JPH0522250A - Spread spectrum communication equipment - Google Patents

Abstract

PURPOSE:To realize the practical spread spectrum communication equipment in which inter-channel interference is eliminated without increasing a code length. CONSTITUTION:A signal modulated by direct spread spectrum processing is subject to optical intensity modulation at a sender side and the result is sent to a transmission line 57 via a directional coupler 48, and the directional coupler 48 demultiplexes a luminous intensity modulation signal by 2-way spread spectrum multiplexed on a same transmission line by receiving a signal subject to luminous intensity modulation via the directional coupler 48 from the transmission line 57.

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 device.

[0002]

2. Description of the Related Art FIG. 2 is a conceptual diagram showing a multiplex transmission system using spread spectrum as a conventional example of an optical data transmission system. In the figure, 1 is a data signal input terminal, 2 is a spread code generator such as a PN series, 3 is an exclusive OR circuit, 4 is an E / O (electrical / optical) converter, and 5 is a branch such as a star coupler. A node, 6 is an optical transmission line, 7 is a branch node similar to 6, 8 is an O / E (optical / electrical) converter, 9 is a correlator (for example, an exclusive OR circuit), and 10 is used on the transmitting side. A spread code generator for generating a code, and 11 is a demodulation signal output terminal.

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.

A plurality of signals thus modulated from the respective E / O converters are multiplexed by the branch node 5, for example, a star coupler, and transmitted by one optical transmission line 6. On the receiving side, after being O / E converted by the O / E converter 8 via the branching node 7, the correlator 9 takes the cross-correlation with the spreading code generated by the spreading code generator 10 to obtain the correlation value. It becomes a demodulated signal.

In this case, although the communication is unidirectional, the communication in the reverse direction can be realized by preparing similar equipment in the reverse direction.

FIG. 3 is a conceptual diagram showing a multiplex transmission system by the same wavelength bidirectional division multiplex connection as another conventional example of the optical data transmission system.

In the figure, 21 and 29 are digital data signal input terminals, 22 and 30 are E / O converters such as semiconductor lasers, 23 and 31 are O / E converters such as photodiodes, and 24 and 32 are Data signal output terminal,
Reference numerals 25 and 28 are directional couplers, 26 is an optical transmission line, and 27 is a connector.

Next, the operation of the circuit shown in FIG. 3 will be described. Bidirectional digital signals input from the data input terminals 21 and 29 of the respective stations are converted into E / O converters 22 and 3
0, the light intensity is modulated by the directional couplers 25 and 28.
Is transmitted to the optical transmission line 26 via. The optical signal passes through the connector 27 existing on the optical transmission line 26, the directional coupler of the partner station, and the O / E converters 23 and 31
A / E conversion is performed to convert into an electric digital signal, which is output from the output terminals 24 and 32. The optical signals transmitted from the E / O converters 22 and 30 and the optical signals received by the O / E converters 23 and 31 are transmitted to the optical transmission line 26 by the directional couplers 25 and 28 in the respective stations. To the O / E and E / O converters. In this case, unlike the example of FIG. 2, bidirectional communication is performed in which the transmission path is shared vertically.

[0009]

In the multiple connection method by spread spectrum described with reference to FIG. 2, there is inter-channel interference due to the cross-correlation value existing between the spread codes. Due to the increase in the number of channels or the difference in reception level due to the distance difference between the transmission and reception of each communication path between channels, the inter-channel interference due to the cross-correlation value between the codes causes the channel separation. It becomes an obstacle to demodulation.

In the prior art, a cross-correlation value between codes is set by a method of setting a large code length of a PN sequence or the like used for spread codes to increase a processing gain by spread spectrum or a method of synchronizing phases with spread codes. Was kept as small as possible so that the inter-channel interference did not become an obstacle to the channel separation / demodulation.

However, in the method of increasing the processing gain,
In order to prevent the inter-channel interference from interfering with the channel separation / demodulation, the code length required is enormous.

Further, in the method of synchronizing the phases between the codes,
When a small error occurs in the synchronization, the cross-correlation value between the codes increases, and because the bidirectional signals also have to be synchronized, delays occur and the data signal speed decreases significantly. Were present.

As described above, in the conventional technique, it is difficult to construct a practical system because the above-mentioned drawbacks exist when the spread spectrum is used in the multiple connection system.

In the same wavelength bidirectional division multiplexing system using a directional coupler as described with reference to FIG. 3, an optical signal transmitted from the E / O converter to the optical transmission line,
The optical signal received by the O / E converter is multiplexed toward the optical transmission line by the directional coupler in each station,
Although separated toward the O / E and E / O converters, the optical signal reflected by the connector on the optical transmission path and transmitted in the opposite direction passes through the directional coupler, and There is a problem that it causes interference between channels.

The present invention has been made in order to solve the problems of both of the above-mentioned prior arts and to realize a practical data transmission system. For demultiplexing a plurality of channels in the same direction, a code by spread spectrum is used. A directional coupler is used at each station to perform demultiplexing, modulate the spread spectrum signal of each channel with optical intensity, and transmit this through an optical fiber. By doing so, it is possible to asynchronously multiplex the transmission / reception signals modulated or code division multiplexed by spread spectrum, thereby providing a spread spectrum communication device that solves the drawbacks of the prior art. To aim.

[0016]

In order to achieve the above-mentioned object, in the present invention, a signal modulated by direct spread spectrum spread is modulated on the transmitting side, and this light intensity modulated signal or Is transmitted to the transmission line via the directional coupler, and on the receiving side,
By receiving the optical intensity modulation signal from the transmission line through the directional coupler, or the optical signal that multiplexes this, the optical intensity modulation by one or multiple sets of bidirectional spread spectrum that are multiplexed on the same transmission line. The signals were demultiplexed by a directional coupler.

[0017]

In the present invention, the modulated signal by the spread spectrum is subjected to optical intensity modulation, this signal is transmitted to the transmission line via the directional coupler on the transmitting side, and is transmitted from the transmission line to the directional coupler on the receiving side. By receiving as a result, it is possible to separate one or a plurality of sets of bidirectional spread spectrum signals multiplexed on the transmission path.

[0018]

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.
What is shown in the figure is a directivity for separating a modulation circuit, a demodulation circuit and an optical signal transmitted from the modulation circuit to the optical transmission line by the direct spread spectrum spread and an optical signal input to the demodulation circuit from the transmission line. It can be said that it is a block diagram of a coupler and a branch node that performs demultiplexing with other bidirectional optical signals.

In FIG. 1, 41 is a data input terminal, 4
2 is a serial / parallel conversion circuit for converting the input data signal into x-bit parallel, 43 is a D-FF circuit for synchronizing the data signal converted into x-bit parallel by 42 with one cycle of the spread code, 44 Is an exclusive OR circuit for generating a modulation signal from a spread code and a data signal, 45
Is a ROM that stores the spread code.

Reference numeral 46 is a parallel / serial conversion circuit for converting an x-bit parallel modulation signal, 47 is an E / O converter, and 48 is a light intensity modulation signal produced by 47 and a light intensity modulation signal received by a demodulation circuit. A directional coupler for separation, 49 is an O / E converter for converting the light intensity modulation separated into 48 into an analog electric signal, 50 is an A / D conversion circuit,
Reference numeral 51 is an accumulator that calculates the cross-correlation value of the modulated signal converted into the y-bit parallel digital signal by the A / D conversion circuit 50 and the spread code for each code cycle.

Reference numeral 52 stores the spread code as the polarity of accumulation in the accumulator 51, and also stores a clear signal of the accumulated value.
OM, 53 is a D / A conversion circuit, 54 is a demodulation signal output terminal, 55 is a synchronization determination circuit, 56 is a counter for generating a read address of the ROM 4, 57 is an optical transmission line such as an optical fiber, and 58 is other bidirectional. A branch node such as a star coupler that performs demultiplexing with the light intensity modulation signal.

The transmission operation in the circuit of FIG. 1 will be described.
The speed of the modulation signal is fc [bps]. In addition, in this embodiment, an L-bit Gold sequence is used as the code. Therefore, the speed of the data signal is fc / L [bp
s]. From these, the operating speed of the block of the modulation circuit in FIG. 1 is calculated by the serial / parallel conversion circuit 42, the exclusive OR circuit 44, and the ROM 45 at fc / x [H
z], fc / xL [Hz] in the D-FF 43, and fc [Hz] in the parallel / serial conversion circuit 46.

Speed fc input to the data input terminal 41
The data signal of / L [bps] is transmitted by the serial / parallel conversion circuit 42 and the D-FF 43 at a speed of fc / xL.
One input port (x-bit input) of the exclusive OR circuit 44 after being converted into an x-bit parallel signal of [bps]
Entered in. To the other input port of the exclusive OR circuit 44, the spread code is input from the ROM 45 at the speed fc / x [bps] in x-bit parallel, and the speed fc / x [H
z], the exclusive OR is calculated, and the exclusive OR circuit 44
Is output at a speed fc / x [bps].

Since this output is x-bit parallel,
After being converted into a serial signal of speed fc by the parallel / serial conversion circuit 46, the E / O converter 47 outputs it as a light intensity-modulated optical signal. Since this light intensity modulated signal is sent to the optical transmission line 57 via the directional coupler 48, it does not leak to the demodulation circuit together with the received signal transmitted through the same transmission line 57. Transmission line 5
The optical signal transmitted to No. 7 is multiplexed with the optical signal spectrum-spread in another modulation circuit by the branch node 58 on the transmission path 57.

Next, the receiving operation will be described. The speed of the received signal transmitted is equal to the speed of the modulation signal on the transmitting side f
c [bps], and the operating speed of each block of the demodulation circuit is fc [Hz]. Also, the spreading code used is a Gold sequence with a code length of L bits, as in the modulation circuit.

Of the optical intensity-modulated bidirectional optical signals multiplexed on the transmission line 57, only the reception signal is separated by the directional coupler 48 and is converted into an analog electric signal through the O / E converter 49. , A / D conversion circuit 50. In the A / D conversion circuit 50, sampling is performed at a speed fc [Hz] and the result is input to the input port of the accumulator 51 as a y-bit parallel digital signal. The input data is accumulated at the speed fc [Hz], and the spread code is 1
The accumulated value is output as a z-bit parallel signal from the output port of the accumulator 51 every cycle (L bits at the speed fc [bps]).

The positive and negative polarities at the time of accumulating in the accumulator 51 are stored in the ROM 52 as a spread code, and if one bit of the code having L bits as one cycle is 1, the cumulative polarity is positive, and if it is 0. If it is negative, it will be accumulated. The ROM 52 also stores a signal for the accumulator 51 that clears the accumulated value for each cycle of the spread code, and accumulates during the period in which the signal corresponding to the last L bit is accumulated for each code cycle. It is input to the container 51.

If the accumulated value is cleared when the level of the clear signal is Low, the falling edge of the clear signal is used as the output clock of the accumulator 51, and
From the output port of, the correlation value with the modulation signal for each cycle of the spreading code is output at fc / L [bps].
The z-bit parallel digital signal from the output port of the accumulator 51 is input to the D / A conversion circuit 53, converted into an analog signal, and then output from the output terminal 54 as a demodulation signal.

Further, this demodulated signal is input to the synchronization determination circuit 55, and a clear pulse is sent to the counter 56 so that the read address of the ROM 52 is cleared when the 1-bit demodulated signal is demodulated in each cycle of the spread code. Is sent out,
The period of the exclusive OR with the spread code applied to the transmitted modulated signal and the period of the correlation between the modulated signal and the code in the accumulator 51 can be synchronized.

When the bidirectional signals are separated by the directional coupler 48 shown in FIG. 1, the transmitted signal is reflected from a connector (not shown) on the transmission path 57, and is transmitted together with the optical signal to be received. It is conceivable to pass through the directional coupler 48. In this case, the spread spectrum signal to be received is asynchronously multiplexed with another spread spectrum signal due to reflection in the demodulation circuit, but the cross-correlation value between code sequences such as the Gold sequence is equal to the spread code. Even if the upper limit value of the received light power of the reflected signal obtained by subtracting the return loss of the connector from the transmission power to the transmission line is assumed by using a code that is uniform and bounded, it does not cause inter-channel interference. Since a code having a small upper bound of the cross-correlation value can be selected as the spreading code, channel separation / demodulation is possible.

[0031]

As described above, according to the present invention, with respect to multiplexing of a transmission signal and a reception signal by spread spectrum,
By modulating the optical intensity of the modulated signal by spread spectrum, transmitting this signal to the optical transmission line via the directional coupler, and receiving at the receiving side from the transmission line via the directional coupler,
It is possible to demultiplex a signal by bidirectional spread spectrum that is asynchronously multiplexed on the transmission line.

Further, in response to reflection from a connector or the like on the transmission path, since the bidirectional optical signal is a spread spectrum signal, a code whose cross-correlation value between code sequences is uniform and bounded for an arbitrary phase difference is used. The use of the spreading code has an effect that interference between bidirectional channels, which is a problem in the same wavelength bidirectional division multiplexing system, can be removed, and the channel can be separated and demodulated.

Further, when performing code division multiplexing for multiplexing a plurality of bidirectional signals on the optical transmission line, since the bidirectional signals are demultiplexed by the directional coupler, the number of channels to be divided and multiplexed by the code is the same. The number of channels can be reduced, and the spreading code length required to remove channel interference can be reduced.

When synchronous multiplex connection is used for multiplexing in the same direction, a small cross-correlation value realized by establishing phase synchronization between codes such as orthogonal sequences is asynchronously multiplexed between bidirectional signals. There is also an effect that can be realized by.

[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 multiplex transmission system using spread spectrum as a conventional example of an optical data transmission system.

FIG. 3 shows another conventional example of an optical data transmission system,
It is a conceptual diagram which shows the multiplex transmission system by the same wavelength bidirectional division multiplex connection.

[Explanation of symbols]

41 ... Data input terminal, 42 ... Serial / parallel conversion circuit, 43 ... D-FF circuit, 44 ... Exclusive OR circuit,
45 ... ROM, 46 ... Parallel / serial conversion circuit, 4
7 ... E / O converter, 48 ... Directional coupler, 49 ... O / E
Converter, 50 ... A / D conversion circuit, 51 ... Accumulator, 52 ...
ROM, 53 ... D / A conversion circuit, 54 ... Demodulation signal output terminal, 55 ... Synchronization determination circuit, 56 ... Counter, 57 ... Optical transmission line, 58 ... Branch node

Claims (2)

[Claims] 1. A direct spread spectrum spread signal is generated using a spread code such that the duration of one cycle composed of a code length of a plurality of bits is the same as the duration of one bit of a data signal. And transmitting means for generating a light intensity modulated signal by this signal and a light intensity modulated signal or an optical signal obtained by multiplexing the same,
A receiving unit that obtains a demodulated signal by despreading using the spreading code used in the transmitting unit, and a transmitting signal from the transmitting unit and a receiving signal to be received by the receiving unit to a common transmission line. A spread spectrum communication device, comprising: a directional coupler for demultiplexing according to the above, and one side and the other side of the transmission line, respectively, and performing bidirectional communication via the transmission line. 2. By sharing a transmission path for a plurality of sets of the spread spectrum communication device according to claim 1,
A spread spectrum communication device, characterized in that two-way communication is multiplexed on the transmission path.