JP4875504B2 - OFDMA radio system and relay station - Google Patents

Description

  The present invention relates to a relay station or the like for relaying an orthogonal frequency division multiple access (OFDMA) signal.

  Currently, the IEEE 802.16e standard called Mobile WiMAX is being put into practical use (for example, see Non-Patent Document 1). Further, standardization of IEEE 802.16j for performing multi-hop in such a mobile environment has been studied (for example, see Non-Patent Documents 2 and 4).

  There is also known an OFDM wireless repeater that receives radio waves in a first radio frequency band from a base station, converts the radio waves into different second radio frequency bands, and transmits them to a terminal (see, for example, Patent Document 1).

JP2002-111571 IEEE Computer Society, IEEE Microwave Theory and Techniques Society, "IEEE Standard for Local and metropolitan area networks, Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems (IEEE802.16e-2005)", [online], 2006 2 May 28, IEEE, [Search December 21, 2006], Internet <URL: http://standards.ieee.org/getieee802/download/802.16e-2005.pdf> Relay Task Group of IEEE 802.16, "Baseline Document for Draft Standard for Local and Metropolitan Area Networks, Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems, Multihop Relay Specification (IEEE 802.16j-06 / 026r1)", [online ], December 1, 2006, [Search December 21, 2006], Internet <URL: http://www.ieee802.org/16/relay/docs/80216j-06_026.pdf> Zou Wei, Jimin Liu, Shan Jin, Gang Shen, Kaibin Zhang, "Neighborhood Discovery and Topology Learning (IEEE C802.16j-06 / 287)", [online], November 8, 2006, IEEE 802.16 Broadband Wireless Access Working Group, [Search December 21, 2006], Internet <URL: http://www.ieee802.org/16/relay/contrib/C80216j-06_287.pdf> Hyukjoon Lee, Hyun Park, Yong-Hoon Choi, Young-uk Chung, Seung hyong Rhee, Yong Su Lee, Young-il Kim, "Link Adaptive Multi-hop Path Management for IEEE 802.16j (IEEE C802.16j-06 / 296 ) ", [Online], November 8, 2006, IEEE 802.16 Broadband Wireless Access Working Group, [Search December 21, 2006], Internet <URL: http://www.ieee802.org/16/relay /contrib/C80216j-06_296.pdf>

  However, in the conventional wireless repeater of Patent Document 1, in order to maintain the bandwidth of the first radio frequency band allocated for the base station, convert only the frequency and retransmit to the relay area, Necessary. Therefore, when used in a broadband mobile radio communication system in which the occupied bandwidth of one carrier can be 10 MHz or more, there is a problem that frequency resources cannot be effectively used.

  The present invention has been made from the above-described background, and an object thereof is to provide an OFDMA radio system, a relay station, and the like that can effectively use frequency resources.

To achieve the above object, an OFDMA radio system and a relay station according to the present invention include:
In an OFDMA wireless system comprising a subscriber station, one or more relay stations, and a base station that accommodates the subscriber station or relay station,
The relay station (RS) is a region on a subcarrier and a time that is not transmitted or received by the base station among a plurality of subcarriers included in a carrier used by a base station (MR-BS) to which the relay station belongs. A part of subcarriers having a small noise + co-channel interference power measured in the above are used for transmission or reception with a subscriber station belonging to the relay station in the area,
The base station provides a time when the number of subcarriers to be used is reduced when a relay station first appears under the base station in a state where all of the subcarriers included in a carrier wave are used. .

Further, it is used in an OFDMA wireless system including a subscriber station, one or more relay stations, and a base station that accommodates the subscriber station or the relay station, and a base station or relay station that is an upstream station, a downstream station, A relay station that performs relaying between a subscriber station or a relay station in the MAC layer,
A plurality of layer 1 processing units (1, 2) each having an independent antenna, transmitting and receiving radio signals of the OFDMA radio system, and measuring RSSI;
Each of the layer 1 processing units is caused to measure the RSSI of the downstream signal from the upstream station, and the layer 1 processing unit having the maximum RSSI is allocated for communication with the upstream station, and any other layer 1 processing is performed. Part for communication with downstream stations,
On the subcarrier where the upstream station does not transmit the noise of the plurality of subcarrier sets included in the carrier used by the upstream station + the co-channel interference power to the layer 1 processing unit allocated for communication with the downstream station And a layer 2 processing unit (3) that is measured in a temporal region and uses one subcarrier set having a small interference power for transmission to the downstream station only in the region.

  According to the OFDMA radio system and relay station according to the present invention, at the receiving end of the mobile device, the transmission signal of the radio base station and the transmission signal of the radio relay station do not interfere with each other, and the same carrier wave as that of the radio base station is used. Thus, the frequency resource can be utilized effectively.

The following description is based on the premise that the OFDMA physical layer specified in IEEE 802.16 is used, and the definition of the terminology used in the description of this example is based on that specification unless otherwise specified.
In addition, all combinations of configurations described in each embodiment are not necessarily essential to the present invention. In addition, any combination of the features of the embodiments and combinations with the cited prior art can be included in the present invention.

First, in order to help the understanding of the present invention, an OFDMA system and types of subcarrier segregation in OFDMA will be described.
FIG. 1 is a schematic diagram of an OFDMA system. OFDMA is an access scheme in which user multiplexing is performed by assigning different users to each subcarrier and each OFDM symbol. The OFDMA system is composed of a radio base station (BS), an MS, and a radio relay station (RS), and a user who owns the MS communicates by accessing the BS directly or indirectly.

Ideally, radio base stations (BS) that form a finite accommodation area should be installed at a density that does not create a gap in the accommodation area, but an RS that relays BS and MS without being connected to the backbone. It is better in terms of the initial investment cost to expand the area using.
A radio base station capable of performing multi-hop relay under the control of a radio relay station (RS) is particularly referred to as MR-BS.

  FIG. 2 is a diagram in which frame configurations when physical layer resources are segregated between a radio base station (MR-BS) and a radio relay station (RS) are classified. The horizontal axis indicates OFDMA symbols (that is, time), and the vertical axis indicates subchannels (that is, frequency). A plurality of (for example, 1024) subcarriers exist in one carrier wave, and a subchannel is a bundle of a plurality of subcarriers extracted continuously or discontinuously. Therefore, the subchannels on the vertical axis are not always continuous in frequency. Moreover, although the case where the transmission frame was synchronized with MR-BS and RS was shown in FIG. 1, it is not limited to this.

FIG. 2 (a) shows a frame in which the sub-channels are differentiated in MR-BS and RS, and FIG. 2 (b) shows a frame in which the OFDMA symbols are differentiated and divided. The vertical axis of FIG. 2 (c) shows a frame that is divided by a combination of subchannels and OFDMA symbols.
What is common to (a) to (c) is that segregation is performed so that resources used in the MR-BS and the RS do not overlap in one carrier wave.

The OFDMA system according to the first embodiment will be described below. In the OFDMA system of this example, a radio relay station (RS) is provided with two antennas, one is assigned to the radio base station (MR-BS) side, the other is assigned to the MS side, and a direct upstream station (MR-BS or RS) is assigned. ) And a different partial frequency (segment) is used for communication with a downstream station (MS or RS).
The configuration of the OFDMA system according to the first embodiment is the same as that in FIG. 1, and TDD (Time Division Duplex) or HFDD (Half Frequency Division Duplex) is used as the duplex method.

FIG. 3 is a functional schematic diagram of the RS of this embodiment. The RS of this example includes a layer 1 processing unit 1, a layer 1 processing unit 2, and a layer 2 processing unit 3.
The layer 1 processing units 1 and 2 have substantially the same configuration, and include antennas 11 and 21, RF units 12 and 22, and PHY signal processing units 13 and 23, respectively. Layer 1 means the physical layer (PHY).

The antennas 11 and 21 are independent antennas having different propagation paths or propagation path characteristics from the MR-BS, and may or may not have directivity. As an example, the polarization characteristics may be different. In particular, when line-of-sight communication (LOS) is possible, one antenna is a directional antenna whose gain is higher with respect to the direction of the directly upstream station (MR-BS or RS), and the other antenna is A directional antenna having a higher gain than the area accommodated by the RS may be used. Alternatively, a detachable reflector may be provided between the two antennas, and when used as an RS, the amount of coupling between the antennas may be reduced, and when diverted to a BS, the reflector may be removed to perform a MIMO operation.
The RF units 12 and 22 are front end units that perform amplification of transmission signals and reception signals, frequency conversion, channel (carrier) selection, control thereof, and the like.
As described later, the PHY signal processing units 13 and 23 perform physical layer signal processing such as interlib processing, encoding processing, and FFT processing on the transmission signal, and perform reverse processing on the reception signal.

  The layer 2 processing unit 3 is a part that performs MAC (Medium Access Control), compresses the header of the packet input from the upper layer to the transmission signal, and creates MAC-PDU (MAC-Protocol Data Units) Then, one or a plurality of MAC-PDUs are combined and output in units of bursts (described later), and the reverse process is performed on the received signals. It also performs adaptive link control for the physical layer, QoS control, network participation and disconnection control, and layer 1 processing of information signals (FCH, MAP, ranging, MAC message, etc. described later) required for them Input / output with part 1 line 2 The RS also has a function of reconfiguring the MAP or burst input from one layer 1 processing unit at the layer 2 level and relaying it to the other layer 1 processing unit. The function of the layer 2 processing unit 3 is often realized by a network processor or MPU (micro processing unit) and its software.

FIG. 4 is an internal configuration diagram of the PHY signal processing units 13 and 23. FIG. 4 mainly explains the flow of transmission data, and control lines that can be normally provided are omitted.
The randomizer 131 randomizes and outputs the burst input from the layer 2 processing unit 3 in order to improve burst error tolerance.
The FEC encoder 132 performs redundant encoding on the input signal from the randomizer 131 and outputs it in order to perform forward error correction on the receiving side. The coding rate is given from the layer 2 processing unit 3.

The mapper 133 converts the input code into a modulation symbol according to an instruction from the layer 2 processing unit 3, and assigns it to a corresponding OFDM symbol and each subchannel (bin).
The IFFT 134 converts the modulation symbol input from the mapper 133 into a time domain signal by IFFT and outputs it as an OFDM symbol.
The CP adder 135 adds a CP (Cyclic Prefix) to the OFDM symbol input from the IFFT 134 and outputs it as a transmission signal to the RF unit 12 or the like.

CP remover 137 establishes OFDM symbol synchronization by CP correlation detection, etc., and cuts out and outputs an OFDM symbol with an appropriate FFT size.
The FFT 138 converts the OFDM symbol input from the CP remover 137 into a frequency domain signal by FFT, and outputs a modulation symbol of each subcarrier.
The wraparound canceller 136 uses the modulation symbol input from the mapper 133 of the other layer 1 processing unit 1 or 2 as a training signal, and the amount of phase rotation of the wraparound signal superimposed on the modulation symbol of each subcarrier input from the FFT 138 The gain is calculated for each subcarrier, a replica of the sneak signal is created from this calculated value and the training signal, and the transmission signal sneaking from the other antenna is canceled by subtracting it from the modulation symbol of FFT138. An internal configuration of the wraparound canceller 136 is shown in FIG. In the wraparound canceller 136 in FIG. 8, the wraparound occurs within one segment (described later), and the segment to be canceled is cut out.

  The equalizer 139 equalizes the OFDM symbol by multiplying the modulation symbol of each subcarrier inputted from the wraparound canceller 136 by the frequency domain propagation path characteristic H (ω). The propagation path characteristics are estimated with reference to known pilot carriers that are dispersed on the frequency (and time) in the subcarrier, and interpolation is performed for a portion where no pilot carrier exists. This interpolation is performed for each station that transmits the modulation symbol, and when phase rotation is also compensated (that is, H (ω) is a complex number), phase interpolation is performed in terms of delay time. Further, the OFDM symbol synchronization can be corrected according to the result of propagation path estimation. In addition, when MIMO is performed, a plurality of propagation path characteristics can be estimated corresponding to propagation paths between a plurality of antennas that transmit and receive.

The RSSI measurement unit 140 measures the power and the like of a known preamble that is a modulation symbol of each subcarrier inputted from the FFT 138 and is located at the head of the frame, and performs an RSSI (Received Signal per symbol). Strength Indicator) and CINR (Carrier to Interference-plus-Noise Ratio) are calculated and output.
The demapper 141 performs a process reverse to the mapper 133 on the modulation symbol input from the equalizer 139 and outputs a code.
The FEC decoder 142 performs error correction decoding on the code input from the demapper 141 and outputs the result.
The derandomizer 143 performs the reverse process of the randomizer 131 on the signal input from the FEC decoder 142 and outputs the original burst data to the layer 2 processing unit 3.

FIG. 4 is described as the RS PHY signal processing unit 13 and the like, but is equivalent to MR-BS and MS except that a wraparound canceller 136 is provided. Therefore, the MR-BS and the RS can be switched by changing the firmware of the layer 2 processing unit 3.
The PHY signal processing unit 13 and the like are often realized by a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), or the like.

Next, operations required in the MAC layer and physical layer of the RS and MR-BS in this example from the installation of a new RS to the relay operation will be described in order.
In the operation of this example, after the RS is turned on, the RS finds a nearby MR-BS etc. and registers its existence, and the registered MR-BS etc. changes the subcarrier set as necessary. A process 2 in which the RS re-establishes a radio and MAC link with an appropriate antenna such as MR-BS after receiving the process 2, and a set of subcarriers used by the RS to measure interference and communicate with the MS, etc. The process 4 for determining the frame length and the process 5 for performing the relay operation are performed.

First, the details of the process 1 will be described. The process 1 is mainly performed on the RS side.
First, in step 101, the RS is turned on.
Next, as step 102, the layer 1 processing unit 1 appropriately receives an instruction from the MAC layer and searches for a carrier wave transmitted by any MR-BS or RS. For example, when the reception frequency is swept and OFDM symbol synchronization can be acquired by the CP removal unit 137, it is estimated that a carrier wave exists at that frequency.
Next, as step 103, the layer 1 processing unit 1 performs symbol timing and frame timing synchronization on the carrier wave found in step 103, and periodically includes a DCD (Downlink Channel Descriptor) and a UCD (Uplink Channel Descriptor) included in the received frame. ) Is detected, parameters such as a modulation method are acquired, and a transmission frame (see FIG. 6 described later) of the MR-BS or the like is demodulated. If demodulation is not possible, the process returns to step 101 to search for a carrier wave.
Next, as step 104, the RSSI measuring unit 140 of the layer 1 processing unit 1 measures the RSSI of the preamble included in the transmission frame such as the MR-BS and reports it to the layer 2 processing unit, and also the layer 2 processing unit 3 Stores the RSSI as RSSI1.
Next, as step 105, the other layer 1 processing unit 2 performs the same processing as steps 102 to 104, and the layer 2 processing unit 3 stores RSSI2.

Next, as step 106, the layer 2 processing unit 3 compares the stored RSSI1 and RSSI2, and communicates the layer 1 processing unit 1 or 2 corresponding to the larger value with the upstream station (MR-BS or the like). It is determined as a layer 1 processing unit to be used. The determined layer 1 processing unit is hereinafter referred to as a layer 1 processing unit (for BS), and the other layer 1 processing unit is referred to as a layer 1 processing unit (for MS). This process is effective when a directional antenna is used as the antenna 11 or the like.
In step 107, the layer 1 processing unit (for BS) receives and demodulates a frame transmitted by the MR-BS or the like.
Finally, as step 108, the layer 2 processing unit 3 registers the presence of the local station (RS) in the MR-BS or the like using the layer 1 processing unit (for BS). Specifically, the initial ranging message is transmitted while gradually increasing the transmission power. When there is a response of successful ranging from the MR-BS, the function request message is transmitted next, and the function negotiation is successfully performed from the MR-BS. If there is a response, authentication with the MR-BS is performed by key exchange, and finally a registration request message is transmitted to confirm the registration response from the MR-BS.
Assuming line-of-sight communication as the radio wave propagation environment between the MR-BS and the RS, the above selection method can also be selected appropriately.

Next, details of the process 2 will be described. The process 2 is mainly performed on the MR-BS side.
First, as step 201, the MR-BS that has received the message of step 108 transmits using all the subcarriers (or subchannels) that the MR-BS can currently use (for example, (Full usage of subchannels)). For example, the subcarrier is segmented into a plurality of sets (for example, 3), and a section for transmitting a DLSub-frame (see FIG. 5 described later) using only one set is provided. However, one set used for transmission is determined in advance at the time of cell design, or the one with the best CINR in the MR-BS is used.

  FIG. 5 is a diagram showing segmentation of the subchannel in this example, which is extracted from 8.4.4.4 of Non-Patent Document 1. Segmentation is one of the purposes of configuring sectors within the same cell. The horizontal axis is the OFDMA symbol index, and the vertical axis is the subchannel index. A plurality of subchannels are divided and assigned to three segments. Each cell ID and a preamble unique to each segment are provided in the first symbol of each segment, followed by FCH (Frame Control Header). A guard band is provided between each segment. Alternatively, if the subcarriers allocated to each segment are distributed over a plurality of subchannels, the effects of frequency diversity and adjacent cell interference reduction can be maintained.

  FIG. 6 is a configuration example of a radio frame between the MR-BS and the RS and between the RS and the MS in this example, and is an excerpt from Non-Patent Document 2. 6A shows a radio frame (MR-BS Frame) used between MR-BS and the like and RS, and FIG. 6B shows a radio frame used between RS and MS etc. (RSFrame). Both show one segment after segmentation. 6 (a) and 6 (b) are shown with the horizontal axis (time) aligned, and in this example, the frame and subframe timings are synchronized between the MR-BS and its subordinate RS. Therefore, the transmission timing of MR-BS and RS can overlap.

The MR-BS Frame in FIG. 6A includes a DL Sub-frame that realizes a downlink from the MR-BS or the like to the RS, a UL Sub-frame that realizes an uplink from the RS to the MR-BS, TTG / RTG (Transmit / Receive Transition Gap) inserted between them.
The DL Sub-frame includes a DL Access Zone transmitted to the MS, a DL Relay Zone transmitted to the RS, and a TTG. The first symbol of the DL Sub-frame is all assigned to the preamble. In the DL Access Zone, bursts such as FCH, DL-MAP, UL-MAP, and user burst (not shown) are appropriately arranged following the preamble. A burst is a unit of data transmitted with the same coding rate and modulation scheme, and subchannels and OFDMA symbols are continuously assigned on a frame. A Zone is a two-dimensional area divided by usage.
The FCH carries information indicating the coding type and length of the DL-MAP. The DL-MAP includes a plurality of burst information in the DL sub-frame (in this example, further in the DL Access Zone), and the UL-MAP is in the subsequent UL Sub-frame (in this example, further in the UL Access Zone). The burst information is transmitted to the MS.
DL Relay Zone is almost the same as DL Access Zone except that it does not have a preamble. The DL Relay Zone may include a plurality of bursts corresponding to a plurality of RSs belonging to the MR-BS. In this example, it is necessary to have a segmented zone in at least one of DL Access Zone and DL Relay Zone.
The UL Sub-frame includes a UL Access Zone where a direct MS transmits, a UL Relay Zone where a direct RS transmits, and an RTG. In addition to user bursts, ULAccess Zone and UL Relay Zone are appropriately provided with subchannels for ranging and bandwidth request, and subchannels for high-speed feedback.
The RS layer 1 processing unit (for BS) receives the DL sub-frame of the MR-BS frame and transmits a burst in the UL relay zone of the UL sub-frame.

  The RS Frame in FIG. 6B is almost the same as the MR-BS Frame, and each DL and UL Sub Frame is an Access Zone transmitted directly to the MS and a Relay Zone relayed by another RS. Can be provided. The RS layer 1 processing unit (for MS) transmits the DL Sub-frame of the RS Frame and receives the ULSub-frame. That is, the layer 1 processing unit (for BS) and the layer 1 processing unit (for MS) perform transmission and reception alternately.

Next, details of the process 3 will be described. The process 3 is mainly performed on the RS side.
First, in step 301, after the RS itself is registered, the MR-BS determines whether there is a change in the segment number of the MR-BS frame, or a change from a state where no segment is performed to a state where a segment is performed. For example, the following processing is continued to reset the layer 1 processing units 1 and 2, and if there is no change, the process 3 is terminated. The presence / absence of the change is determined by, for example, determining a preamble pattern or receiving a message from the MR-BS.
Next, in step 302, the layer 1 processing unit 1 attempts to resynchronize the frame timing and symbol timing transmitted by the MR-BS, detect DCD as appropriate, and receive the MR-BS frame. To.

Next, as step 303, the RSSI measurement unit 140 of the layer 1 processing unit 1 measures the RSSI of the preamble (see FIG. 6A) transmitted by the MR-BS, and the layer 2 processing unit 3 calculates the RSSI. Store as RSSI1.
Next, in step 304, the layer 1 processing unit 2 performs processing equivalent to steps 303 to 304, and the layer 2 processing unit 3 stores RSSI2.
Next, in step 305, the layer 2 processing unit 3 compares RSSI1 and RSSI2, and determines the larger one as the layer 1 processing unit used for communication with the MR-BS, that is, the layer 1 processing unit (for BS). The smaller one is the layer 1 processing unit (for MS). The frame timing of the layer 1 processing unit (for MS) is synchronized with the frame timing of the layer 1 processing unit (for BS) (although neither transmission nor reception is performed at this time).

  The process 3 does not necessarily match the selection of the process 1 because the layer 1 processing unit (for BS) is selected based on the preamble whose segment is changed and the subcarrier frequency is different from the time of the process 1.

Next, details of the process 4 will be described. The process 4 is performed by both the RS and MR-BS.
First, in step 401, the layer 2 processing unit 3 of the RS grasps the OFDMA symbol position where the segment number of the MR-BS frame transmitted by the MR-BS and the number of subcarriers change. These can be grasped by receiving the FCH, DL-MAP, and UL-MAP of the MR-BSFrame in FIG.

  Next, in step 402, the RS layer 1 processing unit (for MS) measures RSSI for each segment in the region where the DL sub-frame is not transmitted from the MR-BS within the DL sub-frame period. Then, the noise of the segment + co-channel interference power is calculated. "Noise + co-channel interference power" is the noise and signal power from other stations that are not the communication partner in the channel that is to be used for communication, and when both the local station and the communication partner station are not transmitting It can be defined as received power (RSSI). Strictly speaking, the layer 1 processing unit (for MS) in this example does not use MR-BS as a communication partner, but since the measurement method is the same, it is referred to as noise + co-channel interference power. The symbol timing to be measured is given from the layer 2 processing unit 3 based on the symbol position grasped in the process 401.

FIG. 7 is a diagram showing a measurement area of interference power. FIG. 7A corresponds to FIG. 2A, and FIG. 7B corresponds to FIG. In this example, segmentation is assumed. Considering the case where the start timing of DLSub-frame is the same between MR-BS and RS as shown in FIG. 6, FIG. 2 (b) is necessarily changed to FIG. 7 (b). Will do. In FIG. 7B, the DL Sub-frame of the RS Frame of FIG. 6B is shorter than the DL Sub-frame of the MR-BS Frame of FIG. 6A, and the latter half of the MR-BS Frame (for example, DL Relay) This corresponds to the case where all subcarriers are used in the Zone or the subsequent Zone.
In FIG. 7, the interference power measurement region is illustrated as the same region as each segment that is not transmitted by the MR-BS, that is, the region that can be allocated to the RS when frequency reuse is not performed. There is no need to measure all of the inside. In addition, in order to confirm the start of interference, constant symbols before and after hitting the outside of the segment are also measured, and symbols for which interference power equal to or greater than a predetermined threshold is detected are excluded from the measurement region, assuming that the MR-BS is transmitting. Anyway. Similarly, in the UL sub-frame period, noise + co-channel interference power may be measured in a region in which no UL sub-frame is transmitted from the MS directly belonging to the MR-BS. .

Next, in step 403, the layer 2 processing unit 3 decides to use the measured noise + the segment with low co-channel interference power among the measured segments for downlink and uplink communication with the downstream station (MS etc.). To do. Thereby, reuse of a segment can be expected in a plurality of RSs while avoiding competition with segments used by other adjacent MR-BSs and existing RSs.
Further, the time domain in the OFDMA symbol direction is set to a position where the MR-BS or the like supplemented by the layer 1 processing unit (for BS) does not interfere with a segment or subchannel transmitted. For example, in FIG. 7 (a), it is the total time of the DL Sub-frame, and in FIG. 7 (b), segmentation is released from the beginning of the DL Sub-frame (another subchannel is used). Time to change to Zone). This region can also be identified from the FCH information, but the measurement result in step 402 is prioritized (symbols with interference above the threshold are excluded from the region) and modified according to the actual environment. The region is notified to the layer 2 processing unit 3. This region (two-dimensional region in the subchannel direction and the OFDMA symbol direction) is set as the MS transmission region. The DL-Sub-frame in FIG. 6B is provided in this MS transmission area. The transmission area for MS can be further modified based on FCH in order to adapt to subsequent changes in zone size and the like.

Next, the details of the process 5 (data communication with relay) will be described. The process 5 is performed by both the RS and MR-BS.
First, in step 501, when downlink data is transmitted from the MR-BS or the like to the RS, the layer 1 processing unit (for BS) of the RS enters the DL Relay Zone in FIG. 6A from the MR-BS or the like. The existing R-FCH, DL R-MAP, UL R-MAP, etc., and data in this Zone are received and output to the layer 2 processing unit 3.

  Next, in step 502, the RS layer 2 processing unit 3 processes the received DL Relay Zone, remaps the DL Sub-frame in the previously determined MS transmission region, and performs the layer 1 processing unit (for MS). ). That is, among the bursts included in the received DLRelay Zone, the burst for the MS that directly belongs to the RS is mapped to the DL Access Zone, the burst for the RS that directly belongs to the RS is mapped to the DLRelay Zone, and DL-MAP and the like are replayed. create. This sort of relay route is called a routing function. The layer 1 processing unit transmits a DLSub-frame according to the mapping performed by the layer 2 processing unit 3. As shown in FIG. 6B, the period during which the RS can transmit the downlink frame to the MS is from the preamble to the relay TTG.

  Thereafter, as a process 503, an MS or the like belonging to the RS appears, a burst is assigned to the MS or the like by UL-MAP, and transmission is performed from the MS or the like in the UL Access Zone of the RS Frame shown in FIG. 6B. In this case, the layer 1 processing unit (for MS) of the RS receives it, the layer 2 processing unit 3 processes it, and the layer 1 processing unit (for BS) transmits it in the ULRelay Zone.

According to this example, the radio repeater (RS) selects the layer 1 processing unit that communicates with the radio base station (MR-BS). High-speed transmission is possible. In particular, when a directional antenna is used in a radio repeater, and the antenna directivity is in the direction where there is a lot of mobile terminals (MS) on one side and MR-BS on the other side, it is very powerful. .
In addition, when the MR-BS is in a state of transmitting all subcarriers when the RS is registered for the first time under its control, the MR-BS automatically shifts to a state in which the segment is performed by a program or the like. This eliminates the need for humans to reconfigure the radio base station (MR-BS) transmission.
Further, the RS measures the noise in the region not transmitted by the MR-BS + the co-channel interference power, and selects the segment number and the MS transmission region for performing communication between the RS and the MS based on the measured value. As a result, better communication quality between the RS and the MS can be ensured. Especially in situations where base station zone design is being carried out, it is very powerful. That is, a plurality of RSs in the base station zone can appropriately reuse limited segments in the same carrier, and interference with adjacent base station zones can be suppressed. Such a zone design is called a fractional frequency reuse plan.
The RS can determine the physical layer parameters such as the segment number and the frame length communicating with the MS by simply turning on the power, so that the construction time for the RS startup can be greatly reduced.

  It is obvious that the RS of this example is applicable not only to the MS as a relay destination but also to an SS (subscriber station) including a fixed station. Further, the selection criteria for the layer 1 processing units 1 and 2 are not limited to those using RSSI, and CINR and other information indicating reception quality may be used.

  In the OFDMA system of the second embodiment, the MR-BS performs transmission / reception using a plurality of (for example, 2) segments or FUSC, and each subordinate RS performs transmission / reception using only one specific segment. Unlike the first embodiment, the other points that are not mentioned are the same as the first embodiment.

  In this example, the process 221 is performed instead of the process 201 of the first embodiment. In step 221, the MR-BS performs subcarrier segmentation, for example, at the time of initial activation or when the message of step 108 is received. And the segment with the smallest interference (hereinafter referred to as the second segment) is selected except for the first segment. Interference is measured using noise + co-channel interference power or other known indicators. Then, DL sub-frame transmission and UL sub-frame reception are performed using the selected plurality of segments. In particular, the first segment uses a frame having a relay zone as shown in FIG. 6A to allocate a burst for RS or MS that is far from the MR-BS, and the second segment has, for example, RelayZone. A burst for the MS having a short distance from the MR-BS is allocated using a frame that is not used. The second segment burst is transmitted with relatively low power.

In place of the process 402 in the first embodiment, the process 422 is performed. In step 422, the RS layer 1 processing unit (for MS) measures RSSI for every segment, and simply sets the value as the noise of the segment + co-channel interference power. During the measurement, neither the RS layer 1 processing unit (for MS) nor (for BS) transmits. The symbol timing to be measured is a period in which the layer 1 processing unit (for MS) is expected to perform transmission / reception within a frame (for example, the first half of DL and UL Sub-frame when multi relay is not performed).
Accordingly, in step 403, if there is no interference other than the MR-BS captured by the layer 1 processing unit (for BS), a segment (hereinafter referred to as the third segment) that is not used for transmission by the BR-BS is selected. However, when another BS using the third segment exists nearby, the second segment may be selected.

  According to this example, since the MR-BS uses a plurality of segments, the capacity is improved. In addition, if the sub-frame interference between the MR-BS and the RS in the MS near the RS and the UL sub-frame interference between the MS relayed by the RS and the MS not relayed in the RS are different for the segment, Can be prevented.

Schematic diagram of OFDMA system The figure which classified the frame structure at the time of dividing physical layer resources with a radio base station (MR-BS) and a radio relay station (RS) Functional schematic diagram of RS of Example 1 Internal configuration diagram of the PHY signal processing units 13 and 23 of the first embodiment. The figure which shows the segmentation of the subchannel of Example 1 Configuration diagram of radio frame between MR-BS and RS and between RS and MS in the first embodiment The figure which shows the measurement area | region of the interference power which RS of Example 1 performs. 1 is an internal configuration diagram of a wraparound canceller 136 according to the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Layer 1 process part 2 ... Layer 1 process part 3 ... Layer 2 process part 11, 21 ... Antenna 12, 22 ... RF part 13, 23 ... PHY signal process part 130 ... MAC-SAP
131 ... Randomizer 132 ... FEC encoder 133 ... Mapper 134 ... IFFT
135 ... CP adder 136 ... wraparound canceller 137 ... CP remover 138 ... FFT
139 ... Equalizer 140 ... RSSI measuring unit 141 ... Demapper 142 ... FEC decoder 143 ... Derandomizer

Claims (2)

In an OFDMA wireless system comprising a subscriber station, one or more relay stations, and a base station that accommodates the subscriber station or relay station,
The relay station is configured to measure noise + same channel in a subcarrier and a temporal region that are not transmitted or received by the base station among a plurality of subcarriers included in a carrier used by a base station to which the relay station belongs. Some subcarriers with small interference power are used for transmission or reception with a subscriber station belonging to the relay station in the area,
The base station provides a time when the number of subcarriers to be used is reduced when a relay station first appears under the base station in a state where all of the subcarriers included in a carrier wave are used. OFDMA wireless system. Used in an OFDMA radio system comprising a subscriber station, one or more relay stations, and a base station that accommodates the subscriber station or relay station, and a base station or relay station serving as an upstream station and a subscription serving as a downstream station A relay station that performs relaying between a user station or a relay station in the MAC layer,
A plurality of layer 1 processing units each having an independent antenna, transmitting and receiving radio signals of the OFDMA radio system, and measuring RSSI;
Each of the layer 1 processing units is caused to measure the RSSI of the downstream signal from the upstream station, and the layer 1 processing unit having the maximum RSSI is allocated for communication with the upstream station, and any other layer 1 processing is performed. Part for communication with downstream stations,
On the subcarrier where the upstream station does not transmit the noise of the plurality of subcarrier sets included in the carrier used by the upstream station + the co-channel interference power to the layer 1 processing unit allocated for communication with the downstream station And a layer 2 processing unit that performs measurement in a temporal region and uses one subcarrier set having a small interference power for transmission to the downstream station in the region.

Images