JPH0661971A - Transmitter/receiver for spectrum diffusion communication - Google Patents

Abstract

PURPOSE:To secure the synchronization of the code patterns at a high speed and in a simple method by using a specific diffusion code, assigning different codes to the signals which are multiplexed, and using a specific resonator at the receiver side. CONSTITUTION:The diffusion code which defines a measure (s) of the code length L as a cycle and is used to a modulation signal repeats the fixed patterns every s1 bits. Thus the peaks exist in the power spectrum density of the modulation signal at the fmuL/s1Hz interval (f: velocity of data signal), and the frequency information can be extracted out of the modulation signal when the resonance frequency of a resonator 28 is set at fmuL/s1Hz. Meanwhile the synchronization of frequency is secured by a PLL consisting of a mixer 30, a local oscillator 29 and an LPF 36. The received signal which is converted into an x-bit parallel digital signal by an A/D converter 31 is inputted to one of both ports of a multiplication accumulator 33. The diffusion code which is multiplied by the digital received signal is inputted to the other input port of the accumulator 33 through a ROM 32 and outputted as a demodulation signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transceiver for spread spectrum communication.

[0002]

2. Description of the Related Art FIG. 2 is a conceptual diagram showing a spread spectrum multiplex transmission system using an optical transmission line as a conventional example of a spread spectrum communication system. In the figure, 1 is a data input terminal, 2 is a spread code generator (ROM) such as a PN series, 3 is an exclusive OR circuit, and 4 is E / O.
(Electric / optical) converter, 5 is an optical coupler, 6 is an optical transmission line, 7
Is a connector, 8 is an O / E (optical / electrical) converter, and 9 is A / E.
D converter, 10 is a correlator (for example, an exclusive OR circuit and an accumulator), 11 is a spreading code generator (ROM) that generates a spreading code used on the transmitting side, 12 is a demodulation signal output terminal, and 13 is a synchronization. The decision circuit, 14 represents a local oscillator.

Next, the circuit operation of FIG. 2 will be described. First, 1 bit of the data signal input from the input terminal 1,
The spread code unique to the channel generated by the spread code generator 2 is processed by the exclusive OR circuit 3 for each bit of the spread code.
A modulation signal by spread spectrum is created by taking the exclusive OR, and the light intensity is modulated by the E / O converter 4.

The light intensity modulation signal thus output from the transmitter is sent to the optical transmission line 6 via the optical coupler 5. A plurality of light intensity modulated signals exist on the optical transmission line 6 in the connector 7
Via the optical coupler 5 of the partner station via the O / E converter 8
After being converted into an electric signal, the A / D converter 9 converts the electric signal into a digital signal. In the correlator 10, the cross-correlation with the spread code generated in the spread code generator (ROM) 11 is obtained, and the correlation value is the demodulated signal as the demodulated signal output terminal 1
It is output from 2. Further, the synchronization determination circuit 13 determines whether or not the code pattern is synchronized, based on the demodulation signal level, and when synchronization is achieved, the local oscillator 1
Lock the frequency of 4.

[0005]

In the communication system described above with reference to FIG. 2, a spread spectrum communication system is used to multiplex and demodulate bidirectional signals. In spread spectrum communication, a demodulated signal is obtained by cross-correlating a channel-specific spreading code with a transmitted signal. When a plurality of channels are multiplexed as in the example of FIG. 2, it is desirable that the spreading codes assigned to the channels have no correlation with each other in order to separate and demodulate the channels from the multiplexed signal. But,
There is a non-zero cross correlation between the actual spreading codes.

Furthermore, since there are reflection points such as connectors and couplers in the optical transmission line on the transmission line, a reflected return signal from the reflection point exists as inter-channel interference due to a non-zero cross-correlation value. Under such circumstances, in order to perform normal demodulation operation, in order to obtain the cross-correlation, the spreading code used for the modulated signal to be demodulated from the multiplex signal and the spreading code generated in the receiver are used. It must be synchronized with the code.

The term "synchronization" as used herein means code pattern synchronization and frequency synchronization. In the conventional technique, it is impossible to synchronize the frequency of the spread spectrum modulation signal multiplexed. Therefore, the code pattern is first synchronized, and the frequency of the local oscillator is adjusted by using the synchronized correlation output. Was synchronized with.

However, in the method of synchronizing the code patterns, the frequency of the local oscillator is not locked until the code patterns are synchronized, so that the relative phase between the codes is gradually shifted to synchronize the code patterns. A search method (sliding correlator) is used, and there is a problem in this method that enormous time is required for synchronization acquisition.

Also, in the method of performing convolution using a matched filter instead of using this sliding correlator, the synchronization of the code pattern is determined from the result of the convolution integration corresponding to the cross-correlation value, and the convolution integration with the code pattern synchronization is performed. To lock the local oscillator using the waveform,
When the code pattern synchronization determination is difficult and time-consuming, as in the case where the above-mentioned inter-channel interference interferes with channel separation and demodulation, the frequency of the local oscillator shifts during code pattern synchronization, There was a drawback that it was difficult to capture synchronization.

The above points cause the same problem in the synchronization acquisition process not only at the initial synchronization acquisition but also when the synchronization of either the frequency or the code pattern is lost. in this way,
In the conventional technology, since code pattern synchronization and frequency synchronization cannot be independently performed at the time of synchronization acquisition, it takes a huge amount of time for synchronization acquisition, and it is difficult to construct a practical method when there is inter-channel interference. Met.

The present invention has been made to solve the above-mentioned problems of the prior art and realize a practical data transmission system. In spread spectrum communication, a simple device is used for frequency synchronization and code phase synchronization. It is an object of the present invention to obtain a system that captures and holds at high speed and reliably.

[0012]

According to the present invention, the above-mentioned problems are solved by the means described in the claims.

That is, according to the invention of claim 1, among the codes of length L bits, a code constituted by repeating a fixed code pattern having s bits (s is a divisor of L) as one cycle is
It is used as a spread code in spread spectrum communication, and the exclusive OR of a data signal and the spread code whose 1-bit duration is equal to the L-bit duration T [sec] of the spread code is 1 of the spread code. A modulated signal is formed by taking each bit, and a spread spectrum communication transmitter equipped with a means for transmitting the modulated signal and the transmitted modulated signal are resonated at L / (T × s) [Hz] on the one hand. A resonator having a frequency is used to extract the frequency and use this as the operating clock of the receiver, or the output of the resonator is used to synchronize the local oscillator and use this as the operating clock of the receiver, while Then, using a digital circuit whose operating clock is the frequency thus obtained, the correlation between the modulated signal and the spreading code equal to that used on the transmitting side is correlated with the L bits of the modulated signal. Taken at time T [sec], and the spread spectrum communication receiver having a demodulating means for the correlation output and the demodulated signal, it is spread spectrum communication transceiver, characterized in consisting of.

According to a second aspect of the present invention, by sharing a transmission line for a plurality of sets of the spread spectrum communication transmission / reception apparatus according to the first aspect, bidirectional communication or multiple communication is multiplexed on the transmission line. Spread spectrum communication system.

[0015]

In the present invention, the spreading code having the length of L bits uses a code having a divisor s of L as one cycle, and when the signals are multiplexed, a code having a different s is assigned, and the receiving side has the L code. /
The frequency of the local oscillator is synchronized by using a resonator having a resonance frequency at (T × s) [Hz] (T is the duration of L bits), and the code pattern is synchronized independently by using a digital circuit. To obtain a demodulated signal.

That is, in the present invention, as described above, by using the code having the divisor s of the code length L as one period, the power spectrum density of the modulated signal is L / (T
Xs) Peaks occur at [Hz] intervals. L / (T
By using a resonator having a resonance frequency of xs) [Hz], frequency synchronization acquisition can be performed independently of code pattern synchronization. Even if a plurality of channels are multiplexed, if codes with different repetition periods s are used,
Since the peaked spectrums are different, these can be discriminated by the individual resonators on the receiving side, and frequency synchronization independent of code pattern synchronization is possible.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention.
Shown in the figure are a modulation circuit, a demodulation circuit by direct spread spectrum spread, an optical coupler for coupling an optical signal transmitted from the modulation circuit to the optical transmission line and an optical signal input from the transmission line to the demodulation circuit, and an optical coupler. It is a block diagram of a transmission line.

FIG. 3 is a block diagram of a branch node for demultiplexing the other bidirectional optical signals.

In FIG. 1, 20 is a data input terminal, 2
1 is a ROM that outputs a spread code, 22 is an exclusive OR circuit that directly generates a spread modulation signal from the spread code and a data signal,
Reference numeral 23 is an E / O converter, 24 is an optical coupler for separating and coupling bidirectional light intensity modulation signals, 25 is an optical transmission line, and 26 is a connector.

Reference numeral 27 is an O for converting the light intensity modulation signal received through the optical coupler 24 into an electric analog signal.
/ E converter, 28 is a resonator, 29 is a local oscillator, 30 is a mixer, and 36 is an LPF (low pass filter).

Further, 31 is an A / D converter, 32 is a ROM in which a spread code and a conventional correlation section of spread spectrum are stored, 33 is a spread code output from the ROM 32, and a digital signal is generated by the A / D converter 31. A multiplication accumulator that accumulates a result of multiplication (exclusive OR) with the converted received signal to generate a demodulated signal by conventional spread spectrum, 34 is a demodulated signal output terminal, 35 is a code pattern synchronization from the level of the demodulated signal It represents a code synchronization determination circuit for determining.

The transmission operation in the circuit of FIG. 1 will be described below. The speed of the data signal is f [b / s]. In this embodiment, a code having a code length of L bits, a code having a divisor s1 of L as one cycle, and a code having s2 as one cycle are used as the bidirectional spreading codes. Since the code length is L bits,
The speed of the spread spectrum modulation signal in FIG. 1 is Lf.
[B / s].

The speed f input to the data input terminal 20
The data signal of [b / s] is input to the exclusive OR circuit 22 in synchronization with the repetition of the spread code L bits output from the ROM 21. At the speed Lf [b / s], the exclusive OR with the spread code input from the other input port is calculated, and a spread spectrum modulated signal is produced. The spread spectrum modulated signal output from the exclusive OR circuit 22 is converted into an optical signal by the E / O converter 23 and transmitted to the optical transmission line 25 via the optical coupler 24.

In the optical transmission line 25, from the other end of the transmission line,
The same speed (Lf
It is assumed that the [b / s]) spread spectrum modulation signal is converted into an optical signal and input.

Next, the receiving operation will be described. The speed of the received signal that is transmitted is equal to the speed of the modulation signal on the transmission side, L
f [b / s]. Of the optical intensity-modulated bidirectional optical signals multiplexed in the transmission line 25, the signal transmitted from the transmitter on the other side is separated by the directional coupler 24, and O /
The E converter 27 converts the analog electric signal.

The analog electric signal converted into the electric signal is input to the resonator 28 on the one hand. If the spreading code used for the modulation signal to be demodulated repeats a fixed pattern for each s1 bit, the power spectrum density of the modulation signal to be demodulated has peaks at intervals of f × L / s1 [Hz]. The resonance frequency of the resonator 28 is set to f × L / s1 [H
z], frequency information can be extracted from the modulated signal, and the mixer 30, the local oscillator 29, and the LPF 3 can be extracted.
A PLL configured with 6 allows frequency synchronization. Since frequency synchronization is possible independently of the spread spectrum demodulation operation, all spread spectrum demodulation processes described below operate using synchronized clock frequencies.

On the other hand, the modulated signal converted into the electric analog signal by the O / E converter 27 is the A / D converter 31.
Entered in. The reception signal converted into the x-bit parallel digital signal by the A / D converter 31 is then input to the input port of the multiplication accumulator 33. The spread code to be multiplied (exclusive OR) with the digital received signal is input from the ROM 32 to the other input port of the multiplication accumulator 33, and the multiplication result is accumulated for each bit of the spread code, and the spread code is L bits. The multiplication accumulation result is output for each time as a demodulation signal by spread spectrum.

On the other hand, the demodulated signal level is input to the code synchronization determination circuit 35, the variance of the absolute value of the demodulated signal level is obtained, and the phase of the code pattern having the minimum variance value is stored in the ROM 3.
The search is performed by changing the read address of 2, and the synchronization of the code pattern is held at the time when it is determined to be the minimum value.

FIG. 3 shows the power spectrum density (relative value) when the code length L = 64 bits and the pattern period s1 = L / 16 bits are used. When compared with the power spectrum density when the pattern period s2 of the spreading code of the other channel multiplexed in both directions is L bits, 16f [H
The peak appears in the z] interval, and the power spectrum is 10 dB or more compared to the other multiplexed channel.

Therefore, the connector 2 existing on the optical transmission line
Even if there is a reflected return signal that is 10 dB larger than the received power of the channel to be demodulated from the reflection points such as 6, frequency information can be extracted by the resonator 28 and frequency synchronization can be performed by the PLL. Recognize.

Since frequency synchronization can be performed independently of the spread spectrum demodulation operation, the read address of the ROM 32 that outputs the code is changed as described above, and the one with the minimum absolute value dispersion is selected from each demodulation level. It is possible to surely synchronize the code patterns by a simple operation of selecting.

[0032]

As described above, according to the present invention,
For spread spectrum communication or spread spectrum multiplex communication, a code formed by repeating a fixed pattern having a divisor s of the code length L as one cycle is used as the spread code.
By assigning codes with different s when signals are multiplexed and using a resonator having a resonance frequency at L / (T × s) [Hz] (T is the duration of L bits) at the receiving side, Frequency synchronization can be performed independently of spread spectrum demodulation, and code patterns can be synchronized at high speed with a simple method.

Further, even when a plurality of channels are multiplexed and the received power of other channels is higher than that of the channel to be demodulated, the positions of the peaks existing in the power spectrum density of the modulated signal are different, so that the frequency is changed by the resonator. It becomes possible to synchronize.

[Brief description of drawings]

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

FIG. 2 is a conceptual diagram showing a spread spectrum multiplex transmission system using an optical transmission line.

FIG. 3 is a diagram showing an example of power spectral density.

[Explanation of symbols]

 1,20 Data input terminal 2 Spread code generator 3,22 Exclusive OR circuit 4,23 E / O converter 5,24 Optical coupler 6,25 Optical transmission line 7,26 Connector 8,27 O / E converter 9, 31 A / D converter 10 Correlator 11 Spreading code generator 12, 34 Demodulated signal output terminal 13 Synchronization determination circuit 14, 29 Local oscillator 21, 32 ROM 28 Resonator 30 Mixer 33 Multiply accumulator 35 Code synchronization determination circuit 36 low pass filter

Claims (2)

[Claims] 1. A code having a length of L bits, which is formed by repeating a fixed code pattern having s bits (s is a divisor of L) as one cycle, is used as a spread code in spread spectrum communication. A modulated signal is obtained by taking the exclusive OR of the data signal and the spreading code for each bit of the spreading code, the duration of which is equal to the L-bit duration T [sec] of the spreading code. On the one hand, the transmitter for the spread spectrum communication having the means for constructing and transmitting this, and the modulated signal transmitted is, on the one hand, L / (T × s)
A resonator having a resonance frequency in [Hz] is used to extract the frequency, and this is used as an operating clock of the receiver, or the output of the resonator is used to synchronize a local oscillator, and this is used for the receiver. On the other hand, by using a digital circuit whose operating clock is the frequency thus obtained, the correlation between the modulated signal and the spreading code equal to that used on the transmitting side is maintained by the L-bit continuation of the modulated signal. A spread spectrum communication transceiver comprising: a spread spectrum communication receiver provided with a demodulation means that takes this correlation output as a demodulated signal at time T [sec]. 2. A spectrum characterized in that a plurality of sets of the spread spectrum communication system device according to claim 1 are made to have a common transmission line, and bidirectional communication or a plurality of communications are multiplexed on the transmission line. Spread communication method.