JPH06232939A - Frame synchronization circuit - Google Patents

Abstract

PURPOSE:To obtain the frame synchronization circuit operated stably even in a transmission line in which a transmission distortion is in existence by solving problems of deterioration in the transmission characteristic due to the transmission line distortion such as multi-path and fading with respect to the frame synchronization circuit used for a time division multiple access system employing a multi-value quadrature amplitude modulation system (hereinafter abbreviated as QAM). CONSTITUTION:A signal point' equivalent to a quadruple phase modulation signal of a multi-value QAM signal is used for a transmission unique word, and a QPSK delay detector 5 applies delay detection to the multi-value QAM signal as a differential coding quadruple phase modulation (hereinafter abbreviated as DQPSK) signal and a correlation device 6 takes correlation between a receiver side unique word employing a DQPSK signal and the transmission unique word to detect the unique word from the delay detection output. Thus, the frame synchronization circuit is obtained, which is stably operated even on a transmission line in which a transmission distortion such as multi-path and fading is in existence in a TDMA system using multi-value QAM system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a time division multiple access (hereinafter abbreviated as TDMA) system such as mobile communication using a multilevel quadrature amplitude modulation (hereinafter abbreviated as multilevel QAM) system as a modulation system. The present invention relates to a frame synchronization circuit.

[0002]

2. Description of the Related Art In recent years, a system for efficiently transmitting more information has been required with the progress of information society.
The multi-valued QAM method can increase the amount of information that can be transmitted without expanding the transmission band, so it is an effective method for effective use of frequencies. Conventionally, it has been used for fixed microwave lines with relatively stable transmission lines. (For example, see Digital Microwave Communication (Moriji Kuwahara, 1974 Planning Center Co., Ltd.)), mobile communication, multipath,
1 for a transmission line that has large fluctuations and that has fading distortion.
Multi-level QAM over 6-ary quadrature amplitude modulation (16QAM)
The method was not used because the transmission characteristics are significantly degraded.

[0003]

However, due to recent advances in waveform equalization technology and the like, attempts have been made to improve transmission characteristics against multipath and fading distortion. Since the waveform equalizer estimates the channel distortion from a known symbol sequence called a training symbol, it is necessary to accurately know the position of the training symbol on the receiving side.
In the multi-level QAM method which is equal to or more than the AM method, it is very difficult to construct a frame synchronizing circuit that operates stably in a transmission path where multipath and fading distortion are present and which has a large fluctuation.

The present invention solves the above-mentioned conventional problems. In the TDMA system using the multilevel QAM system as a modulation system, the present invention stably operates even in a transmission line in which transmission line distortion such as multipath and fading exists. An object is to provide a frame synchronization circuit.

[0005]

In order to achieve the above object, according to the present invention, the transmission side has a maximum amplitude value or a minimum amplitude value of a multi-level QAM signal corresponding to a four-phase phase modulation (hereinafter abbreviated as QPSK) signal. The frame synchronization circuit has a unique word composed of signal points that give
A QPSK delay detector that differentially detects the M signal as a differentially encoded four-phase phase modulation (hereinafter abbreviated as DQPSK) signal; a correlator having a unique word on the receiving side corresponding to the DQPSK signal of the unique word on the transmitting side; A comparator for outputting a correlation pulse when the correlation output of the correlator is a certain value or more, and a digital phase lock loop (hereinafter abbreviated as DPLL) for generating a frame synchronization signal from the correlation pulse output. It has a configuration provided with.

[0006]

According to the present invention, the multi-valued QA is applied to the modulation system by the above-mentioned configuration
In the TDMA method using the M method, a signal point corresponding to the QPSK signal of the multilevel QAM signal is used as a transmission unique word, and a transmission unique word DQPSK signal is used as a reception unique word for correlation detection. Unique word detection can be performed using QPSK differential detection, and even in a transmission path with transmission path distortion such as multipath and fading, the multilevel QAM method is used as the modulation method to deteriorate the transmission characteristics. Therefore, it is possible to provide a stable frame synchronization circuit.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block connection diagram showing an embodiment of the frame synchronization circuit of the present invention. In this example, the case where 16QAM is used as the modulation method will be described.

In FIG. 1, reference numeral 1 is a quadrature demodulator for quadrature detection of a received modulated wave input with a reference signal substantially equal to the received input frequency, and 2 is a local oscillator for supplying the quadrature modulator 1 with a reference signal substantially equal to the received input frequency. Reference numeral 3 denotes in-phase output of quadrature detection output (hereinafter abbreviated as I output), 4 is quadrature output of quadrature detection output (hereinafter abbreviated as Q output), 5 is delay detection of the quadrature detection output of the quadrature demodulator 1 as a QPSK signal. QPSK
The delay detector 6 has a structure shown in FIG.
A correlator that correlates the delay detection output of the K delay detector 5 with the unique word on the receiving side, and 7 compares the correlation output of the correlator 6 with a constant value α, and when the correlation output is greater than or equal to the constant value α Is a comparator for outputting a correlation pulse, and 8 is a DPLL for generating a frame synchronization signal from the correlation pulse output of the comparator 7.
(Digital Phase Lock Loop), 9 is QP
SK differential detector 5, correlator 6, comparator 7, and DPLL 8
It is a frame synchronization circuit composed of.

The operation of the frame synchronization circuit configured as described above will be described. 16QAM shown in FIG.
The transmission signal modulated according to the signal point arrangement of is subjected to transmission path distortion such as multipath and fading in the wireless transmission path,
Received and input to the quadrature demodulator 1. The quadrature demodulator 1 quadrature-detects the input received modulated wave with a reference signal of the local oscillator 2 having a frequency substantially equal to the received modulated wave, and obtains I output and Q output. I output and Q output are QPS of the frame synchronization circuit 9.
The K delay detector 5 performs delay detection as a DQPSK signal,
The DQPSK signal outputs 32a to 32d shown in FIG. 3B are obtained. Then, the correlator 6 correlates the DQPSK signal output with the reception side unique word 21.

The operation of the correlator 6 will be described with reference to FIG. 2, which is a detailed block diagram of the correlator 6.

First, the differential detection output of the QPSK differential detector 5 is input to the shift register 22 for each symbol,
The exclusive OR circuits 23a to 23d determine whether the received unique word matches or does not match, and the adder 24 calculates the correlation. The unique word for transmission is the signal point 3 corresponding to the QPSK signal in the 16QAM signal of FIG.
1a to 31d, the reception side unique word 21 holds the DQPSK signal of the transmission unique word.
For example, a unique word for transmission has a unique word length of 5 symbols (31a, 31c, 31a, 31c, 31a).
Then, when the initial phase of the unique word for transmission is set to 31a in FIG.
(32a, 32c, 32a, 32c, 32a).
Then, when the correlation output of the correlator 6 is equal to or greater than the constant value α, the comparator 7 outputs a correlation pulse. The DPLL 8 generates a frame synchronization signal which is synchronized with the frame interval on average from the correlation pulse output.

[0012]

As described above, the effect of the present invention is to use the QPSK signal as a unique word for transmission in the TDMA method using the multilevel QAM method as the modulation method.
The frame synchronization circuit on the receiving side transmits the multilevel QAM signal to the DQP.
When a QPSK differential detector that performs differential detection as an SK signal, a correlator having a unique word on the reception side corresponding to the DQPSK signal of the unique word on the transmission side, and a correlation output of the correlator above a certain value α, By providing a comparator that outputs a correlation pulse and a digital phase lock loop that generates a frame synchronization signal from the output of the correlation pulse, modulation can be performed even in a transmission path where there is distortion such as multipath and fading. It is possible to provide a frame synchronization circuit that operates stably without being deteriorated in transmission characteristics due to the use of a multilevel QAM system.

[Brief description of drawings]

FIG. 1 is a block connection diagram of a frame synchronization circuit according to an embodiment of the present invention.

FIG. 2 is a block connection diagram of a correlator in the example.

FIG. 3 is a 16QAM signal and DQPSK in the same embodiment.
Diagram showing signal point arrangement of signals

[Explanation of symbols]

 1 Quadrature demodulator 2 Local oscillator 3 I output 4 Q output 5 QPSK delay detector 6 Correlator 7 Comparator 8 DPLL 9 Frame synchronization circuit

Claims (1)

[Claims] 1. A time division multiple access system using a multi-valued quadrature amplitude modulation system, comprising signal points corresponding to a four-phase phase modulation signal which gives a maximum amplitude value or a minimum amplitude value of the multi-valued quadrature amplitude modulation signal. And a four-phase phase modulation delay detector for differentially detecting the multilevel quadrature amplitude modulation signal as a differentially encoded four-phase phase modulation signal, and a differential code for the unique word on the transmission side. A correlator having a unique word on the receiving side corresponding to the quadrature phase-modulated signal, a comparator that outputs a correlation pulse when the correlation output of the correlator is above a certain value, and a frame from the correlation pulse output. Digital phase-locked to generate sync signal
A frame synchronization circuit having a loop.