WO2018043600A1 - 無線通信システムおよび無線通信方法 - Google Patents
無線通信システムおよび無線通信方法 Download PDFInfo
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- WO2018043600A1 WO2018043600A1 PCT/JP2017/031256 JP2017031256W WO2018043600A1 WO 2018043600 A1 WO2018043600 A1 WO 2018043600A1 JP 2017031256 W JP2017031256 W JP 2017031256W WO 2018043600 A1 WO2018043600 A1 WO 2018043600A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B17/00—Monitoring; Testing
- H04B17/30—Monitoring; Testing of propagation channels
- H04B17/309—Measuring or estimating channel quality parameters
- H04B17/345—Interference values
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W24/00—Supervisory, monitoring or testing arrangements
- H04W24/02—Arrangements for optimising operational condition
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/06—TPC algorithms
- H04W52/14—Separate analysis of uplink or downlink
- H04W52/143—Downlink power control
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/18—TPC being performed according to specific parameters
- H04W52/24—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/18—TPC being performed according to specific parameters
- H04W52/24—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters
- H04W52/243—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters taking into account interferences
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/38—TPC being performed in particular situations
- H04W52/386—TPC being performed in particular situations centralized, e.g. when the radio network controller or equivalent takes part in the power control
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W72/00—Local resource management
- H04W72/50—Allocation or scheduling criteria for wireless resources
- H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
- H04W88/18—Service support devices; Network management devices
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/18—TPC being performed according to specific parameters
- H04W52/24—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters
- H04W52/241—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters taking into account channel quality metrics, e.g. SIR, SNR, CIR, Eb/lo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/18—TPC being performed according to specific parameters
- H04W52/26—TPC being performed according to specific parameters using transmission rate or quality of service QoS [Quality of Service]
- H04W52/262—TPC being performed according to specific parameters using transmission rate or quality of service QoS [Quality of Service] taking into account adaptive modulation and coding [AMC] scheme
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/18—TPC being performed according to specific parameters
- H04W52/26—TPC being performed according to specific parameters using transmission rate or quality of service QoS [Quality of Service]
- H04W52/267—TPC being performed according to specific parameters using transmission rate or quality of service QoS [Quality of Service] taking into account the information rate
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W84/00—Network topologies
- H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
- H04W84/10—Small scale networks; Flat hierarchical networks
- H04W84/12—WLAN [Wireless Local Area Networks]
Definitions
- the present invention relates to a wireless communication system and a wireless communication method in which a wireless base station and a plurality of wireless terminals perform wireless communication.
- a radio base station and a radio terminal are collectively referred to as a radio communication device, and a radio base station is abbreviated as AP and a radio terminal is abbreviated as STA as necessary.
- wireless communication devices conforming to the wireless LAN standard defined by IEEE 802.11 have rapidly spread, and a large number of wireless communication devices using an unlicensed band of 2.4 GHz or 5 GHz have been arranged.
- the unlicensed band the state of the channel scheduled to be transmitted is determined based on the prior carrier sense, and transmission is started when the transmission is possible. Therefore, in an environment where a large number of wireless communication devices are mixed in an unlicensed band, a plurality of peripheral wireless communication devices wait for transmission while a certain wireless communication device is transmitting, and throughput is reduced.
- Non-patent Document 1 introduction of a technique for controlling an interference detection threshold used for determining a channel state by carrier sense is expected (Non-patent Document 1).
- the interference detection threshold corresponds to the carrier sense threshold in the case of a wireless LAN.
- Non-Patent Document 1 discloses a technique for controlling the transmission power value together with the control of the interference detection threshold. Further, an upper limit is set for the interference detection threshold value and the transmission power value, and a procedure for controlling each value in conjunction with each other is expected to be introduced.
- Non-Patent Document 2 discloses a technique for suppressing interference with each other on the same channel by using interference information collected from a plurality of wireless communication devices. Control that improves frequency utilization efficiency is possible.
- each AP independently controls the interference detection threshold.
- the throughput of the own AP can be improved, the throughput of the neighboring AP may be reduced.
- the first reason is that there is a possibility that a radio communication apparatus that becomes a new exposed terminal or hidden terminal may be generated by controlling the interference detection threshold value to be higher or lowering the transmission power value.
- the second reason is that there is a possibility that the SINR of the radio frame received by the destination terminal may deteriorate due to an increase in transmission opportunities from the radio communication apparatuses existing in the communication area.
- Non-Patent Document 2 proposes a technique for controlling an interference detection threshold and a transmission power value so that a central control station is provided and the overall frequency use efficiency is not lowered.
- the expected throughput value is calculated by a statistical method using the Shannon capacity, there is a room for improvement when specifically considering the destination of wireless communication. That is, if the distance between the transmission side and the reception side is close and SINR is good, there is an opportunity to lower the transmission power value and raise the interference detection threshold.
- the distance between the transmission side and the reception side is long and the SINR is poor, maintaining the transmission power value and the interference detection threshold value may contribute to the improvement of the overall throughput. In this way, further improvement in throughput is expected by utilizing more information around the AP to be controlled.
- the present invention provides a radio communication system and a radio communication method for controlling a transmission power value and an interference detection threshold of each radio base station in order to improve the throughput of a radio communication system in which a plurality of radio base stations interfere with each other. For the purpose.
- a first invention is a radio communication system comprising a plurality of radio base stations that interfere with each other, a plurality of radio terminals connected to the radio base station, and a centralized management station connected to the radio base station.
- the centralized management station the interference power information including the reception power value of the surrounding radio base station that is the interference source of the radio base station, the reception power value from the radio terminal that is the destination of the radio base station, and the transmission of the radio base station
- An information collection unit that collects transmission power information including a power value, and an interference detection threshold and a transmission power value in a radio base station according to a transmission opportunity acquisition frequency and a throughput approximate value calculated from the collected information based on an interference relationship
- a control value determining means for notifying the radio base station as a control value, and the radio base station controls the interference detection threshold value and the transmission power value based on the control value notified from the centralized management station. It is configured to perform.
- the wireless base station notifies the interference detection threshold value and transmission power value notified from the centralized management station to the subordinate wireless terminal, and the interference detection threshold value and transmission notified by the wireless terminal. In this configuration, control is performed based on the power value.
- control value determining means calculates the interference detection threshold value and the transmission power value temporarily, and calculates the approximate throughput value after control using the temporarily determined value, thereby improving the throughput.
- the provisionally determined value is used as a control value.
- control value determining means is configured to determine an interference detection threshold and a transmission power value in order from a wireless base station having a high transmission opportunity acquisition frequency.
- the control value determining means performs control to lower a transmission power value for a wireless base station whose transmission opportunity acquisition frequency is higher than a threshold among the wireless base stations to be controlled, In this configuration, the control for increasing the interference detection threshold is performed for a radio base station whose opportunity acquisition frequency is lower than the threshold.
- control value determining means uses the received power value from the destination wireless terminal collected by the information collecting means to obtain the lower limit value of the transmission power value from the minimum required SINR value in the target modulation / demodulation method. It is a configuration to set.
- the control value determining means uses the received power value of the radio base station that is higher than the interference detection threshold among the received power values observed by the radio base station as a reference. It is a configuration.
- the control value determining means receives the radio base station whose interference power due to the radio signal transmitted from the radio base station is equal to or higher than a predetermined value or whose SINR is equal to or lower than a predetermined value. The configuration is based on the power value. Further, the control value determining means, when raising the interference detection threshold of the radio base station, uses the received power value that is higher than the current interference detection threshold and closest to the received power value observed by the radio base station as a reference. It is the structure to do.
- the control value determining means searches for the interference detection threshold value and the transmission power value using the particle swarm optimization method (PSO)
- the transmission opportunity acquisition frequency is higher than a predetermined threshold value.
- the interference detection threshold and the coefficient of change in the transmission power value are set to values lower than the reference value for the radio base station, and the interference detection threshold and transmission are transmitted to the radio base station whose transmission opportunity acquisition frequency is lower than the predetermined threshold.
- the coefficient of change in the power value is set to a value higher than the reference value.
- a second invention includes a plurality of radio base stations that interfere with each other, a plurality of radio terminals connected to the radio base station, and a centralized management station connected to the radio base station.
- the centralized management station includes interference power information including a reception power value of a neighboring radio base station that is an interference source of the radio base station, and a radio base station Collects transmission power information including the reception power value from the wireless terminal that is the destination of the station and the transmission power value of the wireless base station, and the transmission opportunity acquisition frequency and throughput estimation value calculated based on the interference relationship from the collected information Accordingly, the interference detection threshold value and transmission power value in the radio base station are determined and notified to the radio base station as control values.
- the radio base station determines the interference detection threshold value and the control value based on the control value notified from the centralized management station. Yo It controls the transmission power value.
- the central management station sets each transmission opportunity for the transmission power value and interference detection threshold of each radio base station. It is possible to control while confirming the acquisition frequency and throughput roughly. Thereby, the throughput of the entire radio communication system can be improved without reducing the throughput of each radio base station.
- FIG. 1 shows a configuration example of a wireless communication system of the present invention.
- each radio base station (AP) 10 and centralized management station 20 are configured to exchange information via respective information signal input / output units 11 and 21.
- the centralized management station 20 transmits a control signal for collecting information from the AP 10 and a control signal for changing the interference detection threshold value and transmission power value of the AP 10 to the AP 10.
- the AP 10 transmits the reception power values collected by the radio signal transmission / reception unit 14 and the reception power value information collection unit 12 to the centralized management station 20.
- the information input to the information signal input / output unit 21 is sent to the information management unit 22, and the reception power value, transmission power value, interference detection threshold, target MCS, etc. collected by the information management unit 22 are connected. Managed for each AP. Further, the control value determination unit 23 connected to the information management unit 22 calculates an approximate value of throughput, determines a transmission power value and an interference detection threshold value in each AP 10, and sends them to each AP 10 from the information signal input / output unit 21. Send.
- the AP 10 sends the transmission power value and the interference detection threshold value input to the information signal input / output unit 11 to the transmission power / interference detection threshold value control unit 13, and the transmission power / interference detection threshold value control unit 13 transmits the transmission power of the radio signal transmission / reception unit 14. Change the value and interference detection threshold.
- an access control unit 15 that performs access control by CSMA / CA is connected to the radio signal transmission / reception unit 14.
- the transmission power value and the interference detection threshold set in the AP 10 are transmitted from the radio signal transmission / reception unit 14 to a subordinate radio terminal (STA) (not shown) to control the transmission power value and the interference detection threshold of the STA.
- the function of the central management station 20 may be configured to be incorporated in any one of the plurality of APs 10. In that case, the AP executes the function as the AP and the function as the centralized management station in parallel.
- FIG. 2 shows an assumed example of the wireless communication system of the present invention.
- the centralized management station 20 is connected to a plurality of AP1, AP2, AP3, and further connected to STA1, STA2, and STA3 that are destinations of each AP. Connections for information signal transmission between the central management station 20 and the AP1 to AP3 are indicated by solid lines. The connections between AP1 to AP3 and the destinations STA1 to STA3 are indicated by solid arrows. Furthermore, interference signals are generated between APs and between APs and STAs other than their destinations, and are indicated by broken line arrows.
- the received power value between AP1 and AP2 is ⁇ 60 dBm
- the received power value between AP1 and AP3 is ⁇ 80 dBm
- the received power value between AP2 and AP3 is ⁇ 62 dBm. is there.
- the interference detection threshold value of all APs is ⁇ 76 dBm and AP1 and AP2 and AP2 and AP3 detect reception powers equal to or greater than the interference detection threshold value.
- 3 to 6 show an example of processing procedure of the centralized management station that determines the transmission power value and interference detection threshold value of each AP.
- the central management station first connects and collects information from the AP to be controlled (S11).
- the transmission opportunity acquisition frequency of each AP is calculated in accordance with the interference relationship between the APs, and the interference power value of the peripheral wireless communication station that transmits at the same time when the transmission opportunity is acquired is considered.
- the optimum MCS is selected from the SINR at the time of signal transmission and the throughput approximate value of all APs is calculated (S12).
- the AP information is arranged in descending order of the calculated transmission opportunity acquisition frequency, that is, in descending order (S13).
- the following processing for determining a transmission power value and an interference detection threshold as control values is executed for each AP in descending order of transmission opportunity acquisition frequency (S14).
- the threshold value used for the determination may be a statistical value such as an average value, median value, or percentile value of transmission opportunity acquisition frequencies, or the number of APs determined such that the number of APs with high and low transmission opportunity acquisition frequency is the same.
- a threshold value may be set.
- the transmission power value is provisionally determined so that becomes smaller (S16a).
- the minimum SINR required for the target MCS is calculated by communication between the AP and the destination STA, and is set as the lower limit value of the transmission power value. The transmission power value below the lower limit is not selected. Further, as shown in FIG. 4, when the interference detection threshold is controlled in conjunction with the transmission power value, a specified interference detection threshold is also set at the same time (S17a).
- OBSS which is a CCA threshold value that can be taken according to the transmission power value.
- the PD level is limited, and the present invention assumes such control of the transmission power value and the interference detection threshold. Also in this case, the maximum value and the minimum value determined by laws and standards are taken into consideration, and a value contrary to this is not selected.
- an approximate throughput value of all APs when the control value is applied is calculated (S18a). It is determined whether or not the throughput value is deteriorated before application in the total value of the calculated throughput values, the throughput value of each AP, or both (S19a). Not applicable (S19a: No). Conversely, if there is no deterioration in the throughput value, the provisionally determined value is recorded as an execution value (S20a).
- the interference detection threshold is provisionally determined so that the transmission opportunity acquisition frequency is increased by increasing the interference detection threshold (S16b).
- a prescribed transmission power value is also set (S17b).
- OBSS which is a CCA threshold value that can be taken according to the transmission power value.
- the PD level is limited, and the present invention is also aware of such transmission power value and interference detection threshold control.
- the maximum and minimum values determined by laws and standards are taken into consideration, and values that do not match this are not selected.
- an approximate throughput value of all APs when the control value is applied is calculated (S18b). It is determined whether or not the throughput value is deteriorated before application in the total value of the calculated throughput values, the throughput value of each AP, or both (S19b). Not applicable (S19b: No). On the other hand, if the throughput value is not deteriorated, the provisionally determined value is recorded as an execution value (S20b).
- the above processing is repeated for the remaining APs whose transmission opportunity acquisition frequency is determined to be lower than the threshold in the determination of step S15 in descending order of transmission opportunity acquisition frequency.
- the transmission power value and the interference detection threshold are determined as control values that provide the best throughput for all APs in descending order of the transmission opportunity acquisition frequency.
- step S14 is repeated a plurality of times. For example, in the process of selecting control values for all APs, the process may be repeated until it is determined that the current control value is not changed, or a finite number may be set as the upper limit of the repeated calculation in consideration of the calculation time. .
- the processing procedure example in FIG. 5 is a modification of the processing procedure example in FIG. 3, and the processing procedure example in FIG. 6 is a modification of the processing procedure example in FIG.
- steps S16a / b to S20a / b in FIGS. 3 and 4 a transmission power value and an interference detection threshold are provisionally determined as control values for an AP having a certain transmission opportunity acquisition frequency, and the control values are applied. If the approximate throughput value of all APs calculated in this way deteriorates, the provisional decision value is not adopted, and if the approximate throughput value of all APs does not deteriorate, the provisional decision value is adopted. This is performed in order from the AP having the highest transmission opportunity acquisition frequency. However, the control value tentative determination process is performed once for each AP.
- the transmission power value and the interference detection threshold provisional determination process are repeated as the control value until reaching the limit value, and then the transition to the AP having the next transmission opportunity acquisition frequency is performed.
- control is performed based on the transmission power value, which is a temporarily determined control value, or the interference detection threshold linked to the transmission power value.
- the approximate throughput value of all APs when the value is applied is calculated (S16a to S18a). It is determined whether or not the deterioration of the throughput value is observed before the application in the total value of the calculated throughput values or the throughput value of each AP or both (S19a). Further, it is determined whether or not the temporarily determined control value has reached the limit value (S21a). If the control value has not reached the limit value, the transmission power value is lowered and the same processing is repeated (S16a to S19a).
- the temporarily determined value When the temporarily determined control value reaches the limit value, the temporarily determined value is recorded as an execution value (S20a).
- the temporary determination value is returned to the previous one (S22a), and the temporary determination value is recorded as an execution value (S20a).
- the control is performed based on the interference detection threshold that is a temporarily determined control value or the transmission power value that is linked to the interference detection threshold.
- the approximate throughput value of all APs when the value is applied is calculated (S16b to S18b). It is determined whether or not deterioration of the throughput value is observed before application in the total value of the calculated throughput values, or the throughput value of each AP, or both (S19b). Further, it is determined whether or not the temporarily determined control value has reached the limit value (S21b). If the limit value has not been reached, the interference detection threshold is increased and the same processing is repeated (S16b to S19b).
- the temporarily determined value When the temporarily determined control value reaches the limit value, the temporarily determined value is recorded as an execution value (S20b).
- the interference detection threshold is increased and the throughput value is deteriorated (S19b: No)
- the previous provisional decision value is returned (S22b), and the provisional decision value is recorded as the execution value (S20b).
- step S16a of FIG. 5 and FIG. 6 when the control for lowering the transmission power value is performed when the temporarily determined transmission power value has not reached the limit value, the target calculated from the reception power value of the STA as the destination You may set the minimum transmission power which can ensure minimum SINR required for MCS from the beginning as a control value.
- the interference detection threshold value and the transmission power value are controlled in conjunction with each other, that is, when the interference detection threshold value is increased by lowering the transmission power value, the transmission opportunity acquisition frequency is increased due to the increase of the interference detection threshold value. It may be a cause to disturb. Considering such a case, it is effective to control the transmission power in stages while confirming that the target AP and the overall throughput are improved.
- the first method for gradually reducing the transmission power is a method for determining the transmission power value from the interference detection power value of the neighboring AP.
- An AP that performs control to reduce transmission power is selected.
- the received power value of the radio signal of AP1 is referred to, and AP2 whose received power value is observed to be higher than the interference detection threshold at this time is selected.
- AP1 and AP3 are selected for AP2, and AP2 is selected for AP3.
- the control value is used to lower the transmission power value.
- the value to be lowered is limited.
- a margin value may be provided when the transmission power is reduced. This method can be expected to increase the number of APs that can be transmitted simultaneously with the AP.
- the second method of gradually reducing the transmission power is a method of determining the transmission power value from the SINR or interference power value of the neighboring AP.
- An AP that performs control to reduce transmission power is selected. In the example of FIG. 2, reference is made to the received power value of the radio signal transmitted from AP1, and the AP having the worst SINR due to the interference caused by the radio signal transmitted from the AP at this time, or the interference power to be given The AP with the largest is selected. However, the AP selected by the above procedure is targeted for an AP whose received power value is equal to or less than the interference detection threshold. In the example of FIG. 2, it is AP3. (2) The transmission power value is lowered until the elected AP becomes SINR satisfying the target MCS or becomes equal to the interference power value from another AP. This method can be expected to improve the communication quality of the AP that transmits simultaneously with the AP.
- Provisional determination method of interference detection threshold In the case where the control for increasing the interference detection threshold is performed when the provisional determination value of the interference detection threshold does not reach the limit value in step S16b in FIGS. Since this control is intended to increase the frequency of acquiring transmission opportunities, the reception power value of the wireless signal transmitted from the neighboring AP is referred to, and the reception power value is higher than and closest to the current interference detection threshold value. The difference from the received power value is used as a provisionally determined value for the interference detection threshold. This method can be expected to increase the simultaneous transmission opportunity of the AP.
- a random value may be selected within the range of values that can be taken with probability P and used as a provisional determination value.
- the particle swarm optimization method which is an optimization method for multivalued variables that aims to be optimized while sharing information of the whole group individually while having randomness ( PSO) may be used.
- search performance can be improved by adjusting PSO parameters based on the transmission opportunity acquisition frequency.
- An example of the processing procedure is shown in FIG. This process is an alternative to the processing procedure shown in FIGS.
- an AP with a high transmission opportunity acquisition frequency sets the coefficient of change in the transmission power value and the interference detection threshold to a value lower than the reference value to narrow the search range, and an AP with a low transmission opportunity acquisition frequency
- the coefficient is set to a value higher than the reference value to widen the search range (S35).
- the transmission power value and interference detection threshold value of each AP are updated using the coefficient (weight) determined based on the PSO technique (S36). The above processing is repeated until the end condition is satisfied (S37).
- the termination condition the case where the improvement of the transmission opportunity acquisition frequency and the throughput is almost converged is used.
- a method for calculating the approximate throughput value in step S18a / b in FIGS. 3 to 6 will be described based on the relationship between the four APs shown in FIG.
- the interference detection threshold value of all APs is ⁇ 73 dBm
- the initial value of the transmission power value of all APs is 20 dBm
- the reception power value of each destination terminal is ⁇ 41 dBm.
- the mutual received power values of AP1 to AP4 are as shown in FIG. 8, and it is assumed that AP1 and AP2, AP2 and AP3, AP2 and AP4, and AP3 and AP4 detect interference signals that are equal to or greater than the interference detection threshold. . Assuming that these APs are in a collision relationship, “1” is set in the contention graph, and APs that are not in a collision relationship are set to “0”.
- the maximum clique which is the combination that maximizes the APs that can be transmitted simultaneously, is AP1 and AP3, and AP1 and AP4.
- the value obtained by averaging for each AP is the normalized throughput ⁇ 1, 0, 1/2, 1/2 ⁇ . By multiplying this value by the transmission rate of each AP, an approximate throughput can be obtained.
- the mutual received power values of AP1 to AP4 based on this are as shown in FIG. 9, and the received power value ⁇ 76 between AP3 and AP4 is less than the interference detection threshold, and AP1 and AP2, AP2 and AP3, and AP2
- the APs 4 detect interference signals that are equal to or greater than the interference detection threshold, and the corresponding contention graph is updated. Since AP3 and AP4 do not detect signals with each other, the maximum clique that can be transmitted simultaneously is a combination of AP1, AP3, and AP4, and the maximum clique and normalized throughput are ⁇ 1, 0, 1, 1 ⁇ , which improves the throughput.
- the interference detection threshold is raised so as to exceed the minimum RSSI. Since AP1, AP3, and AP4 are farthest from AP2, the interference detection threshold and transmission power are determined based on the total RSSI value of ⁇ 67.2 dBm, which is the total value of ⁇ 72 dBm ⁇ 3 frames. Therefore, as indicated by a star in FIG. 10, the interference detection threshold of AP2 is increased from ⁇ 73 to ⁇ 67, and the transmission power value is decreased from 20 to 14.
- the mutual received power values of AP1 to AP4 based on this are as shown in FIG. 10, and the received power value becomes less than the interference detection threshold in all the combinations of APs, and the corresponding contention graph is updated.
- the maximum clique and normalized throughput is ⁇ 1, 1, 1, 1 ⁇ , and the throughput is maximized.
- Radio base station STA radio terminal 10 radio base station (AP) 11 Information Signal Input / Output Unit 12 Received Power Value Information Collection Unit 13 Transmission Power / Interference Detection Threshold Control Unit, 14 Radio signal transmission / reception unit 15 Access control unit 20 Centralized management station 21 Information signal input / output unit 22 Information management unit 23 Control value determination unit
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Abstract
Description
図1において、各無線基地局(AP)10と集中管理局20は、それぞれの情報信号入出力部11,21を介して情報交換が可能な構成になっている。例えば、集中管理局20は、AP10から情報を収集するための制御信号や、AP10の干渉検出閾値や送信電力値を変更するための制御信号をAP10に送信する。AP10は、無線信号送受信部14および受信電力値情報収集部12で収集した受信電力値を集中管理局20に送信する。
なお、集中管理局20の機能は、複数のAP10のいずれか1つに組み込まれる構成であってもよい。その場合には、当該APは、APとしての機能と集中管理局としての機能を並行して実行することになる。
図2において、集中管理局20には、複数のAP1,AP2,AP3が接続され、さらに各APの宛先となるSTA1,STA2,STA3がそれぞれ接続される。集中管理局20とAP1~AP3との間の情報信号伝達用の接続は実線で示している。また、AP1~AP3とそれぞれ宛先となるSTA1~STA3との間の接続は、実線矢印で示している。さらに、各AP間や、APとその宛先以外のSTAとの間は干渉信号となり、破線矢印で示している。
図3および図4におけるステップS16a/b~S20a/bの処理は、ある送信機会獲得頻度のAPに対して、制御値として送信電力値および干渉検出閾値の仮決定を行い、その制御値を適用して算出される全APのスループット概算値が劣化する場合は仮決定値を採用せず、全APのスループット概算値が劣化しなければ仮決定値を採用する。それを送信機会獲得頻度の高いAPから順番に行う。ただし、APごとに制御値の仮決定処理は1回である。
段階的に送信電力を下げる第1の方法は、周辺のAPの干渉検出電力値から送信電力値を決める方法である。(1) 送信電力を下げる制御を実施するAPが選出される。図2の例では、AP1の無線信号の受信電力値を参照し、この中から現時点で干渉検出閾値より受信電力値が高く観測されるAP2が選出される。同様に、AP2に対してAP1およびAP3が選出され、AP3に対してAP2を選出される。(2) 選出されたAPのうち、現時点での各干渉検出閾値と当該受信電力値の差が最小となるAPを決定し、当該APの干渉検出閾値と当該受信電力値の差を計算し、送信電力値を下げる制御値とする。図2の例では、AP2における干渉検出閾値と受信電力値の差が-76-(-62)=14dBで最小となり、その分だけAP2の送信電力値を下げる。なお、このとき送信電力値の下限値や連動して制御される干渉検出閾値の制限があれば、合わせて下げられる値を制限する。また、伝搬チャネル特性を考慮し、送信電力を下げる際にマージン値を設けても構わない。この方法では当該APと同時送信可能なAPの数を増やす効果が期待できる。
段階的に送信電力を下げる第2の方法は、周辺のAPのSINRまたは干渉電力値から送信電力値を決める方法である。(1) 送信電力を下げる制御を実施するAPが選出される。図2の例ではAP1から送信された無線信号の受信電力値を参照し、この中から現時点で当該APから送信される無線信号が与える干渉のためにSINRが最悪となるAP、または与える干渉電力が最大となるAPが選出される。ただし、上記の手順で選出されるAPは、当該APの受信電力値が干渉検出閾値以下のものが対象となる。図2の例ではAP3となる。(2) 選出されたAPがターゲットMCSを満足するSINRとなるか、他のAPからの干渉電力値と等しくなるまで送信電力値を下げる。この方法では当該APと同時送信するAPの通信品質が改善する効果が期待できる。
図5~図6のステップS16bにおいて、干渉検出閾値の仮決定値が制限値に到達していないときに干渉検出閾値を上げる制御を実施する場合は次のようになる。この制御は、送信機会獲得頻度を高くすることが目的であるため、周辺のAPから送信される無線信号の受信電力値を参照し、受信電力値が現在の干渉検出閾値より高く、かつ最も近い受信電力値との差を干渉検出閾値の仮決定値とする。この方法では当該APの同時送信機会を増やす効果が期待できる。
(-41-x)-(-73+x)=20
x= 6
となる。したがって、図9に★印で示すように、AP1,AP3,AP4の干渉検出閾値は-73から-67に上げ、送信電力値は20から14に下げる。
STA 無線端末
10 無線基地局(AP)
11 情報信号入出力部
12 受信電力値情報収集部
13 送信電力/干渉検出閾値制御部、
14 無線信号送受信部
15 アクセス制御部
20 集中管理局
21 情報信号入出力部
22 情報管理部
23 制御値決定部
Claims (11)
- 互いに干渉し合う複数の無線基地局と、当該無線基地局に接続される複数の無線端末と、当該無線基地局と接続される集中管理局とを備える無線通信システムにおいて、
前記集中管理局は、
前記無線基地局の干渉源となる周辺の無線基地局の受信電力値を含む干渉電力情報と、前記無線基地局の宛先となる前記無線端末からの受信電力値と、前記無線基地局の送信電力値を含む送信電力情報を収集する情報収集手段と、
収集した情報から干渉関係に基づいて計算される送信機会獲得頻度およびスループット概算値に応じて、前記無線基地局における干渉検出閾値および送信電力値を決定し、制御値として前記無線基地局に通知する制御値決定手段とを備え、
前記無線基地局は、前記集中管理局から通知された制御値に基づいて干渉検出閾値および送信電力値の制御を行う構成である
ことを特徴とする無線通信システム。 - 請求項1に記載の無線通信システムにおいて、
前記無線基地局は、前記集中管理局から通知された干渉検出閾値および送信電力値を配下の前記無線端末に通知し、該無線端末が通知された干渉検出閾値および送信電力値に基づく制御を行う構成である
ことを特徴とする無線通信システム。 - 請求項1に記載の無線通信システムにおいて、
前記制御値決定手段は、前記干渉検出閾値および送信電力値の仮決定と、仮決定値を用いた制御後のスループット概算値を計算し、スループットが改善する場合に仮決定値を前記制御値とする構成である
ことを特徴とする無線通信システム。 - 請求項1に記載の無線通信システムにおいて、
前記制御値決定手段は、前記送信機会獲得頻度が高い無線基地局から順に前記干渉検出閾値および送信電力値を決定する構成である
ことを特徴とする無線通信システム。 - 請求項1に記載の無線通信システムにおいて、
前記制御値決定手段は、制御対象の無線基地局の中で前記送信機会獲得頻度が所定の閾値より高い無線基地局に対して前記送信電力値を下げる制御を実施し、前記送信機会獲得頻度が該所定の閾値より低い無線基地局に対して前記干渉検出閾値を上げる制御を実施する構成である
ことを特徴とする無線通信システム。 - 請求項5に記載の無線通信システムにおいて、
前記制御値決定手段は、前記情報収集手段で収集した宛先となる無線端末からの受信電力値を利用して、目標とする変復調方式で最低限必要となるSINR値から前記送信電力値の下限値を設定する構成である
ことを特徴とする無線通信システム。 - 請求項5に記載の無線通信システムにおいて、
前記制御値決定手段は、前記無線基地局の送信電力値を下げる場合に、当該無線基地局が観測する前記受信電力値のうち、前記干渉検出閾値よりも高い無線基地局の受信電力値を基準とする構成である
ことを特徴とする無線通信システム。 - 請求項5に記載の無線通信システムにおいて、
前記制御値決定手段は、前記無線基地局の送信電力値を下げる場合に、当該無線基地局から送信される無線信号による干渉電力が所定値以上またはSINRが所定値以下になる無線基地局の受信電力値を基準とする構成である
ことを特徴とする無線通信システム。 - 請求項5に記載の無線通信システムにおいて、
前記制御値決定手段は、前記無線基地局の干渉検出閾値を上げる場合に、当該無線基地局が観測する前記受信電力値のうち、現在の干渉検出閾値より高く、かつ最も近い受信電力値を基準とする構成である
ことを特徴とする無線通信システム。 - 請求項1に記載の無線通信システムにおいて、
前記制御値決定手段は、粒子群最適化法(PSO)を用いて前記干渉検出閾値および送信電力値を探索する際に、前記送信機会獲得頻度が所定の閾値より高い無線基地局に対して前記干渉検出閾値および送信電力値の変化量の係数を基準値より低い値に設定し、前記送信機会獲得頻度が該所定の閾値より低い無線基地局に対して前記干渉検出閾値および送信電力値の変化量の係数を該基準値より高い値に設定する構成である
ことを特徴とする無線通信システム。 - 互いに干渉し合う複数の無線基地局と、当該無線基地局に接続される複数の無線端末と、当該無線基地局と接続される集中管理局とを備え、集中管理局が無線基地局の送信電力値および干渉検出閾値を制御する無線通信方法において、
前記集中管理局は、
前記無線基地局の干渉源となる周辺の無線基地局の受信電力値を含む干渉電力情報と、前記無線基地局の宛先となる前記無線端末からの受信電力値と、前記無線基地局の送信電力値を含む送信電力情報を収集し、
収集した情報から干渉関係に基づいて計算される送信機会獲得頻度およびスループット概算値に応じて、前記無線基地局における干渉検出閾値および送信電力値を決定し、制御値として前記無線基地局に通知し、
前記無線基地局は、前記集中管理局から通知された制御値に基づいて干渉検出閾値および送信電力値の制御を行う
ことを特徴とする無線通信方法。
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