JPH03188736A - Timing extraction system - Google Patents

Abstract

PURPOSE:To extract a baud timing stably up to a low S/N by outputting amplitude information from a QPSK signal subject to n/4 shift modulation and extracting a timing component using a baud timing as a center frequency. CONSTITUTION:When the system is the n/4 shift modulation system and a signal point is transited at least to a position of + or -3/4n, since the amplitude is lowered considerably, a baud timing frequency component is generated. An envelope detection output by a rectifier circuit or an RSSI output whose envelope is subject to LOG transformation is used for an amplitude information detection means 1. The output passes through a narrow band filter 2 to extract the baud timing component.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is directed to a Π/4 shift QP used in mobile communications, etc.
The present invention relates to a method for stably extracting baud timing down to a low S/N with a relatively simple circuit configuration in timing extraction of an SK signal.

(Prior Art) In land mobile communications, fading occurs due to multi-paths and is subject to random carrier wave phase fluctuations. For this reason, it is difficult to employ synchronous detection in low-speed digital communications, and delayed detection is usually used.

To perform delayed detection, it is necessary to know the baud timing in advance. Therefore, the baud timing extraction circuit needs to operate before carrier demodulation.

Conventionally, the method shown in FIG. 2 has been widely adopted as a method for extracting baud timing from Π/4 shift modulated transport. This method includes a frequency discriminator 101, a rectifier circuit 10
2. It is composed of a narrowband filter 103.

In this method, an input carrier signal is passed through a frequency discriminator 101 to detect the frequency, a rectifier circuit 102 generates a baud timing component, and a narrow band filter 103 extracts this timing component.

(Problems to be Solved by the Invention) In the conventional baud and clock extraction method from the Π/4 shift QPSK modulation signal described above, when the input S/N decreases,
The discriminator creates a threshold effect. Furthermore, since a rectifier circuit is used to generate a timing signal, a threshold effect occurs here as well. These effects greatly reduce the stability of baud timing extraction when the S/N decreases.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method capable of stably extracting baud timing down to a low S/N with a simple circuit configuration.

(Means for Solving the Problems) Amplitude information detection means for inputting a QPSK signal subjected to Π/4 shift modulation and outputting its amplitude information, and means for extracting a timing component having a baud timing as a center frequency from the output thereof. It is characterized by having the following.

(Function) In the present invention, a carrier wave envelope detection signal having carrier wave amplitude information and an R85I (Recieved Sign
alStrength Indicator) output signal, and since this signal has a baud timing component, a narrow band filter such as a PLL (Phase Lock Loop) and a tank circuit is used.
Extend bow timing. With this method, stable timing extraction can be achieved even at a relatively low S/H with a small number of additional circuits.

(Example) Next, an example of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the present invention.

The embodiment uses an amplitude information detection means 1 and a narrow band filter 2.

A QPSK carrier wave signal subjected to rr/4 shift modulation is inputted as an input signal, and a baud timing signal component is generated by the amplitude information detection means 1. In the Π/4 shift modulation method, at least when the signal point transitions to a position of ±374n, the amplitude decreases significantly, thereby generating a po timing frequency component. As the amplitude information detection means, an envelope detection output from a rectifier circuit or an R85I output obtained by LOG-converting the envelope is used. By passing this output through the narrow band filter 2, the baud timing component can be extracted. As the narrowband filter, a PLL or tank system can be adopted.

The direct conversion method has an amplitude detection circuit for AGC control, and the normal super-heterodyne reception method currently used in the membrane outputs an R85I signal as a standard for measuring received field strength. ing. Therefore, the timing extraction function can be realized with very little addition of circuits.

(Effects of the Invention) As explained above, according to the present invention, the baud timing extraction function can be realized with a relatively small circuit scale. Furthermore, since the order of nonlinear operation is relatively small, stable baud timing extraction can be expected even at low S/H.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is a system diagram showing an example of a conventional system. In the figure, 1... amplitude information detection means, 2... narrowband filter, 101... frequency detection means, 102...
・Rectifier circuit, 103...Narrow band filter・ Fig. 1

Claims (1)

[Claims] (1) A timing extraction method comprising amplitude information detection means for inputting a QPSK signal subjected to Π/4 shift modulation and outputting its amplitude information, and means for extracting a component whose center frequency is the baud timing from the output.