JPH07154294A - Spread spectrum communication system and spread spectrum receiver - Google Patents

Abstract

PURPOSE:To implement spread spectrum communication by means of a simple equipment. CONSTITUTION:At first a sender side implements spread spectrum processing by using a spread code synchronously with a carrier. The signal subject to spread spectrum processing is received by a receiver side and inputted to a comparator 72, where the waveform is shaped and a carrier modulated by the spread code is extracted. The signal and its inverting signal are given to 1st and 2nd counters 76a, b, in which the period is counted and a long wavelength in the signal is detected. The long wavelength part depends on the rising or trailing of the spread code and the leading and trailing timing of the spread code is detected by 1st and 2nd coincidence discrimination circuits 78a, b. Then the state of the 1st and 2nd flip-flop circuits 80a, b is changed by the output of the 1st and 2nd coincidence discrimination circuits 78a, b and the coincidence of the state is discriminated by a 3rd coincidence discrimination circuit 82, then the spread code is detected.

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 radio communication using a signal spread spectrum by a predetermined code and a spread spectrum receiving apparatus suitable for this system.

[0002]

2. Description of the Related Art Conventionally, various wireless communication systems have been proposed, among which there is a spread spectrum communication system. In this spread spectrum communication system (direct spread system), a primary modulation signal modulated with an information signal is multiplied 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 station side, the received signal is despread by multiplying it by a spreading code to return it to a primary modulated signal, and this is demodulated to obtain an information signal. Since the spectrum-spread signal is wirelessly communicated in this manner, it is possible to perform communication while eliminating interference with radio communication due to an ordinary radio wave of a predetermined frequency.

Here, in the spread spectrum communication system, the received signal must be despread. For this despreading, the spread code must be multiplied by the received signal in synchronization.

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 differing by one chip (one bit of the PN code) generated at 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 22, a correlation signal as shown in FIG. 7C is obtained.

The output of the comparator 22 is the low-pass filter 2
4, the phase of the output signal is input to a voltage controlled oscillator (VCXO) 26 whose phase is controlled by the input voltage. Therefore, according to the output voltage of the comparator 22, the voltage controlled oscillator 2
The phase of the output signal of 6 is controlled. Since the output signal of the voltage controlled oscillator 26 serves as the output control clock of the PN code generator 16, the timing of the PN code output from the PN code generator 16 is changed according to the output of the comparator 22. It Therefore, by this operation, the comparator 2
The output from the PN code generator 16 is controlled so that the output of 2 reaches the point a in FIG. 7C.

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.

[0009]

However, such D
LL can effectively perform follow-up control for shifts within 1 bit, but if out-of-sync is large,
I can't follow. 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.

Therefore, the conventional device has a problem that a large number of correlators are required and the device becomes complicated.

Particularly when constructing a communication network in a relatively narrow range such as in one building, it is very important to construct each receiver at a low cost. And
In such a case, there is often no need for code division multiple access using different spreading codes, and a system different from the conventional system using spread spectrum can be adopted.

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 capable of synchronizing spread codes with a simple device and a spread spectrum receiving device used in this system. To aim.

[0013]

SUMMARY OF THE INVENTION The present invention is a spread spectrum communication system for performing radio communication using a signal spread in spectrum by a predetermined spread code, in which a spread code synchronized with a carrier wave is transmitted on the transmitting side. Spread spectrum code creating means for creating, spread spectrum means for spectrum spreading the transmission signal by the obtained spreading code, and transmitting means for transmitting the spread spectrum transmission signal, the signal spread spectrum on the receiving side Receiving means, a waveform shaping means for shaping the waveform of the received signal, a counter for counting the period of the obtained waveform shaped signal, and a reproduction for reproducing the spread code based on the count value of this counter. Means and despreading means for despreading using the reproduced spreading code.

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, wherein a receiving means for receiving the spread spectrum signal and a waveform of the received signal. A waveform shaping means for shaping, a counter for counting the period of the obtained waveform shaped signal, a reproducing means for reproducing a spread code based on the count value of this counter, and a utilizing the reproduced spread code. And a despreading means for performing despreading.

[0015]

According to the present invention, on the transmitting side, a spread code synchronized with a carrier is generated and thereby spread spectrum is performed. Then, on the receiving side, the carrier wave is reproduced, the waveform is shaped, and the cycle of the reproduced carrier wave is counted. For example, the periods of "0" and "1" of the waveform-shaped signal are counted. Since the spreading code is synchronized with the carrier, the spreading code "0" → "1",
When changing from “1” to “0”, the period of “1” or “0” of the waveform-shaped signal becomes longer. Therefore, the spread code can be reproduced by detecting this and changing the state of the flip-flop. Then, despreading is performed using the reproduced spreading code, whereby the configuration can be simplified and spread spectrum communication can be performed.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

[Overall System Configuration] First, the overall system configuration will be described with reference to FIG. In the present embodiment, in order to detect the spreading code on the receiving side, the carrier code which is primarily modulated by the information signal on the transmitting side is synchronized with the spreading code for spectrum spreading.

That is, on the transmitting side, 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 carrier wave from the carrier wave oscillator 50 is
In the frequency divider 54, after being divided by N, the spread code (PN
Code) generator 56. This spreading code generator 5
6 is a predetermined spreading code “0” for the divided carrier,
The data of "1" is superimposed to generate a spread code. Then, the spread code is supplied to the multiplier 58, the primary modulation signal and the spread code are multiplied, the spectrum is spread, and this is transmitted from the antenna 60. in this way,
The spread code is generated based on a signal obtained by dividing the frequency of a carrier wave. Therefore, this spreading code is synchronized with the carrier wave.

After receiving the radio wave at the antenna 62 on the receiving side, at the spread code reproducing section 64,
The spread code is reproduced, and the multiplier 66 multiplies the received signal by the spread signal to perform despreading. And
An information signal is obtained by demodulating the despread signal in the primary demodulation circuit 68, and communication using spread spectrum is achieved.

[Structure of Spreading Code Detector] Next, the structure of the spreading code detector of this embodiment will be described with reference to FIG. The spread code detector includes a comparator 72, an inverter 74, a first counter 76a, a second counter 76b, a first match determination circuit 78a, a second match determination circuit 78b, a first flip-flop 80a, a second flip-flop 80b, and a second flip-flop 80b. It is composed of three coincidence determination circuits 82. Further, the waveform of each part is shown in FIGS. 3 and 4. The frequency of the normal carrier is much higher than the frequency of the PN code (for example, the frequency of the carrier is 250 MHz, the frequency of the spreading code is 14 MH).
z) is not so different in this figure. The carrier wave CS is a sine wave signal having a predetermined frequency. Then, the signal SPS is obtained by spectrum spreading this with the signal PN. That signal SPS
Is transmitted from the antenna and is received by the receiving side.
Therefore, the received signal is the signal SPS.

The received signal SPS is input to the comparator 72. The comparator 72 obtains the rectangular wave signal DS by determining whether the signal SPS is positive or negative. The rectangular wave signal DS is supplied to the reset end of the first counter 76a as it is, and is also supplied to the reset end of the second counter 76b as an inverted DS signal inverted by the inverter 74. A clock CL having a predetermined frequency (frequency higher than the signal DS) is applied to the clock input terminals of the first and second counters 76a and 76b.
K has been entered. Therefore, the first and second counters 76a and 76b count the period from the rising of the signal DS and the inverted DS to the next rising. And
The first and second counters 76a and 76b count up in a half wavelength period of the carrier wave and output "1" from the start of counting to the count up. Therefore, the period of "1" in the output signals of the first and second counters 76a and 76b is always the period (t) corresponding to half the wavelength of the carrier wave. Therefore, when the period of "1" of the signal DS or the inverted DS is long, a signal which becomes "0" is output earlier.

The output of the first counter 76a is input to the first coincidence determining circuit 78a, where the coincidence with the signal DS is determined. Then, the first match determination circuit 78a outputs "1" when both input signals match, so that the signal D
When the period of "1" of S is long, a signal which is "0" is output only in the latter half of the period (period t from the rise of the signal PN). The output signal of the first match determination circuit 78a is input to the first flip-flop (first FF) 80a. The first flip-flop 80a sequentially changes its state at the falling edge of the input signal.

On the other hand, the output of the second counter 76b is the second
It is input to the coincidence determination circuit 78b, and the coincidence determination with the inverted DS is performed here. Then, the second match determination circuit 78b
Similarly to the first determination circuit 78a, since "1" is output when both input signals match, the latter half of the period when the period of "1" of the signal DS is long (from the fall of the signal PN to t A signal which becomes “0” only during the period (1).
The output signal of the second match determination circuit 78b is the second
Since it is input to the flip-flop (second FF) 80b, this second flip-flop 80a also sequentially changes its state at the falling edge of the input signal.

Then, the outputs of the first and second flip-flops 80a and 80b thus obtained are input to the third coincidence judging circuit 82, and the coincidence between them is judged here. Here, as described above, the timings of changes in the outputs of the first and second flip-flops 80a and 80b are
The signal PN is the rising edge and the falling edge, respectively, and the PN signal is detected by determining the coincidence of these.

[Overall Configuration on the Receiving Side] FIG. 5 is a block diagram showing the overall system of this embodiment. The received signal is input to the despreading multiplier 10 as in the conventional example, and the synchronization is performed here. Multiplication with the stripped spreading code is performed to obtain a despread signal (primary modulated signal). Then, by demodulating this, an information signal can be obtained.

On the other hand, in this embodiment, the received signal is input to the spread code detector 32 having the above-mentioned configuration. Therefore, the spread code detector 32 detects the spread code from the received signal and outputs it.

The signal regarding the spread code detected by the spread code detector 32 is input to the phase detector 34. The phase detector 34 compares the phases of the spreading code supplied from the spreading code detector 32 and the spreading code supplied from the spreading code generator 36. The spreading code used for communication is known in advance, and a signal of the phase shift amount between the two spreading codes is obtained by comparing the two input spreading codes. For example, a plurality of spread codes shifted by a predetermined bit (for example, 1 bit) from the spread code supplied from the code generator 36 are generated, stored in a register, and detected by the spread code detector 32. By comparing the spread code and the spread code stored in each register and detecting the coincidence, the phase shift between the detected spread code and the spread code generated by the spread code generator 36 can be known. Therefore, the phase comparator 34 may output a signal regarding the obtained phase shift.

The signal about the phase shift amount is supplied to the spread code generator 36 as its output control clock through the low pass filter 38 and the voltage controlled crystal oscillator (VCXO) 40. In this example, the spread code generator 36 is an n-bit shift register, and the leftmost register is a signal output point. For this reason, the stored spread code is output in accordance with the input clock by circulatingly shifting the stored data according to the clock supplied to the shift register.

Then, the signal about the phase shift of the phase detector 34 is supplied to the spread code generator 36 through the low pass filter 38 and the voltage control oscillator 40, so that the output of the spread code is controlled. These circuits form a phase locked loop according to the phase of the spreading code. Therefore, the output spread code from the spread code generator 36 is synchronized with the spread code detected by the spread code detector 32 and is synchronized with the spread code of the received signal, and the multiplier 10 is used with this spread code. At, despreading takes place.

As described above, according to this embodiment, the spread code detector 32 detects the spread code. Therefore, it is possible to perform the initial acquisition of the spread code in the received signal by the detected spread code, and it is possible to shorten the time required to establish the synchronization. Furthermore, the structure of the entire device can be made very simple.

As described above, according to this embodiment, the spread code detector 32 detects the spread code. Therefore, it is possible to perform the initial acquisition of the spread code in the received signal by the detected spread code, and it is possible to shorten the time required to establish the synchronization. Furthermore, the structure of the entire device can be made very simple. Since the wireless communication is performed by spread spectrum, it is resistant to noise and can suppress the influence on other wireless communication to the minimum. In particular, when the printer is shared by a plurality of terminals, the present system enables suitable data communication.

[0033]

As described above, according to the present invention,
On the transmitting side, generate a spreading code synchronized with the carrier wave,
This causes spread spectrum. Then, on the receiving side, this carrier wave is regenerated, the waveform is shaped,
The spread code is reproduced by counting the wavelength of the reproduced carrier wave and detecting the long wavelength part. Then, despreading is performed using the reproduced spreading code, whereby the configuration can be simplified and spread spectrum communication can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a system.

FIG. 2 is a block diagram showing a configuration of a spread code detection unit.

FIG. 3 is a waveform diagram showing a waveform of each part at the time of spreading code detection.

FIG. 4 is a waveform diagram showing a waveform of each part at the time of spreading code detection.

FIG. 5 is a block diagram showing the overall configuration of the embodiment.

FIG. 6 is a block diagram showing a configuration of a conventional DLL.

FIG. 7 is a waveform diagram showing the waveform of each part in the DLL.

[Explanation of symbols]

 10, 58, 66 multiplier 32 spreading code detector 72 comparator 76a, b first and second counters 78a first match determination circuit 78b second match determination circuit 80a first flip-flop 80b second flip-flop 82a second 3 Match determination circuit

Claims (2)

[Claims] 1. A spread spectrum communication system for performing wireless communication using a signal spread spectrum by a predetermined spread code, wherein spread code creating means creates a spread code synchronized with a carrier wave on a transmitting side, A spread spectrum unit that spreads the transmission signal by the obtained spread code, and a transmission unit that transmits the spread spectrum transmission signal. At the receiving side, a reception unit that receives the spread spectrum signal and a reception unit. A waveform shaping means for shaping the signal, a counter for counting the period of the obtained waveform shaped signal, a reproducing means for reproducing the spreading code based on the count value of the counter, and a reproducing means for reproducing the spread code. A spread spectrum communication system, comprising: 2. A spread spectrum receiving apparatus for receiving a signal spread spectrum by a spread code synchronized with an information signal, comprising: receiving means for receiving the spread spectrum signal; and waveform shaping means for shaping the waveform of the received signal. A counter for counting the period of the obtained waveform-shaped signal, a reproducing means for reproducing the spread code based on the count value of the counter, and a reverse spreader for performing the reverse spread using the reproduced spread code. A spread spectrum receiving apparatus comprising: a spreading unit.