JPH09130442A - Pi/4 shift qpsk demodulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a π/4 shift QPSK demodulator having the decoding system to obtain high transmission quality with a circuit compensating waveform distortion caused in a radio wave propagation path in a digital radio receiver adopting the π/4 shift QPSK demodulator. SOLUTION: An input signal is given to a synchronization detection circuit 44, its output is given to a waveform equalizer 42, in which waveform distortion is compensated. The compensated is given to a differential decoder 45, where differential decoding is executed and from which transmission data are outputted. Simultaneously the synchronization detection output is differential- processed by a differential processing unit 46 and the result is an input to a synchronization system circuit 43. Through the constitution above, the effect of waveform distortion caused in a radio wave propagation path is reduced and the decoding system excellent in the S/N characteristic is realized.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a π / 4 shift QP.
The present invention relates to a digital demodulation method used for digital mobile radio based on the SK modulation method.

[0002]

2. Description of the Related Art First, a .pi. / 4 shift QPSK modulation system will be briefly described.

Generally, in the digital modulation system,
A signal point (symbol) peculiar to the modulation method is set corresponding to the bit string to be transmitted, and the carrier wave is modulated by this signal. In the π / 4 shift QPSK modulation method, the transmission bit string is divided into two bits and each bit pattern is “00”.
, "01", "11" and "10" are assigned the phase amounts (1/4) π, (3/4) π, (5/4) π and (7/4) π respectively, and the phase amounts Is added to the phase of the symbol one time before, and modulation is performed as the symbol at that time. That is, this is a modulation method in which transmission data is assigned to the phase difference between two consecutive symbols.

In high-speed data transmission by digital mobile radio, distortion of transmission waveform due to fading causes intersymbol interference, which becomes a serious obstacle to communication. Fading is a phenomenon that occurs when a transmitted wave from a transmitter reaches a moving receiver via multiple radio wave propagation paths, and waveform equalization is one of the leading countermeasure techniques to reduce this effect. Is. In actual waveform equalization, the receiving side transmits a known training symbol sequence, and an adaptive filter that minimizes the difference between the equalization output and the training symbol sequence for the received signal is configured to form the waveform of the response of the transmission path. It is realized by canceling out inside the equalizer.

Here, the training symbol sequence is
It is a predetermined fixed symbol sequence and is known to the receiving side. This is transmitted with an unknown symbol sequence created based on the transmitted data. The training symbol sequence generator is for generating this training symbol sequence on the receiving side.

As a waveform equalization method, LMS (Lea
st Mean Square), RLS (Recu
rsive Least Square), MLSE
(Maximum Likelihood Sequence
nce Estimation).

On the other hand, when the digital modulation methods are roughly classified,
Amplitude shift keying (ASK) modulation, frequency shift keying (FSK) modulation, phase shift keying (PS
K) Modulation etc. Π, which is a type of PSK modulation among them
In the / 4 shift QPSK modulation method, the amplitude of the modulated wave does not become zero, so that the level fluctuation range is limited, it is resistant to the distortion due to the nonlinearity of the transmission power amplifier, and it is inherently differentially encoded in the modulation. Since it is possible to easily demodulate by differential detection with a simple configuration, it is optimal as a modulation system for mobile communication.

FIG. 6 shows an example of the configuration of the differential detector. In the figure, 31 is a bandpass filter, 32 and 33 are frequency mixers,
34 is a 90 ° phase shifter, 35 and 36 are low pass filters,
37 is a delay element. The received signal that has passed through the band pass filter 31 is multiplied by the in-phase component and the quadrature component of the signal delayed by the delay element 37 by the frequency mixers 32 and 33, respectively. The quadrature component is generated by a 90 ° phase shifter. From the outputs of the frequency mixers 32 and 33, high-frequency components are removed by low-pass filters 35 and 36, and in-phase and quadrature detection outputs are taken out, respectively.

Now, let us consider a case where the digital demodulator for π / 4 shift QPSK is used, for example. In this example, the above-mentioned delay detector is used as the detector. In the figure, reference numeral 41 is the differential detector shown in FIG. 6, 42 is an equalizer adopting an arbitrary system, and 43 is a synchronous circuit. The synchronization system circuit generates a clock signal, a frame synchronization signal and the like. π
In the case of / 4 shift QPSK modulation, the transmission data is allocated between the symbols of one sample time before and the sample time, so that the differential processing between symbols is indispensable at the time of decoding. In this respect, since differential detection systematically includes differential processing, there is no need to add a differential decoder, which is advantageous in terms of circuit simplicity. However, since the output of the differential detection is the result of the signal operation between two symbols, it is affected by noise over two symbols, and equalization of this signal is also disadvantageous in terms of noise resistance. Become. Furthermore, while the original equalizer aims to compensate for distortion of the transmission waveform, it equalizes the difference waveform from one time before, which complicates the internal configuration of the waveform equalizer. However, there is concern about an increase in processing amount and deterioration of compensation accuracy.

[0010]

DISCLOSURE OF THE INVENTION The object of the present invention is π /
We provide an optimal receiver configuration method when applying a waveform equalizer to a 4-shift QPSK demodulator, effectively compensating for distortion of the radio wave propagation path due to fading, etc., and achieving high-quality digital communication. Aim to achieve.

[0011]

In order to achieve the above object, a π / 4 shift QPSK demodulator of the present invention includes at least a synchronous detector for synchronously detecting an input received signal of π / 4 shift QPSK, and a next stage. And an equalizer for fading correction and a differential decoding for obtaining a QPSK composite signal of the next stage.

As a result, according to the demodulation method of the present invention, the waveform distortion compensation accuracy is high and the noise resistance characteristic of the transmission quality is improved.

[0013]

1 is a block diagram of a basic embodiment of the present invention.

In the figure, 42 is a waveform equalizer, 43 is a synchronous system circuit, 44 is a synchronous detector, 45 is a differential decoder, and 46 is a differential processor. The input signal passes through the synchronous detector 44, and the equalizer 42 compensates the waveform distortion. This signal is differentially decoded by the differential decoder 45 and the transmission data is output. At the same time, the synchronous detection output is differentially processed by the differential processor 46 and becomes the input of the synchronous circuit 43.

Now, the synchronous detector 44 will be described.

FIG. 5 is a block diagram showing an example of the structure of the synchronous detector. In the figure, numeral 38 is a carrier regenerator. 31-
The components of 36 are the same as those of FIG. 6 described above,
The function is also the same. In this synchronous detection system, a reference carrier signal generated by the carrier regenerator 38 is used instead of the delay signal in the differential detection system.

Comparing the two detection methods of the differential detection method and the synchronous detection method, the synchronous detection method is superior in the noise resistance characteristic.
It can be said that the differential detection method is advantageous in terms of circuit simplicity.

An embodiment to which the present invention is applied will be described below.

In the first embodiment shown in FIG. 2, the symbol determination of the equalized output is performed, and the transmission data is determined from the symbol by differential decoding.

In the figure, 44 is the above synchronous detector, 15 is a waveform equalizer, 12 is a training symbol sequence generator,
Here, the training symbol sequence is a predetermined fixed symbol sequence, which is also known to the receiving side. This is transmitted with an unknown symbol sequence created based on the transmitted data. The training symbol sequence generator 12 generates this training symbol sequence on the receiving side.

13 is a differential processor, 14 is a synchronizing circuit, 16
Is a determiner, and 17 is a differential decoder. The distortion of the output of the synchronous detector 11 is compensated by the equalizer 15 using the output of the training symbol sequence generator 12 as a reference signal. The reference carrier wave used for the synchronous detection is a signal obtained by differentially processing the output of the synchronous detector 11 by the synchronous circuit 14
Made by. The output of the equalizer 15 is four-valued determined by the determiner 16, and the differential decoder 1
The transmission data is determined at 7. It should be noted that the decision boundary of the decision device 17 alternately uses two decision surfaces having a phase difference of 45 ° depending on whether the symbol number is odd or even.

In the second embodiment shown in FIG. 3, the equalized output is differentially processed and then a determination is made to directly determine the transmission data.

In the figure, 18 is a differential processor, and 19 is a judging device. The components 11 to 15 are the same as those in FIG. 2 and have the same functions. The equalized output is converted by the differential processor 18 into a difference from the symbol one time before. This output is judged by the judging device 19 into four values, and the transmission data is decided. In this case, unlike the determiner 16 of FIG. 1,
It has the feature that only one judgment surface is required.

The third embodiment shown in FIG. 4 is an example in which the present invention is applied to a configuration including an arbitrary sequence estimator.

In the figure, reference numeral 20 is a sequence estimator, and components 11 to 14 and 17 are the same as those in FIG.
The function is also the same. The sequence estimator 20 estimates a transmission symbol from the received signal and outputs it. A differential decoder 17 differentially decodes this estimated symbol and outputs transmission data.

[0026]

According to the demodulation method of the present invention, the accuracy of waveform distortion compensation is high and the noise resistance of transmission quality is improved. Compared to the demodulation method that includes the differential detection method, a separate detector and differential decoder are required, and a differential processor is required for the synchronous system circuit. In the case of the configuration, since the AFC or the like is used for the local carrier wave generation circuit, there is no great difference in circuit scale. Also, the current L
According to the SI technology, the configuration can be easily done.

According to the present invention, in a digital radio apparatus using the π / 4 shift QPSK modulation system, QPSK
By using a waveform equalizer having the same method as the modulation method, it is possible to effectively compensate for the distortion of the radio wave propagation path due to fading or the like, and realize high-quality digital communication.

[Brief description of the drawings]

FIG. 1 is a π / 4 shift Q showing a basic embodiment of the present invention.
FIG. 3 is a block diagram showing the configuration of a digital demodulator for PSK.

FIG. 2 is a π / 4 shift QP showing a first embodiment of the present invention.
The block diagram of the digital demodulator for SK.

FIG. 3 is a π / 4 shift QP showing a second embodiment of the present invention.
The block diagram of the digital demodulator for SK.

FIG. 4 is a π / 4 shift QP showing a third embodiment of the present invention.
The block diagram of the digital demodulator for SK.

FIG. 5 is a block diagram of a known synchronous detection system.

FIG. 6 is a block diagram of a known differential detection system.

FIG. 7 is a block diagram of a digital demodulator for π / 4 shift QPSK using a differential detection method.

[Explanation of symbols]

11 synchronous detector, 12 training symbol sequence generator, 13 differential processor, 14 synchronous circuit, 15 waveform equalizer, 16 decision device, 17 differential decoder, 18 differential processor, 19 decision device, 20 symbols Sequence estimator, 31
Band pass filter, 32, 33 frequency mixer, 34
90 ° phase shifter, 35, 36 low pass filter, 37
Delay element, 38 carrier recovery circuit, 41 delay detector, 42 waveform equalizer, 43 synchronization system circuit, 44 synchronization detector, 45 differential decoder, 46 differential processor

Claims (4)

[Claims] 1. A receiver used for digital radio transmission by a .pi. / 4 shift QPSK modulation system, having at least a waveform equalizer for compensating for waveform distortion of a received signal after synchronous detection. Shift Q
PSK demodulator. 2. The demodulator according to claim 1, wherein the output after the synchronous detection is waveform-equalized, and the transmission equalized signal is symbol-judged and differentially decoded to decode the transmission data. And a demodulator. 3. The demodulator according to claim 1, wherein the output of the waveform equalizer is differentially processed, and the transmission data is decoded by performing symbol determination on this signal. 4. The demodulator according to claim 2, wherein a symbol sequence estimator for compensating the waveform distortion of the synchronous detection output to estimate a transmission symbol is used, and transmission data is differentially decoded from the estimated symbol sequence. A demodulator which is characterized by decoding.