JP3117549B2 - Transceiver for spread spectrum communication - Google Patents

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 bidirectional data transmission system. In the figure,
1 is a data input terminal, 2 is a spread code generator (ROM) such as a PN sequence, 3 is an exclusive OR circuit, 4 is an E / O (electrical / optical) converter, 5 is an optical coupler, and 6 is optical transmission Path, 7 is a connector, 8 is an O / E (optical / electrical) converter, 9 is an A / D converter, 10 is a correlator (for example, an exclusive OR circuit and an accumulator), and 11 is used on the transmission side. A spread code generator (ROM) 12 for generating a spread code represents a demodulated signal output terminal.

Next, the operation of the circuit shown in FIG. 2 will be described. First, one bit of the data signal input from the input terminal 1 is:
An exclusive OR circuit 3 converts the channel-specific spreading code generated by the spreading code generator 2 for each bit of the spreading code,
An exclusive OR is used to generate a modulated signal by spread spectrum, and the E / O converter 4 modulates the light signal.

[0004] The light intensity modulated signal output from the transmitter is transmitted to the optical transmission line 6 via the optical coupler 5.
The light intensity modulated signal is converted into an electric signal by an O / E converter 8 via an optical coupler 5 of a partner station via a plurality of connectors 7 existing on an optical transmission line 6, and then converted by an A / D converter. 9 is converted into a digital signal. In the correlator 10, a cross-correlation with the spreading code generated by the spreading code generator (ROM) 11 is obtained, and a correlation value is output from a demodulation signal output terminal 12 as a demodulation signal.

[0005]

The bidirectional data transmission system described with reference to FIG. 2 uses a spread spectrum communication system to separate and demodulate bidirectional signals. In spread spectrum communication, a channel signal is separated and demodulated from a multiplexed signal by cross-correlating a channel-specific spreading code with a transmitted signal. Therefore, it is desirable that the spreading codes assigned to the channels have no correlation with each other.

However, there is a non-zero cross-correlation value between actual spreading codes. Furthermore, since there are reflection points such as connectors and couplers on the optical transmission line in the transmission line,
The reflected return signal from the reflection point due to the non-zero cross-correlation value interferes with the separation and demodulation of the channel as inter-channel interference.

In the prior art, as a method of suppressing this inter-channel interference, the cross-correlation value between codes is suppressed to the smallest possible value by setting the spreading code length to a large value and increasing the processing gain by spectrum spreading. However, even if a large reflected return signal is present, countermeasures have been taken so that the inter-channel interference does not hinder the separation and demodulation of channels.

However, the method of increasing the processing gain has a disadvantage that the required code length becomes enormous and the transmission efficiency is extremely reduced. As described above, in the related art, when the spread spectrum is used for the multiplexing technique of the bidirectional data transmission, the above-described disadvantage exists, and thus, it has been difficult to construct a practical scheme.

An object of the present invention is to provide means capable of solving the above-mentioned problems of the prior art and realizing a practical data transmission system.

[0010]

According to the present invention, the above-mentioned problems are achieved by the means as set forth in the appended claims.

That is, according to the first aspect of the present invention, a code length (2k) n × i (n = 2, 2) in which “1” of continuous k bits and “0” of continuous k bits are alternately repeated. 3, ...
i = 1, 2,...) and a continuous length (2k)
A code length (2) in which n-bit (n = 2, 3,...) “1” and a continuous length (2k) n-bit “0” are alternately repeated
k) Any one of n × i ( i = 1, 2,...) codes B is used as a spreading code in spread spectrum communication, and the duration of one bit is equal to the duration of one cycle of the spreading code. A modulated signal is formed by taking the exclusive OR of the data signal and the spreading code for each bit of the spreading code, and a transmitter for spread spectrum communication including a hand-thrower for transmitting the modulated signal has been transmitted. For the modulated signal of one bit of the data signal, the code A different from that used on the transmitter side of the own station in the duration of one bit of the data signal.
Alternatively, when a cross-correlation value is obtained between the modulated signal and the spread code using the spread code of B, the code
The spreading code of length (2k) n × i is divided into (2k) n bits
divided into i blocks, each of the i blocks
Is further divided into 2n blocks for each k bits,
X-th and (x + 1) -th two k-bit chunks
The overall correlation interval length for the correlation interval the (2k) × i bits of the partial correlation intervals and _{P x (x = 1,2, ...} , 2n-1),
This is a spread spectrum communication transceiver including a demodulation means for obtaining, as a demodulated signal, a signal having a minimum absolute value dispersion among partial correlation outputs using each P _x .

[0012]

[0013]

In the present invention, the spread code used for the spread spectrum has an alternating cycle of "1" and "0" of 1: 2n.
(N = 2, 3,...), And a plurality of correlation sections are used on the demodulation side. Since the reflected return signal component appears as the variance of the absolute value of the demodulated signal, of the output levels from the plurality of correlation sections, the one having the smallest variance of the absolute value of the correlation output is used as the demodulated signal, and the reflected return signal is reflected. A correlation value having a large signal component removal effect can be selected as a demodulated signal.

[0014]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 1 shows a modulation circuit, a demodulation circuit, and an optical coupler that couples an optical signal transmitted from the modulation circuit to an optical transmission line with an optical signal input from the transmission line to the demodulation circuit by direct spread spectrum spreading. This is a branch node for demultiplexing a transmission path and other bidirectional optical signals.

In FIG. 1, reference numeral 13 denotes a data input terminal;
4 is a ROM for outputting a spread code, 15 is an exclusive OR circuit for directly generating a spread modulation signal from the spread code and the data signal,
Reference numeral 16 denotes an E / O converter, 17 denotes an optical coupler for separating and coupling bidirectional light intensity modulation signals, 18 denotes an optical transmission line, and 29 denotes a connector.

Reference numeral 19 denotes an O which converts a light intensity modulation signal received via the optical coupler 17 into an electric analog signal.
/ E converter, 20 is an A / D converter, 21 is an RO storing the correlation interval between the spread code and the conventional spread spectrum.
M and 22 are the spreading code output from the ROM 21 and the A / D
This is a multiplication accumulator that accumulates the result of multiplication (exclusive OR) with the received signal digitized by the converter 20 and generates a demodulated signal by spread spectrum as in the related art.

Further, 23 is a ROM in which a spread code and a correlation section are stored, 24 is a multiplication accumulator which accumulates the result of multiplication of the digital reception signal and the spread code only in the correlation section similarly to the multiplication accumulator 22, 25 is A subtraction circuit for outputting a level difference between the demodulated signal based on the correlation output from the multiplier accumulator 24 and the demodulated signal based on the same spread spectrum output from the multiplier accumulator 22. A multiplication accumulator 27 for squaring and accumulating the output value, a detection unit 27 detects a minimum value from the output result from the multiplication accumulator 26, and selects one of the output results from the multiplication accumulator 24 as a final demodulated signal. A minimum value selection circuit 28 represents a demodulated signal output terminal.

The transmission operation in the circuit of FIG. 1 will be described.
The speed of the spread spectrum modulation signal is f [b / s]. Further, in the present embodiment, as the spreading code, two codes of k = 1, n = 2, and i = 2 in the claims, that is, 2 × 1 bit “1” and “0” are alternately repeated.
Length 4 × 2 in which 2 × 2 bit code {10101010} and continuous 4-bit “1” and “0” are alternately repeated
Bit code {11110000} is used. Since the claimed code length is 8 bits, FIG.
Is f / 8 [b / s].

The speed f / inputted to the data input terminal 13
The 8 [b / s] data signal is input to the exclusive OR circuit 15 in synchronization with one cycle of the spread code output from the ROM 14, that is, in this embodiment, the 8-bit cycle. The exclusive OR with the spreading code {10101010} input from the other input port at the speed f [b / s] is calculated, and a spread spectrum modulated signal is generated. The spread spectrum modulated signal output from the exclusive OR circuit 15 is converted into an optical signal by the E / O converter 16 and transmitted to the optical transmission line 18 via the optical coupler 17. Optical transmission line 1
8 has another spreading code # 1 from the other end of the transmission path.
The same speed made using 1110000 ° (f [b /
s]) is converted into an optical signal and input.

Next, the receiving operation will be described. The speed of the received signal transmitted is f equal to the speed of the modulated signal on the transmitting side.
[B / s]. Of the optical intensity modulated bidirectional optical signals multiplexed on the transmission line 18, the signal transmitted from the other party's transmitter is separated by the directional coupler 17, and the O / E
A / D as an analog electric signal through the converter 19
Input to the converter 20.

The received signal converted into an x-bit parallel digital signal by the A / D converter 20 is first input to the input port of the multiplier / accumulator 22. Multiply accumulator 22
A spreading code to be multiplied (exclusive OR) with the digital reception signal is input from the ROM 21 to the other input port of the. This spreading code is {10101010} used in the transmitter.

In the ROM 21, the multiplication accumulator 22
A signal for clearing the accumulated value for each period of the spreading code is also stored. Multiplier accumulator 22 outputs a demodulated signal using a conventional spread spectrum technique. This ROM2
A demodulated signal using the conventional spread-spectrum demodulation technique created by 1 and the multiplying accumulator 22 has one of three correlation intervals.
It is used as a reference value for selecting one. Since only one reference value is required, it is assumed that the reflected return signal, that is, the transmission signal in the opposite direction, is not output to the transmission path during the period in which the 1-bit demodulated signal is generated by the ROM 21 and the multiplier / accumulator 22. I do.

After the reference value has been obtained, the
Demodulation is performed. Partial correlation interval P _xX is 1 to (2n
From -1), three partial correlations for n = 2 spreading codes
A section is prepared. Digital reception from A / D converter
The signal therefore enters the input ports of the three accumulators 24.
Is forced. Also, the other input port of the accumulator 24
Spreading code to be multiplied (exclusive OR) with the received signal
{10101010} is input from the ROM 23.

The multiplication accumulator 24 forms an exclusive OR with the received signal for each bit of the spreading code, accumulates the result, and outputs the result for each period of the spreading code (8 bits in this embodiment). At this time, the three multiplying accumulators do not accumulate the entirety of one cycle of the spreading code, but accumulate only in a certain accumulation section. Cumulative interval is also stored in the ROM 23, the cumulative period stored in three ROM, respectively, if _{P 1, P 2, P 3} , P 1 = {1~2,5~
6th bit, P ₂ = {2-3, 6-7} bit, P
₃ = { _{3rd to} 4th, 7th to 8th} bits.

FIG. 3 shows the cumulative sections for each period of the three types of spreading codes. Each of the three multiplying accumulators 24 outputs a value obtained by accumulating the results of multiplication of the spread code and the received signal only in different accumulation sections shown in FIG. The three output results are subtracted from the reference value generated by the ROM 21 and the multiplication accumulator 22 in the subtraction circuit 25, and the result is output to the multiplication accumulator 26.
, The variance from the reference value is determined, and the variance is accumulated.

The accumulation result is input to the minimum value selection circuit 27, and it is determined which of the three accumulation values is the minimum value. Output values from the three accumulators 24 are input to the minimum value selection circuit, and the demodulated signal whose variance from the reference value from the multiplication accumulator 22 is determined to be the minimum is input to the minimum value selection circuit 2.
7 is output as a demodulated signal.

In FIG. 1, a bidirectional optical signal is transmitted through a transmission line 18.
Let's consider the case of multiplexing. In the E / O converter 19, in addition to the optical signal transmitted from the counterpart transmitter, the optical signal in the opposite direction is reflected at a reflection point such as a connector on the optical transmission line and received as a reflected return signal. The spread code {10101010} is used for the modulated signal transmitted from the other party transmitter, and the spread code {1111000} is used for the reflected return signal.
It is assumed that 0 ° is used. Since the position of the reflection point cannot be defined, one bit of the data signal in the modulation signal from the other party transmitter and one bit of the data signal in the reflection return signal
Any phase difference between bits must be assumed.

The phase difference in one bit of the data signal between the two modulated signals is the phase difference in one cycle of the two spread codes used. In this embodiment, since the length of the spread code is 8 bits, there is a phase difference of 0 to 7 bits between the spread code of the modulated signal from the partner transmitter and the spread code of the reflected return signal.

The reception level of the modulated signal from the partner after being converted into an electric signal by the O / E converter 19 is represented by R
Assuming that ₁ [v], the output level of the demodulated signal in the present embodiment is a partial correlation section, that is, the accumulation section in the multiplication accumulator 24 is equivalent to 4 bits of the spreading code. Demodulation level 8
To R ₁ [v] a half of 4R ₁ [v].

When the level of the reflected return signal received from the modulated signal with a phase difference of 0 to 7 bits is R ₂ [v] after the O / E conversion, the demodulation operation of this embodiment performs Demodulated to the values shown in Table 1 (maximum value). Table 1 also shows the demodulation level (maximum value) of the reflected return signal when the conventional technique is used. From Table 1, it can be seen that the reflected return signal in the case of using the conventional technique has a
If demodulation is performed at level 2R ₂ [v] and R ₂ > 4R ₁ , demodulation completely fails because the reflected return signal has a higher demodulation level than the modulation signal from the other transmitter. You can see that.

[0031]

[Table 1]

On the other hand, in the demodulation operation according to the present invention,
For any phase, the demodulation level of the reflected return signal is 0
It can be seen that there is a correlation section represented by [v]. Therefore, the subtraction circuit 25, the multiplication accumulator 26, the minimum value selection circuit 2
By selecting the correlation section that minimizes the variance of the absolute value of the demodulation level for each data signal, the influence of the reflected return signal, which cannot be eliminated in the related art when there is a phase difference of an odd number of bits, according to the prior art. It can be completely eliminated.

Further, from Table 1, when the demodulation operation of the present invention is used, for any combination of two arbitrary phase differences,
Since there always exists a correlation section in which the demodulation level of the reflected return light is 0 [v], there are two reflected return signals from an arbitrary position having a reception level higher than the modulation signal from the counterpart transmitter. However, this effect can be completely eliminated, and multiplexing of bidirectional signals becomes possible.

[0034]

As described above, according to the present invention, multiplexing of bidirectional signals by spread spectrum is "1".
And an alternating cycle of “0” is 1: 2n (n = 2, 3,...)
Are used, and at the time of demodulation, (2n−
1) A partial correlation result or a correlation result having a code length as a correlation interval, and a correlation result having a minimum variance of an absolute value of a demodulation level are selected from 2n correlation results. By doing so, it is possible to completely eliminate the influence of two reflected return signals from an arbitrary position, which have a higher reception level than the modulation signal from the other party's transmitter, and to enable bidirectional multiplexing.

Further, compared with the conventional spread spectrum technique, the code length is extremely short, at least 4 bits.
Since bidirectional signals can be multiplexed, a circuit having a low operation speed can be used in the transceiver.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one 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 illustrating a partial correlation section in the embodiment.

[Explanation of symbols]

 1,13 Data input terminal 2 Spread code generator 3,15 Exclusive OR circuit 4,16 E / O converter 5,17 Optical coupler 6,18 Optical transmission path 7,29 Connector 8,19 O / E converter 9,20 A / D converter 10 Correlator 11 Spread code generator 12,28 Demodulated signal output terminal 14,21,23 ROM 22,24,26 Multiply accumulator 25 Subtraction circuit 27 Minimum value selection circuit

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04B 1/69-1/713 H04J 13/00-13/06

Claims (1)

(57) [Claims] A code length (2) that alternately repeats “1” having a continuous length of k bits and “0” having a continuous length of k bits.
k) a code A of n × i (n = 2, 3,..., i = 1, 2,...) and a continuous length (2k) n bits (n = 2, 3,
...) and "0" of a length (2k) n bits continuous with "1"
(2k) n × i ( i = 1,2,2)
..) Is used as a spreading code in spread spectrum communication, and the exclusive OR of a data signal having a duration of one bit equal to the duration of one cycle of the spreading code and the spreading code is used. Is generated for each bit of the spread code to form a modulated signal, and a spread-spectrum communication transmitter having a hand-thrower for transmitting the modulated signal, and a modulated signal for one bit of the transmitted data signal, In the duration of one bit of the data signal, the cross-correlation value between the modulated signal and the spread code is used by using the spread code of the code A or B different from that used on the transmitter side of the own station. When calculating , the code length (2k) n
X i spreading codes are divided into (2k) i groups of n bits.
, And in each of the i clusters, k
It is divided into 2n chunks per bit, and
The (x + 1) -th set of two k bits is defined as a correlation section.
The total correlation section length (2k) × i bits is defined as P _x (x = 1, 2,..., 2n−1), and among the partial correlation outputs using each P _x , the variance of the absolute value is calculated. A transmitter for spread spectrum communication, comprising: a receiver for spread spectrum communication, comprising a demodulation means for obtaining a minimum signal as a demodulated signal.