JP2939677B2 - Spread spectrum demodulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum demodulation apparatus in which a code synchronization circuit is improved in order to operate stably even at a low C / N in code synchronization control of the spread spectrum demodulation apparatus.

[0002]

2. Description of the Related Art As shown in FIG. 2, a conventional spread spectrum demodulation apparatus receives a received signal 1 having undergone spread spectrum.
Is branched into three in the next distributor 2. This branch output is sent to each of the mixers 3 to 5, where it is mixed with the PN signal from the PN generator 6. The PN signals are three kinds of signals whose phases are shifted by + Δ / 2, −Δ / 2, 0.
Means a pulse width of 1 bit. This mixer output is
It is supplied to the next band-pass filters 7A to 7C and 13A to 13C. These band-pass filters are connected to pass only the information spectrum after despreading and improve C / N. That is, in order to obtain a processing gain, the band-pass filter 13 is set to have a narrower band than the band-pass filter 7. The outputs of these band-pass filters are supplied to detectors 8A to 8C and 14A to 14C, respectively, where the IF signals are detected and a DC voltage is generated through a low-pass filter (not shown). ing. Detector 8B,
The output of 8C enters the next differentiator 9, and this output is input to the loop filter 10. This output enters a voltage controlled oscillator (VCO) 11 and passes through a gate circuit 12 to a PN
The signal is supplied to the generator 6 to form a delay lock loop (DLL) for despreading. On the other hand, detector 14A
To 14C are input to the determiners 15A to 15C,
When the code synchronization cannot be achieved, the code synchronization controller 16
Pulses at arbitrary intervals are output to the ND gate 12, and VC
The clock of the O11 output is deleted at an arbitrary interval, and the PN code is swept between the received signal 1 and the output of the PN generator 6. If the correlation by despreading is obtained at the outputs of the mixers 3 to 5, voltages appear on the detectors 14A to 14C,
When the voltage exceeds a certain threshold voltage, the determiners 15A to 15C determine that there is a correlation. The code synchronization controller 16 based on this determination output stops the pulse output to the gate circuit 12, and shifts to the steady lock state by the delay lock loop. In the stationary lock state, a despread demodulated signal always appears at the output of the mixer 3, one enters the next PSK demodulator 17, and the other enters the band-pass filter 7A, the detector 8A, and the determiner 15D. Pass sequentially.
The PSK demodulator 17 outputs the demodulated data 18 and the received clock 19. The output of the decision unit 15D is constantly monitored by the code synchronization controller 16, and the decision unit 1D
If it is determined that there is no correlation in 5D, the code synchronization controller 1
Numeral 6 again outputs a sweep pulse to the AND gate 12 and performs sweeping to re-establish code synchronization.

[0003]

The conventional spread spectrum demodulator described above has a drawback that when the output of the decision unit malfunctions at low C / N, the sweep is started by the AND gate regardless of the code synchronization state. There is. As a countermeasure, there is a method of reducing the determination error by narrowing the band of the low-pass filter in the detector, but in this case, the response speed becomes slow, so the sweep speed needs to be slowed. . Therefore, the bandwidth of the low-pass filter cannot be made smaller than a certain value, and when the C / N becomes low, there is a disadvantage that the probability of malfunctioning increases. Note that the DLL loop can be operated sufficiently at a low C / N.

[0004]

SUMMARY OF THE INVENTION A spread spectrum demodulator according to the present invention receives a spread spectrum signal transmitted by spreading an information spectrum by a PN code, and transmits the received spread signal to the same PN as that on the transmitting side. In a spread spectrum demodulator for demodulating an information spectrum by despreading using a code, the information signal after the despread demodulation is PSK.
An OR gate is provided which inputs a synchronization signal indicating that demodulation has been successfully performed by the demodulator and an output signal of the correlation presence / absence determiner in the spread spectrum demodulator and supplies a logical sum output to the code synchronization control circuit.

[0005]

Next, the present invention will be described with reference to the drawings. 1, the same reference numerals as those in FIG. 2 have the same functions. That is, in the embodiment of FIG. 1, the OR gate 20 is connected between the output of the PSK demodulator 17, the output of the decision unit 15D, and the code synchronization controller 16.

Next, the operation of this embodiment will be described. When the synchronization by the despreading is established and the synchronization is also established in the PSK demodulator 17, the synchronizing signal is sent from the PSK demodulator
To the input of Since the OR gate 20 also receives the output of the determiner 15D, once the synchronization of the PSK demodulator 17 is established, the output of the determiner 15 is masked, and the PSK demodulation is performed even if the output of the determiner 15D malfunctions due to low C / N. Table 17
As long as is synchronized, PN generator 16 will not initiate a sweep.

[0007]

As described above, the present invention comprises an OR gate that inputs a synchronization signal generated by a PSK demodulator and an output signal from a decision unit in a spread spectrum demodulator, so that once synchronization is established, There is an effect that the synchronization is stably maintained even in the low C / N state, and the code sweep operation due to the malfunction of the despreading is not performed.

[Brief description of the drawings]

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

FIG. 2 is a block diagram of a conventional spread spectrum demodulator.

[Explanation of symbols]

 Reference Signs List 1 received signal 2 distributor 3-5 mixer 6 PN generator 7A-7C, 13A-13C bandpass filter 8A-8C, 14A-14C detector 9 differentiator 10 loop filter 11 voltage controlled oscillator (VCO) 12 AND Gate 20 OR gate

Claims (1)

(57) [Claims] An information spectrum is spread by a PN code, and a received spread spectrum signal is received, and the received spread signal is despread using the same PN code as that on the transmission side to demodulate the information spectrum. In the spread spectrum demodulator, the information signal after the despread demodulation is PSK.
A spread spectrum demodulator having an OR gate for inputting a synchronization signal indicating that demodulation has been successfully performed and an output signal of a correlation existence / non-existence determiner in the spread spectrum demodulation apparatus and supplying a logical sum output to a code synchronization control circuit; Demodulator.