JP2589501B2 - Demodulation method of spread spectrum receiver - Google Patents

Description

The present invention relates to a demodulation method for a spread spectrum receiver.

The spread spectrum communication system to which the present invention relates refers to a method of spreading a baseband information signal into a spectrum band several hundreds to several thousand times the bandwidth and transmitting the spread spectrum signal. According to the direct spread-spectrum modulation method, a wideband (spread) signal is modulated as a spread spectrum signal by a signal other than the information signal to be transmitted, and modulated. A digital code modulation signal (carrier) whose bit rate is considerably higher than its width is used.

[Summary of the Invention] The present invention relates to the invention of Japanese Patent Application No.
It is suitable to be applied to the multiple spread spectrum communication system disclosed in Japanese Patent Laid-Open No. 61-234183 (JP-A-63-88924).
In such a system, two or more types of pseudo noise codes having different spreading code circulation periods are used. In the present invention, the pseudo-noise code of the synchronizer which is individually synchronized with the transmission-side code is selectively combined and used for the final demodulation of the receiver.

[Prior Art] A multiple spread spectrum communication system has been proposed by the present applicant and disclosed in, for example, Japanese Patent Application No. 61-234183 (Japanese Patent Application Laid-Open No. 63-88924) filed on October 1, 1986. Have been. This can be summarized as follows. That is, in the conventional direct spread spectrum communication system, when realizing higher performance spread processing, the chip time is reduced as much as possible,
Spreading code with a large number of constituent bits, that is, pseudo noise (PN)
In order to attain the increase in the number of bits, the synchronization control on the receiving side becomes sophisticated and the cost increases due to the complexity of the device. In order to solve such a problem, the above-mentioned patent application substantially expands a bit length of a spread code by using a beat phenomenon between two or more pseudonoise codes having different cyclic periods. In this way, more effective spectrum spreading is performed, and accurate demodulation synchronization is realized by a combination of two or more relatively short correlation detection procedures.

Conventionally, in such a multi-spread spectrum receiver, an expensive correlator or a matched filter has been used for demodulation / synchronization processing like an ordinary receiver.

[Problems to be Solved by the Invention] It is an object of the present invention to avoid the use of such expensive correlators and matched filters and to realize synchronization in a short time almost equivalent to these. I do.

[Means for Solving the Problems] In order to achieve this object, the present invention provides a pulse train generator for frequency demodulating a received spread spectrum signal to generate a pulse train signal responsive to a code transition timing of the spread spectrum signal. Means, and a plurality of transmission PN codes corresponding to the transmission side PN code used in the spread modulation process of the spread spectrum signal.
A code synchronization means having a PN generator for detecting synchronization of a PN code between transmission and reception; a system synchronization monitor for outputting PN selection data in response to a synchronization detection signal from the code synchronization means; And a code multiplexer that selectively synthesizes the PN code from the PN code according to the PN selection data and outputs a synthesized PN code, and a demodulation unit that code-demodulates the spread spectrum signal using the synthesized PN code. The gist is that it is provided.

[Operation] The synchronization establishment signal from each of the code synchronizers can be intensively monitored by the monitor device, and pseudo noise from the code synchronizer whose synchronization has not been established is not used for the above-described synthesis. You can do so.

Also, the composite code used for the final demodulation can be used as a modulation code in transmission on the receiving side.

Further, the presence / absence of a synchronization establishment signal from the code synchronizer may be monitored over time, and the presence / absence may be given as a binary numerical code based on a combination of 0 and 1.

[Embodiment] FIG. 1 shows an embodiment in which N PN codes are used on the transmission side in a main part of a spread spectrum receiver incorporating the principle of the present invention. Such a multiple spread spectrum communication system has been proposed by the present applicant, and is disclosed in, for example, Japanese Patent Application No. 61-234183 (Japanese Patent Application Laid-Open No. 63-88924) filed on October 1, 1986. I have.

The present invention is preferably used with such a multiple spread spectrum communication scheme. FIG. 1 shows an R × input terminal 10
Receive the spread spectrum signal modulated by using N PN codes and transmitted by the transmitter via the receiving side. This is supplied to the frequency demodulator 12, where it is converted into a baseband signal having a rise and fall corresponding to the modulation code. In a situation where other direct spread spectrum signals using substantially the same modulation frequency coexist, a baseband signal in which a signal indicating a rising edge and a falling edge different from the above is superimposed is obtained. When a differentiation process is applied to the baseband signal, a pulse train signal can be obtained at each time point where it is considered that there is a code change including the code change point of the code used in the spreading process.

In the figure, the output of the frequency modulator is provided to a differentiator 14 and then to an absolute value generator 16. The absolute value generator 16 changes the pulse train signal from the differentiator 14 to one polarity without changing its time axis and outputs the signal.

When code demodulating the above received signal, a reference code corresponding to the spreading code is generated by a PN generator, and demodulation is achieved under the condition that this phase substantially matches the transmitting side. The rising and falling timings are theoretically all overlapped with a series of pulse groups included in the pulse train. Therefore, if the pulse rate of this group of pulses is monitored within a finite time range by intentionally shifting the chip rate of the PN generator and the chip rate of the transmitting side, the point in time at which demodulation synchronization is achieved is determined. It becomes possible to grasp accurately. Considering further expansion, according to this method, even if a signal (for example, the multiplex spreading method described above) is code-modulated in a complex manner with a plurality of pseudo noises, each of the pseudo noises is separately separated. At the same time, it is possible to maintain the overall synchronization as a set of tracking loops formed by independently applying feedback to the individual PN generator clocks. At this time, even if codes other than the modulation code used in the system are mixed, the influence is greatly reduced in the process of checking the matching with the reference signal.

In the figure, the signal from the absolute value generator 16 has a number of "S units" corresponding to the number N of PN codes used in transmission.
18-1 to 18-N. This S-unit, as described in more detail in connection with FIG.
It has a PN generator corresponding to each PN code, and performs synchronization detection and tracking. The synchronization detection signal from each S unit 18 is provided to a system synchronization monitor 20. The system synchronization monitor 20 provides a control code output on line 22.

S units 18-1 to 18-N are provided with PNs respectively provided.
The generator outputs PN-1 to PN-N are provided to the code multiplexer 26 via lines 24-1 to 24-N, respectively. The sign multiplexer 26 is a logic circuit including an exclusive OR circuit,
The PN selection data is received from the system synchronization monitor 20 via a line 28, and a PN code selectively synthesized from PN-1 to PN-N is supplied to a line 30. This is used in the final code demodulation process in the balanced modulators 32 and 34, and is also used as a modulation code in the transmitter 36. Here, since a signal indicating whether or not a synchronization state is sent from the unit S is sent back to the transmission side via the line 28, the communication environment can be known from the transmission side, and the combination of modulation codes can be determined according to the situation. It is possible to take measures such as change, and to deal with jamming and the like reliably.

FIG. 2 shows a specific configuration of one S unit 18. In the figure, reference numeral 40 denotes a voltage controlled crystal oscillator, and a chip clock rate is controlled according to a control voltage applied to a switch connected to a switch. The switch 42 applies the Vslide voltage to the control input 44 so that the oscillator 40 generates a clock corresponding to a chip rate slightly different from the chip rate of the transmitting side in the synchronization acquisition process.

Reference numeral 46 denotes a pseudo noise generator which generates pseudo noise (PN) based on the chip clock output of the oscillator 40. The pseudo noise generator 46 supplies the pseudo noise to the code multiplexer 26 of FIG. 5 ns delay device 48
And a transition pulse generator 52 comprising an exclusive OR circuit 50. Output D _S of the transition pulse generator 'is given to the AND circuit 54 together with the output D _S of the absolute value generator 16 of FIG. 1. In the synchronization acquisition process, as described above, the oscillator 40 normally generates a clock having a chip rate slightly different from the chip rate of the transmitting side, and thus generates a code pulse train representing the transition timing of the pseudo noise of the PN generator 46. vessel
52 occurs as _DS '. A synchronous state is periodically created between D _S ′ and the corresponding reception pulse train D _S on the transmission side according to the degree of their deviation. In this state, the output pulse train of a portion D _S 'of D _S pulse train is approximately matches. Adder
56 and delayer coherent integrator 60 consisting of 58 will be gradually accumulated pulses of a predetermined interval determined by the difference between the chip rate of the D _S chip rate and D _S and D _S ', PN generator 46 in the opposite As for the pulse train component not related to the output, only a small amount is accumulated since there is only an irregular matching pulse. The output of the coherent integrator 60 is provided to the phase detector 62 together with the output of the oscillator 40. Therefore, as is clear from the above, the output pulse train of the coherent integrator 60 accurately indicates the clock timing of the code component in question included in the received signal, and this and the current PN generator 46 If the clock frequency is fed back via the voltage-controlled crystal oscillator 40 according to the supplied clock phase shift amount, the correct clock phase can be continuously maintained. In this embodiment, the analog switch 42 is switched to the feedback side by the occurrence of a later-described synchronization detection signal on the line 64.

That is, the Vslide described above is normally the control input of the oscillator 40.
After the synchronization is detected, the switch 42 is switched so that the oscillator 40 can generate a clock almost in accordance with the chip timing on the transmission side.
Apply the feedback voltage from phase detector 62 to line 66
Is applied to the control input of the oscillator 40.

As a method of detecting the synchronization, a method of judging from the output level of the coherent integrator 60, a method of judging from the frequency of the coincidence pulse of D _S / D _S ′ and the like can be considered. In the present embodiment, more accurate synchronization detection is performed. Scales also the frequency of matching pulses with sign change and the D _S output signals in the frequency at the same time of the reference signal and the complementary relationship between the match pulses D _S / D _S 'for, it is determined synchronization from these comparisons Things.

2, the output of the voltage controlled crystal oscillator 40 (FIG. 3a) is provided to a T flip-flop or JK flip-flop 70, the output of which is the output of a PN generator 46 (third output).
The output is provided to the exclusive OR gate 72 together with FIG. B). The output of the exclusive OR gate 72 is complementary to the reference signal, that is, the output of the PN generator 46. At the same time, a complementary signal (FIG. 3c) is obtained which is a sequence that causes a sign change only when there is no sign change. This is the transition pulse detection circuit 52 described above.
A given transition pulse detection circuit 47 having the same configuration, the pulse train D _S representing the transition point of the complementary signal at its output "(FIG. 3 e) is output. This is D _S '(FIG. 3 described above d)
Like the match pulse and D _S in the AND gate 54 is detected, consistent pulse and D _S is detected by the AND gate 76. The counter 78 receives the outputs of these AND gates 54 and 76.

Figure 4 is D _S signal (Fig. 4 a) and AND in asynchronous state
Shows the D _S / D _S 'of matching pulses (Fig. 4 b) from the gate 54, D _S / D _S of the D _S signal (FIG. 5 a), the AND gate 54 in FIG. 5 is a synchronous state 'Match pulse (Fig. 5b) and AND
The D _S / D _S ″ match pulse from gate 76 is shown (FIG. 5c).

Figure 6 is 'is intended to illustrate the conditions example for determining synchronization by matching the pulse frequency comparison / D _S ", the horizontal axis _{D S / D S' D S} / D S by the counter 78 pulses (regular match the pulse) count on the vertical axis indicate taking D _S / D _S "pulse (invalid matching pulse) count.

[Effects of the Invention] As described above, as apparent from the detailed description of the embodiment of the present invention, the present invention individually applies the pseudo noise from the S unit 18 to the code multiplexer 26, and establishes the synchronization state of each unit. Is formed selectively on the line 30 by selectively combining in accordance with the data 28 representing the data 28, and this is used for the final modulation by the balance modulator (32, 34) or the like. We will not avoid using correlators and matched filters.

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of a spread spectrum receiver in which the present invention is embodied, FIG. 2 is a detailed circuit diagram of some elements of FIG. 1, and FIGS. FIG. 6 is a waveform diagram for explaining the operation of FIG. 2, and FIG. 6 is an explanatory diagram for the operation related to FIG. In the figure, 12 is a frequency demodulator, 14 is a differentiator, 16 is an absolute value generator, 18-1 to 18-N are S units, and 26 is a code multiplexer.

Claims (1)

(57) [Claims] 1. A pulse train generating means for frequency demodulating a received spread spectrum signal to generate a pulse train signal responsive to a code transition timing of the spread spectrum signal, and a transmission used in a spread modulation process of the spread spectrum signal. A code synchronizing means having a plurality of PN generators corresponding to the side PN codes and detecting synchronization of the PN codes between transmission and reception; and a system for outputting PN selection data in response to a synchronization detection signal from the code synchronizing means A synchronization monitor, a code multiplexer for selectively combining a PN code from the PN generator in accordance with the PN selection data, and outputting a combined PN code; and a spread spectrum signal based on the combined PN code. And a demodulating means for demodulating the code.