JPS62151055A - Timing clock control system - Google Patents

Abstract

PURPOSE:To facilitate the control of a timing clock even for a multipoint and low roll-off ratio QAM signal by using a carrier phase of the QAM signal estimated by deciding a QAM orthogonal amplitude modulation signal and a one-frequency pilot signal. CONSTITUTION:A multiplier 101 multiplies an input signal 10 with an output of an oscillator 102 of an oscillation frequency f1 to apply quasi-synchronization detection in a data MODEM receiver receiving the QAM signal of a carrier frequency f1 attended with a pilot signal of frequency f2. The output of the multiplier 101 is decided by a complex number decider 103 and a phase detector 104 extracts a carrier phase shift by the result of decision and a complex number signal before the decision. The pilot signal 20 uses the multiplier 105 and is multiplied with the output of the oscillator 106 whose oscillation frequency f2 to apply the quasi-synchronization detection. The multiplier 105 outputs the phase detector 104 are given to a phase detector 107, where the difference between phase shifts is detected and its output controls the frequency of the oscillator 108 to obtain a timing clock.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to QAM (quadrature amplifier).
The present invention relates to a timing clock control method for a data modem using a quadrature amplitude modulation (tudemodulation) method.

[Conventional technology]

Conventionally, the timing clock control method for a QAM data modem involves performing nonlinear calculations such as square or full-wave rectification on the demodulated output to generate a line spectrum of the timing clock frequency.

A method of extracting this using a narrowband filter has been used.

[Problem that the invention seeks to solve]

The conventional timing clock control method mentioned above is as follows.

As the transmission speed increases, the data point arrangement becomes more numerous, and as the roll-off rate decreases, extraction becomes difficult.

In order to eliminate the above-mentioned drawbacks, there is a method in which /-PIP signals of two types of frequencies are inserted into the QAM signal, and the timing clock is controlled by these two types of pilot signals.

However, this method is not suitable for QA which transmits normal data.
This is because in addition to the band occupied by the M signal, a band occupied by the two pilot signals is required.

A wider frequency bandwidth is required, which is disadvantageous.

The purpose of the present invention is to eliminate the above-mentioned drawbacks and achieve multiple points.

It is an object of the present invention to provide a timing clock control system that can easily control the timing clock even for a QAM signal with a low roll-off rate by simply adding one type of pilot signal to it.

[Means for solving problems]

The present invention is a method of controlling a timing clock using a pilot signal of -frequency and a carrier wave phase of a QAM signal estimated by determining the QAM signal.

According to the present invention, the signal is transmitted with pilot signals of 9 frequencies and 12. A data modem receiver that receives a QAM signal with a carrier frequency of 11 includes: a first oscillator whose oscillation frequency is fl; a first multiplier that multiplies the output of the first oscillator by the received QAM signal; a first phase detector that obtains a phase on the complex plane from the output of the complex decider and the output of the first multiplier; a second oscillator with an oscillation frequency of 12; a second multiplier that multiplies the second oscillator output by a received pilot signal; and an output phase of the second multiplier and the first phase detector. and a third excavator whose oscillation frequency is controlled by the output of the second phase detector,
A timing clock control method is obtained in which the output of the oscillator is used as the timing clock of the system.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram illustrating a data modem receiver according to the present invention. This data modem receiver has two frequencies f
It is transmitted with the second pilot signal. It receives a signal with a carrier frequency ft multiplied by ωM. In this data modem receiver, a first multiplier 101 receives an input QAM signal 10 and an output from a first oscillator 102 whose oscillation frequency is f+.

By multiplying, quasi-synchronous detection is performed. The output of the first multiplier 101 is a baseband signal subjected to a carrier wave phase shift, but since it does not include a carrier wave component, the amount of deterioration cannot be extracted as is. The output of the first multiplier 101 is determined by the complex determiner 103, and based on this determination result and the complex signal before determination, that is, the output of the first multiplier 101, the carrier phase shift is determined by the first phase detector 104. Extract.

On the other hand, the pilot signal 20 is multiplied by the output of the second oscillator 106 whose two-shot frequency is 12 by a second multiplier 105 to perform quasi-synchronous detection. second multiplier 10
5 outputs the phase shift of the No. 4 pilot signal. and the output of the second multiplier 105.

The output of the first phase detector 104 is transmitted to the second phase detector 1
07, the difference between the respective phase shifts is detected, and the frequency of the third oscillator 108 is controlled by the output of the phase difference, which is used as a timing clock.

〔Effect of the invention〕

As explained above, the present invention provides multi-point timing clock control, which is difficult to control using conventional methods.

Even with a QAM signal having a low roll-off rate, the timing clock can be easily controlled simply by adding a type of pilot signal to it.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram illustrating a data modem receiver according to the present invention. In fig. 101...first multiplier, 102...first excavator. 103... Complex determiner, 104... First phase detector. 105...Second multiplier, 106...Second oscillator. 107...Second phase detector, 108...Third oscillator.

Claims (1)

[Claims] 1. In a data modem receiver that receives a QAM signal of carrier frequency f_1 transmitted with a pilot signal of frequency f_2, the first one whose oscillation frequency is f_1
an oscillator, a first multiplier that multiplies the output of the first oscillator by a received QAM signal, a complex determiner that performs area determination on a complex plane of the output of the first multiplier, and a first phase detector that obtains the phase on the complex plane from the output and the output of the first multiplier; a second oscillator whose oscillation frequency is f_2; a second multiplier that compares the output phase of the second multiplier and the output phase of the first phase detector;
and a third oscillator whose oscillation frequency is controlled by the output of the second phase detector, and the output of the third oscillator is used as a system timing clock. method.