JPH0234537B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a synchronization circuit used in a frequency hopping spread spectrum communication receiver.

[Prior art]

FIG. 1 is a block diagram of a synchronization circuit of a receiver in a conventional frequency hopping spread spectrum communication system. This synchronization circuit includes a frequency synthesizer 8 and a PN code generator 9 for generating a locally spread signal, and a received signal (hereinafter referred to as a preamble signal) in which the frequency of a carrier wave is hopping according to a PN code and predetermined data. ) 101 and a locally spread signal 104 to form a correlation signal 103,
a correlation detector 1 consisting of a balanced modulator 3, a bandpass wave detector 4, and an envelope detector 5; this correlation signal 103;
A first synchronization determination circuit 2 comprising an integrator 6 and a threshold detector 7;
VCO 10 that generates the clock for the PN code generator 9
and; a synchronization tracking circuit 12 that maintains a synchronized state;
The control circuit 11 receives the output of the first determination circuit 2 and controls the VCO 10 and the synchronization tracking circuit 12.

The operation of this synchronous circuit will be explained. FIG. 2 shows a characteristic diagram of the correlation signal output with respect to the phase difference between the preamble signal 101 and the local spread signal 104,
Point A is in sync. The operation of this synchronous circuit is
This can be divided into acquisition, which adjusts the phase of the local spread signal to range B in FIG. 2, and tracking, which adjusts the phase to the synchronized state at point A. First, in acquisition, the control circuit 11 changes the phase of the locally spread signal 104 and the determination circuit 2
monitor the output of Judgment circuit 2 uses locally spread signal 1
When the control circuit 11 outputs that the phase of 04 falls within the range B, the control circuit 11 operates the synchronous tracking circuit 12 to complete the acquisition and perform tracking. Thereafter, the control circuit 11 again determines whether a synchronized state has been obtained based on the output of the first determination circuit 2, and depending on the result, either re-acquires or continues synchronized tracking.

However, in this conventional synchronous circuit, when the received signal level is constant and an automatic gain adjustment circuit (hereinafter referred to as AGC) is not required, the first judgment circuit 2
However, if the received signal level fluctuates and AGC is operated after acquisition to compensate for it, there is a problem that correct determination cannot be made.
For example, when tracking is mistakenly performed due to noise or the like, the first determination circuit 2 misidentifies the noise as a signal due to the action of AGC, and is unable to perform acquisition again.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a synchronization circuit that can eliminate these drawbacks and reliably acquire synchronization of a receiver in frequency hopping spread spectrum communication.

[Structure of the invention]

The present invention comprises a correlation detector that receives a spread spectrum signal modulated by predetermined data and forms a correlation signal indicating a correlation value between the spread spectrum signal and the local spread signal; a first determination circuit that receives the correlation signal of the detector and makes a synchronization threshold determination at a predetermined timing; a spread signal generator that forms the local spread signal; and a clock for the spread signal generator.
a synchronization tracking circuit that receives the spread spectrum signal and maintains a synchronous relationship with the local spread signal; and a synchronization tracking circuit that receives the determination output of the first determination circuit and receives the
A synchronization circuit including a VCO and a control circuit for controlling the synchronization tracking circuit receives the despread signal from the correlation detector and demodulates the data signal.
an FSK demodulator; a second determination circuit that detects a coincidence ratio between the data signal of the demodulator and predetermined data and supplies a determination output for determining synchronization when a coincidence of a predetermined ratio or more is detected to the control circuit; It is characterized by the addition of.

The synchronization circuit according to the present invention utilizes the fact that a preamble signal has a predetermined data pattern, and includes a conventional synchronization circuit, an FSK demodulator that receives a despread signal and generates a data signal,
It is comprised of a second synchronization determination circuit that detects a match between this data signal and a predetermined data pattern.

〔Example〕

The present invention will be described in detail below with reference to the drawings.

FIG. 3 is a block diagram of one embodiment of the present invention, and this embodiment is an example in which the data pattern at the time of the preamble signal is all "1". In this embodiment, the despread signal 1 is different from the conventional circuit shown in FIG.
02, and a counter 14 that determines whether the number of "1"s included in the data signal reaches a predetermined value within a certain period of time. 15.

The operation of the circuit having such a configuration will be explained.

Acquisition of synchronization is performed using the output of the first determination circuit 2, as in the conventional circuit, but in determining synchronization after tracking, the control circuit 11 uses the output of the second synchronization tracking circuit 15.
A timing signal 105 is sent to the data signal, the ratio of "1" in the data signal is counted, and a determination is made based on whether the count value has reached a predetermined value. At this time, the value given to this counter 14 corresponds to the threshold level given to the first determination circuit 2, but this value is set according to the data error rate and can be set in detail.

Furthermore, while the result of the first judgment circuit 1 is affected by the change in the noise level in the detector output due to AGC, the result of the first judgment circuit 2 is that the FSK demodulator 13 is affected by the change in the signal level and noise level. Since the data signal is obtained by relative comparison, it is determined by the signal-to-noise ratio and is not easily affected by AGC. Therefore, compared to conventional circuits, the synchronization circuit of this embodiment can correctly determine whether or not the synchronization state is established after acquisition and tracking.

〔Effect of the invention〕

As described above, the present invention provides a synchronization circuit that can reliably obtain a synchronized state even under conditions where the received signal level fluctuates in a frequency hopping spread communication receiver. Therefore, by using this synchronization circuit, it is possible to effectively carry out mobile spread spectrum communication in which the received signal level fluctuates greatly.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of a synchronization circuit of a conventional frequency hopping receiver, Fig. 2 is a correlation value pattern diagram explaining the operation of Fig. 1, and Fig. 3 is a block diagram of an embodiment of the present invention. It is. In the figure, 1... Correlation detector, 2... First synchronization determination circuit,
3...Balanced modulator, 4...Band pass wave generator, 5...
...Envelope detector, 6...Integrator, 7...Threshold detector, 8...Frequency synthesizer, 9...
... PN code generator, 10 ... VCO, 11 ... control circuit, 12 ... synchronization tracking circuit, 13 ... FSK demodulator, 14 ... counter, 15 ... second synchronization determination circuit.

Claims (1)

[Claims] 1 A correlation detector that receives a spread spectrum signal modulated by predetermined data and forms a correlation signal indicating a correlation value between the spread spectrum signal and the local spread signal; a first judgment circuit that performs a synchronization threshold judgment at a predetermined timing; a spread signal generator that forms the local spread signal; a VCO that generates a clock for the spread signal generator; In the synchronization circuit, the synchronization circuit includes a synchronization tracking circuit that maintains a synchronization relationship with the received local spread signal, and a control circuit that receives a determination output from the first determination circuit and controls the VCO and the synchronization tracking circuit, An FSK demodulator that receives the despread signal from the receiver and demodulates the data signal, and a judgment device that detects the proportion of coincidence between the data signal of this demodulator and predetermined data, and determines synchronization when a coincidence of a predetermined proportion or more is detected. A synchronous circuit further comprising a second determination circuit that supplies an output to the control circuit.