JP4739013B2 - Receiving apparatus and receiving method - Google Patents

Description

  The present invention relates to a receiving apparatus and a receiving method in digital communication using an error correction code.

Currently, a code division multiple access method is used as one of communication methods for mobile phones. In W-CDMA and cdma2000 cellular systems based on the same scheme, a turbo code is used as an error correction code, and transmission characteristics close to the Shannon limit are realized by this turbo code through realistic processing (for example, non-coding). (See Patent Documents 1 and 2).
Here, the mechanism of data communication using the turbo code will be briefly described with reference to FIGS. FIG. 5 is a block diagram of the turbo encoder 30, and FIG. 6 is a block diagram of the turbo decoder 15.

In FIG. 5, the transmitted information bit sequence is input to the element encoder 31 and the turbo interleaver 33, respectively. The element encoder 31 creates and outputs a parity bit sequence p1. The turbo interleaver 33 rearranges the order of the input data and outputs it to the other element encoder 32. The element encoder 32 creates and outputs a parity bit sequence p2. The two parity bit sequences p1 and p2 are simply multiplexed or thinned after being multiplexed according to a desired coding rate, and further multiplexed with the original information bit sequence and transmitted to the communication channel. The
Here, the configurations of the two element encoders 31 and 32 may be the same or different.

Next, in FIG. 6, the turbo decoder 15 includes two element decoders 105a and 105b, two turbo interleavers 106a and 106b, and one turbo deinterleaver 107a.
Element decoder 105a receives and decodes received bit sequence α1 output from channel value calculator 104a, and outputs reliability information of each information symbol included in α1 as an external value. This external value is rearranged in order by the turbo interleaver 106a and input to the element decoder 105b as a prior value t2. On the other hand, received bit sequence α2 whose order is rearranged by turbo interleaver 106b is input to element decoder 105b. The element decoder 105b decodes this received bit sequence α2, and uses the above-described prior value t2 as reliability information of information symbols (included in α2) to be decoded in this decoding process. Then, an external value that is the result of decoding is output.

The external value obtained by the element decoder 105b is returned to the original order by the turbo deinterleaver 107a and then input to the element decoder 105a as a prior value t1. The element decoder 105a uses the prior value t1 as reliability information for α1 in the second and subsequent decoding processes of the received bit sequence α1.
The turbo decoder 15 repeats the above process sufficiently and then outputs a posterior value as a final decoding result from the element decoder 105b. Then, this posterior value is hard-decided, and received information bits corresponding to the transmitted information bit sequence are obtained.

  In this way, the turbo decoder 15 includes a loop (called a feedback loop for probability propagation) that updates reliability information of each bit by two element decoders and feeds it back to the other element decoder. ing. In the communication using the turbo code, efficient MAP (Maximum A posteriori Probability) decoding is realized.

Non-Patent Documents 1 and 2 also propose twin turbo demodulation as a demodulation method for improving the correction capability of turbo codes. FIG. 7 shows a block diagram of the twin turbo demodulator 20.
The twin turbo demodulator 20 includes a probability coupling feedback loop in addition to the same probability propagation feedback loop as the turbo decoder 15. Here, the feedback loop for stochastic coupling refers to the channel value calculator 104b (and the channel value calculator 104a) with the probability of the provisional judgment value obtained by the element decoder 105a (and the element decoder 105b). This is a loop for updating the channel value by inputting feedback and inputting the updated channel value to the other element decoder 105b (and the element decoder 105a) for decoding. In twin-turbo demodulation, this probability coupling feedback loop is used to calculate the likelihood coupling probability of each bit included in the modulation symbol, and to correspond to the received signal point according to this coupling probability (appearance probability of the received signal point). The modulation symbol to be determined is determined.
JP 2004-260423 A JP 2004-159084 A JP 2004-080360 A JP 2004-072469 A JP 2000-082978 A Japanese Patent Laid-Open No. 11-355849 3GPP TSG RAN WG1 # 42 bis, R1-051261, “Enhancement of Distributed Mode for Maximizing Frequency Diversity”, Oct. 2005 T. Suzuki, N. Miyazaki, Y. Hatakawa, “A Proposal of Twin Turbo Detector and Its Evaluation for M-QAM OFDM”, Shingaku So, B-5-6, Sep. 2005

However, in the communication system using the conventional turbo code or twin turbo demodulation described above, the error correction block and the propagation path estimation block are independent in function, so that the reception performance is propagated no matter how much the error correction capability is improved. There was a problem that it depends on the accuracy of the route estimation.
Here, the propagation path estimation will be briefly described. In general, the transmission signal is affected by amplitude fluctuation and phase rotation by propagating through the radio propagation path. Therefore, in order to correctly demodulate and decode in the receiver, the influence of these fluctuations is correctly estimated and corrected to the received signal. It is necessary to apply. The process for estimating the influence of the transmission signal from the propagation path is propagation path estimation.

  As a propagation path estimation method, a known pilot symbol is transmitted together with a data symbol, the amplitude fluctuation and phase rotation of the pilot symbol are measured, and the influence of the propagation path is estimated from the result. . FIG. 8 is a diagram schematically showing pilot symbols embedded between data symbols. In the figure, the influence of the propagation path on the data symbols is estimated by interpolating the measurement results of the pilot symbols in each of the time direction (the figure (a)) and the frequency direction (the figure (b)). However, in order to avoid a decrease in transmission throughput, it is necessary to keep the ratio of pilot symbols within a certain range.

Now, it is possible to improve the reception characteristics of the receiver by complementarily performing channel estimation and error correction using a turbo code. Therefore, Patent Documents 1 to 6 have proposed a method of improving the accuracy by performing propagation path estimation by feeding back a provisional determination value of a data symbol. Specifically, in Patent Documents 1, 2, and 4, the hard decision value after being output from the decoder is output as a temporary determination value, and in Patent Documents 3, 5, and 6, it is output from the channel value calculator. The soft decision values before the decoding process are respectively used.
However, for example, in the method using the hard decision value, the data symbol is treated as either “0” or “1”, and since the probabilistic information is not used, the processing result of the propagation path estimation diverges. There were cases where there were cases.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a receiving apparatus and a receiving method capable of realizing high-quality communication by accurately calculating a propagation path estimated value. It is in.

  The present invention has been made to solve the above problems, and the invention according to claim 1 is a receiving apparatus including a decoder having a feedback loop for probability propagation, and a propagation path for a received signal. A propagation path estimation means for calculating an estimated value; and a means for feeding back to the propagation path estimation means a provisional decision value obtained in the process of decoding a received signal in the decoder and its probability. The means is a receiving apparatus characterized in that a propagation path estimated value corrected based on the inputted temporary determination value and its likelihood is calculated.

  Further, in the second aspect of the present invention, in the receiving apparatus according to the first aspect, the propagation path estimated value is obtained by using the probability of the provisional determination value fed back as the appearance probability of the received signal point. A communication channel value calculating means for demodulating the received signal based on the received signal and calculating the communication channel value of the received signal is further provided.

  According to a third aspect of the present invention, a propagation path estimated value for the received signal is calculated using the provisional determination value obtained in the process of decoding the received signal and its probability, and the propagation path estimated value is calculated. The reception method is characterized in that the received signal is demodulated, and the bit is decoded by using the reliability of the decoded bit as a prior value for the channel value obtained by the demodulation.

  According to a fourth aspect of the present invention, in the reception method according to the third aspect, in the demodulation of the received signal, the channel value is calculated by using the probability of the temporary judgment value as the appearance probability of the received signal point. It is characterized by doing.

According to the present invention, since the propagation path estimated value is sequentially corrected using the provisional determination value obtained in the process of decoding the received signal and its certainty, the propagation path estimated value can be calculated with high accuracy. Is possible. As a result, the reception characteristics of the receiver are improved, and high-quality communication can be realized.
Further, since the channel estimation value is obtained with high accuracy without increasing the number of pilot symbols, it is possible to improve the transmission throughput.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
<< First Embodiment >>
FIG. 1 is a configuration diagram of a receiving device 10a according to the first embodiment of the present invention. This receiving apparatus 10 a includes a loop that feeds back the provisional determination value of the received signal obtained by the turbo decoder 15 and its probability to the propagation path estimator 12.

Demodulation and decoding processing performed in the receiving apparatus 10a will be described.
First, the received modulation symbol is sent to the reception signal point detector 11, and the reception signal point on the IQ plane is detected from the amplitude information and phase information of the symbol. The detected reception signal point is input to the channel value calculator 14.

  On the other hand, when a reference pilot symbol is received, the symbol is sent to the propagation path estimator 12. The propagation path estimator 12 obtains the difference between the pilot symbol actually transmitted through the propagation path and the known original pilot symbol, thereby varying the propagation path to the amplitude and phase of the transmission signal. A propagation path estimated value representing the degree of is calculated. Furthermore, the propagation path estimator 12 calculates propagation path estimated values for all modulation symbols in each of the time direction and the frequency direction by interpolating the propagation path estimated values obtained for the pilot symbols. The propagation path estimation value obtained in this way is input to the reference signal point creation unit 13, and a reception signal point candidate (reference signal point) corresponding to a modulation symbol transmitted by a transmission device (not shown) is created. The The created reference signal point is sent to the channel value calculator 14.

  The channel value calculator 14 determines the most likely modulation symbol corresponding to the received signal point from the input received signal point and the reference signal point, and determines the soft decision value of each bit included in the modulation symbol. The calculated value is output to the turbo decoder 15 as soft decision data (communication channel value). The bit sequence of the channel value is decoded by the turbo decoder 15, and the probability that each information bit obtained by the decoding is “0” or “1” is output as a posterior value.

This posterior value is fed back to the propagation path estimator 12 and used to recalculate the propagation path estimated value. Specifically, the propagation path estimator 12 first calculates, for each modulation symbol, the joint probability of all bits constituting the modulation symbol according to feedback information of each bit, and temporarily determines the most likely modulation symbol. For example, in the case of QPSK modulation, since the modulation symbol is composed of 2 bits, assuming that the probability that the first bit is 0 is 80% and the probability that the second bit is 1 is 90%, the modulation symbol is “01”. ”Is calculated as 72%. This coupling probability is the probability of the modulation symbol.
Then, a temporarily estimated modulation symbol is regarded as a pseudo pilot symbol, and a difference from the actually received signal is obtained to obtain a new propagation path estimation value. However, at this time, the value obtained from the provisional judgment value and the value obtained by the interpolation processing using only the pilot symbol at the time of the initial calculation of the propagation path estimation value are weighted with the probability of the provisional judgment value, A value obtained by weighting is assumed to be a new propagation path estimation value. In the second and subsequent feedbacks, the propagation path estimated value is updated by weighting the propagation path estimated value updated at the previous feedback and the value obtained from the provisional determination value in the same manner.

  Since the propagation path estimated value updated in this way reflects the probability information of the provisional determination value related to the received signal decoded by the turbo decoder 15, the updated value is more accurate than the initial value. It is expected to become. Therefore, the decoding process is performed on the channel value obtained based on the channel estimation value, and the feedback loop process of updating the channel estimation value using the result is repeated sufficiently, so that correct decoding is performed. The possibility of obtaining a result is increased.

Next, the configuration and operation of the turbo decoder 15 in the receiving apparatus 10a described above will be described in more detail. FIG. 2 is a block diagram showing a configuration of the turbo decoder 15.
In the figure, the received signal point and the reference signal point created by the reference signal point creation unit 103a based on the output value of the propagation path estimator 102a are input to the communication path value calculator 104a and communicated bit by bit. The road value is output. The decoder 105a receives this channel value and a prior value obtained by rearranging the order of the external values output from the other decoder 105b by the turbo deinterleaver 107a. The decoder 105a uses this a priori value to decode the bit sequence of the input channel value, and outputs the external value that is reliability information of each decoded symbol and the a posteriori of each bit included in the symbol. Output the value.

  The output external values are rearranged in order by the turbo interleaver 106a and then input to the decoder 105b as prior values. The decoder 105b performs the same processing as the decoder 105a on the bit sequence input from the channel value calculator 104b via the turbo interleaver 106b, and outputs an external value and a posterior value. This external value is fed back to the decoder 105a via the turbo deinterleaver 107a. The loop formed by the two decoders 105a and 105b, the turbo interleaver 106a and the turbo deinterleaver 107a has the same configuration (feedback loop for probability propagation) as the conventional turbo decoder 15 in FIG. Yes, the decoding process performed in this part is the same as the conventional one.

  On the other hand, the a posteriori value output from the decoder 105a is input (feedback) to another propagation path estimator 102b placed in the preceding stage of the decoder 105b. The propagation path estimator 102b uses this posterior value in the calculation of the propagation path estimated value to improve its estimation accuracy. The channel value calculator 104b performs the same processing as the channel value calculator 104a described above using the reference signal point created from this propagation path estimated value, and outputs the channel value. This channel value is input to the decoder 105b via the turbo interleaver 106b.

  The posterior values obtained by decoding in the decoder 105b are sent to the turbo deinterleaver 107b, the order is rearranged, and fed back to the propagation path estimator 102a. The propagation path estimator 102a uses this posterior value to estimate the propagation path estimated value with high accuracy, similar to the above-described propagation path estimator 102b.

  Thus, the turbo decoder 15 feeds back the posterior value obtained by the decoder 105b (decoder 105a) to the propagation path estimator 102a (propagation path estimator 102b), and sequentially updates the propagation path estimated values. A new loop is provided, and the estimation accuracy is improved by reflecting the probability information of the provisional decision value related to the received signal decoded by each decoder in the calculation of the propagation path estimation value. As a result, the reception characteristics of the receiver are improved, and high-quality communication is realized.

<< Second Embodiment >>
Next, another embodiment will be described. FIG. 3 is a configuration diagram of a receiving device 10b according to the second embodiment of the present invention.
The receiving apparatus 10b includes a twin turbo demodulator 20 (having a loop that feeds back the probability of the provisional determination value obtained by decoding to the channel value calculator 14 as the appearance probability of the reception signal point). A loop for feeding back the provisional determination value of the received signal obtained by the turbo decoder 15 and its probability to the propagation path estimator 12 is provided.

That is, in FIG. 3, a loop for returning the probability of the provisional decision value obtained by the turbo decoder 15 to the channel value calculator 14 is a feedback loop for normal twin turbo demodulation, and the provisional decision value is used as the channel estimator 12. The loop to return to is a feedback loop newly created according to the present invention.
Therefore, the receiving apparatus 10b uses the appearance probability of the received signal point obtained based on the likelihood of each bit in the decoded modulation symbol for calculation of the channel value, and also uses the temporary probability related to the decoded modulation symbol. It is intended to further improve the performance of the receiver by using the probability information of the judgment value as a posterior value for calculating the propagation path estimation value.

  FIG. 4 is a block diagram showing a detailed internal configuration of the twin turbo demodulator 20 in the receiving apparatus 10b. In the figure, a loop flowing through the decoder 105a → the turbo interleaver 106a → the decoder 105b → the turbo deinterleaver 107a → the decoder 105a is a feedback loop for probability propagation for performing turbo decoding, and the channel value calculator 104a → the decoder. The loop flowing through 105a → channel value calculator 104b → turbo interleaver 106b → decoder 105b → turbo deinterleaver 107b → channel value calculator 104a is a feedback loop for stochastic coupling that performs twin turbo demodulation. These two feedback loops have the same configuration as that of the conventional twin turbo demodulator 20 in FIG. 7, and their operations are also the same.

  Here, the twin turbo demodulator 20 includes a propagation path estimator 102a → reference signal point creation section 103a → communication path value calculator 104a → decoder 105a → propagation path estimator 102b → reference signal point creation section 103b → communication path. A new feedback loop is formed in which the value calculator 104b → the turbo interleaver 106b → the decoder 105b → the turbo deinterleaver 107b → the propagation path estimator 102a. With this configuration, the posterior value obtained by the decoder 105b (decoder 105a) is returned to the propagation path estimator 102a (propagation path estimator 102b), and the propagation path estimation value is updated.

  As described above, also in the present embodiment, the probability information of the provisional determination value related to the received signal decoded by each decoder is reflected in the calculation of the propagation path estimation value to improve the estimation accuracy. As a result, the reception characteristics of the receiver are improved, and high-quality communication is realized.

As described above, the embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to that described above, and various design changes and the like can be made without departing from the scope of the present invention. It is possible to
For example, when the propagation path estimators 102a and 102b recalculate the propagation path estimation value using the provisional judgment value and its certainty, only when the probability of the provisional judgment value exceeds a predetermined threshold. The value obtained from the provisional determination value may be taken into the update of the propagation path estimation value.

It is a block diagram of the receiver by 1st Embodiment. It is a block diagram which shows the structure of a turbo decoder. It is a block diagram of the receiver by 2nd Embodiment. It is a block diagram which shows the internal structure of a twin turbo demodulator. It is a block diagram of the conventional turbo encoder. It is a block diagram of the conventional turbo decoder. It is a block diagram of the conventional twin turbo demodulator. It is the figure which showed the interpolation method of the propagation path estimated value using a pilot symbol.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10a, 10b ... Reception apparatus 11 ... Received signal point detection part 12 ... Propagation path estimator 13 ... Reference signal point preparation part 14 ... Channel value calculator 15 ... Turbo decoder 20 ... Twin turbo demodulator 30 ... Turbo encoder 31 32 ... Element encoder 33 ... Turbo interleaver 102a, 102b ... Propagation path estimator 103a, 103b ... Reference signal point generator 104a, 104b ... Channel value calculator 105a, 105b ... Decoder 106a, 106b ... Turbo interleaver 107a, 107b ... Turbo deinterleaver

Claims (4)

A receiver comprising a decoder having a feedback loop for probability propagation,
Propagation path estimating means for calculating a propagation path estimated value for the received signal;
Means for feeding back the provisional decision value obtained in the process of decoding the received signal in the decoder and its probability to the propagation path estimation means;
With
The propagation path estimation means calculates a joint probability of all bits constituting a modulation symbol according to the input provisional determination value and its probability , and a propagation path estimation value corrected based on the obtained joint probability A receiving device characterized by: A communication channel that demodulates a received signal based on the propagation path estimated value and calculates a channel value of the received signal by using the probability of the provisional determination value fed back as an appearance probability of the received signal point The receiving device according to claim 1, further comprising a value calculating means. Calculate the joint probability of all the bits constituting the modulation symbol according to the provisional decision value obtained in the process of decoding the received signal and its probability, and estimate the propagation path for the received signal using the obtained joint probability Calculate the value,
Demodulate the received signal based on the propagation path estimated value,
A receiving method, wherein the bit is decoded by using the reliability of the decoded bit as a prior value for the channel value obtained by the demodulation. The reception method according to claim 3, wherein, in demodulation of the received signal, the channel value is calculated using the probability of the provisional determination value as the appearance probability of the received signal point.

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