JPH06252971A - Digital transmission device - Google Patents

Abstract

PURPOSE:To improve transmission quality by executing soft decision maximum likelihood decoding while holding an effect of bit interleave by executing the bit interleave for considering a feature of a circuit error of multi-valued modulation transmission line, and also, calculating a branch metric by a bit unit. CONSTITUTION:A transmitter of a digital transmission equipment for executing a multi-valued amplitude modulation is provided with a bit interleave means 5 for classifying a transmitting bit, and especially, distributing the bit of a class which comes to require an error resistance to a bit position scarcely having an error on signal point arrangement, and its receiver is provided with a likelihood calculating means 17 for approximating a probability distribution function of a received symbol amplitude value in a signal space by the maximum value of an error function value related to plural signal points, and deriving a likelihood value to each received symbol by a bit unit, based on this approximate value, a means 18 for execute be-interleave by a but unit with regard to the likelihood value, and means 19, 20 for selecting the pulse of the highest likelihood by a value obtained by adding successively the likelihood value and decoding digital information.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital transmission device for high efficiency modulation in a digital mobile communication system or the like.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing the structure of a conventional digital transmission device for performing four-level amplitude modulation. In FIG. 4, (a) is a transmitter and (b) is a receiver. In FIG. 4A, 41 is a transmission data input terminal. Four
A convolutional encoder (FEC) 2 performs a convolutional code on the transmission data input from the transmission data input terminal 41. A serial / parallel converter 43 outputs the output of the convolutional encoder 42 in parallel in units of 2 bits. 44
Is a symbol interleaver for rearranging the output of the serial / parallel converter 43 in units of 2 bits. 45 is 4 based on the output of the symbol interleaver 44 based on FIG.
It is a 4-valued pulse generator that generates a value-weighted impulse. A transmission filter 46 limits the Nyquist band with respect to the output of the four-value pulse generator 45. Reference numeral 47 is an analog multiplier that multiplies the output of the transmission filter 46 and the output of the oscillator 48 and outputs the result. Reference numeral 48 is an oscillator that generates a sine wave. Reference numeral 49 is a transmission antenna for transmitting the output of the analog multiplier 47 toward the receiver side.

In FIG. 4B, reference numeral 50 is a receiving antenna for receiving data from the transmitter side. Reference numeral 51 is an analog multiplier for multiplying the received data from the receiving antenna 50 and the output from the oscillator 52. 52 is an oscillator that outputs a sine wave. Reference numeral 53 is a reception filter that limits the Nyquist band for the output from the analog multiplier 51. Reference numeral 54 is a sampler that selects an identification point signal from the output of the reception filter 53. Reference numeral 55 is a symbol deinterleaver which detects a four-valued weighted impulse from the output of the sampler 54 and solves interleaving. Reference numeral 56 is a branch metric calculator that calculates the likelihood (branch metric) for each sampler output unit (symbol unit). 5
A soft-decision Viterbi decoder (DFEC) 7 performs soft-decision Viterbi decoding on the output of the branch metric calculation unit 56.
Is. Reference numeral 58 is a reception data output terminal for outputting the decoding result.

Next, the operation of the above-mentioned conventional 4-value amplitude modulation transmission apparatus will be described. In FIG. 4, when 4 kb / s of transmission data is input from the transmission data input terminal 41, the convolutional encoder 42 performs encoding and outputs 8 kb / s of data. The serial / parallel converter 43 is
The bit interleaved output of the convolutional encoder 42 is output in parallel in 2-bit units, and the symbol interleaver 44
Performs symbol interleaving in 2-bit units. The quaternary pulse generator 45 generates a quaternary weighted impulse based on FIG. Root Nyquist transmission filter 46
Performs band limitation on the four-valued weighted impulse and outputs an analog signal. Analog multiplier 47
Performs frequency conversion by multiplying the output of the root Nyquist transmission filter 46 and the sine wave output from the oscillator 48, and transmits the output from the transmission antenna 49 to the receiver.

On the other hand, the signal received by the receiving antenna 50 of the receiver is frequency-converted by being multiplied by the sine wave output from the oscillator 52 by the analog multiplier 51, and then by the root Nyquist receiving filter 53. External noise is suppressed. The output of the reception filter 53 is the sampler 5
At 4 the identification points are sampled and the amplitude of the 4-value weighted impulse is detected. The symbol interleaver 55
The amplitude values of the weighted impulses are rearranged to solve interleaving. The branch metric calculation unit 56 calculates a negative square value of the distance from each signal point per sampler output unit (symbol unit) as a branch metric (likelihood) based on FIG. Here, FIG. 6 shows the probability distribution of the sampler output amplitude, and white Gaussian noise is superimposed on each signal point as receiver noise. According to this FIG. 6, if the likelihood when the transmission symbol when the amplitude A is received is “−3”, that is, the likelihood is expressed by a logarithmic expression, the distance from the signal point (−3) is 2 It becomes a negative value of the power. The same applies to the likelihoods of the other symbols “−1”, “1”, and “3”. With respect to the branch metric calculated in symbol units in this way, the soft-decision Viterbi decoder 57 calculates the path metric by adding the branch metric for all transmission symbol sequences, and outputs the sequence with the maximum path metric as the decoded value. Then, the data is output from the reception data output terminal 58.

In this way, even the above-mentioned conventional four-level amplitude modulation transmission apparatus can obtain high transmission quality by soft-decision maximum likelihood decoding.

[0007]

However, in the above-mentioned conventional 4-value amplitude modulation transmission apparatus, since the branch metric is calculated for each symbol in the soft decision decoding, it is necessary to perform interleaving on a symbol-by-symbol basis. There was a problem that it was not possible to carry out sufficient dispersion.
In addition, when allocating to bits that need to reduce bit errors and other bits like voice data compressed by a voice codec, even-numbered bits are less susceptible to line errors than odd-numbered bits. There is a problem that bit interleaving that makes use of the characteristics of the transmission path cannot be performed.

The present invention solves such a conventional problem by performing bit interleaving in consideration of the line error characteristics of a multilevel modulation transmission line and calculating a branch metric on a bit-by-bit basis. It is an object of the present invention to provide a digital transmission device capable of performing soft-decision maximum likelihood decoding while maintaining the effect of bit interleaving, thereby improving the transmission quality.

[0009]

According to the present invention, in order to achieve the above-mentioned object, a transmitter of a digital transmission device which performs M (> 2) value amplitude modulation or amplitude phase modulation classifies transmission bits. In particular, a bit interleaving means for allocating bits of a class that requires error resilience to bit positions with few errors due to signal point arrangement is provided.

According to the present invention, a receiver of a digital transmission device that performs M (> 2) -value amplitude modulation or amplitude phase modulation uses the probability distribution function of the received symbol amplitude value in the signal space as an error function value for a plurality of signal points. Of the likelihood value for each received symbol based on this approximate value, a means for deinterleaving the likelihood value in bit units, and a value obtained by successively adding the likelihood values. And a means for decoding the digital information by selecting the path with the highest likelihood.

[0011]

According to the present invention, with the above-mentioned configuration, when the bit error such as voice data compressed by the voice codec that needs to be particularly reduced and the bit other than that are distributed, the line error of the multilevel modulation transmission line is eliminated. It is possible to improve the transmission quality by classifying the bit that is easily received and the bit that is not easily received and performing bit interleaving. Also, by approximating the probability distribution function of the received symbol amplitude value in the received signal space with the maximum value of the error function values for multiple signal points, the branch metric can be calculated in bit units, and the effect of bit interleaving is maintained. However, since soft decision maximum likelihood decoding can be performed, it is possible to further improve the transmission quality.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing the configuration of a digital transmission device for performing four-level amplitude modulation in one embodiment of the present invention. In FIG. 1, (a) is a transmitter and (b) is a receiver. In FIG. 1A, 1 is a transmission data input terminal. Reference numeral 2 is a switch for allocating the transmission data input from the transmission data input terminal 1 to class 1 which needs to particularly reduce bit errors and class 2 other than that.
Reference numeral 3 denotes a first convolutional encoder (FEC (1)) that performs a convolutional code on transmission data of class 1, and 4 denotes a second convolutional encoder (FEC (FEC (1) that performs a convolutional code on transmission data of class 2). 2)). In this embodiment, it is assumed that the first convolutional encoder 3 and the second convolutional encoder have the same number of output bits. A bit interleaver 5 performs bit interleaving on the outputs of the convolutional encoders 3 and 4. A serial / parallel converter 6 outputs the output of the bit interleaver 5 in parallel in units of 2 bits. Reference numeral 7 denotes a 4-value weighted impulse based on FIG. 2 for the output of the serial / parallel converter 6 4
It is a value pulse generator. A transmission filter 8 limits the Nyquist band with respect to the output of the 4-level pulse generator 7.
An analog multiplier 9 multiplies the output of the transmission filter 8 and the output of the oscillator 10. Reference numeral 10 is an oscillator that generates a sine wave. Reference numeral 11 is a transmitting antenna for transmitting the output of the analog multiplier 9 toward the receiver.

In FIG. 1B, reference numeral 12 is a receiving antenna for receiving data from the transmitter side. Reference numeral 13 is an analog multiplier for multiplying the received data from the receiving antenna 12 and the output from the oscillator 14. Reference numeral 14 is an oscillator that outputs a sine wave. Reference numeral 15 is a reception filter that limits the Nyquist band for the output from the analog multiplier 13. Reference numeral 16 is a sampler for selecting an identification point signal from the output of the root Nyquist reception filter 15. Reference numeral 17 denotes a branch metric calculation unit that calculates the likelihood for each bit. Reference numeral 18 is a branch metric bit deinterleaver that performs deinterleaving on a branch metric basis in bit units. Reference numeral 19 denotes a first soft-decision Viterbi decoder (DFEC (1)) for performing soft-decision Viterbi decoding on bits of class 1, and reference numeral 20 indicates a second soft-decision Viterbi decoder for performing soft-decision Viterbi decoding on bits of class 2. DFEC (2)). Reference numeral 21 is a switch for multiplexing the class 1 and class 2 signals output from the soft-decision Viterbi decoders 19 and 20. Reference numeral 22 is a reception data output terminal for outputting the multiplexed data.

Next, the operation of the four-level amplitude modulation transmission apparatus in the above embodiment will be described. In FIG. 1, when transmission data of 4 kb / s is first input from the transmission data input terminal 1, the switch 2 transmits the data to the first convolutional encoder 3 and the second convolutional encoder 4 at 2 kb / s. It is separated into s and transmitted. The first convolutional encoder 3 and the second convolutional encoder 4 respectively perform encoding and perform 4 kb / s.
The data of is output. Then the bit interleaver 5
After performing bit interleaving for each class,
Class 1 bits are inserted into the even bits and class 2 bits are inserted into the odd bits, and are multiplexed and output. As shown in FIG. 2, this is because of the input code consisting of 2 bits of XY,
This is because the even-numbered bits X represent the sign of the amplitude A and the odd-numbered bits Y represent the amplitude value. Next, the serial / parallel converter 6 outputs the output of the bit interleaver 5 in parallel on a 2-bit basis, and the 4-valued pulse generator 7 generates 4-valued weighted impulses based on FIG. Next, route Nyquist transmission filter 8
However, if the four-valued impulse is band-limited and an analog signal is output, the analog multiplier 9
Performs frequency conversion by multiplying this with the sine wave output from the oscillator 10, and transmits from the transmitting antenna 11 to the receiver.

On the other hand, the signal received by the receiving antenna 12 of the receiver is frequency-converted by being multiplied by the sine wave output from the oscillator 14 by the analog multiplier 13 and then converted by the root Nyquist receiving filter 15 into the harmonic and the band. External noise is suppressed. The output of the reception filter 15 is the sampler 1
At 6 the identification points are sampled to detect the amplitude of the 4-valued weighted impulse. Branch metric calculator 17
Calculates the following branch metric (likelihood) per sampler based on FIG.

I. Regarding the first bit X (see FIG. 3A) (1) When the sampler output amplitude is A ≦ −2, the likelihood that the transmission first bit is “0” = − | A−1 |
² Likelihood that the first bit of transmission is “1” = − | A − (−
3) | ² (2) Likelihood that the transmission first bit is “0” when the sampler output amplitude is −2 <A ≦ −2 = − | A−1 |
² Likelihood that the first bit of transmission is “1” = − | A − (−
1) | ² (3) Likelihood that the transmission first bit is “0” when the sampler output amplitude is 2 <A = − | A−3 |
² Likelihood that the first bit of transmission is “1” = − | A − (−
1) | ² II. Regarding the second bit Y (see FIG. 3B) (1) When the sampler output amplitude is A ≦ 0, the likelihood that the second transmitted bit is “0” = − | A − (−
1) | ² Likelihood that second bit of transmission is “1” = − | A − (−
3) | ² (2) Likelihood that the transmission second bit is “0” when the sampler output amplitude is 0 <A = − | A−1 |
² Likelihood that second bit of transmission is “1” = − | A−3 |
²

FIG. 3 shows the probability distribution of the sampler output amplitude, in which white Gaussian noise is superimposed as receiver noise on each signal point. Usually the branch metric is
Since the likelihood, that is, the likelihood when the transmission bit when the amplitude A is received is "0" and when the transmission bit is "1", is expressed by a logarithmic expression, it is the square of the distance from the signal point. However, for the first bit X in FIG. 3A, X = 0
Since the distribution for and X = 1 is the sum of two Gaussian distributions, the likelihood cannot be simply expressed by the square of the distance. Therefore, in the present embodiment, the sum of the two Gaussian distributions is approximated by the Gaussian distribution with the larger probability, and from the signal points close to the amplitude value A in the regions of X = 0 and X = 1, respectively, −1) × (square of distance) is applied to the likelihood. The same applies to the second bit Y.

In this way, with respect to the branch metric calculated on a bit-by-bit basis, the branch metric bit deinterleaver 18 separates into class 1 and class 2 and solves the interleaving. The first soft-decision Viterbi decoder 19 and the second soft-decision Viterbi decoder 20
Calculates the path metric by adding the branch metrics of class 1 and class 2 for all transmission sequences, and outputs the sequence having the maximum path metric as a decoded value. The switch 21 outputs the signals of class 1 and class 2. After multiplexing, the data is output from the reception data output terminal 22.

As described above, according to the above embodiment, since the branch metric can be calculated in bit units, the transmitter performs bit interleaving in consideration of the characteristics of the transmission path, and while maintaining its effect, the bit interleaving is performed. Soft decision maximum likelihood decoding can be performed in units, and high transmission quality can be obtained. Although the above embodiment is an example of a transmission device that performs amplitude modulation, the present invention can be similarly applied to a transmission device that performs amplitude phase modulation.

[0020]

As is apparent from the above embodiments, the present invention improves the transmission quality by performing bit interleaving in consideration of bits that are susceptible to line errors and bits that are not susceptible to line errors in a multilevel modulation transmission line. be able to. Also, the branch distribution metric is calculated bit by bit by approximating the probability distribution function of the received symbol amplitude value in the received signal space by the maximum value of the error function value for multiple signal points, and the soft decision maximum is performed while performing bit deinterleaving. Since the likelihood decoding can be performed, it is possible to further improve the transmission quality. Furthermore, since the amount of each calculation can be reduced as compared with the related art, it is possible to reduce the power consumption and the cost of the device.

[Brief description of drawings]

FIG. 1A is a block diagram of a transmitter of a digital transmission apparatus according to an embodiment of the present invention. FIG. 1B is a block diagram of a receiver of a digital transmission apparatus according to an embodiment of the present invention.

FIG. 2 is a signal point arrangement diagram of a quaternary amplitude modulation transmission signal according to an embodiment of the present invention.

FIG. 3A is a received signal point arrangement according to an embodiment of the present invention and a probability distribution diagram of a received amplitude for the first bit. FIG. 3B is a received signal point arrangement according to the same embodiment and a second distribution diagram.
Probability distribution map of received amplitude for bits

FIG. 4A is a block diagram of a transmitter of a digital transmission device in a conventional example. FIG. 4B is a block diagram of a receiver of a digital transmission device in a conventional example.

FIG. 5 is a signal point arrangement diagram of a 4-value amplitude modulation transmission signal in a conventional example.

FIG. 6 is a probability distribution diagram of reception signal point arrangement and reception amplitude in a conventional example.

[Explanation of symbols]

1 Transmission Data Input Terminal 2 Switch for Distributing Transmission Data into Class 1 and Class 2 3 First Convolutional Encoder (FEC (1)) 4 Second Convolutional Encoder (FEC (2)) 5 Bits Interleaver 6 Serial / parallel converter 7 4-level pulse generator 8 Root Nyquist transmission filter 9 Analog multiplier 10 Oscillator 11 Transmission antenna 12 Reception antenna 13 Analog multiplier 14 Oscillator 15 Root Nyquist reception filter 16 Sampler for selecting discrimination point signal 17 Branch metric calculator 18 Branch metric bit deinterleaver 19 First soft-decision Viterbi decoder (DEFEC (1)) 20 Second soft-decision Viterbi decoder (DEFEC (2)) 21 Multiplexes class 1 and class 2 signals Switch 22 for conversion to reception data output end

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Claims (3)

[Claims] 1. In a digital transmission device for performing M (> 2) -value amplitude modulation or amplitude phase modulation, a transmitter classifies transmission bits into classes, and arranges bits of a class for which error resilience is particularly required at signal points. Digital transmission equipment equipped with bit interleaving means for allocating to bit positions with few errors. 2. In a digital transmission device for performing M (> 2) value amplitude modulation or amplitude phase modulation, a receiver sets a probability distribution function of a received symbol amplitude value in a signal space to a maximum error function value for a plurality of signal points. Value, and means for obtaining the likelihood value for each received symbol on a bit-by-bit basis based on the approximate value; means for deinterleaving the likelihood value in bit units; and a value obtained by sequentially adding the likelihood values. And a means for decoding the digital information by selecting the path with the highest likelihood. 3. A digital transmission device comprising the transmitter according to claim 1 and the receiver according to claim 2.