JPH07107007A - Spreading code generation system - Google Patents

Abstract

PURPOSE:To increase the multiplicity at the time of multilevel phase modulation in a spreading code generation system in direct spread spectrum communication. CONSTITUTION:Optional spreading code patterns (the output of PN code generators 141 and 142) whose code sequences are different are used between respective phases in a multilevel phase modulation system, the code patterns are multiplied with the same code pattern of an optional orthogonal code sequence (the output of an orthogonal code generator 150) and spreading codes are generated. Also, the spreading codes between the respective phases are the combination of the patterns whose mutual correlation value is large inside the code sequence and the code patterns are mutually circulated and used in synchronism at a point where the mutual correlation value of correlation devices 251-254 is minimized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a code division multiple access system,
The present invention relates to a spread code generation method in direct spread spectrum communication.

[0002]

2. Description of the Related Art In recent years, a microcell system and a local wireless LA
A communication system using radio such as N has been studied. As one of the wireless communication methods, code division multiple access (Code-Devision-Multip
le-Access: hereinafter referred to as CDMA) has been studied, and some of them are being put to practical use.

The spread spectrum method is mainly divided into a direct sequence (hereinafter referred to as DS) method and a frequency hopping (hereinafter referred to as FH) method, and the DS method has a frequency higher than that of an information signal (eg, This is a method of directly spectrum spreading an information signal by a spread code pattern consisting of several tens to several thousands. The FH method is a method of spreading a spectrum by, for example, changing the carrier frequency of a narrow-band modulated signal in the order according to a certain spread code pattern, and averaging as a result.

The CDMA system is a DS system (DS / CDM
A) is a communication method for multiplexing in the same frequency band by using different spreading code patterns when performing spreading by the FH method (FH / CDMA) or the like, and the communication channel is identified by the code pattern. As a spread code for spread spectrum, pseudo noise (Pseudo Noise: P
N series) is often used, and typical examples thereof include M series and Gold series. The autocorrelation characteristic of each code pattern of these sequences with itself and the cross-correlation characteristic of other code patterns belonging to the same code sequence differ depending on the code sequence.

In the conventional DS / CDMA system, a two-phase phase modulation (hereinafter referred to as BPSK) system has been mainly used, but recently, in-phase components (hereinafter referred to as I
ch), quadrature component (hereinafter referred to as Qch), and four-phase phase modulation (hereinafter referred to as QPSK) method (hereinafter referred to as DS / QPSK method) that is spread and combined using different code patterns, and more. There are many studies on multi-level phase modulation schemes that transmit the signals in different phases.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the system using the A system, multiplexing is performed in the same frequency band in order to increase the channel capacity.
There is a problem that multiplexing is difficult only with the old sequence.

Further, in the CDMA system, it is desirable to use a spread code pattern having a small cross-correlation value in order to reduce the interference between the spread waves, but the combination is limited. Further, in a system such as the DS / QPSK system, different spreading code patterns are used for Ich and Qch respectively, but if both signal components cannot be completely separated after quadrature detection due to frequency offset or the like on the receiving side, I,
If the cross-correlation characteristics of the spread codes of Q and both channels are large, a problem arises in which they interfere with each other when detecting the correlation of each signal.

Regarding the channel capacity, it is possible to increase the number of multiplexes by lengthening the cycle length of the spreading code and increasing the spreading factor. However, in the case of practical application, it is difficult to increase the code period length because the spreading factor is limited by the conditions such as the relationship between the spreading bandwidth and the information transmission rate and the device operating speed.

In the CDMA system, the relationship between the number of multiplexes and the communication quality largely depends on the cross-correlation property between code patterns, and M series and Gold series have been studied as spread spectrum spread codes. For example,
Since the M-sequence has good autocorrelation characteristics, it is easy to find the peak of the correlation value, but it is known that the number of patterns that can be generated is small. Further, although the number of patterns that can be generated in the Gold series is larger than that in the M series, the cross-correlation characteristics are not good,
When multiplexed, the deterioration of communication quality is significant due to interference from other spread waves. Therefore, the number of channels that can be simultaneously communicated is limited.

On the other hand, recently, a method using an orthogonal code sequence having a good cross-correlation characteristic has been studied. In the orthogonal code sequence, when the orthogonality is maintained between the codes, they are uncorrelated with each other and a large number of multiplexes can be taken, but if the orthogonality is broken, the cross correlation is significantly deteriorated. Therefore, C
When used as a spreading code in a DMA system or the like, inter-code synchronization is required.

In the Hadamard sequence, which is one of the orthogonal code sequences, a Hadamard matrix of code length 2 ^{(n + 1)} is generated by performing Hadamard transformation of a 2 × 2 Hadamard matrix n times. As can be seen from the above, since one code pattern consists of repetition of several code patterns, the autocorrelation characteristic is poor, and there is a problem that synchronization acquisition and multipath separation are difficult.

[0012]

In order to solve the above-mentioned problems, the first spreading code generation method according to the present invention is a multi-level phase modulation method, in which spreading code patterns different between each phase have good autocorrelation characteristics. The number of multiplexes can be increased by using a code sequence and multiplying the code pattern of each phase by an orthogonal code sequence having a good cross-correlation characteristic to generate a spread code pattern.

The second spreading code generation method according to the present invention is a DS method using multi-level phase modulation, in which the maximum cross-correlation value in the spreading code sequence used is larger than other patterns. By combining each phase component, circulating these code patterns mutually, and applying a phase offset at the point where the cross-correlation value between the codes is minimized, it is possible to suppress the interference with other waves and to use each phase on the receiving side. It is possible to minimize the cross-correlation at the time of incomplete component separation. This utilizes the fact that the signals of the respective phase components are always synchronized and their cross-correlation values are constant.

[0014]

According to the first spreading code generation system of the present invention, it is possible to generate a spreading code sequence that makes use of the characteristics of both code sequences. That is, by assigning a code sequence having a good autocorrelation characteristic (here, a PN sequence) to different spreading codes for each phase component of the multilevel phase modulation method, and multiplying each code pattern by the same orthogonal code sequence, As a spread signal wave, interference with other waves is reduced. For example, in the case of a QPSK signal, Ich and Qch in a PN sequence are used.
It becomes possible to carry out separation. That is, one orthogonal code is assigned to one QPSK modulated wave.

At this time, if the inter-code synchronization is established, the orthogonal codes assigned to the signals using the same PN code pattern set for each phase component are not correlated with each other to reduce interference and increase the number of multiplexing. can do.

On the other hand, if code synchronization is not established, PN
Since the sequences are multiplied, deterioration of the cross-correlation characteristic is alleviated as compared with the case of only the orthogonal code sequence, and becomes almost the same as the cross-correlation characteristic of the conventional PN sequence. Similarly, the problem of difficulty in synchronization acquisition and multipath separation due to the low autocorrelation characteristic of the orthogonal code sequence is solved by the high autocorrelation characteristic of the PN sequence.

Further, combinations of patterns having small cross-correlation within a given spreading sequence are limited. However, when code patterns having a large cross-correlation value are cyclically crossed with each other and a phase offset is applied, the cross-correlation value fluctuates and may have a minimum value at an arbitrary offset point. Therefore, paying attention to the fact that each phase component of an arbitrary multi-level phase modulated wave is always code-synchronized, and
In the case where the signal separation of each phase component after receiving and detecting the own wave is incomplete, the combination of code patterns is used so that the cross-correlation with other modulated waves becomes relatively small by the spread code generation method of Also, it is possible to reduce the influence of mutual interference.

In addition, even if an arbitrary phase component receives interference from another diffused wave, the remaining phase components are uncorrelated, so that the interference is small and the possibility of malfunctioning in synchronization acquisition and maintenance is reduced. .

[0019]

(Embodiment 1) A first embodiment of the present invention will be described below with reference to the drawings. In the present embodiment, the QPSK method will be described as an example of the multi-level phase modulation method.

FIGS. 1 (a) and 1 (b) respectively show DS / s that realize the spread code generation method in the first embodiment of the present invention.
In the block connection diagram of the transceiver of QPSK, the transmission amplifier and the reception front end are omitted for explanation of the operating principle of each transceiver configuration.

As shown in the conceptual system diagram of FIG. 2, in the present embodiment shown in FIGS. 1A and 1B, the spreading factor is N times (N = 2 ⁿ : where n> 2 is an integer). The spreading code used is a Hadamard function sequence (Hadamard Function: hereinafter referred to as an HF code) having a code length N _w (N _w = 2 ^n-2 ) in an orthogonal code sequence, and a code pattern with a period of 2 ⁿ -1 in a PN sequence. Codes PN _i and PN _q having a code length N = 2 ⁿ added with 0 are set. H0～HN _w 2 is the code number of the pattern HF code, PN ₁ to PN _k represents different code patterns I configured with the orthogonal spreading code group of Q, respectively. Further, FIG. 3 shows the code synchronization relationship between the PN code and the HF code in this embodiment.

First, FIG. 1 (a) shows a transmission system device 10, in which 100 is a spread code generator, 110 is a QPSK coding circuit for QPSK coding input data, and 14
Numerals 1 and 142 are PNs that generate a PN code based on a clock
A code generator, 150 is an orthogonal code generator that generates an orthogonal code based on a clock. Reference numerals 131 and 132 denote multipliers for multiplying the orthogonal code output from the orthogonal code generator 150 by the PN code output from the PN code generators 141 and 142, respectively. Reference numerals 121 and 122 denote a QPSK code output from the QPSK encoding circuit 110 and a multiplier 131,
It is a multiplier for multiplying the output of 132. A quadrature modulation circuit 160 quadrature-modulates the output signals of the multipliers 121 and 122 based on the local signal generated from the local signal generation source 170. Reference numeral 180 is a wireless antenna for transmission.

In the above structure, first, the data input to the transmission system block 10 is QPSK encoded by the QPSK encoding circuit 110 and sent to the multipliers 121 and 122 as Ich and Qch signal sequences. On the other hand, in the spread code generator 100, the orthogonal code generator 150 generates the HF code at a rate 1/4 of the spread rate, and
The PN code generators 141 and 142 generate PN _i and PN _q having different code patterns at the spreading rate, and the multiplier 131 outputs PN _i and HF code, and the multiplier 132 outputs PN _q and H.
F codes are multiplied by code synchronization as shown in FIG. 3 to generate spread codes. The Ich and Qch data sent to the multipliers 121 and 122 are spread by the spreading code generated by the spreading code generation unit 100, orthogonally modulated by the orthogonal modulation unit 160, and then transmitted from the wireless antenna 180.

FIG. 1 (b) shows a receiving system device 20. Reference numeral 200 denotes a radio antenna for receiving the transmission signal transmitted from the radio antenna 180 shown in FIG. 1 (a), and 201.
Is a BPF (band pass filter). Reference numeral 210 denotes a quadrature detection circuit, which quadrature-detects the output signal of the BPF 201 based on the local signal generated from the local signal generation source 220. 231, 232 are LPFs (low pass filters), 2
41 and 242 are A / D converters 251 to 2 for converting the analog outputs of the LPFs 231 and 232 into digital signals.
54 is a digital correlator that obtains the correlation of the outputs of the A / D converters 241 and 242 by sliding correlation described later, 260 is a data decoding circuit that performs data demodulation based on the outputs of the digital correlators 251 to 254, and 340 is L.
This is a clock recovery circuit that recovers the clock of the transmission system device 10 from the outputs of the PFs 231 and 232. Reference numeral 300 denotes a despreading code generation circuit, and the despreading code generation circuit 300 is composed of the following elements.

Reference numerals 281 and 282 denote clock recovery circuits 340.
And a PN code generator 290 that generates a PN code based on the output of a synchronization acquisition circuit described later, and an orthogonal code generator 290 that generates an orthogonal code based on the outputs of the clock recovery circuit 340 and a synchronization acquisition circuit described below. Reference numeral 272 denotes an orthogonal code output from the orthogonal code generator 290 and each P
It is a modulo 2 multiplier that multiplies the PN code output from the N code generators 281 and 282.

Reference numerals 311, 312 denote correlators 251, 251, respectively.
A square circuit for squaring the output signal of 253, an adder 320 for adding the outputs of the squarers 311, 312, and a synchronization acquisition determination circuit 330 for determining the synchronization acquisition from the output of the adder 320.

In the above configuration, the DS / QPSK modulated wave generated and transmitted by the transmission system device 10 of FIG. 1A is received by the reception system device 20 by the wireless antenna 200, and BP is transmitted.
After passing through F201, the quadrature detection circuit 210 performs quadrature detection by the local signal from the local signal source 220. The Ich and Qch signals are output in parallel from the quadrature detection circuit 210, pass through the LPFs 231 and 232 respectively, undergo A / D conversion by the A / D converters 241 and 242, and then are input to the digital correlators 251 to 254, respectively.

In this embodiment, the digital correlators 251 to 2 are used.
Reference numeral 54 designates a sliding correlation, and four correlators are used to cope with phase rotation due to a frequency offset or the like. The synchronization acquisition circuit 330 determines the synchronization acquisition by the sum of squares of the outputs of the correlators 251 and 253. ing.
That is, these code patterns are circulated to each other and synchronized at the point where the cross-correlation value becomes the minimum.

In the despreading code generation circuit 300, the despreading code generation timing of the despreading code generation circuit 100 is controlled by the synchronization acquisition circuit 330.
Is the same as.

In this embodiment, the PN code length is four times the HF code length, and the clock number converters 150A and 290A are used to make the input clocks of the orthogonal code generators 150 and 290 1/4 rate. However, if N ≧ N _W, it may be multiplied by several times.

As described above, the transmitter / receiver 1 as in this embodiment
By configuring 0 and 20, it is possible to generate a spread code that makes use of the characteristics of the PN code and the HF code, and increase the number of multiplexes.

(Embodiment 2) Next, a second embodiment of the present invention will be described with reference to the drawings, taking the case of the DS / QPSK system as an embodiment.

FIG. 4 shows an embodiment for realizing a spread code generation method by orthogonal spreading in the second embodiment of the present invention, and specifically shows a case of 7-stage M sequence and code length 127. . In the figure, FIG. 4 shows the code patterns of each of the _nine codes C _{1 to} C ₉ in the 7-stage M sequence,
It is assumed that the code pattern state in the figure is a state in which there is no phase offset (the initial values of the registers of the code generator are all 1).

[0034]

[Table 1]

Table 1 shows the maximum value of cross-correlation between the individual patterns shown in FIG. From the table, even if the code patterns are in the same M sequence, such as C ₁ -C ₅ and C ₁ -C ₇ , the maximum value of cross-correlation varies depending on the combination. Therefore, the combination of large code patterns maximum of the cross-correlation _{(C 1 -C 5), (} C 2 -C 6),
(C ₃ -C _7), respectively Ich a (C ₄ -C _8), Qch
It is decided to use as an orthogonal spreading code set of, and a phase offset is applied to one code pattern in each code set,
The cross-correlation value is the minimum value that can be taken by the combination of the codes. FIG. 5 shows a specific example of the orthogonal spreading code set generated in this embodiment based on (Table 1). For example, in the orthogonal spreading code set (C ₁ -C ₅ ), the cross-correlation value of 2 codes is set to 1 by multiplying C ₅ by a phase offset of 7 chips.

As described above, according to the present embodiment, patterns having a large cross-correlation are combined as orthogonal spreading codes and a phase offset is applied, so that even if both the I and Q signal components cannot be completely separated on the receiving side. Interference can be reduced. Furthermore, the cross-correlation with other waves can be made relatively small,
Since the other can be detected even if one of the channels receives interference, the possibility of malfunctioning is reduced as compared with the conventional method.

[0037]

As described above, according to the present invention, a code sequence having a good autocorrelation characteristic is assigned to different spreading codes for each phase component, and the code pattern of each phase is multiplied by the same orthogonal code sequence. The interference with the wave is reduced and the PN
It becomes possible to perform separation between phases in a series.

When the signals between the phases are always code-synchronized, patterns having a large cross-correlation are combined as spread codes to apply a phase offset, so that the cross-correlation with other waves is relatively small. Moreover, even if the separation of the signal components of each phase of the own wave is incomplete, the influence of mutual interference can be reduced. Further, even if an arbitrary phase component receives interference from another wave, the remaining phase components are uncorrelated, so that the possibility of malfunction in synchronization acquisition and maintenance can be reduced.

[Brief description of drawings]

FIG. 1 is a block connection diagram of a DS / QPSK transceiver that realizes a spread code generation system according to a first embodiment of the present invention.

FIG. 2 is a conceptual diagram of a system system in the same DS / QPSK transceiver.

FIG. 3 is a timing relationship diagram between PN code and HF code in the same DS / QPSK transceiver.

FIG. 4 is a code pattern diagram showing a concept of a spread code generation system according to a second embodiment of the present invention.

FIG. 5 is a code pattern diagram showing the concept of a spread code generation method according to the second embodiment of the present invention.

[Explanation of symbols]

 10 transmission system device 100 spreading code generation unit 110 QPSK coding circuit 121, 122 multiplier 131, 132 multiplier 141, 142 PN code generator 150 orthogonal code generator 160 orthogonal modulation circuit 170 local signal source 180 wireless antenna 20 reception System device 200 Radio antenna 201 BPF 210 Quadrature detection circuit 220 Local signal 231, 232 LPF 241, 242 A / D converter 251-254 Digital correlator 260 Data decoding circuit 271, 272 Multiplier 281, 282 PN code generator 290 Quadrature code Generator 300 Despreading code generator 311, 312 square circuit 320 Adder 330 Synchronization acquisition determination circuit 340 Clock recovery circuit

Claims (3)

[Claims] 1. A multi-valued phase using a different code pattern in an arbitrary code sequence for each phase component when performing direct spread spectrum communication using a code division multiple access method having a plurality of terminals. A spreading code generation method that uses a modulation method to generate a spreading code by multiplying each spreading code corresponding to each phase component by the same code pattern in an arbitrary orthogonal code sequence. 2. A multi-level phase modulation method using different code patterns in an arbitrary code sequence for each phase component when performing direct spread spectrum communication using a code division multiple access method having a plurality of terminals. , A combination of code patterns having a large maximum cross-correlation value in the code sequence is selected, each code pattern is assigned to the spread code of each phase component, and the cross-correlation value of these code patterns takes the minimum value. A spreading code generation method that generates a spreading code for multi-level phase modulation in which mutual patterns are circulated up to a point. 3. A multi-level phase modulation method using different code patterns in arbitrary code sequences for each phase component when performing direct spread spectrum communication using a code division multiple access method having a plurality of terminals. , A combination of code patterns having a large maximum cross-correlation value in the code sequence is selected, each code pattern is assigned to the spread code of each phase component, and the cross-correlation value of these code patterns takes the minimum value. After generating a multi-level phase modulation spreading code in which mutual patterns are circulated up to the point, each spreading code corresponding to each phase component is multiplied by the same code pattern in an arbitrary orthogonal code sequence. A spread code generation method for generating.