JP5579551B2 - Receiving device, receiving method and program - Google Patents

Description

  The present invention relates to a receiving device used in a communication system that makes an automatic retransmission request.

  In the field of wireless communication, channel estimation is performed by a receiving device in order to grasp the state of wireless propagation. Since the receiving apparatus performs demodulation and decoding using the channel estimation result, if the channel estimation accuracy is deteriorated, the transmission characteristics are also greatly deteriorated.

  In many cases, channel estimation is performed using a pilot signal which is a known signal in a transmission / reception apparatus. In general, if many pilot signals are arranged in a transmission signal, channel estimation accuracy is improved. However, when the pilot signal increases, the data signal decreases, so the data rate decreases. Therefore, in order to perform high-speed data transmission, a technique for improving channel estimation accuracy without increasing the pilot signal is required.

  Conventionally, for example, Patent Literature 1 discloses a technique for improving channel estimation accuracy using HARQ (Hybrid Automatic Repeat reQuest). FIG. 12 is a flowchart of the channel estimation method of Patent Document 1.

  In step s511, the receiving apparatus performs channel estimation on the received data block p, obtains a data symbol estimation value, demodulates the data symbol estimation value, and performs data bit estimation (for example, coded bit LLR (Log Likelihood Ratio: Log Likelihood Ratio). )). In step s512, the data bit estimation is subjected to error correction decoding, and a data determination value (data bit estimation, for example, encoded bit LLR in Patent Document 1) is obtained. Step s513 performs channel estimation of the following block p + 1 using the coded bit LLR. The data of block p and block p + 1 are related. As described above, in Patent Document 1, since the data determination value of the block p transmitted immediately before is regarded as a pilot signal and the channel estimation of the block p + 1 is performed, the channel estimation accuracy of the block p + 1 can be improved.

Special table 2008-518522 gazette

  However, in Patent Document 1, the propagation path estimation accuracy of block p + 1 depends on the reliability of the data determination value of block p. For example, when the reliability of the data determination value of block p is low, the propagation path estimation accuracy of block p + 1 is increased. There was a problem that it could hardly be improved.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a receiving apparatus and the like that can improve the propagation path estimation accuracy of the block p + 1 without using a data determination value.

  In order to solve the above-mentioned problems, the present invention employs the configuration described below and has the following features.

The receiving apparatus of the present invention is a receiving apparatus used in a communication system that performs an automatic retransmission request,
A reception unit that receives an initial transmission signal and at least one retransmission signal as a reception signal;
A channel estimation unit for performing channel estimation on the latest retransmission signal received by the reception unit to obtain a frequency response estimation value;
A channel information generator for generating channel information from a received signal prior to the latest retransmission signal,
The channel estimation unit obtains the frequency response estimation value using the channel information.

The receiving apparatus of the present invention includes a scattered pilot signal,
The channel estimation unit obtains the frequency response estimation value using the scattered pilot signal and the channel information.

  In the receiving apparatus of the present invention, the channel information is channel statistics.

  In the receiving apparatus of the present invention, the channel statistic is time correlation, and the frequency response estimation value is obtained using the time correlation.

  In the receiving apparatus of the present invention, the channel statistic is a frequency correlation, and the frequency response estimation value is obtained using the frequency correlation.

  In the receiving apparatus of the present invention, the channel statistic is a path position, and the frequency response estimated value is obtained from a channel impulse response estimated value using the path position.

  In the receiving apparatus of the present invention, the statistics of the channel are time correlation and frequency correlation, and the frequency response estimation value is obtained using the time correlation and frequency correlation.

  In the receiving apparatus of the present invention, the statistics of the channel are time correlation and path position, a channel impulse response estimation value is obtained using the time correlation and path position, and the frequency response estimation is performed from the channel impulse response. It is characterized by obtaining a value.

  In the receiving apparatus of the present invention, the channel information is a channel estimation value.

  Further, in the receiving apparatus of the present invention, the channel estimation value is a channel impulse response estimation value, and the channel estimation unit uses the forgetting coefficient to determine the channel in the latest retransmission signal and the reception signal before the retransmission signal. The impulse response estimation value is synthesized.

  Further, in the receiving apparatus of the present invention, the channel estimation value is a frequency response estimation value, and the channel estimation unit uses the forgetting coefficient to determine the channel impulse in the latest retransmission signal and the reception signal before the retransmission signal. A response estimation value is synthesized.

  In the receiving apparatus of the present invention, the channel estimation unit uses the forgetting coefficient and a signal received during a period of the latest retransmission signal and the previous retransmission signal in addition to a reception signal before the retransmission signal. Channel estimation.

  In the receiving apparatus of the present invention, the channel information is a channel statistic and a channel estimation amount, and the channel estimation unit uses the channel statistic and the channel estimation value to transmit the latest retransmission signal and the retransmission information. The channel impulse response estimation value or the frequency response estimation value in the received signal before the signal is synthesized.

  In the receiving apparatus of the present invention, the channel estimation unit obtains a frequency response estimated value from the scattered pilot signal, the channel information, and a data determination value in the previous received signal.

  In the receiving apparatus of the present invention, the channel estimation unit obtains a channel impulse response using the scattered pilot signal, the channel information, and a data determination value in the previous received signal, and then calculates the frequency response estimated value. It is characterized by seeking.

  In the receiving apparatus of the present invention, the channel estimation unit obtains the frequency response estimated value by performing interpolation in time and frequency directions.

  In the receiving apparatus of the present invention, a soft decision value is used as the data decision value.

  In the receiving apparatus of the present invention, the soft decision value equal to or greater than a certain threshold is used as the data decision value.

  In the receiving apparatus of the present invention, a hard decision value is used as the data decision value.

  In the receiving apparatus of the present invention, the hard decision value is weighted.

  In the receiving apparatus of the present invention, the weight used when the hard decision value is weighted is obtained according to the reliability of the soft decision value.

The receiving method of the present invention includes:
A receiving method used in a communication system that performs an automatic retransmission request,
A reception process of receiving an initial transmission signal and at least one retransmission signal as a reception signal;
A channel estimation process for performing frequency estimation on the latest retransmission signal received by the reception process to obtain a frequency response estimate;
Generating channel information from a received signal before the latest retransmission signal, and
In the channel estimation process, the frequency response estimation value is obtained using the channel information.

The program of the present invention
A program executed in a receiving device used in a communication system that performs an automatic retransmission request,
A reception function for receiving an initial transmission signal and at least one retransmission signal as a reception signal;
A channel estimation function for performing frequency estimation on the latest retransmission signal received by the reception function to obtain a frequency response estimation value;
A channel information generating function for generating channel information from a received signal prior to the latest retransmission signal; and
The channel estimation function realizes obtaining the frequency response estimation value using the channel information.

  As described above, in the present invention, channel estimation is performed using channel information obtained from the previous transmission. Therefore, even if the reliability of the data determination value is low, the channel estimation accuracy during retransmission can be improved.

It is a figure for demonstrating the function structure of the transmitter in 1st Embodiment. It is a figure for demonstrating the function structure of the encoding part in 1st Embodiment. It is a figure for demonstrating operation | movement of the puncture part in 1st Embodiment. It is a schematic diagram for demonstrating the signal in 1st Embodiment. It is a figure for demonstrating the function structure of the receiver in 1st Embodiment. It is a figure for using for operation | movement description in 1st Embodiment. It is a flowchart for demonstrating the reception process in 1st Embodiment. It is a figure for using for operation | movement description in 2nd Embodiment. It is a flowchart for demonstrating the reception process in 2nd Embodiment. It is a figure for demonstrating the function structure of the receiver in 3rd Embodiment. It is a flowchart for demonstrating the reception process in 3rd Embodiment. It is a flowchart for demonstrating the process of the conventional receiver.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

[1. First Embodiment]
FIG. 1 is a block diagram showing a configuration of a transmission apparatus 10 in the present embodiment. Transmitting apparatus 10 includes encoding section 101, interleaving section 102, modulating section 103, pilot signal generating section 104, pilot signal multiplexing section 105, IFFT (Inverse Fast Fourier Transform) section 106, transmission signal information multiplexing section. 107, a GI (Guard Interval) insertion unit 108, a radio transmission unit 109, a radio reception unit 110, a GI removal unit 111, an FFT unit 112, a demodulation unit 113, and a response signal analysis unit 114.

  Encoding section 101 performs error correction encoding on the encoded bits and outputs encoded bits at a predetermined encoding rate. Here, the encoding unit 101 will be described in detail with reference to the drawings.

  FIG. 2 is a block diagram illustrating a configuration of the encoding unit 101. The encoding unit 101 includes an error correction encoding unit 201, a transmission data storage unit 202, and a puncturing unit 203.

  The error correction encoding unit 201 is a functional unit that encodes input information bits using an error correction code such as a convolutional code or a turbo code. The encoded information bits are output to the transmission data storage unit 202 and the puncture unit 203.

  The transmission data storage unit 202 is a functional unit that stores encoded information bits. The puncturing unit 203 performs puncturing processing on the encoded information bits with a predetermined pattern, and outputs the encoded bits. The signal stored in the transmission data storage unit 202 is transmitted at the time of retransmission.

  FIG. 3 shows an example of a turbo code puncture pattern with a coding rate of 1/3 in the puncturing unit 203. In the figure, x indicates information bits, and p1 and p2 indicate redundant bits (parity bits) generated from the information bits in the error correction encoding unit. In the figure, 1 represents a bit to be transmitted and 0 represents a bit not to be transmitted.

Pattern 1 is a pattern for setting a predetermined coding rate. CC is one of retransmission methods for transmitting transmission data for the first time (initial transmission) or HARQ (Hybrid Automatic Repeat Request). Used when (Chase Combining) is used. A case of pattern 1 with a coding rate of 1/2 will be described as an example. Now, a sequence with a coding rate of 1/3 is assumed to be [i ₁ p _1,1 p _2,1 i ₂ p _1,2 p _2,2 ]. i ₁ and i ₂ are information bits, p _1,1 , p ₁ and ₂ are parity bits 1, and p _2,1 and p _2,2 are parity bits 2. At this time, when puncturing is performed with a pattern 1 with a coding rate of 1/2, a sequence with a coding rate of 1/2 [i ₁ p _1,1 i ₂ p _2,2 ] is obtained.

Pattern 2 is used when using IR (Incremental Redundancy) which is one of HARQ retransmission methods. There are several types of methods for performing IR. For example, a type of transmitting information bits at the time of retransmission and a parity bit that was not transmitted at the time of initial transmission (example of coding rate 1/2), a type of transmitting a parity bit that was not transmitted at the time of initial transmission at the time of retransmission (coding rate) 3/4 example). For example, a case where a pattern 2 with a coding rate of 1/2 is used will be described. Similar to the example of pattern 1, when a sequence [i ₁ p _1,1 p _2,1 i ₂ p _1,2 p _2,2 ] with a coding rate of 1/3 is punctured, a sequence with a coding rate of 1/2 [I ₁ p _2,1 i ₂ p _1,2 ], and a parity bit different from that of the pattern 1 is transmitted.

  Returning to the description of FIG. 1 again. The coded bits output from the coding unit 101 are interleaved by the interleaving unit 102, and modulated by the modulation unit 103 such as PSK (Phase Shift Keying) and QAM (Quadrature Amplitude Modulation). Maps to a symbol. The pilot signal generation unit 104 generates a pilot signal that is a known signal on the transmission / reception side. Pilot signal multiplexing section 105 multiplexes modulation symbols and pilot signals in a predetermined pattern.

  FIG. 4 shows an example of mapping between pilot signals and information data modulation symbols. In FIG. 4, the horizontal axis represents time, the vertical axis represents frequency, the pilot signal is represented in black, and the information data modulation symbol is represented in white. Although there are a plurality of OFDM symbols having pilot signals discretely arranged in the frequency direction, the arrangement of pilot signals in which subcarriers (referred to as pilot subcarriers) in which pilots are arranged is different is shown. An information data modulation symbol is arranged on a subcarrier on which no pilot signal is arranged. A subcarrier in which an information data modulation symbol is arranged is called a data subcarrier. Note that the discretely arranged pilot signals are referred to as scattered pilot signals.

  The output of pilot signal multiplexing section 105 is frequency-time converted by IFFT section 106 and multiplexes information related to transmission signals such as whether the data transmitted by transmission signal information multiplexing section 107 is the initial transmission or retransmission. The transmission signal information may be transmitted so that it can be separated on the receiving side. For example, time division multiplexing, frequency division multiplexing, and code division multiplexing can be performed.

  The GI insertion unit 108 inserts a GI into the frequency-time converted signal. The wireless transmission unit 109 performs digital-analog conversion, frequency conversion, and the like on the signal into which the GI is inserted and transmits the signal.

  The wireless reception unit 110 receives a signal including a response signal transmitted from the receiver, and performs frequency conversion and analog-digital conversion. In this response signal, the receiving apparatus 20 notifies the transmitting apparatus 10 whether the information bits transmitted from the transmitting apparatus to the receiving apparatus have been correctly received (ACK: ACKnowledgement) or not correctly received (NACK: Negative ACKnowledgement). Signal.

  The GI removal unit 111 removes the GI, the FFT (Fast Fourier Transform) unit 112 performs time frequency conversion, and the demodulation unit 113 performs demodulation.

  The response signal analysis unit 114 analyzes the response signal with respect to the demodulated signal, and determines whether the information bit transmitted from the transmission device 10 to the reception device 20 is ACK or NACK. When the response signal is ACK, retransmission is not performed. On the other hand, when the response signal is NACK, retransmission is performed. In the case of the above-described retransmission by CC, the same coded bits as the initial transmission are retransmitted. In the case of IR, encoded bits including parity bits that are not transmitted in the initial transmission are retransmitted.

  FIG. 5 is a block diagram showing a configuration of the receiving device 20 in the present embodiment. The reception apparatus 20 includes a radio reception unit 501, a GI removal unit 502, a separation unit 503, a transmission signal information analysis unit 504, an FFT unit 505, a channel estimation unit 506, a channel information generation unit 507, a propagation path compensation unit 508, and a demodulation unit 509. A deinterleave unit 510, a received signal storage unit 511, a HARQ synthesis unit 512, a decoding unit 513, a retransmission control unit 514, a response signal generation unit 515, a modulation unit 516, an IFFT unit 517, a GI insertion unit 518, and a radio transmission unit 519. Consists of including.

  First, a case where an initial transmission signal is received will be described. The wireless reception unit 501 performs frequency conversion, analog-digital conversion, and the like on the received signal. The GI is removed from the signal output from the wireless reception unit 501 by the GI removal unit 502, and the transmission signal information is separated by the separation unit 503.

  Based on the transmission signal information separated by the separation unit 503, the transmission signal information analysis unit 504 obtains information on the transmission signal such as whether the received signal is an initial transmission or a retransmission, and the result is obtained as a channel estimation unit 506. The data is output to the HARQ combining unit 512.

  The FFT unit 505 performs time-frequency conversion on the received signal excluding the transmission signal information separated by the separation unit 503. Since it is an initial transmission signal now, the channel information generation unit 507 does not have information on the channel (channel information). Therefore, channel estimation section 506 performs channel estimation using the pilot signal and obtains a channel estimation value. The channel estimation value includes a channel impulse response estimation value and a frequency response estimation value. The channel information generation unit 507 obtains channel statistics mainly using channel estimation values.

  The propagation path compensation unit 508 performs propagation path compensation on the received signal using the channel estimation value obtained by the channel estimation unit 506. The signal after propagation path compensation is demodulated by the demodulator 509, and the coded bit LLR (Log Likelihood Ratio) is output. Deinterleaving section 510 performs deinterleaving with a reverse pattern of interleaving performed on the transmission side. The output of deinterleaving section 510 is output to received signal storage section 511 and HARQ combining section 512.

  The HARQ combining unit 512 performs LLR combining of the bit LLR obtained from the received signal storage unit 511 obtained up to the previous retransmission and the output of the deinterleaving unit 510, and depunctures the bits that have not been transmitted yet. In the case of the initial transmission signal, only depuncturing is performed.

  The decoding unit 513 performs error correction decoding on the output of the HARQ combining unit 512. The retransmission control unit 514 determines whether or not there is an error in the error correction decoding result, and generates error detection information. When it is determined that there is no error in the decoding result, information bits obtained by decoding are output, and error detection information indicating that there is no error is output to the response signal generation unit 515. On the other hand, if it is determined that there is an error in the decoding result, error detection information indicating that there is an error is output to response signal generation section 515. Note that CRC (Cyclic Redundancy Check) can be used to determine whether or not there is an error in the decoding result.

  The response signal generation unit 515 generates an ACK or NACK response signal based on the error detection information output from the retransmission control unit 514. Modulation section 516 maps the response signal to a modulation symbol, and IFFT section 517 performs frequency time conversion on the modulation symbol. The GI insertion unit 518 inserts a guard interval into the frequency-time converted signal, and the wireless transmission unit 519 performs digital-analog conversion, frequency conversion, and the like and transmits the signal.

  Next, a case where a retransmission signal is received will be described. Here, the retransmission signal represents a transmission signal after the second HARQ. Here, description will be made centering on channel estimation section 506 and HARQ combining section 512 whose processing changes when a retransmission signal is received. In the case of a retransmission signal, the channel estimation unit 506 of the present embodiment performs channel estimation using the channel statistics generated by the channel information generation unit 507. Channel statistics include, for example, path position, frequency correlation, time correlation, power delay profile, and the like.

  Since the channel statistic is considered not to change much with time, if the channel statistic is obtained when the previous transmission is performed, the statistic can be used for channel estimation of the current transmission. If channel statistics are used for channel estimation, channel estimation accuracy can be improved even with the same number of pilots. The details of channel statistic calculation and channel estimation using the statistic will be described below.

In the present embodiment, the case of the pilot arrangement as shown in FIG. 4 will be described. When the pilot signals are discretely arranged as shown in FIG. 4, the frequency response of the pilot subcarrier can be estimated by the pilot signal, but the frequency response of the data subcarrier cannot be directly obtained by the pilot signal. Therefore, it is necessary to interpolate the frequency response of the data subcarrier using the frequency response of the pilot subcarrier. MMSE (Minimum Mean Square Error) channel estimation is a technique for obtaining good channel estimation accuracy under such conditions. MMSE channel estimation is performed as follows.

Incidentally, H ^ _p is the frequency response vector of the pilot subcarrier, F _p is the line size of the number of pilot sub-carrier, the column size of the Fourier transform matrix of pass number. h is the channel impulse response to be estimated. E [] represents an expected value. ＾ is the estimated channel impulse response, and the frequency response of the data subcarrier can be obtained with high accuracy by Fourier transforming this. Specifically, h ^ may be obtained as in (2).

  Note that an optimum value of α is determined by SNR (signal-to-noise power ratio), but an appropriate fixed value such as 0.001 may be used without obtaining the optimum value. Although this MMSE channel estimation can obtain the frequency response of the data subcarrier with excellent accuracy, it is necessary to know the path position of the channel impulse response.

  In the present embodiment, the channel information generation unit 507 obtains a path position at the previous transmission (or transmission up to the previous) of HARQ. For example, the pass position can be obtained as follows. It is possible to IFFT the frequency response of the pilot subcarrier, select a path with a large amplitude, and obtain the path position. Further, after responding with NACK in the previous transmission, it is also possible to obtain the path position by performing repeated channel estimation in which channel estimation, demodulation and decoding are repeated. Alternatively, a path position where the estimation accuracy of the frequency response is maximized may be obtained using an information criterion.

Next, a technique for obtaining the frequency response of data subcarriers using channel correlation will be described. Channel correlation includes time correlation and frequency correlation. For example, as shown in FIG. 6, the frequency response estimate H _d data subcarrier from the frequency response estimate H1~H4 obtained from the pilot can be determined as follows.

<> Represents a set average, H is a four-dimensional vector having the frequency response of pilot subcarriers as elements, H ^ = [H1, H2, H3, H4] ^T , σ _n ² is noise power, and I ₄ is A 4-by-4 unit matrix is represented, and a superscript T represents a transposed matrix. Also, a superconjugate H complex conjugate transpose matrix is represented. R _d represents the correlation between H _d and H ^ as follows.

Σ _t () represents time correlation, and σ _f () represents frequency correlation. Further, t _n represents an nOFDM symbol interval, and f _n represents an n subcarrier interval. Further, σ _t ^* (t) = σ _t (−t) and σ _f ^* (f) = σ _f (−f). The superscript * represents a complex conjugate.

Furthermore, σ _t and σ _f can be obtained as follows, for example.

J ₀ is a first-order zeroth-order Bessel function, f _D is a maximum Doppler frequency, τ _D is a maximum delay time of a channel impulse response, and τ _rms is a delay spread. The maximum Doppler frequency can be obtained by f _D = vf _c / c, where the carrier frequency f _c , the speed of light c, and the moving speed v of the terminal. The moving speed of the terminal can be measured using, for example, GPS (Global Positioning System). τ _D and τ _rms can be calculated from the power delay profile obtained from the channel impulse response. Even if only the power delay profile is used, the frequency correlation can be obtained as in the following equation.

Here, F _p is a Fourier transform matrix whose row size is the number of subcarriers for obtaining frequency correlation and column size is the number of paths, and _Ch is a diagonal matrix having a power delay profile as a diagonal element. In the above equation, the correlation between subcarriers corresponding to the row elements of F _p can be obtained.

  It is not always necessary to obtain both time correlation and frequency correlation, and only one of them may be obtained. When the correlation value is not calculated, the correlation value may be set to 1, or another fixed value may be used.

  Further, the channel estimation value obtained at the previous retransmission can also be used. This can be done by updating the channel estimation value at the previous retransmission using time correlation using H1 to H4 in FIG. 6 and obtaining Hd using the updated H1 to H4. By using the channel estimation value at the time of the previous retransmission, the accuracy of estimating the frequency response of the pilot subcarrier is improved, so that the accuracy of interpolation can also be improved.

  Next, the reception process in this embodiment is demonstrated using the flowchart of FIG. First, in step s701, the p-1th retransmission signal is received, and reception processing is performed. Note that p> 2, and the first retransmission signal represents the initial transmission signal. An error is detected in the p-1th reception process, and a NACK is returned.

  In step s702, a statistic of a channel is calculated as channel information using the p-1 retransmission signal or the p-1 retransmission signals. Step s703 receives the p-th retransmission signal.

  In step s704, channel estimation is performed using the channel information obtained in step s702 and the pilot signal received by the p-th retransmission signal. Step s705 performs channel compensation using the channel estimation value. In step s706, demodulation processing and decoding processing are performed on the signal after propagation path compensation, and error detection is performed. Step s707 generates a response signal according to the error detection result and responds to the transmitting side.

  As described above, in this embodiment, since channel estimation at the current transmission is performed using the statistics of the channel at the previous transmission in HARQ, channel estimation with high accuracy is possible.

[2. Second Embodiment]
In the first embodiment, channel estimation is performed using channel information such as channel statistics and estimated values at the time of previous retransmission. Next, in the second embodiment, a technique for updating the channel estimation value at the previous retransmission until the next retransmission signal is transmitted will be described.

  Since this embodiment is different from the first embodiment in the channel estimation unit and the channel information generation unit, other description is omitted.

The receiving apparatus receives the common pilot signal even when data is not transmitted. The common pilot signal can be received by a receiving apparatus belonging to the cell. Therefore, the channel estimation value can be updated until the next retransmission signal is sent. The channel estimation value can be updated using a forgetting factor. An example will be described with reference to FIG. If the frequency response of the n-th subcarrier after updating the i-th received signal is H to _{i, n} , H to _n can be obtained as follows, for example.

However, H ^ _{i, n} represents the frequency response estimation value of the n-th subcarrier of the received signal for the i-th time, and λ is a forgetting factor. (7) represents the update from the (i-1) th time, but it is also possible to update from a plurality of past signals as in (8), (9), and (10).

However, i = 0 may be the time of the previous retransmission, b _{0, n} may be the estimated frequency response value for the previous retransmission, and a _{0, n} = 1.

  As described above, if the channel estimation value from the (p-1) th retransmission to the pth retransmission is updated, the estimation accuracy of the frequency response of the pilot subcarrier is improved, so that the accuracy of the frequency response estimation of the data subcarrier is also improved. . It is also possible to update only from the (p-1) th retransmission without updating between the (p-1) th retransmission and the pth retransmission.

  In addition, although the past signal was used in order to improve the estimation accuracy of the p-th retransmission signal, it is also possible to use a future signal. This is achieved by updating the channel estimation value of the p-th retransmission signal using the common pilot signal received after receiving the p-th retransmission signal.

  FIG. 9 is a flowchart of the reception process of the second embodiment. In step s901, a NACK response is made to the p-1th retransmission signal. In step s902, it is determined whether the p-th retransmission signal is received. If the p-th retransmission signal is not received, the channel estimation value is updated using the common pilot signal in step s903. In step s902, it is determined again whether the p-th retransmission signal has been received.

  When the p-th retransmission signal is received, channel estimation is performed in step s904 using the pilot signal of the p-th retransmission signal and the updated channel estimation value generated in step s903. Thereafter, propagation path compensation is performed in step s905, error detection is performed after demodulation and decoding in step s906, a response signal is transmitted in step s907, and the process ends.

  In the present embodiment, the case where the channel estimation value at the previous retransmission is updated until the next retransmission using the forgetting factor has been described. However, the channel estimation may be updated using the statistics of the channel. When channel statistics are used, Equation (3) described in the first embodiment may be used.

[3. Third Embodiment]
Next, a third embodiment will be described. In the third embodiment, a technique for performing channel estimation using a data determination value in addition to channel information obtained at the previous retransmission will be described.

  FIG. 10 is a block diagram showing the configuration of the receiving device 23 in the third embodiment. The reception device 23 includes a radio reception unit 501, a GI removal unit 502, a separation unit 503, a transmission signal information analysis unit 504, an FFT unit 505, a channel estimation unit 1006, a channel information generation unit 507, a propagation path compensation unit 508, and a demodulation unit 509. A deinterleave unit 510, a received signal storage unit 511, a HARQ synthesis unit 512, a decoding unit 513, a retransmission control unit 514, a response signal generation unit 515, a modulation unit 516, an IFFT unit 517, a GI insertion unit 518, and a radio transmission unit 519. It is configured to include.

  Since the receiving apparatus of the third embodiment is different from the first and second embodiments in the channel estimation unit 1006, the channel estimation unit 1006 will be described. In addition, the same code | symbol is attached | subjected to the function part same as 1st, 2nd embodiment, and description is abbreviate | omitted. The channel estimation unit 1006 of the third embodiment performs channel estimation using the encoded bit LLR obtained from the decoding unit 513 in addition to the channel information obtained from the channel information generation unit 507.

  The channel estimation of the third embodiment will be described with reference to FIG. In the figure, black fill is a pilot signal, and hatched lines with left and right diagonal lines are modulation symbol replicas. The modulation symbol replica is a modulation symbol replica obtained from the data determination value. Channel estimation is performed using pilot signals and modulation symbol replicas. The data judgment value includes a soft judgment value and a hard judgment value.

In order to generate a symbol replica, a hard decision value may be mapped to a modulation symbol in the same manner as in the transmission apparatus. In the case of a soft decision value, QPSK will be described as an example. Two bits constituting the QPSK symbol are b ₀ and b _1, and each bit LLR is represented by λ (b ₀ ) and λ (b ₁ ). At this time, the symbol replica X of QPSK is obtained as follows.

The received signal Y _k when the data modulation symbol S _k is transmitted on the k-th subcarrier is expressed as follows. H _k is a frequency response, and N _k is noise.

And a replica of the S _k and S _{^ k,} the frequency response estimate H _{^ k} obtained from S _{^ k} is as follows.

Let H ^ be the frequency response estimated value vector. H ^ has frequency response estimation values estimated from all H ^ _k and pilot signals as elements. The channel impulse response estimation value h ^ can be obtained on the basis of the MMSE using the path position obtained in the retransmission from H ^ to the previous time as follows.

A frequency response estimation value can be obtained by performing a Fourier transform on ＾ obtained by Expression (14). When a soft decision value is used, if S _k is unreliable, the amplitude of S _k is small. At this time, Equation (13) becomes a very large value. In order to avoid this, when performing channel estimation using soft decision values, it is only necessary to use symbol replicas with a certain degree of reliability.

Next, a case where a hard decision value is used will be described. The symbol replica obtained from the hard decision value may be used in the same manner as the pilot signal, but weighting may be performed according to the reliability of the symbol replica. If H ^ is a vector having elements of frequency response estimation values estimated from pilot signals and hard decision value symbol replicas, a channel impulse response estimation value can be obtained as follows.

Q is a diagonal matrix having the weight of each symbol replica as a diagonal element. The weight can be obtained by the ratio of the power of the soft decision symbol replica and the power of the hard decision symbol replica. That, _{S 1} soft-decision symbol replica, hard decision symbol replica _{S 2,} and when the weight is _| S ¹ _| 2 _{/ |} may be the ^{2 |} S 2. If | S ₂ | ² = 1, the weight of the soft decision symbol replica can be obtained only by S ₁ .

The data determination value can also be used for time / frequency interpolation. Only the hard decision value symbols may be used for time / frequency interpolation, or weighting may be performed according to the reliability of the symbol replica as described above. This can be done by transforming Equation (3) as follows using Q.

  The third embodiment can be applied to all HARQ schemes in CC and IR. In the case of CC, the description may be applied as it is. In the case of IR, if duplicate bits are transmitted in the previous retransmission and the current retransmission, it can be easily applied. Even for bits that do not overlap (that is, have never been transmitted), the bit LLR can be obtained by error correction decoding and can be applied.

  As described above, in the third embodiment, channel estimation is performed using the data determination value at the previous retransmission in addition to the channel information. For this reason, the number of pilot signals can be virtually increased, and the channel estimation accuracy can be improved.

[4. Modified example]
The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and the design and the like within the scope of the present invention are also within the scope of the claims. include.

  In the first to third embodiments, the case of the scattered pilot has been described, but the present invention is not limited to this.

  In the first to third embodiments, OFDM has been mainly described as an example. However, the present invention is not limited to this, and other multi-carrier schemes such as MC-CDMA (Multi-Carrier-Code Division Multiple Access). It is also applicable to single carrier schemes such as SC-FDMA (Single Carrier-Frequency Division Multiple Access) and CDMA.

  In the first to third embodiments, the case of a single antenna has been described. However, the present invention is not limited to this, and the present invention is also extended to MIMO (Multiple Input Multiple Output) transmission having a plurality of antennas on the transmission / reception side. be able to. For example, in the case of MIMO transmission with two transmission antennas and two reception antennas, transmission antenna 1 and reception antenna 1, transmission antenna 1 and reception antenna 2, transmission antenna 2 and reception antenna 1, and transmission antenna 2 and reception Each channel of the antenna 2 may be estimated as in the above embodiment.

  In the first to third embodiments, the case where the modulation scheme is not changed during retransmission has been described. However, the present invention is not limited to this. As the modulation method, a modulation method having a larger multi-level number than that in the previous retransmission may be used, or a modulation method having a smaller multi-value number may be used. When transmitting with the same number of bits as in the previous retransmission, if a large multi-level modulation scheme is used, transmission can be performed with fewer resources (for example, the number of subcarriers, etc.) than before. When a large multi-level modulation scheme is used, transmission is performed with more resources than the previous time. In addition, when the same number of resources as in the previous retransmission are used, a larger number of bits than in the previous retransmission can be transmitted when a large multi-level modulation scheme is used. When a small multi-level modulation scheme is used, a smaller number of bits are transmitted than in the previous retransmission.

  The program that operates in the receiving apparatus according to the above-described embodiment is a program (a program that causes a computer to function) that controls the CPU and the like so as to realize the functions of the above-described embodiment according to the present invention. Information handled by these devices is temporarily stored in the RAM at the time of processing, then stored in various ROMs and HDDs, read out by the CPU, and corrected and written as necessary. As a recording medium for storing the program, a semiconductor medium (for example, ROM, nonvolatile memory card, etc.), an optical recording medium (for example, DVD, MO, MD, CD, BD, etc.), a magnetic recording medium (for example, magnetic tape, Any of a flexible disk etc. may be sufficient. In addition, by executing the loaded program, not only the functions of the above-described embodiment are realized, but also based on the instructions of the program, the processing is performed in cooperation with the operating system or other application programs. The functions of the invention may be realized.

  In addition, when distributing to the market, the program can be stored and distributed in a portable recording medium, or transferred to a server computer connected via a network such as the Internet. In this case, the storage device of the server computer is also included in the present invention. Moreover, you may implement | achieve part or all of the mobile station apparatus and base station apparatus in embodiment mentioned above as LSI which is typically an integrated circuit. Each functional block of the receiving apparatus may be individually chipped, or a part or all of them may be integrated into a chip. When each functional block is integrated, an integrated circuit controller for controlling them is added.

  Further, the method of circuit integration is not limited to LSI, and may be realized by a dedicated circuit or a general-purpose processor. In addition, when an integrated circuit technology that replaces LSI appears due to the advancement of semiconductor technology, an integrated circuit based on the technology can be used.

DESCRIPTION OF SYMBOLS 10 Receiver 101 Code stock 102 Interleave part 103 Modulation part 104 Pilot signal generation part 105 Pilot signal multiplexing part 106 IFFT part 107 Transmission signal information multiplexing part 108 GI insertion part 109 Wireless transmission part 110 Radio reception part 111 GI removal part 112 FFT part 113 demodulation unit 114 response signal analysis unit 20 transmission device 501 wireless reception unit 502 GI removal unit 503 separation unit 504 transmission signal information analysis unit 505 FFT unit 506 channel estimation unit 507 channel information generation unit 508 propagation path compensation unit 509 demodulation unit 510 de Interleave unit 511 Received signal storage unit 512 HARQ synthesis unit 513 Decoding unit 514 Retransmission control unit 515 Response signal generation unit 516 Modulation unit 517 IFFT unit 518 GI insertion unit 519 Radio transmission unit

Claims (9)

A receiving device used in a communication system that performs an automatic retransmission request,
A reception unit that receives an initial transmission signal and at least one retransmission signal as a reception signal;
A channel estimation unit for performing channel estimation on the latest retransmission signal received by the reception unit to obtain a frequency response estimation value;
A channel information generating unit that generates a path position of a channel from a received signal prior to the latest retransmission signal, and
The channel estimation unit
The receiving apparatus, wherein the frequency response estimation value is obtained using a path position of the channel . The received signal includes a scattered pilot signal,
The receiving apparatus according to claim 1, wherein the channel estimation unit obtains the frequency response estimated value by using a data determination value in a path position of the channel, a scattered pilot signal, and a previous received signal. . The receiving apparatus according to claim 2, wherein a soft decision value is used as the data decision value. The receiving apparatus according to claim 3, wherein the soft decision value equal to or greater than a certain threshold is used as the data decision value. The receiving apparatus according to claim 2, wherein a hard decision value is used as the data decision value. The receiving apparatus according to claim 5, wherein the hard decision value is weighted. The receiving apparatus according to claim 6, wherein the weight used when the hard decision value is weighted is obtained according to the reliability of the soft decision value. A receiving method used in a communication system that performs an automatic retransmission request,
A reception process of receiving an initial transmission signal and at least one retransmission signal as a reception signal;
A channel estimation process for performing frequency estimation on the latest retransmission signal received by the reception process to obtain a frequency response estimate;
A channel information generating process for generating a channel path position from a received signal before the latest retransmission signal,
The channel estimation process includes:
A receiving method, wherein the frequency response estimation value is obtained using a path position of the channel. A program executed in a receiving device used in a communication system that performs an automatic retransmission request,
A reception function for receiving an initial transmission signal and at least one retransmission signal as a reception signal;
A channel estimation function for performing frequency estimation on the latest retransmission signal received by the reception function to obtain a frequency response estimation value;
A channel information generation function for generating a channel path position from a received signal prior to the latest retransmission signal,
The channel estimation function is:
A program characterized in that the frequency response estimation value is obtained using a path position of the channel.

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