JP2004248216A - Signal processing apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate the need of retransmission as much as possible by improving the possibility of rightly decoding received data. <P>SOLUTION: The signal processing apparatus is provided with a decoding means 201 for operating a state metric value of received data for decoding, a storage means 204 for storing one or a plurality of highly reliable decoded results from one of the highest reliability on the basis of the state metric value calculated in the decoding means, an error detecting means 203 for detecting an error in decoded data outputted from the decoding means, and a control means 205 for outputting the other decoded result and supplying it to the error detecting means when any error is detected by the error detection in the error detecting means and the other decoded result is stored in the storage means. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a signal processing apparatus and method suitable for application to decoding processing of, for example, convolutional codes and turbo codes.
[0002]
[Prior art]
Conventionally, when constructing a wireless communication system, a transmission side adds an error detection code such as a CRC (Cyclic Redundancy Check) to prepared data, and then performs encoding such as a convolutional code or a turbo code. Then, the receiving side decodes the code to obtain the original data.
[0003]
By applying a convolutional code or a turbo code as an encoding method, it is possible to properly decode data even when the transmission path condition is poor. In addition, it is possible to determine whether the decoded data is correct data by using the error detection code added to the data.
[0004]
Patent Literature 1 describes a Viterbi decoding process, which is one of decoding methods of a convolutional code, and a processing configuration for performing an error detection process on the Viterbi-decoded data.
[0005]
[Patent Document 1]
JP 2002-8324 A
[Problems to be solved by the invention]
As described above, decoding such as Viterbi decoding and error detection processing are combined. The processing when error detection is performed using an error detection code includes, for example, data having an error. , A process of sending a retransmission request to retransmit the data of the same packet to the transmission source and decoding the retransmitted data may be considered. However, when the transmission path environment is bad, retransmission requests are frequently sent, so that the radio resources for transmitting the retransmission request and the radio resources for the radio channel for transmitting the retransmission data based on the retransmission request are increased. There was a problem of large consumption.
[0007]
The present invention has been made in view of the above point, and has as its object to increase the possibility that correct decoding of received data can be performed and eliminate the need to perform retransmission as much as possible.
[0008]
[Means for Solving the Problems]
The present invention performs decoding by performing calculation of a state metric value of received data, and, based on the state metric value calculated by the decoding, generates one or more highly reliable decoding results from those having the highest reliability. A plurality of stored data are stored, and error detection is performed on the stored decoded data. When an error is detected by the error detection and another decoding result is stored, the other decoding result is output to perform error detection. It was made.
[0009]
According to the present invention, a correct decoding result is selected and output from candidate decoding results, and the possibility of correct decoding is increased.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
[0011]
FIG. 1 is an example showing the overall configuration of the wireless communication system of the present example. In the transmitting apparatus 100, the information signal a is supplied to the encoder 101, encoded by a predetermined encoding method, and the encoded signal is supplied to the modulator 102 for wireless transmission. The signal is modulated and transmitted to a communication path (wireless communication path). The transmission from the transmission device 100 is performed, for example, in a predetermined packet unit. Here, an error detection (correction) code such as a CRC (Cyclic Redundancy Check) code is added to the information signal a supplied to the encoder 101 in advance.
[0012]
As the encoding in the encoder 101, for example, encoding such as convolutional code or turbo code is performed. Here, an example of performing convolutional coding will be described. FIG. 2 is a diagram illustrating a general configuration example of a convolutional encoder. When the information word is input to the output terminal 111, the convolutional encoder directly supplies the input to the adders 112 and 113, and also supplies the signal delayed by a predetermined clock period by the delay circuit 114 to the adder 112. The signals delayed by the delay circuits 114 and 115 (the delay amounts of both delay circuits are the same) are also supplied to adders 112 and 113, and the added signals from these adders 112 and 113 are converted into parallel / serial data. And supplies the encoded codeword as a serial signal of one system.
[0013]
Returning to the description of FIG. 1, the receiving apparatus 200 will be described. In the receiving apparatus 200 that receives a signal wirelessly transmitted from the transmitting apparatus 100, the received signal is supplied to the demodulator 201 to cope with the modulation on the transmitting side. Perform demodulation processing. The demodulated received signal is supplied to a decoder 202 to perform a decoding process corresponding to the encoding on the transmission side. Here, a so-called soft decoding process for obtaining an optimum decoding result by calculating a state metric value which is an inter-symbol distance is performed.
[0014]
For example, when convolutional encoding is performed as the encoding process, Viterbi decoding is performed. In the Viterbi decoding process, a process of performing a state metric value calculation, selecting a path having the smallest state metric value, and obtaining a codeword as a decoding result is performed. The decoding result is supplied to an error detection unit 203 via a storage unit 204 described later, and an error detection (correction) process using an error detection (correction) code added to the transmitted information signal is performed. If there is no such signal, the decoded signal (or the decoded signal corrected when the error is correctable) is output as decoded information b obtained by reception.
[0015]
Here, in the present example, the storage unit 204 is connected to the decoding unit 202, and the decoding result of the decoding unit 202 is temporarily stored. If there are a plurality of decoded values that are likely to be correct decoding results, the storage unit 204 stores the plurality of decoded values. That is, in the Viterbi decoding by the decoding unit 202, the reliability of the decoding result is higher as the state metric value is smaller. All the codewords corresponding to the path are stored in the storage unit 204. Although the storage unit 204 is described as a circuit separate from the decoding unit 202 for the sake of explanation, a storage unit provided for decoding by the decoding unit 202 may be used.
[0016]
With respect to the decoding result output from the decoding unit 202, the presence or absence of an error is determined by the error detection in the error detection unit 203. In response, if another decoding result for the same signal is stored in the storage unit 204 under the control of the control unit 205, the other decoding result is supplied to the error detection unit 203, and the error detection unit 203 At 203, an error is detected. If no error is detected in the error detection, the decoding result is output as decoding information b.
[0017]
When an error is detected by the error detection unit 203 with respect to all decoding results stored in the storage unit 204, a retransmission request instruction is generated by the control unit 205, and the retransmission request instruction c is transmitted to the transmitting device 100 side. Sent. In FIG. 1, only the configuration for transmitting from the transmitting device 100 to the receiving device 200 is shown, so that the configuration for transmitting the retransmission request instruction c to the transmitting device 100 is omitted. Processing for wireless transmission to the device 100 is performed.
[0018]
The transmitting apparatus 100 that has received the retransmission request causes the same packet to be wirelessly transmitted again, and the receiving apparatus 200 that has received the packet performs the same processing as the above-described receiving processing.
[0019]
Next, the reception processing in this example will be described with reference to the flowchart in FIG. When the receiving process starts (step S10), the decoding process in the decoder 201 is performed, and the state metric value calculation is performed (step S11). The path having the minimum state metric value obtained by this state metric value calculation is selected, and the corresponding decoding result is stored in the storage unit 204 (step S12). Thereafter, it is determined whether there is a path having a metric value close to the minimum state metric value (step S13), and if there is, a decoding result corresponding to the path is stored in the storage unit 204 (step S14). ).
[0020]
When it is determined in step S13 that there is no other path having a metric value close to the minimum state metric value, and when a decoding result corresponding to a path having a metric value close to the minimum state metric value is stored in step S14 Then, the process proceeds to step S15, and the error detection unit 203 performs an error detection process on the decoding results stored in the storage unit 204 in descending order of reliability. If it is determined in the error detection process in step S15 that there is no error, it is determined that the decoding result is correct decoded data, and the decoding process of the codeword here is terminated, and the next codeword is decoded. (Step S21).
[0021]
If it is determined in step S16 that there is an error, it is determined whether any of the decoding results stored in the storage unit 204 has not been subjected to error detection (step S17). If there is any that has not been tried, the corresponding decoding result is transferred from the storage unit 204 to the error detection unit 203 (step S18). By transferring the decoding result to the error detection unit 203, the error detection processing in step S15 is executed again, and the presence or absence of an error is determined in step S16.
[0022]
If it is determined in step S17 that error detection has been tried for all decoding candidates for the codeword at that time, a retransmission request signal for a packet including the corresponding codeword is generated, and (Step S19), and returns to the start of Step S10 (Step S20), and waits until the next packet is received.
[0023]
Here, when the decoding result is stored in the storage unit 204 connected (or incorporated) to the decoding unit 202, for example, the following case can be considered as the decoding result selection process. That is, as one example, as shown in FIG. 3, when the SNR of the received signal is good (that is, in a good wireless communication state), a certain state metric value within ± 30% from the minimum state metric value If there is a path based on the path, all the decoding results of the path are stored in the storage unit 204. Further, when the SNR of the received signal is poor (that is, in a poor wireless communication state), if there is a path based on a certain state metric value within ± 10% from the minimum state metric value, decoding of the path is performed. All the results are stored in the storage unit 204.
[0024]
As another example, as shown in FIG. 4, for example, when the SNR of the received signal is good (that is, in a good wireless communication state), the decoding results of the two paths starting with the smaller state metric value are stored in the storage unit 204. To save. Further, when the SNR of the received signal is poor (that is, in a poor wireless communication state), the storage unit 204 stores the decoding results of the four paths with the smaller state metric values.
[0025]
Here, an example of selecting a decoding result based on the state metric value will be described with reference to FIGS. FIG. 6 shows a trellis diagram when a decoded word having the shortest state metric (code distance) is estimated from a certain signal sequence, and FIG. 7 shows a decoding having the second state metric from the same signal sequence. FIG. 3 shows a trellis diagram for estimating a word. What is indicated by a solid line in FIGS. 6 and 7 is the selected path.
[0026]
First, it is assumed that the information word input on the transmission side is [1, 0, 1, 1, 1, 0, 0]. It is assumed that this information word is encoded by the convolutional encoder shown in FIG. 2 and transmitted wirelessly. Here, [1,1,1,1,1,0,0,0,0,1,0,0,1,0,0] is obtained as a binarized reception sequence obtained on the receiving device 200 side. I do. FIG. 6 shows a trellis diagram when a decoded word having the shortest state metric (inter-code distance) is found from the received sequence by sending the binarized received sequence to the decoder 202. In the trellis diagram having the minimum state metric value shown in FIG. 6, the decoded word is [1, 1, 0, 1, 0, 0, 0], and the information word [1, 1, 0, 1, 1, 1, 0, 0], the error detection unit 203 detects an error.
[0027]
Here, if the decoding results stored in the storage unit 204 are set to, for example, two from the smaller state metric value, the trellis diagram from the smaller one is as shown in FIG. A decoded word [1, 0, 1, 1, 1, 0, 0] that matches the information word obtained is obtained, and the error detection unit 203 detects no error, and a correct decoding result is obtained.
[0028]
If the reception environment is good, the possibility of correct decoding is quite high if about two such decoding results are prepared, but if the reception environment is poor, the number of correct decoded words is larger. Since there is a high possibility that the decoding result is selected from among the decoding results, by preparing more decoding results, the possibility of accurate reception can be increased. The reception environment (communication environment) may be determined from the average error rate of the received signal, from the received electric field strength, or the like, or may be determined from the number of paths when multipath is received. good.
[0029]
As described above, by changing the selection state of the decoding result to be stored according to the wireless communication state at that time, the minimum storage processing is sufficient when the communication environment is good, and when the communication environment is poor. In this case, more candidates are stored, and even if the communication environment is poor, the possibility of correct decoding can be secured to some extent.
[0030]
Therefore, by performing the processing of the present example, the necessity of performing the retransmission processing of the transmitted packet is reduced, and the use efficiency of the wireless channel for transmitting the retransmission request can be improved, and based on the retransmission request, Thus, the use efficiency of a wireless channel for transmitting retransmission data can be improved, and efficient wireless communication can be performed.
[0031]
In the above-described embodiment, convolutional coding is performed as encoding on the transmitting side, and Viterbi decoding is performed as decoding on the receiving side. However, similar decoding is performed on the receiving side. As long as decoding based on calculation of a metric value (intersymbol distance) is performed, the present invention can be applied to other methods. For example, the present invention is also applicable to a case where turbo encoding is performed on the transmission side and decoding of the turbo code is performed on the reception side. Also, as to how to take the reference example shown in FIGS. 3 and 4, an example is shown, and the present invention is not limited to this example. Further, in the above-described embodiment, the state in which the decoding result is stored is changed according to the communication environment.
[0032]
Further, in the above-described embodiment, an example in which wireless communication is performed has been described. However, the present invention is also applicable to reception processing for wired communication in which similar reception processing is performed.
[0033]
Further, in the above-described embodiment, a dedicated receiving device that performs the processing of the present example is configured. However, for example, a board or the like that performs wireless communication is incorporated in a data processing device such as a personal computer device and the like, and the data processing device includes In the software processing described above, the decoding processing of this example as shown in the flowchart of FIG. 3 described above may be performed.
[0034]
【The invention's effect】
According to the present invention, a correct decoding result is selected and output from candidate decoding results, and the possibility of correct decoding is increased. Therefore, a communication system with high retransmission efficiency can be realized, and a communication system with high data transmission efficiency can be realized.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration example according to an embodiment of the present invention.
FIG. 2 is a block diagram illustrating a configuration example of a convolutional encoder.
FIG. 3 is a flowchart illustrating a processing example according to an embodiment of the present invention;
FIG. 4 is an explanatory diagram showing a reference example of a state metric value stored in a decoder according to an embodiment of the present invention.
FIG. 5 is an explanatory diagram showing a reference example of a state metric value stored in a decoder according to an embodiment of the present invention.
FIG. 6 is an explanatory diagram showing an operation example of a trellis diagram when estimating a decoded word having the shortest code distance when estimating a decoded word from a received sequence.
FIG. 7 is an explanatory diagram showing an operation example of a trellis diagram when estimating a decoded word having the second closest code distance when estimating a decoded word from a received sequence.
[Explanation of symbols]
Reference Signs List 100 transmitter, 101 encoder, 102 modulator, 112, 113 adder, 114, 115 delay circuit, 116 parallel / serial converter, 200 receiver, 201 demodulator, 202 Viterbi Decoder, 203: error detection unit, 204: storage unit, 205: control unit

Claims (8)

In a signal processing device that receives and decodes data that has been subjected to error-detectable encoding,
Decoding means for calculating the state metric value of the received data to perform decoding,
Based on the state metric value calculated by the decoding means, storage means for storing one or more highly reliable decoding results from the one with the highest reliability,
Error detection means for performing error detection of the decoded data output and stored by the decoding means,
When an error is detected in the error detection by the error detection unit and another decoding result is stored in the storage unit, the control unit causes the other decoding result to be output and supplied to the error detection unit. Equipped signal processing device. The signal processing device according to claim 1,
A signal processing device, wherein the control unit issues a retransmission request to a source of received data when an error is detected by the error detection unit for all decoding results stored in the storage unit. The signal processing device according to claim 1,
The signal processing device according to claim 1, wherein the decoding result stored in said storage means is a decoding result whose reliability using a state metric value as an index is not less than a predetermined reliability. The signal processing device according to claim 1,
A signal processing device for changing the number of decoding results stored in the storage means according to a reception environment. In a signal processing method of receiving and decoding data subjected to encoding capable of error detection,
Calculate and decode the state metric value of the received data,
Based on the state metric value calculated in the decoding, one or more highly reliable decoding results are stored from the one with the highest reliability, and error detection of the stored decoded data is performed. A signal processing method in which, when an error is detected and another decoding result is stored, the other decoding result is output to perform error detection. The signal processing method according to claim 5,
A signal processing method for issuing a retransmission request to a source of received data when an error is detected for all of the stored decoding results. The signal processing method according to claim 5,
The signal processing method, wherein the stored decoding result is a decoding result whose reliability using a state metric value as an index is equal to or higher than a predetermined reliability. The signal processing method according to claim 5,
A signal processing method for changing the number of stored decoding results according to a reception environment.

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