JPH0821889B2 - Simplified Viterbi equalizer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention finds application in digital wireless communication systems, especially high speed, wideband digital land mobile communications.

[0002]

In a conventional Viterbi equalization method for compensating the symbol number of the states (combinations of possible data), using the impulse response of the channel, by the closest become series to the transmission data sequence Viterbi algorithm, Maximum likelihood
Perform sequence estimation. On the other hand, as a simplification method in which the calculation amount is reduced, a state considered in Viterbi equalization is m symbols (m <
L; L is the total number of compensation symbols), and for the intersymbol interference due to Lm symbols, by using the already determined data and adding a correction term in the calculation of the metric, a delayed wave with a large delay time is obtained. There is a method of applying the Viterbi algorithm within a limited delay time by removing the influence of the inter-code interference of. In addition, there is a method in which Viterbi equalization with a number of states smaller than the number of states that can be compensated is performed a plurality of times to remove the influence of intersymbol interference due to a delayed wave with a large delay time.

[0003]

In the Viterbi equalization system,
When the number of delay symbols to be compensated increases, the amount of calculation increases exponentially, which makes it difficult to realize the device. On the other hand, in the conventional simplification method, a wave with a small delay time is subjected to sequence estimation by the Viterbi algorithm , while a delay wave with a large delay time is removed so that equalization may be performed depending on the delay time of the delay wave. Performance deteriorates.

[0004]

The delay wave to which the Viterbi algorithm is applied is limited to n waves (n <the total number of delay waves to be compensated) to suppress an increase in the amount of calculation. In addition, the estimated
L is the total number of delayed waves to be compensated using the pulse response.
By selecting n waves with large received power from among the delayed waves with delay times up to the symbol , sequence estimation is always performed for waves with large power, so that the delay of delayed waves is reduced as in the conventional simplification method. No characteristic deterioration with time.

[0005]

1 is a block diagram of the present invention. The impulse response estimation unit 11 estimates the impulse response of the propagation path. The temporary decision unit 12 decodes the initial temporary decision data. Next, using the impulse response estimated by the applied wave selection unit 13, the delay up to the compensable delay time (L symbol) is used.
From among the delay waves with an extended time, a large n wave power (slow
Delay wave D1, delay wave D2, ..., Delay wave Dn: 0 ≦ D1
<L, D1 <D2 <L, ..., Dn-1 <Dn ≦ L)
And the intersymbol interference removing unit 14 uses the impulse response estimated to be the temporary determination data to select the selected n
Intersymbol interference other than waves is eliminated. The Viterbi equalization unit 15 sets the estimated impulse response due to a wave other than the selected n wave to 0, and performs Viterbi equalization on the selected n wave.

At this time, in the application of the Viterbi algorithm, if the selected waves are not continuous, the Viterbi algorithm is divided and applied. As an example, consider a case where two waves are selected and the delayed wave for Viterbi equalization is a direct wave and a wave delayed by three symbols. FIG. 2 shows a model of the situation at this time. The transmission data sequence 21 indicates the time-series order of transmission data. In the propagation path model 22, taps connected by solid lines are combined. That is, the direct wave and the wave delayed by 3 symbols are added.
This received wave is divided as shown by the divided reception sequence 23. Here, the numbers in parentheses indicate the order of the added transmission data series. Each received sequence is equalized by the Viterbi equalization unit 24 and becomes a sequence 25 after division equalization. This is synthesized and the equalization result sequence 2
Get 6. At this time, each received sequence is
The processing amount for sequence estimation is not divided because it becomes shorter.
Same as the case. The above operation is for any dark blue combination
Applicable.

Assuming that the multi-valued number of modulation is k bits and the number of compensable symbols is L, the Viterbi algorithm is performed on 2 ^kL states in the conventional system, whereas in the system of the present invention,
Since 2 ^kn and n <L, the calculation amount can be reduced.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A case where the present invention is applied to a time division multiplex transmission system where the modulation method is 4-value orthogonal modulation will be described here.

FIG. 3 shows a block diagram of the embodiment. Antenna 3
The signal received at 1 has its out-of-band noise removed by the band-pass filter unit 32, and then the reception level fluctuation is compensated by the automatic gain adjustment unit 33. In the quadrature demodulation unit 34,
The in-phase component and the quadrature component are separated, and each component is converted into digital data by the analog / digital conversion unit 25. The converted digital data is sent to the equalization processing unit 36. In the equalization processing unit 36, the digital signal processor performs equalization processing.

FIG. 4 shows the details of the equalization processing unit 36. FIG.
And the symbols A, B, and C in FIG. 4 indicate the input / output relationship to the equalization processing unit 36 in FIG.
It is transmitted according to the transmission format of FIG.

In the impulse response estimation unit 41, the impulse response at each time point is estimated by the Kalman algorithm in the preamble 51 and the postamble 52, and the data of both are interpolated to obtain the impulse response in the information unit. To estimate. The matched filter unit 42 forms a matched filter using the estimated impulse response to maximize the S / N ratio. The provisional determination unit 43 obtains provisional determination data by using the estimated impulse response and removing the intersymbol interference due to the delayed wave at the time of the determination and performing a determination. Applied wave selection unit 4
In 4, the n waves are selected in descending order of power from the estimated impulse response. The intersymbol interference removing unit 45 removes the intersymbol interference components of the waves other than the selected n waves from the data from the matched filter 42 by using the temporary determination data and the impulse response. The matched filter unit 46 forms a matched filter using an impulse response in which the impulse response other than the selected wave is set to 0 among the impulse responses estimated in the data excluding the intersymbol interference other than the selected wave. To maximize the S / N ratio. The equalizer 47 uses the data from the matched filter 46 to select the selected n
The Viterbi algorithm is applied to the waves and equalization is performed.

FIG. 6 shows a transmission rate of 256 ksymbol /
s, preamble length 20 symbols, postamble length 2
When the present invention is not applied when 0 symbols and the data length is 200 symbols, and when Eb / NO (1
The result of the computer simulation of the error rate characteristics with respect to the signal power to noise power density ratio per bit) is shown. In the simulation, the number of symbols that can be compensated for selective fading is set to 5 symbol delay, and the number of waves to be selected is 2.

In the conventional simplification method, the case where one symbol delay is compensated by Viterbi equalization and the other delayed waves are removed is indicated by a circle, and when the present invention is applied, a tentative determination is performed, and then Viterbi is performed. The case where the equalization by the algorithm is performed once is marked with ■, the tentative judgment is performed, then the equalization by the Viterbi algorithm is performed, the result is used as the tentative judgment data, and the case where the equalization by the Viterbi algorithm is performed again is marked Indicate.

As a propagation path model, there is a three-wave model in which there are a preceding wave, a wave delayed by two symbols and a wave delayed by four symbols, their average powers are equal, and each wave is subjected to Rayleigh fading. There is. The maximum Doppler frequency of fading is 100 Hz.

In FIG. 6, in the conventional simplified system, 1
Equalization characteristics are poor because only Viterbi equalization compensates for symbol delay. It can be seen that when the present invention is applied, even when the Viterbi algorithm is applied only once, the equalization characteristic is superior to the conventional simplified method. Furthermore, applying the Viterbi algorithm twice improves the characteristics. Even when the Viterbi algorithm is applied twice, up to 1 symbol delay is compensated by Viterbi equalization by the conventional simplification method, and other delay waves are almost the same as when they are removed. Even in the conventional simplification method, if the number of symbols to be compensated by Viterbi equalization is increased, the equalization characteristic is improved, but the amount of calculation increases exponentially.

It is possible to use a conventional simplification method in the tentative decision estimating section.

[0017]

According to the present invention, as a measure against selective fading in wide band transmission, an equalizer having a small device scale and excellent equalization characteristics can be realized.

[Brief description of drawings]

FIG. 1 is a configuration diagram of the present invention.

FIG. 2 is an example of a case where Viterbi equalization is performed by division.

FIG. 3 is a configuration diagram of an embodiment of the present invention.

FIG. 4 is a transmission frame format of a transmission signal.

FIG. 5 is a detailed configuration diagram of an equalization processing unit of the present invention.

FIG. 6 is an error rate characteristic under multipath fading conditions when the present invention is applied.

[Explanation of symbols]

 11 ... Impulse response estimation unit 12 ... Temporary determination unit 13 ... Applied wave selection unit 14 ... Intersymbol interference removal unit 15 ... Viterbi equalization unit 21 ... Transmission data sequence 22 ... -Propagation path model 23 ... Divided reception sequence 24 ... Viterbi equalization unit 25 ... Sequence after division equalization 26 ... Sequence of equalization result 31 ... Antenna 32 ... Band Pass filter unit 33 ... Automatic gain adjustment unit 34 ... Quadrature demodulation unit 35 ... Analog / digital conversion unit 36 ... Equalization processing unit 41 ... Impulse response estimation unit 42 ... Matched filter unit 43 ... Temporary determination unit 44 ... Applied wave selection unit 45 ... Intersymbol interference removal unit 46 ... Matched filter unit 47 ... Equalization unit 51 ... Preamble 52 ... Information 53. ..Postamble

Claims (1)

[Claims] 1. In a transmission line in which intersymbol interference occurs due to multipath fading, a transmission line estimation unit that estimates an impulse response of the transmission line, a temporary determination unit that makes a temporary determination, and delays that can be seen from the estimated impulse response. Wave delay time and
Using the applied wave selector that selects in order from the highest received level in order to limit the waves to which the Viterbi algorithm is applied rather than the magnitude of the received level , the temporarily determined data and the estimated impulse response are used. The intersymbol interference remover that removes the effect of intersymbol interference other than the selected wave and only the intersymbol interference of the selected wave, and the estimated impulse that targets only the intersymbol interference of the selected wave A simplified Viterbi equalizer characterized by performing a multipath fading distortion compensation by including a Viterbi equalization unit using a Viterbi algorithm using a response .