JP2005260608A - Receiving unit, portable communication terminal and decoding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce power consumption and a decoding processing period of time without greatly impairing decoding performance when a receiving environment is inferior in turbo decoding. <P>SOLUTION: In decoding a received signal, a reception SIR estimating part 204 estimates a reception SIR (signal to interference ratio) of the received signal, a normalizer 202 sets an operation word long when the reception SIR is satisfactory, sets the operation word short when the reception SIR is not satisfactory and outputs the received signal as a reception sequence, and a turbo decoder 203 decodes the reception sequence, corrects errors with reliability information and the reception sequence predetermined times and outputs a decoding result. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a reception unit, a mobile communication terminal, and a decoding method for outputting a decoding result while performing error correction on a reception sequence of a reception signal using reliability information included in the reception sequence.

  In recent mobile communications, it is possible to perform error correction by encoding an information signal on the transmitting side and decoding it on the receiving side, and various developments and practical applications of this error correction method Has been made. When performing this error correction, if the signal-to-noise ratio or Eb / N0 (Eb: power per bit, noise power per N0: 1 Hz) becomes low, the information signal is demodulated at a predetermined error rate. Whether this is possible is important in the reliability of wireless communication. There is Shannon's theorem as a theorem to support the theoretical limit of error correction, and there is a turbo code as a code that asymptotically approaches the Shannon limit (for example, Non-Patent Document 1).

  In this turbo code, an information sequence is input to two encoders, respectively, and a parity bit string is generated. At this time, the information sequence is input as it is to one encoder, and the other encoder is input with the order rearranged by an interleaver. Then, these two parity bit strings are simply multiplexed or multiplexed while being punctured, and further multiplexed with an information sequence and transmitted to the communication path.

  On the other hand, in the turbo decoder corresponding to the above-described turbo code, first, the received sequence is received, the first decoder performs decoding processing, and the decoding result of the information symbol and its reliability information are acquired. Then, the second decoder performs decoding processing using the reliability information and the reception sequence from the first decoder rearranged by the interleaver, and the reliability information obtained by the decoding processing is converted by the deinterleaver. After rearrangement, it is sent to the first decoder. In the second and subsequent iterations, the first decoder performs a decoding process based on the received sequence and the reliability information from the second decoder. After this process is repeated a predetermined number of times, a final determination is made and output.

When implementing the above-described turbo decoder in hardware, it is usual to limit the operation word length, for example, from 32 bits to 8 bits in consideration of circuit scale, current consumption, and decoding processing time. It is.
C.Berrou, A.Glavieux and G.Montorsi: "NEAR SHANNON LIMIT ERROR-CORRECTING CODING AND DECODING: TURBO-CODES (1) '', Proc.of ICC '93 (Geneva, Switzerland), pp.1064-1070

  However, in the turbo decoder, as the operation word length is shortened, the circuit scale can be reduced, the power consumption can be reduced, and the decoding processing time can be shortened. On the other hand, if the operation word length is set too small. As a result, the efficiency of error correction decreases and it becomes difficult to obtain desired decoding characteristics. Therefore, when implementing hardware, it is necessary to consider the balance between the processing time and the decoding characteristics.

  On the other hand, when the reception environment is inferior, even if the operation word length is set to a large value, the effect of sufficient error correction cannot be obtained and the decoding characteristics are limited, and the operation word length is uniform regardless of the reception environment. When hardware is used, there is a problem that the efficiency is reduced in terms of current consumption and decoding processing time.

  The present invention has been made to solve the above problem, and by varying the operation word length in encoding according to the reception quality, without greatly impairing the decoding performance when the reception environment is poor, It is an object of the present invention to provide a receiving unit, a mobile communication terminal, and a decoding method that can reduce power consumption and decoding processing time.

  In order to solve the above problems, the present invention estimates the reception quality of a received signal in a reception quality estimation unit when decoding a received signal, and sets the operation word length when the reception quality is good in an operation word length adjustment unit. If the reception quality is poor, the operation word length is set short, the reception signal is output as a reception sequence, the reception sequence is decoded by the turbo decoder, and there is an error depending on the reliability information and the reception sequence. Correction is performed a predetermined number of times, and the decoding result is output.

  According to the present invention, the operation word length is set short when the reception environment is poor, the decoding characteristic is improved by increasing the processing speed, and the operation word length is set long when the reception environment is good. Thus, the decoding characteristics can be improved by improving the efficiency of error correction.

  In the present invention, the reception quality is estimated from the SIR (desired wave to interference wave power ratio) of the information signal included in the received signal based on the received power of the control signal and the received power of the noise signal included in the received signal. It is preferable. In this case, it is possible to estimate the reception quality using a control signal (pilot signal) whose transmission power is known, and it is possible to estimate the reception quality more accurately.

  As described above, according to the present invention, when decoding a received signal, in turbo decoding in which error correction is performed a predetermined number of times based on reliability information acquired by decoding and a received sequence, in the encoding according to the reception quality. By making the operation word length variable, it is possible to reduce power consumption and decoding processing time without greatly degrading decoding performance when the reception environment is poor.

(Configuration of communication system)
Embodiments of the present invention will be described with reference to the drawings. In this embodiment, a case where the receiving unit and the communication terminal device according to the present invention are applied to the communication system shown in FIG. 1A will be described as an example. FIG. 1A is a block diagram showing an overall configuration of a communication system according to the present embodiment.

  As shown in FIG. 1 (a), the communication system according to the present embodiment includes a communication terminal 1 on the transmission side and a communication terminal 2 on the reception side. Here, encoding is performed in the communication terminal 1. The information signal D1 is received by the communication terminal 2 and decoded as the information signal D3.

  The communication terminal 1 includes a turbo encoder 101 that encodes the information signal D1 as a transmission system module, a modulator 102 that modulates the encoded signal, and a multiplex that multiplexes the pilot signal D2 into the modulated signal. And a transmission unit 100 that transmits the multiplexed signal.

  FIG. 2A is a block diagram showing a configuration of the turbo encoding unit 101. As shown in the figure, the input information signal D1 is input to the encoder 101b and encoded. On the other hand, the other of the input information signal D1 is interleaved with a predetermined size by the interleave circuit 101a and then encoded by the encoder 101c. Here, the encoding in the encoder 101c and the encoder 101c is encoding by a systematic tatami code (n1, k).

  The outputs from the encoders 101b and 101c are input to the switch 101d, and the switch 101d is alternately switched and output corresponding to the interleave circuit 101a. Further, the output from the switch 101d is input to the parallel / serial converter 101e, and the uncoded bit (bit of input information) and the coded bit are switched (parallel / serial conversion), and the encoder output is output. Is output as

  On the other hand, as shown in FIG. 1A, the communication terminal 2 serves as a receiving module, a receiving unit 200 that receives a received signal, a demodulator 201 that demodulates the received signal, and a predetermined demodulated signal. A normalizer 202 that cuts out to an operation word length of 2), a turbo decoder 203 that performs turbo decoding and outputs an information signal D3, and a reception SIR estimation unit 204 that estimates an SIR (desired wave-to-interference wave power ratio) of the reception signal. ing.

  FIG. 2B is a block diagram showing the configuration of the turbo decoder 203. The turbo decoder 203 is a decoder that decodes a received sequence, performs error correction a predetermined number of times using reliability information obtained by decoding and the received sequence, and outputs a decoding result. In the turbo decoder 203, as shown in the figure, the input signal is serial / parallel converted by the serial / parallel converter 203a and input to the MAP decoders 203b and 203d. One output of the MAP decoder 203b is input to the interleave circuit 203c, sorted by the data length corresponding to the interleaving at the time of encoding on the communication terminal 1 side, and input to the MAP decoder 203d.

  In the MAP decoder 203d, these signals are decoded, subjected to a rearrangement process reverse to interleaving in the deinterleave circuit 203f, and output as a decoded output. On the other hand, a part of the output of the MAP decoder 203d is rearranged in reverse to the interleaving by the deinterleave circuit 203e, and is input to the MAP decoder 203b as reliability information. This operation is repeated as many times as necessary.

となる。 Here, MAP decoding will be described. When encoding is performed on the transmission side and the code word wj is transmitted, in order to correctly decode on the reception side, the received word y enters the decoding region Rj of the code word wj. Accordingly, the establishment Pc of correct decoding in this case is P (wj) where the establishment that each codeword is sent is P (wj)

It becomes.

  In the above equation, the connection establishment (wj, y) = P (wj) · P (y | wj) is maximized. That is, it is determined that a code word that maximizes conditional establishment P (y | wj) is sent for a given received word y. Conditional establishment P (y | wj) is called a posteriori probability, and decoding that estimates that a codeword that maximizes this probability has been sent is called maximum a posteriori probability decoding (MAP code). Regarding this algorithm, for example, the document “LRBahl, J. Cocke, F. Jelinek, and J. Raviv ,:” Optimal decoding of linear codes for minimizing symbol error rate, ”IEEE Trans. Inform. Theory, Vol. IT-20. , pp.284-287, 1974 ”.

The use of “The Log-Lkelihood Ratios (hereinafter LLR)” as an input signal to the turbo decoder 203 is described in the document “C. Berrou, A. Glavieux and Member, IEEE:“ NEAR Optimum Error Correcting Coding And ”. Decoding: Turbo-Codes'', Proc. Of IEEE' October, 1996, Vol. 44, NO. 10, pp. 1261-1271 ", and LLR is defined as follows.

In AWGN Channel, Equation 2 is defined as follows.

  In the above equation, Es is energy per symbol (1 bit after turbo coding), and N0 is noise power per 1 Hz.

  The normalizer 202 is an arithmetic word length adjustment unit that outputs the reception signal demodulated by the demodulator 201 as a reception sequence with an arithmetic word length corresponding to the reception SIR estimated by the reception SIR estimation unit 204. In the embodiment, as shown in FIG. 1B, a lookup table T1 for associating the reception SIR with the operation word length is provided, and the operation word length is set according to the reception SIR estimated by the reception SIR estimation unit 204. Switch. That is, with respect to the reception SIR estimated by the reception SIR estimation unit 204, the lookup table T1 is referred to, and when the reception quality is good, the operation word length is set longer, and when the reception quality is poor, the operation word length is set. Set it short.

  In the lookup table T1, as shown in FIG. 1B, when the reception SIR is 0 to 4, the operation word length is set to 4 bits, and when the reception SIR is 4 to 8 dB, the operation word length is set to 6 bits. When the received SIR is 8 dB or more, the operation word length is set to 8 bits. This lookup table T1 can be arbitrarily changed according to the performance required in the communication system.

  The reception SIR estimation unit 204 is a module that estimates the degree of deterioration of the S / N ratio generated in the communication path with respect to the reception signal. Here, the operation of reception SIR estimation section 204 will be described in detail. Here, it is assumed that the information signal D1 is mapped to DSCH.

First, the RSCP of CPICH (Pilot channel) is calculated by Equation 4.

Next, CPICH ISCP is calculated by Equation 5.

Then, the CPICH_SN ratio is calculated. Here, since CPICH_RSCP corresponds to the power of the signal component and CPICH_ISCP corresponds to the power of the interference component, the SN ratio of CPICH is obtained by the following equation.

Next, the DSCH_SN ratio (= received SIR) is calculated.

(Operation of communication system)
The operation of the communication system according to the present embodiment described above will be described. First, in the communication terminal 1, the information signal D1 is encoded by the turbo encoder 101, the encoded signal is modulated by the modulator 102, and the pilot signal D2 is multiplexed on the modulated signal by the multiplexer 103. The multiplexed signal is transmitted by the transmitter 100 to the communication terminal 2 through the communication path. Then, the transmitted signal is received by the communication terminal 2. The processing in the communication terminal 2 is shown in FIG.

  When a signal is received at the communication terminal 2 (S101), the received signal is input to the demodulator 201 and demodulated, and is also input to the reception SIR estimation unit 204. Reception SIR estimation section 204 estimates the reception SIR of information signal D1 included in the reception signal based on the reception power of the pilot signal and the noise signal included in the reception signal (S102).

  Then, with respect to the estimated reception SIR, the normalizer 202 refers to the lookup table T1 (S103), and sets the operation word length corresponding to the reception quality (steps S104 to S106). That is, the normalizer 202 sets the operation word length longer when the reception quality is good, sets the operation word length shorter when the reception quality is poor, and receives the reception signal with the set operation word length. The sequence is output to the turbo decoder 203. The turbo decoder 203 decodes the received sequence with the operation word length adjusted by the normalizer 202, performs error correction a predetermined number of times using the reliability information acquired by decoding and the received sequence, and outputs the decoding result (S108). ).

(Effects of this embodiment)
As described above, according to the present embodiment, when the received signal is decoded by the turbo decoder, the reception environment is inferior by making the operation word length in the encoding variable according to the reception quality such as the reception SIR. In such a case, the power consumption and the decoding processing time can be reduced without significantly degrading the decoding performance.

  That is, as shown in FIG. 4, when the received SIR is inferior (when Eb / N0 is small) in the relationship between the arithmetic word length and the BLER (block error rate) characteristic, the characteristic due to the arithmetic word length is small. When the reception SIR is good (when Eb / N0 is large), the characteristic difference due to the operation word length is large. Therefore, according to the present embodiment, the operation word length is set short when the reception SIR is low, and the operation word length is set long when the reception SIR is high, so that the turbo decoder does not incur a large BLER characteristic. It is possible to reduce current consumption and shorten the decoding processing time.

  In the present embodiment, the reception quality is estimated from the SIR (desired wave to interference wave power ratio) of the information signal included in the reception signal based on the reception power of the pilot signal and the noise signal included in the reception signal. Therefore, it is possible to estimate the reception quality using a control signal (pilot signal) whose transmission power is known, and it is possible to estimate the reception quality more accurately.

(A) is a block diagram which shows the structure of the communication system which concerns on embodiment, (b) is explanatory drawing which shows the data structure of lookup table T1. (A) is a functional block diagram which shows the structure of the turbo encoding part 101 which concerns on embodiment, (b) is a functional block diagram which shows the structure of the turbo decoder 203 which concerns on embodiment. It is a flowchart figure which shows operation | movement of the turbo decoder 203 which concerns on embodiment. It is a graph which shows the relationship between the arithmetic word length and BLER (block error rate) characteristic in fading frequency 240Hz.

Explanation of symbols

D1 information signal, D2 pilot signal, D3 information signal, T1 lookup table, 1, 2 communication terminal, 100 transmitter, 101 turbo encoder, 101a interleave circuit, 101b, 101c encoder, 101d switch, 101e parallel / Direct converter, 102 modulator, 103 multiplexer, 200 receiver, 201 demodulator, 202 normalizer, 203 turbo decoder, 203a direct / parallel converter, 203b MAP decoder, 203c interleave circuit, 203d MAP decoder, 203e , 203f Deinterleave circuit, 204 reception SIR estimation unit

Claims (6)

A reception quality estimation unit for estimating the reception quality of the received signal;
Based on the estimation result by the reception quality estimation unit, the operation word length is set long when the reception quality is good, the operation word length is set short when the reception quality is bad, and the reception signal is received An arithmetic word length adjustment unit that outputs as
A turbo decoder that decodes the received sequence output from the arithmetic word length cut unit, performs error correction a predetermined number of times using the reliability information acquired by the decoding and the received sequence, and outputs a decoding result A receiving unit characterized by that.   The reception quality estimation unit estimates the reception quality from a desired signal to interference signal power ratio of an information signal included in the reception signal based on reception power of a control signal included in the reception signal and reception power of a noise signal. The receiving unit according to claim 1, wherein: A reception demodulator that receives a radio signal, demodulates it, and outputs it as a received signal;
A reception quality estimation unit for estimating the reception quality of the received signal;
Based on the estimation result by the reception quality estimation unit, the operation word length is set long when the reception quality is good, the operation word length is set short when the reception quality is bad, and the reception signal is received An arithmetic word length adjustment unit that outputs as
A turbo decoder that decodes the received sequence output from the arithmetic word length cut unit, performs error correction a predetermined number of times using the reliability information acquired by the decoding and the received sequence, and outputs a decoding result A mobile communication terminal characterized by the above.   The reception quality estimation unit estimates the reception quality from a desired signal to interference signal power ratio of an information signal included in the reception signal based on reception power of a control signal included in the reception signal and reception power of a noise signal. The mobile communication terminal according to claim 3, wherein: In the reception quality estimation unit, the step (1) of estimating the reception quality of the received signal,
In the operation word length adjustment unit, according to the estimation result in the step (1), when the reception quality is good, set the operation word length long, and when the reception quality is bad, set the operation word length short, Outputting the received signal as a received sequence (2);
In the turbo decoder, decoding the received sequence output in the step (2), performing error correction a predetermined number of times with the reliability information acquired by the decoding and the received sequence, and outputting a decoding result ( And 3) a decoding method.   In the step (1), based on the received power of the control signal and the received noise signal included in the received signal, the received quality is estimated from the desired signal to interference power ratio of the information signal included in the received signal. The decoding method according to claim 5, wherein:

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