JP4680047B2 - Wireless relay system and method - Google Patents

Description

  The present invention relates to a wireless relay system and method.

In recent years, research and development has been actively conducted toward the practical use of the IEEE 802.16 standard, which is a communication standard that enables high-speed wireless access in a wide area. In this IEEE802.16, as a method for separating uplink / downlink communication between a base station and a subscriber station, a TDD (Time Division Duplex) system for switching between transmission and reception in the time domain, and transmission and reception in the frequency domain An FDD (Frequency Division Duplex) method is used.
For example, in the TDD scheme, each frame to be transmitted and received is divided into a downlink DL (Down Link) subframe and an uplink UL (Up Link) subframe for communication. As shown in FIG. 2, the data in these subframes is transmitted as burst data that is further finely divided for each communication partner, but if the communication partner transmits or receives data at any time (section). Whether it is good is defined in section allocation information such as DL-MAP and UL-MAP (which are included in DL burst # 1) created by the base station, and each subscriber station has their “time table”. Data communication is performed according to the above. As described above, IEEE802.16 employs a mechanism in which the base station takes the initiative in controlling communication.

IEEE802.16 defines two types of connection, that is, network topology, of each node: PMP (Point-to-Multipoint) type and Mesh type. Here, as in a general cellular system, the PMP type basically has a configuration in which a plurality of subscriber stations are accommodated for one base station, and the base station is a subscriber located in its own area. Cover station communication. On the other hand, the Mesh type has a configuration in which a large number of subscriber stations are connected in a daisy chain, and communication is realized by performing multi-hop by a plurality of terminals (subscriber stations) in an ad hoc manner.
IEEE 802.16-2004, IEEE Standard for local and metropolitan area networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems

  By the way, in general, in wireless communication, it is important to enhance the coverage area (coverage area) by reducing the area where radio waves cannot be received. For example, in IEEE802.16, it is assumed that a frequency band of 2 GHz or higher is used. However, due to the characteristics of this frequency band, reception of radio waves may be unstable due to the influence of topography and surrounding buildings. In addition, indoors and underground, it may be out of service area and communication is impossible. As one method for solving such a situation, there is a method of securing a wider coverage area by providing a relay station and relaying communication radio waves between a base station and a subscriber station. In addition, a larger multi-level modulation scheme can be selected by arranging a relay station for a subscriber station that cannot obtain high throughput due to the distance between the base station and the subscriber station, thereby improving throughput. Expected to be effective.

In the case of IEEE802.16, the above Mesh mode can easily expand the coverage area because each subscriber station functions as a relay station in the first place, but there are the following restrictions. Therefore, there is a problem that it is not practical. In other words, the Mesh mode is an optional standard and is not compatible with the PMP mode in the frame configuration, and because it uses multi-hop, it has a higher frame overhead than the PMP mode and lowers the throughput. The limitation is that the duplex method is only the TDD method.
On the other hand, the PMP type does not have such a Mesh type limitation, but the current PMP standardization standard does not specify relaying. Therefore, in order to expand the coverage area, there is a means other than adding a high-cost base station. Absent. Therefore, in a PMP type IEEE802.16 system, if a simple relay station corresponding to the number of accommodated users assumed in the target area can be installed and used, high-quality communication with great cost advantages can be achieved. It is expected that the system can be constructed.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a radio relay system and method that can easily and flexibly realize expansion of communication range and improvement of throughput.

  The present invention has been made to solve the above problems, and the invention according to claim 1 is directed to a relay station and the relay station in wireless communication in which data is transmitted and received using a band designated by a base station. Means for notifying a subscriber station in the communication range of the same identifier, and means for setting a band that can be used only by the subscriber station that has been notified of the identifier, and using the set band A wireless relay system is characterized in that a user station transmits data and the relay station relays the data to the base station.

  The invention according to claim 2 is the wireless relay system according to claim 1, wherein the relay station relays communication with the subscriber station based on data transmitted from each subscriber station. The identifier is notified to a subscriber station that is determined to be relayed.

  The invention according to claim 3 is the wireless relay system according to claim 1 or 2, wherein the relay station is provided with storage means, and the identifier of the subscriber station transmitted from the base station is: When the identifier is the same as the identifier notified to the relay station, the subscriber station is stored in the storage means as a relay target.

  According to a fourth aspect of the present invention, in the wireless relay system according to any one of the first to third aspects, the number of subscriber stations accommodated in the base station and the number of the relay stations are data. And a means for adaptively allocating the bandwidth that can be used only by the relayed subscriber station based on the number of subscriber stations that relay the channel.

  According to the fifth aspect of the present invention, in wireless communication in which data is transmitted and received using a band designated by a base station, the same identifier is notified to a relay station and a subscriber station within the communication range of the relay station. The base station sets a band that can be used only by the subscriber station notified of the identifier, and the subscriber station transmits data using the set band, and the relay station transmits the data to the base station. A radio relay method characterized by relaying to a station.

According to the present invention, subscriber stations are grouped in units of relay stations by an identifier, a communication band dedicated to the group is allocated, and data from the subscriber station is transmitted to the base station using the band. Even a subscriber station that is not located within the communication range can perform wireless communication, and the communication range can be expanded.
In addition, it is possible to select a larger multi-level modulation scheme by arranging a relay station for a subscriber station that cannot obtain high throughput due to the distance between the base station and the subscriber station. Improvements can be realized.
In addition, when the present invention is applied to a wireless system of the IEEE802.16 standard, the identifier can be notified using an MCA message defined in the standard, so that the modification to the standard by introducing the relay function is relatively easy. There is a merit that there are few.
In addition, since grouping is performed in units of relay stations, various bandwidths are adaptively allocated according to the number of subscriber stations that are directly connected to the base station and subscriber stations that are relayed by the relay station. It is possible to perform relaying that can flexibly cope with changes in communication conditions.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram illustrating a configuration of a wireless relay system according to an embodiment of the present invention. In the figure, a relay station (RS) 20 is located in a range where direct communication with the base station (BS) 10 can be performed, and two subscriber stations (SS1, SS2) 30 and 40 communicate with the relay station 20. Although it can, it exists in the position which cannot communicate with the base station 10 directly. Thus, the present invention is based on a PMP type network configuration in which a plurality of subscriber stations are accommodated in a base station via relay stations.

FIG. 2 is a diagram showing the structure of a frame used in the PMP mode in the IEEE 802.16 TDD system. As shown in the figure, the data to be communicated is divided into each frame (..., Frame n-1, frame n, frame n + 1, frame n + 2,...), And each frame is divided into a DL subframe and a UL subframe. It is made up of.
The DL subframe is composed of a broadcast message at the head part and burst data (after DL burst # 2) into which actual data addressed to each subscriber station enters. The broadcast message includes a preamble, FCH, and DL burst #. 1 is composed. Furthermore, DL burst # 1 includes UCD (Uplink Channel Descriptor), DCD (Downlink Channel Descriptor), and the above-described DL-MAP and UL-MAP. The broadcast message is defined by defining communication parameters in the above element data, and is transmitted in the broadcast mode and received by all subscriber stations.

The UL subframe is composed of a contention interval (hereinafter referred to as a contention period) at the beginning, and subsequent burst data from each subscriber station. The contention period is a slot used by a subscriber station that wants to start communication to inform the base station of the contention period, and is composed of two parts for initial ranging and BW (Bandwidth) request.
The initial ranging slot notifies its existence when each subscriber station first starts communication (for example, when the power is turned on), so the BW request slot actually communicates and transmits data. Is used to request the necessary bandwidth. Each subscriber station can freely speak (send) by back-off control based on a CW (Contention Window) value in the contention period, and the base station performs processing in the order of transmission. Note that the contention period does not need to be provided for all frames, and may be provided for every several frames, for example, only one of the odd and odd frames in order to increase the communication throughput.

Next, processing performed in the wireless relay system according to the present embodiment will be described in detail with reference to FIGS. 3 to 10 showing the first frame to the eighth frame in time series.
Here, the description proceeds with the assumption that the ranging process for the relay station 20 has been completed. The ranging process is a process in which each terminal (in this case, the relay station 20) notifies its own existence, or determines a modulation method and adjusts reception power, etc. as preparation for starting communication with the base station 10 That is. Specifically, the ranging process is started when the terminal transmits a predetermined request command (RNG-REQ; ranging request) in the above-described initial ranging contention period, and finally a response command from the base station 10 The ranging process is completed by receiving (RNG-RSP; ranging response).
Hereinafter, each process in the wireless relay system will be described separately for each stage.

1. Registration of Relay Station First, the relay station 20 receives a broadcast message from the base station 10. As described above, the broadcast message includes the DL-MAP that specifies which data in the DL subframe the relay station 20 should receive, and the relay station 20 refers to this so that A REG-RSP (registration response) command transmitted from the base station 10 is received (the relay station 20 has transmitted a corresponding request command (REG-REQ; registration request) after completion of the above ranging process. Suppose). Registration is completed by receiving this REG-RSP. <(1) (2) of the first frame (FIG. 3) (circle numbers in the figure are shown in parentheses. The same applies hereinafter)>

  In this embodiment, a parameter called CID (connection ID) is described in the registration request command REG-REQ. A value other than a predetermined value 0 (zero) is set in this parameter. By doing so, the base station 10 that has received the REG-REQ can identify that the relay station 20 has transmitted the REG-REQ. Note that the value 0 of the parameter cannot be used here because it is a value reserved for normal ranging processing.

2. Establishment of Relay Connection When the registration is completed, the relay station 20 transmits a BW-REQ (Bandwidth request) command to the base station 10 using backoff control based on the CW value in the contention period for the BW request. Upon receiving the command, the base station 10 sets a band according to the request, creates a UL-MAP reflecting the request, and transmits it to the relay station 20 as a broadcast message. The relay station 20 transmits a DSA-REQ (Dynamic Service Addition request) to the base station 10 in accordance with the band (time) specified by the UL-MAP. Here, DSA-REQ is a message used to newly establish a connection for data communication, and is a connection for relaying data transmitted from a subscriber station under the relay station 20 to the base station 10. The purpose here is to make. <(3) of the first frame (FIG. 3), (1) (2) of the second frame (FIG. 4)>

  The base station 10 receives the DSA-REQ, updates the UL-MAP, and transmits a broadcast message to the relay station 20. As a result, a relay connection having a band specified by UL-MAP is established in the UL subframe. Thereafter, among the data transmitted from the subscriber station, data (for example, RNG-REQ and BW-REQ, which will be described later) to which a specific band is not allocated by UL-MAP is used as a relay connection created here. Then, it is transferred to the base station 10. <(1) (4) of the third frame (FIG. 5)>

3. On the other hand, when registration of the relay station 20 is completed, the base station 10 recognizes that the relay station 20 is a terminal station responsible for data relay, and performs the following processing.
That is, first, the base station 10 secures a band for the relay station 20 to transfer data in the DL subframe, and designates it by DL-MAP. The relay station 20 transmits (broadcasts) the received broadcast message to a subscriber station existing in its own area according to DL-MAP. However, at this time, the relay time here is added to the “start time” which is a parameter of DL-MAP and UL-MAP in the broadcast message to be transferred. <(1) (2) of the third frame (FIG. 5)>

  Further, the base station 10 transmits an MCA-REQ (Multicast Assignment request) to the relay station 20 in the band specified by the transmitted DL-MAP. This MCA-REQ message is for performing Join / Leave to / from the multicast group, but here it is used as a Join command. FIG. 11 shows the format of the message. Members belonging to the multicast group share the parameter “multicast CID” specified by the MCA-REQ, and multicast communication is realized when these members receive data having the same ID. It is assumed that the transmission destination of the MCA-REQ is specified in the parameter “primary management CID”, and the numerical value is given in the ranging process. <(3) of the third frame (FIG. 5)>

  When receiving the MCA-REQ (Join), the relay station 10 recognizes that it belongs to the group identified by the multicast CID. In this way, a multicast group having the relay station 20 as a member is created via the multicast CID notified from the base station 10. In this embodiment, the relay station 20 is notified of the ID (multicast CID) for specifying the relay group by using the MCA-REQ message prepared as the multicast function. <(3) of the third frame (FIG. 5)>

In order to clearly indicate that the multicast group created as described above is for controlling relay with the subscriber station (not for original multicast communication), the MCA-REQ includes It is also possible to newly define a numerical value indicating that in Multicast group type which is a parameter of.
The subscriber stations 30 and 40 also need to belong to the same multicast group as the relay station 20, and the process will be described in the process (5) described later.

4). Ranging Request from Subscriber Station As described above, the broadcast message sent from the base station 10 is transferred by the relay station 20 to the subscriber stations existing in the area. The subscriber stations 30 and 40 receive this broadcast message by a method such as frequency search, and grasp the contention period for initial ranging in the UL subframe by referring to the obtained UL-MAP. . <(1) (2) of the fourth frame (FIG. 6)>

Here, since the multicast group to which the relay station 20 belongs is created as described above, a contention period for the multicast group is newly set by the base station 10. That is, here, there are two contention periods for the base station 10 (used by terminals directly connected to the base station) and a contention period for the relay station 20 (used by terminals under the relay station). Yes. At this point, the subscriber stations 30 and 40 cannot determine whether they are accommodated in the base station 10 or the relay station 20, and therefore use the contention period for base stations provided for all subscriber stations. And transmit.
The contention period for the multicast group is adaptively determined in size (section length) according to the number of subscriber stations included in the multicast group. By doing so, it is possible to allocate the optimum bandwidth according to the network configuration.

The subscriber stations 30 and 40 transmit an RNG-REQ command using backoff control based on the CW value during the contention period (for initial ranging with respect to the base station). The command is received by the relay station 20 and transferred to the base station 10 using the relay connection created in the third frame. <(3) (4) of the fourth frame (FIG. 6)>
At this time, the relay station 20 stores the received RNG-REQ and the identifier (MAC address or the like) of the subscriber station that has transmitted the RNG-REQ as a subscriber station list. Further, the base station 10 determines that the request of the subscriber station has been received via the relay station 20 by receiving the request from the subscriber stations 30 and 40 in the relay connection section allocated to the relay station 20. To do.

The base station 10 determines whether each subscriber station that has transmitted the RNG-REQ is directly connected to the base station 10 or the relay station 20 relays communication. As the determination method, for example, the following method is applied.
That is, the base station 10 stores a history list of subscriber stations to which the base station 10 has already been directly connected, and if the subject subscriber station is in the list, the base station 10 is entered. If not, it is determined to connect to the relay station 20. In this embodiment, as shown in FIG. 1, the subscriber stations 30 and 40 are located in a place where radio waves from the base station 10 do not reach. It is determined to connect.

  Also, unlike the configuration of FIG. 1, when the subscriber station is in a position where it can receive radio waves from the base station, a decision is made to determine which one to connect in consideration of the reception power of the radio waves. You can also.

5. Ranging response from the base station and participation of the subscriber station in the multicast group When the connection form of the subscriber stations 30 and 40 is thus determined, the base station 10 transmits the RNG-RSP corresponding to the received RNG-REQ. To do. In the present embodiment, since it is determined that the subscriber stations 30 and 40 are placed under the relay station 20 as described above, the base station 10 sets the same multicast CID that is already notified to the relay station 20. The transmitted MCA-REQ is also transmitted. Here, in the DL-MAP in the broadcast message, a band for relaying to the subscriber stations 30 and 40 as well as a band for communication between the base station 10 and the relay station 20 are designated, and RNG-RSP and MCA-REQ is transmitted and received according to these bands. <(1) to (4) of the fifth frame (FIG. 7)>

  From the received RNG-RSP and MCA-REQ (multicast CID included) and the stored subscriber station list, the relay station 20 determines that the subscriber stations 30 and 40 are under its control, that is, the same. Recognize that they belong to a multicast group. These messages are relayed to the subscriber stations 30 and 40 using the relay band specified by the DL-MAP. <(5) (6) of the fifth frame (FIG. 7)>

  The subscriber stations 30 and 40 complete the ranging process by receiving the RNG-RSP, and recognize that they belong to the multicast group by receiving the MCA-REQ and acquiring the multicast CID. As a result, the subscriber stations 30 and 40 can request a bandwidth necessary for data transmission via the relay station 20, that is, by using a contention period (for the multicast group) for the relay station 20. Communication with the base station 10 can be started. The specific processing is as described in (6) below.

  When the base station 10 determines that the subscriber stations 30 and 40 are not directly under the relay station 20 and communicates directly with the base station 10, the above MCA-REQ is not transmitted and only the RNG-RSP is transmitted. Is sent. Then, the subscriber stations 30 and 40 do not receive the notification of the multicast CID, and recognize that the direct connection with the base station 10 is performed. In this case, after that, communication is performed according to a conventional normal sequence.

6). Registration of subscriber stations The communication processing performed by the subscriber stations belonging to the multicast group using the contention period is basically the same regardless of the type of message, but here the subscriber stations 30 and 40 A description will be given by taking as an example a process of registering the base station 10.
The subscriber stations 30 and 40 start communication using the contention period for the multicast group. This contention period is allowed to be used only by terminals having the same multicast CID as the relay station 20. The subscriber stations 30 and 40 transmit the BW-REQ using back-off control based on the CW value in the BW request slot in the contention period. The message is received by the relay station 20 and transferred to the base station 10 using the relay connection created in the third frame. <(3) (4) of the sixth frame (FIG. 8)>

  When the base station 10 receives the command, the base station 10 sets a band according to the request (a band for performing transmission from the subscriber stations 30 and 40 to the relay station 20 and transfer to the base station 10 by the relay station 20). Then, a UL-MAP reflecting the same is created and transmitted to the relay station 20 as a broadcast message. The relay station 20 relays the broadcast message to the subscriber stations 30 and 40. The subscriber stations 30 and 40 transmit the REG-REQ to the relay station 20 according to the band specified by the obtained UL-MAP, and the relay station 20 similarly transmits the REG-REQ to the base station 10 according to the specified band. Forward. <(1) to (4) of the seventh frame (FIG. 9)>

  The base station 10 transmits a REG-RSP corresponding to the received REG-REQ. Here, since the destination subscriber stations 30 and 40 are under the control of the relay station 20, the base station 10 transmits the communication band between the base station 10 and the relay station 20 to the DL-MAP in the broadcast message of this frame. The bands for relaying to the subscriber stations 30 and 40 are designated, and the REG-RSP is transmitted / received according to these bands. The relay station 20 relays the REG-RSP using the designated band, and the registration is completed when the REG-RSP is received by the subscriber stations 30 and 40. <(1) to (4) of the eighth frame (FIG. 10)>

As described above, the embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the scope of the present invention. It is possible to
For example, in the present embodiment, the case where TDD is used as the duplex system has been described, but the present invention can also be applied to the FDD system. In this case, the DL subframe and the UL subframe are simultaneously transmitted and received using different frequencies.

Further, a plurality of relay stations can be installed in parallel under the base station, and a plurality of relay stations can be configured in multiple stages. However, a different multicast CID is assigned to each of the plurality of relay stations.
In addition, the subscriber station list stored in the relay station 20 is stored separately in the fifth frame, for example, as shown in FIG. Only subscriber stations (referred to as A, B, and D) that have been notified of the same multicast CID as the relay station 20 may be registered as relay targets. At this time, the subscriber stations (C and E) that are not notified of the multicast CID are not relayed by the relay station and are directly connected to the base station 10.

  The present invention is suitable for use in a wireless relay system according to the next-generation high-speed wireless communication standard IEEE802.16.

1 is a configuration diagram of a wireless relay system according to an embodiment of the present invention. It is a structural diagram of a frame used in the PMP mode in the IEEE 802.16 TDD scheme. It is a sequence diagram of the first frame. It is a sequence diagram of the 2nd frame. It is a sequence diagram of the 3rd frame. It is a sequence diagram of the 4th frame. It is a sequence diagram of the 5th frame. It is a sequence diagram of the 6th frame. It is a sequence diagram of the seventh frame. It is a sequence diagram of the 8th frame. This is the format of the MCA-REQ message. It is an example of a subscriber station list stored in the relay station.

Explanation of symbols

10 ... Base station 20 ... Relay station 30, 40 ... Subscriber station

Claims (5)

In wireless communication that transmits and receives data using the band specified by the base station,
Means for notifying the relay station and the same identifier to a subscriber station within the communication range of the relay station;
Means for setting a band that can be used only by the subscriber station notified of the identifier;
With
A wireless relay system, wherein a subscriber station transmits a command requesting a bandwidth required for data transmission using the set bandwidth, and the relay station relays the command to the base station. Communication with the subscribers station comprises means for determining whether to relay to the relay station,
The wireless relay system according to claim 1, wherein an identifier identical to an identifier previously notified to the relay station is notified to a subscriber station determined to be relayed. A storage means is provided in the relay station,
Radio relay system according to 請 Motomeko 2 and to store in the memory means the subscriber station is notified the identifier from the base station as a relay target. Before SL relay station based on the number of subscriber stations for relaying data, according to claim 1 in which only the subscriber station is notified the identifier is characterized in that it comprises means for allocating adaptively a bandwidth that can be used The wireless relay system according to any one of claims 1 to 3. In wireless communication that transmits and receives data using the band specified by the base station,
The same identifier is notified to the relay station and the subscriber station within the communication range of the relay station,
The base station sets a band that can be used only by the subscriber station to which the identifier is notified,
A wireless relay method, wherein a subscriber station transmits a command for requesting a bandwidth required for data transmission using the set bandwidth, and the relay station relays the command to the base station.

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