JP2003258775A - Iteration decoding system and power consumption reduction method therein - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an iteration decoding system in which power consumption can be reduced. <P>SOLUTION: The iteration decoding system is provided with first and second soft input and soft output decoders 2 and 3 for performing soft input and soft output decoding, an interleaver/deinterleaver for interleaving/deinterleaving reliability information likelihoods respectively outputted from the first and second soft input and soft output decoders and respectively supplying them to the second and first soft input and soft output decoders, a detection means for detecting the quality of a received signal, and a weighting means for multiplying a coefficient in which the value is high when the quality of the received signal is high and the value is low when the quality of the received signal is low, to at least one of the reliability information likelihood supplied from the first soft input and soft output decoder to the second soft input and soft output decoder and the reliability information likelihood supplied from the second soft input and soft output decoder to the first soft input and soft output decoder. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an iterative decoding system such as a turbo decoding system, and more particularly to an iterative decoding system capable of reducing power consumption when the quality of a received signal is good.

[0002]

2. Description of the Related Art In recent years, the turbo decoding system has been in the limelight as a decoding system approaching the limit of Shannon, and W-CDMA and CDMA-20, which are the standards for next-generation mobile communication.
It is also used for 00.

[0003]

The element decoder is S
Since an ISO (Soft In Soft Output) decoder is used and an element decoder uses an interleaver to perform iterative decoding, accelerating the convergence of the decoding result in this iterative decoding reduces power consumption. Lead to things. Especially for a mobile terminal that wants to extend the life of the battery as much as possible, it is important to reduce power consumption.

SI applied to turbo decoder element decoder
As an SO (Soft In Soft Output) algorithm, the selection of whether the path between the time points is "1" or "0" is simplified by selecting the maximum value (MAX) of the result of likelihood calculation. Max-log-MAP (Max Logarithmi
c Maximum A Posteriori), SOVA (Soft in SoftOu
Methods such as tput Viterbi Algorism) are generally widely used. Since iterative decoding is performed in any method, an appropriate decoding stop criterion that uses the soft-decision decoding result obtained at each iteration, for example, the hard-decision decoding result obtained during the iterative decoding, The power consumption can be reduced by using a device that counts the number of inversion bits compared with the result and determines that the decoding result has converged sufficiently if it is less than a certain number of inversions and stops decoding. It is possible. In addition to this, various decoding suspension norms have been published for the purpose of reducing power consumption by iterative decoding.

The present invention makes it possible to speed up the convergence of the decoding result by iterative decoding when the radio wave propagation path is good, and consequently to reduce the power consumption, by adding a small amount of processing. And a power consumption reduction method therefor.

[0006]

According to the present invention, a first soft-input soft-output decoder for performing soft-input soft-output decoding and a second soft-input soft-output decoder for performing soft-input soft-output decoding are provided. An interleaver that interleaves the reliability information likelihood output from the first soft-input soft-output decoder and supplies the reliability information likelihood to the second soft-input soft-output decoder; and the second soft-input soft-output decoder. A deinterleaver for supplying the reliability information likelihood output by the first soft input soft output decoder to the first soft input soft output decoder, and the first soft input soft output decoder and the second soft input soft output decoder. In an iterative decoding method in which the input soft output decoder alternately repeats the decoding of the received signal, the detection means for detecting the quality of the received signal, the value is high when the quality of the received signal is high, and the quality of the received signal is When the value is low, the coefficient is low, Wherein the serial the reliability information likelihood and the second SISO decoder is supplied to the second SISO decoder from the first SISO decoder first
Weighting means for multiplying at least one of the reliability information likelihoods supplied to the soft-input soft-output decoder of.

In the above-mentioned iterative decoding method, the quality may be a signal-to-interference ratio of the received signal.

The iterative decoding system may include averaging means for taking a time average of the quality, and the weighting means has a high value when the time average of the quality of the received signal is high, and the weighted means has a high value. When the time average of the quality is low, the coefficient having the low value is supplied from the first soft-input soft-output decoder to the second soft-input soft-output decoder and the reliability information likelihood and the second soft-input soft-output decoder. At least one of the reliability information likelihoods supplied from the second soft-input soft-output decoder to the first soft-input soft-output decoder may be multiplied.

In the above iterative decoding method, the time average period may be a period corresponding to the decoding length of the received signal.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention can be applied to a case where iterative decoding is performed among a plurality of SISO element decoders via reliability information likelihood. For simplification, the features of the present invention will be described by taking a turbo decoder (FIG. 1) composed of two SISO element decoders as an example. In FIG. 1, 101 is a received data memory unit, 102 is a first SISO element decoder, 103 is a second SISO element decoder, 104 is an interleaver (denoted as “π” here), and 105 is a deinterleaver. Lever (denoted here as "π ^-1 "), 10
Reference numeral 6 is a coefficient for weighting reliability information likelihood information obtained by each SISO element decoder (referred to as “h coefficient” here). Here, the reliability information likelihood indicates a soft decision value given in advance for each information bit. Further, an information bit is obtained by performing a hard decision on this reliability information likelihood. A hard decision processing unit 7 performs a hard decision on the reliability information likelihood obtained by the SISO element decoder. Reference numeral 108 denotes a reliability information likelihood memory unit for passing the reliability information likelihood which is the decoding result of each SISO element decoder to the next SISO element decoder. SISO
When using MAX-Log-MAP for the element decoder, the h coefficient is multiplied by the reliability information likelihood as a constant value,
Iterative decoding is performed. A feature of the present invention is that the propagation path environment (for example, SIR (Signal estimated from Pilot symbol) is used.
to Interference Ratio) value)
By changing the weighting of the h coefficient, the decoding result can be converged with a smaller number of iterations.

A SISO (Soft In Soft Output) element decoder is a decoder that determines the transmission sequence using the Euclidean distance by using the soft decision received value as it is. Further, since turbo decoding is performed using two decoders, each decoder is called an element decoder.

FIG. 2 shows the configuration of an embodiment of the receiving apparatus according to the present invention. In FIG. 2, 201 is an antenna, 202 is a transmission / reception separation unit, 203 is a reception radio unit, 204 is a despreading unit, 205 is a demodulation unit, 206 is a reception SIR estimation unit, 10
1 is the received data memory unit also shown in FIG. 1, 208 is the received SIR processing unit, 209 is the turbo decoding unit, and 210 is the SIR.
The -h coefficient lookup table, 107 is the hard decision processing unit also shown in FIG. The turbo decoding unit 209 has the configuration shown in FIG.

The operation of the receiving apparatus will be described with reference to FIGS. 1 and 2.

The spread signal transmitted from the base station or the mobile terminal is received by the antenna 201, and the transmission / reception separating unit 20.
It is input to the reception wireless unit 203 via 2. In the reception radio section 203, the received signal is a band pass filter (BP).
The received signal, which has passed through F) and has the out-of-band component removed, is frequency-converted into an intermediate frequency band (IF) by a local oscillation signal of a local oscillator (not shown). The received signal whose frequency has been changed to the IF band passes through the BPF, and then the automatic gain control circuit (AG
After being corrected to an appropriate signal level by C), quasi-coherent detection is performed and the frequency is converted into a baseband signal. The received signal whose frequency has been converted to the base band is passed through a low pass filter (LPF), A / D converted, and output as a digital signal.

The receiving digital signal output from the receiving radio section 203 is despread in the despreading section 204 and output as a narrow band modulated signal. The signal output from the despreading unit 204 is demodulated by the demodulating unit 205, subjected to predetermined soft decision processing, and stored in the received data memory unit 207. Reception SIR estimation section 206 estimates the reception SIR using the pilot signal used for demodulation, and reception SIR value processing section 208 averages the estimated reception SIRs to obtain a reception SIR average value. In the turbo decoding unit 209, the reception data memory unit 101 and the reliability information likelihood memory unit 1
Iterative decoding is executed while updating the reliability information likelihood based on the data of 08. During the updating operation of the reliability information likelihood, the turbo decoding unit 209 receives the reception SIR estimating unit 206.
The SIR-h coefficient lookup table 210 is referred to based on the obtained SIR estimated value, and the reliability information likelihood is weighted by multiplying the referred h coefficient value,
Executes iterative decoding.

After it is determined that the decoding result has converged according to an appropriate decoding stopping criterion, or after the predetermined number of iterations has been reached, the iterative decoding operation ends and the hard decision processing unit 107 makes a hard decision. Information bits are extracted. An example of a suitable decoding stopping criterion is a method using cross entropy. This compares the hard-decision decoding result obtained during the iterative decoding with the hard-decision decoding result at the time of the next iterative decoding, and counts the number of inversion bits. It is a device that determines and stops decoding. Further, it is possible to use a method of using a decoding stop criterion such that when CRC (Cyclic Redundancy Check bits) is interpolated in the data, iterative decoding is stopped when the CRC check is correct.

The SISO element decoder having the configuration of FIG.
Details will be described in a turbo decoding device using ax-log-MAP. Before the incorporation of the optimum value of the h coefficient into the circuit, since the appropriate value of the h coefficient differs depending on how reliable the encoded data is in radio wave propagation and the algorithm of the SISO element decoder used. 210 needs to be determined. However, once decided, each SISO element decoder 102, 103
Since it is only necessary to multiply the reliability information likelihood obtained in step 1 by the h coefficient obtained from this lookup table 210,
It can be realized by adding a very simple circuit. The following example can be given as a method of calculating the SIR estimated value when creating the lookup table.

(1) Method using SIR estimation value by pilot signal (2) 3GPP (3rd Generation Partnership Projec)
t) In the W-CDMA terminal based on the standard, the downlink C
Propagation path SI using PICH (Common Pilot Channel)
Method using R estimated value

When transmitting encoded data, assuming that the sequence transmitted by encoding one data is A, the reception SIR is averaged at the time intervals at which A is transmitted. . For example, when the decoding length of the data is long and the decoding length extends over a plurality of wireless frames, the SIR estimation value uses the received SIR averaged over the entire spanning frames. For the propagation path estimation, a lookup table may be created using a method other than the above example.

The look-up table is the estimated SIR
The higher the value of, the larger the h coefficient is, and the lower the estimated SIR value is, the smaller the h coefficient is.

The following table shows an example of the relationship between the received SIR estimated value and the h coefficient in the SIR-h coefficient lookup table 210.

[0022]

[Table 1] By defining the h coefficient as shown in the above table, the bits forming the reliability information likelihood represented by a binary number are left-shifted by 1 bit to the left, and the reliability information likelihood is represented by a value of 1/2, represented by a binary number. Reliability information likelihood shifted by 2 bits to the left, reliability information likelihood multiplied by 1/4, reliability represented by binary numbers forming the reliability information likelihood shifted by 3 bits to the left Value of likelihood information × 1/8, reliability information likelihood value, reliability information likelihood × 1/2 value, reliability information likelihood × 1
The multiplier for multiplying the reliability information likelihood by a coefficient corresponding to the received SIR estimated value by appropriately combining and adding the value of / 4 and the reliability information likelihood × 1/8 value with each other has a simple configuration. Can be realized.

In order to accelerate the convergence of the decoding result, if the h coefficient value is a high SIR estimated value, it takes a value greater than 1,
If the SIR estimated value is low to some extent, the value of the h coefficient is set to a value smaller than 1. By setting the look-up table as shown in the above table, the weighting is increased because the reliability information likelihood value obtained as a result of the decoding operation of the SISO element decoder is likely to be certain during data transmission with a high received SIR estimation value. It is possible to speed up the convergence of the decoding result by the operation of multiplying the one obtained and passing it to the other SISO element decoder. Further, when the reliability information likelihood is passed from the SISO element decoder 1 to the SISO element decoder 2, MAX-log-
In MAP, a fixed value in which the h coefficient is set to, for example, 3/4 is used, and only when the reliability information is passed from the SISO element decoder 2 to the SISO element decoder 1, the value of the h coefficient is set to the value selected from the lookup table. You may take the method of using.

Whether or not the decoding result has converged is determined by, for example, using the CRC interpolated in the data to judge whether or not the data can be correctly decoded, or by determining the reliability information likelihood of the SISO element decoder. Each time the judgment value is repeatedly decoded, how many bits are inverted compared to the previous iteration is used as a guide, and if the number of inverted bits is less than a certain number, a method of stopping the iterative decoding is proposed. Therefore, it may be performed using a suitable decoding stop criterion.
By using the present invention, it is possible to improve the convergence of the number of repetitions in a good radio wave propagation path (high SIR estimation value), so it is possible to reduce power consumption by using an appropriate decoding stop criterion.

[0025]

As described above, the present invention has the following effects.

The first effect is that the power consumption required for turbo decoding in a good radio wave propagation environment can be reduced by adding a very small amount of processing and combining it with an appropriate decoding stopping criterion.

The reason is that the processing required in the present invention is only a multiplier that shifts the reliability information likelihood value and a lookup table that holds the correspondence relationship between the averaged SIR estimated value and the h coefficient. This is because, by adding these processes, the convergence of iterative decoding can be accelerated in a good radio wave propagation environment, and when viewed comprehensively, the power consumption required for turbo decoding can be reduced.

The second effect is that the complexity of the circuit to which the present invention is added is not different from the complexity of the circuit which performs the conventional turbo decoding system, and therefore the present invention cannot be incorporated due to the limitation of the circuit scale. In addition, the power consumption does not increase even if the processing according to the present invention is added.

The reason is that the SIR estimation unit uses W-CDMA.
This is because it already exists because it is indispensable for performing the power control that is standard in. Also,
Since the reception SIR-h coefficient look-up table can be realized with a very small circuit scale, it is only necessary to directly give the h coefficient together with the reception data to the turbo decoder 209, and the basic configuration of the turbo decoder is the same as the conventional one. Is.

[Brief description of drawings]

FIG. 1 is an SI to which a power consumption reduction method according to the present invention is applied.
It is a block diagram which shows the structure of the iterative decoding device provided with an SO element decoder, an interleaver, and a deinterleaver.

FIG. 2 is a block diagram showing a configuration of a receiving device including an iterative decoding device to which the power consumption reduction method shown in FIG. 1 is applied.

[Explanation of symbols]

101 Received data memory unit 102 first SISO element decoder 103 Second SISO Element Decoder 104 Interleaver 105 Deinterleaver 106 h coefficient 107 Hard decision processing unit 108 Reliability Information Likelihood Memory 201 antenna 202 Transmission / reception separation unit 203 reception wireless unit 204 despreader 205 demodulator 206 Reception SIR estimation unit 208 Reception SIR value processing unit 209 Turbo decoding unit 210 SIR-h coefficient lookup table

Claims (8)

[Claims] 1. A first soft-input soft-output decoder for soft-input soft-output decoding, a second soft-input soft-output decoder for soft-input soft-output decoding, and a first soft-input soft-output decoding An interleaver that supplies the reliability information likelihood output from the receiver to the second soft-input soft-output decoder, and a reliability information likelihood output from the second soft-input soft-output decoder. A deinterleaver for interleaving and supplying the first soft-input soft-output decoder to the first soft-input soft-output decoder, wherein the first soft-input soft-output decoder and the second soft-input soft-output decoder alternately receive signals In an iterative decoding method that repeats the decoding of, a detection unit that detects the quality of the received signal, a high value when the quality of the received signal is high, and a coefficient that is low when the quality of the received signal is low, First soft-input soft-output decoding From the reliability information likelihood supplied to the second soft-input soft-output decoder from the second soft-input soft-output decoder to the first soft-input soft-output decoder An iterative decoding method comprising: a weighting unit that multiplies at least one of the information likelihoods. 2. The iterative decoding system according to claim 1, wherein the quality is a signal-to-interference ratio of the received signal. 3. The iterative decoding system according to claim 1, further comprising an averaging unit that takes a time average of the quality, wherein the weighting unit has a high value when the time average of the quality of the received signal is high, The reliability information likelihood that the coefficient having the low value when the time average of the quality of the received signal is low is supplied from the first soft-input soft-output decoder to the second soft-input soft-output decoder. And the at least one of the reliability information likelihoods supplied from the second soft-input soft-output decoder to the first soft-input soft-output decoder. 4. The iterative decoding method according to claim 3, wherein the time average period is a period corresponding to a decoding length of the received signal. 5. A first soft-input soft-output decoder for performing soft-input soft-output decoding, a second soft-input soft-output decoder for performing soft-input soft-output decoding, and the first soft-input soft-output decoding. An interleaver that supplies the reliability information likelihood output from the receiver to the second soft-input soft-output decoder, and a reliability information likelihood output from the second soft-input soft-output decoder. A deinterleaver for interleaving and supplying the first soft-input soft-output decoder to the first soft-input soft-output decoder, wherein the first soft-input soft-output decoder and the second soft-input soft-output decoder alternately receive signals In a method of reducing power consumption in an iterative decoding method that repeats decoding of, a detection step of detecting the quality of the received signal, a high value when the quality of the received signal is high, and a value when the quality of the received signal is low. Has a low coefficient The reliability information likelihood supplied from the first soft-input soft-output decoder to the second soft-input soft-output decoder and the first soft-input soft-output decoder from the second soft-input soft-output decoder. A weighting step of multiplying at least one of the reliability information likelihoods supplied to the output decoder, and the power consumption reduction method. 6. The repeated power consumption reduction method according to claim 5, wherein the quality is a signal-to-interference ratio of the received signal. 7. The power consumption reduction method according to claim 5, further comprising an averaging step of taking a time average of the quality, wherein the weighting step has a high value when the time average of the quality of the received signal is high. , The reliability information likelihood supplied to the second soft-input soft-output decoder from the first soft-input soft-output decoder with a coefficient having a low value when the time average of the quality of the received signal is low. And at least one of the reliability information likelihoods supplied from the second soft-input soft-output decoder to the first soft-input soft-output decoder. 8. The power consumption reduction method according to claim 7, wherein the time average period is a period corresponding to a decoding length of the received signal.