JPH07154296A - Spread spectrum communication system and spread spectrum receiver - Google Patents

Abstract

PURPOSE:To synchronize a spread code at a high speed. CONSTITUTION:A SAW convolver 32 detects an information signal and an initial value of a spread code generated in a spread code generator 16 is set based on the information signal. Since the spread code and the information signal are synchronized in the transmission of the signal, the inverse spread processing in a multiplier 10 is implemented properly by using the spread code synchronously with the information signal obtained by the SAW convolver 32. Furthermore, the succeeding tracking of the synchronization is implemented by using a delay lock loop similarly to a conventional system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum communication system for performing communication using a signal spread spectrum by a predetermined code and a spread spectrum receiver used in this system.

[0002]

2. Description of the Related Art Conventionally, various wireless communication systems have been proposed, and a spread spectrum communication system is one of them. In this spread spectrum communication system (particularly, direct spread system), the transmission side multiplies the primary modulation signal modulated by the information signal by a spread code to obtain a spread spectrum signal. Then, the spectrum-spread signal is wirelessly transmitted. On the other hand, on the receiving side, the received signal is despread by multiplying it by a spreading code to return to a primary modulated signal, and this is demodulated to obtain an information signal. in this way,
Since the spectrum-spread signal is wirelessly communicated, it is possible to perform communication by eliminating interference with radio communication due to radio waves of a predetermined frequency.

Here, in the spread spectrum communication system, the received signal must be despread. Then, for despreading, the spreading code generated on the receiving side must be multiplied in synchronization with the spreading code (reception spreading code) in the received signal.

As one of such demodulating means, there is a delay lock loop (hereinafter referred to as DLL). This DLL is, as shown in FIG.
Despreading is performed by multiplying the received signal by a spreading code. Then, the spread code (PN (pseudo noise) code in this example) multiplied by the received signal in the multiplier 10 must be synchronized with the spread code superimposed on the received signal. Therefore, in this device, the two multipliers 12 and 14 multiply the received signals by the PN codes at different timings. In this example, the PN code generator 16
Two PN codes which are different by 1 bit are supplied to the multipliers 12 and 14.

Envelope detectors 18 and 20 detect the envelopes of the obtained signals, and obtain correlation outputs 1 and 2. The correlation outputs 1 and 2 are at a high level when they are synchronized. Therefore, as shown in FIG.
As shown in (B), a triangular wave which becomes high level when synchronized and which becomes 0 when shifted by 1 bit or more is output from the envelope detectors 18 and 20. And
The two triangular waves are shifted by one bit and are input to the comparator 22. When the difference between the two triangular waves is taken in the comparator 2, a correlation signal as shown in FIG. 4 (C) is obtained.

The output of the comparator 22 is the low-pass filter 2
4, the phase of the output signal is input to the voltage controlled crystal oscillator (VCXO) 26 whose phase is controlled by the input voltage.
Therefore, the phase of the output signal of the voltage controlled crystal oscillator 26 is controlled according to the output voltage of the comparator 22. Since the output signal of the voltage controlled crystal oscillator 26 is the output control clock of the PN code generator 16, the comparator 22
Output from the PN code generator 16 according to the output of
The code timing is changed. Therefore, by this operation, the output from the PN code generator 16 is controlled so that the output of the comparator 22 reaches the point a of FIG. 4 (C).

Here, the point a is located in the middle of the synchronization points of the outputs of the two 1-bit shifted PN codes which are the outputs of the PN code generator 16. The time corresponding to 1 bit of the PN code is 1T (chip), and the signal in which the phase of the PN code generator 16 is advanced is a 1 / 2T delay unit 2
By delaying by 1 / 2T at 8, a PN code synchronized with the received signal can be obtained. Therefore, by supplying this PN code to the multiplier 10, despreading can be performed in this multiplier 10.

In this way, the DLL can despread the signal spectrum-spread with the predetermined PN code,
Can demodulate signals.

However, such a DLL can effectively perform follow-up control with respect to a shift within 1 bit, but cannot follow when there is a large loss of synchronization. Therefore, another device is required for the initial synchronization acquisition. As such a device, a sliding correlator that detects a correlation output while changing the phase of the PN code to be multiplied and stops the phase change when a predetermined correlation output is output is used.

On the other hand, as an element for demodulating an information signal from a signal that has been spectrum-spread by a spread code, S
SAW devices such as AW convolvers and SAW matched filters are known. For example, the SAW Convolver
It inputs two signals and acts as a correlator for these signals. Therefore, this SAW convolver can be used to demodulate the spread spectrum signal. For example, on the transmitting side, FSK modulation for changing the frequency of the carrier wave to f1 and f2 by the information signal is performed, and this is directly spread-modulated with the PN code and transmitted. On the receiving side, the received signal is input to a SAW convolver to which a signal subjected to two-phase shift keying (BPSK) having a center frequency f1 is added as a reference signal. As a result, the SAW convolver outputs the correlation signal only during the period of the frequency f1,
This allows demodulation of the signal. Therefore, this SAW
Suitable demodulation can be performed using a convolver.

[0011]

However, the conventional DLL is used.
In the system using, there is a problem that a large number of correlators and the like are required and the apparatus becomes complicated.
In addition, the system using the SAW convolver can simplify the configuration, but there is a problem that the information transmission speed cannot be sufficiently increased due to the limitation due to the processing time of the SAW convolver. That is, an 8-bit spreading code is used and the spreading bandwidth is 66 MHz (the PN code clock is 3
3 MHz), the processing speed is 255 chips / 33 MHz = 8 μsec.

One piece of information must be within this 8 μsec, and the information speed is limited to 1/8 μsec = 125 kHz or less.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a spread spectrum communication system which can be adapted to a high information rate and can perform high-speed synchronization acquisition with a simple structure. To aim.

[0014]

SUMMARY OF THE INVENTION The present invention is a spread spectrum communication system that uses a signal that has been spread spectrum by a predetermined spreading code, and a primary modulation means for primary modulating a carrier wave by an information signal on the transmitting side. And a spreading means for spreading the spectrum by multiplying the primary-modulated signal by a spreading code, and a synchronizing means for synchronizing the spreading code supplied to the spread spectrum means with the information signal. A spread code generator for generating is generated, the received signal is multiplied by two spread code of different phases, the phase of the spread code generated by the spread code generator is adjusted from the state of the two obtained correlation outputs, and the received signal is received. A delay lock loop that outputs a spreading code that is synchronized with the received signal in the signal, and a spreading code that is output from this delay lock loop Despreading means for multiplying the signal and despreading, SAW device for demodulating the information signal from the correlation between the received signal and the reference signal, and the spreading code of the spreading code according to the change state of the signal obtained by this SAW device. Initializing means for estimating the repetition period and initializing the spreading code generator in the delay lock loop according to the estimation,
It is characterized by having.

Further, the present invention is a spread spectrum receiving apparatus for receiving a signal spread spectrum by a spread code synchronized with an information signal, including a spread code generator for generating a spread code, wherein the received signal has two signals. Multiplying spreading codes having different phases, and adjusting the phase of the spreading code generated from the spreading code generator based on the obtained two correlation output states,
A delay lock loop that outputs a spreading code that is synchronized with the received signal in the received signal, a despreading means that performs despreading by multiplying the spread code output from this delay lock loop with the received signal, and the received signal and the reference signal The SAW device that demodulates the information signal from the correlation with and the spread code repetition period is estimated according to the change state of the signal obtained by this SAW device, and the spread code generator in the delay lock loop is accordingly estimated. And initial setting means for performing initial setting.

[0016]

According to the present invention, the repetition period of the spread code is estimated by at least a part of the information signal obtained by the SAW device such as the SAW convolver or the SAW matched filter. Then, the initial value of the spreading code generated in the DLL is set according to this estimation result. In this way, since the SAW device performs initial acquisition of the spread code in the received signal, high-speed initial acquisition can be performed. And this S
Since the spreading code of the DLL is initialized according to the detection result of the AW device, it is possible to appropriately control the generation of the spreading code in the DLL. Therefore, reliable despreading can be performed.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 1 shows the configuration of the transmission side of the system of this embodiment. In this way, the carrier wave output from the carrier wave oscillator 50 is input to the primary modulation circuit 52. An information signal is also input to the primary modulation circuit 52, and a primary modulation signal in which a carrier wave is modulated by the information signal is obtained.

On the other hand, the information signal is also supplied to the initial value setting circuit 54. Then, the initial value setting circuit 54 sets the initial value of the spreading code generated in the spreading code generating circuit 56. Therefore, in the spread code generating circuit 56, it is generated in synchronization with the information signal. The oscillator 58 supplies a clock for generating a spread code in the spread code generation circuit 56.

Then, the spread code from the spread code generator 56 is supplied to the multiplier 10, where the primary modulation signal and the spread code are multiplied, the spectrum is spread, and this is transmitted from the antenna. In this way, the spreading code is set to an initial value according to the information signal. Therefore, this spreading code is synchronized with the carrier wave.

FIG. 2 is a block diagram showing the receiving side system of this embodiment. The received signal is input to the delay circuit 30, delayed by a predetermined amount, and then input to the despreading multiplier 10. Here, multiplication with a synchronized spreading code is performed, and a despread signal (primary modulated signal) is obtained. Then, by demodulating this, an information signal can be obtained. The delay circuit 30 is for matching with the time required for initial setting by the reception spread code obtained from the SAW convolver 32 described later.

Then, the multipliers 12 and 14, the spreading code generator 16, the envelope detectors 18 and 20, the comparator 22, the low pass filter 24, the voltage controlled crystal oscillator 26 and (1 /
2) Delay lock loop DL including T delay circuit 28
Similar to the above-mentioned conventional example, L follows the deviation of the spreading code in the received signal and the spreading code from the spreading code generator 16 within 1 bit, and secures the synchronization between the two.

On the other hand, in this embodiment, the received signal is SAW.
It is input to the convolver 32. This SAW Convolver 3
A signal obtained by modulating a signal of the same frequency as one of the carrier waves output from the oscillator 34 with the spread code from the spread code generator 16 is supplied to 2. Therefore, the SAW convolver 32 takes out a plurality of pulses corresponding to the information signal. The output of this SAW convolver 32 is
The information signal is reproduced by being input to the envelope detection circuit 40 and detecting the envelope here.

Then, the reproduced information signal is supplied to the initial value setting circuit 44 through the switch 42. The initial value setting circuit 44, depending on the information signal provided,
A predetermined initial value is set in the spread code generation circuit 16. Therefore, the spreading code generated from the spreading code generation circuit 16 is
The generation timing is determined by the detected information signal.

Here, the information speed is the SAW convolver 32.
If the processing time is shorter than the processing time of, the information signal cannot be reliably extracted by the SAW convolver 32.
However, in this embodiment, what is required is the timing of the spread code and the switching timing of the timing of the information signal. Then, even when the information signal is faster than the processing time of the SAW convolver, it is possible to detect the rise at the time of data switching of the information signal.
Therefore, by controlling the initial value setting circuit 44 by the rise of the detected information signal to determine the output spreading code of the spreading code generator 16, it is possible to synchronize with the spreading code in the received signal. .

In this embodiment, a lock detector 46 is further provided. The lock detector 46 detects the level at the output of the multiplier 10, and when sufficient carrier waves are detected, it is detected that the multiplier 10 is performing suitable despreading. Therefore, this lock detector 46
Controls the switch 42 to stop the input of the data from the envelope detection circuit 40 to the initial value setting circuit 44. As a result, the control of the spread code generator 16 using the SAW convolver 32 is stopped, and the spread code supplied to the multiplier 10 is controlled by the DLL. Therefore, after the initial synchronization acquisition is performed, the tracking control can be performed by the DLL, and the spreading code supplied to the multiplier 10 can be appropriately controlled.

[0026]

As described above, according to the spread spectrum communication system and spread spectrum receiving apparatus of the present invention, the SAW device detects the information signal synchronized with the spread code. Since the phase of the spreading code used for despreading is controlled according to this information signal, high-speed synchronization can be achieved. Also, the structure can be simplified.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a configuration of a transmission side according to an embodiment.

FIG. 2 is a block diagram showing a configuration of a receiving side of the embodiment.

FIG. 3 is a block diagram showing a configuration of a conventional DLL.

FIG. 4 is a waveform diagram showing the waveform of each part in the DLL.

[Explanation of symbols]

 10, 12, 14 Multiplier 16 Spreading code generator 32 SAW convolver 44 Initial value setting circuit 46 Lock detector

Claims (2)

[Claims] 1. A spread spectrum communication system using a signal spread spectrum by a predetermined spread code, wherein at a transmitting side, primary modulation means for primary modulating a carrier wave by an information signal, and a primary modulated signal. Includes a spread spectrum unit that multiplies the spread code and spreads the spectrum, and a synchronization unit that synchronizes the spread code supplied to the spread spectrum unit with the information signal. , 2 obtained by multiplying the received signal by two spreading codes with different phases
A delay lock loop that adjusts the phase of the spreading code generated from the spreading code generator based on the state of one correlation output, and outputs the spreading code that is synchronized with the received signal in the received signal, and the spreading lock output from this delay locked loop. Despreading means for multiplying the code and the received signal to perform despreading, and S for demodulating the information signal from the correlation between the received signal and the reference signal.
An AW device, and an initial setting means for estimating the repetition period of the spread code according to the change state of the signal obtained by the SAW device, and for performing the initial setting of the spread code generator in the delay lock loop in accordance therewith, And a spread spectrum communication system. 2. A spread spectrum receiving apparatus for receiving a signal spread spectrum by a spread code synchronized with an information signal, comprising: a spread code generator for generating a spread code, wherein the received signal has two mutually different phases. 2 obtained by spreading code multiplication
A delay lock loop that adjusts the phase of the spreading code generated from the spreading code generator based on the state of one correlation output, and outputs the spreading code that is synchronized with the received signal in the received signal, and the spreading lock output from this delay locked loop. Despreading means for multiplying the code and the received signal to perform despreading, and S for demodulating the information signal from the correlation between the received signal and the reference signal.
An AW device, and an initial setting means for estimating the repetition period of the spread code according to the change state of the signal obtained by the SAW device, and for performing the initial setting of the spread code generator in the delay lock loop in accordance therewith, A spread spectrum receiver comprising: