JP2990260B2 - Code decision error mitigation 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 method for reducing a code decision error in a digital mobile radio communication system.

[0002]

2. Description of the Related Art CMA is available from JR Treichler and BG.
Agree: "A New Approach to MultipathCorrection of Co
nstant Modulus Signals ", IEEE Trans., ASSP-31, pp. 45
As described in 9-472 (1983), this is an algorithm that uses information that a signal envelope is constant, multiplies each input signal by a weight, and combines them to obtain an output signal. The phase modulation signal is subject to band limitation,
The envelope fluctuates greatly.

[0003]

Therefore, when an output signal is obtained by using CMA in a signal in which the above-mentioned envelope fluctuation has occurred, the weight of the signal changes with the influence of the envelope fluctuation. When this change reaches the data at the time of code determination, the output signal is distorted, causing a problem that a code determination error occurs as described in the following document. MG Larimore and JR Treichler, "Data equaliza
tion based on the constant modulus adaptive filte
r ", Proc. ICASSP, 4, pp. 949-952 (1986-04)

[0004]

According to the present invention, when an output signal is obtained by using a CMA in a band-modulated phase-modulated signal, the influence of envelope fluctuation caused by band-limiting the phase-modulated signal is obtained. In order to alleviate this, first, control is performed by the CMA using the received signal to obtain an output signal. Since the output signal has reduced distortion due to the propagation path, the time of code determination is extracted from the output signal.

Next, the received signal at the above point and the above C
Using the weight value converged by the MA control as an initial value, control by the CMA is performed again to obtain an output signal. As described above, it is possible to reduce the influence of envelope fluctuation caused by band-limiting the phase-modulated signal, and reduce code determination errors.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle of the present invention will be described.
The phase modulated signal before band limiting is a constant envelope,
By limiting the band, the envelope changes. on the other hand,
CMA is an algorithm for restoring a signal using information called a constant envelope. Therefore, when CMA is applied to the band-limited phase modulated signal, the sign determination point value of the restored signal is distorted due to the influence of the envelope fluctuation, thereby increasing the possibility of causing a sign determination error.

On the other hand, even in a band-limited phase modulated signal, the received signal at the time of code determination has a constant envelope characteristic. Therefore, when control is performed by the CMA using this data, the envelope fluctuation is reduced. The change in weight due to the influence is small. However, if only data at the time of code determination is used, many symbols are required for convergence of the algorithm. In addition, it is difficult to extract a code determination point from a signal that has been distorted by a propagation path. Therefore, by performing CMA using all of the data obtained by sampling, the algorithm is converged and an output signal is obtained.

[0008] Since the output signal corrects the distortion received in the propagation path, the time of code determination can be easily extracted. Further, the data at the time of the sign determination and the first CM
The control by CMA is performed again using the weight value converged by the control by A as the initial value. As a result, it is possible to reduce distortion of the output signal at the time of code determination due to fluctuation of the envelope caused by performing band limitation on the phase modulation signal, and to reduce code determination errors.

The present invention can be applied to a system for obtaining an output signal using a CMA in a band-limited phase modulated signal. Among these, an embodiment in the case of using an adaptive array antenna will be described. First, an embodiment of a code decision error mitigation method by applying CMA to a phase modulation signal according to the present invention will be described with reference to the accompanying drawings. And
FIG. 1 shows an outline of signal processing steps on the transmission side and the reception side.
This will be described with reference to FIGS.

On the transmitting side, an information sequence to be transmitted is encoded and further symbolized. This is referred to as an information sequence a after symbolization. On the receiving side, the transmitted signal sequence is received, sampled, and band-limited. This is called a received signal sequence b. CMA using received signal sequence b
To obtain an output signal sequence c. The output signal sequence c is decoded. This is called a decoded signal sequence d. The code determination point is extracted from the output signal sequence c.

Further, using the data of the received signal sequence b at the time of the code determination and the weight value converged by the previous CMA control as the initial weight value, control by CMA is performed again to obtain an output signal sequence e. The output signal sequence e is decoded. This is called a decoded signal sequence f. The decoded signal sequence d is affected by the envelope fluctuation caused by band-limiting the phase-modulated signal, and a code determination error occurs. However, since the decoded signal sequence f is not affected by the envelope fluctuation, No determination error occurs.

[0012]

Next, a first embodiment of a transmitting station and a receiving station embodying a digital mobile radio communication system for reducing the influence of envelope fluctuation due to band limitation of a phase modulation signal according to the present invention will be described with reference to FIGS. It will be described based on. The modulation method used in the embodiment is π / 4 shift differential encoding QPSK.

First, on the transmitting side in FIG. 4, an information sequence 1 to be transmitted is encoded by an encoding unit 2 and is converted into a symbol by a signal point arrangement unit 3. Further, the symbolized transmission signal sequence 4 is band-limited through a transmission-side root Nyquist filter unit 5, converted to a high-frequency signal by a transmission-side local oscillator unit 6 and a quadrature modulation unit 7, and transmitted to a transmission-side antenna 8.
Is output.

On the receiving side in FIG. 5, receiving antennas 9, 10,.
The high-frequency signals received from 11 and 12 are converted into local oscillator units 13, 14, 15, having the same frequency as the transmitting side.
The quasi-synchronous detectors 17, 18, 1
Quasi-synchronous detection is performed by 9 and 20. Further, the band is limited by the receiving-side root Nyquist filter units 21, 22, 23, and 24.

The received signal series 25, 26, 27, 28
, An output signal sequence 30 is obtained under the control of the CMA control unit 29. Further, a code determination time point 33 is extracted from the output signal sequence 30 by a code determination time point extraction unit 32. Received signal sequences 25, 26, 2 at the time of code determination 33
Using the weights 31 and 28 and the weight value 31 converged by the control of the CMA control unit 29 as a weight initial value, an output signal sequence 35 is obtained again by the control of the CMA control unit 34, demodulated by the demodulation unit 36, and output. I do.

FIG. 6 shows the bit error rate characteristics at the time of static characteristics in the present embodiment by computer simulation when the desired wave arrives at the moving body from the front in the traveling direction of the moving body. The horizontal axis is Eb / N0 (power-to-noise power density ratio per bit), and the vertical axis is BER (bit error rate). In this computer simulation, bursts in which 384-bit data were added with a preamble of 75 bits and a unique word of 31 bits as a header were transmitted 1000 times, and the BER was measured. The transmission speed is 256 ksy
The simulation was performed with mbol / sec and the number of samples per symbol being 16.

As a result, as shown in FIG.
It can be seen that the characteristics of the embodiment (indicated by ● in the figure) are superior to the characteristics in the case of decoding the output signal sequence 35 when only the first CMA control is performed (indicated by ▲ in the figure).

Next, there will be described a second embodiment of the present invention in which the influence of envelope fluctuation due to band limitation of a phase modulation signal is reduced to further suppress the influence of a delayed wave. The configuration of the transmitting / receiving station is the same as that of the first embodiment, and a description thereof will be omitted.

FIG. 7 shows the bit error rate characteristics at the time of dynamic characteristics in this embodiment by computer simulation when a desired wave arrives at the mobile unit from the front in the traveling direction of the mobile unit and a delayed wave arrives at the mobile unit from the rear. The horizontal axis is Eb / N0 (1
Power per bit to noise power density ratio), and the vertical axis is BER (bit error rate).

In this computer simulation, 384
A burst consisting of 10 bits of data with a preamble of 75 bits and a unique word of 31 bits as a header is 10 bits.
Transmitted 00 times and measured the BER. The maximum Doppler frequency is 5 Hz, and the transmission speed is 256 ksymb.
The simulation was performed with ol / sec, the number of samples per symbol being 16.

As a result, as shown in FIG.
It can be seen that the characteristics of the embodiment (indicated by ● in the figure) are superior to the characteristics in the case of decoding the output signal sequence 35 when only the first CMA control is performed (indicated by ▲ in the figure).

Next, a description will be given of a third embodiment of the present invention in which the influence of envelope fluctuation due to band limitation of a phase modulation signal is reduced to further suppress the influence of co-channel interference waves with reference to the drawings.

The configuration of the transmitting station is the same as that of the first embodiment, and the description is omitted. On the receiving station side, as a method for reducing co-channel interference, a method described in Japanese Patent Application No. 8-211908 filed by the present applicant is used. Also, regarding the configuration of the receiving station, the same reference numerals are given to the same configurations as in the first embodiment, and the description will be omitted. Therefore, in the third embodiment, the demodulated signal sequence 37 and subsequent steps in FIG. 8 will be described.

First, a demodulation signal sequence 37 is obtained by processing the output signal sequence 35 in a demodulation unit 36,
At 8, it is determined whether or not the signal sequence is the desired signal sequence. On the other hand, if it is not the desired signal sequence, the control signal 40 is sent to the interference wave removing units 41, 42, 43, and 44 to remove the interference wave.

In the interference wave removing units 41, 42, 43, 44, the signal sequence which has become the output signal sequence 35 from the received signal sequences 25, 26, 27, 28 is removed.
Signal sequences 45, 46, 47, and 48 to be sent to the signal processing unit 50 that performs the same processing as in No. 9 are generated. Since the adaptive array antenna has a degree of freedom to remove an incoming signal sequence of the number of antenna elements minus 1, the same processing as described above is performed in the signal processing units 50, 51, and 52 to obtain a desired signal sequence. Can be.

FIG. 9 shows the bit error rate characteristics at the time of static characteristics in the present embodiment by computer simulation when the desired wave arrives at the mobile unit from the front in the traveling direction of the mobile unit and the co-channel interference wave arrives at the mobile unit from the rear. . The horizontal axis is C / I
(Desired wave power to co-channel interference wave power ratio), and the vertical axis represents BER (bit error rate).

In this computer simulation, 384
A burst consisting of 10 bits of data with a preamble of 75 bits and a unique word of 31 bits as a header is 10 bits.
Transmitted 00 times and measured the BER. The simulation was performed with a transmission rate of 256 ksymbol / sec and 16 samples per symbol.

As a result, as can be seen in FIG. 9, the characteristics of the third embodiment in which the present invention is combined with the method described in Japanese Patent Application No. 8-211908 (interference wave removing method) (in FIG.
Are the characteristics when only the interference wave removal method is used (▲ in the figure).
It can be seen that it is superior to that of the mark.

[0029]

As described above, according to the code decision error mitigation method of the present invention, when an output signal is obtained using a CMA in a band-modulated phase-modulated signal, the phase-modulated signal is band-limited. Even without being affected by the envelope fluctuation, the output signal is obtained by using the received signal and the converged weight value at the time of the code determination at which the constant envelope property is maintained. A reduced output signal can be obtained, and the reception characteristics can be improved.

Thus, in a digital mobile radio communication system, it is possible to minimize the deterioration of reception characteristics when applying CMA to a phase modulated signal whose envelope fluctuates due to band limitation.

[Brief description of the drawings]

FIG. 1 is a timing chart showing an outline of processing steps on a transmitting side and a receiving side in CMA.

FIG. 2 is a timing chart showing an outline of processing steps on a transmitting side and a receiving side in CMA.

FIG. 3 is a timing chart showing an outline of processing steps on a transmitting side and a receiving side in CMA.

FIG. 4 is a block diagram showing a transmitting side according to the first embodiment of the present invention.

FIG. 5 is a block diagram showing a receiving side according to the first embodiment of the present invention.

FIG. 6 is a characteristic diagram showing characteristics of the first embodiment of the present invention.

FIG. 7 is a characteristic diagram showing characteristics of the second embodiment of the present invention.

FIG. 8 is a block diagram showing a third embodiment of the present invention.

FIG. 9 is a characteristic diagram showing characteristics of the third embodiment of the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 information sequence 2 coding unit 3 signal point arrangement unit 4 transmission signal sequence 5 transmission side route Nyquist filter unit 6 transmission side local oscillator unit 7 orthogonal modulation unit 8 transmission side antenna 9, 10, 11, 12 reception side antenna 13, 14, 15, 16 Receiving-side local oscillator section 17, 18, 19, 20 Quasi-synchronous detecting section 21, 22, 23, 24 Receiving-side root Nyquist filter section 25, 26, 27, 28 Received signal sequence 29 CMA control section 30 Output signal sequence 31 Weight value 32 Code determination time extraction unit 33 Code determination time point 34 CMA control unit 35 Output signal sequence 36 Demodulation unit 37 Decoded signal sequence 38 Signal determination unit 39 Signal control unit 40 Control signal 41, 42, 43, 44 Interference Wave removal unit 45, 46, 47, 48 Signal sequence 49, 50, 51, 52 Signal processing unit

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-9-260940 (JP, A) JP-A-10-41732 (JP, A) JP-A-3-179852 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) H04L 27/22 H04B 14/04 H04L 1/00

Claims (1)

(57) [Claims] 1. A digital mobile radio communication system for performing radio communication using a phase-modulated signal whose band is limited between a base station and a mobile station or between mobile stations.
Means for obtaining an output signal by performing control by CMA using a received signal when obtaining an output signal by performing control according to (Constant Modulus Algorithm); means for extracting a code determination point from the output signal; Using the received signal at the time and the weight value converged by the CMA control as an initial value,
A code determination error mitigation method, comprising: means for obtaining an output signal by performing control according to A; and reducing a code determination error due to the influence of envelope fluctuation caused by band-limiting the phase-modulated signal.