CN1529438A - CDMA spectrum-spreading method, despreading method and receiver - Google Patents

Abstract

Basic points of the invention are that a special code set for spread spectrum is adopted when spectrum is spreaded. In the said code set, M pieces of spread spectrum codes are divided into N code group. Each code group contains K pieces of spread spectrum codes, M=NxK. Each code group represents a user group, and each code represents a user. It is orthogonal between frequency divisions. It is also orthogonal between spread spectrum codes in each code group. Since the feature of orthogonal frequency divisions, only cross talk on signals in group is needed to consider in succeeding signal processing. Thus, complexity of frequency-domain equalizer for CDMA user's signal is reduced greatly and cross talk between codes is lowered.

Description

CDMA spread spectrum method, despreading method and receiver

Technical field:

The invention belongs to mobile communication system, relate in particular to spectrum spreading method, despreading method and the receiver of system based on code division multiple access (CDMA).

Background technology:

After one of greatest difficulty of traditional code division multiple access (CDMA) technology was its spread-spectrum signal process frequency selective fading channels, the multiple access that received signal occurs disturbed, and the reason that its produces is the orthogonality that multipath delay has destroyed spreading code.One of it is the main reason of restriction cdma system capacity that multiple access disturbs, and under the situation that the future communications bandwidth increases, data rate improves, and multipath disturbs will become more serious, so the following especially wideband CDMA system key of success of the problems referred to above factor.Traditional cdma system receiving terminal utilizes the orthogonality of spreading code, extract required subscriber signal by RAKE receiver, but for the signal that has passed through frequency selective fading, each user's spreading code is because multipath delay no longer keeps quadrature, traditional RAKE receiver performance descends significantly, in order to address this problem, people have proposed a lot of methods.The method that traditional elimination multiple access disturbs can be divided into two kinds of transmitting terminal and receiving terminals, and transmitting terminal mainly contains design time-delay orthogonal code, preequalization etc.; Receiving terminal mainly contains equilibrium, Multiuser Detection etc.But design time-delay still keeps the code efficiency of spreading code of cross-correlation and autocorrelation performance too low, though and preequalization, equilibrium and multiuser detection better performances, its complexity is all divided the increase of number of users along with sign indicating number and is sharply increased.Solving the cdma system multiple access and disturb under lower complexity, is the current problem that presses for solution, and following especially CDMA is to the important prerequisite of broadband transition more.

Summary of the invention:

In traditional C DMA system, its basic thought is to utilize spreading code to make the information of each user/code channel be dispersed on the whole frequency bandwidth, so that utilize RAKE receiver to obtain the signal frequency diversity gain.Yet the problem that this spectrum spreading method brings in broadband connections is: (1) implements any balancing technique (as: MMSE equalizer) all needs bigger hardware costs.(2) in frequency selective fading channels, for arbitrary user/code channel information, all subscriber signal/code channels all can become its interference.Thereby hindered the application of multiuser detection.(3) lowered the efficient of RAKE receiver greatly.

The present invention is directed to the multiple access interference problem that exists in the existing cdma system, proposed a kind of to utilize spreading code frequency domain frequency division and time domain orthogonal to distinguish user's solution simultaneously.

First purpose of the present invention provides a kind of CDMA spread spectrum method, and the spreading code that it adopted is the frequency domain packet orthogonal intersection.

Second purpose of the present invention provides a kind of corresponding code division multiple access despreading method.

The 3rd purpose of the present invention provides the receiver that adopts above-mentioned despreading method.

Used alphabetical implication is in this specification: M is the length of spreading code, and N is the group number of spreading code grouping, and K is the number of every group of spreading code.

Technical scheme of the present invention is as follows:

The CDMA spread spectrum method comprises:

(1) modulation step: modulation system as required, binary digit is carried out the information symbol modulation, be about to binary message and be modulated to symbol; Described modulation system can adopt modes such as BPSK/QPSK or QAM;

(2) spread spectrum step: will select for use spreading code to implement the CDMA band spectrum modulation through the data based spreading ratio of ovennodulation and the code channel at place; Described spreading code is selected from a spreading code set, and in described spreading code set, M spreading code is divided into N code character, and each code character comprises K spreading code, M=N * K; Each code character is represented one group of user, and each sign indicating number represent a user, interblock frequency division quadrature, also quadrature between the interior spreading code of each code character.We define such sign indicating number and are the frequency domain packet orthogonal intersection.

(3) step of transmitting: the data symbol that spread spectrum obtains is launched after carrier modulation.

Above-mentioned CDMA spread spectrum method, in order to solve the problem of symbols streams front and back intersymbol interference, we use the recycling-guard position that is similar to the OFDM technology to guarantee the integrality of spreading code.Concrete scheme is: described spreading code itself comprises the recycling-guard position, is prefix CDMA sign indicating number, suffix CDMA sign indicating number or prefix and suffix CDMA sign indicating number; Perhaps, itself does not comprise the recycling-guard position described spreading code, and the data symbol that step (2) band spectrum modulation obtains adds the recycling-guard position earlier and forms prefix CDMA sign indicating number, suffix CDMA sign indicating number or prefix and suffix CDMA sign indicating number, enters step (3) again.The length L of recycling-guard position depends on the maximum multipath time-delay.The concrete method of recycling-guard position of adding is referring to the description in Chinese patent application 03109957.7 specification.

Above-mentioned CDMA spread spectrum method, the mode that we provide a kind of OFDM of employing and CDMA combination produces the generation method of described spreading code set frequency domain grouping orthogonal intersection, wherein the OFDM method has guaranteed the frequency division orthogonal property of different interblocks, and the CDMA method has guaranteed the relevant orthogonality on the time domain.Specific as follows:

1. frequency domain packet orthogonal intersection set design philosophy is as follows:

The central idea of spectrum spreading method of the present invention is a kind of spreading code set of design, and signal can be distinguished at frequency domain (by the frequency division characteristic of spreading code) and time domain (by the orthogonality of spreading code) under this set.Just orthogonal code sets is separable on frequency domain, has the frequency division orthogonal property between code character, and all sign indicating numbers have orthogonality in each code character.

1). the formation of code character quadrature

The spread-spectrum signal total frequency bandwidth of uniting of setting up departments is B _c, M equally spaced frequency of definition on this bandwidth utilizes M orthogonal intersection of the pairing complex-exponential function structure of this M frequency.At first this M frequency is divided into the N group, every group of K Frequency point.The adequate condition of each group code quadrature (that is: quadrature between the code character) is: do not have any group and use identical frequency.

2). the formation of quadrature in the code character

If K the frequency that satisfies above-mentioned orthogonality arranged: { ω in certain code character ₁, ω ₂.... and ω _K, these frequencies can be adjacent or discrete, corresponding quadrature basic vector is a complex-exponential function: ${\mathrm{\α}}_k=e^{j{\mathrm{\ω}}_{\mathrm{ki}}t},$ K=1,2, the ..K. spreading code can be by quadrature basic vector α _iCarry out unitary transformation and obtain, be shown below:

$P_m^{\left(i\right)}=\underset{k}{\mathrm{\Σ}}{u}_{\mathrm{ik}}{e}^{j{\mathrm{\ω}}_k{t}_m}---i=\mathrm{1,2},...K---\left(1\right)$

P wherein _m ⁽ⁱ⁾Be m chip value of i sign indicating number, u _IkBe the element in the tenth of the twelve Earthly Branches (U) matrix.Seek the spreading code that suitable unitary transformation just can constitute each code character.

2. simple frequency domain packet orthogonal spectrum expansion code constructing method:

Process for fear of the suitable unitary transformation of the search of complexity, the present invention further provides a kind of comparatively simple method that constitutes the frequency domain packet orthogonal intersection that satisfies above-mentioned condition, its central idea is to use one group of orthogonal code repeated arrangement on time domain to obtain all orthogonal codes in the code character, its frequency spectrum is made of the equally spaced Frequency point of being separated by, and then obtains the orthogonal code of other code characters by frequency spectrum translation.Two conditions of said frequency domain packet orthogonal intersection above so just having satisfied.Concrete building method is described below: suppose that we will constitute the spreading code that the satisfies condition set code that spreading ratio is M, requirement can be divided into it the N group, and every group is K=M/N spreading code, and each group takies different Frequency point set.We construct new spreading code in two steps:

The structure of (1) the 1st group of spreading code:

As mentioned above, the 1st group of spreading code is to repeat gained by one group of orthogonal code, at first we to find one group of spreading ratio be traditional spreading code of K, we can be referred to as generated code (Mother_Code), see Fig. 1 (a), its frequency spectrum is shown in Fig. 2 (a).Then generated code is repeated N time as the 1st group of spreading code code1 among the code, shown in Fig. 1 b.

Because repeating N time by generated code, code1 constitutes, so its frequency spectrum only accounts for the 0th in the total frequency spectrum M numerical frequency point, and N, 2N ... (K-1) this K of N Frequency point, shown in Fig. 2 b, satisfy the requirement that spreading code that we will design is gathered.

(2). the structure of other spreading codes

Because the frequency spectrum of the 1st group of spreading code (code1) of our (1) step structure only accounts for the 0th in the total frequency spectrum, N, 2N ... (K-1) this K of N Frequency point, if so with the frequency spectrum of the 1st group of spreading code ω that moves right ₀₂(ω ₀₂Be the frequency interval of spreading code frequency spectrum, ${\mathrm{\ω}}_{02}=\frac{2\mathrm{\π}}{{\mathrm{MT}}_c}$ ), be about to the 1st group of spreading code and on time domain, be multiplied by

(n represents the spreading code chip timing), just can obtain another group orthogonal code, and its frequency spectrum only takies the 1st, N+1,2N+1, ..., (K-1) this K of N+1 Frequency point is with the 1st group of spreading code frequency spectrum aliasing not, satisfy the condition of frequency domain packet orthogonal intersection set, organize orthogonal code as the 2nd group of spreading code code2 with this, by that analogy, with the 1st group of spreading code difference frequency displacement 2 ω ₀₂, 3 ω ₀₂..., (N-1) ω ₀₂Can obtain the 3rd, 4,,,,,,,, N organizes spreading code, and its frequency spectrum is shown in Fig. 2 c.Time domain waveform can be obtained by first group of spreading code and corresponding complex-exponential function dot product, shown in Fig. 1 c.

By (1) (2) two steps, we have just constituted the frequency domain packet orthogonal intersection set that satisfies condition like this, and the sign indicating number in each code character is orthogonal, and each code character takies a part of Frequency point, and any two groups do not have identical Frequency point.

Spectrum spreading method of the present invention, its inventive point are to design a kind of spreading code set, and they are divided into some groups, have the frequency division orthogonal property between every group code, and also have orthogonality between the sign indicating number in each group.Because interblock has the frequency division orthogonal property, need only the consideration group on signal processing subsequently in the crosstalking of signal, reduce the complexity of CDMA subscriber signal frequency-domain equalizer greatly and reduce intersymbol interference.This method makes traditional technology, as balancing technique, multiuser detection etc., enforcement can in a less signal subspace, carry out.Therefore, created a good condition for the practicability of these technology.

At aforesaid CDMA spread spectrum method, the present invention proposes its corresponding code division multiple access despreading method, comprises the steps:

(1) receiving symbol step: according to synchronizing information, the data flow that receives is divided into the serial data that length is M chip, M refers to the number of chips of spreading code, i.e. spreading ratio;

(2) code character separating step: from an above-mentioned N block signal, extract the frequency signal (for example: use FFT) of a required code character, the signal of other frequencies is changed to 0; (3) user profile separating step: utilize traditional method from K subscriber signal of a code character being extracted, to extract a required user's signal; , concrete grammar can be selected according to actual needs.

(4) demodulation judgement: according to the modulation system that transmitting terminal adopts, the symbol that obtains is separated the mediation judgement, output binary bits information.

Above-mentioned code division multiple access despreading method if the data flow that receives comprises the recycling-guard position, is removed the recycling-guard position of containing intersymbol interference in the data flow earlier in the then described step (1), residue does not contain the complete symbols of intersymbol interference.

Above-mentioned code division multiple access despreading method, described step (2) can be finished by M point FFT and decimation in frequency, or replaces traditional M point FFT by frequency spectrum translation and N K point FFT and finish, and the latter can reduce the complexity of realization.

Above-mentioned code division multiple access despreading method, described step (3) is finished as follows: earlier the code group information of separating is carried out the equilibrium of K point on frequency domain, again to the despreading of being correlated with of the signal after the equilibrium, extract required user's information.

The despreading method that traditional cdma system adopts is directly all users to be carried out equilibrium or Multiuser Detection, complexity is very high, amount of calculation is very big, despreading method of the present invention utilizes frequency spectrum that a part of subscriber signal is separated earlier, more remaining user is handled, and greatly reduces complexity, though each spreading code only accounts for a part of Frequency point, but as long as Frequency point is not very little, still can reach diversity, can not make decreased performance.

At aforesaid code division multiple access despreading method, CDMA receiver of the present invention comprises:

Code character separator: be used for obtaining a required code character frequency signal N the code character, the signal of other frequencies is changed to 0, the block signal that obtains separating from received signal;

Subscriber signal separation of user device: the signal that is used in a block signal that is separated, extracting a required user K user of this code character;

Demodulation judgment device: be used for that the modulation system that required subscriber signal adopts according to transmitting terminal is carried out demodulation and declare and determine.

Above-mentioned CDMA receiver; when received data flow comprises the recycling-guard position; described CDMA receiver comprises that is also removed a recycling-guard position device, is used to abandon the recycling-guard bit code sheet of information symbol, and intercepting does not have a segment signal of intersymbol interference.

Above-mentioned CDMA receiver, described code character separator can be finished by M point FFT and decimation in frequency, also can replace traditional M point FFT with frequency spectrum translation and N K point FFT and finish, and the latter can reduce the complexity of realization.

Above-mentioned CDMA receiver, described subscriber signal separator comprises frequency-domain equalizer and relevant despreading device, described frequency-domain equalizer carries out the equilibrium of K point to the code group information of separating on frequency domain; Signal after the equilibrium by the despreading of being correlated with of described relevant despreading device, is extracted required user's information.

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 a kind of construction process of the spreading code set in the spectrum spreading method of the present invention, wherein:

Fig. 1 (a) shows the structure of generated code;

Fig. 1 (b) shows the structure of first group of spreading code;

The vector that Fig. 1 (c) need be multiplied by when showing i group spreading code structure, wherein ω _iBe of the frequency displacement of I group spreading code with respect to the 1st group of spreading code, ${\mathrm{\ω}}_i=(i-1)\frac{2\mathrm{\π}}{{\mathrm{MT}}_c},$ M is a spreading ratio, T _cBe chip duration.

Fig. 2 shows the digital spectrum of the frequency domain packet orthogonal intersection of the present invention's structure, wherein:

Fig. 2 (a) is the digital spectrum of generated code K point DFT gained, and frequency interval is:

${\mathrm{\ω}}_{01}=\frac{2\mathrm{\π}}{{\mathrm{KT}}_c},$ (T _cBe chip duration)

Fig. 2 (b) illustrates the digital spectrum of the 1st group of spreading code M point DFT gained, and frequency interval is:

${\mathrm{\ω}}_{02}=\frac{2\mathrm{\π}}{{\mathrm{MT}}_c}$

Fig. 2 (c) shows the digital spectrum of i group spreading code M point DFT gained, and frequency interval is

${\mathrm{\ω}}_{02}=\frac{2\mathrm{\π}}{{\mathrm{MT}}_c}$

Fig. 3 illustrates traditional C DMA system flow chart;

Fig. 4 illustrates and adopts cdma system flow chart of the present invention;

Fig. 5 illustrates traditional frequency-domain equalizer flow chart;

Fig. 6 illustrates the employed frequency-domain equalizer flow chart of receiver of the present invention;

Fig. 7 illustrates system's bit error rate curve of emulation gained.

Embodiment:

At first with reference to the traditional C DMA mobile communication system of Fig. 3 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.

Introduce the communication system that adopts spread spectrum of the present invention, despreading method below with reference to Fig. 4.

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.Just the needed spreading code of spread spectrum need be chosen the designed frequency domain packet orthogonal intersection of the present invention, needs behind the spread spectrum to insert Cyclic Prefix by 21 before each symbol, like this, has guaranteed that the symbol frequency spectrum is not subjected to the influence of intersymbol interference.

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 22, and intercepting does not have a segment signal Y1 of intersymbol interference.Remaining signal Y is obtained the information of required user profile place Frequency point by code character separator 23, other frequency point values are changed to 0, we have just obtained only comprising the signal Y2 of K user profile on the same group like this, the code character separator can use as shown in the figure M point FFT and decimation in frequency to constitute, also can replace M point FFT with frequency spectrum translation and N K point FFT, the signal that obtains is a frequency-region signal.From the signal of a code character, extract required user's signal then by subscriber signal separator 24.The subscriber signal separator can be taked diverse ways as required, the flow chart of drawing among the figure that is to use equalizer and relevant despreading method, and we illustrate as example.According to the channel of estimating gained signal is passed through equalizer, can obtain the signal Y3 after the equilibrium, Y3 is equivalent to the signal stack that spreading ratio after the equilibrium is all users of traditional C DMA system of K (seeing hereinafter the explanation to Fig. 6 for details), again by relevant despreading 25 utilize length for the generated code of K to the signal despreading of being correlated with, can only be comprised required subscriber signal s ^(k)With the signal Y4 of system noise, then Y4 is carried out demodulation judgement 19 and obtain binary message.

Introduce traditional frequency-domain equalizer below with reference to Fig. 5.

At first channel carries out the frequency domain response that M point FFT obtains channel by step 31, utilize this frequency response to calculate the frequency response of equalizer by step 32 again, directly the frequency response of equalizer and frequency-region signal are multiplied each other by step 33 and obtain frequency-region signal after the equilibrium, this signal is carried out time-domain signal after M point IFFT obtains equilibrium by step 34, and this moment, system was the spreading ratio M point cdma system after the equilibrium.

Introduce the applied frequency-domain equalizer of receiver of the present invention with reference to Fig. 6 at last.

Because the signal frequency domain of native system receiving terminal after by the code character separator only comprises K Frequency point, and K different Frequency point of CU on the same group not, so at first channel is carried out different frequency spectrum translations by step 41 according to the difference of the group at required user place, this can be realized by directly multiply by a complex-exponential function, and then carry out K point FFT by step 31 pair channel, so just obtained the frequency response of channel at required Frequency point, obtain the frequency response of equalizer by step 32 again at required Frequency point, the frequency response of this K point and the signal that only comprises K Frequency point are multiplied each other by step 33, obtain the frequency-region signal after the subscriber signal equilibrium on the same group, owing to carried out frequency spectrum translation, frequency domain characteristic according to the frequency domain packet orthogonal intersection, this moment, no matter the signal of gained was the signal of which group, all be equivalent to the frequency spectrum of this group subscriber signal by first group of spreading code spread spectrum gained signal, because this code character is 0 at the energy of other frequencies, so this K frequency has comprised the energy of these all signals of code character, by step 34 it is carried out the time-domain signal that K point IFFT can obtain comprising these all signal energies of code character again, and each symbol has only K chip on the time domain at this moment, according to the frequency domain characteristic of frequency domain packet orthogonal intersection and the character of IFFT conversion, we know that signal that this moment, the time-domain signal that obtains was equivalent to this code character is the signal that the generated code of K carries out the spread spectrum gained with length under the prerequisite that does not reduce symbol energy, promptly having obtained N spreading gain doubly this moment, is that spreading ratio after the equilibrium is the traditional C DMA system of K with system transition.

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.Frequency spreading code division is the N group, every group K.

1. the structure thought of frequency domain packet orthogonal intersection

The structure thought of frequency domain packet orthogonal intersection is that M spreading code is divided into the N group, and every group K, every group of acquisition frequency point situation can be expressed in matrix as:

Any two elements (2) inequality in the matrix

Spreading code in one group is orthogonal and only take K Frequency point, and can be lost by orthogonal basis has conversion to obtain, and we can rewrite as follows with matrix-style formula (1):

P＝UE

P=[p wherein _Km] _{K * M}, be the matrix that the spreading code in the code character is formed

U=[u _Ik] _{K * K}, be K dimension unitary matrice (3)

$E=[e_{\mathrm{km}}{]}_{K\×M}=[e^{j{w}_{\mathrm{nk}}{t}_m}{]}_{K\×M},$ The base that is the shared frequency of n group spreading code loses the matrix that constitutes

2. the straightforward procedure of the structure of frequency domain packet orthogonal intersection

In the straightforward procedure of structure frequency domain packet orthogonal intersection provided by the invention, generated code is K the orthogonal code that length is K, and it can be the spreading code in the traditional C DMA system, and he with vector representation is:

$M^{\left(k\right)}=[m_0^{\left(k\right)},m_1^{\left(k\right)},m_2^{\left(k\right)}\·\·\·,m_{K-1}^{\left(k\right)}](k=\mathrm{0,1}..,K-1)---\left(4\right)$

It satisfies

Its digital spectrum can be expressed as

F _M ^(k)＝[F _M0 ^(k)，F _M1 ^(k)，F _M2 ^(k)，...，F _MK-1 ^(k)] (k＝0，1..，K-1) (6)

Shown in Fig. 2 (a).

The 1st group of spreading code that obtains by generated code can be expressed as:

$Q^{\left(k\right)}=[q_0^{\left(k\right)},q_1^{\left(k\right)},......q_{\mathrm{SF}-1}^{\left(k\right)}]=[m_0^{\left(k\right)},m_1^{\left(k\right)},\·\·\·,m_{M-1}^{\left(k\right)},m_0^{\left(k\right)},m_1^{\left(k\right)},\·\·\·,m_{M-1}^{\left(k\right)},...m_0^{\left(k\right)},m_1^{\left(k\right)},\·\·\·,m_{M-1}^{\left(k\right)}]$

$k=\mathrm{0,1},...,K-1---\left(7\right)$

Shown in Fig. 1 (b), because it repeats gained by (4), so it also satisfies orthogonal property.

Its digital spectrum can be expressed as

${F_Q}^{\left(k\right)}=[{F_{Q0}}^{\left(k\right)},{F_{Q1}}^{\left(k\right)},{F_{Q2}}^{\left(k\right)},...,{F_{\mathrm{QSF}-1}}^{\left(k\right)}]$

$k=\mathrm{0,1},...,K-1---\left(8\right)$

Shown in Fig. 2 (b).

I group spreading code can be expressed as

$Q^{\left(k\right)}=[q_0^{\left(k\right)},q_1^{\left(k\right)},......q_{\mathrm{SF}-1}^{\left(k\right)}]=$

$[m_0^{\left(k\right)},m_1^{\left(k\right)},\&CenterDot;\&CenterDot;\&CenterDot;,m_{M-1}^{\left(k\right)},m_0^{\left(k\right)},m_1^{\left(k\right)},\&CenterDot;\&CenterDot;\&CenterDot;,m_{M-1}^{\left(k\right)},...,m_0^{\left(k\right)},m_1^{\left(k\right)},\&CenterDot;\&CenterDot;\&CenterDot;,m_{M-1}^{\left(k\right)}]\&CenterDot;[1,{\mathrm{<figure-callout\; id="2"\; label="e\; ji"\; filenames="A0313494100201.png"\; state="\{\{state\}\}">e</figure-callout>}}^{\mathrm{ji}},{\mathrm{<figure-callout\; id="2"\; label="e\; ji"\; filenames="A0313494100201.png"\; state="\{\{state\}\}">e</figure-callout>}}^{\mathrm{ji}},...,e^{\mathrm{ji}(\mathrm{SF}-1)*2\mathrm{\&pi;}/\mathrm{SF}}]$

$k=K*(i-1),K*(i-1)+1,...,K*i-1---\left(9\right)$

Shown in Fig. 1 (c), it is equivalent to first group of spreading code and is multiplied by a scrambler gained, thus still satisfy orthogonality, so the spreading code of respectively organizing that neotectonics is come out satisfy,

Its frequency spectrum is

${F_Q}^{\left(k\right)}=[{F_{Q0}}^{\left(k\right)},{F_{Q1}}^{\left(k\right)},{F_{Q2}}^{\left(k\right)},...,{F_{\mathrm{QSF}-1}}^{\left(k\right)}]$

$k=K*(i-1),K*(i-1)+1,...,K*i-1---\left(11\right)$

Shown in Fig. 2 (c).Organize the spreading code frequency spectrum as can be seen by the 1st group of spreading code and i, each spread spectrum code character takies K Frequency point, and its matrix element with respect to formula (2) is

ω _ij＝Ω _(i-1)N+(j-1) i＝1，2，...，K，j＝1，2，...，K (12)

Wherein Ω represents the total frequency spectrum of spreading code.

According to formula (10) and (12) as can be seen the spreading code that comes out of neotectonics satisfy the thought of the frequency domain packet orthogonal intersection in 1, can construct the frequency domain packet orthogonal intersection.

3. signal transmitting method

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

$Z^{\left(k\right)}\left(n\right)=s_i^{\left(k\right)}{q}_n^{\left(k\right)}\mathrm{\&Gamma;}(t-n{T}_c)---n=\mathrm{0,1},......,M---\left(13\right)$

N is the chip sequence number that transmits in the formula, 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:

Interpolation length is that the mathematic(al) representation behind the L Cyclic Prefix is:

The mathematic(al) representation that multi-user's prefix CDMA transmits is

$\mathrm{\&Phi;}\left(n\right)=\underset{k=0}{\overset{\mathrm{SF}-1}{\mathrm{\&Sigma;}}}{S}^{\left(k\right)}\left(n\right)---\left(16\right)$

4. frequency selective fading footpath channel

If: a frequency selective fading channels wideband pulse response characteristic is:

$h\left(t\right)=\underset{l=0}{\overset{L}{\mathrm{\&Sigma;}}}{h}_l^{\left(k\right)}\mathrm{\&delta;}(t-l{T}_c)---\left(17\right)$

T in the formula _cRepresent time that chip continued and time delay sequence number respectively with l, L is the footpath number.

5. signal acceptance method

For the cdma system that has added Cyclic Prefix, removed at receiving terminal that the signal Y1 of gained is equivalent to not have the symbol of prefix and the circular convolution of channel behind the Cyclic Prefix, the mathematic(al) representation of an one symbol can be expressed as:

Y1＝[S′ ₀，S′ ₁，...S′ _SF][h ₀(t)，h ₁(t)，...，h _L(t)]+n

Wherein ${S^{\&prime;}}_n=\underset{k=0}{\overset{\mathrm{SF}-1}{\mathrm{\&Sigma;}}}{Z}^{\left(k\right)}\left(n\right),$ For all remove the spread symbol stack of prefix, ₍₁₈₎

 represents circular convolution, and n is a system noise

Only comprised the required user Y2 of signal on the same group through the code character separator again, the mathematic(al) representation of a symbol of its time domain is:

Y2＝[S″ ₀，S″ ₁，...S″ _SF][h ₀(t)，h ₁(t)，...，h _L(t)]+n′

Wherein ${S^{\&prime;\&prime;}}_n=\underset{k=(K-1)i}{\overset{\mathrm{Ki}-1}{\mathrm{\&Sigma;}}}{Z}^{\left(k\right)}\left(n\right),$ For the spread symbol with required user all removal prefixes on the same group superposes (19)

I represents the group at user place, and  represents circular convolution, and n ' is the noise after the frequency selection purposes

Pass through equalizer then, obtain signal Y3 (explaining the explanation of literary composition to Fig. 6 of seing before in detail), the mathematic(al) representation of its each symbol is

Y3＝[S ₀，S ₁，...S _K]+n″

Wherein ${S^{\&prime;\&prime;\&prime;}}_n=\underset{k=(K-1)i}{\overset{\mathrm{Ki}-1}{\mathrm{\&Sigma;}}}{s}^{\left(k\right)}{q}_n^{\left(\mathrm{mod}(k,K)\right)}\mathrm{\&Gamma;}(t-n{T}_c),$ Mod () represents complementation (20)

I represents the group at user place, n " is the noise after the equilibrium

Through relevant despreading, obtain signal Y4 then, the mathematic(al) representation of its each symbol is

Y4＝s ^(k)+n+MAI

s ^(k)Be required subscriber signal, n is last equivalent noise, and MAI is that remaining multiple access disturbs (21)

6. analysis of complexity

Adopt the communication system of technical solution of the present invention, its transmitting terminal and common prefix CDMA are just the same, the demodulation judgement part of receiving terminal is also just the same, below we analyze the complexity of other parts of receiving terminal, and and common prefix CDMA compare, still to use frequency-domain equalizer to be example.Technical scheme of the present invention, receiving terminal are mainly considered the complexity of code character separator, user's separator, and the code character separator constitutes by M point FFT and decimation in frequency, and its complexity is Mlog ₂(M), if replace M point FFT with frequency spectrum translation and N K point FFT, its complexity is Mlog ₂(K)+M.User's separator comprises equalizer and relevant despreading two parts.Owing to the invention enables the signal after the frequency selection purposes only to comprise K Frequency point, so balanced part is thereafter all only used the situation of considering K Frequency point, according to shown in Figure 6, the employed equalizer complexity of system of the present invention is: 2Klog ₂(K)+and 3K+L multiplication, need be the relevant of K only when system of the present invention is correlated with despreading, so total complexity of system of the present invention can be expressed as: 2Klog as length ₂(K)+4K+L+Mlog ₂(M) inferior multiplying separates if finish code character with frequency spectrum translation with N K point FFT replacement M point FFT, and its total complexity can be reduced to: (2K+M) log ₂(K)+4K+L+M multiplying; For common prefix cdma system, only with the complexity of considering equalizer and relevant despreading, they all need as length is the calculating of M to its receiving terminal, and according to Fig. 5, its total complexity can degree of being expressed as be: 3Mlog ₂(M)+4M multiplying, because M=K * N＞＞K＞L, so communication system of the present invention greatly reduces complexity for common prefix CDMA.

7. simulation result

(1) simulated conditions

Adopt the Matlab programming, under WindowsXP, implement to adopt the emulation of the designed cdma system of technical solution of the present invention, with the MMSE equilibrium treatment on the same group signal be example, and as a comparison, also carried out using the performance simulation of the prefix cdma system of traditional spreading code and MMSE equilibrium.Emulation comprises the down channel error ratio characteristic that adopts the designed system of technical solution of the present invention, and compares with the RAKE receiver of traditional C DMA system and the error rate using common spreading code spread spectrum and use the prefix cdma system of MMSE equilibrium.

The information symbol of system is the BPSK modulation.Spreading ratio M=64, spreading code designs by method provided by the invention, the scrambler that provides among the TD-SCDMA is provided for the Walsh sign indicating number its generated code, determine the length of generated code according to the difference of packet count, the packet count N=4 that uses during emulation, every group of spreading code number K=M/N=16 is so the length of generated code also is 16.Circulating prefix-length equals the time delay extension width.

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. 7 has provided the error rate of system simulation result of the present invention that uses the MMSE equilibrium, and uses the performance of MMSE equilibrium to compare with the RAKE receiver of traditional C DMA system and common prefix CDMA.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, have destroyed the orthogonality of spreading code, well do not improve by RAKE receiver yet, and along with the footpath number to increase performance more abominable.And adopted the prefix cdma system of MMSE equilibrium, the error rate has had tangible improvement, and systematic function is increasing and descend with the footpath number not, has clear superiority than traditional C DMA systematic function, the present invention uses the system of MMSE equilibrium and common prefix cdma system performance about the same, and the front was discussed computational complexity of the present invention and was significantly less than common prefix cdma system, so system of the present invention has been issued to the performance same with common prefix CDMA at lower complexity, has tangible technical advantage.

Although hereinbefore and with reference to preferred embodiment of the present invention technical scheme of the present invention and embodiment 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, distinguish subscriber signal on the same group with the method for equilibrium in this specification, but also can use methods such as Multiuser Detection, maximum likelihood method; In addition in selection, the frequency selection purposes of the production method of spreading code, generated code, also other method or the like can be arranged on the process such as subscriber signal differentiation on the same group.These distortion and improvement example do not depart from the scope of the present invention.

Claims (13)

1. CDMA spread spectrum method comprises:

(1) signal modulation step: modulation system as required, binary digit is carried out the information symbol modulation;

(2) spread spectrum step: will adopt spreading code to implement the CDMA band spectrum modulation through the data based spreading ratio of ovennodulation and the code channel at place;

(3) step of transmitting: the data symbol that spread spectrum obtains is launched after carrier modulation;

It is characterized in that,

Described spreading code is selected from a spreading code set, and in described spreading code set, M spreading code is divided into N code character, and each code character comprises K spreading code, M=N * K; Each code character is represented one group of user, and each sign indicating number is represented a user, interblock frequency division quadrature, quadrature between the spreading code in each code character.

2. CDMA spread spectrum method as claimed in claim 1 is characterized in that described spreading code itself comprises the recycling-guard position, is prefix CDMA sign indicating number, suffix CDMA sign indicating number or prefix and suffix CDMA sign indicating number.

3. CDMA spread spectrum method as claimed in claim 1; it is characterized in that; itself does not comprise the recycling-guard position described spreading code; after step (2) band spectrum modulation obtains data symbol; add the recycling-guard position earlier and form prefix CDMA sign indicating number, suffix CDMA sign indicating number or prefix and suffix CDMA sign indicating number, enter step (3) again.

4. CDMA spread spectrum method as claimed in claim 1 is characterized in that, described spreading code set produces as follows:

The spread-spectrum signal total frequency bandwidth of uniting of setting up departments is B _c, M equally spaced frequency of definition on this bandwidth, with M orthogonal intersection of complex-exponential function structure of this M frequency, all complex-exponential functions are in the information symbol duration T _sLast quadrature; Concrete building method comprises the structure of code character and the structure of the interior orthogonal code of code character:

The structure of code character is that this M frequency is divided into the N group, and every group comprises K Frequency point, does not have any code character and uses identical frequency, has so just constructed N frequency division orthogonal code sets;

In the code character structure of orthogonal code be complex-exponential function with this K frequency as basic vector, make K the spreading code that the unitary transformation formation satisfies orthogonality condition, its spreading ratio is M.

5. CDMA spread spectrum method as claimed in claim 4, it is characterized in that, described spreading code set produces as follows: use one group of K orthogonal code repeated arrangement on time domain to obtain all orthogonal codes in first code character for N time, its frequency spectrum is made of the equally spaced Frequency point of being separated by, and then first code character is obtained the orthogonal code of other (N-1) individual code characters by frequency spectrum translation.

6. the code division multiple access despreading method comprises the steps:

(1) receiving symbol step: according to synchronizing information, the data flow that receives is divided into the serial data that length is M chip, M refers to the number of chips of spreading code, i.e. spreading ratio;

(2) code character separating step: from an above-mentioned N block signal, extract the frequency signal of a required code character, the signal of other frequencies is changed to 0;

(3) user profile separating step: the signal that from K subscriber signal of a code character being extracted, extracts a required user;

(4) demodulation judgement:, the symbol judgement that obtains is exported binary bits information according to the modulation system that transmitting terminal adopts.

7. code division multiple access despreading method as claimed in claim 6; it is characterized in that; if the data flow that receives comprises the recycling-guard position, remove the recycling-guard position of containing intersymbol interference in the data flow in the then described step (1) earlier, residue does not contain the complete symbols of intersymbol interference.

8. code division multiple access despreading method as claimed in claim 6 is characterized in that, described step (2) is to finish by M point FFT and decimation in frequency, or finishes by frequency spectrum translation and N K point FFT.

9. code division multiple access despreading method as claimed in claim 6, it is characterized in that, described step (3) is finished as follows: the code group information of separating is carried out the K point on frequency domain balanced, again to the despreading of being correlated with of the signal after the equilibrium, extracts required user's information.

10. CDMA receiver is characterized in that comprising:

Code character separator: be used for obtaining a required code character frequency signal N the code character, the signal of other frequencies is changed to 0, the block signal that obtains separating from received signal;

Subscriber signal separator: the signal that is used in a block signal that is separated, extracting a required user K user of this code character;

Demodulation judgment device: be used for the modulation system that the gained subscriber signal adopts according to transmitting terminal is separated the mediation judgement.

11. CDMA receiver as claimed in claim 10; it is characterized in that; when received data flow comprises the recycling-guard position; described CDMA receiver comprises that is also removed a recycling-guard position device; be used for abandoning the recycling-guard bit code sheet of received information symbol, intercepting does not have a segment signal of intersymbol interference.

12. CDMA receiver as claimed in claim 10 is characterized in that, described code character separator comprises a M point FFT device and a decimation in frequency device; Perhaps, comprise frequency spectrum translation device and a K point FFT device.

13. CDMA receiver as claimed in claim 10 is characterized in that, described subscriber signal separator comprises frequency-domain equalizer and relevant despreading device, and described frequency-domain equalizer carries out the equilibrium of K point to the code group information of separating on frequency domain; Signal after the equilibrium by the despreading of being correlated with of described relevant despreading device, is extracted required user's information.

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