CN1121760C - Design method for frequency-extending sequential code blocks for non-interference quasi-synchronous CDMA communication system - Google Patents

Abstract

The present invention discloses a signal design technology for a non-interference quasi-synchronous CDMA communication system. A spread spectrum sequential code block is created by non-periodic mutual supplementing sequence sets, and moreover, the spread spectrum sequential code block is a sequence having the zero correlation area characteristics. Simultaneously, a spread spectrum modulation signal contains an additional protective code chip. When the maximal synchronous error of the system and the maximal multi-path of a channel extend in a time delay way in a defined range, the non-interference transmission is realized. The parameters of the spread spectrum sequential code block and the system efficiency can be regulated in a real time way according to the actual factors, and furthermore, the parameters of the spread spectrum sequential code block can be flexibly selected. Thus, the power control and synchronous requirements of the CDMA communication system can be reduced, and simultaneously, the system realizing complexity can also be lowered.

Description

Non-interference quasi-synchronous CDMA communication system spread spectrum sequence code group generation method

(1) technical field

The present invention relates to a kind of direct sequence spread spectrum wireless communication technology, particularly work in a kind of noiseless CDMA communication frequency expansion sequence code generating method and correlation technique thereof under the accurate method of synchronization.

(2) background technology

The arrival of information age makes people propose new demand to communication system.Future broadband wireless communication systems should have characteristics such as two-forty, high-quality and high flexibility.Compare with traditional frequency division multiple access (FDMA), time division multiple access wireless multiple access technology such as (TDMA), code division multiple access (CDMA) technology has significant advantage, as soft capacity, anti-multipath and antijamming capability etc.CDMA communication has become the one preferred technique of next generation mobile communication system.

The cellular wireless mobile communication system has local noise (LN), intersymbol interference (ISI), multiple access interference (MAI) and the four kinds of interference such as (ACI) of adjacent area interference usually.For code division multiple address communication system, except local noise can not be eliminated, other three kinds of interference all can be by reducing the spread spectrum code character of making good use of or eliminate, thereby improve the capacity or the performance of system.

In order to reduce the interference in the code division multiple address communication system, people have proposed synchronous code division multiple access communication system, and the Walsh (Walsh) of employing quadrature or A Daqi (Adachi) sign indicating number are as spread spectrum sequence code group.For mobile communication system, the accurately assurance not too easily synchronously of up link, and also the multipath transmisstion of wireless channel makes system synchronization become difficult more.The intersymbol their cross correlation of Walsh or its yard of A Da only is zero synchronously the time, when between code character when asynchronous cross correlation value non-vanishing, just exist multiple access to disturb.Because the existence of near-far interference will further reduce the performance of synchronous code division multiple access communication system, and power system capacity is restricted.In order to alleviate the influence of near-far interference as far as possible, in utility systems such as IS-95, adopted complicated power control techniques.

In order to reduce the requirement of system to synchronization accuracy, the someone proposes synchronously accurate or near-synchronous code division multiple address communication system in recent years, make the synchronous error of system be controlled within the certain limit (as one or several chip period), and on spreading code design, launched research work.More existing at present relevant patents.As Chinese patent PCT/CN98/00151 (CN1175828A), adopt a kind of ternary spread spectrum sequence code group with zero correlation block; Japan Patent TY99002 (11-023252) adopts a kind of binary spread spectrum sequence code group with zero correlation block; Japan Patent PCT/JP97/03272 (JP271858/96) adopts a kind of spread spectrum sequence code group with pectination frequency spectrum, or the like.

In the ideal case, the spread spectrum sequence code group of using in the code division multiple address communication system should have following correlation properties: the auto-correlation function of each frequency expansion sequence sign indicating number should be an impulse function, and promptly except that zero time delay, its value should be zero everywhere; The cross-correlation function value of every pair of frequency expansion sequence sign indicating number should be zero everywhere.Unfortunately, no matter be binary, polynary or sequence of complex numbers, the verified spread spectrum sequence code group with this desirable correlation properties is non-existent, promptly to given sequence length N and number M, maximum auto-correlation function limit peak value and maximum cross correlation functional value can not be zero simultaneously, and they are subjected to the restriction of some theoretical limits, when requiring one to diminish, another must increase, as Weir strange (Welch) limit, this De Nikefu (Sidelnikov) limit etc.

Though can not design spread spectrum sequence code group, can design the zero correlation block or the low relevant spread spectrum sequence code group of distinguishing that near zero time delay, have certain-length with desirable auto-correlation and their cross correlation.This respect has had some paper publishings.For example, " A generalized QS-CDMA system and the designof new spreading codes, IEEE Trans.on Vehicular Technology; vol.47; no.4, pp.1268-1275, November 1998 (a kind of popularization QS-CDMA system and novel spreading code design; IEEE vehicle technology transactions; the 47th volume, the 4th phase, 1268-1275 page or leaf; in November, 1998) " proposed the method that a kind of design has the spread spectrum sequence code group in low relevant district; " A class of binarysequences with zero correlation zone; IEE Electronics Letters, vol.35, no.10; pp.777-779; May 1999 (class has the binary sequence of zero correlation block, IEE electronics wall bulletin, the 35th volume; the 10th phase; 777-779 page or leaf, in May, 1999) " provided a kind of binary complementary series that utilizes to designing the method for the spread spectrum sequence code group with zero correlation block; " Lower bounds on thecorrelation of sequence set with low or zero correlation zone; Proceedingsof WPMC ' 99; pp.343-345; Amsterdam; The Netherlands; September 1999 (the correlation lower limit of low/zero-correlation zone sequence, WPMC ' 99 international conference collected works, the 343-345 page or leaf, Amsterdam, Holland, in September, 1999) ", provided theoretical limits about spread spectrum sequence code group with zero correlation block or low relevant district.

For having the individual long spread spectrum sequence code group { S of N of being of M _i, i=1,2 ..., M} is if its zero correlation section length is Z _CZ, this spread spectrum sequence code group just is called ZCZ-(N, M, a Z so _CZ) the sequence code character.Z wherein _CZ=min{Z _ACZ, Z _CCZ, Z _ACZWith Z _CCZBe respectively the zero auto-correlation district and zero cross-correlation section length of this sequence code character, it is defined as

Z _ACZ＝max{T：θ _rr(τ)＝0，r，τ≠0，|τ|≤T}

Z _CCZ=max{T: θ _Rs(τ)=0, r ≠ s, τ, | τ |≤T} is θ wherein _Rs(τ) be sequence S _rWith S _sPeriodic cross-correlation functional value at time delay τ.

(3) summary of the invention

The objective of the invention is to propose a kind of flexible, simple non-interference quasi-synchronous CDMA communication system signal creating method, make code division multiple address communication system realize noiseless transmission under certain condition, thereby reduce system to power control and synchronous requirement, the reduction system realizes complexity.

The present invention finishes according to following technical scheme:

In quasi-synchronous CDMA communication system, do not need the synchronous of very strictness between system base-station and each mobile subscriber.Thereby realizing simply, this system is that near the cross-correlation function value of in the synchronous error scope (zero time delay) is as far as possible little to the requirement of employing spread spectrum sequence code group correlation properties.In addition, because the wireless multipath transmission that mobile environment exists, system also requires near the auto-correlation function value the frequency expansion sequence sign indicating number zero time delay as far as possible little.The present invention has provided a kind of generation method with spread spectrum sequence code group of zero correlation block, for realizing that in quasi-synchronous CDMA communication system noiseless transmission provides a kind of effective means.

The spread spectrum sequence code group that adopts in the system of the present invention is constructed in two steps, at first generates one group of quadrature complementary sequence set aperiodic CS (2 by computer search or recursion method ^NM, 2 ^NL), M＞2, again by this aperiodic complementary sequence set form by the method construct that connects or connect double cutting in back with delegation's sequence order.

Spreading code proposed by the invention is based on one group of quadrature complementary sequence set aperiodic.This quadrature complementary sequence set aperiodic is to be L by sub-sequence length, the complementary series number be M complementary sequence set CS aperiodic (L, M) the recurrence structure forms as follows:

1. obtain M quadrature complementary sequence set CS aperiodic (M, L): { A _1i, i=1,2 ..., M}, { A _2i, i=1,2 ..., M) ..., { A _Mi, i=1,2 ..., M}, each sequence length is L, and is arranged as with matrix form: ${\mathrm{\&Delta;}}^{\left(0\right)}=\left[\begin{array}{cccc}{A}_{11}& A_{12}& \mathrm{\&Lambda;}& A_{1M}\\ A_{21}& A_{22}& \mathrm{\&Lambda;}& A_{2M}\\ M& M& M& M\\ A_{M1}& {\mathrm{<figure-callout\; id="2"\; label="A\; M"\; filenames="C00103282.800141.png"\; state="\{\{state\}\}">A</figure-callout>}}_M& \mathrm{\&Lambda;}& A_{\mathrm{MM}}\end{array}\right]$ Wherein the capable j of i is listed as an elements A _IjRepresent i j the sequence that aperiodic, complementary series was concentrated.The matrix Δ ⁽⁰⁾Dimension be M * M (be M capable M row).Therefore this matrix comprises M sequence sets, and it is the sequence of L that M length is arranged in each sequence sets.The initial matrix Δ ⁽⁰⁾Can obtain or obtain by computer search by the recursion method structure.

2. generate one group of quadrature complementary sequence set aperiodic CS (2 by recursion method in the n step (n 〉=1) ⁿM, 2 ⁿL), recursion Δ ⁽ⁿ⁾Be defined as: ${\mathrm{\&Delta;}}^{\left(n\right)}=\left[\begin{array}{cc}{\mathrm{\&Delta;}}^{(n-1)}{\mathrm{\&Delta;}}^{(n-1)}& (-{\mathrm{\&Delta;}}^{(n-1)}){\mathrm{\&Delta;}}^{(n-1)}\\ (-{\mathrm{\&Delta;}}^{(n-1)}){\mathrm{\&Delta;}}^{(n-1)}& {\mathrm{\&Delta;}}^{(n-1)}{\mathrm{\&Delta;}}^{(n-1)}\end{array}\right]$ Wherein ,-matrix that forms after each element negate in the Δ representing matrix Δ.If Δ ₁With Δ ₂Be the matrix that two dimensions equate, and the corresponding sequence length of each element is identical, uses Δ ₁Δ ₂The expression Δ ₁In each element and Δ ₂In each order of elements connect the matrix that the back forms.Above-mentioned recursive procedure process can repeat unlimited.Resulting matrix Δ ⁽ⁿ⁾Comprise 2 ⁿComplementary sequence set aperiodic of M quadrature has 2 in each sequence sets ⁿM length is 2 ⁿThe sequence of L.

The Δ that obtains according to said process ⁽ⁿ⁾, can be by obtaining having the spread spectrum sequence code group of zero correlation block with the method construct of delegation's sequence order connection (n 〉=0) or connection double cutting in back (n 〉=1).That is:

Method 1: the Δ that said process is obtained ⁽ⁿ⁾Each the row each sequence order connect to form sequence, then a Δ ⁽ⁿ⁾All M _n=2 ⁿZCZ-(4 of the capable formation of M ⁿLM, 2 ⁿM, 2 ^N-1L) sequence code character.

Method 2: when n＞1, the Δ that said process is obtained ⁽ⁿ⁾Be divided into two equal parts, i.e. Δs ⁽ⁿ⁾=[Δ _L| Δ _R], Δ wherein _LWith Δ _RBe respectively Δ ⁽ⁿ⁾About half part, then Δ _L(Δ _R) all row constitute a ZCZ-(2 ^2n-1LM, 2 ⁿM, 2 ^N-2L) sequence code character.

For example, given M=4, L=3 can be arranged as complementary sequence set CS aperiodic (4,3) of the quadrature of correspondence with matrix form: ${\mathrm{\&Delta;}}^{\left(0\right)}=\left[\begin{array}{cccc}---& -+-& +--& +--\\ --+& --+& +++& +-+\\ +-+& ---& +--& -++\\ --+& ++-& -+-& +++\end{array}\right]$

So, can obtain Δ by method 1 ⁽¹⁾, and Δ ⁽¹⁾All row constitute a ZCZ-(48,8,3) sequence code characters, that is:

S1＝{-------+--+-+--+--+--+--+++---+-+-+--+++---+++--}

S2＝{--+--+--+--++++++++-++-+++---+++---+---+++-+-+-+}

S3＝{+-++-+------+--+---++-++-+-+-++++----+++--+---++}

S4＝{--+--+++-++--+--+-++++++++---+--+++-+-+-+----+++}

S5＝{+++---+-+-+--+++---+++---------+--+---++--+--+--}

S6＝{++---+++---+---+++-+-+-+--+--+--+--++++++++-++-+}

S7＝{-+-+-++++----+++--+---+++-++-+------+--+---++-++}

S8＝{++---+--+++-+-+-+----+++--+--+++-++--+--+-++++++}

Equally, by method 2, Δ ⁽²⁾All row of a left side (right side) half part then constitute a ZCZ-(96,16,3) sequence code character, as shown in Figure 1.

For quasi-synchronous CDMA communication system of the present invention, in order to make full use of the excellent specific property of above-mentioned spreading code, modulated spread spectrum signal is made up of with the product of corresponding frequency expansion sequence sign indicating number and the supplementary protection chip at head and the tail two ends each signal element.The supplementary protection number of chips (G) at this modulated spread spectrum signal head and the tail two ends is desirable to be not more than zero correlation section length (Z in the spread spectrum sequence code group _CZ) arbitrary value.Owing to adopted this special spread spectrum modulation signal format, if between signal relative time delay within the supplementary protection chip lengths, remain quadrature between each frequency expansion sequence sign indicating number, thereby can eliminate because multipath effect or multiple access insert the interference that is brought.

Beneficial effect of the present invention:

Maximum synchronous error of system and channel maximum multipath delay spread can realize noiseless transmission within the scope of defined the time.The parameter of spread spectrum sequence code group and system effectiveness can be adjusted in real time according to practical factor, choose flexibly.Reduced code division multiple address communication system to power control and synchronous requirement, reduced system and realized complexity.

(4) description of drawings:

Fig. 1 is the spread spectrum sequence code group example ZCZ-(96,16,3) with zero correlation block of the present invention.

Fig. 2 is periodic auto-correlation function figure of the present invention (is example with sequence among Fig. 1 1).

Fig. 3 is periodic auto-correlation function figure of the present invention (is example with sequence among Fig. 1 2).

Fig. 4 is periodic cross-correlation functional arrangement of the present invention (is example with sequence 2 with sequence among Fig. 1 1).

Fig. 5 is the signal format figure of the modulated spread spectrum signal of direct sequence CDMA communication system.

Fig. 6 is the modulated spread spectrum signal format chart of each code element correspondence among the present invention.

Fig. 7 is the signal transmission schematic diagram of cellular CDMA communication system down link.

Fig. 8 is the signal transmission schematic diagram of cellular CDMA communication system up link.

(5) embodiment:

Table 1 has been described the restriction relation between the spread spectrum sequence code group parameter with zero correlation block.

Below in conjunction with accompanying drawing the embodiment of the invention is described in detail:

Referring to Fig. 1, it is a ZCZ-who is example with 16 frequency expansion sequences (96,16, a 3) sequence code character, can use for 16 users.Each sequence is formed by 96+1 or-1.

Referring to Fig. 2 and Fig. 3, they are respectively the periodic auto-correlation function figure of sequence 1 and sequence 2 among Fig. 1.Other sequence has the periodic auto-correlation function of all fours, and promptly time delay is ± 1, ± 2, and ± 3 o'clock, its periodic auto-correlation function value was zero.

Referring to Fig. 4, it is the periodic cross-correlation functional arrangement of sequence 1 and sequence 2 among Fig. 1.Other arbitrary sequence is to having the periodic cross-correlation function of all fours, and promptly time delay is 0, ± 1, and ± 2, ± 3 o'clock, its periodic cross-correlation functional value was zero.

Any spread spectrum sequence code group that other has zero correlation block of the present invention all has the periodic auto-correlation function and the periodic cross-correlation function of all fours.Be characterized in:

The periodic auto-correlation function of arbitrary sequence has zero correlation block in zero displacement both sides, and arbitrary periodic cross-correlation function to sequence has zero correlation block in zero displacement both sides (comprising zero displacement) in the spread spectrum sequence code group.

Sequence length N, sequence number M, zero correlation section length Z in the spread spectrum sequence code group _CZSatisfy and concern 2MZ _CZ=N.

Zero auto-correlation district equates that with zero cross-correlation section length Z is promptly arranged in the spread spectrum sequence code group _ACZ=Z _CCZ=Z _CZ

Referring to Fig. 5, it is the modulated spread spectrum signal format chart of conventional direct sequence CDMA communication system.Wherein received signal R (t) is by useful signal V _S(t) and interference signal V _X(t) form, they are to modulate the A that corresponding binary information bit obtains ,-A, B ,-B by the spread-spectrum signal of sequence A and B correspondence respectively.Since the not exclusively synchronous or multipath effect of system, V _S(t) and V _X(t) has τ in relative time delay between.Suppose that receiving terminal can make despread signal V by conventional method _D(t) with desired transmitting terminal signal V _S(t) synchronous, but V _D(t) and V _X(t) be asynchronous in itself, thereby the correlation function nonzero value will bring inevitable interference aperiodic in the demodulating process.

For overcoming by the interference that causes relative time delay, system works is in the accurate method of synchronization, and promptly by the base station pilot signal transmitted, the transmission that makes each travelling carriage in the sub-district is controlled at the transmission of each travelling carriage in certain scope as far as possible synchronously relative time delay.In order to eliminate the influence of correlation function aperiodic, can in modulated spread spectrum signal, add the protection chip.

Referring to Fig. 6, it is the modulated spread spectrum signal format chart of each code element correspondence.A wherein _CLength be NT _C(T _CBe chip period), take from ZCZ-(N, M, Z by one _CZ) spread-spectrum signal of sequence correspondence of sequence code character forms, as this user's signature signal.A _HWith A _TLength be GT _C, be respectively A _CG the chip at middle head and the tail two ends is as the protection chip.

The supplementary protection number of chips (G) at head and the tail two ends is desirable in the described modulated spread spectrum signal is not more than zero correlation section length (Z in the spread spectrum sequence code group _CZ) arbitrary value, when relative time delay between signal was within the supplementary protection chip lengths, described frequency expansion sequence sign indicating number was a quadrature.

Referring to Fig. 7, it is the signal transmission schematic diagram of cellular CDMA communication system down link, all signals from the base station to the travelling carriage synchronous transmission, so useful signal V _S(t) and interference signal V _X(t) arrive receiving terminal simultaneously.But, since the existence of multipath effect, V _S(t) and V _X(t) the signal V behind time-delay τ ' _S' (t) and V _X' (t) just become interference in the system.As long as τ ' is no more than GT _C, system interference is only relevant with periodic correlation function.If adopt ZCZ-(N, M, Z _CZ) the sequence code character is as each user's signature address sequence, and satisfy G≤Z _CZ, system realizes noiseless transmission.

Referring to Fig. 8, it is the signal transmission schematic diagram of cellular CDMA communication system up link, because travelling carriage can not be accomplished fully synchronously interference signal V to the signal of base station transmits _X(t) with useful signal V _S(t) non-vanishing their cross correlation has just caused the interference in the system between.But because system works is in the accurate method of synchronization, the transmission τ in relative time delay of each travelling carriage in the sub-district " is controlled in certain scope.As long as τ " is no more than GT _C, system interference is only relevant with periodic correlation function.If adopt ZCZ-(N, M, Z _CZ) the sequence code character is as each user's signature address sequence, and satisfy G≤Z _CZ, system realizes noiseless transmission.

Therefore; have the signature address sequence of the spread spectrum sequence code group of zero correlation block as each user by use; and, just can realize the noiseless transmission of quasi-synchronous CDMA communication system up link and down link at the suitable protection chip of modulated spread spectrum signal adding.

Referring to table 1, have between the parameter of spread spectrum sequence code group of zero correlation block and have certain trade-off relation, be i.e. 2MZ _CZ=N.As can be seen, when fixed sequence program length, if the system channel condition is good, little to the zero correlation section length requirement, the spread spectrum sequence code group that just can generate big figure is used simultaneously for a large number of users; If system channel condition variation just can suitably reduce the number of users that system can hold simultaneously, generate the big spread spectrum sequence code group of zero correlation section length ,-correspondingly increase the protection chip of modulated spread spectrum signal simultaneously, to deal with the channel conditions of deterioration.

Table 1

Claims (2)

1. the signal creating method of a non-interference quasi-synchronous CDMA communication system, it is characterized in that: the spread spectrum sequence code group that adopts in this system is L by sub-sequence length, the complementary series number is complementary sequence set CS (L aperiodic of M, M), step recurrence structure forms as follows: (1) obtain M quadrature complementary sequence set CS aperiodic (M, L): { A _1i, i=1,2 ..., M}, { A _2i, i=1,2 ..., M} ..., { A _Mi, i=1,2 ..., M}, each sequence length is L, and is arranged as with matrix form: ${\mathrm{\&Delta;}}^{\left(0\right)}=\left[\begin{array}{cccc}{A}_{11}& A_{12}& \mathrm{\&Lambda;}& A_{1M}\\ A_{21}& A_{22}& \mathrm{\&Lambda;}& A_{2M}\\ M& M& M& M\\ A_{M1}& A_{M2}& \mathrm{\&Lambda;}& A_{\mathrm{MM}}\end{array}\right]$ (2) go on foot at n by recurrence method, generate one group of quadrature complementary sequence set aperiodic CS (2 ⁿM, 2 ⁿL) n is 〉=1 positive integer, the recursion Δ ⁽ⁿ⁾Be defined as: ${\mathrm{\&Delta;}}^{\left(n\right)}=\left[\begin{array}{cc}{\mathrm{\&Delta;}}^{(n-1)}{\mathrm{\&Delta;}}^{(n-1)}& (-{\mathrm{\&Delta;}}^{(n-1)}){\mathrm{\&Delta;}}^{(n-1)}\\ (-{\mathrm{\&Delta;}}^{(n-1)}){\mathrm{\&Delta;}}^{(n-1)}& {\mathrm{\&Delta;}}^{(n-1)}{\mathrm{\&Delta;}}^{(n-1)}\end{array}\right]$

The modulated spread spectrum signal of this system is made up of with the product of corresponding frequency expansion sequence sign indicating number and the supplementary protection chip at head and the tail two ends each code element, and wherein supplementary protection number of chips G is desirable is not more than zero correlation section length Z in the spread spectrum sequence code group _CZArbitrary value,

The Δ that obtains according to said process ⁽ⁿ⁾, when n 〉=0, can be by will connecting with delegation's sequence order, or when n 〉=1, the method construct that connects double cutting afterwards obtains having the spread spectrum sequence code group of zero correlation block,

Sequence length N, sequence number M, zero correlation section length Z in the described spread spectrum sequence code group _CZThe satisfied 2MZ that concerns of each parameter _CZ=N,

Zero auto-correlation section length Z in the described spread spectrum sequence code group _ACZ, zero cross-correlation section length Z _CCZ, zero correlation section length Z _CZThe satisfied Z that concerns of each parameter _ACZ=Z _CCZ=Z _CZ

2. according to the signal creating method of right 1 described a kind of non-interference quasi-synchronous CDMA communication system, it is characterized in that: when relative time delay between signal was within the supplementary protection chip lengths, described frequency expansion sequence sign indicating number was a quadrature.

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