JPH1131996A - Code division multiplex communication equipment - Google Patents

Abstract

(57) [Summary] [Problem] It was difficult to capture initial synchronization at high speed. SOLUTION: A sequencer 707 controls a code generator 703 so as to generate a spread code for initial synchronization acquisition,
Also, it controls the multiplexer 108 to transmit the spread code for initial synchronization acquisition. After a predetermined time, the sequencer 707
Controls the code generator 703 and the multiplexer 108 to generate a code division multiplexing spread code,
Transmit the code division multiplex signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synchronous type code division multiplexing system for multiplexing a communication path using a plurality of different spreading codes having a small cross-correlation value by using a spread spectrum communication system to increase an information transmission speed. The present invention relates to a communication device.

[0002]

2. Description of the Related Art In spread-spectrum communication, a code division multiplex communication system has been conceived which utilizes a low cross-correlation characteristic of a spread code to multiplex a plurality of communication paths in the same band to increase the information transmission speed. I have. Generally, in a single-channel spread spectrum communication system, a receiver has as a replica the same spreading code as that used for spread spectrum of a transmission signal, and performs a periodic correlation operation between the replica and the reception signal. Thereby, code synchronization can be maintained at the same time as information transmission.

On the other hand, in the code division multiplex system described at the beginning, since information signals are multiplexed by a plurality of spread codes, once code synchronization is established, the cross-correlation characteristics between spread codes at a synchronization point are low. Since they are correlated or orthogonal, each information symbol can be independently demodulated. However, since the periodic cross-correlation characteristics of the plurality of spreading codes are not always low correlation, even if the periodic correlation operation is performed using any one of the spreading codes, the correlator output is affected by the cross-correlation characteristics between channels. It is difficult to recognize a steep correlation peak, and it is extremely difficult to always capture and maintain synchronization while transmitting information. Therefore, in such a code division multiplex communication system, the transmitter transmits a pilot signal, which is spread with a single spreading code, as a preamble for a certain period of time prior to the transmission of the information signal, in order to acquire synchronization at the receiver, After acquiring synchronization with this pilot signal, during the information transmission period, the receiver
It is general to capture and hold code synchronization by holding a clock or the like.

FIG. 6 shows a transmitter of a conventional code division multiplex communication apparatus, FIG. 7 shows an example of a packet configuration in code division multiplex communication, FIG. 8 shows a configuration of a receiver of the communication apparatus, and FIG. FIG. 3 is a diagram illustrating a detailed configuration of a synchronization circuit of the receiver. In this example, the modulation method is phase shift keying, and the demodulation method is synchronous demodulation.

In FIG. 6, high-speed transmission data is converted into low-speed parallel data 102 by a serial / parallel converter 101, and these parallel data are mutually exclusive with a plurality of different spreading codes generated from a code generator 103. The signal is subjected to spread spectrum modulation by the logical OR 104 and is added by the adder 105 to obtain a code division multiplexed signal. The multiplexed code division multiplexed signal passes through the multiplexer 108 and is converted into an analog baseband signal 110 by the digital / analog converter 109. On the other hand, prior to the code division multiplex signal, a pilot signal spectrum-spread by a single spreading code is transmitted as a preamble. The function of the multiplexer 108 is to select a pilot signal and a code division multiplexed signal, and the timing of selecting both is determined by the sequencer 107. When the pilot signal is selected, the code generator 1
From 03, a single spreading code (for example, PN ₁ ) determined in advance from among a plurality of spreading codes (PN _{1 to} PN _n ) used for code division multiplexing is used as the signal line 106 by the multiplexer 108. The signal is passed through a digital / analog converter 109 to be converted into an analog baseband signal 110.

FIG. 7 is a diagram showing an example of a packet configuration in code division multiplex communication. In the figure, the preamble signal is transmitted prior to the code division multiplex signal, and the two are switched under the control of a sequencer that transmits the code division multiplex signal.

In FIG. 8, a received signal converted to an intermediate frequency signal 201 is multiplied by a carrier 402 reproduced by a carrier recovery circuit 401 by a mixer 402, passed through a low-pass filter 403 and converted to a baseband signal. . Further, the baseband signal is converted by the AD converter 404 into a digital multiplexed signal. The demodulation circuit of the receiver has the same number of digital correlators 40 as the number of multiplexes.
5, a correlation demodulation process is performed on the multiplexed digital signal using the plurality of spreading codes 204 generated from the synchronization circuit 407, and multiplexed information data of each channel is obtained. At this time, for example, when the received multiplexed data at the time of performing the correlation operation is expressed in a positive / negative signed binary number, in the two-phase modulation, the sign bit of the correlator output can be regarded as the demodulated data. The low-speed parallel data 206 demodulated in this manner becomes a high-speed serial data stream 207 by the last parallel-to-serial converter 407.

Finally, the detailed configuration of the synchronization circuit 407 used in the conventional demodulator will be described with reference to FIG. The received signal converted to the intermediate frequency is input to the correlator 301,
A correlation operation with the reference signal is performed. The reference code is a spread code for initial synchronization acquisition, and a spread code used for code division multiplexing having a good autocorrelation characteristic is selected in advance, and is the same as the spread code for the pilot signal. . The output of the correlator 301 is obtained as a peak signal through a peak detector 302. In an ideal reception state where the influence of noise or the like is small, the output of the peak detection unit 302 becomes maximum at the code synchronization point. A code reset unit 303 resets the code generator 304 according to the phase difference between the peak signal and the code generation timing signal generated from the code generator 304. Reference numeral 305 denotes a phase shift unit, and the reference signal generator 3 outputs a signal corresponding to the phase difference between the peak signal and the code generation timing generated from the code generator 304.
06 is shifted. As described above, synchronization is obtained between the pilot signal and the receiving code generator.

Here, in the packet type data transfer system based on such a code division multiplexing method, in order to obtain an initial capture of code synchronization, the transmitter conventionally has to select from among spreading codes used for code division multiplexing. Prior to transmission of the information signal, a signal having good correlation characteristics is selected, and a pilot signal that has been spectrum-spread by such a spreading code is transmitted as a preamble for a certain period of time. The receiver performs a periodic correlation operation between the replica of the spreading code and the pilot signal. And the peak of the correlation value was recognized as the synchronization point.

[0010]

However, if an attempt is made to recognize the spread code used for code division multiplexing and the result of the correlation operation using its replica as in the prior art, the spread code itself will not be able to communicate with each other at the synchronization point. Since the correlation characteristic is selected from criteria such as low correlation or orthogonality, even if the best autocorrelation characteristic is used as a preamble signal spreading code among a plurality of spreading codes, it is true. It is difficult to recognize a steep correlation peak in the correlator output only at the synchronization point, and it is extremely difficult to reliably acquire high-speed initial synchronization.

[0011]

In order to achieve the above object, according to a first aspect of the present invention, there is provided a generating means for generating a spreading code for initial synchronization acquisition and a spreading code for code division multiplexing,
Selecting means for selecting the two types of spreading codes, and communication means for communicating communication data by using a code division multiplexing spreading code output from the generating means, and generating a preamble signal and a code division multiplexing signal with different spreading codes; I do.

According to a second aspect of the present invention, there is provided a generating means for generating a spreading code for initial synchronization acquisition and a spreading code for code division multiplexing, and a selecting means for selecting the two kinds of spreading codes with the passage of time. Communication means for communicating the multiplexed information signal, and has a function of despreading the preamble signal and the code division multiplexed signal with different spreading codes.

[0013]

FIG. 1 is a diagram showing a configuration of a transmitter according to an embodiment of the present invention. In the figure, a sequencer 707 controls the code generator 703 not only to switch the multiplexer 108 but also to switch between a spreading code for pilot signal and a spreading code for modulation of each information channel for code division multiplexing.

FIG. 2 is a diagram showing a spread code generation sequence of the code generator 703 of the transmitter. First, the transmitter controls the code generator 703 by the sequencer 707 to generate a spreading code dedicated to initial synchronization acquisition. At the same time, the sequencer 707 controls the multiplexer 108 to select an initial synchronization acquisition spreading code (PN ₀ ). After a predetermined period (preamble transmission period) has elapsed, the transmitter transmits sequencer 707 to perform spread modulation with transmission data.
Controls the code generator 703 to generate a code division multiplexing spread code (PN _{1 to} PN _n ). Sequencer 1 at the same time
07, the multiplexer 108 is controlled to select and output a code division multiplexed signal.

Therefore, as described above, a spreading code having a very good autocorrelation characteristic, which is different from the spreading code for code division multiplexing, can be used for the pilot signal, so that the initial synchronization acquisition in the receiver is more reliable. Further, since the time required for initial synchronization acquisition can be reduced, the preamble transmission period can be shortened.

[0016] In this case, PN ₀ is different from any of the PN ₁ ~PN _n.

[0017] In Figure 1, the code generator 703, while outputting the PN ₀ through the same signal line as one (e.g., PN _n) of the PN ₁ to PN _n, the PN ₀ PN ₁ ~ it may be output through another signal line to the PN _n. In that case, the code generator 703 does not necessarily need to be controlled by the sequencer.

FIG. 3 is a diagram showing a configuration of the synchronization circuit 407 (FIG. 8) of the receiver according to the embodiment of the present invention.
The overall configuration of the receiver is the same as that of FIG. In the figure, the control performed on the code generator 364 is performed not only by the phase shift unit 305 but also by the peak detection number measurement unit 307. Here, the description will focus on the differences from the conventional example. In this code division multiplex communication device, as described with reference to FIGS. 1 and 2, a preamble signal using a spreading code dedicated to initial synchronization acquisition is transmitted for a predetermined period before transmission data is transmitted. In order to obtain initial synchronization acquisition on the receiver side using the same preamble signal,
The code generator 364 is initialized so that a replica of the spread code for initial synchronization acquisition is generated. Since the correlation value between the replica and the received signal is obtained by the correlator 301,
Under ideal line conditions with little noise, interference, etc., when a preamble signal arrives as a received signal, the peak detector 302 detects a peak point of a correlation value for each spreading code. Therefore, when the peak number of the correlation value detected for each spreading code length during reception of the preamble signal is detected by the number-of-times-of-detection measuring unit 307 the number of times corresponding to the preamble signal duration, it is recognized as the start point of the code division multiplex communication data. By controlling the code generator 364 to generate a despreading code for code division multiplexing instead of a spreading code exclusively for synchronization acquisition, it is possible to demodulate code division multiplexed communication data.

Next, supplementary examples of the autocorrelation characteristics of the spreading code for code division multiplex communication and the spreading code dedicated to initial synchronization acquisition will be described with reference to FIGS. 4 and 5. As is clear from FIG. 4, when the code phases match, the spreading code sequence for code division multiplex communication has a sharp peak in the correlation value,
Side lobes remain at other points where the code phase is shifted. On the other hand, in FIG. 5, as represented by the M-sequence code (however, the initial synchronization acquisition dedicated code is not limited here), it has a sharp peak at the synchronization point of the initial synchronization acquisition dedicated spreading code, Otherwise, it is flat and has no peak value. Therefore, when the peak value at the synchronization point is detected by the peak detection unit 302 as is clear from the above characteristics, the detection accuracy of the peak value is improved by using the initial synchronization acquisition dedicated spreading code for the synchronization circuit. In addition, the initial synchronization acquisition time can be reduced.

The spreading code dedicated to initial synchronization acquisition corresponds to PN ₀ on the transmitter side, and the despreading code for code division multiplex communication is the spreading code PN ₁ -P for code division multiplex communication on the transmitter side.
N _n .

A correlator in which a spreading code dedicated to initial synchronization acquisition is written in advance may be used as the correlator 301.
In this case, in synchronization with the output of the peak detection unit 302, when the number-of-times-of-detection measurement unit 307 detects the peak points the number of times corresponding to the preamble signal duration, the despread output is started.

[0022]

As described above, according to the present invention, by using different spreading codes for initial synchronization acquisition and code division multiplexing, reliable high-speed initial synchronization acquisition becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration example of a transmitter according to an embodiment of the present invention.

FIG. 2 is a diagram showing a spread code generation sequence of a code generator of a transmitter.

FIG. 3 is a diagram illustrating a configuration of a synchronization circuit of the receiver according to the embodiment of the present invention.

FIG. 4 is a diagram illustrating an autocorrelation characteristic of a code division multiplexing spreading code.

FIG. 5 is a diagram illustrating an autocorrelation characteristic of a spreading code dedicated to initial synchronization acquisition.

FIG. 6 is a diagram illustrating a configuration of a modulator of a conventional code division multiplex transmission device.

FIG. 7 is a diagram illustrating an example of a packet configuration in code division multiplex communication.

FIG. 8 is a diagram illustrating a configuration of a receiver of the code division multiplex communication device.

FIG. 9 is a diagram showing a detailed configuration of a synchronization circuit of a receiver of a conventional code division multiplex communication device.

[Explanation of symbols]

 Reference Signs List 101 serial / parallel converter 108 multiplexer 301 correlator 302 peak detection unit 303 code reset unit 305 phase shift unit 306 reference signal generator 307 detection count measurement unit 364 code generator 703 code generator 707 sequencer

Claims (4)

[Claims] 1. A synchronous code division multiplexing communication apparatus for multiplexing a communication path using a plurality of different pseudo-random sequences as spreading codes to increase an information transmission speed, the spread code for initial synchronization acquisition and the code division multiplexing. Generating means for generating a spreading code for use, selecting means for selecting the two types of spreading codes, and communication means for communicating communication data by a code division multiplexing spread code output from the generating means, and A code division multiplex communication device for communicating an initial synchronization acquisition spreading code that is not included in a code division multiplexing spread code before performing division multiplex communication. 2. A synchronous code division multiplexing communication apparatus for multiplexing a communication path using a plurality of different pseudo-random sequences as spreading codes to increase an information transmission speed. Generating means for generating a spreading code for use, selecting means for selecting the two kinds of spreading codes in accordance with time measurement, and communication means for communicating a multiplexed information signal, for communicating a multiplexed information signal. A code division multiplexing communication apparatus for communicating an initial synchronization acquisition spreading code that is not included in the code division multiplexing spreading code before performing. 3. A spread code for initial synchronization acquisition is communicated, and after synchronizing with the spread code for initial synchronization acquisition, an information signal is communicated using a plurality of code division multiplexing spread codes different from the spread code for initial synchronization acquisition. And a code division multiplex communication method. 4. A spread code for initial synchronization acquisition is received, and when a spread code for initial synchronization acquisition is received a predetermined number of times, it is multiplexed using a plurality of code division multiplexing spread codes different from the spread code for initial synchronization acquisition. A code division multiplex communication method characterized by demodulating an information signal.