CN1387335A - CDMA spread and despread-spectrum method and its transmitter, receiver and communication system - Google Patents

Abstract

The present invention relates to a method of spread and de-spread spectrum for code division multiple access and relevant transmitter in order to eliminate the multipath disturbance. The continuous spread spectrum mode of each symbol in the information symbol flow, which is used in the orthogonal spread spectrum code on the spreading steps of the conventional CDMA is replaced by the discrete mode in the present invention. But the information of the different user is still in the format of the CDMA. From the viewpoint of the receiver, the invented transmitting technique converts the multiple addresses interfere, which caused by the multi-path happened in the conventional CDMA system, into the symbol overlapping (so called the cross talk between symbols in the conventional technique) in each user completely. Based on the elimination of the multiple addresses interfere, the symbol information of each user can be obtained from the overlapped symbols by using the method of solving the equation.

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

In existing C DMA system, multi-user's information transmission is distinguished by sign indicating number, therefore is a kind of parallel multi channel structure under certain bandwidth.In high-quality synchronous CDMA direct spread system, above-mentioned parallel multichannel is distributed to a plurality of users, and user's information symbol comes spread spectrum with orthogonal intersection.Receiver utilizes the method for related operation, obtains certain user profile.Other subscriber signals are then owing to orthogonality is eliminated.

But in multi-path environment, the orthogonality that above-mentioned technology can't keep each user's spreading code to have.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 superposition signal that belongs to Different Diameter has thereon been lost orthogonality (signal time delay is the signal of Different Diameter greater than the signal definition of a chip duration in the time domain), thereby caused each user's phase mutual interference, be also referred to as multiple access and disturb (MAI).This interference is the main factor that limits the cdma system capacity at present.In the Direct-Spread communication system, consider the time delay of frequency selective fading channels, this time delay is that the characteristic by channel is determined that impersonal force can change, and this just time delay has caused the generation of multipath, and system has been caused great interference.

The notion of the 4th third-generation mobile communication system can be described as wideband (Broadband) and inserts and distributed network, and its message transmission rate all substantially exceeds 3-G (Generation Three mobile communication system) under indoor, outdoor and mobile environment.Because the increase of communication bandwidth, multipath disturbs more seriously.Therefore, multiple access disturbs becomes the problem that we press for solution.

Summary of the invention

It is key technology---the discrete type spectrum spreading method of the 4th third-generation mobile communication (4G) design that the defective that the present invention is directed to existing spread spectrum mode has proposed a kind of.

First purpose of the present invention provides a kind of orthogonality of spreading code of utilizing and eliminate the discrete spectrum spreading method that multipath disturbs under frequency selective fading channels.

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

The 3rd purpose of the present invention provides a kind of discrete method of separating, and makes traditional despreading method also can be used for the signal demodulation.

The 4th purpose of the present invention provides a kind of method of separating the symbol that superposes.

The 5th purpose of the present invention provides a kind of transmitter, receiver and the communication system that can eliminate the multipath interference.

According to the discrete spectrum spreading method of one aspect of the invention, wherein each user profile symbol is to implement spread spectrum with the spreading code of quadrature.Information symbol can be BPSK QPSK or QAM mode modulate.Therefore, the notion of code division multiple access still is suitable in present technique.Contrast traditional CDMA spectrum spreading method, we are with corresponding to the spread spectrum data of information symbol discrete distribution on sequential one by one equally spaced.If this is spaced apart the duration of (M+L) individual chip, chip of every backward time delay then can be placed the information symbol of a spread spectrum.Add up to (L+M) individual information symbol until placement.We define these (L+M) individual data is a data block.In data block, it is independently that M information symbol arranged, and L information symbol is multipath prefix data symbol.The information prefix sign is got last L symbol among the M.During emission, prefix sign is preceding, independently information symbol after.

Should be pointed out that above-mentioned modulator approach is applicable to the situation of multipath maximum delay less than the L chip.In addition, if spreading ratio is n, then data block length is the individual chip duration of n (L+M).

First kind of demodulation method according to a further aspect of the present invention is correlated with to the discrete message symbol spreading code with the user on its discrete correspondence position through multipath channel, then obtains the stack result of user's current information symbol and preceding several information symbols.We define this correlation technique is the discrete correlation method.Related operation should be from L+1 sign-on.That is: preceding L prefix sign of forgo data piece.Attention: the stack of information symbol is caused by multipath.

Second kind of demodulation method according to a further aspect of the present invention rearranges the discrete message symbol through multipath channel.The symbol that the footpath of winning is arrived is arranged as traditional continuous spread spectrum mode by symbol sequence.Utilize traditional despreading method, that is: continuous solution expanding method is from L+1 symbol demodulation.

Information symbol separation method according to another aspect of the present invention to above-mentioned two kinds of method demodulation result (they provide same result), is solved an equation and is separated institute's information transmitted symbol.Thereby realize the transmission of information symbol.

Transmitter and receiver according to another aspect of the present invention adopts above-mentioned discrete spectrum spreading method and discrete correlation method respectively or separates discrete and traditional despreading method enforcement and communicate by letter.

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 is the flow chart that existing mobile communication system is shown;

Fig. 2 is the structure chart according to system of the present invention;

Fig. 3 is the flow chart that illustrates according to discrete spectrum spreading method of the present invention;

Fig. 4 illustrates the flow chart of separating discrete spectrum spreading method according to of the present invention;

Fig. 5 is the structured flowchart according to frequency multiplier in the transmitter of the present invention and discretizer;

Fig. 6 is according to the structured flowchart of separating discretizer and despreader in the receiver of the present invention;

Fig. 7 illustrates when spreading ratio is n=16 according to the error rate of system of the present invention change curve along with signal to noise ratio; And

Fig. 8 is for illustrating when the SNR=0dB, and error rate of system is along with the change curve of spreading ratio.

Embodiment

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

Transmitter 14 sides, read the packet that will send successively from packet memory 11.In modulator 12, modulate, the mode of modulation can adopt BPSK QPSK or QAM mode.Data after the modulation are sent to frequency multiplier 13, in frequency multiplier 13, utilize the PN sign indicating number to carry out the CDMA spread spectrum.Send by the antenna (not shown) then.Undertaken being received by receiver 16 after the multipath channel by the signal that transmitter sent, through obtaining original packet after despreader 17 and the judgement demodulation 18.Thereby finish a process of communication.

Referring now to Fig. 2.In the communication system of discrete type spread spectrum of the present invention, in reflector 23, between existing packet memory 11 and modulator 12, increase the device 21 that prefix is set, it is used for the packet that will send is provided with prefix, so that can enough draw original packet by solving an equation to received signal at receiver.And increase a discretizer 22 between frequency multiplier 13 and antenna (not shown), it is used for carrying out the method that the chip that will send symbol is dispersed and arranges of the present invention before sending information symbol.

In receiver 24, the information symbol that is received is earlier by separating discretizer 25, and it is used for separating discrete to the information symbol that is sent by transmitter 23.Then through a timer 26, be used for choosing one section required information and be sent to despreader 17 and carry out despreading in the information after discrete of separating.Keep orthogonality relation between the multipath information owing to this user profile that is comprised in the segment information selected in timer and other users, so eliminated other users' multipath interference after the despreading in the resulting information.Although other users' that the information after the process despreading is eliminated information, but between this user's main footpath information and the other footpath information is to postpone an integer symbol and overlapped, therefore need be sent to equation solver 27 to the data after the despreading and set up equation group, try to achieve original packet by solving an equation.

Further specify the workflow of discretizer 22 of the present invention referring to Fig. 3.At first should be pointed out that before the step S1 shown in Fig. 3 being divided into M symbol is a data block to the data that will send, last L symbol of the symbol of the M in each data block appended to before this symbols, as L prefix sign.Thereby form M+L symbol and be one group data block.Wherein, L is an integer more than or equal to the maximum delay number of chips in multipath channel; M is an integer greater than L.

At step S1, to send symbol sebolic addressing with an above-mentioned M+L symbol be one group of sequential storage in register, suppose that each symbol has n chip.

At step S2, storage one group code prepares to disperse arrangement in register.

In step S3-S6,, i chip of each symbol in this group code taken out successively and send according to the precedence of symbol.Till each chip in having got M+L symbol of this group.

At step S7, judge whether all packets that will send are dispersed and arrange and send.If send this end operation in discretizer that finishes.

The operating process of separating discretizer 25 in receiver 24 is described below with reference to Fig. 4.

Adopt conventional timing and synchronous method to determine each data block of cutting apart in Transmitter side at step S11.As indicated above, each data block has M+L symbol lengths, has (M+L) * n chip.

At step S12, data block of storage in register.

In step S13-S16 process, at first pointer i is initialized as 1, i chip of the described data block of storing from register then begins to take out successively i, M+L+i, 2 (M+L)+i ..., (n-1) * (M+L)+i chip, and output to timing device.After every circulation primary the numerical value of i is added 1, carrying out circulation next time, up to having got all chips.Thereby finish the processing of separating in the discretizer 25.

The effect and the function of timer 26, despreader 17, equation solver 27 are described below, being stored in according to precedence in the register of timer 26 by separating the chip that discretizer 25 taken out, the timing method by routine takes out last M symbol in these group data in timer 26.The main footpath signal that in a last M symbol, comprises required user and other user, and these users' multidiameter signal, but postpone an integer symbol between main footpath signal and the multidiameter signal, although therefore have multidiameter, keep orthogonality relation (this will describe in detail hereinafter more) between the signal of different user.Then the M that an is taken out symbol is sent to despreader 17 and carries out conventional despreading processing.Because the signal between the different user still keeps orthogonality relation, therefore through having eliminated other user's main footpath signal and multipath signal in the signal that despreading drew fully.But, be to be the result that unit gets according to different amplitude ratio staggered superposition with the symbol between required user's main footpath signal and this user's the multipath signal through the data of despreading gained.Therefore can solve an equation and try to achieve each symbol by in equation solver 27, setting up equation group.And each symbol of being tried to achieve is arranged according to the precedence that sends, be sent to judgement demodulator 18 and carry out demodulation.

Up to the present, principle of the present invention and concrete steps are described synoptically referring to figs. 1 through Fig. 4.To principle of the present invention be described in further detail by the mode of mathematical expression below.

The discrete type spread spectrum is that each information symbol in the information flow is disperseed by the mode in cycle, multiplies each other with this user's orthogonal intersection on the position of correspondence then, that is: discrete spread spectrum mode.From the emission data mode, quite with traditional C DMA emission data carried out the discrete type arrangement.

1. the basic mode of discrete spread spectrum

At first for the ease of understanding, we provide the data flow form of traditional C DMA.With chip duration is the minimum unit of time course, and the data flow of M data composition can be written as among the traditional C DMA: $\left(1\right)s_0^{\left(k\right)}{p}_{k,0},s_0^{\left(k\right)}{p}_{k,1}\…s_0^{\left(k\right)}{p}_{k,n-1},s_1^{\left(k\right)}{p}_{k,0},s_1^{\left(k\right)}{p}_{k,1}\…s_1^{\left(k\right)}{p}_{k,n-1}\…s_{M-1}^{\left(k\right)}{p}_{k,0},s_{M-1}^{\left(k\right)}{p}_{k,1}\…s_{M-1}^{\left(k\right)}{p}_{k,n-1}$

Expression formula Be data flow, wherein k represents it is k user's signal, S _iI information symbol representing this user, p _{K, j}Expression is used for j spread spectrum code value of i symbol.Under orthogonal code modulation, orthogonality is expressed from the next:

Above-mentioned (1) described sequence is adopted discrete spectrum spreading method of the present invention, is one group with M symbol, adjusts the order of transmission of each chip in each symbol.Specifically, i chip of each symbol in M the symbol sequence arrangement of putting together, for example send the 1st chip of each symbol earlier according to the sequencing of symbol $s_0^{\left(k\right)}{p}_{k,0},s_1^{\left(k\right)}{p}_{k,0},s_2^{\left(k\right)}{p}_{k,0}\…s_{M-1}^{\left(k\right)}{p}_{k,0},$ Send the 2nd chip of each symbol again $s_0^{\left(k\right)}{p}_{k,1},s_1^{\left(k\right)}{p}_{k,1},s_2^{\left(k\right)}{p}_{k,1}\…s_{M-1}^{\left(k\right)}{p}_{k,1},$ Or the like the rest may be inferred.

(L+M) the discrete spread data streams of individual symbol composition then can be expressed as: $s_0^{\left(k\right)}{p}_{k,0},s_1^{\left(k\right)}{p}_{k,0},s_2^{\left(k\right)}{p}_{k,0}\…s_{L+M-1}^{\left(k\right)}{p}_{k,0},s_0^{\left(k\right)}{p}_{k,1},\…s_1^{\left(k\right)}{p}_{k,1},\…s_2^{\left(k\right)}{p}_{k,1}\…s_0^{\left(k\right)}{p}_{k,n-1},\…s_1^{\left(k\right)}{p}_{k,n-1},\…$ $s_{L+M-1}^{\left(k\right)}{P}_{k,n-1}----\left(3\right)$

Under the synchronous condition of emission, the mathematical notation formula that multiuser channel transmits: $S\left(t\right)=\underset{k}{\mathrm{\Σ}}\underset{j}{\mathrm{\Σ}}{s}_j^{\left(k\right)}{u}_k(t-j{T}_c)----\left(4\right)$

Wherein $u_k\left(t\right)=\underset{i=0}{\overset{n-1}{\mathrm{\Σ}}}{p}_{k,i}\mathrm{CP}(t-\mathrm{iM}{T}_C)----\left(5\right)$

Expression user's characteristic function, wherein S (t) is a transmitter output signal, the t express time, CP (u) is a square wave function:

2. the orthogonality under the multipath channel condition

Suppose: the maximum delay of multipath channel is the L chip duration, and discrete spread-spectrum signal is after this multipath channel of experience, and its data flow has following form

Wherein: υ (t) is a received signal, α _lIt is the multipath fading coefficient; T _cRepresent a chip duration, l is whole number, its sign time delay size.

If the receiver correlation function is defined as: $d_{k^{\′}{j}^{\′}}\left(t\right)=\underset{i=0}{\overset{n-1}{\mathrm{\Σ}}}{p}_{k^{\′}i}\mathrm{\δ}(t-\mathrm{iM}{T}_c-j^{\′}{T}_c-L{T}_c)---(j^{\′}=\mathrm{0,1,2}\…,L-1)----\left(8\right)$

Wherein: j ' is the receiver synchronous coefficient.By following related operation: $R_{j^{\′}}^{\left(k\right)}=\underset{(L+j^{\′})T_c}{\overset{(L+j^{\′}+\mathrm{nM})T_c}{\∫}}\mathrm{\υ}\left(t\right){d^{*}}_{k^{\′}{j}^{\′}}\left(t\right)\mathrm{dt}=\underset{l=0}{\overset{L}{\mathrm{\Σ}}}{\mathrm{\α}}_l{s}_{L-l+j^{\′}}^{\left(k\right)}----\left(9\right)$

We obtain k user profile symbol, and other subscriber signals are eliminated owing to orthogonality.

That is to say that adopting the discrete spectrum spreading method spread spectrum of the present invention signal process multipath passage of gained afterwards, the signal of gained after the recipient is with despreading method despreading of the present invention is with other users' multipath signal maintenance orthogonality relation.Therefore eliminated the multipath interference.

On the other hand, for the demodulation method 2 that spectrum spreading method of the present invention more clearly is described, hypothesis is certain user's signal chip below

Be expressed as a _Ij(i, j=0,1,2,3), wherein each symbol has 4 chips, that is to say that spreading ratio is 4, then has:

In the prior art:

Original transmission data are: a ₀₀a ₀₁a ₀₂a ₀₃

a ₂₀a ₂₁a ₂₂a ₂₃a ₃₀a ₃₁a ₃₂a ₃₃

Through after the multipath channel, for because the delay of multipath forms a plurality of footpaths that postpone an integer chip, there are a footpath and main signal only to postpone a chip in this hypothesis, then have:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Therefore A is a main signal, and B is for postponing the other footpath of a chip, and A, B have fading coefficients separately respectively, and they are mutual superposition on the chip of correspondence.A5, A6, A7, A8 in the last table is the symbol that 4 chips of main signal A constitute, it and a stagger chip and superposeing of corresponding symbol B6, B7, B8, B9 among the other footpath B.Because multidiameter makes the integer chip that staggers between certain user's the other footpath signal of main signal and itself and other users' delay, thereby the destruction quadrature produces so-called multipath interference.

According to the present invention, before sending data, adopt discrete spectrum spreading method of the present invention to carry out spread spectrum.Suppose that with M=3 symbol be one group, with the number of L=1 as prefix sign.The information prefix sign is got last L symbol among the M.During emission, prefix sign is preceding, independently information symbol after.

Suppose that this M group that symbol constituted is: a ₀₀a ₀₁a ₀₂a ₀₃

a ₂₀a ₂₁a ₂₂a ₂₃

In order to be clearly shown that the position of each chip in one of them symbol, choose As a reference.

Then prefix sign is:

a ₂₀ a ₂₁ a ₂₂ a ₂₃

The symbols that being provided with in Fig. 2 is provided with in the prefix device 21 after the prefix is:

a ₂₀ a ₂₁ a ₂₂ a ₂₃ a ₀₀ a ₀₁ a ₀₂ a ₀₃

a ₂₀ a ₂₁ a ₂₂ a ₂₃

The symbols that disperses after arranging through discretizer 22 is:

a ₂₀ a ₀₀

a ₂₀ a ₂₁ a ₀₁ a ₂₁ a ₂₂ a ₀₂ a ₂₂ a ₂₃ a ₀₃ a ₂₃

Suppose this group data block through having only the delay of a chip after the multipath passage, then the signal that receives at receiver is:

A is a main footpath signal, and B is for postponing the multipath signal of a chip.

Suppose that receiver receives the data block that sends behind the same discrete spread spectrum of the process of another user b and the multidiameter signal of this user b simultaneously:

Because user a and the shared same frequency range of user b, when therefore receiving in receiver, they are mutual superposition:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Separate discrete after the data block of gained be: 123456789 10 11 12 13 14 15 16 17

Because separating discrete is the inverse transformation of discrete processes, the original ordering of the capable recovery of A as can be seen.In the 5-16 row, the symbol that each symbol sequence is capable with respect to A was adjusted to some extent after B passed through and resequences, with the symbol aligned of A row.

Capable and the D of C is capable also to be the integral symbol alignment in the 5-16 row, owing to adopt spreading code and each symbol to multiply each other in transmitter.In timer 26, choose the signal of 5-16 row, carry out despreading by timing and synchronous method.

5 6 7 8 9 10 11 12 13 14 15 16

Spreading code between user a and the user b has orthogonality relation.If in receiver, adopt the spreading code identical to carry out despreading, then can eliminate the signal of user b fully with user a.

Signal after the despreading is:

5 6 7 8 9 10 11 12 13 14 15 16

This is the A footpath signal of user a and the result of B footpath signal stack.Can obtain each symbol by the mode of setting up equation.

For example establish unknown symbols x ₁=a ₀₀, a ₀₁, a ₀₂, a ₀₃x ₂=a ₁₀, a ₁₁, a ₁₂, a ₁₃x ₃=a ₂₀, a ₂₁, a ₂₂, a ₂₃The fading coefficients in A footpath is k _AThe fading coefficients in B footpath is k _BThis fading coefficients can be by before sending signal or termly with methods such as frequency pilot signs, carry out channel guess value and draw, and this fading coefficients generally can not change in the signal process of transmitting.The superposed signal that is received is R ₁, R ₂And R ₃

Can draw from above-mentioned stack result:

k _Ax ₁+k _Bx ₃＝R ₁；

k _Ax ₂+k _Bx ₁＝R ₂；

k _Ax ₃+k _Bx ₂＝R ₃；

Wherein, k _A, k _B, R ₁, R ₂And R ₃Be known, three unknown numbers and three equations are arranged, therefore can solve each symbol x ₁, x ₂And x ₃Numerical value.

More general equation group is following matrix multiplication form, wherein k _iBe the mould of i footpath fading coefficients, through k after the channel guess value _iKnown, R _iBe that relevant despread values also is known, x _iBe data symbol to be asked, i=1,2,3 ... M.

Below with reference to a Fig. 5 and 6 an explanations specific embodiment of the present invention.Fig. 5 is the structured flowchart according to frequency multiplier in the transmitter of the present invention and discretizer, and Fig. 6 is according to the structured flowchart of separating discretizer and despreader in the receiver of the present invention.

In Fig. 5, adopt a kind of circuit structure to realize discrete spectrum spreading method of the present invention.This circuit structure is realized the frequency multiplier 13 shown in Figure 2 and mentioned above and the function of discretizer 22.Comprising symbols module 31, circulating register 32, multiplier 33, synchro system 34, orthogonal code maker 35, chip clock 36 and frequency divider 37.This wherein stores original symbol to be sent in the symbols module 31.Under the driving of chip clock 36, symbols module 31 outputs one group code, symbol numbers is M+L, under the control of synchro system 34, symbol module is in wait state subsequently.This group code is input in the circulating register 32, under the driving of chip clock 36, n time (n is a spreading ratio) of circulation output, then synchro system 34 again the trigger symbol pack module export another group code, symbol numbers still is M+L.Frequency divider 37 is the frequency division of the frequency of the clock of chip clock 36 frequency of 1/ (M+L), the data that drive orthogonal code maker 35 output pn sign indicating numbers and circulating register output with the clock behind the frequency division multiply each other in multiplier 33, can know, each numeral of pn sign indicating number all multiplies each other with a group code, has so just finished discrete type spread spectrum process.

In Fig. 6, adopt a kind of circuit structure to realize the discrete spectrum spreading method of separating of the present invention.This circuit structure realization Fig. 2 and despreader 17 mentioned above are conciliate the function of discretizer 25.This circuit comprises: multiplier 41, adder 42, shift register 43, equation solver 44, orthogonal code maker 45, frequency divider 46, chip clock 47, synchro system 48 and channel estimator 49.Frequency divider 46 is the clock frequency frequency division from chip clock 47 frequency of 1/ (M+L), drives orthogonal code maker 45 output pn sign indicating numbers with the clock behind the frequency division.N * (M+L) individual chip was sent to multiplier 41 and channel estimator 49 by receiver received.The pn sign indicating number that in multiplier 41 chip sequence that is received and orthogonal code maker 45 is produced multiplies each other.Multiplied result is imported into adder 42 and shift register 43.Under the driving of chip clock 47, this shift register 43 turns back to the signal of displacement output in the adder 42 with afterwards signal and carries out relevant summation, and outputs to equation solver 44.The signal that is received is estimated channel parameter, for example decay factor in the every footpath of Rayleigh channel or the like at channel estimator 49.Resulting channel parameter is transported to equation solver 44.Solve primary signal by equation solver 44 by setting up equation group.

Please note that example mentioned above only is one embodiment of the present of invention rather than realizes sole mode of the present invention.

In the scheme that this paper proposed, owing to do not need spreading code to have good auto-correlation and their cross correlation, only need spreading code to have orthogonality, the walsh sign indicating number then just in time meets this requirement.The way of understanding equation group is then adopted in the inhibition that multipath disturbs, and system interference is eliminated fully, and all interference all come from the nonsystematic noise, so performance is greatly improved.The multipath number that system can resist is relevant with the redundant size of inserting, and redundancy is big more, and the footpath number of opposing is many more.

The scheme that this paper proposed also has a benefit, be exactly irrelevant with spreading ratio, the change of spreading ratio size does not influence the conceptual design of system, so, we can obtain higher processing gain with this by improving spreading ratio, in fact, spreading ratio whenever increases and is twice, and just there is the improvement of 3dB in system.

It below is computer artificial result.

A. simulated conditions is as follows:

The inventor adopts the programming of Matlab emulational language, moves under Windows2000 and passes through.In the SSS-CDMA spread spectrum system of emulation, transmitting terminal adopts the BPSK modulation, and promptly each symbol is only represented the information of a bit.Under multipath channel, the maximum delay multipath comprises the delay of 8 chips, the identical rayleigh distributed of whose amplitude obeys average power of the decay factor in each footpath, and phase place is obeyed the even distribution of (0,2 π).A plurality of users' signal sends simultaneously, and the nonsystematic noise is additive white Gaussian noise (AWGN), makes ideal communication channel at the receiving terminal supposing the system and estimates that promptly hypothesis is separated the decay factor in the every footpath of timing known channel.Each group comprises M=17 symbol, wherein has 8 symbols to repeat to send as Cyclic Prefix.

B. result

1. referring to the BER-SNR curve of Fig. 7, it illustrates when spreading ratio is n=16, and error rate of system is along with the change curve of signal to noise ratio.What wherein SNR represented is the ratio of the average power homologous ray noise power spectral density in each footpath.

2. referring to the BER-n curve of Fig. 8, it illustrates when SNR=0dB, and error rate of system is along with the change curve of spreading ratio.

Although hereinbefore and with reference to the preferred embodiments of the present invention principle of the present invention and implementation are described in detail, those of ordinary skill in the art can make each improvement without departing from the present invention.For example, be the redundancy that example increases signal to be sent so that prefix to be set in this specification, so that solve an equation in receiver side, but also can adopt the mode that suffix is set, preceding L symbol in this data block placed the end of this data block, or place other positions; Can also change the precedence of some step or execution simultaneously, for example in receiver, can first despreading carry out regularly step again.These improvement and variant embodiment do not break away from the scope of the present invention of defined in claims of the present invention.

Claims (15)

1. CDMA spread spectrum method, comprising following steps:

The packet step, it is a plurality of data blocks of one group that data to be sent are divided into M symbol, M is the integer greater than 1;

Redundant step is set, selecting L symbol in the data block of each grouping and duplicating other positions that are put in this data block, forms the data block of M+L symbol, L is an integer that is less than or equal to M;

Modulation step is modulated the data block that redundant step gained is set;

The spread spectrum step is carried out CDMA spread spectrum to the data block after the modulation;

Discrete step rearranges the symbols behind the spread spectrum, chooses in M+L the symbol in each symbol the transmission of putting together of the 1st～n chip sequentially, and wherein each symbol comprises n chip.

2. spectrum spreading method according to claim 1 wherein in redundant step is set, copies to back L symbol of the symbol of the M in this data block before this data block, forms the data block of M+L symbol.

3. spectrum spreading method according to claim 1 wherein in redundant step is set, copies to preceding L symbol of the symbol of the M in this data block after this data block, forms the data block of M+L symbol.

4. code division multiple access despreading method is characterized in that comprising following steps:

Receive the grouping step, receive the data segment that sends corresponding in groups, every group of data segment comprises (M+L) * n chip;

It is rapid to separate discrete step, from the i of described one group of data block (i=1,2 ..., M+L) individual chip begins to take out successively i, M+L+i, 2 (M+L)+i ..., (n-1) * (M+L)+i chip, and output to extraction step in proper order, up to having got all chips;

Extraction step according to the position that redundant symbol is set before sending in these data, takes out M suitable symbol from separate the rapid symbol sebolic addressing that obtains afterwards of discrete step;

The despreading step is carried out despreading to the M that an is extracted symbol and is handled;

Solution procedure is set up equation group to the symbol of gained after the despreading, solves an equation, and tries to achieve the symbol sebolic addressing of original transmission.

5. despreading method according to claim 4 is characterized in that, chooses a last M symbol in described extraction step.

6. despreading method according to claim 4 is characterized in that, the fading coefficients that adopts each footpath that draws by channel estimating in described solution procedure is set up equation group according to the number of chips of the delay between each footpath and found the solution as parameter.

7. CDMA transmitters, comprising as lower device:

Packet memory, it is that a plurality of data blocks of one group are stored that data to be sent are divided into M symbol, M is the integer greater than 1;

Redundant apparatus is set, selecting L symbol in the data block of each grouping and duplicating other positions that are put in this data block, forms the data block of M+L symbol, L is an integer that is less than or equal to M;

Modulating device is modulated the data block that redundant step gained is set;

The spread spectrum discrete device, data block after the modulation is carried out the orthogonal code division multiple access spread spectrum, then the symbols behind the spread spectrum is rearranged, choose in M+L the symbol in each symbol the transmission of putting together of the 1st～n chip sequentially, wherein each symbol comprises n chip.

8. transmitter according to claim 7 wherein in redundant apparatus is set, copies to back L symbol of the symbol of the M in this data block before this data block, forms the data block of M+L symbol.

9. transmitter according to claim 7 wherein in redundant apparatus is set, copies to preceding L symbol of the symbol of the M in this data block after this data block, forms the data block of M+L symbol.

10. transmitter according to claim 7, described spread spectrum discrete device comprises symbols register (31), circulating register (32), multiplier (33), synchro system (34), orthogonal code maker (35), chip clock (36) and frequency divider (37), wherein:

Storage original symbol to be sent in the symbols register (31);

Symbols register (31) is connected to chip clock (36), and exports a group code under the driving of chip clock (36), and symbol numbers is M+L, and under the control of synchro system (34), symbols register (31) is in wait state subsequently;

Circulating register (32) receives this group code from symbols register (31), under the driving of chip clock (36), n time (n is a spreading ratio) of circulation output, then synchro system (34) again trigger symbol group register (31) export another group code, symbol numbers still is M+L;

Frequency divider (37) is the frequency division of the frequency of the clock of chip clock (36) frequency of 1/ (M+L), the data that drive orthogonal code maker (35) output pn sign indicating number and circulating register (32) output with the clock behind the frequency division multiply each other in multiplier (33), draw the discrete result of spread spectrum and output to subsequent conditioning circuit.

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

The grouping register, reception and storage are corresponding to the data segment that sends in groups, and every group of data segment comprises (M+L) * n chip;

In bulk the putting of dissociating, the i of the described data block of from register, storing (i=1,2 ..., M+L) individual chip begins to take out successively i, M+L+i, 2 (M+L)+i..., (n-1) * (M+L)+i chip, and output to extraction element in proper order, up to having got all chips;

Extraction element according to the position that redundant symbol is set before sending in these data, takes out M suitable symbol from separate the rapid symbol sebolic addressing that obtains afterwards of discrete step;

Despreading device carries out despreading to the M that an is extracted symbol and handles;

Solving device is set up equation group to the symbol of gained after the despreading, solves an equation, and tries to achieve the symbol sebolic addressing of original transmission.

12. receiver according to claim 11 is characterized in that, chooses a last M symbol in described extraction element.

13. receiver according to claim 11 is characterized in that, the fading coefficients that adopts each footpath that draws by channel estimating in described solving device is set up equation group according to the number of chips of the delay between each footpath and is found the solution as parameter.

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

Multiplier (41), adder (42), shift register (43), equation solver (44), orthogonal code maker (45), frequency divider (46), chip clock (47), synchro system (48) and channel estimator (49), wherein:

Frequency divider (46) is the clock frequency frequency division from chip clock (47) frequency of 1/ (M+L), drives orthogonal code maker (45) output pn sign indicating number with the clock behind the frequency division;

N * (M+L) individual chip was sent to multiplier (41) and channel estimator (49) by receiver received;

The pn sign indicating number that in multiplier (41) chip sequence that is received and orthogonal code maker (45) is produced multiplies each other;

Multiplied result is imported into adder (42) and shift register (43);

Under the driving of chip clock (47), this shift register (43) turns back to the signal of displacement output in the adder (42) with afterwards signal and carries out relevant summation, and outputs to equation solver (44);

The signal that is received is estimated channel parameter at channel estimator (49), and resulting channel parameter is transported to equation solver (44);

Solve primary signal by equation solver (44) by setting up equation group.

15. a code division multiple address communication system comprises transmitter and receiver, it is characterized in that:

Described transmitter comprises as lower device:

Packet memory, it is that a plurality of data blocks of one group are stored that data to be sent are divided into M symbol, M is the integer greater than 1;

Redundant apparatus is set, selecting L symbol in the data block of each grouping and duplicating other positions that are put in this data block, forms the data block of M+L symbol, L is an integer that is less than or equal to M;

Modulating device is modulated the data block that redundant step gained is set;

The spread spectrum discrete device, data block after the modulation is carried out CDMA spread spectrum, then the symbols behind the spread spectrum is rearranged, choose in M+L the symbol in each symbol the transmission of putting together of the 1st～n chip sequentially, wherein each symbol comprises n chip; Described receiver comprises as lower device:

The grouping register, reception and storage are corresponding to the data segment that sends in groups, and every group of data segment comprises (M+L) * n chip;

In bulk the putting of dissociating, the i of the described data block of from register, storing (i=1,2 ..., M+L) individual chip begins to take out successively i, M+L+i, 2 (M+L)+i ..., (n-1) * (M+L)+i chip, and output to extraction element in proper order, up to having got all chips;

Extraction element according to the position that redundant symbol is set before sending in these data, takes out M suitable symbol from separate the rapid symbol sebolic addressing that obtains afterwards of discrete step;

Despreading device carries out despreading to the M that an is extracted symbol and handles;

Solving device is set up equation group to the symbol of gained after the despreading, solves an equation, and tries to achieve the symbol sebolic addressing of original transmission.

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