JP5761644B2 - Wireless communication system and wireless communication method - Google Patents

Description

  The present invention relates to a technique for assigning channels to a plurality of base station apparatuses.

  In recent years, as a high-speed wireless access system using the 2.4 GHz band or the 5 GHz band, base station apparatuses (AP: Access Point) based on the IEEE802.11g standard, the IEEE802.11a standard, and the like are widely used. In systems based on these standards, an orthogonal frequency division multiplexing (OFDM) modulation method, which is a technology for stabilizing the characteristics in a multipath fading environment, is used, and a transmission rate of 54 Mbps is realized at the maximum. doing.

  However, the transmission rate described above is a transmission rate on the physical layer, and is not a data throughput effective for the user. Actually, transmission efficiency in a MAC (Medium Access Control) layer is about 50 to 70%. Therefore, the upper limit of the throughput is about 30 Mbps.

  On the other hand, the communication speed of a wired LAN (Local Area Network) has been increasing due to the spread of FTTH (Fiber To The Home). For this reason, it is assumed that further increase in transmission speed will be required in the wireless LAN in the future. Various spatial signal processing techniques such as MIMO (Multiple Input Multiple Output) and multi-user MIMO are being studied in order to increase the throughput of the radio section. On the other hand, the communication frequency band has been expanded as another method. In IEEE802.11a, a frequency band of 20 MHz is used for each channel. In IEEE802.11n, a frequency band of 40 MHz is used. Further, IEEE 802.11ac is considered up to 160 MHz when options are included. In this way, channel band expansion is progressing.

  Thus, the frequency band of the channel is expanded 8 times from IEEE 802.11a to 11ac. However, no major expansion has been recognized for the entire frequency band that can be used for a wireless LAN. Therefore, with the spread of wireless terminals, frequency resources are becoming insufficient. For example, an environment in which a plurality of base station apparatuses use the same frequency band is increasing. For this reason, depending on the channel selected by the base station apparatus, the throughput may decrease due to the influence of packet signals from other base station apparatuses with which communication cells overlap each other, or the throughput efficiency of the entire system may decrease. There was a problem. Thus, inter-cell interference can be avoided and throughput can be improved by controlling the channel of each base station apparatus using an access point controller (AC).

  A method of connecting a plurality of base station apparatuses to a central control station and assigning a channel to each base station apparatus is described in Patent Document 1. In Patent Document 1, a communication state such as throughput in a base station apparatus can be used as input information, and a channel can be selected so as to maximize system throughput.

JP 2007-74097 A

  However, when it is necessary to control a very large number of base station apparatuses, if the central control station determines channels for all base station apparatuses, the amount of computation for selecting the optimum channel becomes enormous. . As a result, a large amount of time is spent on channel setting, resulting in a problem that communication efficiency decreases.

  Further, in an actual wireless communication system, a wireless terminal does not always communicate with a base station apparatus and may not communicate. In addition, the wireless terminal may move. Therefore, the traffic volume and channel status between each wireless terminal and the base station device change from moment to moment. Therefore, if channel setting is performed each time so as to follow such changes, it is necessary to optimize all base station apparatuses, and the amount of calculation (or setting time) becomes enormous. . For this reason, there is a problem that the efficiency of communication is reduced.

  In view of the above circumstances, an object of the present invention is to provide a technique for improving the efficiency of wireless communication in a situation where other wireless terminal devices using overlapping frequencies exist in the vicinity and an interference signal is generated.

  One aspect of the present invention is a collection unit that collects communication quality information from a plurality of base station devices, a grouping unit that groups the plurality of base station devices based on the communication quality information, and A wireless communication system includes a channel notification unit that determines and notifies a usable channel group, and a use channel determination unit that determines a channel to be used by the own apparatus from the notified usable channel group.

  One aspect of the present invention is a collection step of collecting communication quality information from a plurality of base station devices, a grouping step of grouping the plurality of base station devices based on the communication quality information, and for each group A wireless communication method comprising: a channel notification step for determining and notifying a usable channel group; and a used channel determination step for determining a channel to be used by the own apparatus from the notified usable channel group.

  According to the present invention, even when other wireless communication devices using overlapping frequencies exist in the vicinity and an interference signal is generated, it is possible to reduce the calculation amount of channel assignment and shorten the setting time. As a result, the efficiency of wireless communication can be improved.

It is a conceptual diagram which shows the structure of the radio | wireless communications system 1 by one Embodiment of this invention. It is a conceptual diagram which shows the cell radius of base station apparatus AP1-AP9 in the radio | wireless communications system by this embodiment. It is a conceptual diagram which shows an example of the frequency channel of the radio | wireless communications system by this embodiment. It is a flowchart which shows the specific example of the channel determination method in this embodiment. It is a figure which shows the specific example of the result of grouping. It is a flowchart which shows the specific example of the grouping method by this embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In the following description, “AC” indicates a centralized control station, and “AP” indicates a base station apparatus that is wired to the centralized control station. The central control station AC and the base station apparatus AP are not necessarily connected by wire, and it is sufficient that control signals can be exchanged between the central control station AC and the base station apparatus AP, such as wireless connection.

  In the present invention, a wireless LAN system based on CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) such as IEEE 802.11a / b / g / n / ac is assumed as an example. It can be easily applied.

  FIG. 1 is a conceptual diagram showing a configuration of a wireless communication system 1 according to an embodiment of the present invention. In FIG. 1, a black triangle indicates the wireless terminal 20. The wireless communication system 1 includes one centralized control station 10 and M (M is an integer of 2 or more) base station apparatuses AP. Each base station apparatus AP is connected to Si (i is an AP number; an integer greater than or equal to 0) radio terminals 20, 20,... (C is greater than or equal to 2). (Integer) frequency channels are used for wireless communication.

  Hereinafter, in order to simplify the description, the following wireless communication system 1 is assumed and described. The wireless communication system 1 includes one central control station 10 and M = 9 base station apparatuses AP1 to AP9 connected to the central control station 10 by wire. Each base station device AP1 to AP9 performs wireless communication with a plurality of wireless terminals 20 as indicated by arrows.

In the present embodiment, the central control station 10 includes a collection unit, a grouping unit, and a channel notification unit. The collection unit collects communication quality information from each of the plurality of base station devices AP. Based on the communication quality information collected by the collection unit, the grouping unit groups a plurality of base station apparatuses AP adjacent to each other according to a predetermined restriction condition. The channel notification unit determines and notifies an available channel group for each group grouped by the grouping unit.
Further, the base station apparatus AP includes a use channel determination unit. The used channel determination unit determines a channel to be used from the available channel group notified from the central control station 10 according to a predetermined determination condition.

  FIG. 2 is a conceptual diagram showing cell radii of the base station devices AP1 to AP9 in the wireless communication system according to the present embodiment. As shown in FIG. 2, base station apparatuses AP1 to AP9 each form cells C1 to C9 each having a communicable cell radius (dotted line) centered on itself.

  FIG. 3 is a conceptual diagram illustrating an example of a frequency channel of the wireless communication system according to the present embodiment. As shown in FIG. 3, each base station apparatus AP1 to AP9 shares the frequency channels of channels CH1 to CH6 (C = 6). All base station apparatuses AP1 to AP9 perform wireless communication in the same frequency band (mode). It should be noted that there is no need to be limited to such usage of channels, and the number of frequency channels and their bands (modes) may be different.

Next, a specific example of the operation of the embodiment will be described.
FIG. 4 is a flowchart showing a specific example of the channel determination method in the present embodiment. The centralized control station (AC) 10 collects communication quality information from each of the base station devices AP1 to AP9 (step S101). Communication quality information refers to the signal strength of signals transmitted from the base station apparatuses AP1 to AP9, the position information of the base station apparatuses AP1 to AP9, and the like. For example, as signal strength, there is an RSSI (Received Signal Strength Indication) value. The signal intensity from each base station apparatus AP1 to AP9 can be measured using the beacon transmitted from each base station apparatus AP1 to AP9. Further, as the position information, information obtained using GPS (Global Positioning System) may be used.

When the centralized control station (AC) 10 obtains the communication quality information of each of the base station devices AP1 to AP9, N types of base station devices AP1 to AP9 (N is an integer equal to or greater than 1) based on the obtained communication quality information. ) Are divided into groups using the available channel list (step S102). As a restriction condition for performing grouping, there are the following conditions.
(1) Make adjacent APs the same group (2) Do not overlap communication cells between groups using the same channel

  FIG. 5 is a diagram illustrating a specific example of the grouping result. In the configuration of the wireless communication system as shown in FIG. 1, when the group type is N = 4 and grouping is performed so as to satisfy the above conditions (1) and (2), for example, the result is shown in FIG. It becomes like this. For each group, the signal reachable range is indicated by different line types (dotted line, broken line, one-dot chain line, two-dot chain line), four groups A {AP1, AP4}, group B {AP2, AP3, AP6}, group C {AP5, AP8, AP9} and group D {AP7}. A detailed grouping method will be described later.

  As described above, after grouping (grouping), the centralized control station (AC) 10 determines a channel in each group so that the channel is not redundantly used between the groups. Then, the centralized control station 10 notifies the base station devices AP1 to AP9 of the channel determination result (step S103). For example, when there are channels CH1 to CH6, the central control station 10 assigns channel CH1 to group A, channels CH2 and CH3 to group B, channels CH4 and CH5 to group C, and channel CH6 to group D. assign.

  Specific examples of a method for assigning channels to each group include the following methods. Assign the same number of channels to each group. A method for determining the number of channels to be allocated based on the communication status such as the amount of traffic for each group and the number of connected terminals. For example, if there are three groups and the ratio of the number of connected terminals in each group is 2: 3: 1, the number of allocated channels is two for the first group and two for the second group. One in each of the third and third groups. By making such an allocation, it is possible to maintain the fairness by using the same bandwidth for each group of terminals.

  The base station devices AP1 to AP9 select and set a channel to be actually used from selectable channels notified from the central control station (AC) 10 (step S104). As a specific example of a method for each base station apparatus AP to select a channel in each group, there is the following method. Random selection method. The method of selecting so that the RSSI value of base station apparatus AP of the same group may become the minimum. A method of selecting the RSSI value to be the largest by selecting the same channel as that of the adjacent base station device AP.

  By selecting channels so that the RSSI values between the base station devices AP of the same group are minimized, channel selection that does not interfere with each other can be performed autonomously and distributedly. Conversely, by selecting the same channel as the adjacent base station apparatus AP and selecting the RSSI value to be the largest, it is possible to increase the overlapping area of the communication cells of each other and reduce the hidden terminal problem. Become.

  Further, the base station apparatus AP may perform channel selection so that the communication quality is the best based on the throughput, the bit error rate characteristic, or the packet error rate characteristic. Further, the base station apparatus AP may perform channel selection based on information such as communication frequency, QoS, and the number of streams.

  The wireless communication system may be executed from step S101 at regular intervals. Further, the wireless communication system may always repeatedly execute the process of step S101 and execute the processes after step S102 at regular intervals. Further, the wireless communication system may start the process of shifting to step S101 triggered by the change in the number of base station apparatuses AP. The change in the number of base station devices AP may be detected by the base station device AP located near the added or deleted base station device AP and notifying the central control station 10 of the detection. .

  In addition, the channel selection in step S104 may be performed in an autonomous and distributed manner at each time Δt in each base station apparatus AP1 to AP9. In this case, it is possible to flexibly cope with the surrounding environment, the number of terminals, and the traffic volume.

  In the present embodiment, when performing grouping, it is necessary to measure a communication cell range as communication quality information. When measuring the amount of interference from each base station apparatus AP1 to AP9 using a beacon, a control signal is transmitted from the centralized control station 10, and each base station apparatus AP1 to AP9 transmits a beacon in order. Interference power (RSSI value) can be measured.

  In addition, when a plurality of base station apparatuses AP transmit beacons at the same time, the reception side may separate signals by interference canceller, multi-user detection, etc., and measure the RSSI value for each transmitted base station apparatus AP. . The interference power (RSSI value) may be an instantaneous value or an average power value during the time ΔT. It is also possible to set a threshold value P and allow the communication cells of the groups to overlap within a range that does not exceed the threshold value.

  Further, in the above description, in order to simplify the description, it is assumed that all base station apparatuses AP1 to AP9 use the same communication bandwidth, but all base station apparatuses AP1 to AP9 do not necessarily have the same bandwidth. There is no need to make it. For example, one base station apparatus AP can use a plurality of channels simultaneously. In this case, however, the selection is made within the range of available channels notified from the centralized control station 10 in advance.

Next, the grouping method in step S102 will be described.
FIG. 6 is a flowchart showing a specific example of the grouping method according to the present embodiment. First, in the base station apparatuses AP1 to AP9 connected to the centralized control station 10, the grouping order is determined (step 201).

  The order in which the combinations are performed may be any order, may be performed randomly, or may be performed with priority for each of the base station devices AP1 to AP9, and the combination processing may be performed in descending order of priority. As a method of determining the priority, for example, the priority may be set higher in descending order of the traffic volume, the number of terminals, and the QoS, or the high priority may be changed by rotation.

  Next, it is determined whether or not there is a combination of base station apparatuses AP whose RSSI value is equal to or greater than the threshold Q for the m-th base station apparatus AP (step S202). If there is a combination of base station apparatuses AP whose RSSI value is equal to or greater than the threshold value Q (YES in step S202), it is determined whether or not a restriction condition is satisfied (step S203).

  If the restriction condition is satisfied (YES in step S203), the target base station devices AP are grouped (step S204). On the other hand, if the restriction condition is not satisfied (NO in step S203), a new group is formed for the base station apparatus AP (step S205).

  If there is no combination of base station apparatuses AP whose RSSI value is equal to or greater than the threshold Q (NO in step S202), a new group is generated with the mth base station apparatus AP as an independent group (step S206). ).

  Here, the restriction conditions will be described. As an example of the restriction condition, there is an upper limit value J (J is an integer of 2 or more) of the number of base station devices AP in the group, a total number of subordinate terminals of the base station device AP, a threshold value of a total value of traffic amount, and the like. It is done. Also, at the time of combination determination, at least one of the above conditions may be added as a limiting condition. At this time, the order of priority added to the group may be performed in the order of the priorities described above, or a new order may be set and performed in that order. Furthermore, it is not necessary to add a restriction condition. Further, instead of the RSSI value, grouping may be performed with the base station apparatus AP whose distance between the base station apparatuses AP is L or less as the same group.

  Next, it is determined whether m is equal to or greater than M (the number of base station apparatuses AP), that is, whether all the base station apparatuses AP are grouped (step S207). If m ≧ M is not satisfied, that is, if grouping has not been completed for all base station apparatuses AP (NO in step S207), 1 is added to m (step S209), and the process returns to step S202. The above-described processing is repeated for the base station apparatus AP.

  On the other hand, if m is equal to or greater than M, that is, if grouping is completed for all the base station devices AP (YES in step S207), the channels assigned to each group are determined from the number N of groups and the number W of assignable channels. Calculate and decide (step S208). Then, the process ends.

Next, the channel determination method according to the present embodiment will be described in more detail.
In the embodiment described above, as a channel determination method, for example, in order to simply set the number N of channel lists (sets) to be assigned in advance or assign the same number of channels to each group, Allocate the largest integer number of channels within the same or smaller value than the calculation result, and when the remainder is available, distribute it appropriately, traffic volume of each group, number of APs, number of controlled terminals In consideration of the total value and the like, if it is larger than that value, the number of allocated channels can be increased.

  Here, as an example, in the case of the AP arrangement as shown in FIG. 1, the grouping order is base station apparatuses AP1, AP2,..., AP9, Q is greater than 0, AP number J is 3, and allocatable channels. A case where the flowchart shown in FIG. 6 is executed when CH1 to CH6 (W is 6) will be described.

  First, since the base station apparatus AP1 observes the RSSI value of only the base station apparatus AP4 in which the cells overlap (the RSSI value exists), the base station apparatuses AP1 and AP4 have a limitation of Q> 0. Are grouped as group A. Next, the base station device AP2 performs grouping with the base station device AP3 under the same conditions as described above. Although the base station apparatus AP3 has the RSSI values of the base station apparatuses AP2 and AP6, the base station apparatuses AP2 and AP3 are already grouped. Therefore, the ungrouped base station apparatus AP6 is newly added to the group B. In addition, a group B called {AP2, AP3, AP6} is formed.

  The base station device AP4 is targeted only for the base station device AP1, but since it has already been grouped, it remains the group A of {AP1, AP4}. The base station apparatus AP5 is targeted for the base station apparatuses AP6 and AP9, but the base station apparatus AP6 already belongs to another group B {AP2, AP3, AP6}. In the group B, the number of APs is 3 Therefore, it cannot be newly added. Therefore, a new group C {AP5, AP9} is formed. Since there is no other base station apparatus AP that can form a group, the base station apparatus AP7 forms a group D independently as shown in step S203.

  The base station apparatus AP8 is targeted for the base station apparatus AP9, but since the base station apparatus AP9 has already formed the group C with {AP5, AP9}, the base station apparatus AP9 is newly added to the group C {AP5, AP9}. The device AP8 is added to form a group C {AP5, AP8, AP9}. The base station device AP9 is targeted for the base station devices AP8 and AP5, but since the base station devices AP8 and AP5 have already formed a group C, no new grouping is performed. Thus, four groups A {AP1, AP4}, B {AP2, AP3, AP6}, C {AP5, AP8, AP9}, and D {AP7} are formed.

Next, a channel allocation method will be described.
In step S204 shown in FIG. 6, since the group is G = 4, W / G = 6/4, and channels are allocated one by one as the largest integer among the same or smaller values. Considering that the remaining channels are allocated where the number of APs is large, {CH1} for group A {AP1, AP4}, {CH2, CH3} for group B {AP2, AP3, AP6}, group C { A channel list of {CH4, CH5} is assigned to AP5, AP8, AP9} and {CH6} is assigned to group D {AP7}.

  Here, if the allocated channel list is insufficient, the allocated channel list is redistributed. At this time, since it is desirable to use the same channel list as far as possible from the same channel list, the distance is measured by GPS and set so that groups apart by a certain distance or more are used. Alternatively, an RSSI value between APs or an average value thereof may be measured, and among them, a combination of values below a certain value may be set. Alternatively, the RSSI values with all the base station devices AP1 to AP9 are measured from the wireless terminals 20, 20,..., And the results are collected by the central control station 10, and the group cells do not overlap each other based on the results. Alternatively, the overlap region may be set to be the smallest (the RSSI value is small).

  When a limited number of frequency channels are shared by a plurality of base station apparatuses AP, the number of channels is insufficient, so that efficient channel allocation by centralized control is required. However, when the number of base station apparatuses increases, there is a problem that a lot of time is spent on channel setting processing in all base station apparatuses.

  On the other hand, according to the above-described embodiment, the central control station 10 divides the plurality of base station devices AP into a plurality of groups based on information from the plurality of base station devices AP, and can be used for each group. Determine the list. Each base station apparatus AP determines a channel autonomously and distributedly from the channel list. By such processing, the same channel is shared by a plurality of adjacent AP groups, and channel allocation is performed in an autonomous and distributed manner. Therefore, it is possible to reduce the amount of calculation (calculation time) rather than determining all by centralized control. In particular, it is effective in an environment where the number of wireless terminals changes, and as a result, the amount of interference can be reduced and the throughput can be improved.

In the wireless communication system described above, the central control station 10 includes a collection unit, a grouping unit, and a channel notification unit. On the other hand, the radio communication system does not include the central control station 10, and any of the base station apparatuses AP may include a collection unit, a grouping unit, and a channel notification unit. In addition, the collection unit, the grouping unit, and the channel notification unit do not have to be provided in a single device, and may be distributed and implemented in a plurality of devices (for example, a plurality of base station devices AP).
The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes designs and the like that do not depart from the gist of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Wireless communication system, 10 ... Central control station (AC), AP, AP1-AP9 ... Base station apparatus, 20 ... Wireless terminal, C1-C9 ... Cell, AD ... Group

Claims (2)

A collection unit for collecting communication quality information from a plurality of base station devices;
There is a combination of the base station devices with the communication quality information equal to or greater than a predetermined value, and the upper limit value of the number of base station devices in the group to be grouped, the total number of terminals under the base station device, and the total traffic amount When at least one of the predetermined thresholds is exceeded, a new group is generated so that the base station apparatus of this combination is a different group, and when the predetermined threshold is not exceeded, A grouping unit for grouping the base station devices of this combination into the same group ;
A channel notification unit that determines and notifies available channels for each group; and
A used channel determining unit that determines a channel to be used by the own device from the notified usable channel group;
A wireless communication system comprising: A collection step of collecting communication quality information from a plurality of base station devices;
There is a combination of the base station devices with the communication quality information equal to or greater than a predetermined value, and the upper limit value of the number of base station devices in the group to be grouped, the total number of terminals under the base station device, and the total traffic amount When at least one of the predetermined thresholds is exceeded, a new group is generated so that the base station apparatus of this combination is a different group, and when the predetermined threshold is not exceeded, A grouping step of grouping the base station devices of this combination into the same group ;
A channel notification step for determining and notifying a usable channel group for each group;
A used channel determining step for determining a channel to be used by the own device from the notified usable channel group;
A wireless communication method.

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