JP2008118472A - Communication system, communication method, receiver, and transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a MIMO signal detection system capable of detecting a signal with high precision. <P>SOLUTION: A receiver receives a plurality of transmission signals that a transmission device having a plurality of transmitting antennas transmits nearly at the same time. The receiver mainly includes a minimum Euclidian distance estimating unit 226 which calculates minimum Euclidian distances corresponding to the respective transmitting antennas based upon a channel matrix representing transmission characteristics of a radio transmission line, and a ranking information generator 228 which generates ranking information indicating the sequencing of the respective transmitting antennas based upon the large/small relation among the minimum Euclidian distances corresponding to the respective transmitting antennas. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a communication system, a communication method, a receiving device, and a transmitting device.

  2. Description of the Related Art Conventionally, a MIMO (Multiple-Input Multiple-Output) system signal transmission technique is known as one of techniques for speeding up wireless communication. This method is literally based on signal input / output using a plurality of antennas. The feature of this method is that a plurality of transmission data can be transmitted at the same time and at the same frequency using a plurality of different antennas. If the number of channels that can be transmitted simultaneously increases, the amount of communication per unit time can be increased by the increased number of channels, so that the communication speed can be substantially improved. Further, this method has an advantage that the frequency band to be used does not increase even if the communication speed is improved.

  However, as described above, since a plurality of modulated signals having carrier components of the same frequency are transmitted at the same time, a device for separating the interfering modulated signals is required on the receiving side. In the case of the MIMO system, the modulation signal is separated using a channel matrix representing the transmission characteristics of the wireless transmission path. This channel matrix can be detected by, for example, a channel estimation method using pilot symbols.

  However, depending on the configuration of the channel matrix, each modulated signal at the time of transmission may not be accurately reproduced due to the influence of noise or the like. Therefore, various studies have been made to improve the accuracy of MIMO signal detection, and the results have been published. As an example, there is known a signal detection means of MIMO-OFDM (Multiple-Input and Multiple-Output Orthogonal Division Division Multiplexing) method using interference canceling. This is done by selecting correctly estimated packet data from the packet data estimated by the MIMO signal detecting means, and receiving a replica signal (hereinafter referred to as a received replica signal) of the received signal generated using this packet data. This is a method of subtracting from a signal to calculate a residual signal, and using this residual signal to apply a signal separation algorithm again to estimate packet data with high accuracy. However, this method has a problem that it cannot be applied when all packet data is not correctly decoded.

  As a specific example of one solution to this problem, Japanese Patent Application Laid-Open Publication No. 2004-228620 detects the received power for each substream in the receiving apparatus, executes the ranking of the transmission antenna based on the received power, and performs this ranking. A configuration for returning information to a transmission device is disclosed. If the above configuration is adopted, for example, the transmission device can allocate all the subcarrier signals of the specific packet to the transmission antenna having a high ranking based on the ranking information for each subcarrier fed back from the reception device. The transmission characteristics of a specific subcarrier can be improved. As a result, it is estimated that interference canceling can be used effectively, and MIMO signal detection with higher accuracy can be realized.

Japanese Patent Laid-Open No. 2006-13680

  However, when a signal separation algorithm based on the MLD (Maximum Likelihood Detection) method is used for the MIMO signal detection means, the average Euclidean distance between the received replica signal points is an indicator of the transmission characteristics. Even if transmission antenna allocation is executed for each subcarrier using the transmission antenna ranking information based on the transmission antenna, appropriate transmission antenna allocation is not always performed. Therefore, it is required to generate transmission antenna ranking information more suitable for the MLD method and to further improve the transmission characteristics using this.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a MIMO signal by precoding using ranking information of a transmission antenna estimated based on the minimum Euclidean distance. It is an object of the present invention to provide a new and improved communication system, communication method, receiving apparatus and transmitting apparatus capable of improving detection accuracy.

In order to solve the above-described problem, according to a first aspect of the present invention, a transmission apparatus configured to transmit a plurality of transmission signals via corresponding transmission antennas and a reception apparatus configured to receive a plurality of transmission signals are provided. A communication system is provided.
In addition, the receiving device included in the communication system has a minimum Euclidean distance estimation unit that calculates a minimum Euclidean distance for each transmission antenna based on a channel matrix that represents transmission characteristics of a wireless transmission path, and a magnitude relationship between the minimum Euclidean distance. Based on the transmission antenna, and a ranking information generation unit that generates ranking information indicating the order of the transmission antenna, a signal detection unit that estimates each transmission signal using a channel matrix, and a correctly decoded transmission signal A reception replica generation unit that generates a reception replica signal based on the received signal; and an interference canceller unit that generates a residual signal by subtracting the reception replica signal from the reception signal.
Furthermore, the transmission device included in the communication system described above receives a predetermined transmission from each of the reception unit that receives the ranking information generated by the reception device and each transmission antenna having the minimum minimum Euclidean distance based on the ranking information. A precoding unit for allocating a signal; and a transmission unit for transmitting a predetermined transmission signal via each transmission antenna allocated by the precoding unit.

  The receiving apparatus further includes a dimension reduction channel matrix generation unit that generates a dimension reduction channel matrix by excluding the column vector corresponding to the maximum value of the minimum Euclidean distance from the column vectors constituting the channel matrix. It may be. Further, the minimum Euclidean distance estimation unit may be configured to calculate a minimum Euclidean distance corresponding to each transmission antenna based on the dimension reduction channel matrix.

  In addition, the reception device may further include a reception power calculation unit that calculates reception power corresponding to each transmission signal. Further, the ranking information calculation unit may be configured to order the transmission antennas with large received power in order of the plurality of transmission antennas having the same minimum Euclidean distance.

In order to solve the above problems, according to a second aspect of the present invention, there is provided a communication method for transmitting a plurality of transmission signals via corresponding transmission antennas and receiving the plurality of transmission signals. .
According to the above communication method, on the receiving side, the minimum Euclidean distance estimation step for calculating the minimum Euclidean distance for each transmission antenna based on the channel matrix representing the transmission characteristics of the wireless transmission path, and the magnitude relationship between the minimum Euclidean distances Based on the ranking information generation step of ordering the transmission antennas and generating the ranking information indicating the order of the transmission antennas, the signal detection step of estimating each transmission signal using the channel matrix, and the correctly decoded transmission signal A reception replica generation step for generating a reception replica signal and an interference canceller step for generating a residual signal by subtracting the reception replica signal from the reception signal are included. On the transmitting side, a receiving step for receiving the ranking information generated by the receiving device, and a precoding step for assigning a predetermined transmission signal to each transmitting antenna having the maximum minimum Euclidean distance based on the ranking information, Transmitting a predetermined transmission signal via each transmission antenna assigned by the precoding unit.

  The receiving side further includes a dimension reduced channel matrix generation step of generating a dimension reduced channel matrix by excluding the column vector corresponding to the maximum value of the minimum Euclidean distance from the column vectors constituting the channel matrix. Also good. The minimum Euclidean distance estimation step may be configured to calculate a minimum Euclidean distance corresponding to each transmission antenna based on the dimension reduction channel matrix.

  The reception side may further include a reception power calculation step for calculating reception power corresponding to each transmission signal. Then, the ranking information calculation step may be configured such that a plurality of transmission antennas having the same minimum Euclidean distance are ordered higher in order of transmission antennas having higher reception power.

Moreover, in order to solve the said subject, according to the 3rd viewpoint of this invention, the receiver which receives the some transmission signal transmitted from the some transmission antenna is provided.
The receiving device orders a minimum Euclidean distance estimation unit that calculates a minimum Euclidean distance for each transmission antenna based on a channel matrix that represents a transmission characteristic of a wireless transmission path, and a transmission antenna based on the magnitude relationship of the minimum Euclidean distance A ranking information generator, a signal detector that estimates each transmission signal using a channel matrix, a reception replica generator that generates a reception replica signal based on a correctly decoded transmission signal, and a reception replica signal from the reception signal And an interference canceller unit that generates a residual signal by subtracting.

  The receiving apparatus further includes a dimension reduction channel matrix generation unit that generates a dimension reduction channel matrix by excluding the column vector corresponding to the maximum value of the minimum Euclidean distance from the column vectors constituting the channel matrix. It may be. The minimum Euclidean distance estimation unit may be configured to calculate a minimum Euclidean distance corresponding to each transmission antenna based on the dimension reduction channel matrix.

  The dimension reduction channel matrix generation unit excludes a column vector corresponding to the maximum value of each minimum Euclidean distance calculated for the dimension reduction channel matrix from the column vectors constituting the dimension reduction channel matrix. Further, the dimension reduction may be further performed, and a dimension reduction channel matrix may be newly generated.

  In addition, the reception device may further include a reception power calculation unit that calculates reception power corresponding to each transmission signal. Then, the ranking information calculation unit may be configured to order a plurality of transmission antennas having a large reception power in order of a plurality of transmission antennas having a plurality of minimum Euclidean distances having substantially the same value.

  The minimum Euclidean distance estimation unit may be configured to calculate a minimum Euclidean distance for each transmission antenna using a plurality of channel matrices estimated for each subcarrier. Furthermore, the ranking information calculation unit may be configured to generate ranking information for each subcarrier based on the magnitude relationship of the minimum Euclidean distance.

In order to solve the above problem, according to a fourth aspect of the present invention, a minimum Euclidean distance is provided in a receiving apparatus that has a plurality of transmission antennas that transmit a plurality of transmission signals and that receives the plurality of transmission signals. Provided is a transmission device capable of assigning a predetermined transmission signal to a predetermined transmission antenna so as to be maximized.
The above transmitting apparatus has a receiving unit that receives ranking information of transmitting antennas generated based on the magnitude relationship of the minimum Euclidean distance estimated for each transmitting antenna, and the minimum Euclidean distance is maximized based on the ranking information. A precoding unit that allocates a predetermined transmission signal to each transmission antenna, and a transmission unit that transmits a predetermined transmission signal via each transmission antenna allocated by the precoding unit.

  The transmission apparatus may further include a serial / parallel conversion unit that performs serial / parallel conversion on the transmission packet to generate a plurality of transmission signals corresponding to the plurality of subcarriers. And said receiving part may be comprised so that the ranking information of the transmission antenna calculated based on the magnitude relationship of the minimum Euclidean distance for every subcarrier may be received. Furthermore, the precoding unit may be configured to assign all transmission signals corresponding to the transmission packet to each transmission antenna having the maximum minimum Euclidean distance based on the ranking information for each subcarrier.

Further, the precoding unit transmits all transmission signals corresponding to the nth transmission packet (n = 1 to N _T , N _T is the number of transmission antennas) based on the ranking information for each subcarrier. Each minimum Euclidean distance may be configured to be assigned to each transmission antenna having the highest nth.

In addition, the receiving unit is configured to receive ranking information for each subcarrier for each transmitting antenna up to the top Nth (N <N _T , where N _T is the number of transmitting antennas) having a large minimum Euclidean distance. Also good. Further, the precoding unit sends all transmission signals corresponding to the nth (n = 1 to N) transmission packets to each transmission antenna whose lowest Euclidean distance is the highest nth based on the ranking information. It may be configured to allocate.

  In addition, the reception unit may be configured to receive ranking information generated based on the minimum Euclidean distance for each subcarrier group configured by a plurality of adjacent subcarriers. Further, the precoding unit may be configured to assign all transmission signals corresponding to the subcarrier group to each transmission antenna having the maximum minimum Euclidean distance based on ranking information for each subcarrier group. Good.

  In addition, the above-described receiving device may further include a transmission unit that returns ranking information to the transmission side. Further, the transmission unit may be configured to transmit only information related to a predetermined number of transmission antennas ranked higher in the ranking information to the transmission device.

  Further, the transmission unit selects a predetermined subcarrier from a subcarrier group configured by a plurality of adjacent subcarriers, and transmits ranking information for the predetermined subcarrier as ranking information of the subcarrier group. It may be configured to transmit to the device.

  Based on each of the above aspects, the receiving apparatus according to the present invention estimates the minimum Euclidean distance for each transmission antenna (or substream) based on the channel matrix, and ranks the transmission antennas based on the minimum Euclidean distance. can do. In addition, the transmission apparatus according to the present invention performs precoding (or transmission antenna allocation) so as to transmit a predetermined transmission signal from a transmission antenna having the maximum minimum Euclidean distance based on the ranking information regarding the ranking. Can do. Furthermore, the receiving apparatus can detect each transmission signal with high accuracy by combining interference canceling and maximum likelihood detection. Note that the minimum Euclidean distance corresponds to the accuracy with which each transmission signal is discriminated when separating a plurality of transmission signals interfering on the transmission path. The Euclidean distance is obtained, for example, by calculating a difference between two reception symbol vectors corresponding to two different transmission symbol vectors and calculating a square norm of the calculated difference reception symbol vector. In other words, the minimum value extracted from all the obtained Euclidean distances is the minimum Euclidean distance for all the differential reception symbol vectors that are possible according to the modulation scheme. Therefore, the larger the minimum Euclidean distance, the easier it is to detect the difference in the transmission symbol vector, so that it can be used as an index relating to the separation signal discrimination accuracy.

  In order to solve the above problems, according to another aspect of the present invention, a program for causing a computer to realize the functions of the communication system, the transmission device, and the reception device can be provided. According to still another aspect, a recording medium on which the above program is recorded is provided.

  As described above, according to the present invention, it is possible to improve the MIMO signal detection accuracy by performing precoding using the ranking information of the transmitting antenna estimated based on the minimum Euclidean distance.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

<Configuration example of a general MIMO signal detection system>
First, prior to describing the preferred embodiment of the present invention, in order to clarify the difference between the configuration of the present embodiment and the general configuration, the general configuration of the MIMO signal detection system will be described with reference to FIGS. This will be briefly described with reference to FIG. FIG. 1 is an explanatory diagram illustrating a general configuration example of a transmission apparatus 10 constituting a MIMO signal detection system. FIG. 2 is an explanatory diagram illustrating a general configuration example of the reception device 30 configuring the MIMO signal detection system. FIG. 3 is an explanatory diagram illustrating another general configuration example of the reception device 50 that configures the MIMO signal detection system. FIG. 4 is an explanatory diagram illustrating a problem included in the receiving device 50. FIG. 5 is an explanatory diagram showing a general configuration example of a MIMO signal detection system using interference canceling. FIG. 6 is an explanatory diagram showing the effect of precoding using received power. In the following, a signal sequence transmitted from each transmission antenna branch is referred to as a substream, and a data sequence that is encoded with one error correction code and modulation-mapped is referred to as a packet.

[Configuration Example of Transmitting Device 10]
First, a configuration example of the transmission device 10 will be described with reference to FIG.
The transmission apparatus 10 mainly includes an error correction coding unit 12, a modulation mapping unit 14, a serial-parallel conversion unit 16, a pilot channel multiplexing unit 18, an IFFT & GI addition unit 20, and an antenna 22. . Although not explicitly shown in the figure, the transmission device 10 may include, for example, a CPU (Central Processing Unit), a memory, a storage device, or the like as a component. Note that the storage device may be, for example, a hard disk, a semiconductor memory, an optical recording medium, or a magnetic recording medium. The memory may be, for example, a ROM (Read Only Memory), a RAM (Random Access Memory), or other storage devices. In addition, some or all of the functions of the error correction coding unit 12, the modulation mapping unit 14, the serial-parallel conversion unit 16, the pilot channel multiplexing unit 18, and the IFFT & GI addition unit 20 are recorded in a memory or other storage device. It may be realized by a CPU based on a program, or may be realized by dedicated hardware.

The error correction encoding unit 12 performs error correction encoding on each of a plurality of packet data #n (n = 1 to N _T ) in each transmission antenna branch. Further, the modulation mapping unit 14 maps each packet data subjected to error correction coding to a modulation signal point, and modulates a carrier wave for each packet data to generate a plurality of modulated signals. Further, the serial / parallel conversion unit 16 accumulates a plurality of mapped modulation signals, performs serial / parallel (S / P) conversion, and generates subcarrier signals corresponding to a plurality of subcarriers orthogonal to each other. Convert. Pilot channel multiplexing section 18 multiplexes a pilot signal for estimating a channel matrix for each subcarrier in the receiving apparatus. Further, IFFT & GI adding section 20 converts a subcarrier signal on which a pilot signal is multiplexed into a time domain signal by using an inverse fast Fourier transform (IFFT; Inverse Fast Fourier Transform). Further, IFFT & GI adding section 20 inserts a guard interval (GI; Guard Interval) in the time domain signal in order to avoid interference between symbols. Thereafter, the time domain signals to which the guard interval is added are transmitted simultaneously at the same frequency via the antenna 22.

[Configuration Example of Receiving Device 30]
Next, a configuration example of the receiving device 30 will be described with reference to FIG. The receiving device 30 is an example of a receiving device that constitutes a general MIMO-OFDM communication system.

  The receiving apparatus 30 mainly includes an antenna 32, a GI removal & FFT unit 34, a channel estimation unit 36, a MIMO signal detection unit 38, and an error correction decoding unit 40. Although not clearly shown in the figure, the receiving device 30 may include, for example, a CPU, a memory, a storage device, or the like. Also, some or all of the functions of the GI removal & FFT unit 34, channel estimation unit 36, MIMO signal detection unit 38, and error correction decoding unit 40 are performed by the CPU based on a program recorded in a memory or other storage device. It may be realized or may be realized by dedicated hardware.

  The GI removal & FFT unit 34 removes the guard interval from the time domain signal received via the antenna 32, and then transforms the time domain signal into a subcarrier signal by using Fast Fourier Transform (FFT; Fast Fourier Transform). The MIMO signal detector 38 uses the channel matrix estimated by the channel estimator 36 to separate a plurality of subcarrier signals that interfered in the transmission path for each substream. At this time, the MIMO signal detection unit 38 can use, for example, a method such as a spatial filter or maximum likelihood detection as a signal separation algorithm. In addition, the channel estimation unit 36 can estimate a channel matrix representing the transmission characteristics of the wireless transmission path using, for example, pilot symbols added to the received modulated signal. Further, the MIMO signal detection unit 38 performs parallel / serial (P / S) conversion on the separated subcarrier signal to restore the packet, and demaps the packet into a bit sequence. Thereafter, the error correction decoding unit 40 can reproduce the packet data by performing error correction decoding.

[Configuration Example of Receiving Device 50]
Next, a configuration example of the receiving device 50 will be described with reference to FIG. The receiving device 50 is an example of a receiving device that constitutes a MIMO-OFDM mobile communication system, like the receiving device 30, but in a configuration including signal estimation means using a parallel interference canceller (PIC; Parallel Interference Canceller). This is different from the receiving device 30. Hereinafter, the same reference numerals are assigned to substantially the same components as those of the receiving device 30 described above, and detailed description thereof is omitted.

  The receiving apparatus 50 mainly includes an antenna 32, a GI removal & FFT unit 34, a channel estimation unit 36, a MIMO signal detection unit 38, an error correction decoding unit 40, a parallel interference canceller unit 52, and a positive packet selection unit. 54, an error correction encoding unit 56, a modulation mapping unit 58, and a replica generation unit 60. Note that the function of each component described above may be realized by a CPU or the like using software, as in the above-described receiving device 30, or may be realized by dedicated hardware.

  Similarly to the receiving device 30 described above, the receiving device 50 removes the guard interval from the time domain signal received via the antenna 32, and then converts the signal into a subcarrier signal using FFT. Then, the MIMO signal detection unit 38 separates the subcarrier signal for each substream using a signal separation algorithm, and further, the packet obtained by parallel-serial conversion is demapped to a bit sequence. Then, the error correction decoding unit 40 performs error correction decoding on the demapped packet, and the reproduction packet data is estimated.

  The correct packet selection unit 54 performs error detection for determining whether or not the estimated reproduction packet data is correctly decoded. If all packets are correctly decoded, the decoding process is terminated. On the other hand, when the correct packet selection unit 54 determines that a part of the estimated reproduction packet data includes an error, the error correction encoding unit 56 uses the correctly decoded packet to code the error correction code. Execute the conversion. Further, the modulation mapping unit 58 maps the packet data re-encoded by the error correction encoding unit 56 to each modulation signal point. Thereafter, the replica generation unit 60 generates a reception replica signal that is a replica of the reception signal, using a channel estimation value that represents a wireless transmission path characteristic between each transmission antenna and each reception antenna.

  The parallel interference canceller unit 52 generates a residual signal by subtracting the replica signal from the received signal. Furthermore, the MIMO signal detection unit 38 applies a signal separation algorithm to the residual signal and executes the signal separation process again. At this time, since the number of transmission substreams is equivalently reduced by the number of correctly estimated packets, the signal separation accuracy by the MIMO signal detection unit 38 is improved. Furthermore, the effect of error correction by the error correction decoding unit 40 is improved, and an error-free packet can be estimated. Of course, when packet data including an error remains, a reception replica signal is generated again from newly estimated error-free packet data to calculate a residual signal, and for this residual signal, By executing signal separation processing, demapping, and error correction decoding processing, correct packet data can be estimated. The receiving apparatus 50 can correctly estimate all the packet data by repeating the above interference canceling until all the packet data are correctly estimated.

  However, as shown in FIG. 4, when all reproduced packet data includes an error, a reception replica signal cannot be generated, and thus there is a problem that interference cancellation cannot be performed using the reception replica signal. If re-encoding is performed from a bit sequence containing an error, the error expands to the encoded bit sequence and an incorrect modulation mapping signal is generated. As a result, the packet data is estimated. The accuracy is significantly degraded.

  Furthermore, even if a received replica signal is generated from a correctly decoded packet and interference cancellation can be performed, if the newly decoded packet data is not included in the estimated packet data, a new one is generated. There is also a problem that it is impossible to generate a reception replica signal, and it is impossible to improve transmission characteristics by repeatedly executing interference canceling.

[Configuration Example of MIMO Signal Detection System 70]
In view of the serious problems related to interference cancellation described above, various trials and errors have been made so far. As one countermeasure, MIMO using pre-coding of subcarrier signals according to received power for each substream. -An OFDM signal detection system is known. FIG. 5 is an explanatory diagram showing a configuration example of a MIMO signal detection system 70 based on the idea of this signal detection system. The basic concept of the MIMO signal detection system 70 is that a specific packet is determined based on the ordering information by feeding back to the transmitting side the ordering information in which the transmitting antennas are ordered based on the received power of each substream estimated on the receiving side. The subcarrier signal corresponding to is transmitted from a specific transmitting antenna. That is, by assigning all subcarrier signals of a specific packet to a transmission antenna having a high reception power, the probability that the specific packet can be correctly estimated on the receiving side can be increased. As a result, a reception replica signal for a specific packet can be generated, and interference cancellation can be executed.

  Therefore, referring to FIG. 5, the MIMO signal detection system 70 includes a transmission device 72 and a reception device 74.

(Configuration example of receiving device 74)
First, a configuration example of the receiving device 74 will be described.
The receiving device 74 mainly includes an antenna 32, a GI removal & FFT unit 34, a channel estimation unit 36, a canceling & nulling unit 78, an error correction decoding unit 40, a positive packet selection unit 54, and an error correction encoding unit 56. A modulation mapping unit 58, a replica generation unit 60, a substream received power estimation unit 80, and an ordering information generation unit 82. In addition, about the component substantially the same as said receiver 30 or receiver 50, the same code | symbol is attached | subjected and detailed description is abbreviate | omitted.

  Similarly to the above-described receiving device 50, the receiving device 74 performs error detection to determine whether or not the estimated reproduction packet data is correctly decoded, and then uses the correctly decoded packet to perform processing on the received substream. A replica signal is generated, and interference cancellation is performed using the received signal and the received replica signal. At that time, the Cancelling & Nulling unit 78 performs nulling (Nulling) to remove the influence of fading using the received signal and the received replica signal for each substream based on the BLAST (Bell Laboratories Layered Space-Time) algorithm. Then, canceling that cancels the influence of interference in the transmission path is executed.

  Further, the substream received power estimation unit 80 estimates the received power for each substream using the channel estimation value estimated by the channel estimation unit 36. Further, the ordering information generation unit 82 generates ordering information in which the substream detection order used for the BLAST algorithm is determined for each subcarrier based on the estimated reception power for each substream, and the transmission apparatus 72.

(Configuration example of transmission device 72)
The transmission apparatus 72 mainly includes an error correction encoding unit 12, a modulation mapping unit 14, a serial-parallel conversion unit 16, a transmission antenna allocation unit 76, a pilot channel multiplexing unit 18, an IFFT & GI addition unit 20, and an antenna. 22. In addition, about the component substantially the same as said transmission apparatus 10, the detailed description is abbreviate | omitted by attaching | subjecting the same code | symbol.

Similarly to the transmission apparatus 10 described above, the transmission apparatus 72 performs error correction encoding on each of a plurality of packet data #n (n = 1 to N _T ) in each transmission antenna branch, and performs error correction code. Each packet data is mapped to modulation signal points, and a carrier wave is modulated for each packet data to generate a plurality of modulation signals. Further, after serially parallel (S / P) conversion of the plurality of mapped modulation signals and conversion into subcarrier signals, pilot signals for channel estimation are multiplexed. At that time, the transmission antenna allocation unit 76 allocates each subcarrier signal of a specific packet to a specific transmission antenna based on the ordering information received from the reception device 74. More specifically, the transmission antenna allocation unit 76 allocates all subcarrier signals corresponding to a specific packet to each transmission antenna whose reception power increases for each subcarrier. Then, IFFT & GI adding section 20 converts the pilot signal into a time domain signal using IFFT and inserts a guard interval. Thereafter, the time domain signals to which the guard interval is added are simultaneously transmitted at the same frequency via the antenna 22 corresponding to the transmission antenna allocation described above.

  Here, the effect of transmission antenna assignment based on received power will be briefly described with reference to FIG. Referring to FIG. 6 (A), a typical received power characteristic is shown. This received power characteristic has a shape in which a plurality of smooth peak structures are combined, and a deep dip formed between the peak structures is characteristic. For example, paying attention to the reception power characteristic (solid line) for the transmission antenna (Tx antenna) # 1 shown in FIG. 6A, four peaks are drawn, and a dip is formed between each peak. I understand that Therefore, the reception power of the subcarrier signal corresponding to the dip position is very small. As a result, the packet estimation accuracy in the receiving apparatus is reduced.

  However, as shown in FIG. 6B, the reception power characteristics can be improved by distributing the subcarrier signals corresponding to a specific packet to the transmission antennas each having a large reception power. FIG. 6B shows that the packet (Packet) # 1 is distributed to a specific transmission antenna having the maximum received power for each subcarrier, and high received power is obtained for all the subcarrier signals corresponding to the packet # 1. This is an example. As is clear from FIG. 6B, the subcarrier signal corresponding to packet # 1 is assigned a transmission antenna that maximizes the reception power corresponding to the position of the subcarrier, and corresponds to packet # 2. A sub-carrier signal to be transmitted is assigned a transmission antenna with the next highest received power. Predetermined transmission antennas are also assigned in order to the subcarrier signals corresponding to packet # 3 and packet # 4. As a result, high reception power is detected for all subcarrier signals corresponding to packet # 1, and the probability that packet # 1 is correctly decoded increases. By performing such precoding, it is possible to reduce the probability that interference canceling cannot be performed because all packets are not correctly decoded.

  As described above, it is possible to improve transmission characteristics by assigning each subcarrier signal of a specific packet to a specific transmission antenna using ordering information based on received power. However, when the MLD method is used for the MIMO signal detection means, since the index for determining the transmission characteristics depends on the average Euclidean distance between the reception replica signal points, the transmission antenna is not necessarily assigned depending on the ordering information based on the reception power. It cannot be said that the transmission characteristics are improved. Therefore, in the following, as a preferred embodiment of the present invention, a MIMO signal detection system capable of precoding using the minimum Euclidean distance estimated for each substream is disclosed. Then, a configuration example of a transmission device, a configuration example of a reception device, and a precoding method constituting the MIMO signal detection system will be described in detail.

<First Embodiment of the Present Invention>
First, with reference to FIGS. 7 to 14, configuration examples of the transmission device 100 and the reception device 200 that configure the MIMO signal detection system according to the first embodiment of the present invention will be described in detail. FIG. 7 is an explanatory diagram illustrating a configuration example of the transmission device 100 included in the MIMO signal detection system according to the present embodiment. FIG. 8 is an explanatory diagram showing a method for generating a precoding matrix in the transmission apparatus 100. FIG. 9 is an explanatory diagram illustrating another method for generating the precoding matrix in the transmission apparatus 100. FIG. 10 is an explanatory diagram illustrating a configuration example of the reception device 200 included in the MIMO signal detection system according to the present embodiment. FIG. 11 is an explanatory diagram illustrating a transmission antenna ranking method in the receiving apparatus 200. FIG. 12 is an explanatory diagram showing a configuration of the transmission antenna ranking method. FIG. 13 is an explanatory diagram showing a configuration of another transmitting antenna ranking method. FIG. 14 is an explanatory diagram showing grouping of subcarriers.

  Note that the basic concept of the present embodiment is that transmission antenna ranking information is generated based on the minimum Euclidean distance for each substream, and each subcarrier signal corresponding to a specific packet is transmitted to a specific transmission antenna based on this ranking information. Is to allocate to. More specifically, the MLD method is applied to the MIMO signal detection means included in the receiving apparatus 200 by allocating all the subcarrier signals corresponding to a specific packet to the transmission antenna in which the minimum Euclidean distance for each subcarrier becomes large. Even when it is used, accurate precoding is possible, and good transmission characteristics can be obtained.

[Configuration Example of Transmitting Device 100]
First, a configuration example of the transmission device 100 will be described with reference to FIG.
Referring to FIG. 7, transmission apparatus 100 mainly includes error correction coding section 102, modulation mapping section 104, serial-parallel conversion section 106, precoding section 108, pilot channel multiplexing section 110, and IFFT & GI addition. The unit 112 and the antenna 114 are configured. Although not clearly shown in the figure, the transmission device 100 may include a reception unit that receives ranking information calculated by the reception device 200 and a transmission unit that transmits a transmission signal, for example. In addition, the transmission device 100 may include, for example, a CPU, a memory, or a storage device. Note that some or all of the functions of the error correction coding unit 102, modulation mapping unit 104, serial-parallel conversion unit 106, precoding unit 108, pilot channel multiplexing unit 110, or IFFT & GI addition unit 112 may be memory or other storage. The function may be realized by a CPU based on a program recorded in the device, or by a dedicated hardware.

The error correction encoding unit 102 performs error correction encoding on each of a plurality of packet data #n (n = 1 to N _T ) in each transmission antenna branch. Further, the modulation mapping unit 104 maps each packet data subjected to error correction coding to a modulation signal point, and modulates a carrier wave for each packet data to generate a modulation signal. Further, the serial / parallel conversion unit 106 accumulates the mapped modulation signal, performs serial / parallel (S / P) conversion, and converts it into a subcarrier signal corresponding to each subcarrier.

  Precoding section 108 generates a precoding matrix based on the transmission antenna ranking information fed back from the receiving apparatus, and uses this precoding matrix to send each subcarrier signal corresponding to a predetermined packet to a specific transmission antenna. assign. Pilot channel multiplexing section 110 multiplexes a pilot signal for estimating a channel matrix in the receiving apparatus. Also, IFFT & GI adding section 112 converts a pilot signal multiplexed using IFFT into a time domain signal. Furthermore, IFFT & GI adding section 112 inserts a guard interval into the time domain signal in order to avoid interference between symbols. Thereafter, the time domain signals to which the guard interval is added are simultaneously transmitted through the antenna 114 at the same frequency.

(Precoding matrix generation method)
Here, a method of generating a precoding matrix and a method of assigning transmission antennas by the precoding unit 108 will be described with reference to FIG. FIG. 8 shows, as an example, a precoding matrix generation method by a 4 × 4 MIMO-OFDM system configured by the number of transmission antennas N _T = 4 and the number of reception antennas N _R = 4. It is assumed that transmission antenna ranking information O (m) for the m-th subcarrier is calculated based on the minimum Euclidean distance for each substream. Of course, the precoding matrix generation method according to the present embodiment is not limited to this, and can also be implemented in the same manner, for example, when N _T ≠ 4 and N _R ≠ 4.

  First, as a specific example, it is assumed that ranking information O (m) = {3, 4, 2, 1} of transmitting antennas for the m-th subcarrier is calculated by the receiving apparatus 200. However, in the description of the ranking information O (m), it is assumed that the index of the transmitting antenna is arranged so that the minimum Euclidean distance decreases from left to right. The precoding unit 108 generates a precoding matrix F (m) based on the ranking information O (m). Each step related to the precoding matrix generation will be described in order.

(Step 1)
First, the precoding unit 108 transmits the transmit antenna index (3) located in the first (leftmost) ranking information O (m) among the elements arranged in the first column of the precoding matrix F (m). 1 is arranged in the row indicated by () (third row), and 0 is arranged in the other rows (first, second and fourth rows).
(Step 2)
Next, the precoding unit 108 indicates the row indicated by the transmission antenna index (4) positioned second in the ranking information O (m) among the elements arranged in the second column of the precoding matrix F (m). 1 is arranged in the (fourth row), and 0 is arranged in the other rows (first, second, and third rows).
(Step 3)
Next, the precoding unit 108 indicates the row indicated by the transmission antenna index (2) positioned third in the ranking information O (m) among the elements arranged in the third column of the precoding matrix F (m). 1 is arranged in the (second row), and 0 is arranged in the other rows (first, third, and fourth rows).
(Step 4)
Next, the precoding unit 108 indicates the row indicated by the transmission antenna index (1) positioned fourth in the ranking information O (m) among the elements arranged in the fourth column of the precoding matrix F (m). 1 is arranged in the (first row), and 0 is arranged in the other rows (second, third and fourth rows).

The precoding matrix F (m) shown in FIG. 8 is generated by the above (Step 1) to (Step 4). In more general terms, the precoding unit 108 acquires ranking information O (m) indicating the ordering of transmission antennas regarding the mth subcarrier, and the kth (k = 1) of the ranking information O (m). ,..., N _T ), if this transmit antenna index is i, the element located in the i-th row and k-th column of the precoding matrix F (m) Is set to 1 and the other elements in the k-th column are set to 0. Similarly, precoding section 108 sets each element of precoding matrix F (m) with reference to the transmission antenna index for other elements of ranking information O (m).

As described above, when the precoding matrix F (m) is determined, the precoding unit 108 transmits the transmission signal s _i (m) of each packet transmitted by the mth subcarrier, as shown in FIG. ) (I = 1, 2, 3, 4) as a transmission signal vector s (m) = [s ₁ (m), s ₂ (m), s ₃ (m), s ₄ (m)] ^T Is applied to the precoding matrix F (m). However, the nth (n = 1 to 4) position from the left of the transmission signal vector corresponds to the nth transmission antenna. As a result, the precoding unit 108 can suitably allocate a transmission signal transmitted using the mth subcarrier to each transmission antenna for each packet. That is, the precoding matrix F (m) is a permutation matrix for a transmission signal vector having a transmission signal for each packet as a component. So far, the precoding method in the m-th subcarrier has been described. However, by performing the same precoding process for all m included in the packet, a suitable transmission antenna for all subcarrier signals can be obtained. Is assigned.

  The precoding method according to the present embodiment has been described above. By performing this precoding, for example, packet # 1 is transmitted from the transmission antenna having the smallest minimum Euclidean distance in all subcarriers, and packet # 2 is transmitted from the transmission antenna having the second smallest Euclidean distance. Similarly, packets # 3 and # 4 are transmitted from the third and fourth transmission antennas having the minimum Euclidean distance, respectively. As a result, it is possible to increase the probability that the packet data that has been subjected to maximum error detection includes packet data that is correctly decoded for error correction.

(Precoding matrix generation method: Modification 1)
Note that the precoding unit 108 can also perform precoding using ranking information for some transmission antennas having a minimum minimum Euclidean distance instead of using ranking information for all transmission antennas. In this case, the ranking information fed back from the receiving device only needs to include the transmission antenna indexes corresponding to the top several rankings, and the amount of information to be fed back from the receiving device to the transmitting device can be reduced. Hereinafter, a method for generating such a precoding matrix will be briefly described with reference to FIG.

  First, as a specific example, it is assumed that ranking information O (m) = {3, 4} of transmitting antennas for the m-th subcarrier is calculated by the receiving apparatus 200. Note that the left element of the ranking information O (m) is an index indicating a transmission antenna having the maximum minimum Euclidean distance, and the right element is an index indicating a transmission antenna having the second smallest Euclidean distance. The precoding unit 108 generates a precoding matrix F (m) based on the ranking information O (m). Each step related to the precoding matrix generation will be described in order.

(Step 1)
First, the precoding unit 108 transmits the transmit antenna index (3) located in the first (leftmost) ranking information O (m) among the elements arranged in the first column of the precoding matrix F (m). 1 is arranged in the row indicated by () (third row), and 0 is arranged in the other rows (first, second and fourth rows).
(Step 2)
Next, the precoding unit 108 indicates the row indicated by the transmission antenna index (4) positioned second in the ranking information O (m) among the elements arranged in the second column of the precoding matrix F (m). 1 is arranged in the (fourth row), and 0 is arranged in the other rows (first, second, and third rows).
(Step 3)
Next, the precoding unit 108 is a row in which 1 is not arranged in the above (Step 1) and (Step 2) among the elements arranged in the third and fourth columns of the precoding matrix F (m). 1 is placed in the other row, and 0 is placed in the other rows. At this time, the third and fourth columns are set so that 1 is not arranged in the same row. For example, as shown in FIG. 9, 1 may be arranged in ascending order.

A precoding matrix F (m) as shown in FIG. 9 is generated by the above (Step 1) to (Step 3). Similarly to the precoding method shown in FIG. 8, when the precoding matrix F (m) is determined through the above steps, the precoding unit 108, as shown in FIG. The transmission signal vector s (m) = [s ₁ (m), s ₂ (m), with the transmission signal s _i (m) (i = 1, 2, 3, 4) of each packet transmitted by s ₃ (m), s ₄ (m)] ^{T is applied} to the precoding matrix F (m). As a result, the precoding unit 108 can suitably allocate a transmission signal transmitted using the mth subcarrier to each transmission antenna for each packet. Also in the first modification shown here, it is possible to increase the signal estimation probability for a specific packet, so that it is possible to improve transmission characteristics by parallel interference canceling. Further, since only the upper part of the transmission antenna ranking information obtained on the receiving side is sent back to the transmitting side, the amount of information to be fed back can be reduced compared to the case where all ranking information is fed back.

  The configuration example of the transmission device 100 according to the present embodiment has been described above. Transmitting apparatus 100 includes precoding section 108 that performs precoding based on ranking information of transmitting antennas fed back from receiving apparatus 200 described later. The precoding unit 108 assigns a subcarrier signal corresponding to a specific packet to a transmission antenna having a minimum minimum Euclidean distance for each subcarrier, thereby improving the probability that a specific packet is correctly estimated on the receiving side. Can be made. Hereinafter, a configuration example of the receiving apparatus 200 capable of generating ranking information used for executing the above precoding will be described in detail.

[Configuration Example of Receiving Device 200]
First, a configuration example of the receiving device 200 will be described with reference to FIG. Note that the receiving apparatus 200 calculates a minimum Euclidean distance for each substream, and generates ranking information of transmitting antennas based on the calculated Euclidean distance. Furthermore, the receiving apparatus 200 can receive the transmission signal precoded by the transmitting apparatus 100, and can estimate each packet data with high accuracy using a signal separation algorithm based on interference cancellation and the MLD method.

  Referring to FIG. 10, receiving apparatus 200 mainly includes antenna 202, GI cancellation & FFT section 204, parallel interference canceller section 206, MIMO signal detection section 208, decoding section 210, and error correction decoding section 212. A correct packet selection unit 214, an error correction coding unit 216, a modulation mapping unit 218, a precoding unit 220, a replica generation unit 222, a channel estimation unit 224, and a sub-stream minimum Euclidean distance estimation unit 226. And a ranking information calculation unit 228. However, the correct packet selection unit 214, the error correction coding unit 216, the modulation mapping unit 218, the precoding unit 220, and the replica generation unit 222 are an example showing the configuration of the reception replica generation unit. Note that the function of each component described above may be realized by a CPU or the like (not shown) using software, or may be realized by dedicated hardware.

  GI removal & FFT section 204 removes the guard interval from the time domain signal received via antenna 202, and then converts the time domain signal to a subcarrier signal using FFT. The MIMO signal detection unit 208 uses the channel matrix estimated by the channel estimation unit 224 and separates substreams that have interfered in the transmission path for each subcarrier. At this time, the MIMO signal detection unit 208 desirably uses a signal separation algorithm based on the MLD method, and may use an application algorithm such as a QRD-MLD method that combines QR decomposition and the MLD method. Furthermore, MIMO signal detection section 208 performs parallel-serial (P / S) conversion on the separated subcarrier signals to reproduce packets, and demaps them into bit sequences.

  Decoding section 210 restores the transmission signal vector precoded in transmission apparatus 100 in the same order as the transmission signal vector before precoding. For example, the decoding unit 210 may calculate a decoding matrix corresponding to the inverse matrix of the precoding matrix based on the ranking information of the transmission antenna, similarly to the precoding unit 108 included in the transmission apparatus 100. Also, the decoding unit 210 can estimate the transmission signal vector before precoding by applying the transmission signal vector detected by the MIMO signal detection unit 208 to the decoding matrix. That is, the decoding matrix is a replacement matrix that reverses the replacement of the transmission signal vector by precoding. Thereafter, the error correction decoding unit 212 can obtain reproduction packet data by performing error correction decoding.

  The correct packet selection unit 214 performs error detection that determines whether or not the estimated reproduction packet data is correctly decoded. If all the packet data are correctly decoded, the decoding process is terminated. On the other hand, when it is determined that an error is included in a part of the estimated reproduction packet data, the error correction encoding unit 216 performs error correction encoding using the correctly decoded packet data. Further, the modulation mapping unit 218 maps the packet re-encoded by the error correction encoding unit 216 to each modulation signal point. Thereafter, precoding section 220 precodes the re-encoded transmission signal based on the ranking information of the transmission antennas, similarly to precoding section 108 provided in transmitting apparatus 100. Thereafter, the replica generation unit 222 generates a reception replica signal by using a channel estimation value that represents a transmission characteristic of a wireless transmission path between each transmission antenna and each reception antenna.

  The parallel interference canceller unit 206 subtracts the received replica signal from the received signal to generate a residual signal. Further, the MIMO signal detection unit 208 performs signal separation processing again by applying a signal separation algorithm to the residual signal. At this time, since the number of transmission substreams is equivalently reduced by the amount of correctly estimated packet data, the signal separation accuracy by the MIMO signal detection unit 208 is improved. Furthermore, since the error correction effect by the error correction decoding unit 212 is also improved, it is possible to estimate an error-free packet. Of course, if packet data containing errors remains, a received replica signal is generated again from newly estimated packet data without error, and is subtracted from the received signal, so that signal separation processing, demapping, and error are performed. By executing the correction decoding process, a correct packet can be estimated. The receiving apparatus 200 can correctly estimate all packet data by repeating the above-described interference canceling.

The sub-stream minimum Euclidean distance estimation unit 226 uses the channel matrix estimated by the channel estimation unit 224 to estimate the minimum Euclidean distance for each sub-stream. In general, it is very difficult to estimate the minimum Euclidean distance for each substream. For example, according to a certain method, a difference modulation symbol that is a difference between two different modulation symbols is calculated for all modulation signal points included in a signal point arrangement of a predetermined modulation method, and is configured by a combination of difference modulation symbols. The Euclidean distance must be calculated for each of a number of differential modulation symbol vectors. The Euclidean distance is given by the square norm of the received differential modulation symbol vector obtained by applying the differential modulation symbol vector to the channel matrix. After that, a differential modulation symbol vector that minimizes the Euclidean distance is selected from differential modulation symbol vectors in which the differential modulation symbol corresponding to each substream is not zero. Then, the Euclidean distance corresponding to the differential modulation symbol vector is determined as the minimum Euclidean distance. Based on this method, the modulation level M, when the number of transmitting antennas and the N _T, the number of combinations of differential modulation symbol vector is expressed as M ^NT street. For example, when the number of transmission antennas is 4 and the modulation scheme is 16QAM, the Euclidean distance must be calculated for 49 ⁴ = 5,764,801 combinations. As a result, the calculation amount becomes enormous and it becomes extremely difficult to implement.

  However, the applicant has developed a very effective solution to the above problem and has already filed an application with the Japan Patent Office (Japanese Patent Application No. 2006-282376). Among them, the present applicant performs QR decomposition of the channel matrix into a unitary matrix and an upper triangular matrix, and selects candidate differential modulation symbol vectors so that each Euclidean distance corresponding to each row vector of the upper triangular matrix becomes small. A trellis search algorithm that extracts a differential modulation symbol vector that minimizes the Euclidean distance corresponding to a predetermined condition under selection is proposed. The sub-stream minimum Euclidean distance estimation unit 226 according to the present embodiment can also estimate the minimum Euclidean distance for each sub-stream using this algorithm. Note that the Euclidean distance estimation unit 226 for each substream uses the channel matrix estimated for each subcarrier to calculate the minimum Euclidean distance for each substream for each subcarrier.

  The ranking information calculation unit 228 generates ranking information of the transmission antenna based on the minimum Euclidean distance for each substream estimated by the substream minimum Euclidean distance estimation unit 226. For example, the ranking information calculation unit 228 refers to the minimum Euclidean distance for each substream estimated for the mth subcarrier, and rank information O (m) in which the indices of the transmission antennas are arranged in order of increasing minimum Euclidean distance. Is generated. Here, a ranking method of transmitting antennas will be described with a specific example with reference to FIG.

(Transmission antenna ranking method)
FIG. 11 is an explanatory diagram showing the configuration of the transmission antenna ranking method in the 4 × 4 MIMO-OFDM signal detection system. First, the channel matrix H corresponding to the m-th subcarrier is input to the sub-stream minimum Euclidean distance estimation unit 226, and the minimum Euclidean distance for each sub-stream with respect to the m-th subcarrier is estimated. As shown in FIG. 11, for example, the minimum Euclidean distances d _{min, 1 to} d _{min, 4} corresponding to the first to fourth substreams are d _{min, 1} = 0.65, d _{min, 2} = Assume 0.98, d _{min, 3} = 2.08, d _{min, 4} = 1.26. In this case, the transmission antenna rankings are 3, 4, 2, 1 in order of increasing minimum Euclidean distance. This number is an index of a transmission antenna that represents the kth (k = 1 to 4) transmission antenna. Therefore, the ranking information O (m) of the transmission antenna is O (m) = {3, 4, 2, 1}.

  The transmission antenna ranking method has been specifically described above. The ranking information calculation unit 228 can generate ranking information of transmission antennas based on the above-described transmission antenna ranking method. According to the above configuration, on the transmitting side, by transmitting a subcarrier signal of a specific packet using a transmission antenna that increases the minimum Euclidean distance for each subcarrier, this specific packet is used in the maximum likelihood estimation on the receiving side. It becomes easy to be estimated correctly. Furthermore, since the likelihood is increased, the effect of error correction is improved and errors are less likely to occur. Of course, other packets are transmitted from a transmission antenna with a smaller minimum Euclidean distance, which is likely to be erroneous. However, the probability that a specific packet transmitted from a transmission antenna with a large minimum Euclidean distance will be correctly decoded increases, so It becomes possible to generate a replica signal and perform interference canceling. As a result, the number of transmission substreams is equivalently reduced, and the minimum Euclidean distance is increased. Therefore, it is possible to compensate for a loss in transmission characteristics for a packet transmitted from a transmission antenna having a small minimum Euclidean distance. As a result, higher signal detection accuracy can be obtained, so that packet data can be decoded more correctly.

  By using the above method, it is possible to generate transmission antenna ranking information. Based on this ranking information, by reducing the dimension of the channel matrix, it is possible to perform more accurate transmission antenna ranking. It is. In the following, a transmission antenna ranking method accompanied by such dimension reduction of the channel matrix will be described.

(Transmission antenna ranking method: Modification 1)
With reference to FIG. 12, a description will be given of a transmit antenna ranking method with channel matrix dimension reduction. In addition, in order to implement | achieve the said transmission antenna ranking method, the receiver 200 is further provided with the dimension reduction channel matrix production | generation part 230. FIG. This ranking method utilizes the fact that substreams with a large minimum Euclidean distance are equivalently removed by interference canceling, and that the estimation accuracy of the minimum Euclidean distance is improved by using a dimension-reduced channel matrix. It is characterized in that

First, the minimum Euclidean distance estimation unit 226 for each substream calculates the minimum Euclidean distance for each substream using the channel matrix H estimated for the m-th subcarrier. Then, the ranking information calculation unit 228 calculates the ranking information of the transmission antenna based on the calculated minimum Euclidean distance for each substream. At this time, the ranking information calculation unit 228 can calculate the ranking information of the transmission antenna in the same manner as the transmission antenna ranking method shown in FIG. For example, as shown in FIG. 12, the minimum Euclidean distances d _{min, k} corresponding to the k th (k = 1 to 4) substreams are d _{min, 1} = 0.65, d _{min, 2} = Assuming that 0.98, d _{min, 3} = 2.08, d _{min, 4} = 1.26, the ranking information calculation unit 228 calculates the ranking information O (m) = {3,4,2,1}. Can be generated. Here, the ranking information calculation unit 228 extracts only the transmission antenna index (3) having the smallest minimum Euclidean distance, and selects the first component of the ranking information O (m) as the transmission antenna index (3). To decide.

Next, the dimension reduction channel matrix generation unit 230 generates a channel matrix H ′ excluding the column vector of the channel matrix corresponding to the first transmission antenna index based on the ranking information. In the example shown in FIG. 12, since the minimum Euclidean distance corresponding to the third transmission antenna is maximum, the matrix excluding the column vector of the third column of the channel matrix is defined as a channel matrix H ′ whose dimension is reduced. Is set. Thus, the minimum Euclidean distance estimation unit 226 for each substream uses the channel matrix H ′ set by the dimension reduction channel matrix generation unit 230 to estimate the minimum Euclidean distance for each substream again. For example, the minimum Euclidean distance d _{min, k} corresponding to the k th (k = 1, 2, 4) substream calculated for the channel matrix H ′ is d _{min, 1} = 0.98, respectively. Assume d _{min, 2} = 1.85 and d _{min, 4} = 1.49. Based on this result, the ranking information calculation unit 228 determines the second transmission antenna index based on the minimum Euclidean distance. In the case of this example, since the minimum Euclidean distance for the second substream is the maximum, the ranking information calculation unit 228 selects the second component of the ranking information O (m) as the transmission antenna index (2). To decide. Similarly, the dimension reduction channel matrix generation unit 230, the sub-stream minimum Euclidean distance estimation unit 226, and the ranking information calculation unit 228 also determine the third and fourth components of the ranking information O (m).

  The modification 1 of the transmission antenna ranking method has been specifically described above. The ranking information calculation unit 228 can generate more accurate transmission antenna ranking information based on the above method. According to the above configuration, the receiving apparatus 200 performs ranking using the minimum Euclidean distance for each substream, and transmits a transmission antenna for a channel matrix equivalent to the case where the highest-ranked substream is removed. The ranking accuracy can be further improved. Therefore, the receiving apparatus 200 can remove one packet by interference canceling and can prevent the remaining packets from being erroneous when performing maximum likelihood detection on the remaining packets.

  However, the transmission antenna ranking method described above is more effective because it can be configured to select a substream based on an arbitrary or predetermined condition when the minimum Euclidean distances for a plurality of substreams match. A condition for selecting a substream is required. Therefore, in the following, a configuration in which substreams are selected by comparing the magnitudes of received power when the minimum Euclidean distances corresponding to a plurality of substreams match each other is shown.

(Transmitting antenna ranking method: Modification 2)
With reference to FIG. 13, when a plurality of substreams having the same minimum Euclidean distance are detected, a transmission antenna ranking method capable of selecting an effective transmission antenna index to be positioned higher in the ranking information explain. The basic concept of this transmission antenna ranking method is that when a plurality of substreams having the same minimum Euclidean distance are detected, the received power for each of the plurality of substreams is detected and compared, and the substream having a larger received power The transmission antenna index corresponding to is placed at the top of the ranking information. Therefore, the configuration of the receiving apparatus 200 that realizes the above basic concept is shown below.

Referring to FIG. 13, reception apparatus 200 further includes a reception power calculation unit 232 for each substream. The reception power calculation unit 232 for each substream can detect the reception power for each substream. For example, the minimum Euclidean distance estimation unit 226 for each substream uses the channel matrix for the m-th subcarrier, and the minimum Euclidean distance d _{min, k} (k = 1 to 4) for each substream is set to d _{min, 1.} = 1.26, _{dmin, 2} = 0.98, _{dmin, 3} = 0.98, _{dmin, 4} = 1.26. Further, the reception power calculation unit 232 for each substream causes the reception power P _k (k = 1 to 4) for each substream to be P ₁ = 2.65, P ₂ = 2.12, P ₃ = 1.74, P Assume that ₄ = 3.19. At this time, the ranking information calculation unit 228 selects the first and fourth substreams having the maximum minimum Euclidean distance as candidates. At this time, since the minimum Euclidean distances of the first and fourth substreams match, the ranking information calculation unit 228 compares the received powers P ₁ and P ₄ for the first and fourth substreams. To do. In this example, the direction of P ₄ is larger than P _1, the ranking information calculating unit 228 arranges the fourth sub-stream corresponding to P ₄ to the upper ranking information O (m). Similarly, since the minimum Euclidean distance for the second and third substreams is also the same value, the ranking information calculation unit 228 compares the received powers P ₂ and P ₃ and compares the received power P ₂ with the larger value P ₂ . The second substream is arranged on the higher rank of the ranking information O (m). As a result, the ranking information O (m) is determined as O (m) = {4, 1, 2, 3}.

  As described above, the transmission antenna ranking method that can select a suitable substream to be positioned higher in the ranking information with reference to the received power when including a plurality of substreams having the same minimum Euclidean distance has been described. . According to the above configuration, when ranking is performed by estimating the minimum Euclidean distance for each substream, if there are substreams having the same minimum Euclidean distance, the received power is referred to by referring to the received power for each substream. By ranking the transmission antenna having a large value higher, the possibility that the average Euclidean distance increases further increases, and the effect that the signal detection accuracy is further improved can be obtained. In addition, said structure can be used in combination with the other transmission antenna ranking method mentioned above. As a result, more accurate transmission antenna ranking information can be calculated.

(About subcarrier grouping)
As described above, the receiving apparatus 200 can calculate the minimum Euclidean distance for each substream using the channel matrix estimated for each subcarrier, and can generate the ranking information of the transmission antenna based on this. Become. However, since there are few cases in which transmission path characteristics are greatly deviated between neighboring subcarriers, a plurality of neighboring subcarriers are grouped rather than calculating ranking information for all subcarriers. It is also possible to pre-code using ranking information for representative subcarriers of each group.

  As illustrated in FIG. 14, for example, the receiving apparatus 200 is configured to combine B consecutive subcarriers into one subcarrier group, and to return the transmission antenna ranking information to the transmitting apparatus 100 for each subcarrier group. Is done. At this time, the nth subcarrier group includes the (B (n−1) +1) th subcarrier to the Bnth subcarrier. On the other hand, transmitting apparatus 100 performs precoding on each subcarrier in the subcarrier group based on ranking information for each subcarrier group. According to such a configuration, the ranking information is not fed back for each subcarrier, but the ranking information is faded back for each subcarrier group, so that the amount of information to be fed back can be reduced.

  As described above, according to the first embodiment of the present invention, when the MLD method is used in the receiver in the MIMO system, it is possible to reduce the possibility of errors occurring in all packet data on the receiving side. The parallel interference canceller can be effectively used. Furthermore, since the rate of occurrence of errors in all packet data detected after performing interference canceling is reduced and interference canceling can be performed repeatedly, further improvement in communication quality can be expected.

<Second Embodiment of the Present Invention>
Next, configuration examples of the transmission apparatus 300 and the reception apparatus 400 constituting the MIMO signal detection system according to the second embodiment of the present invention will be described with reference to FIGS. Note that components that are substantially the same as those of the transmission device 100 and the reception device 200 according to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. FIG. 15 is an explanatory diagram illustrating a configuration example of the transmission device 300 according to the present embodiment. FIG. 16 is an explanatory diagram illustrating a configuration example of the receiving device 400 according to the present embodiment. FIG. 17 is an explanatory diagram showing a modification of the transmission antenna ranking method according to the present embodiment.

[Configuration Example of Transmitting Device 300]
First, a configuration example of the transmission device 300 will be described with reference to FIG.
Referring to FIG. 15, transmission apparatus 300 mainly includes LDPC encoding section 302, modulation mapping section 104, serial-parallel conversion section 106, precoding section 108, pilot channel multiplexing section 110, and IFFT & GI adding section. 112, an antenna 114, and a precoding matrix setting unit 304. Although not clearly shown in the figure, the transmission apparatus 300 may include, for example, a CPU, a memory, a storage device, or the like as a component. Note that a part or all of the functions of the LDPC encoding unit 302, the modulation mapping unit 104, the serial-parallel conversion unit 106, the precoding unit 108, the pilot channel multiplexing unit 110, or the IFFT & GI addition unit 112 are a memory or other storage device The function may be realized by a CPU based on a program recorded in the above, or by a dedicated hardware.

The LDPC encoding unit 302 performs error correction encoding on each of a plurality of packet data #n (n = 1 to N _T ) by LDPC (Low Density Parity Check) code in each transmission antenna branch. Also, the modulation mapping unit 104 maps each packet data subjected to error correction coding to each modulation signal point, and modulates a carrier wave for each packet data to generate a plurality of modulated signals. Further, the serial / parallel conversion unit 106 performs serial / parallel (S / P) conversion of the mapped modulated signals into subcarrier signals. The precoding matrix setting unit 304 generates a precoding matrix based on the ranking information of the transmission antennas fed back from the receiving device, or stores it in a predetermined table in a storage unit (not shown) provided in the transmitting device 300. Read the stored precoding matrix. The precoding unit 108 assigns each subcarrier signal corresponding to a predetermined packet to a specific transmission antenna using the above precoding matrix. Pilot channel multiplexing section 110 multiplexes a pilot signal for estimating a channel in the receiving apparatus. Also, IFFT & GI adding section 112 converts a pilot signal multiplexed using IFFT into a time domain signal. Furthermore, IFFT & GI adding section 112 inserts a guard interval into the time domain signal in order to avoid interference between symbols. Thereafter, the time domain signals to which the guard interval is added are simultaneously transmitted through the antenna 114 at the same frequency.

[Configuration Example of Receiving Device 400]
Next, a configuration example of the receiving device 400 will be described with reference to FIG.
Referring to FIG. 16, receiving apparatus 400 mainly includes antenna 202, GI removal & FFT section 204, parallel interference canceller section 206, MIMO signal detection section (QRD-MLD) 402, decoding section 210, LLR calculation section 404, LDPC decoding section 406, positive packet selection section 214, error correction coding section 216, modulation mapping section 218, precoding section 220, replica generation section 222, channel estimation section 224, The sub-stream minimum Euclidean distance estimation unit 226 and the ranking information calculation unit 228 are configured.

  The GI removal & FFT unit 204 converts the time domain signal excluding the guard interval into a subcarrier signal by FFT. A MIMO signal detection unit (QRD-MLD) 402 separates each substream based on a predetermined signal separation algorithm. Here, it is assumed that the MIMO signal detection unit (QRD-MLD) 402 uses a QRD-MLD method combining a QR decomposition (QR Decomposition) and a maximum likelihood detection (MLD) method as a signal separation algorithm. The QRD-MLD method is a method of converting the channel response of the received signal vector into an upper triangular matrix R by multiplying the received signal vector by the complex conjugate transpose of the unitary matrix Q obtained by QR decomposition of the channel matrix. When the QRD-MLD method is used, a more efficient transmission symbol vector search can be performed.

  The MIMO signal detection unit (QRD-MLD) 402 estimates received power for each substream corresponding to each transmission antenna before performing QR decomposition, and a channel matrix based on a comparison result of received power for each substream. Swap the column vectors of (ordering). Also, the decoding unit 210 performs decoding (decoding) on precoding based on ranking information for the transmission signal vector detected by the MIMO signal detection unit (QRD-MLD) 402. Then, the LLR calculation unit 404 performs modulation demapping on the decoded transmission signal vector, and calculates a log-likelihood ratio (LLR) for each bit (Log-Likelihood-Ratio). Further, the LDPC decoding unit 406 decodes the LDPC code.

  Here, the normal packet selection unit 214 determines that the packet data that has been decoded within a predetermined number of repetitions in decoding the LDPC code is correctly reproduced packet data. Conversely, the normal packet selection unit 214 determines that packet data that has not been decoded within a predetermined number of repetitions is packet data in which an error has occurred. In response to the result, the LDPC encoding unit 216 performs LDPC encoding on the correctly decoded packet data. Also, the modulation mapping unit 218 maps the LDPC encoded packet data to the modulation signal point. Then, the precoding unit 220 performs precoding on the obtained modulated signal. Further, replica generation section 222 generates a replica signal of the received signal using the channel estimation value for the precoded modulated signal. After that, the parallel interference canceller unit 206 subtracts the obtained replica signal from the received signal to generate a residual signal. Then, the MIMO signal detection unit (QRD-MLD) 402 estimates the transmission symbol vector again using the signal separation algorithm based on the QRD-MLD method.

(Transmission antenna ranking method: Modification 3)
Next, the transmission antenna ranking method will be briefly described with reference to FIG. The transmission antenna ranking method shown in FIG. 17 has the same basic configuration as the transmission antenna ranking method described in the first embodiment, but the minimum Euclidean distance check unit 502 and the ranking correction unit 504 The configuration is different.

  First, the minimum Euclidean distance estimation unit 226 for each substream estimates the minimum Euclidean distance for each transmission antenna using a channel matrix corresponding to the mth subcarrier. Also, the ranking information calculation unit 228 calculates the ranking information of the transmission antenna based on the minimum Euclidean distance for each transmission antenna. At this time, the minimum Euclidean distance check unit 502 detects whether there is a transmission antenna having the same minimum Euclidean distance. If there are transmission antennas having the same minimum Euclidean distance, the ranking correction unit 504 corrects the ranking using the reception power for each substream estimated by the reception power calculation unit 232 for each substream. Note that the reception power calculation unit 232 for each substream does not need to newly calculate reception power as long as the reception power calculation for each substream calculated when determining the ordering is held.

<Evaluation results>
FIG. 18 is a graph showing an average PER (Packet Error Rate) characteristic when the second embodiment of the present invention is applied. In FIG. 18, for comparison, (method 1) when QRD-MLD method is used, (method 2) when combination of PIC and QRD-MLD method is used, (method 3) ordering information based on received power is shown. When the combination of the precoding used, PIC, and QRD-MLD method is used (Method 4 (present invention)), the combination of precoding using ranking information based on the minimum Euclidean distance, PIC, and QRD-MLD method is used. The four evaluation results for each case are shown. Other main evaluation conditions are the number of transmission antennas N _T = 4, the number of reception antennas N _R = 4, error correction code = LDPC code, and modulation scheme = 16QAM.

  As is apparent from the graph shown in FIG. 18, the (method 4), which is the evaluation result of the present invention, performs precoding based on the received power for each substream as well as (method 1) and (method 2). It can be seen that the average PER characteristic is improved as compared with the result of (Method 3). That is, when a signal separation algorithm based on the MLD method is used for the MIMO signal detection means, the method of the present invention in which precoding is performed using ranking information based on the minimum Euclidean distance for each substream is particularly effective for increasing the estimation accuracy of transmission packets. As a result, it was confirmed that the transmission characteristics can be improved.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

It is explanatory drawing which shows the structural example of the general transmission apparatus which comprises a MIMO-OFDM signal detection system. It is explanatory drawing which shows the structural example of the general receiver which comprises a MIMO-OFDM signal detection system. It is explanatory drawing which shows the structural example of the general receiver which comprises the MIMO-OFDM signal detection system which combined PIC. It is explanatory drawing for demonstrating the problem which the general MIMO-OFDM signal detection system which combined PIC has. It is explanatory drawing which shows the structural example of the general MIMO-OFDM signal detection system which combined the precoding by ordering information of received power, and PIC. It is explanatory drawing which shows the effect of the precoding based on received power. It is explanatory drawing which shows the structural example of the transmitter which concerns on 1st Embodiment of this invention. It is explanatory drawing which shows the production | generation method of the precoding matrix which concerns on the embodiment. It is explanatory drawing which shows the production | generation method of the precoding matrix which concerns on the embodiment. It is explanatory drawing which shows the structural example of the receiver which concerns on the same embodiment. It is explanatory drawing which shows the transmission antenna ranking method which concerns on the same embodiment. It is explanatory drawing which shows the other transmission antenna ranking method which concerns on the same embodiment. It is explanatory drawing which shows the other transmission antenna ranking method which concerns on the same embodiment. It is explanatory drawing which shows grouping of the subcarrier which concerns on the same embodiment. It is explanatory drawing which shows the structural example of the transmitter which concerns on 2nd Embodiment of this invention. It is explanatory drawing which shows the structural example of the receiver which concerns on the same embodiment. It is explanatory drawing which shows the transmission antenna ranking method which concerns on the same embodiment. It is an evaluation result which shows the average PER characteristic at the time of applying the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Transmitter 102 Error correction encoding part 104 Modulation mapping part 106 Serial / parallel conversion part 108 Precoding part 110 Pilot channel multiplexing part 112 IFFT & GI addition part 114 Antenna 200 Receiver 202 Antenna 204 GI removal & FFT part 206 Parallel interference canceller part 208 MIMO Signal detection unit 210 Decoding unit 212 Error correction decoding unit 214 Positive packet selection unit 216 Error correction coding unit 218 Modulation mapping unit 220 Precoding unit 222 Replica generation unit 224 Channel estimation unit 226 Minimum Euclidean distance estimation unit for each substream 228 Ranking Information calculation unit 230 Dimensional reduced channel matrix generation unit 232 Received power calculation unit for each substream 300 Transmitter 302 LDPC encoding unit 304 Recoding matrix setting unit 400 Receiver 402 MIMO signal detection unit (QRD-MLD)
404 LLR calculation unit 406 LDPC decoding unit 502 Minimum Euclidean distance check unit 504 Ranking correction unit

Claims (16)

A communication system including a transmission device that transmits a plurality of transmission signals via corresponding transmission antennas and a reception device that receives the plurality of transmission signals,
The receiving device is:
A minimum Euclidean distance estimation unit that calculates a minimum Euclidean distance for each of the transmission antennas based on a channel matrix representing transmission characteristics of a wireless transmission path;
A ranking information generation unit that orders the transmission antennas based on the magnitude relation of the minimum Euclidean distance, and generates ranking information indicating the order of the transmission antennas;
A signal detector for estimating each of the transmission signals using the channel matrix;
A reception replica generation unit that generates a reception replica signal based on the correctly decoded transmission signal;
An interference canceller unit that generates a residual signal by subtracting the received replica signal from the received signal;
With
The transmitter is
A receiving unit for receiving the ranking information generated by the receiving device;
A precoding unit that allocates the predetermined transmission signal to each of the transmission antennas having the smallest minimum Euclidean distance based on the ranking information;
A transmitter that transmits the predetermined transmission signal via each of the transmission antennas assigned by the precoding unit;
A communication system comprising: The receiving device is:
A dimension-reduced channel matrix generation unit that generates a dimension-reduced channel matrix by excluding the column vector corresponding to the maximum value of the minimum Euclidean distance from the column vectors constituting the channel matrix;
The minimum Euclidean distance estimation unit is
The communication system according to claim 1, wherein a minimum Euclidean distance corresponding to each transmission antenna is calculated based on the dimension reduction channel matrix. The receiving device is:
A reception power calculation unit for calculating reception power corresponding to each transmission signal;
The ranking information calculation unit
3. The communication system according to claim 1, wherein the plurality of transmission antennas having a plurality of the minimum Euclidean distances having the same value are ordered in order of the transmission antenna having the large reception power. 4. A communication method of transmitting a plurality of transmission signals via corresponding transmission antennas and receiving the plurality of transmission signals,
On the receiving side,
A minimum Euclidean distance estimation step for calculating a minimum Euclidean distance for each transmission antenna based on a channel matrix representing transmission characteristics of a wireless transmission path;
A ranking information generation step of ordering the transmission antennas based on the magnitude relation of the minimum Euclidean distance and generating ranking information indicating the order of the transmission antennas;
A signal detection step of estimating each of the transmission signals using the channel matrix;
A reception replica generation step for generating a reception replica signal based on the correctly decoded transmission signal;
An interference canceller step of generating a residual signal by subtracting the received replica signal from the received signal;
Including
On the sender side,
Receiving the ranking information generated by the receiving device; and
A precoding step of allocating the predetermined transmission signal to each of the transmission antennas having the minimum minimum Euclidean distance based on the ranking information;
A transmission step of transmitting the predetermined transmission signal via each of the transmission antennas assigned by the precoding unit;
A communication method comprising: On the receiving side,
A dimension reduced channel matrix generating step of generating a dimension reduced channel matrix by excluding the column vector corresponding to the maximum value of the minimum Euclidean distance from the column vectors constituting the channel matrix;
In the minimum Euclidean distance estimation step,
5. The communication method according to claim 4, wherein a minimum Euclidean distance corresponding to each transmission antenna is calculated based on the dimension reduction channel matrix. On the receiving side,
A reception power calculation step of calculating reception power corresponding to each transmission signal;
In the ranking information calculation step,
6. The communication method according to claim 4, wherein, for a plurality of the transmission antennas having a plurality of the minimum Euclidean distances, the transmission antennas having a large received power are ordered in a higher order. A receiving device that receives a plurality of transmission signals transmitted from a plurality of transmitting antennas,
A minimum Euclidean distance estimation unit that calculates a minimum Euclidean distance for each of the transmission antennas based on a channel matrix representing transmission characteristics of a wireless transmission path;
A ranking information generator for ordering the transmission antennas based on the magnitude relationship of the minimum Euclidean distance;
A signal detector for estimating each of the transmission signals using the channel matrix;
A reception replica generation unit that generates a reception replica signal based on the correctly decoded transmission signal;
An interference canceller unit that generates a residual signal by subtracting the received replica signal from the received signal;
A receiving apparatus comprising: A dimension-reduced channel matrix generation unit that generates a dimension-reduced channel matrix by excluding the column vector corresponding to the maximum value of the minimum Euclidean distance from the column vectors constituting the channel matrix;
The minimum Euclidean distance estimation unit is
The receiving apparatus according to claim 7, wherein a minimum Euclidean distance corresponding to each transmission antenna is calculated based on the dimension reduction channel matrix. The dimension reduction channel matrix generation unit includes:
The column vector corresponding to the maximum value of each minimum Euclidean distance calculated for the dimension-reduced channel matrix is excluded from the column vectors constituting the dimension-reduced channel matrix, and the dimension is further reduced. 9. The receiving apparatus according to claim 8, wherein the receiving apparatus generates a reduced dimension channel matrix. A reception power calculation unit for calculating reception power corresponding to each transmission signal;
The ranking information calculation unit
The receiving apparatus according to any one of claims 7 to 9, wherein a plurality of transmitting antennas having the same minimum Euclidean distance are arranged in a higher order with respect to a plurality of transmitting antennas having a large received power. The minimum Euclidean distance estimation unit is
Using the plurality of channel matrices estimated for each subcarrier, each calculating a minimum Euclidean distance for each of the transmission antennas,
The ranking information calculation unit
The receiving apparatus according to any one of claims 7 to 10, wherein the ranking information for each subcarrier is generated based on a magnitude relation of the minimum Euclidean distance. A plurality of transmission antennas for transmitting a plurality of transmission signals are provided, and a predetermined transmission signal is assigned to the predetermined transmission antenna so that a minimum Euclidean distance is maximized in a receiving apparatus that receives the plurality of transmission signals. A possible transmission device,
A receiving unit that receives ranking information of the transmission antennas generated based on a magnitude relationship of the minimum Euclidean distance estimated for each transmission antenna;
Based on the ranking information, a precoding unit that allocates the predetermined transmission signal to each of the transmission antennas with the minimum minimum Euclidean distance;
A transmitter that transmits the predetermined transmission signal via each of the transmission antennas assigned by the precoding unit;
A transmission device comprising: A serial-parallel conversion unit that performs serial-parallel conversion on the transmission packet to generate a plurality of transmission signals corresponding to a plurality of subcarriers,
The receiver is
Receiving the ranking information of the transmitting antenna calculated based on the magnitude relation of the minimum Euclidean distance for each subcarrier;
The precoding unit includes:
The transmission according to claim 12, wherein all the transmission signals corresponding to the transmission packet are allocated to the transmission antennas with the minimum minimum Euclidean distance based on ranking information for each subcarrier. apparatus. The precoding unit includes:
Based on the ranking information for each subcarrier, all the transmission signals corresponding to the nth (n = 1 to N _T , where N _T is the number of transmission antennas) transmission packets are set to the minimum Euclidean distance for each subcarrier. The transmission apparatus according to claim 13, wherein the transmission apparatus is assigned to each of the transmission antennas having the highest nth. The receiver is
Receiving ranking information for each of the subcarriers for each of the transmission antennas up to the top Nth (N <N _T , where N _T is the number of transmission antennas) having the smallest minimum Euclidean distance;
The precoding unit includes:
Based on the ranking information, all the transmission signals corresponding to the nth (n = 1 to N) transmission packets are allocated to the respective transmission antennas having the lowest n Euclidean distance. The transmission device according to claim 13. The receiver is
Receiving the ranking information generated based on the minimum Euclidean distance for each subcarrier group composed of a plurality of adjacent subcarriers;
The precoding unit includes:
The base station according to claim 14 or 15, wherein all transmission signals corresponding to the subcarrier group are allocated to the transmission antennas having the minimum minimum Euclidean distance based on ranking information for each subcarrier group. The transmitting device described.

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