JP2006197483A - Transmission control method, wireless base station and wireless terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the transmission control method which can realize a further high system throughput while avoiding a hidden terminal problem in CFP. <P>SOLUTION: The transmission control method of the present invention is a transmission control method in a wireless communication system which is composed of AP(1) providing a specific communication area and a plurality of STA devices (11, 12, 13) that exist in the area. For example, AP(1) requests for a list of devices that can communicate with STA devices (11, 12, 13). The wireless terminal devices (11, 12, 13) search the devices with which the terminal device can communicate, respectively, produce the list of the devices that is a search result, and then transmit the produced list to the AP(1). Furthermore, the AP(1) compiles every lists, divides the devices (11, 12, 13, 14, 15) described in the list into groups while avoiding occurrence of a hidden terminal device and performs a predetermined transmission control for each group. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a transmission control method in a digital wireless communication system, and in particular, in wireless LAN communication, a problem that wireless signals collide with each other due to the influence of distance between wireless terminals, obstacles that do not transmit radio waves, That is, the present invention relates to a transmission control method for solving a hidden terminal problem.

  One of the common random access techniques used in conventional digital radio communication systems is a system called CSMA (Carrier Sense Multiple Access), and this CSMA is used, for example, in radio packet communications. . In CSMA, each wireless terminal performs carrier sense of a wireless channel prior to transmission of the wireless packet. For example, if it is confirmed that the channel is in use (channel busy), the wireless terminal refrains from transmitting the wireless packet, When it is confirmed that the channel is not used (channel idle), a radio packet is transmitted.

  Note that in the US wireless LAN standard IEEE802.11 (see Non-Patent Document 1 below), CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) is used. In contrast, the European wireless LAN standard HiperLAN (see Non-Patent Document 2 below) uses TDMA (Time Division Multiple Access) that provides a transmission opportunity in response to a transmission request from a wireless terminal.

  IEEE802.11 discloses the following technology. For example, in CFP (Contention Free Period), which is an access period in which collisions do not occur basically, PCF (Point Coordination Function) and HCCA (HCF Controlled Channel Access) are available as polling access methods based on CSMA / CA. (Refer to Non-Patent Documents 3 and 4 below). For example, in the access method using PCF, the PCF period is started using a carrier sense time PIFS (PCF Inter Frame Space) that is shorter than that during normal data transmission. Then, after the radio base station transmits the Beacon frame, communication is performed between the radio base station and the plurality of radio terminals using a shorter SIFS (Short Inter Frame Space).

  Also, in a state in which a wireless base station can communicate with all wireless terminals in the communication area provided by itself, it exists in the same communication area due to the distance between wireless terminals and obstacles that do not transmit radio waves. However, a situation occurs in which wireless signals between wireless terminals do not reach each other. A wireless terminal in such a situation is called a “hidden terminal”, and a problem caused by this hidden terminal is called a “hidden terminal problem”. That is, in the case of a system that detects by carrier sense that other wireless terminals are not communicating, there is a possibility that a hidden terminal may occur due to the above-described reason. In terminal traffic, radio signals may collide with each other.

  As a method of reducing the influence of the hidden terminal problem, for example, in Non-Patent Document 1, when a data collision occurs by transmitting and receiving a short control frame called “RTS / CTS” prior to data that the wireless terminal wants to send. A method to reduce the influence of the is defined.

  In Non-Patent Document 5 below, it is recognized that a wireless terminal uses a message “Hidden Node Request / Report” for notifying other wireless terminals (including wireless base stations) information about hidden terminals. Yes. This message is a message for causing other wireless terminals to investigate or report the presence or absence of a hidden terminal. For example, a Data frame from a third party terminal can be received, but an ACK frame for the frame is received. Cannot be received, or an ACK frame addressed to a third party can be received, but if a Data frame transmitted by a third party transmitted prior to the ACK frame cannot be received, the third party is treated as a hidden terminal.

IEEE802.11 Standard HyperLAN2 Standard IEEE Wireless LAN Edition "A Compilation based on IEEE Std 802.11-1000 (R2003) and its amendments" IEEE802.11e IEEE802.11k-Draft1.0

  As a method of reducing the influence of the hidden terminal problem described above, a method of reducing the hidden terminal problem by RTS / CTS exchange described in Non-Patent Document 1 or a “Hidden Node” described in Non-Patent Document 5 Although there is a method such as “Request / Report”, there is a problem that the system throughput is lowered due to a certain amount of overhead. In addition, Non-Patent Document 4 has a problem that the method of using a message is not defined.

  In addition, only the polling order is notified to all wireless terminals in advance by using a Beacon frame or other broadcast frame from the wireless base station, and then the wireless terminal transmits a frame transmitted by the other terminal in the transmission order of its own terminal. In the case of using an access method ascertained by analysis, and when the specific wireless terminals exist in positions where they are hidden terminals, the uplink traffic collides between the specific wireless terminals. There was a problem that it might be. In addition, there has been a problem that the bandwidth cannot be effectively used as described above. Specifically, for example, when one wireless terminal in a certain transmission order and the other wireless terminal immediately after the transmission order exist at the position of a hidden terminal, the other wireless terminal performs carrier sense. However, since it is not possible to detect that the one wireless terminal is transmitting, it is determined that the channel is not used, and then transmission starts even though the one wireless terminal is transmitting. It becomes. As a result, Uplink traffic collides.

  The present invention has been made in view of the above, and provides a specific transmission control method capable of realizing higher system throughput while avoiding the hidden terminal problem in CFP that does not assume radio signal collision. The purpose is to obtain.

  In order to solve the above-described problems and achieve the object, a transmission control method according to the present invention includes a radio base station that provides a specific communication area and a plurality of radio terminals that exist in the communication area. In the wireless communication system, a transmission control method for solving the hidden terminal problem, for example, a list request step in which the wireless base station requests a list of devices that can communicate with each wireless terminal; Each wireless terminal requested for the list searches for a device that can communicate with the terminal, generates a list of devices as a result of the search, and then generates the generated list for the wireless base station. The list search step to be transmitted, and the radio base station that has received the list totalize each list, group the devices described in the list so that hidden terminals do not occur, and Characterized in that it comprises a and a transmission control step of performing a predetermined transmission control to flop units.

  According to the present invention, the radio base station divides the radio terminal existing in the communication area provided by the own station and the communication apparatus that may cause interference of the radio terminal into groups in which there are no hidden terminals, The predetermined transmission control is performed every time.

  According to the present invention, the radio base station divides the radio terminal existing in the communication area provided by the own station and the communication apparatus that may cause interference of the radio terminal into groups in which there are no hidden terminals, Since predetermined transmission control is performed every time, for example, in the CFP, it is possible to eliminate collision in the BSS (resolve the hidden terminal problem). In addition, since the hidden terminal problem can be completely avoided by the above grouping, the overhead that has been a problem in the prior art is eliminated, and a further higher system throughput can be realized.

  Embodiments of a transmission control method according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

  FIG. 1 is a diagram showing a configuration example of a communication system that realizes a transmission control method according to the present invention, and shows a communication status between a base station (AP) and a wireless terminal (STA). As shown in the figure, the STAs 11, 12, and 13 exist in a communication area provided by the AP1, and communicate with each other belonging to the AP1. The STAs 14 and 15 exist in a communication area provided by another AP, and communicate with each other belonging to the AP. Note that the STAs 14 and 15 may directly communicate with each other and may form an ad hoc network in an autonomous and distributed manner.

  Here, the transmission control method according to the present embodiment, which realizes high system throughput while avoiding the hidden terminal problem in the communication system, will be described.

  In FIG. 1, first, AP1 exists in a communication area provided by itself and transmits a frame (Communicatable STAs list Request: CSLReq) for requesting a list of communicable STAs list, which will be described later. Broadcast to all STAs belonging to the station. Alternatively, the CSLReq is multicast or unicast to a specific STA. The CSLReq includes a measurement time (for example, in units of μsec) for searching for communicable devices (including AP and STA: “communicable devices” will be described later). The CSLReq may be transmitted by the STA. In this case, CSLReq is transmitted to all STAs (including its own STA) that exist in the communication area provided by AP1 and belong to AP1. Further, when searching for a device that can communicate with the STA (or AP) that has received CSLReq, it is performed so as not to interfere with the current communication.

  Next, the STA (11, 12, 13) that has received the CSLReq from the AP 1 monitors the wireless line based on the measurement time included in the CSLReq, and can communicate with the device (“communication capable device”). "" Means a device existing in the communicable area of the STA (denoted by a dotted line)), and the search result is stored in a predetermined table in the STA. In the present embodiment, a list “Communicatable STAs list” based on “MAC Address” of communicable devices (including STA and AP) is generated and stored as the predetermined table.

  The data held individually (the above search result) may be simply the “list of detected communication devices (STA List)”, and in addition, the “BSS ID of the detected device” is the own STA. "Same BSS", "Detection time", "Received power value", "Communication target device (communication target)", "Traffic type (Application such as HDTV, VoIP, Data, Streaming)", “Priority” may be included. However, the communicable device means a device (AP, STA, etc.) in a communicable area that can receive both a frame addressed to a specific address and its response frame.

  For example, in FIG. 1, the “Communicatable STAs List” held by the STA 11 can be expressed as shown in FIG. 2, and the “Communicatable STAs List” held by the STA 13 can be expressed as shown in FIG.

  That is, in the table of FIG. 2, AP1, STA12, and STA13 are recorded as “STA List”, “Y (the same“ BSS ID ”)” is recorded as “Same BSS”, and AP1 as “communication target”. Is recorded as “Y (communication target)”, STAs 12 and 13 are recorded as “N (not communication target)”, and the traffic type of the communication target AP 1 is VoIP as “Application”. As the “priority”, it is recorded that the priority of the communication target AP1 is “3 (high)”. Here, it is recorded that the communication target of the STAs 12 and 13 is “N (not communication target)”, but for example, when the operation in the ad hoc mode is permitted under the control of the AP1, The communication target is “Y”, and the Application and priority at that time are also recorded.

  3, AP1, STA11, STA14, and STA15 are recorded as “STA List”, and AP1 and STA11 are “Y (the same“ BSS ID ”)” as “Same BSS”. It is recorded that STAs 14 and 15 are “N (different“ BSS ID ”)”, AP1 is “Y (communication target)” as “communication target”, and STAs 11, 14 and 15 are “N (communication)”. ”Is recorded as“ Application ”, and the traffic type of the communication target AP 1 is“ Data ”, and the priority of the communication target AP 1 is“ 1 ( Low) ”. The table “Communicatable STAs List” held by the STA 13 includes information on the STAs 14 and 15 that exist in the communicable range of the STA 13 and can be interference STAs, in addition to the STA that exists in the communication area of the AP 1.

  Subsequently, the STA that has received the CSLReq returns a frame “Communicatable STAs List report: CSLRep” including the contents of the table “Communicatable STAs list” created as described above to the requesting AP 1. However, when the measurement time is “0”, the STA (or AP) that has received CSLReq sends the CSLRep that contains the contents of the table “Communicatable STAs list” held at that time to the requesting AP1. Reply to. In addition, if CSLReq with a measurement time of “0” is received again from AP1 (or another STA) in the unicast frame before the end of the measurement time, the CSLRep held at that time may be returned immediately. Is possible. When CSLReq is received, for example, CSLRep information may be PiggyBacked to an ACK frame for CSLReq, or according to STA scheduling requested in CFP (Contention Free Period) or CP (Contention Period). It is also possible to respond.

  Next, the AP 1 that has received CSLRep from each STA in the communication area of its own station adds up the CSLRep and creates a table indicating the STA group so that no hidden terminal is generated. FIG. 4 is a diagram illustrating an example of a STA group table created by AP1, for example. Here, it records which STA (including other APs) and which STA is communicating (communication partner), and further records the traffic type (HDTV, VoIP, Streaming, Data, etc.). . Also, the priority “Traffic Type Priority” is determined from the communication quality of the STA and recorded. It is also possible to indicate how devices (STA, AP) other than the own BSS exist (Same BSS). In the present embodiment, as an example, STAs present in the communication area provided by AP1 are grouped so as not to cause hidden terminals (corresponding to Group 1 and Group 2), and each STA in the communication area is further grouped. And a group of communication devices (including other APs and STAs belonging to the other APs) that may cause interference (corresponding to Group 3). Other methods may be used for grouping.

  Although not shown, the access category (AC) can be determined from the communication quality of the STA. In addition to the above, it is also possible to record the received power value at the antenna end between the devices. Furthermore, it is also possible to create and record a composite priority based on the line quality including the “Traffic Type Priority” and the received power value.

  Finally, AP1 performs transmission control for the CFP period for each group, for example, based on the table created above. In the present embodiment, the overall priority of each group is determined based on “Traffic Type Priority” shown in FIG. For example, the “Traffic Type Priority” in each group is totaled, and as a result, the predetermined transmission control (Non-patent Documents 1 and 3) is performed so that Group 1 has the highest overall priority and is in the order of Group 2, Group 3,. See).

  As described above, in the present embodiment, a STA that exists in a communication area provided by AP1 and a communication device (including STA and AP) that can interfere with the STA are included in a STA group in which no hidden terminal exists ( Group) and transmission control is performed for each group. Thereby, for example, in the CFP, it is possible to eliminate the collision in the BSS (resolve the hidden terminal problem). Moreover, since the hidden terminal problem can be completely avoided by the above grouping, the overhead due to the exchange of RTS / CTS is eliminated, and higher system throughput can be realized. In addition, since information on neighboring STAs (including neighboring APs) other than the communication area of the local station is also returned, for example, AP1 establishes a neighboring cell or a neighboring ad hoc network (in this embodiment, STA14, It is possible to grasp that the STA 13 in the own BSS is receiving interference.

  Furthermore, when each communication apparatus sends the received power value at the antenna end to AP 1 using CSLRep, AP 1 receives, for example, how much interference is received by STA 13, which is an interfered STA, from STAs 14 and 15. You can see if you are. In addition, it can be understood how much the amount of interference is different from the average received power value between AP1 and STA13. Furthermore, the information on the interference can be used as a parameter when creating a composite priority.

  In the present embodiment, grouping is performed in the CFP so as to eliminate collisions within the BSS. However, since the wireless LAN system is a communication in which the access methods CFP and CP occur alternately, For example, the ratio of assigning the CFP period based on the priority for each group may be set individually (including when not assigned), and communication may be performed using the CP period when no CFP is assigned. Specifically, CFP is assigned to Group 1 at a rate of once every two times, Group 2 is assigned a CFP at a rate of once every three times, and Group 3 is assigned a CFP at a rate of once every four times. A transmission control method such as... Thereby, as described above, it is possible to reliably execute communication of a group having a higher priority while realizing high system throughput.

  As described above, the transmission control method according to the present invention is useful for a digital wireless communication system, and is particularly suitable as a method for solving the hidden terminal problem in wireless LAN communication.

It is a figure which shows the example of 1 structure of the communication system which implement | achieves the transmission control method concerning this invention. It is a figure which shows the specific example of "Communicatable STAs List." It is a figure which shows the specific example of "Communicatable STAs List." It is a figure which shows an example of the table of the STA group produced so that a hidden terminal may not arise.

Explanation of symbols

1 AP
11, 12, 13, 14, 15 STA

Claims (10)

A transmission control method for solving a hidden terminal problem in a wireless communication system including a wireless base station that provides a specific communication area and a plurality of wireless terminals that exist in the communication area. There,
A list requesting step in which the radio base station requests a list of devices (including a radio base station and a radio terminal) that can communicate with each radio terminal;
Each wireless terminal requested for the list searches for a device that can communicate with itself, generates a list of devices as a result of the search, and then transmits the generated list to the wireless base station. A list search step to
The radio base station that has received the list totals each list, groups the devices described in the list so that hidden terminals do not occur, and a transmission control step for performing predetermined transmission control in units of groups;
A transmission control method comprising: A transmission control method for solving a hidden terminal problem in a wireless communication system including a wireless base station that provides a specific communication area and a plurality of wireless terminals that exist in the communication area. There,
A list of devices (including wireless base stations and wireless terminals) capable of communicating with all wireless terminals (including its own terminal) that are present in the communication area and belong to the wireless base station. A requesting list request step;
Each wireless terminal requested for the list searches for a device that can communicate with itself, generates a list of devices as a result of the search, and then transmits the generated list to the wireless base station. A list search step to
The radio base station that has received the list totals each list, groups the devices described in the list so that hidden terminals do not occur, and a transmission control step for performing predetermined transmission control in units of groups;
A transmission control method comprising:   The transmission control according to claim 1 or 2, wherein in the list search step, a search is also made for a peripheral device capable of communication other than a communication area provided by the radio base station, and the result is included in the list. Method.   In the list search step, a device capable of communication is searched based on a measurement time instructed together with the list request. If the measurement time is 0, a list held at that time is stored in the radio base station. The transmission control method according to claim 1, 2, or 3, wherein   5. The transmission control method according to claim 1, wherein in the list search step, communication quality between the terminal and the communicable device is included in the list.   6. The transmission according to claim 5, wherein, in the transmission control step, priority is determined for each group based on communication quality between devices included in the list, and transmission control is performed based on the priority. Control method.   7. The transmission control method according to claim 6, wherein, in the transmission control step, an allocation ratio of each group to a CFP (Contention Free Period) period is set based on a priority for each group. In a radio base station that configures a radio communication system together with a plurality of radio terminals existing in the communication area provided by the own station, and performs transmission control to solve the hidden terminal problem (Hidden Terminal Problem),
Request each wireless terminal for a list of communicable devices (including wireless base stations and wireless terminals), and further count each received list as a response to the request so that hidden terminals do not occur A radio base station characterized in that the devices described in the list are grouped and predetermined transmission control is performed in units of groups. In a radio base station that configures a radio communication system together with a plurality of radio terminals existing in the communication area provided by the own station, and performs transmission control to solve the hidden terminal problem (Hidden Terminal Problem),
A list of devices (including wireless base stations and wireless terminals) capable of communicating with all wireless terminals (including its own terminal) that are present in the communication area and belong to the wireless base station. If requested,
A radio base station that aggregates each list received from each radio device, groups the devices described in the list so that hidden terminals do not occur, and performs predetermined transmission control in units of groups. In a wireless terminal that configures a wireless communication system together with a wireless base station that provides a specific communication area and performs communication belonging to the wireless base station,
It searches for devices (including wireless terminals and wireless base stations inside and outside the communication area) that can communicate with its own terminal, generates a list of devices as a result of the search, and then sends the generated list to the wireless base station. A wireless terminal characterized by transmitting.

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