JP2017224949A - Radio communication system and radio communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To calculate an optimum carrier sense threshold and transmission power value or an attenuation value used for data transmission, by using radio environment information on the periphery of a radio communication station performing data transmission, and SINR in a destination communication station.SOLUTION: In a radio communication system including multiple radio communication stations performing radio communication on a sharing frequency band, the radio communication station includes: radio environment information acquisition means for acquiring peripheral radio environment information and the information of signal power vs interference power ratio SINR in a destination communication station; and parameter setting means for simultaneously calculating and setting the transmission power value of own station where throughput of the destination communication station becomes maximum and a correction value of a carrier sense threshold, according to the SINR in the destination communication station and the number of peripheral radio communication stations using the sharing frequency band detected by the own station.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a wireless communication system and a wireless communication method that improve a 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). .

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

  In the wireless LAN of IEEE802.11b standard or IEEE802.11g standard, 13 channels are prepared at intervals of 5 MHz between 2400 MHz and 2483.5 MHz. However, when a plurality of channels are used at the same location, 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, 4 channels can be used simultaneously.

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

  The maximum transmission speed of the wireless LAN is 11 Mbps for the IEEE802.11b standard, and 54 Mbps for the IEEE802.11a standard or the IEEE802.11g standard. However, the transmission rate here is the transmission rate on the physical layer. Actually, since the transmission efficiency in the MAC (Medium Access Control) layer is about 50 to 70%, 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 rate further decreases as the number of wireless stations that attempt to transmit information increases.

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

  Therefore, in the IEEE802.11n standard, which was standardized in 2009, the channel bandwidth, which had been fixed at 20 MHz, has been expanded to a maximum of 40 MHz, and the multiple input multiple output (MIMO) technology The introduction was decided. When transmission / reception is performed by applying all functions defined in the IEEE802.11n standard, a maximum communication speed of 600 Mbps can be realized in the physical layer.

  In addition, the IEEE802.11ac standard, which was standardized in 2013, expanded the channel bandwidth to 80 MHz and up to 160 MHz (or 80 + 80 MHz), and applied multiple divisions using space division multiple access (SDMA). The introduction of the user MIMO (MU-MIMO) transmission method has been decided. If transmission and reception are performed by applying all the functions specified in the IEEE802.11ac standard, a maximum communication speed of about 6.9 Gbps can be realized in the physical layer.

  The IEEE802.11 standard wireless LAN operates in the 2.4 GHz band or the 5 GHz band in the license-free frequency band. Therefore, the IEEE802.11 standard wireless base station forms a wireless LAN cell (BSS: Basic Service Set). In addition, one frequency channel is selected from the frequency channels that can be handled by the own radio base station.

  The channel used in the own cell, bandwidth and other parameter settings, and other parameters that can be supported by the own radio base station are the Beacon frame that is periodically transmitted and the Probe for the Probe Request frame that is received from the radio terminal. A cell is operated by transmitting a frame on a frequency channel described in a response frame or the like and determined to be used, and notifying the subordinate radio terminal and other neighboring radio stations.

In the radio base station, there are the following four methods for selecting and setting the frequency channel, bandwidth and other parameters.
(1) Using the default parameter values set by the wireless base station manufacturer as they are
(2) Method to use manually set values by users operating radio base stations
(3) A method for autonomously selecting and setting parameter values based on the radio environment information detected by each radio base station at startup
(4) Method for setting parameter values determined by a central control station such as a wireless LAN controller

  Also, the number of channels that can be used simultaneously in the same location is 3, 2.4, 9 or 19 for 2.4 GHz wireless LAN depending on the channel bandwidth used for communication. Therefore, when actually introducing a wireless LAN, it is necessary to select a channel used by the wireless base station within 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 in the same place in the 5 GHz band is 19 channels with a channel bandwidth of 20 MHz. Less. That is, as the channel bandwidth increases, the number of usable channels decreases.

  In a dense environment of wireless LAN where the number of BSSs is larger than the number of usable channels, a plurality of BSSs use the same channel (OBSS: Overlapping BSS). Therefore, in the wireless LAN, autonomous distributed access control that uses CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) to transmit data only when a channel is free due to carrier sense is used.

  Specifically, a wireless station that has made a transmission request first performs carrier sense for a predetermined sensing period (DIFS: Distributed Inter-Frame Space) to monitor the state of the wireless medium, and during this time, transmission by other wireless stations is performed. If no signal is present, a random backoff is performed. The radio station continues to perform carrier sense during the random back-off period, and obtains the right to use the channel when there is no transmission signal from another radio station during this period. Note that transmission / reception by other radio stations is determined by whether or not a signal larger than a preset carrier sense threshold 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 performing such CSMA / CA control, in a dense environment of a wireless LAN using the same channel, the frequency of the channel becoming busy due to carrier sense increases, and the throughput decreases. Therefore, it is important to monitor the surrounding environment and select an appropriate channel, transmission power to be used, carrier sense threshold to be used, and attenuation value to be used.

  The channel selection method in the radio base station is not determined by the IEEE802.11 standard, so 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 for selecting the items in an autonomous and distributed manner. The radio base station performs carrier sense on all channels for a certain period, selects the channel with the lowest interference power, and transmits / receives data to / from the terminal devices under the selected channel. The interference power is a level of a signal received from a neighboring BSS or another system.

  The IEEE802.11 standard stipulates the procedure for changing the channel when the radio conditions around the BSS change. Basically, the selected channel is reselected except for forced transition by radar detection. Not. That is, in the current wireless LAN, the channel is not optimized according to changes in the wireless status.

  The IEEE802.11 standard defines the maximum transmission output value of a signal to be transmitted in accordance with the radio wave law defined in each country. The carrier sense threshold is defined as -82 dBm when the detection signal is a wireless LAN signal, and -62 dBm otherwise.

  As described above, the maximum values of the transmission power and the carrier sense threshold are defined, but the optimum value according to the change in the radio conditions is not defined when a plurality of radio stations perform transmission / reception on the same channel. (Non-patent document 2).

Supervised by Masahiro Morikura and Shuji Kubota, “802.11 High-Speed Wireless LAN Textbook”, revised edition, Impress R & D, March 2008. Robert Stacey, “Specification Framework for TGax,” January 28, 2016.

  How to select and set the frequency channel, bandwidth and other parameters described above (1) to (4), especially for the inexpensive base station, use the default parameters set by the manufacturer of (1) as they are. Often to do. 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, so interference occurs between wireless base stations. As a result, there is a problem that communication quality deteriorates.

  In a relatively small network such as a general home, it is conceivable that a user operating the wireless LAN (2) sets appropriate parameters. However, although it is possible to set various parameters in an environment where there is no external interference source, it is appropriate for users or managers in environments where wireless LAN is used in urban areas, apartment buildings, etc., or in medium or large networks. Parameter setting is difficult.

  A radio base station capable of autonomous distributed operation can autonomously select parameter values based on 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 an environmental change occurs, such as a change in the number of active radio base stations, a change in radio terminal devices under each radio base station, or a change in the amount of data transmitted by radio devices in each cell, Since the use channel, use transmission power, use carrier sense threshold, and use attenuation value are not optimized, there is a problem that a difference occurs between the throughputs of the respective cells or the throughput of the entire system deteriorates.

  The present invention uses radio environment information around a radio communication station that performs data transmission and signal power to interference power ratio (SINR) at a destination communication station in an environment where radio communication stations using a shared radio frequency band are dense. Thus, an object of the present invention is to provide a radio communication system and a radio communication method capable of calculating the optimum carrier sense threshold value and transmission power value or attenuation value used for data transmission.

  A first aspect of the present invention is a wireless communication system including a plurality of wireless communication stations that perform wireless communication on a shared frequency band, wherein the wireless communication station is configured to receive a peripheral wireless environment information and a signal power to interference power ratio SINR at a destination communication station. Depending on the radio environment information acquisition means for acquiring the information of the mobile station, the SINR at the destination communication station, and the number of wireless communication stations in the vicinity using the shared frequency band detected by the local station, the throughput of the destination communication station is maximized. Parameter setting means for simultaneously calculating and setting the transmission power value of the station and the correction value of the carrier sense threshold value.

  In the wireless communication system of the first invention, the parameter setting means is configured to set the attenuation value of the attenuator according to the transmission power value and the correction value of the carrier sense threshold.

と表され、該スループットが最大となる補正値ａ_i を算出する構成である。 In the wireless communication system of the first invention, the parameter setting means includes a SINR in the wireless communication station i when the maximum value P of the transmission power in the wireless communication station i, the link gain is G _ii , and the minimum value Θ of the carrier sense threshold is set. When the transmission power value and the carrier sense threshold correction value a _i at the wireless communication station _{i are} set to δ = 2 / α with respect to the peripheral wireless communication station number M and the propagation coefficient α, the correction value a _i Throughput for

And the correction value a _i that maximizes the throughput is calculated.

と表され、該スループットが最大となる補正値ａを算出する構成である。 In the radio communication system of the first invention, the parameter setting means sets the SINR in the radio communication station when the maximum value P of transmission power in all radio communication stations, the link gain is G, and the minimum value Θ of the carrier sense threshold is set. Used, correction value a of transmission power value and carrier sense threshold, average number E of peripheral wireless communication stations within a certain period E [M], and correction value when δ = 2 / α with respect to propagation coefficient α Throughput for a

And the correction value a that maximizes the throughput is calculated.

  According to a second aspect of the present invention, in the wireless communication method including a plurality of wireless communication stations that perform wireless communication on a shared frequency band, the wireless communication station is configured to include the surrounding wireless environment information and the signal power to interference power ratio SINR in the destination communication station. Wireless environment information acquisition step for acquiring information on the destination, the SINR at the destination communication station, and the number of wireless communication stations in the vicinity that use the shared frequency band detected by the local station. A parameter setting step for simultaneously calculating and setting the transmission power value of the station and the correction value of the carrier sense threshold value.

  In the wireless communication method of the second invention, the parameter setting step sets the attenuation value of the attenuator according to the transmission power value and the correction value of the carrier sense threshold.

と表され、該スループットが最大となる補正値ａ_i を算出する。 In the radio communication method of the second invention, the parameter setting step includes the SINR in the radio communication station i when the maximum value P of the transmission power in the radio communication station i, the link gain is G _ii , and the minimum value Θ of the carrier sense threshold is set. When the transmission power value and the carrier sense threshold correction value a _i at the wireless communication station _{i are} set to δ = 2 / α with respect to the peripheral wireless communication station number M and the propagation coefficient α, the correction value a _i Throughput for

And a correction value a _i that maximizes the throughput is calculated.

と表され、該スループットが最大となる補正値ａを算出する。 In the wireless communication method of the second invention, the parameter setting step includes the SINR in the wireless communication station when the maximum value P of transmission power in all the wireless communication stations, the link gain is G, and the minimum value Θ of the carrier sense threshold is set. Used, the correction value a of the transmission power value and the carrier sense threshold, the average number of peripheral wireless communication stations E [M] within a certain period, and the correction when δ = 2 / α with respect to the propagation coefficient α. Throughput for value a

The correction value a that maximizes the throughput is calculated.

  According to the present invention, in an environment where radio communication stations using a shared radio frequency band are densely populated, the waiting time until the radio communication station acquires an access right (channel use right) when performing data transmission is shortened. As a result, the throughput of the receiving radio communication station is improved, and the communication quality of the application being used and the quality of experience of the user are improved.

It is a figure which shows the structural example of the radio | wireless communications system of this invention. It is a figure which shows the structural example of a radio | wireless communication station. It is a flowchart which shows the process sequence example of a radio | wireless communication station. It is a figure which shows the probability distribution of the number of the surrounding radio | wireless communication stations with respect to the correction value a of attenuation value.

FIG. 1 shows a configuration example of a wireless communication system of the present invention.
In FIG. 1, radio base stations AP1 to AP5 each perform radio communication with the belonging terminal in the shared radio frequency band. AP1 performs wireless communication with the belonging terminals STA11 to STA13, AP2 performs wireless communication with the belonging terminal STA21, AP3 performs wireless communication with the belonging terminal STA31, AP4 performs wireless communication with the belonging terminals STA41 to STA42, and AP5 Wireless communication is performed with the belonging terminal STA51.

FIG. 2 shows a configuration example of a wireless communication station of the wireless communication system of the present invention. Note that the radio communication station is a radio base station AP or an affiliated terminal STA, both of which have the same configuration.
In FIG. 2, the wireless communication station performs scanning of the surrounding wireless environment information with the wireless communication unit 11 that performs data transmission and reception with the destination station, the wireless environment information such as the usage parameters of the surrounding wireless communication stations, and the destination communication station. A radio environment information acquisition unit 12 that acquires information on the signal power to interference power ratio SINR in FIG. 1, and a parameter calculation unit 13 that calculates parameters such as a transmission power value, a carrier sense threshold, and an attenuation value using the acquired radio environment information; A parameter setting unit 14 for setting parameters such as a calculated transmission power value, a carrier sense threshold value, and an attenuation value, and an access right acquiring unit 15 for acquiring an access right by carrier sense using the set parameters. .

FIG. 3 shows a processing procedure example 1 of the wireless communication station of the wireless communication system of the present invention.
In FIG. 3, the radio environment information acquisition unit 12 of the radio communication station acquires radio environment information such as usage parameters of neighboring radio communication stations (S11), and the signal at the destination communication station at the currently operating transmission power value. Information on the power-to-interference power ratio SINR is acquired (S12). Next, the parameter calculation unit 13 calculates the optimum transmission power value and carrier sense threshold correction value in the wireless communication station using each acquired information (S13). Next, the parameter setting unit 14 sets a transmission power value and a carrier sense threshold using the calculated correction value (S14), and starts operation.

  The feature of the present invention resides in that it is easy to acquire the access right by carrier sense by increasing the carrier sense threshold by the amount corresponding to the decrease in the transmission power value, and control is performed so that the SINR is not significantly lowered. That is, when the transmission power is reduced by a [dB], the SINR in the destination wireless communication station deteriorates and the throughput decreases. On the other hand, when the carrier sense threshold is increased by a [dB], the number of peripheral wireless communication stations is reduced, access rights are easily acquired, and throughput is increased. Therefore, the transmission power value and the carrier sense threshold have an optimum correction value a that maximizes the throughput and does not significantly reduce the SINR, and the present invention shows a method for calculating the optimum correction value a.

  Here, lowering the transmission power value by a [dB] and simultaneously raising the carrier sense threshold by a [dB] is equivalent to increasing the attenuation value of the attenuator (attenuator) of the radio communication station by a [dB]. . That is, if the attenuation value is increased by a [dB] with respect to the current value, the transmission power of the wireless communication station decreases by a [dB], and the reception power at the wireless communication station decreases by a [dB]. This is equivalent to increasing the threshold by a [dB]. Therefore, for example, in a radio communication station in which the carrier sense threshold cannot be changed, or in a radio communication station in which the correction value of the transmission power value and the correction value of the carrier sense threshold cannot be adjusted to a positive / negative symmetric value, there is a method of adjusting the attenuation value. It is done.

Example 1
In the first embodiment, a method for calculating the correction value a of the attenuation value in consideration of SINR will be described. The transmission power value and the carrier sense threshold correction value a may be used. The transmission power value and carrier sense threshold value or attenuation value of the wireless communication station are values corrected by the correction value a calculated by the following method.

The communication capacity (Shannon capacity) C in the unit bandwidth is given as follows.

When the number of peripheral wireless communication stations that perform wireless communication using the shared frequency band is M, the total number of wireless communication stations that acquire the access right to the shared frequency band is (1 + M) units. Therefore, the throughput per wireless communication station is expressed as follows.

Here, assuming that the transmission power at the wireless communication station i is p _i , the link gain is G _ii , and the carrier sense threshold is θ _i , the SINR at the wireless communication station i can be expressed as follows.

If the maximum value of the transmission power is P and the minimum value of the carrier sense threshold is Θ, the following relationship is established for normal transmission / reception at the wireless communication station i.

Here, setting the correction value a _i of the attenuation value of the radio communication station i, the following relation holds.

Therefore, the optimum correction value a ^* of the attenuation value that maximizes the throughput in the wireless communication station i is expressed as follows using the equations (2) and (5).

Here, M (a _i ) is the number of peripheral wireless communication stations that can be detected when the correction value a _i of the attenuation value of the wireless communication station _i is set. E [x] represents an average value of the random variable x.

FIG. 4 shows a probability distribution function of the number of surrounding wireless communication stations with respect to the attenuation value correction value a.
In FIG. 4, the horizontal axis represents the attenuation value correction value a, and the larger the cell size, the smaller the cell size. The vertical axis represents the probability of the number M of surrounding wireless communication stations. Here, the probability distribution of the number M of surrounding wireless communication stations, that is, the channel occupancy rate is shown with respect to the correction value a.

When the propagation coefficient is α and δ = 2 / α, when the wireless communication stations M are uniformly arranged according to the binomial point process (BPP), the optimum correction value a ^* is expressed as follows: Can do.

Further, the optimum correction value a ^* can be expressed as follows using the lower limit value of the throughput (Lower bound).

Further, the optimum correction value a ^* can be expressed as follows using an approximate value of throughput.

(Example 2)
In the second embodiment, consider a case where wireless communication stations are uniformly arranged according to a Poisson point process (PPP). That is, a plurality of wireless communication stations adopt the same attenuation value correction value a, and the average number of peripheral wireless communication stations that can be detected is E [M]. Assuming that all wireless communication stations use p _i = p and θ _i = θ, and all wireless communication stations use the attenuation correction value a _i = a, the following formulas (7) and (8) are used. The portion relating to the number of peripheral wireless communication stations M (a _i ) = M (a) that can be detected by the above can be expressed as follows.

Therefore, in an environment where wireless communication stations are uniformly arranged according to the Poisson point process (PPP), when all wireless communication stations use attenuation value correction values, attenuation that maximizes throughput in all wireless communication stations The optimum correction value a ^* of the value can be expressed as follows. However, the link gain is set to G _ii = G in all wireless communication stations.

AP radio base station STA belonging terminal 11 radio communication unit 12 radio environment information acquisition unit 13 parameter calculation unit 14 parameter setting unit 15 access right acquisition unit

Claims (8)

In a wireless communication system including a plurality of wireless communication stations that perform wireless communication on a shared frequency band,
The wireless communication station is
Radio environment information acquisition means for acquiring peripheral radio environment information and information of signal power to interference power ratio SINR in the destination communication station;
Depending on the SINR at the destination communication station and the number of surrounding wireless communication stations using the shared frequency band detected by the own station, the transmission power value and carrier sense of the own station that maximizes the throughput of the destination communication station A wireless communication system comprising: parameter setting means for simultaneously calculating and setting a threshold correction value. The wireless communication system according to claim 1, wherein
The wireless communication system, wherein the parameter setting means is configured to set an attenuation value of an attenuator in accordance with the transmission power value and a correction value of a carrier sense threshold. The wireless communication system according to claim 1, wherein
The parameter setting means uses the SINR at the radio communication station i when the maximum value P of the transmission power at the radio communication station i, the link gain is G _ii , and the minimum value Θ of the carrier sense threshold, and the transmission power value and the carrier When the correction value a _i of the sense threshold, the number of neighboring wireless communication stations M, and the propagation coefficient α are set to δ = 2 / α, the throughput for the correction value a _i is

The wireless communication system is characterized in that it is configured to calculate a correction value a _i that maximizes the throughput. The wireless communication system according to claim 1, wherein
The parameter setting means uses the SINR in the radio communication station when the maximum value P of transmission power in all radio communication stations, the link gain is G, and the minimum value Θ of the carrier sense threshold is used. When the threshold value correction value a, the average number E [M] of neighboring wireless communication stations within a certain period, and δ = 2 / α with respect to the propagation coefficient α, the throughput for the correction value a is

The wireless communication system is characterized in that a correction value a that maximizes the throughput is calculated. In a wireless communication method including a plurality of wireless communication stations that perform wireless communication on a shared frequency band,
The wireless communication station is
A radio environment information acquisition step of acquiring peripheral radio environment information and information of signal power to interference power ratio SINR in the destination communication station;
Depending on the SINR at the destination communication station and the number of surrounding wireless communication stations using the shared frequency band detected by the own station, the transmission power value and carrier sense of the own station that maximizes the throughput of the destination communication station And a parameter setting step for simultaneously calculating and setting a correction value for the threshold value. The wireless communication method according to claim 5, wherein
The parameter setting step sets an attenuation value of an attenuator in accordance with the transmission power value and a correction value of a carrier sense threshold value. The wireless communication method according to claim 5, wherein
The parameter setting step uses the SINR at the radio communication station i when the maximum value P of the transmission power at the radio communication station i, the link gain is G _ii , and the minimum value Θ of the carrier sense threshold, and the transmission power value and the carrier When the correction value a _i of the sense threshold, the number of neighboring wireless communication stations M, and the propagation coefficient α are set to δ = 2 / α, the throughput for the correction value a _i is

And a correction value a _i that maximizes the throughput is calculated. The wireless communication method according to claim 5, wherein
The parameter setting step uses the SINR in the radio communication station when the maximum value P of the transmission power in all radio communication stations, the link gain is G, and the minimum value Θ of the carrier sense threshold is used, and the transmission power value and the carrier sense When the threshold value correction value a, the average number E [M] of neighboring wireless communication stations within a certain period, and δ = 2 / α with respect to the propagation coefficient α, the throughput for the correction value a is

And a correction value a that maximizes the throughput is calculated.

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