JPH11225100A - Receiving method and receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute efficient reception even for a largely delayed wave by executing system estimation from a direct wave and a selected delayed wave through the use of a Viterbi algorithm with a multi-trellis structure corresponding to the delayed amount of a selected delayed wave. SOLUTION: An array processing part for extracting a direct wave consists of an adaptive array for extracting a direct array 10 and an adaptive algorithm with a constraining condition 11 to extract the direct wave from the demodulation signal of each array antenna. An array processing part for extracting a maximum power delayed wave consists of an adaptive array for extracting a maximum power delayed wave 16 and an adaptive algorithm with a constraining condition 17 similarly to the array processing part for extracting the direct wave. Then, a channel impulse response is obtained by using a training signal to select the delayed wave of maximum receiving power to extract each path by setting the direct wave and the selected delayed wave as desired waves. Then, a group estimation is executed from the direct wave outputted from the array and the selected delayed wave components.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving method and a receiving apparatus, and more particularly to a digital mobile communication and a wireless LAN.
TECHNICAL FIELD The present invention relates to a multipath countermeasure technique which becomes a problem in the above, and relates to a receiving method and a receiving apparatus which can overcome frequency selective fading.

[0002]

2. Description of the Related Art In recent years, a path diversity receiving system combining an adaptive array antenna and a Viterbi algorithm has been proposed as a multipath countermeasure technology. FIG.
The present inventor has established a conference (1997 IEEE 6th International Co.
nferrence on Universal Personal Communications, 12-
FIG. 16 is a functional block diagram showing a signal processing content of a conventional example announced in 16 October 1997).

This technique prepares not only a direct wave but also a candidate signal for a one-symbol delayed wave when calculating a steering vector array weight for direct wave extraction.
When calculating a steering vector array weight for extracting a symbol delayed wave, by preparing a candidate signal for a direct wave as well as a one-symbol delayed wave, it is possible to form a directivity null point for another desired wave. Takes in the desired wave component and outputs multiple array outputs using a maximum likelihood sequence estimator (Maximum Likel
ihood Sequence Estimation (hereinafter referred to as MLSE) performs branch metric synthesis to estimate a transmission signal sequence. The MLSE is described in, for example, "Waveform Equalization Technology for Digital Mobile Communication", published by Trikefs, June 1996, pp. 77-100.

[0004]

In the above-mentioned conventional path diversity receiving system, when all the delayed waves from the direct wave to the delay of several symbols are considered, the number of states of the Viterbi algorithm increases, and the amount of calculation increases exponentially. There was a problem that it increased. Therefore, the desired wave is 1
There is a problem that the path diversity effect cannot be obtained in an environment where the arrival paths are limited to only the symbol delay wave and only one direct wave and one long delay wave arrive. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a receiving method and a receiving apparatus capable of receiving signals with high accuracy even when the delay amount of a delayed wave is large.

[0005]

According to the present invention, in order to solve the above-mentioned problems, a channel impulse response is estimated using a training signal, a delayed wave having a maximum received power is selected, and a direct wave is selected. A steering vector array weight and its output response are calculated so that each path is extracted using the selected delayed wave as a desired wave. Then, sequence estimation is performed from the direct wave output from the array and the selected delayed wave component using a Viterbi equalizer having a multi-trellis structure.

In the present invention, the delay amount of a delayed wave is suppressed by using a Viterbi equalizer having a multi-trellis structure corresponding to the delay amount of the delayed wave by suppressing other than the direct wave and the selected delayed wave by an array process. Even in the case of a large size, it is possible to realize a receiving method in which the amount of calculation does not increase and the error rate does not deteriorate.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 6 is a block diagram illustrating an example of a hardware configuration of the receiving device of the present invention. As the adaptive array antenna 1, for example, a linear array antenna or a planar array antenna having about 4 to 8 elements is used. The linear demodulator 2 amplifies a received signal, performs frequency conversion, performs quadrature detection, and downconverts the signal to a baseband. The A / D converter 3 A / D converts the received baseband signal. The signal processing unit 4 includes, for example, a DSP (Digital Signal Processor) or the like, and executes an adaptive array antenna process and a process related to a maximum likelihood sequence estimator according to the present invention, which will be described later.

FIG. 1 is a functional block diagram showing the signal processing function of the present invention in the signal processing section 4 of FIG. Also,
FIG. 2 is an explanatory diagram illustrating an example of power of a direct wave and a delayed wave received by each antenna. As a signal type in the embodiment, it is assumed that a known training signal is added before a data portion to be transmitted, and the signal is transmitted by a TDMA method.

The channel impulse response estimating / desired wave selecting section 24 estimates the channel impulse response from a direct wave to a several-symbol delayed wave for each branch using signals received from all antennas during the training period. . In addition, a composite profile as shown in FIG. 2 is calculated, and the one with the largest power among the delayed waves, that is, a three-symbol delayed wave in the example of FIG. 2 is selected.

The direct wave extraction array processing section comprises a direct wave extraction steering vector array 10 and an application algorithm 11 with constraints, and operates so as to extract a direct wave from a demodulated signal of each array antenna. Although various teaching principles are known as a control method of an adaptive antenna, a feedback type is generally used, and an array algorithm is used to adjust an array weight so that a mean square error between an array output and a reference signal is minimized. When the control is performed, the null point of the directivity is directed to the arrival direction of the delayed wave, and the delayed wave is suppressed.

As a weight determination algorithm used for an adaptive antenna, LMS ((Least Mean Square)
e) Adaptive array, RLS (Recursive Least Squares)
There are adaptive arrays and SMI (Sample Matrix Inversion) arrays. Such an adaptive antenna signal processing method is described in, for example, Kazuaki Takao: “Adaptive Antenna Theory System”, IEICE (B-II), Vol.J75-B-II, N
o.11, pp.713-720 (Issued November 1992), Yasutaka Ogawa, Nobuyoshi Kikuma: “Progress and Future Prospects of Adaptive Antenna Theory”, IEICE (B-II), Vol.J75-B- II, No.11, pp.721-
732 (issued in November 1992) or "Waveform Equalization Technology for Digital Mobile Communication", published by Trikefs in June 1996, 101-
It is well known as described on page 116.

As the application algorithm 11 with the constraint condition, a simple LMS (Least Mean Square) algorithm, an RLS (Recursive Least Squares) algorithm having excellent convergence characteristics, and the like can be used. Control weights.

The maximum power delay wave extraction array processing unit is composed of a maximum power delay wave extraction steering vector array 16 and a constrained condition application algorithm 17 like the direct wave extraction array processing unit. The algorithm 17 is the same as the algorithm 11, and operates so as to extract the maximum power delay wave from the demodulated signal of each array antenna.

FIG. 3 is an explanatory diagram showing the operation in the array processing section. The output of the direct wave extraction array 10 is 1,
A direct wave and a three-symbol delayed wave component are output by suppressing the two- and four-symbol delayed waves. Also in the maximum power delay wave extraction array, the three-symbol delay wave and the direct wave component are output by suppressing the 1, 2, and 4 symbol delay waves. In FIG. 3, the solid line shows the directivity of the direct wave extraction array, and the dotted line shows the directivity of the maximum power delay wave extraction array.

The joint processing unit for the array processing and the MLSE includes replica generators 12 and 18, which are array output estimators, a multi-trellis Viterbi algorithm 23, and the like. The replica generators 12 and 18 use a transversal filter or the like to determine the obtained channel impulse response (CIR).
And a known training signal or candidate signal to generate a reference signal or replica for the desired wave.

The adders 13 and 19 subtract the outputs of the replica generators 12 and 18 from the outputs of the arrays 10 and 16 and output an error signal. The error signal is input to the application algorithms 11 and 17 with constraint conditions, respectively, and is also input to the absolute value square calculators 14 and 20. Output signals of the absolute value square calculators 14 and 20 are input to multipliers 15 and 21, respectively, multiplied by weight coefficients # 0 and # 1 described later, and output as branch metrics in the respective arrays. The adder 22 adds the output signals of the respective multipliers and outputs the result to the Viterbi algorithm 23. The Viterbi algorithm 23 estimates a received signal sequence based on the combined branch metrics and outputs the sequence and a candidate signal.

The multi-trellis Viterbi algorithm will be described. For example, assuming that a tap of a direct wave and a three-symbol delayed wave is selected in the path selection in the training mode, a combined wave of the direct wave and the three-symbol delayed wave is obtained by passing the received signal through the array. Therefore, a maximum likelihood sequence estimator is prepared for only the selected two-tap difference, that is, three sets, and the combined branch metric sequence is sequentially allocated to each set in parallel. For example, the first set # 1 has the first,
The seventh, seventh,... Branch metrics are assigned. The array output signal corresponding to the assigned branch metric is a continuous convolution signal.
For this reason, when a well-known Viterbi algorithm is used as three sets of sequence estimators, the number of states of the Viterbi algorithm can be reduced to a modulation multi-level number, and the amount of calculation is greatly reduced.

FIG. 5 is an explanatory diagram showing the operation of the replica generator. In the Viterbi algorithm, candidate signals for the direct wave and the maximum power delay wave are generated. The array output replica generators 12 and 18 are composed of, for example, transversal filters, and include candidate signals corresponding to the direct wave and the maximum power delay wave (three-symbol delay wave) and their estimated channel impulse responses (h ^ in FIG. 5). 0 (k), h ^ 3 (k))
To generate replicas for each array output.

Next, the operation during the training period will be described. In the training period, the impulse response of the transmission path, the delayed wave to be taken, the array weight, and the weight coefficient are determined. First, a channel impulse response of up to a direct wave and a several symbol delay wave is estimated for each antenna by using a reception signal from each antenna. Then, the square of the absolute value of the channel impulse response of each delay wave is calculated, and the sum of the powers of the channel impulse responses at all the antennas is calculated for each delay timing. Thereafter, a delay timing having the maximum power sum of the channel impulse response is detected from among the delay timings. In the example shown in FIG. 2, when the powers of the respective delayed waves are compared, the power of the three-symbol delayed wave is the maximum, so that the three-symbol delayed wave is selected as the desired wave.

Next, the array weight and the array output response (channel impulse response) are calculated using the least squares method with the constraint condition, using the impulse response of the direct wave as a constraint vector for determining the response of the direct wave component in the array output. . At this time, the array output response is performed not only for the direct wave but also for the 3-symbol delayed wave. As shown in FIG. 3, an array that controls the impulse response of a direct wave as a constraint vector outputs the direct wave and a three-symbol delayed wave component, and suppresses other delayed waves.

Next, using the impulse response of the selected delay wave as a constraint vector, an array weight and an array output response are calculated using a least squares method with a constraint condition. As shown in FIG. 3, this array also outputs a direct wave component and a three-symbol delayed wave, and suppresses other delayed waves.

Further, using the obtained array weight and output response, the cumulative error power is calculated from the error signal by using the received signal in the training section again, and normalized (divided) by the cumulative number of symbols at the end of training. To find the average error power. Then, the quality of the array output signal is estimated by calculating the power sum of the channel impulse response vector of the direct wave and dividing the sum by the average error power. This operation is similarly performed for the selected delay wave extraction array.
Estimated quality of each path diversity branch ((SINR)
, A weighting factor # proportional to the quality of the array output signal for direct wave extraction and the selected array output signal for delayed wave extraction
0 and # 1 are obtained.

In the data section, a subset trellis of the Viterbi algorithm is prepared for maximum likelihood sequence estimation according to the delay timing of the selected delay wave. The number of subset trellises corresponds to the number of delay symbols of the selected delay wave. That is, if the number of delay symbols is 3, three subset trellises are prepared.

Next, for the candidate signal, the error between the array output and the replica from the maximum likelihood sequence estimator is calculated. Also,
The same operation is performed on the same candidate signal for an array for extracting a three-symbol delayed wave, and an error is calculated. Then, using the path diversity combining coefficient calculated in the training mode by calculating the absolute value square of these errors, weighting is performed as shown in FIG. 4 to perform branch metric combining.

Thereafter, the branch metric is serial-to-parallel converted by a serial-to-parallel converter 30 as shown in FIG. Then, a transmission signal is estimated using a Viterbi algorithm for each subset trellis. Finally, the estimated sequence of each Viterbi algorithm is converted to a parallel-serial converter 31.
To perform a parallel-serial conversion to estimate a transmission sequence.

FIG. 8 is a functional block diagram showing the configuration of the embodiment. Here, the adaptive algorithm is a single constraint LMS
An algorithm or a single constraint SMI algorithm can be used. FIG. 7 is a graph showing an example of the characteristic improvement of the embodiment by computer simulation. The vertical axis represents the bit error rate, and the horizontal axis represents the delay amount of the maximum power delay wave.

The condition is that the modulation method is QPSK and the demodulation method is quasi-synchronous detection. The algorithm calculates the array weight and impulse response using the single constraint SMI algorithm during the training period, and calculates the average error power using the last 16 symbols of the training period. Further, a path diversity combining weight coefficient is obtained and used in the data section. In addition, since the array output signal includes a direct wave component and a two-symbol delayed wave component, the multi-trellis Viterbi equalizer prepares two Viterbi algorithms and performs serial-to-parallel conversion on the received signal sequence alternately to become independent. The transmission signal is estimated using the Viterbi algorithm. Therefore, the number of Viterbi algorithm states remains four.

The number of antennas is four. The condition of the arriving wave is two waves, the first wave is a direct wave, the second wave is a delay wave, and the delay time of the delay wave is changed from 0 to 4 symbols. Further, it is assumed that fading of each arriving wave is independent for each antenna. Further, the average power of each wave is assumed to be equal.

Although the embodiments have been disclosed above, the following modified examples are also conceivable. As an embodiment, an example in which a direct wave and a delayed wave are fetched in the array processing and the branch metric is synthesized is disclosed. However, in the embodiment of the present invention, the branch metric synthesis processing is not an essential component. It is also effective to provide only an extraction array and perform multi-trellis Viterbi algorithm processing using an error as a branch metric.

[0030]

As described above, according to the present invention,
Since a delayed wave having a large received power can be used as a desired wave, a larger path diversity gain can be obtained as compared with the conventional method, which greatly contributes to an improvement in transmission quality.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing a signal processing function of the present invention.

FIG. 2 is an explanatory diagram illustrating an example of received power of a direct wave and a delayed wave.

FIG. 3 is an explanatory diagram showing an operation in an array processing unit.

FIG. 4 is a functional block diagram illustrating a branch metric synthesis process.

FIG. 5 is an explanatory diagram showing an operation of a replica generator.

FIG. 6 is a block diagram illustrating a hardware configuration example of a receiving apparatus according to the present invention.

FIG. 7 is a graph showing a characteristic improvement example of the example.

FIG. 8 is a functional block diagram illustrating a configuration of an embodiment.

FIG. 9 is a functional block diagram showing signal processing content of a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Array antenna, 2 ... Linear demodulator, 3 ... A / D converter, 4 ... Signal processing part, 10, 16 ... Adaptive array processing part, 11, 17 ... Adaptive algorithm, 12, 18 ...
Replica generators, 13, 19 ... adders, 14, 20 ... absolute value square calculators, 15, 21 ... multipliers, 22 ... adders,
23 Multi-trellis Viterbi equalizer

Claims (3)

[Claims] In a receiving method combining adaptive array antenna processing and maximum likelihood sequence estimation processing, a channel impulse response is estimated from a received signal in each array to calculate a delayed wave profile, and a maximum of Selects a delayed wave with power, calculates the direct wave and the selected delayed wave as the desired signals, respectively, calculates the steering vector array weight for direct wave extraction and the selected steering vector array weight for delayed wave extraction, and receives path diversity. And performing a sequence estimation from the direct wave and the selected delay wave using a Viterbi algorithm having a multi-trellis structure corresponding to the delay amount of the selected delay wave. 2. The method comprises the following steps (1) to (6):
A receiving method in which adaptive array antenna processing and decision feedback type maximum likelihood sequence estimation processing are combined. (1) A step of estimating a channel impulse response for a signal received from an antenna and calculating a delayed wave profile. (2) a step of selecting a delayed wave having the maximum power from each of the delayed waves; (3) The impulse responses of the direct wave and the selected delayed wave are defined as constraint vectors for determining the responses of the direct wave and the delayed wave component at the respective array outputs, and the respective array weights and the channel impulse response of the maximum likelihood sequence estimator are obtained. Controlling and estimating at the same time. (4) calculating the error between the output of the array for direct wave extraction and the array for delay wave extraction and the replica from the maximum likelihood sequence estimator for the candidate signal, respectively; (5) The weighting is performed on the branch metric which is the error information based on the quality information, and the transmission signal sequence is synthesized using a maximum likelihood sequence estimator having a multi-trellis structure corresponding to the delay amount of the selected delay wave. The step of making an estimate. (6) A step of simultaneously updating the array weight and the channel impulse response in the maximum likelihood sequence estimator according to the surviving path for each state of the maximum likelihood sequence estimator. 3. A receiving apparatus comprising a receiving means for executing the receiving method according to claim 1.