless terminal station STA21 to which it belongs, AP3 performs wireless communication with the wireless terminal station STA31 to which it belongs, and AP4 performs wireless communication with the wireless terminal station STA31 to which it belongs. Wireless communication is performed with stations STA41 to STA42, and AP5 wirelessly communicates with wireless terminal station STA51 to which it belongs.

FIG. 2 shows a comparison between a conventional wireless communication system and the wireless communication system of the present invention.
In the conventional radio communication system shown in FIG. 2(1), channel setting and attenuator (ATT) setting are performed separately. For example, ATT setting is performed after channel setting.

In the wireless communication system of the present invention shown in FIG. 2(2), since channel and ATT optimization settings are performed simultaneously, convergence characteristics are improved, and frequency resources can be effectively utilized by overall optimization without falling short of local optimization. It becomes possible.

FIG. 3 shows a configuration example of a radio communication station of the radio communication system of the present invention. The radio communication station is a radio base station AP or a radio terminal station STA, both of which have the same configuration.
In FIG. 3, a wireless communication station includes a wireless communication unit 11 that performs data transmission/reception with a destination station, and scans surrounding wireless environment information to obtain wireless environment information such as usage parameters of surrounding wireless communication stations and the destination communication station. A parameter calculation for calculating parameters such as a frequency channel, a transmission power value, a carrier sense threshold value, an attenuation value, etc. using a radio environment information acquisition unit 12 that acquires information on the signal power to interference power ratio SINR in 13, a parameter setting unit 14 for setting parameters such as the calculated frequency channel, transmission power value, carrier sense threshold, and attenuation value, and an access right acquisition unit for acquiring access rights by carrier sensing using the set parameters. 15.

FIG. 4 shows an example of a processing procedure of a radio communication station of the radio communication system of the present invention.
In FIG. 4, when this procedure is started, the radio environment information acquisition unit 12 of the radio communication station acquires the radio environment information such as the usage parameters of the surrounding radio communication stations (S11). Information of the signal power to interference power ratio SINR at the destination communication station at the value is obtained (S12). Next, the parameter calculator 13 calculates the optimum frequency channel, transmission power value, and carrier sense threshold adjustment amount for the wireless communication station using each piece of acquired information (S13). Next, the parameter setting unit 14 sets the optimum frequency channel, sets the calculated transmission power value and carrier sense threshold adjustment amount as an attenuator correction value (S14), and starts operation.

FIG. 5 shows an example of an environment information notification procedure in a radio base station of the radio communication system of the present invention. In FIG. 5, when this procedure is started, the radio base station starts operation using the initial channel C, transmission power value P, and carrier sense threshold Θ (S21). Information on P and Θ is notified to other neighboring radio base stations (S22).

FIG. 6 shows an example of a parameter calculation procedure in a radio communication station of the radio communication system of the present invention.
In FIG. 6, when this procedure is started, using the C, P, Θ information of the adjacent wireless base station, the radio environment information, and the C, P, Θ of the own wireless base station, A gain function _u3i designed in advance to maximize the throughput is calculated (S31). Then, C ^* , P ^* , Θ ^* that maximize the gain function u3 _i in the own radio base station i are set as operation parameters of the own radio base station i (S32).

Here, the gain function u3 will be explained. A gain function u3 _i of the radio base station i is expressed as follows.
u3 _i =(1−w)·u1 _i (a _Ni ,c _Ni )+w·u2 _i (a _Si ,c _Si )

Here, c is the operating frequency channel, a is the adjustment amount of the transmission power value P and the carrier sense threshold Θ, which is the correction value of the attenuator. u1 is a gain function based on information a _Ni and c _Ni of all neighboring radio base stations Ni including the own station, u2 is a gain function based on information a _Si and c _Si of neighboring radio base stations _Si within two hops including the own _station is the gain function based on This gain function is a function of the SINR at the destination terminal and the number of surrounding wireless communication stations using the shared frequency channel detected by the own station. This gain function has the property that the value increases in proportion to the SINR and the value decreases according to the number of surrounding wireless communication stations. w is a weighting factor.

FIG. 7 shows effect 1 of the present invention by comparing average throughputs.
In FIG. 7, 40 wireless base stations and 80 wireless terminal stations are assumed, and the communication distance is uniformly distributed from 3 to 10 m. “Random selection” is the case where each radio base station selects a channel completely randomly. "Only attenuator control" and "only channel control" are the results when only the channel setting of the "current wireless communication system" in FIG. 2(1) is performed and when only the ATT setting is performed. On the other hand, the present invention (attenuator + channel control) is the result when the channel and ATT are simultaneously set in the "wireless communication system of the present invention" in FIG. 2(2). It can be confirmed that by using the present invention, a higher average throughput can be obtained compared to other methods.

FIG. 8 shows effect 2 of the present invention by comparing the number of wireless communication stations in the exposed state.
In FIG. 8, the conditions are the same as for effect 1 in FIG. It can be confirmed that, by using the present invention, the number of wireless communication stations that cannot acquire the right to transmit and are in an exposed state can be greatly reduced to almost zero, as in the case of channel control alone.

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 (2)

In a radio communication system comprising a plurality of radio communication stations performing radio communication on a shared radio frequency band,
The wireless communication station
a radio environment information obtaining means for obtaining surrounding radio environment information and information on a signal power to interference power ratio SINR at a destination radio communication station;
the SINR of the destination wireless communication station and the frequency channel of the own station that maximizes the throughput of the destination wireless communication station according to the number of surrounding wireless communication stations using the shared radio frequency band detected by the own station; , a parameter calculation and setting means for simultaneously calculating and setting the transmission power value and the adjustment amount of the carrier sense threshold ,
The radio environment information acquisition means collects, as the surrounding radio environment information, the operating frequency channel, transmission power value, and carrier sense threshold of all adjacent radio communication stations within two hops, and the SINR of the destination radio communication station. is the configuration,
Based on the radio environment information collected by the radio environment information acquisition means, the parameter calculation/setting means is configured to: is calculated and set at the same time,
The gain function is
u3 _i =(1−w)·u1 _i (a _Ni ,c _Ni )+w·u2i(a _Si ,c _Si )
where c is the operating frequency channel, a is the transmission power value and carrier sense threshold adjustment amount, and u1 is a gain function based on information a Ni and c Ni of all adjacent radio base stations _Ni including the _own station _. , u2 is a gain function based on the information a _Si and c _Si of neighboring radio base stations _Si within two hops including the own station , w is a weighting factor,
The gain functions u1 and u2 are functions of the SINR at the destination wireless communication station and the number of surrounding wireless communication stations using a shared frequency channel detected by the own station, and the value increases in proportion to the SINR. and has the property that the value decreases according to the number of wireless communication stations in the vicinity.
A wireless communication system characterized by: In a radio communication method in which a plurality of radio communication stations perform radio communication on a shared radio frequency band,
The wireless communication station
a radio environment information obtaining step of obtaining surrounding radio environment information and information of a signal power to interference power ratio SINR at a destination radio communication station;
the SINR of the destination wireless communication station and the frequency channel of the own station that maximizes the throughput of the destination wireless communication station according to the number of surrounding wireless communication stations using the shared radio frequency band detected by the own station; , a parameter calculation/setting step of simultaneously calculating and setting the transmission power value and the adjustment amount of the carrier sense threshold ,
The radio environment information obtaining step collects, as the surrounding radio environment information, the operating frequency channel, transmission power value, and carrier sense threshold value of all adjacent radio communication stations within two hops, and the SINR of the destination radio communication station. including steps
In the parameter calculation/setting step, based on the radio environment information collected in the radio environment information acquisition step, the frequency channel of the local station that maximizes a predetermined gain function, the transmission power value, and the adjustment amount of the carrier sense threshold. simultaneously calculating and setting
The gain function is
u3 _i =(1−w)·u1 _i (a _Ni ,c _Ni )+w·u2i(a _Si ,c _Si )
where c is the operating frequency channel, a is the transmission power value and carrier sense threshold adjustment amount, and u1 is a gain function based on information a Ni and c Ni of all adjacent radio base stations _Ni including the _own station _. , u2 is a gain function based on the information a _Si and c _Si of neighboring radio base stations _Si within two hops including the own station , w is a weighting factor,
The gain functions u1 and u2 are functions of the SINR at the destination wireless communication station and the number of surrounding wireless communication stations using a shared frequency channel detected by the own station, and the value increases in proportion to the SINR. and has the property that the value decreases according to the number of wireless communication stations in the vicinity.
A wireless communication method characterized by:

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