JP3061108B2 - Receiving device and receiving method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving apparatus and a receiving method, and more particularly to a digital mobile communication and a wireless LA.
TECHNICAL FIELD The present invention relates to a receiving apparatus and a receiving method for performing joint processing of an adaptive array antenna and an adaptive equalizer in order to take measures against a multipath that causes a problem in N.

[0002]

2. Description of the Related Art In digital mobile communication, high-speed transmission is affected by frequency selective fading, and transmission characteristics are significantly degraded. Powerful techniques are needed to overcome this frequency selective fading. Representative examples of conventional multipath countermeasures include an adaptive array antenna technique and an adaptive equalization technique. The adaptive array antenna technology is based on the fact that a delayed wave having a long delay time is considered to come from a direction different from that of a direct wave, and has an effect of spatial path separation. The adaptive antenna is composed of a plurality of antenna elements, and controls directivity by utilizing the fact that the reception phase of each arrival path received by each element is different depending on the respective arrival directions and path differences resulting from element arrangement.

[0003] As a method of controlling an adaptive antenna, various teaching principles are known, but a feedback type as shown in FIG. 12 is generally used, and a mean square error between an array output and a reference signal is minimized. When the array weight is controlled using an adaptive algorithm, the delay wave is suppressed by directing the null point of the directivity to the arrival direction of the delay wave. The adaptive antenna has a feature that the effect of suppressing a delayed wave having a long delay time is high.

The algorithms used for the adaptive antenna include a CMA (Constant Modulus Algorithm) adaptive array, an LMS (Least Mean Square) adaptive array, an RLS (Recursive Least Squares) adaptive array, and an SMI (Sample Matrix Inversion) array. 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, No.11, pp.71
3-720 (published November 1992), or Yasutaka Ogawa and Nobuyoshi Kikuma: "Progress and Future Prospects of Adaptive Antenna Theory", IEICE (B-II), Vol.J75-B-II, No.11 , Pp.721-
732 (published November 1992).

On the other hand, the adaptive equalization technique has the effect of temporal path synthesis. For land mobile communication, the decision feedback equalizer (
DFE: Decision Feedback Equalizer) and Maximum Likelihood Sequence Estimator (MLSE: Maximum Likelihood Sequence Estimator)
Has been energetically studied. Since MLSE can effectively combine direct and delayed waves, its equalization characteristics are better than DFE. As shown in FIG. 13, the MLSE uses the known training signal on the receiving side to derive the LMS algorithm and RLS from the received signal.
A channel impulse response is estimated using an adaptive algorithm such as an algorithm, and a transmission signal is estimated based on a criterion of what kind of transmission signal sequence is transmitted from the estimated channel impulse response and becomes close to the reception signal sequence.

For the estimation of the transmission signal sequence, a Viterbi algorithm which is efficient in operation is used. Furthermore, by estimating the channel impulse response for each state of the Viterbi algorithm, a delay error in estimating the channel impulse response due to the determination delay is eliminated, and the ability to follow the transmission path fluctuation is improved. In addition, as a well-known document of a prior art,
For example, Kamio: "Frequency-selective fading compensation by limited-state sequence estimation in land mobile communications", IEICE (B-II) Vol. J78-B-II, No. 5, pp. 393-400 (1995 5
Month).

[0007]

In the case of an adaptive array antenna, when the angle between the arriving paths is small, the array tends to direct the null point of the antenna directivity to the arrival direction of the unnecessary wave. There is a problem that the output SINR characteristic deteriorates, and there is a problem that the adaptive array antenna selects only one of the multipath waves, so that the power of the incoming wave cannot be used effectively. .

On the other hand, the adaptive equalizer has a problem that the error rate characteristics deteriorate when a long delay wave exceeding the number of delay symbols of the set delay wave is present. In order to cope with the problem, there is a problem that the amount of calculation becomes enormous with an increase in the number of delay symbols, and particularly in the MLSE, there is a problem that the amount of calculation increases exponentially with an increase in the number of delay symbols.

For this reason, the adaptive array antenna and the adaptive equalizer both have advantages and disadvantages, and there has been a problem that it is difficult to provide an effective multipath countermeasure technique by using each alone.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to simultaneously reduce the characteristic deterioration in the presence of a delay wave close to a desired wave in an adaptive array antenna and the increase in the amount of calculation due to the increase in the number of delay symbols in the MLSE. It is an object of the present invention to provide a receiving apparatus and a receiving method for performing a joint processing of an adaptive array antenna and an MLSE to be solved.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention employs a high-affinity structure and algorithm that can complement each other's drawbacks, and uses an adaptive array antenna and an adaptive equalizer. There is a characteristic in the place where the combination is performed. That is, during the training period, path selection is performed indirectly by selecting a tap that minimizes the cumulative square error between the array output of the array weight and the reference signal from among combinations of taps of the estimated channel impulse response. There is a feature in the point. Also, select the desired wave from the incoming path, prepare arrays and MLSEs by the number of differences between the selected taps, sort the received signals in parallel, and
Another feature is that the amount of computation is reduced by performing the MLSE combining process.

Further, using a replica of a desired wave in an adaptive maximum likelihood sequence estimator as a reference signal for controlling an adaptive array antenna, a plurality of desired waves having different delay times are fetched and synthesized by the MLSE, thereby making the MLSE unnecessary. The path is characterized in that unnecessary signals are suppressed by giving a reference signal from the MLSE to the array. It is also characterized in that channel impulse responses are estimated for signals received from all antennas, respectively, the same processing as described above is performed, and branch metric synthesis is performed in the Viterbi algorithm.

In the present invention, with the above configuration, a path (delayed wave) likely to contribute to the improvement of characteristics can be selected, and a delayed wave having a small arrival angle difference with respect to a direct wave is simultaneously captured and synthesized by the MLSE. Thereby, the received power can be effectively used. Also, a delay wave unnecessary for the adaptive maximum likelihood sequence estimator can be attenuated by the array antenna processing, and the bit error rate is reduced. Further, the number of states of the Viterbi algorithm can be suppressed to a feasible range by the parallel processing.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 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 or a planar array of 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 is configured by, for example, a DSP (Digital Signal Processor), and executes, for example, adaptive array antenna processing and processing relating to an adaptive maximum likelihood sequence estimator as shown in each block of FIG.

First, during a training period at the beginning of a signal burst, an impulse response of a transmission channel as shown in FIG. 6 is estimated. The impulse response of the transmission channel can be obtained by a known method from a known training signal and a received signal obtained by actually receiving the training signal. Next, as shown in FIG. 7, among the taps of the estimated channel impulse response,
The tap coefficients of other taps except for any two taps are set to 0. Then, a channel impulse response with limited taps and a known training signal are convolved by a digital filter or the like to generate a reference signal for a plurality of desired waves.

Next, the weight of the adaptive array is controlled from the error between the array output and the reference signal using a known adaptive algorithm. At the same time, a cumulative square error between the array output and the reference signal is calculated. This operation is performed for all combinations of two taps, and path selection is indirectly performed by selecting a combination of taps that minimizes the accumulated square error. FIG. 8 is an explanatory diagram showing a state in which the path is selected, and shows an example in which the direct wave 0T and the delayed wave 3T are selected, and the other delayed waves are suppressed by the array processing.

FIG. 9 is an explanatory diagram showing the data portion of the received wave burst for each symbol. It is assumed that the direct wave is affected by a delayed wave of up to four symbols as shown in the figure. At the end of the training mode, the weight of the array that spatially selects the path is obtained. For example, if the tap of the direct wave and the three-symbol delayed wave is selected in the path selection of the training mode, the received signal is passed through the array. As a result, a combined wave of a direct wave and a three-symbol delayed wave is obtained. Therefore, an array and a sequence estimator are prepared only for the difference of the selected two taps, that is, three sets, and the received symbol sequence is sequentially allocated to each set in parallel.

For example, the first set # 1 has first, fourth,
The seventh received symbol is assigned. This assigned signal is a continuous convolution signal. Therefore, when a well-known Viterbi algorithm is used as a sequence estimator, the number of states of the Viterbi algorithm can be reduced to the number of modulation levels, and the amount of calculation is greatly reduced.

FIG. 10 is a functional block diagram showing a configuration of a combined processing of the array antenna processing and the MLSE. When the received signal is passed through the array, a combined wave of a direct wave and a three-symbol delayed wave is output. The desired wave replica generator 14 is configured by a digital filter, and convolves the direct wave, the candidate signal corresponding to the three-symbol delayed wave, and each estimated channel impulse response, and generates a replica for the array output. Then, the transmission signal is estimated by the Viterbi algorithm using the square of the absolute value of the error between the array output and the replica as the branch metric. Next, the array weight vector and the impulse response vector are updated for each state of the Viterbi algorithm according to the surviving path in the Viterbi algorithm.

A replica of a composite wave of two desired waves having different delay times based on an estimated channel impulse response from a signal received by one of the array antennas
When an operation is performed to generate a (reference signal) and simultaneously capture a plurality of desired waves in an array, when the arrival angles of the two waves are close, the same component as the reference signal is included in the reception signal received by each antenna. Therefore, a characteristic improvement effect can be obtained. But,
If the angle of arrival increases, the phase relationship between the two waves at each antenna will differ, so that the same signal component as the reference signal will not be included in the signals received at other antennas, and the array output There is a problem that the SNR characteristic is deteriorated.

Therefore, as shown in FIG. 4, a reference signal is generated based on the estimated channel impulse response at each antenna, the array weight is controlled using an adaptive algorithm, and the error between the array output and the replica is calculated. The estimated channel impulse response of the desired wave is updated using the adaptive algorithm. Then, the absolute value square of the error is calculated, branch metric synthesis is performed, and the transmission signal sequence is estimated.

FIG. 3 is a block diagram showing an embodiment of the path selection algorithm. As described above, during the training period, the impulse response of the transmission channel as shown in FIG. 6 is estimated, and tap coefficients of other taps are set to 0 except for any two taps among the taps of the estimated channel impulse response. Yes (tap selection). Then, a reference signal for a plurality of desired waves is generated by convolving a channel impulse response with limited taps and a known training signal using a digital filter or the like.

Next, the weight of the adaptive array is controlled using an adaptive algorithm based on the error between the array output and the reference signal. As an adaptive algorithm, a simple
LMS (Least Mean Square) algorithm, RLS (Recursive Least Squares) algorithm with excellent convergence characteristics, UD-RLS algorithm with further excellent numerical stability, etc. are used.
At the same time, a cumulative square error between the array output and the reference signal is calculated. This operation is performed for all combinations of two taps, and path selection is performed indirectly by selecting a combination of taps that minimizes the accumulated square error.

FIG. 5 is a block diagram showing an embodiment of a calculation amount reduction algorithm. A well-known Viterbi algorithm is used as a sequence estimation algorithm. As described above with reference to FIG. 9, a plurality of combining processes of the array and the Viterbi algorithm are prepared, and the received symbol sequences are distributed in parallel.

FIG. 1 is a functional block diagram showing the configuration of an embodiment of the tracking algorithm in the signal processing section 4. As the adaptive algorithm for array weight control, for example, the UD-RLS algorithm 11 is used. Further, it is necessary to keep the reference signal average power constant in order to keep the array output average power constant. For example, the norm-constrained LMS algorithm 13 or the like is used for estimating the desired wave channel impulse response. In the norm-constrained LMS algorithm, tap coefficients updated in a normal LMS algorithm are normalized by their magnitude (norm).

FIG. 4 is a block diagram showing an embodiment of extension to branch metric synthesis. Channel impulse responses are estimated for signals received from all antennas, and reference signals are generated from the respective channel impulse responses to control the array weight. Then, the sum of squares of the error between each received signal received by each antenna and each replica is calculated, and the transmission signal is estimated by the divided Viterbi algorithm as a branch metric.

FIG. 11 is a graph showing characteristics of the embodiment by computer simulation. The condition is that the modulation method is 8
The phase PSK and the demodulation method are quasi-synchronous detection, and the algorithm is as described in the above embodiment. The antenna arrangement is a four-element Y-shaped array. FIG. 11A is a graph showing an example of a characteristic improvement effect according to the present invention. The condition of the arriving wave is set to three, and it is set that the direct wave arrives from the -50 degree direction, the one symbol delayed wave arrives from the -50 degree direction, and the two symbol delayed wave arrives from the 40 degree direction. In this embodiment, the direct wave and the one-symbol delayed wave are simultaneously captured by the array,
An array of symbol delay waves is suppressed. Next, the direct wave and 1
The combined wave of the symbol delayed waves is sequence-estimated by MLSE to obtain decision data.

A normal adaptive array antenna operates to take in only a direct wave and suppress other paths. However, if the direct wave and the delayed wave are close to each other, the characteristics deteriorate. In the MLSE that compensates for up to one symbol delay, 2
The characteristic is degraded due to the presence of the symbol delay wave. However, according to the present embodiment, paths having a small arrival angle difference can be taken in an array at the same time and combined by the maximum likelihood sequence estimator, so that there is an effect of improving characteristics as compared with the array alone.

FIG. 11B is a graph showing an example of the characteristic improvement effect according to the present invention. Arrival wave condition is 3
It is set that a direct wave arrives from a direction of 40 degrees, a one-symbol delayed wave arrives from a direction of -50 degrees, and a two-symbol delayed wave arrives from a direction of 40 degrees. In this embodiment, a direct wave and a two-symbol delayed wave are simultaneously captured by an array, and a one-symbol delayed wave is suppressed by the array. Although the sequence estimation is performed on the combined wave of the direct wave and the two-symbol delayed wave, the amount of calculation does not increase by dividing the received symbol sequence and applying the array and the Viterbi algorithm. The same property improving effect as in the case of taking in is obtained.

FIG. 11C is a graph also showing an example of the characteristic improvement effect according to the present invention. Arrival wave condition is 3
It is assumed that a 1-symbol delayed wave arrives from a direction of -50 degrees and a 2-symbol delayed wave arrives from a direction of 40 degrees.
The direction of arrival of the direct wave is changed from -180 degrees to 180 degrees. In the present invention, the direct wave and the one-symbol delayed wave or the direct wave and the two-symbol delayed wave are simultaneously captured by the array by the path selection, and the path not selected is suppressed. The synthesized wave captured by the array is estimated by a sequence estimator to obtain decision data.

When the arrival angles between the two selected paths are close to each other, the effect of improving characteristics can be obtained by controlling the array by regarding the combined waves as one wave, but there is an angle difference between the selected paths. In this case, the same component as the reference signal is not included in the received signal received by each antenna, so that the array output SINR decreases. Therefore, the reference signal is generated based on the estimated channel impulse response for each antenna, the array is controlled, and branch metric synthesis is performed, so that the SIR characteristics are improved at each array output. This is because, since the phase relations of a plurality of desired waves in each antenna are different, by performing branch metric synthesis, the probability of transition to an error sequence on the Viterbi algorithm is reduced and SNR characteristics are improved.

FIG. 11D is a graph also showing an example of the characteristic improvement effect according to the present invention. Arrival wave condition is 3
It is assumed that a 1-symbol delayed wave arrives from the -50 degree direction and a 2-symbol delayed wave arrives from the 40 degree direction.
Also, the arrival direction of the direct wave is randomly changed for each burst. In this embodiment, the direct wave and the one-symbol delayed wave or the direct wave and the two-symbol delayed wave are simultaneously captured by the array by the path selection, and the path not selected is suppressed. Branch metric synthesis is performed based on the difference between each synthesized wave captured by the array and each replica, and estimation is performed by a sequence estimator to obtain determination data. The characteristics of the array alone deteriorate when an unnecessary wave approaches the desired wave, and the characteristics of an MLSE that compensates for up to one symbol delay are deteriorated because a two-symbol delayed wave exists.

On the other hand, according to the present invention, a plurality of paths which are likely to contribute to the improvement of the characteristics by selecting the paths are selected, these are taken in by an array, and unnecessary waves are suppressed. Since the acquired synthesized wave can be sequence-estimated by MLSE, there is an effect of improving characteristics.
Further, when the angle difference between the selected paths is large, the characteristics can be further improved by performing branch metric synthesis.

[0034]

As described above, in the present invention,
Paths that are likely to contribute to improved characteristics can be selected.Paths with small differences in arrival angles can be captured at the same time and synthesized by MLSE.Also, the number of states of the Viterbi algorithm can be suppressed to a feasible range, so multipath There is an effect that the performance of the separation / synthesis technique is improved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an embodiment of a path selection algorithm.

FIG. 2 is a block diagram illustrating a hardware configuration example of a receiving apparatus according to the present invention.

FIG. 3 is a block diagram illustrating an embodiment of a path selection algorithm.

FIG. 4 is a block diagram illustrating an embodiment of an extension to branch metric synthesis.

FIG. 5 is a block diagram showing an embodiment of a calculation amount reduction algorithm.

FIG. 6 is a conceptual diagram illustrating an impulse response of an estimated transmission channel.

FIG. 7 is a conceptual diagram illustrating an estimated channel impulse response after tap selection.

FIG. 8 is an explanatory diagram showing a state in which a path is selected.

FIG. 9 is an explanatory diagram showing parallel processing of an estimator.

FIG. 10 is a functional block diagram showing a configuration of a combined processing of the array antenna processing and the MLSE.

FIG. 11 is a graph showing characteristics of the example by simulation.

FIG. 12 is a block diagram showing a configuration of a conventional adaptive array antenna.

FIG. 13 is a block diagram showing a configuration of a conventional adaptive maximum likelihood sequence estimator.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Array antenna, 2 ... Linear demodulator, 3 ... A / D converter, 4 ... Signal processing part, 10 ... Adaptive array processor, 11, 13 ... Adaptive algorithm, 12 ... Maximum likelihood sequence estimator, 14 ... Hope Wave replica generator

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-57-38002 (JP, A) JP-A-54-116868 (JP, A) JP-A-57-20001 (JP, A) JP-A-4- 182968 (JP, A) JP-A-7-336129 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01Q 21/00-21/30 H03H 17/00 601 H04B 1/10 H04B 7/08

Claims (5)

(57) [Claims] 1. A receiving signal from a plurality of antennas is input,
An error signal between the reference signal replica and the output signal of the adaptive array is obtained, and an array weight is controlled so as to suppress unnecessary waves for the adaptive maximum likelihood sequence estimator and output only a plurality of desired waves having different delay times. A first step of executing an adaptive array antenna process, and a second step of inputting the error signal, estimating a transmission data sequence in an adaptive maximum likelihood sequence estimator, and outputting a candidate signal
And a third step of, based on the candidate signal, generating a replica that is a reference signal for a composite wave of a plurality of desired waves having different delay times. A reception method combining a maximum likelihood sequence estimator. 2. During the training period of the array weight, a tap which minimizes a cumulative square error between an adaptive array output signal and a reference signal is selected from a combination of taps of an estimated channel impulse response. 2. The method according to claim 1, wherein a desired wave is selected.
Receiving method described in. 3. A Viterbi algorithm is adopted as the adaptive maximum likelihood sequence estimator, a channel impulse response is estimated for a signal received from each antenna, and a replica of a desired wave is generated for each antenna. 2. The receiving method according to claim 1, wherein array signals are processed for the number of antennas using the replicas as reference signals, and the obtained error signals for the number of antennas are subjected to branch metric synthesis. 4. A set of adaptive array antenna processing means and adaptive maximum likelihood sequence estimators is prepared by the number of differences between the selected taps, and the received signals are sequentially allocated to each set, and each of the sets is divided into one set. A receiving method, which performs a combining process of the array according to any one of the above and an adaptive maximum likelihood sequence estimator. 5. A receiving signal from a plurality of antennas is input,
An error signal between the reference signal replica and the output signal of the adaptive array is obtained, and an array weight is controlled so as to suppress unnecessary waves for the adaptive maximum likelihood sequence estimator and output only a plurality of desired waves having different delay times. Adaptive array antenna processing means, to input the error signal and estimate a transmission data sequence,
An adaptive maximum likelihood sequence estimator that outputs a candidate signal; and a replica generation unit that generates a replica that is a reference signal for a composite wave of a plurality of desired waves having different delay times based on the candidate signal. Receiving device.