JP2008211752A - Radio communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communication system capable of restricting deterioration in the transmission quality, even in an area where the interference between the cells exerts large effects. <P>SOLUTION: In step 5a, a mobile-station measures a reception level and an interference level with the other base stations, for a base-station considered as a communication partner. In step 5b, the mobile station transmits a measurement result obtained in step 5a as control information to the base station which is to be considered as the communication partner. In step 5c, the base-station determines a transmission format in a transmission format candidate group used for the transmission to the mobile station, on the basis of the control information, and so on. If the base-station discriminates that an area where the mobile-station considered as the transmission destination is located has a large effect, since an interference level indicated by the control information received from the mobile station exceeds a preset threshold value, the base station determines the use of a transmission format in which reception is executed at more than two times, after executing interleaving resistant to the interference, in the transmission format candidate group. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wireless communication system using a communication method using multicarrier modulation such as OFDM (Orthogonal Frequency Division Multiplexing).

  As is well known, the mobile station measures the wireless transmission path quality based on the received signal from the base station, and selects a transmission format from a preset table MCS (Modulation and Coding set) based on the measurement result. There is AMC (Adaptive Modulation and Coding).

  In a system that uses the CDM (Code Division Multiplex) system as a multiplexing system, even if AMC is used, interference between radio zones (cells) formed by each base station can be identified with thermal noise. Even if this transmission format was used, there was little influence on the transmission.

However, when the multiplexing method is the FDM (Frequency Division Multiplex) method or the TDM (Time Division Multiplex) method, the interference between the cells cannot be identified with the thermal noise, so the effect on the transmission is large. was there. This problem also arises in the OFDM modulation system (for example, see Non-Patent Document 1), which is being developed recently, because the multiplexing system is FDM or TDM.
3GPP, TS 25.214 V5.11.0 (2005-06), 6A HS-DSCH-related procedures.

In a conventional wireless communication system using multicarrier modulation, there is a problem that interference between cells cannot be identified with thermal noise, and thus has a large influence on transmission.
The present invention has been made to solve the above problem, and an object of the present invention is to provide a wireless communication system capable of suppressing deterioration of transmission quality even in an area where the influence of interference between cells is large. .

  To achieve the above object, the present invention determines a transmission format based on reception quality in a first communication device, and performs multi-carrier modulation for performing data transmission from the second communication device to the first communication device in this transmission format. In a wireless communication system using the above, a selection unit that selects a transmission format from a transmission format candidate group having at least two transmission formats, and data from the second communication device to the first communication device in the transmission format selected by the selection unit Wireless communication means for performing transmission, and at least one transmission format in the transmission format candidate group is a transmission format for performing transmission more than twice after interleaving the transmission data. Configured.

As described above, in the present invention, the interference generated in the reception signal of the first communication device is detected, the transmission format corresponding to the detection result is selected, and the first communication device uses the first transmission format to select the first transmission format. Data transmission is performed to the communication device.
Therefore, according to the present invention, since data transmission can be performed in a transmission format according to the state of occurrence of interference in the first communication device, it is possible to suppress deterioration in transmission quality even in an area where the influence of interference between cells is large. It is possible to provide a wireless communication system capable of

Embodiments of the present invention will be described below with reference to the drawings. In the following description, a case where the OFDM scheme is adopted as a modulation scheme for communication between a base station and a mobile station will be described as an example.
First, the configuration of the mobile station in the wireless communication system according to the first embodiment of the present invention will be described. FIG. 1 mainly shows the configuration of a downlink reception system provided in this mobile station.

  As shown in FIG. 1, the mobile station includes a control unit 100, a radio reception unit 101, a GI (Guard Interval) removal unit 102, an FFT (Fast Fourier Transform) unit 103, a signal separation unit 104, and a quality measurement. Unit 105, control channel demodulation unit 106, orthogonal code multiplication unit 107, depreciation unit 108, demodulation unit 109, channel deinterleaver 110, channel decoder 111, and transmission system 112. .

The radio receiving unit 101 receives a radio signal transmitted from the base station, removes noise outside the desired band from the received signal, and converts the signal that has passed through the filter into a baseband digital signal. An AD converter.
The GI removal unit 102 removes the guard interval from the baseband digital signal output from the wireless reception unit 101.

  The FFT unit 103 performs fast Fourier transform on the digital signal from which the guard interval has been removed by the GI removal unit 102 and converts the signal from the time domain to the frequency domain, thereby dividing the signal into signals for each subcarrier.

  The signal separation unit 104 separates the signal divided for each subcarrier by the FFT unit 103 into a phase reference signal, a control signal, a data signal, and the like, and outputs the separated signals to corresponding modules. In this example, the phase reference signal is output to the quality measurement unit 105 and the demodulation unit 109, the control signal is output to the control channel demodulation unit 106, and the data signal is output to the orthogonal code multiplication unit 107.

  Quality measuring section 105 measures the power level or power density of the signal received from each base station by taking the cross-correlation between the scrambling pattern assigned to each base station and the received phase reference signal. Quality measuring section 105 determines a base station that performs radio communication from the measurement result, and obtains an interference level from the received power level and the received power level ratio of other base stations.

  As shown in FIG. 2, even when one base station forms a plurality of sectors, an antenna pattern cannot be ideally created. Therefore, interference occurs between sectors of the same base station, and transmission is difficult. Impact will occur. The quality measurement unit 105 distinguishes the received signal of each sector by the scrambling pattern even for the same base station, and obtains interference generated between the sectors.

  The control channel demodulation unit 106 demodulates the control signal given from the signal separation unit 104, extracts control information regarding the physical layer, and outputs this control information to the control unit 100. This control information includes MCS information indicating a transmission format sent from the base station.

  The orthogonal code multiplication unit 107 multiplies the data signal by the complex conjugate of the orthogonal code corresponding to the parameter N instructed from the control unit 100, cancels the signal component from the other base station, and obtains the multiplication result. Output. When the parameter N = 1, the data signal is output as it is without performing the complex conjugate multiplication of the orthogonal code on the data signal.

  The depreciation unit 108 cumulatively adds the multiplication results of the orthogonal code multiplication unit 107 by the parameter N instructed from the control unit 100, and outputs the result as one data. Note that when the parameter N = 1, the multiplication result is not accumulated and output as it is.

  Demodulation section 109 obtains a channel estimated value of the subcarrier frequency from the phase reference signal, uses this to channel-equalize the output of depreciation section 108, and obtains the equivalent result from the demodulation scheme instructed by control section 100. By demodulating the data, the bit string constituting the data signal is reproduced.

Channel deinterleaver 110 performs channel deinterleaving on the bit string output from demodulation section 109 based on the interleave pattern instructed from control section 100.
The channel decoder 111 performs channel decoding on the bit string output from the channel deinterleaver 110 at the coding rate R instructed from the control unit 100, and reproduces transmission data.

The control unit 100 generates control information indicating the interference level obtained by the quality measurement unit 105 and transmits the control information to the base station through the transmission system 112.
The control unit 100 stores a transmission format table as shown in FIG. This transmission format table associates MCS information for identifying a transmission format with information such as a modulation method M, a coding rate R, a repetition factor, and a parameter N for determining orthogonalization.

  Then, the control unit 100 detects MCS information from the control information extracted by the control channel demodulation unit 106, and determines that the transmission format used by the base station for transmission to the mobile station is the transmission format indicated by the MCS information. recognize. Then, the control unit 100 refers to the transmission format table and controls each unit of the mobile station in an integrated manner with parameters corresponding to the MCS information so that information transmitted from the base station can be received.

  Next, the structure of the base station of the radio | wireless communications system concerning one Embodiment of this invention is demonstrated. FIG. 4 mainly shows the configuration of the downlink transmission system provided in this base station. As shown in FIG. 4, the base station includes a control unit 200, a channel encoder 201, a channel interleaver 202, a modulation unit 203, a repetition unit 204, an orthogonal code multiplication unit 205, a subcarrier allocation unit 206, An IFFT (Inverse Fast Fourier Transform) unit 207, a GI (Guard Interval) adding unit 208, a wireless transmission unit 209, a reception system 210, a control information detection unit 211, and a signal quality detection unit 212. .

The channel encoder 201 performs channel encoding on the bit string constituting the transmission data at the coding rate R instructed from the control unit 200.
Channel interleaver 202 performs channel interleaving on the output of channel encoder 201 based on the interleave pattern instructed from control unit 200.
Modulation section 203 modulates the output of channel interleaver 202 by modulation scheme M instructed from control section 200 to generate a data signal represented by a complex value.

  The repetition unit 204 performs repetition (repetition) processing on the data signal based on the parameter N instructed from the control unit 200, and extends each bit constituting the data signal to N bits. If N = 1 is instructed, no repetition is performed.

  Based on the parameter N instructed from the control unit 200, the orthogonal code multiplication unit 205 multiplies the output of the repetition unit 204 by an N-bit length orthogonal code. When N = 1 is instructed, orthogonal code multiplication is not performed.

  Based on an instruction from control unit 200, subcarrier allocation unit 206 generates a signal in which the data signal output from orthogonal code multiplication unit 205, the control signal, and the phase reference signal are allocated to the corresponding subcarriers. To do.

  IFFT section 207 performs OFDM modulation on the signal output from subcarrier allocation section 206 to generate an OFDM signal that is a sequence of a plurality of OFDM symbols. That is, IFFT section 207 generates an OFDM signal by converting a frequency domain signal into a time domain signal.

The GI adding unit 208 adds a guard interval to the OFDM signal output from the IFFT unit 207 and outputs the OFDM signal.
The wireless transmission unit 209 includes a digital-analog converter that performs digital-analog conversion on the output of the GI adding unit 208, an up-converter that up-converts the output, and a power amplifier that amplifies the output. RF) signal is generated and transmitted from the antenna.

The receiving system 210 receives a radio signal transmitted from a mobile station.
The control information detection unit 211 detects control information transmitted to the base station from a signal received by the reception system 210 from the mobile station.
The signal quality detection unit 212 detects the quality of the signal received by the reception system 210 from the mobile station.

  The control unit 200 stores a transmission format table as shown in FIG. Based on the control information (including information indicating the interference level) detected by the control information detection unit 211 and the signal quality detected by the signal quality detection unit 212, the control unit 200 performs transmission to the mobile station. Which transmission format is used is determined, and MCS information indicating the transmission format is included in the control information and transmitted to the mobile station.

  The transmission format stored in advance by the control unit 200 is a combination of a modulation scheme M, a coding rate R, a repetition factor, and a parameter N that determines orthogonalization, and the distribution to the coding rate R and the repetition factor N is different. ing. Based on the control information and the signal quality, the transmission format selection criterion is to determine whether or not the location where the mobile station is located is in an area subject to interference, and according to the determination result, the transmission format is determined. To decide.

  When the control unit 200 determines the transmission format as described above and transmits MCS information indicating the determined transmission format to the mobile station, thereafter, the control unit 200 transmits a data signal in the transmission format to the mobile station. As such, each part of the mobile station is controlled in an integrated manner.

  For example, when the control unit 200 determines that the area where the mobile station to be transmitted is located is a large interference area because the interference level indicated by the control information received from the mobile station exceeds a preset threshold, It instructs the repetition unit 204 and the orthogonal code multiplication unit 205 to execute a repetition process corresponding to the magnitude of interference on the data signal transmitted to the mobile station.

Next, the operation of the radio communication system having the above configuration will be described with reference to FIG.
First, in step 5a, in the mobile station, the quality measuring unit 105 measures the reception level and the interference level with other base stations for the base station to be communicated, and proceeds to step 5b.

  In Step 5b, the mobile station controls the transmission system 112 by the control unit 100, transmits the measurement result measured in Step 5a to the base station to be communicated as control information, and proceeds to Step 5c.

In step 5c, the base station determines the transmission format used for transmission to the mobile station based on the control information detected by the control information detector 211 and the detection result of the signal quality detector 212. To do. Here, when the control unit 200 determines that the area where the mobile station to be transmitted is located is a large interference area because the interference level indicated by the control information received from the mobile station exceeds a preset threshold, Decide to use a transmission format that is resistant to interference.
In step 5d, the base station controls each part of the transmission system by the control unit 200, notifies the mobile station of the transmission format determined in step 5c as MCS information, and proceeds to step 5e.

In step 5e, the mobile station extracts the MCS information notified from the base station by the control channel demodulator 106. And the control part 100 controls each part of a receiving system so that it may receive data with the transmission format based on the said MCS information, and it transfers to step 5f.
In step 5f, the base station controls each part of the transmission system so that the control unit 200 performs data transmission in the transmission format notified in step 5.

  For example, in the transmission format table shown in FIG. 3, when the total coding rate is Rt = 1/6, 2 and 2a are considered as transmission formats to be used. In the transmission format 2, as shown in FIG. 6A, Rt = 1/6 is realized by error correction coding. On the other hand, as shown in FIG. 6 (b), format 2a performs R = 2/3 error correction coding and then performs quadrature (= N) repetition in order to perform orthogonalization. Thus, Rt = 1/6 is realized.

  In general, the coding gain becomes larger when error correction coding is performed by an appropriate operation than when it is simply repeated. Therefore, when the required SNR is compared, the format 2 is lower than the format 2a, and the noise N is constant. For example, format 2 allows good reception with less reception power S. Therefore, in step 5c, the control unit 200 selects the format 2 in an area where there is little inter-sector interference other than the sector boundary.

  However, when there is inter-sector interference like a sector boundary, after performing repetition, interference can be suppressed by the effect of orthogonalization by multiplying different orthogonal sequences for each sector of the same length as repetition. . As a result, a gain higher than that obtained by reducing the coding gain can be obtained, so that the transmission rate is increased. For this reason, when interference is strong, the control part 200 selects the format 2a in step 5c.

  Further, in the transmission format table of FIG. 3, not only the error correction coding rate and the number of repetitions but also the modulation multi-value number (modulation method M) are changed as in transmission formats 3 and 3a and transmission formats 4 and 4a. It is also possible to obtain an equivalent transmission rate (relative value).

  FIG. 7 is an example of Rt = 1/6 in consideration of a channel interleaver that is often used in an actual system. Interleaving can enhance the effect of error correction coding by arranging data in random order. Therefore, interleaving is usually performed after repetition.

  However, as in the base station shown in FIG. 4, when orthogonalization is performed, it is desirable that the transmission path characteristics of the bits to be orthogonalized are the same, and therefore, a configuration for selectively performing repetition after interleaving is provided. . That is, in the base station, transmission that does not repeat after channel interleaving as shown in FIG. 7A and transmission that repeats after channel interleaving and multiplies with orthogonal codes as shown in FIG. 7B. Each format is provided.

  The repetition after interleaving includes, for example, a bit-unit repetition performed before mapping of QPSK modulation and a symbol-unit repetition performed after mapping, either of which may be applied.

  FIG. 8 shows a transmission format for performing (a) repetition or (b) puncturing at the time of encoding. The repetition here is different from the repetition for orthogonalization, and is used for adjusting the encoding rate. The coding rate may be adjusted by such repetition or puncturing.

For example, the repetition of FIG. 7A is this operation. R = 1/6 is made by repeating the error correction code of R = 1/3 twice.
For example, R = 1/6 in FIG. 6A can be generated as shown in FIG. FIG. 7B shows the format 2a. Also, the transmission format 1 in FIG. 3 can be generated by repeating an error correction code of R = 1/3 8/3 times as shown in FIG. Therefore, the transmission format 2a that performs repetition four times after interleaving has the same transmission speed as the transmission format 2 that performs repetition before interleaving. Further, the transmission speed is higher than that of the transmission format 1 that performs repetition before interleaving.

  As described above, in the radio communication system having the above-described configuration, it is determined whether or not the mobile station is affected by interference, and a transmission format suitable for the case where the mobile station is affected by interference according to the determination result ( On the other hand, when the influence of interference is small, the transmission format giving priority to the coding gain is selected and communicated. Therefore, according to the wireless communication system configured as described above, even in an area where the influence of interference between cells is large, it is possible to suppress the deterioration of transmission quality and improve the transmission speed. In an area where the influence of interference is small, Throughput can be improved in the entire system.

  In general, as shown in FIG. 9, a transmission format with a higher transmission rate can be assigned as the transmission rate is closer to the base station. When the transmission format is determined without considering the influence of interference, as shown in FIG. 9, even in the areas where the transmission rates are S1 and S2 at the sector boundary, As shown in FIG. 10, the transmission speed is improved to S3, S4 (S1 <S4 <S3) and S5 (S2 <S5).

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. Further, for example, a configuration in which some components are deleted from all the components shown in the embodiment is also conceivable. Furthermore, you may combine suitably the component described in different embodiment.

  As an example, for example, in the above embodiment, the transmission format is determined according to the interference level measured by the base station at the mobile station, and data transmission is performed in accordance with the transmission format. For example, the mobile station may determine the transmission format, and the base station may perform transmission to the mobile station using a transmission format corresponding to the transmission format.

  In addition, position information where the mobile station is located is detected, and based on this position information, it is determined whether the mobile station is located in a place affected by interference. Then, the transmission format may be determined based on the determination result or the determination result and the interference level measured by the mobile station. Also in this case, the transmission format may be determined by the mobile station or the base station.

Various methods are conceivable for detecting the position information of the mobile station. For example, a method in which the mobile station has a GPS (Global Positioning System) receiver to determine its own position, or a method in which the mobile station detects a position based on arrival time differences of signals received from a plurality of base stations can be considered. .
In addition, it goes without saying that the present invention can be similarly implemented even if various modifications are made without departing from the gist of the present invention.

  Next, the configuration of the mobile station in the radio communication system according to the second embodiment of the present invention will be described. FIG. 11 mainly shows the configuration of the downlink reception system provided in this mobile station. In the following, in order to simplify the explanation, the allocation pattern of data signals to subcarriers and the transmission format are described separately. However, in actual processing in a mobile station and a base station, the above pattern is used. It can also be handled as a transmission format.

  As shown in FIG. 11, the mobile station includes a control unit 100, a radio reception unit 101, a GI (Guard Interval) removal unit 102, an FFT (Fast Fourier Transform) unit 103, a signal separation unit 104, and a quality measurement. Unit 105, control channel demodulation unit 106, orthogonal code multiplication unit 107, depreciation unit 108, demodulation unit 109, channel deinterleaver 110, channel decoder 111, and transmission system 112. .

The radio receiving unit 101 receives a radio signal transmitted from the base station, removes noise outside the desired band from the received signal, and converts the signal that has passed through the filter into a baseband digital signal. An AD converter.
The GI removal unit 102 removes the guard interval from the baseband digital signal output from the wireless reception unit 101.

  The FFT unit 103 performs fast Fourier transform on the digital signal from which the guard interval has been removed by the GI removal unit 102 and converts the signal from the time domain to the frequency domain, thereby dividing the signal into signals for each subcarrier.

  Based on the subcarrier allocation pattern specified by the control unit 100, the signal separation unit 104 separates the signal divided for each subcarrier by the FFT unit 103 into a phase reference signal, a control signal, a data signal, and the like. The separated signals are output to the corresponding modules. In this example, the phase reference signal is output to the quality measurement unit 105 and the demodulation unit 109, the control signal is output to the control channel demodulation unit 106, and the data signal is output to the orthogonal code multiplication unit 107.

  Quality measuring section 105 measures the power level or power density of the signal received from each base station by taking the cross-correlation between the scrambling pattern assigned to each base station and the received phase reference signal. Quality measuring section 105 determines a base station that performs radio communication from the measurement result, and obtains an interference level from the received power level and the received power level ratio of other base stations.

  As shown in FIG. 12, even when one base station forms a plurality of sectors, an antenna pattern cannot be ideally created. Therefore, interference occurs between sectors of the same base station, and transmission is difficult. Impact will occur. The quality measurement unit 105 distinguishes the received signal of each sector by the scrambling pattern even for the same base station, and obtains interference generated between the sectors.

  The control channel demodulation unit 106 demodulates the control signal given from the signal separation unit 104, extracts control information regarding the physical layer, and outputs this control information to the control unit 100. This control information includes MCS information indicating a transmission format sent from the base station.

  The orthogonal code multiplication unit 107 multiplies the data signal by the complex conjugate of the orthogonal code specific to the target base station corresponding to the parameter N instructed from the control unit 100, and cancels signal components from other base stations. , This multiplication result is output. When the parameter N = 1, the data signal is output as it is without performing the complex conjugate multiplication of the orthogonal code on the data signal.

  The depreciation unit 108 cumulatively adds the multiplication results of the orthogonal code multiplication unit 107 by the parameter N instructed from the control unit 100, and outputs the result as one data. Note that when the parameter N = 1, the multiplication result is not accumulated and output as it is.

  Demodulation section 109 obtains a channel estimated value of the subcarrier frequency from the phase reference signal, uses this to channel-equalize the output of depreciation section 108, and obtains the equivalent result from the demodulation scheme instructed by control section 100. By demodulating the data, the bit string constituting the data signal is reproduced. In addition, the channel equivalent processing can be performed before the cumulative addition by obtaining channel estimation values for all subcarriers.

Channel deinterleaver 110 performs channel deinterleaving on the bit string output from demodulation section 109 based on the interleave pattern instructed from control section 100.
The channel decoder 111 performs channel decoding on the bit string output from the channel deinterleaver 110 at the coding rate R instructed from the control unit 100, and reproduces transmission data. Further, the channel decoder 111 performs depreciation and depuncturing corresponding to repetition and puncturing performed to adjust the coding rate R on the base station side in accordance with an instruction from the control unit 100. And a function of decoding a desired coding rate R.

The control unit 100 generates control information indicating the interference level obtained by the quality measurement unit 105 and transmits the control information to the base station through the transmission system 112.
The control unit 100 stores a transmission format table as shown in FIG. This transmission format table associates MCS information for identifying a transmission format with information such as a modulation method M, a coding rate R, a repetition factor, and a parameter N for determining orthogonalization.

  Then, the control unit 100 detects pattern information indicating an allocation pattern to the subcarriers of the MCS information and the data signal from the control information extracted by the control channel demodulation unit 106, and the base station performs the addressing to the mobile station from these information. It is recognized that transmission is performed by subcarrier allocation indicated by the pattern information in the transmission format indicated by the MCS information. The control unit 100 controls the signal separation pattern in the signal separation unit 104 based on the pattern information and refers to the transmission format table so that the information transmitted from the base station can be received. Control each part of the mobile station with parameters corresponding to.

  Next, the configuration of the base station of the radio communication system according to the second embodiment of the present invention will be described. FIG. 14 mainly shows the configuration of a downlink transmission system provided in this base station. In the following, in order to simplify the explanation, the allocation pattern of data signals to subcarriers and the transmission format are described separately. However, in actual processing in a mobile station and a base station, the above pattern is used. It can also be handled as a transmission format.

  As shown in FIG. 14, the base station includes a control unit 200, a channel encoder 201, a channel interleaver 202, a modulation unit 203, a repetition unit 204, an orthogonal code multiplication unit 205, a subcarrier allocation unit 206, An IFFT (Inverse Fast Fourier Transform) unit 207, a GI (Guard Interval) adding unit 208, a wireless transmission unit 209, a reception system 210, a control information detection unit 211, and a signal quality detection unit 212. .

  The channel encoder 201 performs channel encoding on the bit string constituting the transmission data at the coding rate R instructed from the control unit 200. Further, the channel encoder 201 has a function of adjusting the coding rate R by performing repetition or puncturing on the result of channel encoding in accordance with an instruction from the control unit 200.

Channel interleaver 202 performs channel interleaving on the output of channel encoder 201 based on the interleave pattern instructed from control unit 200.
Modulation section 203 modulates the output of channel interleaver 202 by modulation scheme M instructed from control section 200 to generate a data signal represented by a complex value.

  The repetition unit 204 performs repetition (repetition) processing on the data signal based on the parameter N instructed from the control unit 200, and extends each bit constituting the data signal to N bits. If N = 1 is instructed, no repetition is performed.

  Based on the parameter N instructed from the control unit 200, the orthogonal code multiplication unit 205 multiplies the output of the repetition unit 204 by an N-bit length orthogonal code. When N = 1 is instructed, orthogonal code multiplication is not performed.

  Based on the subcarrier allocation pattern instructed from control unit 200, subcarrier allocation unit 206 assigns the data signal output from orthogonal code multiplication unit 205, the control signal, and the phase reference signal to the corresponding subcarriers. Generate the assigned signal.

  IFFT section 207 performs OFDM modulation on the signal output from subcarrier allocation section 206 to generate an OFDM signal that is a sequence of a plurality of OFDM symbols. That is, IFFT section 207 generates an OFDM signal by converting a frequency domain signal into a time domain signal.

The GI adding unit 208 adds a guard interval to the OFDM signal output from the IFFT unit 207 and outputs the OFDM signal.
The wireless transmission unit 209 includes a digital-analog converter that performs digital-analog conversion on the output of the GI adding unit 208, an up-converter that up-converts the output, and a power amplifier that amplifies the output. RF) signal is generated and transmitted from the antenna.

The receiving system 210 receives a radio signal transmitted from a mobile station.
The control information detection unit 211 detects control information transmitted to the base station from a signal received by the reception system 210 from the mobile station.
The signal quality detection unit 212 detects the quality of the signal received by the reception system 210 from the mobile station. Specifically, when receiving a known signal, in addition to the reception quality for each subcarrier, the correlation between the subcarriers is obtained for each of the time axis direction and the frequency axis direction, and these are received as the reception quality to the control unit 200. Notice.

  The control unit 200 stores a transmission format table as shown in FIG. Based on the control information (including information indicating the interference level) detected by the control information detection unit 211 and the signal quality detected by the signal quality detection unit 212, the control unit 200 performs transmission to the mobile station. Which transmission format is used is determined, and MCS information indicating the transmission format is included in the control information and transmitted to the mobile station.

  The transmission format stored in advance by the control unit 200 is a combination of a modulation scheme M, a coding rate R, a repetition factor, and a parameter N that determines orthogonalization, and the distribution to the coding rate R and the repetition factor N is different. ing. Based on the control information and the signal quality, the transmission format selection criterion is to determine whether or not the location where the mobile station is located is in an area subject to interference, and according to the determination result, the transmission format is determined. To decide.

  Then, the control unit 200 determines a subcarrier allocation pattern for allocating data signals to subcarriers distributed in the frequency axis direction and / or time axis direction, and performs subcarrier allocation based on the subcarrier allocation pattern. The unit 206 is instructed. That is, the control unit 200 changes the subcarrier allocation pattern as necessary, and allocates the subcarriers to the subcarriers at regular intervals in the frequency axis direction, for example.

  When the control unit 200 determines the transmission format and the subcarrier allocation pattern as described above, and transmits the MCS information indicating the determined transmission format and the pattern information indicating the subcarrier allocation pattern to the mobile station, the above-described movement is performed thereafter. For each station, each part of the mobile station is controlled so as to transmit a data signal in the transmission format and the subcarrier allocation pattern.

  For example, when the control unit 200 determines that the area where the mobile station to be transmitted is located is a large interference area because the interference level indicated by the control information received from the mobile station exceeds a preset threshold, It instructs the repetition unit 204 and the orthogonal code multiplication unit 205 to execute a repetition process corresponding to the magnitude of interference on the data signal transmitted to the mobile station.

  In addition, for example, when the interference level is high and the correlation between the time axis direction and the frequency axis direction is large to some extent, the control unit 200 transmits the data signal in the frequency axis direction and / or the time axis direction in order to enhance the frequency diversity effect. Change to the distributed subcarrier allocation pattern.

Next, the operation of the radio communication system having the above configuration will be described with reference to FIG.
First, in step 15a, in the mobile station, the quality measuring unit 105 measures the reception level and the interference level with other base stations for the base station to be communicated, and proceeds to step 15b.

  In step 15b, the mobile station controls the transmission system 112 by the control unit 100, transmits the measurement result measured in step 15a to the base station to be communicated as control information, and proceeds to step 15c.

  In step 15c, the base station determines whether the control unit 200 uses the control information detected by the control information detection unit 211 and the detection result of the signal quality detection unit 212, the transmission format used for transmission to the mobile station, and the sub format. Determine the carrier allocation pattern. Here, when the control unit 200 determines that the area where the mobile station to be transmitted is located is a large interference area because the interference level indicated by the control information received from the mobile station exceeds a preset threshold, It is determined to use a transmission format that is resistant to interference and to use a subcarrier allocation pattern that disperses the data signal in the frequency axis direction and / or the time axis direction according to the correlation in the time direction and the frequency direction.

  Here, the subcarrier allocation pattern determined by the control unit 200 is a frequency in which data signals are consecutive at the same time as in the subcarrier allocation pattern implemented in the first embodiment as shown in FIG. In addition to the pattern assigned to the subcarriers of FIG. 16B, as shown in FIG. 16B, as shown in FIG. There is a pattern in which a further interval is assigned in the frequency axis direction so as to be equally spaced. This interval is determined by the control unit 200 based on the reception quality obtained by the signal quality detection unit 212.

  In addition, as shown in FIG. 17, the control unit 200 allocates data signals to subcarriers having different intervals for each mobile station to be transmitted based on the reception quality obtained by the signal quality detection unit 212. Also good. That is, the control unit 200 determines an allocation interval for each mobile station from a trade-off between the frequency diversity effect and the increase in the amount of interference caused by the collapse of the correlation between the subcarriers in the frequency axis direction and the time axis direction.

  Furthermore, as shown in FIG. 18, based on the reception quality obtained by the control unit 200 in the signal quality detection unit 212, the upper limit of the allocation interval of data signals to subcarriers is set for each mobile station to be transmitted. The allocation interval may be determined in consideration of the scheduling of other mobile stations within the upper limit range.

  Further, as shown in FIG. 19, the control unit 200 may dynamically change the interval for assigning subcarriers to the same mobile station in accordance with the reception quality that changes over time. .

  In step 15d, the base station controls each part of the transmission system by the control unit 200, notifies the mobile station of the transmission format and subcarrier allocation pattern determined in step 15c as MCS information, and proceeds to step 15e.

In step 15e, the mobile station extracts the MCS information notified from the base station by the control channel demodulator 106. And the control part 100 controls each part of a receiving system so that it may receive data with the transmission format and subcarrier allocation pattern based on the said MCS information, and it transfers to step 15f.
In step 15f, the base station controls each part of the transmission system so that the control unit 200 performs data transmission using the transmission format and subcarrier allocation pattern notified in step 15.

  For example, in the transmission format table shown in FIG. 13, when the total coding rate is Rt = 1/6, 2 and 2a are considered as transmission formats to be used. In the transmission format 2, as shown in FIG. 20A, Rt = 1/6 is realized by error correction coding. On the other hand, as shown in FIG. 20 (b), format 2a performs R = 2/3 error correction coding, and then performs quadruple (= N) repetition for orthogonalization. Thus, Rt = 1/6 is realized.

  In general, the coding gain becomes larger when error correction coding is performed by an appropriate operation than when it is simply repeated. Therefore, when the required SNR is compared, the format 2 is lower than the format 2a, and the noise N is constant. For example, format 2 allows good reception with less reception power S. Therefore, in step 15c, the control unit 200 selects format 2 in an area where there is little inter-sector interference other than the sector boundary.

  However, when there is inter-sector interference like a sector boundary, after performing repetition, interference can be suppressed by the effect of orthogonalization by multiplying different orthogonal sequences for each sector of the same length as repetition. . As a result, a gain higher than that obtained by reducing the coding gain can be obtained, so that the transmission rate is increased. For this reason, when interference is strong, the control part 200 selects the format 2a in step 15c.

  Further, in the transmission format table of FIG. 13, not only the error correction coding rate and the number of repetitions but also the modulation multi-level number (modulation method M) are changed as in transmission formats 3 and 3a and transmission formats 4 and 4a. It is also possible to obtain an equivalent transmission rate (relative value).

  FIG. 21 is an example of Rt = 1/6 in consideration of a channel interleaver that is often used in an actual system. Interleaving can enhance the effect of error correction coding by arranging data in random order. Therefore, interleaving is usually performed after repetition.

  However, when orthogonalization is performed as in the base station shown in FIG. 14, it is desirable that the transmission path characteristics of the bits to be orthogonalized are the same, so that repetition is selectively performed after interleaving (channel interleaver 202). (Repetition unit 204). That is, in the base station, a transmission format in which repetition is not performed after channel interleaving as shown in FIG. 21A and transmission in which repetition is performed after channel interleaving and multiplication with orthogonal codes as shown in FIG. Each format is provided.

  The repetition after interleaving includes, for example, a bit-unit repetition performed before mapping of QPSK modulation and a symbol-unit repetition performed after mapping, either of which may be applied.

  FIG. 22 shows a transmission format for performing repetition or FIG. 22 (b) puncturing in FIG. 22 (a) at the time of encoding by the channel encoder 201. The repetition here is different from the repetition for orthogonalization (implemented by the repetition unit 204), and is used to adjust the encoding rate. The coding rate is adjusted by such repetition and puncturing.

  For example, the repetition of FIG. 21A is this operation, and this may be performed by the channel encoder 201. That is, the channel encoder 201 repeats the error correction code of R = 1/3 twice to make R = 1/6.

  For example, R = 1/6 in FIG. 20A can be generated as shown in FIG. FIG. 21B shows the format 2a. Further, the transmission format 1 of FIG. 13 can be generated by repeating an error correction code of R = 1/3 8/3 times as shown in FIG. Therefore, the transmission format 2a that performs repetition four times after interleaving has the same transmission speed as the transmission format 2 that performs repetition before interleaving. Further, the transmission speed is higher than that of the transmission format 1 that performs repetition before interleaving.

  Also, for example, as shown in the transmission format table shown in FIG. 13, when the total coding rate is Rt = 1/12, 0 and 0a can be considered as transmission formats to be used. As shown in FIG. 23A, the transmission format X is 4 in order to adjust the total coding rate Rt to 1/12 after performing error correction coding with a coding rate R = 1/3. Double repetition is performed by the channel encoder 201 and interleaving is performed.

  That is, when realizing a plurality of different total coding rates Rt, after encoding at a common coding rate (mother rate), the channel encoder 201 performs repetition or puncturing to realize a desired coding rate. Use the technique.

  On the other hand, as shown in FIG. 23B, the format 0a is encoded by performing error correction coding at a coding rate R = 1/3 and then performing repetition by the channel encoder 201 twice. The rate is adjusted to 1/6, then channel interleaving is performed, and then the orthogonalization is performed, so that repetition is performed by the repetition unit 204 to realize R = 1/12 in total.

  As described above, in the radio communication system having the above-described configuration, it is determined whether or not the mobile station is affected by interference, and a transmission format suitable for the case where the mobile station is affected by interference according to the determination result ( (Interference suppression by orthogonalization) and a subcarrier allocation pattern that distributes data signals are selected and communicated. On the other hand, if the influence of interference is small, a transmission format that prioritizes coding gain is selected and communicated. Yes. Therefore, according to the wireless communication system having the above configuration, even in an area where the influence of interference between cells is large, the frequency diversity effect can be obtained by the dispersion of the data signal, thereby suppressing the deterioration of the transmission quality and improving the transmission speed. In an area where the influence of interference is small, the throughput of the entire system can be improved.

  An example of the simulation result is shown below. The simulation specifications shown here are in accordance with 3GPP, TR25.814 (V7.1.0), “Physical Layer Aspects for Evolved UTRA”. Currently, 3GPP (3rd Generation Partnership Project) has begun to study Long Term Evolution (LTE) for new radio access and radio access networks following W-CDMA (Wideband Code Division Multiple Access) (for example, Patent Document 1). This document is a technical document released by 3GPP and describes a framework for standards related to the physical layer.

  FIG. 24 shows simulation conditions for the present simulation other than those defined above. Further, the phase reference signal and the data signal are arranged as shown in FIG. 25, and the data per mobile station is arranged over 12 subcarriers in the frequency direction and 5 symbols in the time direction.

  The parameter of this simulation is interference between sectors. Therefore, as shown in FIG. 26, the range from the center of the antenna pattern of sector 1 to the boundary between sector 1 and sector 2 was evaluated. Azimuth angle = 0 degrees at the center of the sector is dominated by radio waves from sector 1, whereas Azimuth angle = 60 degrees at the sector boundary is an environment where radio waves from sector 1 and sector 2 are at the same level In this environment, the relative power difference from each base station is the smallest. The relative power difference in the figure is calculated using the antenna pattern described in the above non-patent document.

  Then, in the generation routine as shown in FIGS. 27A to 27C, data signals of the respective formats 1 to 4 were generated, and performance evaluation was performed for these formats. Format 1 corresponds to 2 in the MCS table shown in FIG. 13, and formats 2 to 4 correspond to 2b. In formats 2 to 4, the subcarrier arrangement pattern is defined as shown in FIG. That is, format 2 corresponds to the first embodiment, and formats 3 and 4 correspond to the second embodiment.

  FIG. 29 shows the result of the simulation. The vertical axis represents the required signal-to-noise ratio (SNR) required to achieve BLER 1%. The graph shows that the lower the performance, the better the performance. Therefore, in this simulation environment, format 4 (second embodiment) shows the best performance from Azimuth angle = 0 to 55 degrees, and the first embodiment shows the best from 55 degrees to 60 degrees. Shows performance.

  Generally, as shown in FIG. 30, a transmission format with a higher transmission rate can be assigned as the transmission rate is closer to the base station. When the transmission format is determined without considering the influence of interference, as shown in FIG. 30, even in the areas where the transmission rates are S1 and S2 at the sector boundary, As shown in FIG. 31, the transmission speed is improved to S3, S4 (S1 <S4 <S3) and S5 (S2 <S5).

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. Further, for example, a configuration in which some components are deleted from all the components shown in the embodiment is also conceivable. Furthermore, you may combine suitably the component described in different embodiment.

  As an example, for example, in the above embodiment, the transmission format is determined according to the interference level measured by the base station at the mobile station, and data transmission is performed in accordance with the transmission format. For example, the mobile station may determine the transmission format, and the base station may perform transmission to the mobile station using a transmission format corresponding to the transmission format.

  In addition, position information where the mobile station is located is detected, and based on this position information, it is determined whether the mobile station is located in a place affected by interference. Then, the transmission format may be determined based on the determination result or the determination result and the interference level measured by the mobile station. Also in this case, the transmission format may be determined by the mobile station or the base station.

Various methods are conceivable for detecting the position information of the mobile station. For example, a method in which the mobile station has a GPS (Global Positioning System) receiver to determine its own position, or a method in which the mobile station detects a position based on arrival time differences of signals received from a plurality of base stations can be considered. .
In addition, it goes without saying that the present invention can be similarly implemented even if various modifications are made without departing from the gist of the present invention.

1 is a circuit block diagram showing a configuration example of a mobile station of a wireless communication system according to a first embodiment of the present invention. The figure which shows an example of the area which interference produces. The figure which shows an example of the transmission format table which the mobile station and base station of the radio | wireless communications system concerning this invention memorize | store. 1 is a circuit block diagram showing a configuration example of a base station of a wireless communication system according to a first embodiment of the present invention. The flowchart for demonstrating the operation | movement flow of the radio | wireless communications system concerning this invention. The figure for demonstrating the signal production | generation according to the transmission format determined by the operation | movement flow shown in FIG. The figure for demonstrating the signal production | generation according to the transmission format determined by the operation | movement flow shown in FIG. The figure for demonstrating the signal production | generation according to the transmission format determined by the operation | movement flow shown in FIG. The figure which shows distribution of the transmission rate at the time of determining a transmission format without considering interference. The figure which shows distribution of the transmission rate at the time of determining a transmission format in consideration of interference. The circuit block diagram which shows the structural example of the mobile station of the radio | wireless communications system concerning 2nd Embodiment of this invention. The figure which shows an example of the area which interference produces. The figure which shows an example of the transmission format table which the mobile station and base station of the radio | wireless communications system concerning this invention memorize | store. The circuit block diagram which shows the structural example of the base station of the radio | wireless communications system concerning 2nd Embodiment of this invention. The flowchart for demonstrating the operation | movement flow of the radio | wireless communications system concerning this invention. The figure for demonstrating an example of the transmission format determined by the operation | movement flow shown in FIG. The figure for demonstrating an example of the transmission format determined by the operation | movement flow shown in FIG. The figure for demonstrating an example of the transmission format determined by the operation | movement flow shown in FIG. The figure for demonstrating an example of the transmission format determined by the operation | movement flow shown in FIG. The figure for demonstrating the signal production | generation according to the transmission format determined by the operation | movement flow shown in FIG. The figure for demonstrating the signal production | generation according to the transmission format determined by the operation | movement flow shown in FIG. The figure for demonstrating the signal production | generation according to the transmission format determined by the operation | movement flow shown in FIG. The figure for demonstrating the signal production | generation according to the transmission format determined by the operation | movement flow shown in FIG. The figure which shows the simulation conditions of embodiment of this invention. The figure which shows an example of the subcarrier arrangement | positioning of the phase reference signal and data signal in simulation. The figure which shows the evaluation object area | region of simulation. The figure which shows an example of the production | generation routine of the transmission format of the evaluation object of simulation. The figure which shows the subcarrier arrangement | positioning pattern of evaluation object of simulation. The figure which shows the result of simulation. The figure which shows distribution of the transmission rate at the time of determining a transmission format without considering interference. The figure which shows distribution of the transmission rate at the time of determining a transmission format in consideration of interference.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Control part 101 ... Radio | wireless receiving part 102 ... GI removal part 103 ... FFT part 104 ... Signal separation part 105 ... Quality measurement part 106 ... Control channel demodulation part 107 ... Orthogonal code multiplication part 108 ... Derivation unit 109 ... demodulation unit 110 110 channel deinterleaver 111 channel decoder 112 transmission system 200 control unit 201 channel encoder 202 channel interleaver 203 modulation unit 204 repeatability 205: Orthogonal code multiplication unit, 206 ... Subcarrier allocation unit, 207 ... IFFT unit, 208 ... GI addition unit, 209 ... Radio transmission unit, 210 ... Reception system, 211 ... Control information detection unit, 212 ... Signal quality Detection unit.

Claims (12)

In a wireless communication system using multicarrier modulation that determines a transmission format based on reception quality in a first communication device and performs data transmission from the second communication device to the first communication device in this transmission format.
Selecting means for selecting a transmission format from a transmission format candidate group having at least two transmission formats;
Wireless communication means for performing data transmission from the second communication device to the first communication device in the transmission format selected by the selection means;
The wireless communication system, wherein at least one transmission format in the transmission format candidate group is a transmission format for performing repetition of at least twice after interleaving the transmission data.   The transmission format candidate group has a transmission format other than the transmission format that performs repetition more than twice, and the information transmission rate of at least one transmission format includes transmission that performs repetition greater than or equal to the repetition. 2. The wireless communication system according to claim 1, wherein the information transmission rate is not more than the highest information transmission rate among the formats.   The wireless communication system according to claim 2, wherein at least one transmission format in the transmission format candidate group is orthogonalized by multiplying an orthogonal code after repetition.   The wireless communication system according to claim 1, wherein at least one transmission format in the transmission format candidate group is a transmission format in which interleaving is performed after repetition is performed on transmission data. In a wireless communication system using multicarrier modulation that determines a transmission format based on reception quality in a first communication device and performs data transmission from the second communication device to the first communication device in this transmission format.
Selecting means for selecting a transmission format from a transmission format candidate group having at least two transmission formats;
Wireless communication means for performing data transmission from the second communication device to the first communication device in the transmission format selected by the selection means;
In at least one transmission format in the transmission format candidate group, the transmission data is interleaved and then subjected to a repetition of twice or more, and a plurality of data signals obtained by this repetition are transmitted in the frequency axis direction. A wireless communication system characterized in that it is a distributed transmission format assigned to distant subcarriers.   In the distributed transmission format, the transmission data is interleaved and then subjected to a repetition of twice or more, and three or more data signals obtained by the repetition are set to a frequency set in advance in the frequency axis direction, etc. 6. The wireless communication system according to claim 5, wherein the transmission format is assigned to subcarriers spaced apart from each other.   When the second communication device communicates with the first communication device and the third communication device, the selection means includes subcarriers separated by a frequency interval different from a distributed transmission format used for communication with the first communication device. 6. The wireless communication system according to claim 5, wherein a distributed transmission format for allocating a data signal is selected for the third communication device. Furthermore, a detection means for detecting a correlation between subcarriers is provided,
6. The radio communication system according to claim 5, wherein the selection unit selects a distributed transmission format to be allocated to subcarriers separated by a frequency interval corresponding to the correlation detected by the detection unit. A detecting means for detecting a correlation between the subcarriers;
Determining means for determining an upper limit of the frequency interval according to the correlation detected by the detecting means;
6. The radio communication system according to claim 5, wherein the selection unit selects a distributed transmission format to be allocated to subcarriers separated by a frequency interval within an upper limit range determined by the determination unit.   The transmission format candidate group has a transmission format other than the transmission format that performs repetition of twice or more, and the information transmission rate of at least one transmission format includes transmission that performs repetition of the repetition of twice or more. 6. The wireless communication system according to claim 5, wherein the information transmission rate is equal to or less than the highest information transmission rate among the formats.   The wireless communication system according to claim 10, wherein at least one transmission format in the transmission format candidate group is orthogonalized by multiplying by an orthogonal code after repetition.   6. The wireless communication system according to claim 5, wherein at least one transmission format in the transmission format candidate group is a transmission format for performing interleaving after repetition of transmission data.

Images