JPH0522251A - Transmitter-receiver for spread spectrum communication - Google Patents

Abstract

PURPOSE:To attain demultiplex demodulation of plural channels while suppressing inter-channel interference by adding a bit number equivalent to a phase difference between maximum channels resulting from a distance difference between channels in a transmission line to a preceding part and a succeeding part of a code. CONSTITUTION:An (L+2n)-bit code resulting from adding n-bits to a preceding part and a succeeding part of an L-bit M series code is used for a diffusion code stored in a ROM 25 at a sender side according to the cyclic rule of the M series to permit an inter-channel phase difference. In the case of demodulation in each receiver, except an n-bit part added before and after each original code, the correlation between the original code and the modulation signal is used as a demodulation signal to exclude the increment of the correlation resulting from a change in the data signal of other channel due to an inter- channel phase difference.

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. 7 is a block diagram showing a conventional transceiver for spread spectrum communication. More specifically, it can be said that this is a block diagram in the case of light intensity modulation using direct spread as an example of multiple connections using spread spectrum. 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, 5 is a branch node such as a star coupler, 6 is an optical transmission line, 7 is a branching node similar to 6, and 8 is an O / E (optical / electrical) converter, 9 is a correlator, 10
Is a spread code generator for generating the code used on the transmission side, 1
Reference numeral 1 is a demodulation signal output terminal.

Next, the circuit operation will be described. First, the data signal 1 bit input from the input terminal 1 and the channel-specific spreading code generated by the spreading code generator 2 are processed by the exclusive OR circuit 3 for each bit of a plurality of bits forming the spreading code. By taking the exclusive OR, a modulation signal by spread spectrum is created, and the E / O converter 4 modulates the light intensity. The plurality of signals thus modulated 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 branch node 7, the correlator 9
At, the cross-correlation with the spread code generated by the spread code generator 10 is obtained, and the correlation value becomes the demodulated signal.

[0004]

The conventional multiple connection system using the transmitter / receiver for spread spectrum communication is configured as described above, and there is a distance difference between transmission and reception of each communication path (channel). Due to the distance difference, a level difference and a phase difference occur between the modulated signals of the respective channels on the receiving side, so that the cross-correlation value between the codes on the receiving side increases. This increase in the cross-correlation value causes inter-channel interference. Therefore, in the conventional technology, this problem is solved by devising a method of setting a large code length such as a PN sequence used for a spreading code or a method of synchronizing the spreading code. Was dealing with.

However, the method of increasing the code length of the PN sequence or the like allows a level difference and a phase difference between the modulated signals, and thus has a problem that the required code length becomes enormous. In order to shorten the code length, a sequence with a small cross-correlation value, such as an orthogonal sequence where the cross-correlation value between the codes is zero, is used as the spreading code. There is a problem that inter-channel interference increases when there is no such error or when a small error occurs in synchronization.

The present invention has been made in order to solve such a problem. For example, a code obtained by extending the front and back of a code such as the M series is used, and the receiving side excludes the extended part. By obtaining the demodulated signal by correlating and suppressing the increase of the cross-correlation value due to the change of the data signal of each channel, even if there is the level difference between channels and the phase difference between channels, the interference between channels is suppressed and the It is an object of the present invention to provide a transceiver for spread spectrum communication that enables separation and demodulation of the above channels.

[0007]

In order to achieve the above object, according to the present invention, the duration of one cycle constituted by the code length corresponds to the duration of one bit of the data signal.
As the spreading code, for example, a code such as an M sequence (code length L1 bit (including the code length 1)) or a plurality of k codes (such as an orthogonal sequence formed by adding 0 to the end of the M sequence ( For a code configured by connecting code lengths L1, L2, ..., Lk), one bit equal to the first 1 bit of each code of Li (1 ≦ i ≦ k) bits is added to the end of the code. An operation of adding a bit, such as adding 1 bit equal to the end bit of Li (1 ≤ i ≤ k) bits to the beginning of the code, and then adding Li (1
≦ i ≦ k) Repeating such an operation n times, such as adding the same 1 bit to the second bit from the beginning and the second bit from the end of the code of the bit, respectively, at the end and the beginning of the code. Therefore, Li (1 ≦
A code having a code length ΣLi + 2kn bits newly formed by adding n bits before and after the code of i ≦ k) bits is used as a spreading code (where ΣLi is from i = 1 to i =
(means to add up to k)), a modulation means for generating a modulation signal is provided on the transmission side.

[0008] Further, when the receiving side uses the same spreading code as that used on the transmitting side for the transmitted signal to obtain the cross-correlation value for each cycle of the spreading code, Excluding the n-bit portion added to the above of each code, a demodulation means for obtaining a cross-correlation value only for the part of each code of the original Li (1 ≦ i ≦ k) bits and using this as a demodulation signal is provided. It was

[0009]

In the present invention, the number of bits corresponding to the maximum phase difference between channels due to the distance difference between the channels in the transmission line at the time of modulation in each transmitter of code division multiplex communication using spread spectrum. A code configured by adding n before and after the code, or a code configured by connecting a plurality of such codes is used as a spread code,
At the time of demodulation, when calculating the cross-correlation value between the spread code and the received signal, the correlation is taken excluding the part of the bits added before and after the code, which causes the change in the data signal due to the phase difference between channels. It is possible to eliminate the increase in cross-correlation value, and when there is no phase difference between channels, there is no inter-channel interference equivalent to the demodulated signal obtained by using the code before adding bits before and after as the spreading code. A demodulated signal can be obtained.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of a transmitter according to the present invention, and is a block diagram of a circuit for generating a modulation signal by spread spectrum, and FIG. 2 is a block diagram of a circuit of a receiver for demodulating the modulation signal. is there.

In FIG. 1, 21 is a data input terminal, 2
2 is a serial / parallel conversion circuit for converting the input data signal into x-bit parallel, 23 is a D-FF circuit for synchronizing the data signal converted into x-bit parallel by 22 with one cycle of the spread code, 24 Is an exclusive OR circuit for generating a modulation signal from a spread code and a data signal, 25
Is a ROM storing a spread code, 26 is a parallel / serial conversion circuit for converting an x-bit parallel modulated signal, and 27 is a modulated signal output terminal.

The operation of the transmitter shown in FIG. 1 will be described. The speed of the modulated signal in this transmitter is fc [bps]. Further, in the present embodiment, a (L + 2n) -bit code in which n bits are added before and after the L-bit M series according to the cyclic rule of the M series to allow the phase difference between channels is used as the spreading code. Therefore, the speed of the data signal is fc
/ (L + 2n) [bps].

From these, the operation speed of each block in FIG. 1 is as follows: serial / parallel conversion circuit 22, exclusive OR circuit 24, ROM 25: fc / x [Hz], D-
The FF 23 has fc / x (L + 2n) [Hz], and the parallel / serial conversion circuit 26 has fc [Hz].

Speed fc input to the data input terminal 21
The data signal of / (L + 2n) [bps] is transmitted by the serial / parallel conversion circuit 22 and the D-FF 23 at the speed f.
It is converted into an x-bit parallel signal of c / x (L + 2n) [bps] and input to one input port (x-bit input) of the exclusive OR circuit 24. The other input port of the exclusive OR circuit 24 is connected to the speed f from the ROM 25.
The spread code is input in x-bit parallel at c / x [bps], the exclusive OR is calculated at the speed fc / x [Hz], and the speed fc / is output from the output port of the exclusive OR circuit 24.
It is output at x [bps]. Since this output is x-bit parallel, it is converted into a serial signal of speed fc by the parallel / serial conversion circuit 26 and output from the output terminal 27 as a modulation signal.

In FIG. 2, 31 is a modulation signal input terminal,
Reference numeral 32 is an A / D conversion circuit, 33 is an accumulator that calculates a cross-correlation value of the modulation signal converted into a y-bit parallel digital signal by the A / D conversion circuit 32 and the spread code for each code cycle, and 34 is a transmission A ROM that stores the same spreading code as that used in the machine as the polarity of accumulation in the accumulator, and also stores a clear signal of the accumulated value, 35 is a D / A conversion circuit,
36 is a demodulation signal output terminal, 37 is a synchronization determination circuit, and 38 is a counter for generating a read address of the ROM 34.

The operation of the receiver shown in FIG. 2 will be described. It is assumed that the speed of the modulated signal input to the receiver of FIG. 2 is the same as fc [bps] of the transmitter. Further, the spreading code used is the same code as that used in the transmitter of FIG. 1 and has a code length (L bit added by n bits before and after the M sequence of L bits).
+ 2n) bits are used. The operating speed of each block of the receiver shown in FIG. 2 is fc [Hz].

The transmitted modulated signal is input to the input terminal 31.
After being input to the A / D conversion circuit 3 as an analog signal
2 is sampled at a speed fc [Hz], and is input to the input port of the accumulator 33 as a y-bit parallel digital signal. The input data is the speed fc
[Hz] is accumulated and one cycle of the spread code (speed fc [b
ps] L + 2n bits), the cumulative value is output from the output port of the accumulator 33 as a z-bit parallel signal.

The positive and negative polarities at the time of accumulation in the accumulator 33 are the same spreading code as that used in the transmitter, and RO
If one bit of the code stored in M34 and having (L + 2n) bits as one cycle is 1, the cumulative polarity is positive, 0
If so, it is accumulated as negative. The ROM 34 has an accumulator 33.
On the other hand, a signal for clearing the accumulated value for each cycle of the spread code is also stored, but in the present embodiment, n is added before and after the M sequence.
Bits added bit by bit are used as the spreading code, and in this case, the clear signal is input to the accumulator 33 during the accumulation period in which the bits added before and after are used as the polarities.

As a result, in the accumulation of the spread code for each cycle, only the signal obtained by the exclusive OR with the M sequence at the time of modulation is accumulated, and the period of 2n bits added before and after is not accumulated. When the level of the clear signal is Low,
If the accumulated value is cleared, the trailing edge of the clear signal is used as the output clock of the accumulator 33, so that the output port of the accumulator 33 has the polarity of the M-sequence part excluding n bits before and after the spread code. The accumulated value of the modulated signal is fc /
The output will be (L + 2n) [bps]. The z-bit parallel digital signal from the output port of the accumulator 33 is input to the D / A conversion circuit 35, converted into an analog signal, and then output from the output terminal 36 as a demodulation signal.

Further, this demodulated signal is input to the synchronization judgment circuit 37, and a clear pulse is sent to the counter 38 so that the read address of the ROM 34 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 33 are synchronized.

FIG. 3 is a time chart of the data signal and the modulated signal A modulated by the conventional spread spectrum technique. Further, a spread code (M sequence) a that takes an exclusive OR with the data signal is shown above the data signal (code length L = 7).

FIG. 4 is also a time chart of the data signal and the modulated signal A'by the transmitter of FIG. 1 according to the present invention. Further, a code a'composed of adding 2 bits before and after the M sequence a in FIG. 3 is shown on the data signal as a spreading code that takes an exclusive OR with the data signal (code length L '. = L + 2n = 9: L = 7, n = 1). Figure 5
3 is the modulation signal A of FIG. 3, the spreading code (M sequence) b used for another channel when the modulation signal A is multiplexed by the spread spectrum technique, and the code b and the modulation signal A are exclusive. It is a cross-correlation value for each logical sum and each code cycle.
At this time, it is assumed that there is a phase difference between channels due to a distance difference between the channels.

In FIG. 5, the exclusive OR "01000"
Although (cross-correlation value) is described as (-3) for 10 ", since" 0 "is transmitted as" -1 "and" 1 "is transmitted as" +1 "on the transmission path. As a result, the cross-correlation value becomes (-3).

FIG. 6 shows the modulation signal A'of FIG. 4 and the modulation signal A
A spreading code b ′ used for another channel when ′ is multiplexed with another channel by spread spectrum, and a code b
′ Is the exclusive OR of the modulated signal A ′ and the cross-correlation value for each code cycle. Further, the code b ′ is a code configured by adding 2 bits before and after the M sequence which is the embodiment of the present invention, like the code a ′ used for the modulated signal A ′. At this time, the same phase difference between channels as in FIG. 5 is given between the channels.

The spreading code shown in FIG. 4 is one bit added before and after the M sequence according to the cyclic rule. The conventional technique and spread spectrum multiplexing using this code as a spreading code will be compared with each other in FIGS. When equal phase differences are given to the multiplexed channels, the related art cannot maintain the cross-correlation values (-1) and (+1) when the M sequence is used as a code when there is no phase difference. However, when the demodulation method according to the present invention is employed, the cross-correlation value for each cycle of the code does not include the increase due to the change in the data of the other channels, and the increase in the cross-correlation value can be suppressed.

Furthermore, by using a cyclic code such as an M sequence to which bits are added according to a cyclic rule as a spreading code, a cross-correlation value between cyclic codes can be obtained even if there is a phase difference between channels. Therefore, it is possible to obtain a demodulated signal having the same amplitude when there is no phase difference (a demodulated signal with less inter-channel interference, which is equivalent to the case where there is no phase difference).

Therefore, by using an M sequence as the cyclic code and adding a code corresponding to the inter-channel phase difference before and after to the spread code, the cross-correlation value of the inter-channel code depends on the phase difference. (-1) can be maintained. In addition, by using the M sequence and 0 as the cyclic code, adding bits corresponding to the inter-channel phase difference for each, and using the code obtained by connecting the bits as the spreading code, the cross-correlation value between the channels is 0 can be maintained regardless of A smaller inter-channel cross-correlation value means less inter-channel interference.

[0028]

As described above, according to the present invention, when modulation is performed in each transmitter of code division multiplex communication by spread spectrum, a code or a plurality of codes corresponds to a phase difference between channels as a spread code. A code formed by adding n bits before and after each code, or a code formed by connecting these bits is used. When demodulating by each receiver, it is added before and after each original code. N
By excluding the bit part and using the cross-correlation value between the original code and the modulated signal as the demodulation signal, it is possible to eliminate the increase in the correlation value caused by the change in the data signal of the other channel due to the phase difference between the channels. There is.

Further, by using a cyclic code such as an M sequence or a plurality of cyclic codes as the original code, the phase relationship of the codes between the channels is set to the cyclic code with the inter-channel phase difference = 0 in the period for obtaining the cross-correlation. Or a cyclic code connected to each other can be made equal to the phase relationship when a spreading code is used, so a cyclic code or a code formed by connecting multiple cyclic codes regardless of the magnitude of the phase difference between channels. There is an effect that it is possible to obtain a demodulated signal having an amplitude of the same value as that used in the spreading code.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a transmitter for spread spectrum communication according to the present invention.

FIG. 2 is a block diagram showing an embodiment of a spread spectrum communication receiver according to the present invention.

FIG. 3 is a time chart of a data signal and a modulation signal A modulated by using a spreading code according to a conventional technique.

FIG. 4 is a time chart of a data signal and a modulation signal A ′ by the transmitter according to the present invention.

5 shows the modulated signal A of FIG. 3, a spread code (M sequence) b used for another channel when the modulated signal A is multiplexed by a spread spectrum technique, the code b and the modulated signal A. 3 is a time chart showing the exclusive OR of the above and the cross-correlation value for each code cycle.

6 is a modulation signal A ′ of FIG. 4, a spreading code b ′ used for another channel when the modulation signal A ′ is multiplexed on another channel by a spread spectrum technique, and the code b ′.
6 is a time chart showing an exclusive OR of the modulated signal A ′ and a cross-correlation value for each code period.

FIG. 7 is a block diagram showing a conventional transceiver for spread spectrum communication.

[Explanation of symbols]

21 ... Data input terminal, 22 ... Serial / parallel conversion circuit, 23 ... D-FF, 24 ... Exclusive OR circuit, 25
... ROM, 26 ... Parallel / serial conversion circuit, 27 ...
Modulation signal output terminal, 31 ... Modulation signal input terminal, 32 ... A
/ D conversion circuit, 33 ... Accumulator, 34 ... ROM, 35 ... D
/ A conversion circuit, 36 ... Demodulated signal output terminal, 37 ... Synchronization determination circuit, 38 ... Counter

Claims (4)

[Claims] 1. A k number of codes whose code lengths are Li (where 1 ≦ i ≦ k, including Li = 1) and which have different code lengths are denoted by Ci (where 1 ≦ i ≦). k), for the convenience of the following operation, the same code as the code Ci is separately set as Ci ′, and the j-th bit from the head bit position of the code Ci (where j ≧ 1 and j> Li is satisfied). Is (j-
1) The value obtained by adding 1 to the remainder of / Li is newly set as j), 1 bit located at the bit position is added to the end of the code Ci ′, and the bit position at the end of the code Ci is added to the beginning. By adding one bit located at the j-th bit position toward the beginning of the code Ci ′, the code Ci ′
The code C having a code length (ΣLi + 2kn) configured by connecting the codes Ci ′ (that is, k codes) obtained after repeating the operation of reconstructing (However, ΣLi is i = 1
To i = k), the exclusive OR of the data signal and the spreading code is calculated such that the duration of one bit of the data signal is equal to the duration of one cycle of the spreading code. , A spread spectrum communication transmitter having means for forming a modulated signal by sending the spread code for every 1 bit, and a modulated signal for 1 bit of the transmitted data signal, When the same spreading code C as that used on the transmitter side is used for the duration of one bit of the data signal and the cross-correlation value is obtained between the two, the code for each of the codes Ci ′ constituting the spreading code C Spread spectrum including demodulation means for obtaining a cross-correlation value obtained for (ΣLi) bits after removing the bit portions corresponding to n bits added before and after Ci as a demodulation signal A transmitter / receiver for spread spectrum communication, comprising: a receiver for communication. 2. The transceiver for spread spectrum communication according to claim 1, wherein the code Ci is a cyclic code. 3. The transceiver for spread spectrum communication according to claim 1, wherein the code Ci comprises an M-sequence code as one code. 4. The spread spectrum communication transmitter / receiver according to claim 1, wherein the code Ci is composed of an M sequence code and a code of 0 as two codes. Machine.