CN1449144A - CDMA frequency spreading and despreading method and transmitter, receiver and communication system - Google Patents

Abstract

The present invention relates to a new code division multiple access (CDMA) system, including a new method of spreading and de-spreading spectrum for code division multiple access (CDMA), and its relevant transmitter, receiver and communication system. The spread spectrum code in the spread spectrum method of this invention is the traditional CDMA code added to a cycle protecting code in order to eliminate signal disturbance when de-spreading. Correspondingly the de-spread spectrum method includes the step of eliminating cycle protecting bits. At the same time, solving the channel reverse matrix according to the characteristics of the channel, and eliminating signal disturbance by matrix multiplication.

Description

CDMA spread spectrum and despreading method and transmitter thereof, receiver and communication system

Technical field:

The present invention relates to a kind of based on code division multiple access spread spectrum and despreading method and adopt this method and the transmitter, receiver and the communication system that realize.

Background technology:

After one of greatest difficulty that traditional C DMA technology runs into was its spread-spectrum signal process frequency selective fading channels, intersymbol interference that received signal occurs and multiple access disturbed.They come from the time delay auto-correlation result and the cross correlation results of spreading code respectively.Because multidiameter, two of adjacent transmission symbols can produce the problem of intersymbol interference owing to different the crosstalking time of delay in each footpath on the time.Prior art can't keep the orthogonality that each user's spreading code has under the multipath channel in addition.Reason is the synchronous modulation technology can only guarantee to belong to same footpath different user spreading code in time domain a orthogonality, and the stack signal that belongs to Different Diameter has thereon been lost orthogonality, thereby has caused the phase mutual interference of each yard channel.These two interference are the main factors of restriction cdma system capacity, they are the very cruxs of cdma system dilatation amount, under the situation that the future communications bandwidth increases, data rate improves, one of multipath disturbs will become more serious, so the key factor of the following especially wideband CDMA system success or failure of the problems referred to above.

Summary of the invention:

The present invention is directed to the intersymbol interference and the multiple access that exist in the existing cdma system and disturb two problems, proposed a kind of to spread to the solution on basis with the spreading code that adds protected code.This scheme is used the guard bit that adds and is eliminated intersymbol interference, and then utilizes the method for solving an equation that the cross correlation value of remnants is turned to useful information, thereby finds the solution the information symbol of transmission.

First purpose of the present invention provides a kind of method with increase protected code on traditional C DMA spreading code basis and eliminates the spectrum spreading method of crosstalking between information symbol.

Second purpose of the present invention provides a kind of corresponding despreading method.

The 3rd purpose of the present invention provides a kind of transmitter, receiver and the communication system that can eliminate intersymbol interference and multiple access interference.

Technical scheme of the present invention is as follows:

A kind of CDMA spread spectrum method, comprising following steps:

(1) the serial to parallel conversion step of data: carry out serial to parallel conversion on demand, give different sign indicating number channels with data allocations; If the parallel sign indicating number of a N channel is arranged, can primary distribution go out the data of a N to be sent symbol;

(2) modulation step: modulation system as required, the data of each yard channel allocation are carried out the binary digit modulation, be about to binary message and be modulated to symbol; Described modulation system can adopt modes such as BPSK/QPSK or QAM;

(3) generate prefix or/and suffix CDMA sign indicating number step:

Adopting one of following manner is that traditional CDMA spreading code prefixing is or/and suffix recycling-guard sign indicating number to former spreading code; thereby constitute a new prefix or/and suffix CDMA sign indicating number; if M chip of former spread spectrum code length, the recycling-guard sign indicating number is the L position, and M, L are the positive integer more than or equal to 1:

A. prefix CDMA sign indicating number: last L chip in the spreading code duplicate be added on former spreading code as the recycling-guard sign indicating number before, form the spreading code of M+L chip;

B. suffix CDMA sign indicating number: the most preceding L chip in the spreading code is duplicated the back of adding former spreading code as the recycling-guard sign indicating number to, form the spreading code of M+L chip;

C. prefix and suffix CDMA sign indicating number: adopt aforementioned a and b simultaneously, prefix and suffix length overall are L;

(4) spread spectrum step: will give different prefixes or/and suffix CDMA sign indicating number channel utilizes its to implement CDMA band spectrum modulation through the data allocations of ovennodulation, and the signal of the different sign indicating number channels behind the spread spectrum is stacked up, the serial data that to obtain a length be M+L chip.

In the above-mentioned spectrum spreading method, described former spreading code can be the product of orthogonal code, non-orthogonal codes or orthogonal code and traditional scrambler.

With prefixing recycling-guard sign indicating number is example, adds L prefix protection chip in the traditional C DMA spreading code front that a length is the M chip.Utilize between the information symbol of this L chip elimination in their duration and crosstalk.

We define above-mentioned new spreading code: prefix CDMA sign indicating number.

For example: the Walsh sign indicating number a that length is M=4 ₁=1, a ₂=-1, a ₃=-1, a ₄=1, traditional C DMA is expressed as:

a 1

?a 2

?a 3

??a 4

When getting L=2, prefix CDMA sign indicating number is:

Prefix		Original symbol
						??a 3	??a 4	?a 1	?a 2	?a 3	??a 4

As seen, the sign indicating number of the long M+L=6 after prefixing arbitrarily intercepting one segment length be M=4 yard, all be the sign indicating number sequence that the cyclic shift of former spreading code obtains, its character is identical with the character of former spreading code.If true form is quadrature, then sign indicating number after the intercepting remains quadrature.

As long as the character that satisfies above-mentioned this cyclic shift all is fine the symbol of the sign extended growth M+L of long M.For example also can adopt the method that adds suffix, preceding L chip of former symbol copied to the back of symbol, the same like this intersymbol interference that can protect symbol not brought by multidiameter.Can also adopt the method for while prefixing and suffix, preceding several chips that are about to former symbol copy to the back of symbol, simultaneously back several chips of former symbol are copied to the front of symbol.Realizing and aspect of performance that these diverse ways do not have great difference.

Correspondingly, a kind of code division multiple access despreading method, comprising following steps:

(1) receiving symbol step: according to synchronizing information, the data flow that receives is divided into the serial data that length is M+L chip, promptly obtains the data of a symbol lengths; Here M refers to the number of chips of former spreading code, and L is the number of chips of recycling-guard sign indicating number;

(2) remove recycling-guard position step: remove the recycling-guard position of containing L chip of intersymbol interference in the data segment of (1) receiving, residue does not contain M chip of intersymbol interference;

(3) eliminate multipath and disturb step: find the solution the channel reverse matrix according to known channel parameter, M chip be multiply by the channel reverse matrix, M the chip that the channel multi-path that is eliminated disturbs;

(4) despreading step: carry out the despreading processing eliminating M the chip that obtains after the intersymbol interference, promptly M chip sequence done relevant despreading with former spreading code;

(5) judgement demodulation step:, the symbol judgement after the despreading is exported binary bits information according to the modulation system that transmitting terminal adopts.

It is balanced that above-mentioned despreading method utilization takes advantage of the method for channel reverse matrix to replace traditional F IR filter that channel is done.Traditional F IR filter can not be eliminated multipath fully owing to be subjected to the restriction of exponent number and complexity.And this patent in conjunction with prefix or/and this signal format of suffix CDMA, adopt the received signal vector to multiply by the way of channel reverse matrix, can eliminate intersymbol interference fully, its performance reaches desirable zero forcing equalization device performance.And because channel matrix belongs to a class Special matrix-circular matrix, it is found the solution also and can invert simply than general matrix.

The transmitter and receiver of another aspect of the present invention adopts above-mentioned spectrum spreading method and despreading method to implement to communicate by letter respectively.

Description of drawings:

Illustrate according to a preferred embodiment of the invention that with reference to the accompanying drawings identical reference number is represented identical or similar parts among the figure.

Fig. 1 illustrates the flow chart of existing mobile communication system;

Fig. 2 illustrates according to system construction drawing of the present invention;

Fig. 3 illustrates according to the form after a symbols spread of the present invention and the prefixing;

Fig. 4 illustrates through the received signal schematic diagram after the multipath channel;

Fig. 5 illustrates former spreading code and adds recycling-guard sign indicating number device schematic diagram;

Fig. 6 illustrates receiver and removes the prefix flow chart;

Fig. 7 illustrates channel reverse matrix computations flow chart;

Fig. 8 illustrates the FIR filter implementation method of taking advantage of the channel reverse matrix;

Fig. 9 illustrates under the 2 footpath channel situation according to the ber curve of analogue system of the present invention and traditional C DMA system;

Figure 10 illustrates under the 8 footpath channel situation according to the ber curve of analogue system of the present invention and traditional C DMA system.

Embodiment:

At first with reference to the traditional C DMA mobile communication system of Fig. 1 explanation according to prior art.

Transmitter 14 sides, read successively from data storage 11 and will send data.Data are delivered in the signal modulator 12 and are modulated, and the mode of modulation can adopt BPSK/QPSK or QAM mode, thus the information symbol that obtains launching.Then information symbol is sent in the frequency multiplier 13 and implements band spectrum modulation, after launch after the carrier modulation.The signal of emission becomes to being received machine 16 receptions behind the multipath signal with time delay extended attribute through frequency selective fading channels 15.Receiver utilizes user code to aim at the despreading respectively of these delay time signals, utilizes RAKE receiver 18 that the despreading component is carried out maximum signal to noise ratio again and merges.Channel estimation module 17 is estimated the parameter of multipath channel, and these parameters are offered RAKE receiver, and RAKE receiver utilizes these parameters to merge multipath signal.The signal of RAKE receiver output obtains original data after judgement demodulation 19, thereby finishes a process of signal demodulation.

Below to constitute new prefix CDMA sign indicating number with prefixing recycling-guard sign indicating number be example, describe the present invention.

Introduce communication system of the present invention below with reference to Fig. 2.

The information modulation of transmitter of the present invention, the spreading code modulation is consistent with conventional method.In transmitter 14, read the data that will send successively from data storage 11.Data are modulated, are implemented spread spectrum in the frequency multiplier 13 through signal modulator 12.The needed spreading code 21 of spread spectrum needs the device 22 of elder generation through a prefixing, becomes prefix CDMA sign indicating number, and then is used for frequency multiplier 13 spread spectrums.Like this, just inserted recycling-guard prefix code (recycling-guard prefix code form is seen Fig. 3) in the information symbol front of each traditional C DMA spread spectrum, can reach whereby and eliminate the purpose of crosstalking between information symbol.

The signal of emission becomes to being received machine 16 receptions behind the multipath signal with time delay extended attribute through frequency selective fading channels 15.At receiver 16, suppose that signal Synchronization and channel parameter obtain.Received signal abandons preceding L chip of information symbol earlier by removing prefix device 23.As shown in Figure 4, intercepting does not have a segment signal Y of intersymbol interference.To M remaining chip, in taking advantage of channel reverse matrix arrangement 25, make vector and multiplication of matrices, make multipath signal become the signal of Dan Jing.Be the calculating channel inverse matrix, need in channel estimation module 17, estimate channel parameter, and utilize these parameters to make channel reverse matrix computations 24.Data after matrix is handled utilize user's spreading code 27 to carry out despreading through despreader 26, through judgement demodulation 19 output symbols.

Prefixing device above-mentioned can be that exponent number is the shift register of M among the figure as shown in Figure 5, and when selecting switch to dial to the input data terminal, length is in the spreading code input shift register of M chip.Selector switch is dialled to feedback tap then, and the chip that shifts out register is fed back to input port, the output tap dateout in the middle of the register, and after M+L clock cycle, shift register is exported M+L chip data through M+L cyclic shift.This M+L chip data promptly are the prefix CDMA sign indicating numbers that satisfies behind the adding protected code of cyclic shift relation.Also the spreading code behind the adding protected code can be deposited in the register in the reality, the spread spectrum process of transmitting terminal and traditional C DMA system are consistent like this, and only used spreading code is prefix (or suffix)-CDMA sign indicating number different with conventional method.

The prefix device that goes above-mentioned can adopt flow chart as shown in Figure 6 to handle.Find the original position of symbol earlier according to synchronizing information; Counter i zero clearing; I adds i the chip that 1 correspondence is received this symbol at every turn; Judge whether i equals L.If i＜L, illustrating that current chip is still contains the chip that symbol is crosstalked, and then abandons this chip; If i 〉=L, then this chip is the chip that does not have intersymbol interference, sends this chip to next module and deals with.This sign-off when i=M+L, counter O reset prepare to receive next symbol.As seen this flow process has been removed preceding L the chip of making guard bit in symbol M+L chip, and has stayed a back M chip to next resume module.

Introduce a kind of implementation structure of channel inverse matrix computing module below with reference to Fig. 7.These module input data are the channel parameter c of channel estimator output ₁, c ₂..., c _M, this M data are made fast Fourier transform (FFT), obtain a new M data, again this M data are got inverse, pass through inverse-Fourier transform (IFFT) again, promptly obtain M element b in the channel reverse matrix B ₁, b ₂..., b _M

Take advantage of a kind of FIR filter implementation method of channel reverse matrix below with reference to Fig. 8 introduction.The shift register exponent number is M, and is provided with feedback, i.e. the data of displacement output are input to the data input pin of register.Begin to read in pending data in computing, promptly received signal is removed a remaining M data after the prefix.This moment, the selector switch of register input was dialled to the input FPDP.After data were filled up register, selector switch was dialled to feedback tap, and shift register carries out cyclic shift under the driving of clock.Whenever move once, the data in the shift register all will with the plain b of channel reverse entry of a matrix ₁, b ₂..., b _MDo multiplying, and with the multiplication result summation, dateout is the single drive signal x that has eliminated multipath ₁, x ₂..., x _MThis device can obtain M and export the result after shift register displacement M-1 time, promptly finished x ₁To x _MComputing, can read in next then and organize data to be processed, carry out computing next time.

Specifically introduce the principle of this patent below by mathematic(al) representation:

In this Mathematical Modeling, the length of employing is that the spreading code of M is total to M, can adopt M sign indicating number channel, and M sign indicating number of hypothesis channel is all occupied, and promptly each yard channel all is used for transmission information.May only use N sign indicating number channel wherein in the reality, only need that the symbol that idle code channel transmits is got zero this moment and get final product.1. the structure of prefix CDMA spreading code

In the traditional C DMA system, spreading code can be with a vector representation: $P^{\left(k\right)}=\[p_0^{\left(k\right)},p_1^{\left(k\right)},p_2^{\left(k\right)}\·\·\·,p_{M-1}^{\left(k\right)}\](k=\mathrm{0,1}..,M-1)---\left(1\right)$ Wherein

It is vector ^{P (k)}I component, M is a spreading gain.If orthogonal code spread spectrum then has:

Prefix spreading code of the present invention is to increase the protection prefix code before the sign indicating number of formula (1).Method is that last L in (1) sign indicating number duplicated, and doses the front (seeing accompanying drawing 3) at it.New sign indicating number form is: $Q^{\left(k\right)}=\[q_0^{\left(k\right)},q_1^{\left(k\right)},........q_{M+L-1}^{\left(k\right)}\]=\[p_{M-L}^{\left(k\right)},p_{M-L+1}^{\left(k\right)},\·\·\·,p_{M-1}^{\left(k\right)},p_0^{\left(k\right)},p_1^{\left(k\right)},\·\·\·,p_{M-1}^{\left(k\right)}\]---\left(4\right)$ If:

Be 1 information symbol of k user, the signal mathematic(al) representation behind the spread spectrum:

N is the chip sequence number that transmits in the formula, and L is the length of prefix, and t is the time, T _cRepresent the time that a chip continues, Γ (t) is a square wave function, and it is defined by following formula:

The mathematic(al) representation that multi-user's prefix CDMA transmits is $\mathrm{\Φ}\left(n\right)=\underset{k}{\mathrm{\Σ}}{s}_1^{\left(k\right)}{q}_n^{\left(k\right)}\mathrm{\Γ}(t-n{T}_c)---\left(7\right)$ 2. frequency selective fading footpath channel

If: a frequency selective fading channels wideband pulse response characteristic is: $h\left(t\right)=\underset{l=0}{\overset{L_k}{\mathrm{\Σ}}}{h}_l^{\left(k\right)}\mathrm{\δ}(t-{\mathrm{lT}}_c)---\left(8\right)$ T in the formula _cRepresent time that chip continued and time delay sequence number respectively with l.Transmit through behind the frequency selective fading channels, it shows as the different multipath superposed signal of delay as shown in Figure 4.3. signal demodulating method

The model of communication system that adopts below is: with length is that M+L prefix CDMA spreading code is assigned to M CDMA Channel, through behind the identical channel, receiver with following algorithm with all signal demodulation.

We use vector representation received signal and transmitting users information symbol.After abandoning prefix, the relation between them can be represented by the form of matrix:

Y represents the part after received signal is removed prefix in Y=HLPS (9) (9) formula, the user profile that the S representative will send: $s=\left[\begin{array}{c}{s}_1\\ {\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="A0310955700192.png"\; state="\{\{state\}\}">s</figure-callout>}}_2\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ s_M\end{array}\right]---\left(10\right)$ P represents transmitter spreading code matrix; I spread spectrum code sequence is expressed as column vector p _iSpread spectrum matrix p is by vectorial p _iM * Metzler matrix of forming:

P=[p ₁, p ₂..., p _M] (11) prefixing procedural representation is matrix L: $L_{(M+L)\&times;M}=\left(0_{\stackrel{L\&times;(M-L)}{I_M}}{I}_L\right)---\left(12\right)$ Wherein 0 represents null matrix, I representation unit matrix.Make Q=LP, then each of Q is classified a prefix CDMA sign indicating number sequence as.Make Z=QS, then Z is the signal behind the spread spectrum.H represents multipath channel: Attention: the module of each matrix and vector representative or signal are as shown in Figure 2.Make C=HL, then:

As long as receiving terminal will receive the inverse matrix B=C that vector multiply by C ^-1, just can eliminate the intersymbol interference that multipath channel is brought.The C matrix belongs to circular matrix, and promptly each provisional capital of matrix cyclic shift of can be regarded as first row obtains:

Its inverse matrix B also is a circular matrix

Wherein $b_j=\frac{1}{M}\underset{k=0}{\overset{M-1}{\mathrm{\&Sigma;}}}{\mathrm{\&lambda;}}_{M-j-1}^k{\&lsqb;f\left({\mathrm{\&lambda;}}_k\right)\&rsqb;}^{-1}(j=\mathrm{2,3},\&CenterDot;\&CenterDot;\&CenterDot;,M)$ ${\mathrm{<figure-callout\; id="1"\; label="b"\; filenames="A0310955700191.png,A0310955700192.png"\; state="\{\{state\}\}">b</figure-callout>}}_1=\frac{1}{M}\underset{k=0}{\overset{M-1}{\mathrm{\&Sigma;}}}{\mathrm{\&lambda;}}_0^k{\&lsqb;f\left({\mathrm{\&lambda;}}_k\right)\&rsqb;}^{-1}---\left(17\right)$

Here ${\mathrm{\&lambda;}}_k={\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="A0310955700192.png"\; state="\{\{state\}\}">e</figure-callout>}}^{\frac{2\mathrm{k\&pi;}}{n}j}$ , f (x)=c ₁+ c ₂X+c ₃x ²+ ... + c _Mx ^M-1, above-mentioned computing can utilize fast Fourier transform (FFT) to calculate.As shown in Figure 7, first row element of C matrix is made Fourier transform, can obtain f (λ _k) (k=0,1 ... M-1), then each value is asked reciprocal, obtain f (λ _k) ^-1, carry out inverse-Fourier transform again and can obtain b _iBy the received signal vector be multiply by the channel reverse matrix B, eliminated the intersymbol interference that brings owing to multipath channel, thereby made each spreading code still keep quadrature.Get by (9) formula and (16) formula:

S=P ^HB ^-1Y (18) despreading process is expressed as matrix P ^H, P ^HIt is the P transposition.Can accurately demodulate primary signal S and not have systematic error at the situation receiving terminal that does not have plus noise.Under the situation that has nonsystematic to disturb, (18) formula table is:

Y '=S+n=P ^HB ^-1N represents because the nonsystematic caused by noise is disturbed in Y (19) (19) formula.4. simulation result (1) simulated conditions adopts the Matlab programming, implements the emulation of prefix cdma system under Windows2000.Emulation comprises the down channel error ratio characteristic of prefix cdma system, and compares with the error rate of the RAKE receiver of traditional C DMA system.

The information symbol of system is the BPSK modulation.Prefix CDMA spreading code is based on that TDD-WCDMA sign indicating number prefixing obtains.All user codes are that to increase length before length is traditional spreading code of 16 chips be the L guard bit, the last L chip of this yard is duplicated, and before being inserted in this spreading code, obtaining length like this are the new spreading code of 16+L chip.

Each footpath coefficient h of frequency selective fading channels _iBe independent identically distributed Rayleigh random number, phase place is obeyed [0,2 π] and is evenly distributed, and the time delay extension width is a L chip.(2) simulation result

Fig. 9 and Figure 10 have provided the error rate of system result of multipath channel time delay diffusion L=2 and L=8 respectively, and compare with the RAKE receiver performance of traditional C DMA system.As seen from the figure, traditional C DMA system is under the multipath situation, and intersymbol interference and multiple access interference effect are very big, does not also well improve by RAKE receiver, and along with the footpath number to increase performance more abominable, the error rate in L=8 footpath will be higher than the situation in L=2 footpath.And adopt system of the present invention, the error rate that tangible improvement has been arranged, and systematic function has clear superiority not with the increasing and descend of footpath number than traditional C DMA system.

Although hereinbefore and with reference to preferred embodiment of the present invention principle of the present invention and implementation are described in detail, those of ordinary skill in the art can make various distortion and improvement without departing from the present invention.For example, be the length that example increases signal to be sent so that prefix to be set in this specification, but also can adopt the mode that suffix is set, perhaps add protection in the rear and front end; Adding the recycling-guard sign indicating number, removing the recycling-guard position, separating the channel reverse matrix, also other method or the like can arranged on the solution that received signal is taken advantage of the channel reverse matrix in addition.These distortion and improvement example do not break away from the scope of the present invention of defined in claims of the present invention.

Claims (10)

1. CDMA spread spectrum method, comprising following steps:

(1) the serial to parallel conversion step of data: carry out serial to parallel conversion on demand, give different sign indicating number channels with data allocations; If the parallel sign indicating number of a N channel is arranged, can primary distribution go out the data of a N to be sent symbol;

(2) modulation step: modulation system as required, the data of each yard channel allocation are carried out the binary digit modulation, be about to binary message and be modulated to symbol;

(3) generate prefix or/and suffix CDMA sign indicating number step:

Adopting one of following manner is that traditional CDMA spreading code prefixing is or/and suffix recycling-guard sign indicating number to former spreading code; thereby constitute a new prefix or/and suffix CDMA sign indicating number; if M chip of former spread spectrum code length, the recycling-guard sign indicating number is the L position, and M, L are the positive integer more than or equal to 1:

A. prefix CDMA sign indicating number: last L chip in the spreading code duplicate be added on former spreading code as the recycling-guard sign indicating number before, form the spreading code of M+L chip;

B. suffix CDMA sign indicating number: the most preceding L chip in the spreading code is duplicated the back of adding former spreading code as the recycling-guard sign indicating number to, form the spreading code of M+L chip;

C. prefix and suffix CDMA sign indicating number: adopt aforementioned a and b simultaneously, prefix and suffix length overall are L;

(4) spread spectrum step: will give different prefixes or/and suffix CDMA sign indicating number channel utilizes its to implement CDMA band spectrum modulation through the data allocations of ovennodulation, and the signal of the different sign indicating number channels behind the spread spectrum is stacked up, the serial data that to obtain a length be M+L chip.

2. CDMA spread spectrum method as claimed in claim 1 is characterized in that, described former spreading code is the product of orthogonal code, non-orthogonal codes or orthogonal code and traditional scrambler.

3. code division multiple access despreading method, comprising following steps:

(1) receiving symbol step: according to synchronizing information, the data flow that receives is divided into the serial data that length is M+L chip, promptly obtains the data of a symbol lengths; Here M refers to the number of chips of former spreading code, and L is the number of chips of recycling-guard sign indicating number;

(2) remove recycling-guard position step: remove the recycling-guard position of containing L chip of intersymbol interference in the data segment of (1) receiving, residue does not contain M chip of intersymbol interference;

(3) eliminate multipath and disturb step: find the solution the channel reverse matrix according to known channel parameter, M chip be multiply by the channel reverse matrix, M the chip that the channel multi-path that is eliminated disturbs;

(4) despreading step: carry out the despreading processing eliminating M the chip that obtains after the intersymbol interference, promptly M chip sequence done relevant despreading with former spreading code;

(5) judgement demodulation step:, the symbol judgement after the despreading is exported binary bits information according to the modulation system that transmitting terminal adopts.

4. code division multiple access despreading method as claimed in claim 3 is characterized in that: eliminate multipath and disturb the method for finding the solution the channel reverse matrix in the step to be: with channel parameter c ₁, c ₂..., c _M, M data are made fast fourier transform, obtain a new M data, again this M data are got inverse, pass through inverse-Fourier transform again, promptly obtain M element b in the channel reverse matrix ₁, b ₂..., b _M

5. CDMA transmitters is characterized in that comprising as lower device:

(1) serial-parallel converter: carry out serial to parallel conversion on demand, give different sign indicating number channels with data allocations, if N parallel sign indicating number channel arranged, then primary distribution goes out the data of a N to be sent symbol;

(2) modulating device: modulation system as required is modulated to symbol with binary bits information;

(3) add recycling-guard sign indicating number device: adopt one of following manner that former spreading code is added the recycling-guard sign indicating number:

A. prefix CDMA sign indicating number: last L chip in the spreading code duplicate be added on former spreading code as the recycling-guard sign indicating number before, form the spreading code of M+L chip;

B. suffix CDMA sign indicating number: the most preceding L chip in the spreading code is duplicated the back of adding former spreading code as the recycling-guard sign indicating number to, form the spreading code of M+L chip;

C. prefix and suffix CDMA sign indicating number: adopt aforementioned a and b simultaneously, prefix and suffix length overall are L;

(4) spread spectrum device: will give different prefixes or/and suffix CDMA sign indicating number channel utilizes its to implement CDMA band spectrum modulation through the data allocations of ovennodulation, and the signal of the different sign indicating number channels behind the spread spectrum is stacked up, the serial data that to obtain a length be M+L chip.

6. CDMA transmitters as claimed in claim 5 is characterized in that, described former spreading code is the product of orthogonal code, non-orthogonal codes or orthogonal code and traditional scrambler.

7. CDMA transmitters as claimed in claim 5; it is characterized in that; the described recycling-guard sign indicating number device that adds is that exponent number is the shift register of M; when selecting switch to dial to the input data terminal; length is in the spreading code input shift register of M chip; selector switch is dialled to feedback tap then; the chip that shifts out register is fed back to input port; output tap dateout in the middle of the register; after M+L clock cycle; shift register is exported M+L chip data through M+L cyclic shift.

8. CDMA receiver is characterized in that comprising as lower device:

(1) sign register: receive and stored symbols,, the data flow that receives is divided into the data segment that length is M+L chip, promptly obtain the data of a symbol lengths according to synchronizing information;

(2) remove recycling-guard position device: be subjected to the recycling-guard position of intersymbol interference in the chip that removal (1) receives, residue does not contain M chip of intersymbol interference;

(3) countermeasure set between blanking code: find the solution the channel reverse matrix according to known channel parameter, M chip be multiply by the channel reverse matrix, M the chip that the channel multi-path that is eliminated disturbs;

(4) despreading device: carry out the despreading processing eliminating M the chip that obtains after the intersymbol interference, promptly M chip sequence done relevant despreading with former spreading code;

(5) judgement demodulating equipment:, the symbol judgement after the despreading is exported binary bits information according to the modulation system that transmitting terminal adopts.

9. CDMA receiver as claimed in claim 8, it is characterized in that, taking advantage of in the countermeasure set between described blanking code and separating the channel reverse matrix is to adopt the FIR filter to realize, the shift register exponent number of described FIR filter is M, and feedback is set, i.e. the data of displacement output are input to the data input pin of register; Begin to read in pending data in computing, promptly received signal is removed a remaining M data after the prefix, and this moment, the selector switch of register input was dialled to the input FPDP; After data were filled up register, selector switch was dialled to feedback tap, and shift register carries out cyclic shift under the driving of clock, whenever move once, the data in the shift register all will with the plain b of channel reverse entry of a matrix ₁, b ₂..., b _MDo multiplying, and with the multiplication result summation, dateout is the single drive signal x that has eliminated multipath ₁, x ₂..., x _M, can obtain M after shift register displacement M-1 time and export the result, promptly finished x ₁To x _MComputing, can read in next then and organize data to be processed, carry out computing next time.

10. a code division multiple address communication system is characterized in that comprising claim 5 or 6 or 7 described transmitters and claim 8 or 9 described receivers.

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