JP2800811B2 - Synchronous acquisition method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a synchronization acquisition system, and more particularly to a synchronization acquisition system that detects transmission off timing during burst communication in spread spectrum communication and acquires synchronization.

[0002]

2. Description of the Related Art In a spread spectrum (SS) communication system, after a transmission side transmits a transmission wave of a certain frequency for a certain period, the transmission is turned off for a desired period to prevent interference.
In this off period, so-called burst communication for transmitting a transmission wave of another frequency is performed. In a receiving apparatus receiving a spread spectrum communication signal of a desired frequency subjected to the burst communication, synchronization is lost if the despread demodulation circuit is kept operating even when transmission on the transmission side is turned off, and then Since despreading cannot be performed unless initial synchronization is performed when transmission is turned on, synchronization is performed to detect whether transmission (received wave) has been turned on from off or turned on from off and synchronize the spreading code. Capture is required.

In this case, conventionally, in order to determine that transmission has been turned off from on, it is necessary to check the demodulated data at a subsequent stage or to perform despreading demodulation using the same spreading code as that on the transmitting side. There is no other method than to judge the carrier to be detected by the detection circuit. When the transmission is turned off, the timer is started, and based on the off-period information obtained from the demodulated data, the timer is operated until the transmission is likely to be turned on. It has been conventionally performed to start operation of a circuit and acquire synchronization.

[0004]

However, in the conventional method of confirming at a later stage by using demodulated data or performing synchronous acquisition by determining that transmission has been turned off from on by a carrier detection circuit, a certain determination time is required. Required,
Therefore, the shorter the burst transmission off time, the more difficult it is to detect the transmission off, and it becomes difficult to start the despread demodulation operation at the next transmission on timing. There is a problem that the probability of missing is high.

[0005] Further, even if a timer is provided between transmission off and transmission on to always perform the despreading demodulation operation only when transmission is on, detection of transmission off requires the time required for determination as described above. In addition, since the time varies depending on the timing, it is difficult to always provide stable synchronization by providing a timer.

[0006] The present invention has been made in view of the above points,
It is an object of the present invention to provide a synchronization acquisition method capable of setting a timer until the next transmission on time in order to quickly detect a transmission-off timing and perform stable synchronization during burst communication. I do.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a receiving means for receiving a burst-transmitted spread spectrum communication signal, and a spread code for generating the same spread code as the received spread spectrum communication signal. A generator, a despreading demodulation circuit that despreads and demodulates the received spread spectrum communication signal using a spreading code from the spreading code generator, and a relation between ON and OFF of the transmission side transmission that transmits the spread spectrum communication signal. It is always operating without any need, and calculates the correlation peak of the spread code based on the received spread spectrum communication signal and the spread code from the spread code generator, and sends it based on whether the correlation peak is larger than the threshold. An initial synchronization determination circuit that obtains a determination result of ON or OFF, and when transmission OFF is determined based on an output determination result of the initial synchronization determination circuit, Is obtained by a configuration in which a control unit for stopping the operation of the spread demodulation circuit.

According to the present invention, the fact that the transmission has been turned off during burst transmission can be determined not based on the output signal of the despreading demodulation circuit but on the basis of the disappearance of the correlation code peak of the spreading code by the always operating initial synchronization determination circuit. .

Further, according to the present invention, when it is determined that the transmission is off, the control unit operates a timer for a transmission off period obtained from output data of the despreading demodulation circuit from the time when the transmission is determined. At the end, the despreading demodulation circuit is controlled from a stop state to an operating state.

In the present invention, the timer is operated during the transmission off period, and the despreading demodulation circuit is controlled from the stop state to the operating state at the end of the timer operation. Control.

[0011]

FIG. 1 is a block diagram showing an embodiment of a synchronization acquisition system according to the present invention. As shown in FIG. 1, this embodiment includes a despreading integrator 1, a PLL circuit 2, a carrier detection circuit 3, a spreading code generator 4, an initial synchronization determination circuit 5, and a control unit 6. PLL
The circuit 2 detects a phase difference between the I (in-phase) signal and Q (negative-phase) signal input from the despreading integrator 1 and the output signal of the multiplier 23, and the two outputs of the phase shifter 21. A comparator 22 for detecting whether one of the values of the signal is 1 or -1;
A multiplier 23 multiplies the output signal of the comparator 22 by the other of the output signals of the phase shifter 21 and feeds back to the phase shifter 21.

The carrier detection circuit 3 has an absolute value (ABS) circuit 31 to which the I signal and the Q signal are input.
And 32 and the output signals of the absolute value circuits 31 and 32 are I /
And a divider 33 that divides and outputs Q. The despreading integrator 1, the PLL circuit 2, and the carrier detection circuit 3 constitute a despreading demodulation circuit 10.

In this embodiment, as shown in FIG.
The target is a signal that repeats burst transmission at intervals of Δt (transmission off time).

Next, the operation of the embodiment of the present invention will be described with reference to FIGS. A burst signal having a transmission timing as shown in FIG. 2 is received by the spread spectrum signal receiver, and the received digital signal is input to the despreading integrator 1 and the initial synchronization determination circuit 5 during the transmission ON period. The despreading integrator 1 despreads the input received digital signal using the output spreading code of the spreading code generator 4 to obtain I and Q signals which are the original digital signals. Synchronization is performed, and the carrier is detected by the carrier detection circuit 3. A signal indicating the presence or absence of carrier detection obtained by the carrier detection circuit 3 is input to the control unit 6.

On the other hand, the initial synchronization determination circuit 5
It is configured to always operate irrespective of the off state, and to despread the received digital signal using the output spreading code of the spreading code generator 4 to determine whether or not the correlation peak of the spreading code is equal to or greater than a threshold value. The determination is made, and when it is equal to or greater than the threshold value, a determination signal indicating the determination result of transmission ON is input to the control unit 6.

When the transmission is turned off after the valid data (data valid) # 1 in the transmission-on period shown in FIG. 2, the correlation peak of the initial synchronization determination circuit 5 falls below the threshold value in a very short time (disappears). ). The control unit 6, which monitors the presence or absence of a correlation peak, determines that transmission is OFF based on the input without the correlation peak from the initial synchronization determination circuit 5, and outputs the signal to the despreading integrator 1 from the spread code generator 4, for example. The operation of the despreading demodulation circuit 10 is stopped by a method such as blocking the spreading code, and the built-in timer is started, and the timer is operated for the transmission off period Δt obtained from the immediately preceding demodulated data.

The control unit 6 supplies the despreading code to the despreading demodulation circuit 10 so that the despreading demodulation circuit 10 operates again at the end of the operation of the timer after the time Δt. To start, when the transmission is turned on, the despread demodulation circuit 10 operates again.

According to this embodiment, since the initial synchronization determination circuit 5 is always operating and monitors when the correlation peak has disappeared, transmission off during burst communication can be performed much more quickly than in the prior art. By setting the timer, the despreading demodulation circuit 10 is always operating when the transmission is on. If only the carrier detection circuit 3 is used as in the related art, Δt is short and the transmission off is not performed. It is possible to prevent the loss of valid data (data valid) # 2 in FIG. 2 which has occurred in the system in which the determination cannot be made, and to shorten the transmission-off time interval Δt.

Also, since a timer from transmission off to transmission on can be set, the despread demodulation circuit 1 is turned on when transmission is on.
Since 0 can be operated, stable initial synchronization acquisition can be performed.

FIG. 3 is a block diagram showing another embodiment of the present invention. In the figure, an RF signal burst-transmitted by spread spectrum communication is converted into an intermediate frequency (IF) signal by a receiving unit 11, down-converted by a down-converting unit 12, and converted into a baseband signal. The baseband signal is converted into a digital signal by the A / D converter 13 and then input to the despreading unit 141 in the SS demodulation unit 14 where it is despread and returned to the original I and Q signals. A first digital signal processor (DSP) 142 and a second digital signal processor
The signals are input to the processor (DSP) 143, respectively. D
SP142 is the PLL circuit 2 and the carrier detection circuit 3 of FIG.
The circuit operation including the control unit 6 is realized by software processing, and the presence or absence of a carrier is detected and the demodulation operation is performed. On the other hand, the DSP 143 is constantly operating in a circuit that implements the operation of the initial synchronization determination unit 5 of FIG. 1 by software processing, and outputs a determination signal indicating whether transmission is on or not based on the presence or absence of a correlation peak. As a result, transmission off can be quickly detected as in FIG. 1, and the transmission is always on when transmission is on, so that stable initial synchronization can be acquired.

As a receiver, phase modulation (P
Although it is assumed that a signal subjected to SK (Phase Shift Keying) modulation is received, in spread spectrum communication, frequency modulation (FSK: Frequency) is performed.
The above embodiment can be applied to a signal that is modulated by Shift Keying.

[0022]

As described above, according to the present invention,
Since transmission off during burst transmission can be determined based on the disappearance of the correlation code peak of the spreading code by the always operating initial synchronization determination circuit instead of the output signal of the despreading demodulation circuit, it is faster than in the past. Transmission off can be detected, so that the transmission off interval during burst communication can be made shorter.

Further, according to the present invention, the timer is operated during the transmission off period, and the despreading demodulation circuit is controlled from the stop state to the operating state at the end of the timer operation. Since the operation is controlled as if it were operating, stable initial synchronization acquisition can be performed, and the reliability of the spread spectrum receiving apparatus for performing burst communication can be improved as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a diagram illustrating transmission timings of signals input to FIG. 1;

FIG. 3 is a block diagram of another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Despreading integrator 2 PLL circuit 3 Carrier detection circuit 4 Spreading code generator 5 Initial synchronization determination circuit 6 Control unit 14 SS demodulation unit 141 Despreading unit 142, 142 Digital signal processor (DSP)

Claims (1)

(57) [Claims] 1. A receiving means for receiving a burst-transmitted spread spectrum communication signal, a spread code generator for generating the same spread code as the received spread spectrum communication signal, and the spread spectrum communication signal A despreading demodulation circuit for despreading and demodulating by using a spreading code from a generator; and a transmitting side for transmitting the spread spectrum communication signal, which is always operating irrespective of ON / OFF of transmission, and the received spread spectrum signal is transmitted. A correlation peak of the spread code is obtained based on the communication signal and the spread code from the spread code generator, and a determination result of transmission ON or OFF is determined based on whether the correlation peak is larger than a threshold value. an initial synchronization determination circuit for obtaining, when determining the transmission-off based on the output determination result of the initial synchronization determination circuit, from the determination time Between the signal-off period
Activate the timer to stop the operation of the despread demodulation circuit
The despread demodulation circuit is stopped at the end of the timer operation.
And a control unit for controlling the operation state to an operation state .