JP3178138B2 - Frame synchronization circuit and frame synchronization method - Google Patents

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. Related 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 the information society.
The multi-level QAM method can increase the amount of information that can be transmitted without expanding the transmission band, and is an effective method for effective use of frequency. Conventionally, it is used for a fixed microwave line with a relatively stable transmission line. (See, for example, Digital Microwave Communication (by Moruji Kuwahara, published by Planning Center Co., Ltd. in 1974)), multi-path, mobile communication, etc.
In a fluctuating transmission line where fading distortion exists, 1
Multi-level QAM over 6-level quadrature amplitude modulation (16QAM)
The method was not used because the transmission characteristics deteriorated significantly.

[0003]

However, recent advances in waveform equalization technology and the like have attempted to improve transmission characteristics with respect to multipath and fading distortion. Since the waveform equalizer estimates channel distortion from a known symbol sequence called a training symbol, it is necessary to know the position of the training symbol accurately on the receiving side.
With the multi-level QAM system equal to or higher than the AM system, it has been very difficult to configure a frame synchronization circuit that operates stably on a transmission line where there is multipath and fading distortion and where the fluctuation is severe.

The present invention solves the above-mentioned conventional problems. In a TDMA system using a multi-level QAM system as a modulation system, it operates stably even on a transmission line where transmission line distortion such as multipath and fading exists. It is an object to provide a frame synchronization circuit.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a multi-level QAM signal corresponding to a four-phase phase modulation (hereinafter abbreviated as QPSK) signal which provides a maximum amplitude value or a minimum amplitude value. Enter a unique word composed of dots
Signal, and the frame synchronization circuit performs the multi-level QA on the transmitting side.
And QPSK differential detector for differential detection as M signal (hereinafter abbreviated as DQPSK) differentially encoded quadrature phase shift keying signal, Yu
Receives a signal equivalent to a signal obtained by delay-detecting a neak word
Output from the 4-phase phase modulation delay detector
Correlator for correlating force with the unique word of the receiving side
And when the correlation output of the correlator is above a certain value,
A comparator for outputting a correlation pulse, and a digital phase generator for generating a frame synchronization signal from the correlation pulse output.
And a lock loop (hereinafter abbreviated as DPLL).

[0006]

According to the present invention, with the above configuration, a multi-level QA is applied to the modulation method.
In the TDMA system using the M system, a signal point corresponding to a QPSK signal of a multi-level QAM signal is used as a unique word for transmission, and a DQPSK signal of the unique word for transmission is used as a unique word for reception for correlation detection. Unique word detection can be performed using QPSK differential detection, and transmission characteristics deteriorate due to the use of a multi-level QAM method as a modulation method even on a transmission path having transmission path distortion such as multipath and fading. And a frame synchronization circuit that operates stably can be provided.

[0007]

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

In FIG. 1, reference numeral 1 denotes a quadrature demodulator for quadrature detection of a reception modulation wave input by a reference signal substantially equal to the reception input frequency, and 2 denotes a local oscillator for supplying a quadrature modulator 1 with a reference signal substantially equal to the reception input frequency. Reference numeral 3 denotes an in-phase output of a quadrature detection output (hereinafter, abbreviated as I output), 4 denotes a quadrature output of a quadrature detection output (hereinafter, abbreviated as Q output), and 5 denotes delayed detection of a quadrature detection output of the quadrature demodulator 1 as a QPSK signal. QPSK
The delay detector 6 has a configuration shown in FIG.
A correlator 7 for correlating the differential detection output of the K delay detector 5 with the unique word on the receiving side. 7 compares the correlation output of the correlator 6 with a constant value α, and when the correlation output is equal to or more than the constant value α. And a comparator 8 for generating a frame synchronization signal from the correlation pulse output of the comparator 7.
(Digital phase locked loop), 9 is QP
SK delay detector 5, correlator 6, comparator 7, DPLL 8
This is a frame synchronization circuit composed of:

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

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

First, the delay detection output of the QPSK delay detector 5 is input to the shift register 22 for each symbol.
The exclusive OR circuits 23a to 23d determine whether or not the received unique word matches or does not match, and the adder 24 calculates the correlation. The transmission unique word is a signal point 3 corresponding to the QPSK signal in the 16 QAM signal of FIG.
1a to 31d, the receiving-side unique word 21 holds the DQPSK signal of the transmission unique word.
For example, the unique word for transmission is changed to (31a, 31c, 31a, 31c, 31a) having a unique word length of 5 symbols.
Then, when the initial phase of the unique word of transmission is set to 31a in FIG.
(32a, 32c, 32a, 32c, 32a).
When the correlation output of the correlator 6 is equal to or larger than the predetermined 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, according to the present invention, in the TDMA system using the multi-level QAM system as the modulation system, a QPSK signal is used as a transmission unique word,
The frame synchronization circuit on the receiving side converts the multilevel QAM signal to DQP
When a QPSK delay detector that performs delay detection as an SK signal, a correlator having a unique word on the receiving side corresponding to the DQPSK signal of the unique word on the transmitting side, and a correlation output of the correlator is equal to or more than a certain value α, By providing a comparator that outputs a correlation pulse and a digital phase-locked loop that generates a frame synchronization signal from the output of the correlation pulse, modulation can be performed even on a transmission path where transmission path distortion such as multipath or fading exists. It is possible to provide a frame synchronization circuit that operates stably without suffering deterioration of transmission characteristics due to the use of the multi-level QAM method.

[Brief description of the drawings]

FIG. 1 is a block 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 embodiment.

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

[Explanation of symbols]

 DESCRIPTION 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

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-71640 (JP, A) JP-A-58-185753 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04L 27/00-27/38

Claims (2)

(57) [Claims] 1. A time-division multiple access system using a multilevel quadrature amplitude modulation system, comprising signal points corresponding to a four-phase modulation signal giving the maximum amplitude value or the minimum amplitude value of the multilevel quadrature amplitude modulation signal. Signal with the unique word
And the multi-level quadrature amplitude modulation signal is a differentially encoded four-phase phase modulation signal.
A four-phase phase-modulation delay detector that performs delay detection as a signal and a phase detection signal that detects the unique word of the input signal.
The corresponding signal is defined as a unique word on the receiving side,
Between the output of the tunable delay detector and the unique word of the receiving side
A correlator for obtaining a correlation, a comparator for outputting a correlation pulse when the correlation output of the correlator is a certain value or more, and a digital phase-locked loop for generating a frame synchronization signal from the correlation pulse output. A frame synchronization circuit provided. 2. A time division multiplexing method using a multilevel quadrature amplitude modulation method.
The maximum amplitude value of the multilevel quadrature amplitude modulation signal
Or equivalent to a 4-phase modulated signal giving the minimum amplitude value
A signal having a unique word composed of signal points
And the multi-level quadrature amplitude modulation signal is a differentially encoded four-phase phase modulation signal.
Delayed detection as No., phases delay detection signal of the unique word of the input signal
The corresponding signal is defined as a unique word on the receiving side,
Between the output of the tunable delay detector and the unique word of the receiving side
Takes a correlation and outputs a correlation pulse when the correlation is above a certain value,
Generate a frame synchronization signal from the correlation pulse output
Frame synchronization method .