Spread spectrum communication system

Abstract

In a spread spectrum communication system, in which correlation output is obtained by giving a correlator a sender side output code and a receiver side output code, communication channels obtained by dividing the whole channel by using GOLD codes as the sender and receiver side output codes are used and the GOLD codes are constructed by adding preferred pairs of the two m sequences modulo 2.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A GOLD code generating system used in a spread spectrum communication system, in which a correlation output is obtained by giving a correlator a sender side output code and a receiver side output code, comprising:

means for generating a first m sequence u and a second m sequence v at the sender side;

sender side control means for generating a sender side GOLD code which is a spreading code and which is an element of a set of GOLD codes G(u,v) where

G(U,v)={u,v,u.sym.v,u.sym.Tv, . . . , u.sym.T.sup.N-1 v}

and where

T: state transition matrix of v

N: code length of each sequence in G(u,v);

means for generating image codes u and vof said first and second m sequences at the receiver side; and

receiver side control means for generating a receiver side GOLD code which is a spreading code and which is an element of a set of GOLD codes G(u,v) where

G(u,v)={u,v,u.sym.v,u.sym.T.sup.N-1 v, . . . , u.sym.Tv}.

2. A system according to claim 1, including a surface acoustic wave convolver which is said correlator and has two inputs to which are respectively applied said sender side GOLD code and said receiver side GOLD code.

Description

FIELD OF THE INVENTION

This invention relates to a spread spectrum communication (hereinbelow abbreviated to SSC) system permitting to obtain correlation output by means of a sender side output code and a receiver side output code.

BACKGROUND OF THE INVENTION

As conditions for the spreading code, which can be used in an SSC system, the followings can be enumerated:

(i) that a large number of communication channels can be obtained;

(ii) that the mutual correlation value between the codes is small;

(iii) that the side lobe value of the self correlation value of the codes themselves is small;

and so forth. As a code satisfying such conditions the GOLD code generated by using preferred pairs of maximum length linearly occurring code sequences (hereinbelow abbreviated to m sequence) can be cited.

OBJECT OF THE INVENTION

However no example, in which the GOLD code stated above is applied as the spreading code in an SSC system using surface acoustic wave (hereinbelow abbreviated to SAW) convolvers, is known heretofore and in addition the correspondence relation between the communication channels obtained by dividing the whole channel by means of the GOLD code and the preferred pairs of the m sequences used for generating the GOLD code is not clearly known.

The object of this invention is to provide a method for obtaining the GOLD code used on the sender and receiver sides in an SSC system permitting to obtain means for dividing the communication channel, when the GOLD code stated above is used as the spreading code in an SSC system using SAW convolvers.

SUMMARY OF THE INVENTION

In order to achieve the object described above, an SSC system for obtaining a correlation output by the sender side output code and the receiver side output code according to this invention utilizes communication channels obtained by dividing the whole channel by means of the GOLD code as the sender and receiver side output codes.

The GOLD code stated above is constructed by adding preferred pairs of two m sequences modulo 2.

In a preferred form of realisation the sender side code described above is a spreading code obtained by using an set of GOLD codes generated from two m sequences {u, v}, which is represented by the following formula:

G(u,v)={u,v,u.sym.v,u.sym.Tv, . . . , u.sym.T.sup.(N-1 V}

where

T: state transition matrix of v

N: code length of each sequence in G(u,v)

and the receiver side code is a spreading code obtained by using

G(u,v)={u,v,u.sym.v,u.sym.T.sup.N-1 v, . . . , u.sym.Tv}

where u and v represent image codes of u and v, respectively (time-inverted m sequences of u and v, respectively).

In the m sequences having a code length N(=2.sup..eta. -1, n being the number of stages of the shift register in the m sequence generator) the mutual correlation value R.sub.c takes the following three values. The pairs of codes are called preferred pairs of the m sequence, which have good correlation characteristics. ##EQU1## where t(n) is represented by;

t(n)=1+2.sup.[(n+2)/2] ( 2)

where [ ] is a Gauss's symbol.

For example, among 18 m sequences of N=127 there are 6 preferred pairs and R.sub.c is as follows; ##EQU2##

A sequence obtained by adding m sequences u and v modulo 2 is called a GOLD code G(u,v). This can be schematically represented as indicated in FIG. 2.

When the initial phase of the m sequences is taken into account, a set G(u,v) of GOLD codes produced by the two m sequences {u, v} can be represented by the following equation (3);

G(u,v)={u,v,u.sym.v,u.sym.Tv, . . . , u.sym.T.sup.N-1 v} (3)

where

T: state transition matrix of v

N: code length of each sequence in G(u,v)

In general, the number of sequences .alpha. contained in G(u,v) is given by

.alpha.=N+2=2.sup..eta. +1 (4)

For example, when N=127, .alpha.=129.

{u, v} in Eq. (3) are adopted as preferred pairs of the m sequence.

Now, supposing that two sequences y and z are

y,z.epsilon.G(u,v), (5)

the following properties are known.

(1) For l, the mutual correlation value of y and z .theta..sub.y,z (l) can be represented as follows; ##EQU3##

(2) The side lobe value .theta..sub.y (l) of the self correlation function is; for l.notident.0 mod. N ##EQU4##

That is, .theta..sub.y,z (l) and .theta..sub.y (l) are in accordance with R.sub.c given by Eq. (1) and consequently the set of the GOLD codes generated by preferred pairs of the m sequence show good correlation characteristics.

As explained above, it can be recognized that the GOLD codes are useful as spreading codes satisfying the conditions (i).about.(iii).

That is, it is possible to assign each of the sequences in Eq. (3) u, v, u.sym.v, . . . , u.sym.T.sup.N-1 v as one communication channel.

Now, in an SSC system using SAW convolvers a pair of sequences, which are in an image relation to each other, are necessary and thus, in the case where Eq. (3) is used as the sequence for the sender side, the sequence for the receiver side is as follows;

G(u,v)={u,v,u.sym.v,u.sym.T.sup.N-1 v, . . . , u.sym.Tv} (8)

where u and v are image codes of u and v, respectively. That is, the communication is effected by using corresponding sequences in { } in Eqs. (3) and (8).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the construction of an m sequence generator according to this invention used on the sender and receiver sides;

FIG. 2 is a scheme indicating the generation of an m sequence;

FIGS. 3 and 4 are block diagrams illustrating the principal construction of the modular type m sequence generator;

FIGS. 5 and 6 are block diagrams illustrating the construction of the simple construction type m sequence generator;

FIG. 7 is a scheme showing the phase relation between the sender and the receiver side m sequences;

FIG. 8 is a flow chart indicating the process for obtaining the initial phase information in the m sequence generator;

FIG. 9 is a block diagram showing a concrete example of the m sequence generator and the control circuit therefore;

FIG. 10 indicates a switching gate circuit; and

FIG. 11 is a timing chart for the code generator.

DETAILED DESCRIPTION

FIG. 1 illustrates the construction of a GOLD code generating portion used in the sender or the receiver and TABLE 1 shows an example of the communication channel division (in the case where the GOLD code length is 127).

                  TABLE 1
    ______________________________________
             Sender side output
                             Receiver side output
    Channel  sequence        sequence
     No.      PNG 1    PNG 2
                                  ##STR1##
                                         ##STR2##
    ______________________________________
    0        u        L          -u     L
    1        L        v          L      -v
    2        u        v          -u     -v
    3        u        Tv         -u     T.sup.126 -v
    4        u        T.sup.2 v  -u     T.sup.125 -v
    .        .        .          .      .
    .        .        .          .      .
    .        .        .          .      .
    128      u        T.sup.126 v
                                 -u     T-v
    ______________________________________

• Inventors
  Hamatsu, Masahiro; Kurihara, Takao;
• Assignee
  Clarion Co., Ltd. (Tokyo, JP)
• Published
  Aug-29-1989
• Current US Classes:
  375/142
  380/34
• Application #
  107378
• International Classes
  H01L 009/00
• Field of Search
  375/1 380/34
• Examiner
  Cangialosi; Salvatore
• Agent
  Flynn, Thiel, Boutell & Tanis
• US Patent References:
  4538281
  4689626