CN101499817A - Demodulation method and apparatus in synchronous CDMA receiving system - Google Patents

Abstract

The invention discloses a demodulating method in a synchronous CDMA receiving system and a device thereof, which are used for eliminating intersymobl interference existing in the demodulated signals. The demodulating method comprises the following steps of: receiving signals transmitted by a signal transmitter to obtain received signals; utilizing channel estimation to structure a system matrix, estimating transmitted signals of the transmitter by the system matrix and the received signals and obtaining estimated and transmitted signals; and de-spreading and demodulation are carried out to the estimated and transmitted signals to obtain demodulated signals. The invention is used for demodulating the received signals in a CDMA receiving system and eliminating the intersymobl interference of the signals.

Description

Demodulation method in a kind of synchronous CDMA receiving system and device

Technical field

The present invention relates to communication technical field, relate in particular to demodulation method and device in a kind of S-CDMA access (CDMA) receiving system.

Background technology

In TD SDMA inserted (TD-SCDMA) grid, the signal that base station (NodeB) will send to each user carried out superposed and transmitted and goes out a plurality of users' signal Synchronization incoming terminal, (receiver).

Mobile telecommunication channel is a kind of multidiameter fading channel, and the spread-spectrum signal that transmitter sends is subjected to the reflection and the refraction of various barriers such as different buildings, hummock in transmission course, and each wave beam has different delays when arriving receiver, forms multipath signal.If the delay of different path signals surpasses the chip time delay of a pseudo-code, then different wave beam differences can be come at receiving terminal.

In the prior art, user terminal adopts RAKE receiver to receive the signal that NodeB sends usually, RAKE receiver receives each road signal respectively and carries out demodulation, those amplitudes are obviously taken out greater than the multipath component of background noise, it is delayed time and phasing, make it at a time to align, and merge by certain rule, become vector and merge into the algebraically summation, being originally that interference signals becomes useful signal and combines, strengthen reception, reach that multipath signal is become can be for the favorable factor of utilizing, effectively utilize multipath component, improve the effect of rake.

But, RAKE receiver can be the signal of other code channels as noise when the signal of this code channel of demodulation, each spreading code is not that 0 o'clock auto-correlation and cross correlation value is not 0 in skew, therefore, can not eliminate intersymbol interference (ISI) and multiple access interference (MAI) that the multipath transmission brings fully.Moreover, since spreading gain less relatively to capability of restraining noise a little less than, therefore can not bring good demodulation effect.

Existing user terminal substantially all adopts the algorithm detection signal of joint-detection, and the algorithm of this joint-detection is quite complicated, and reason comprises:

1, user terminal is only known the resource allocation information of own and common signal channel by air interface signaling, can not know before demodulation whether other users have taken code channel resource in the same time slot.

When 2, NodeB sent signal, through rate-matched, the code channel that may distribute in a certain time slot of a certain subframe did not send signal, and terminal is not known in advance.

3, some are current not at the common signal channel of this terminal, as physical access channel (FPACH, Fast Physical Access Channel) and other dedicated channels can adopt the wave beam forming technology, in the time of near other user terminals move to this terminal, these other user terminal signals are just stronger to the interference of this terminal, when other user terminals during away from this terminal, these user terminal signals have diminished again to the interference of this terminal, and this terminal is before demodulation and do not know the situation of change of these interference.

4, joint detection algorithm also needs each code channel signal that will receive in the current time slots, comprises that this user's channel, common signal channel and other users' channel detects demodulation together.Owing to above-mentioned 3 reasons, adopt joint-detection to separate timing in end side, need activate detection to the employed code channel of the signal that arrives in the current time slots, increased the complexity of algorithm greatly.

In sum, the demodulating algorithm that existing receiving terminal adopts to received signal is too complicated, can not eliminate the intersymbol interference that the multipath transmission brings fully.

Summary of the invention

The embodiment of the invention provides demodulation method in a kind of synchronous CDMA receiving system and the receiver in a kind of synchronous CDMA receiving system, in order to eliminate the intersymbol interference that exists in the restituted signal.

The demodulation method of a kind of synchronous CDMA receiving system that the embodiment of the invention provides comprises:

The signal that the received signal transmitter sends obtains received signal;

Utilize channel estimating tectonic system matrix, and, estimate the transmission signal of described transmitter, obtain estimating to send signal by this sytem matrix and described received signal;

Described estimation is sent signal carry out despread-and-demodulation, obtain restituted signal.

Receiver in a kind of synchronous CDMA receiving system that the embodiment of the invention provides comprises:

The received signal unit is used for the signal that the received signal transmitter sends, and obtains received signal;

Estimate to send signal element, be used to utilize channel estimating tectonic system matrix, and, estimate the transmission signal of described transmitter, obtain estimating to send signal by this sytem matrix and described received signal;

The restituted signal unit is used for that described estimation is sent signal and carries out despread-and-demodulation, obtains restituted signal.

The embodiment of the invention, the signal by the received signal transmitter sends obtains received signal; Utilize channel estimating tectonic system matrix, and, estimate the transmission signal of described transmitter, obtain estimating to send signal by this sytem matrix and described received signal; Described estimation is sent signal carry out despread-and-demodulation, obtain restituted signal, thereby avoided RAKE receiver can't eliminate problem in the restituted signal fully, the problem includes: the problem of intersymbol interference has improved the demodulation effect.

Description of drawings

Demodulation method schematic flow sheet in a kind of synchronous CDMA receiving system that Fig. 1 provides for the embodiment of the invention;

System's sending metrix schematic diagram that Fig. 2 provides for the embodiment of the invention;

Receiver structure schematic diagram in a kind of synchronous CDMA receiving system that Fig. 3 provides for the embodiment of the invention.

Embodiment

The embodiment of the invention provides the demodulation method in a kind of synchronous CDMA system reception, and the receiver in a kind of synchronous CDMA system, in order to the intersymbol interference that exists in the elimination restituted signal, and, reduce amount of calculation, improve demodulation efficient and effect.

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

Referring to Fig. 1, the demodulation method in a kind of synchronous CDMA receiving system that the embodiment of the invention provides comprises:

The signal that S101, reception send from signal transmitter, and calculate received signal e.

S102, employing least mean-square error piece linear equalization (MMSE-BLE) algorithm e are to received signal handled, to eliminate the intersymbol interference that sampling deviation brings, estimate the transmission signal d of transmitter, obtain estimating to send signal, the i.e. estimated vector that is superimposed by the chip signal that sends to each code channel user.

S103, utilize the spreading code of transmitter, the estimation of corresponding code channel is sent signal carry out despreading, the estimation that obtains after the despreading of each code channel sends signal b.

S104, utilize the estimation after the despreading of each code channel to send the signal to noise ratio that signal b calculates each code channel, and judge according to the signal to noise ratio of each code channel whether self code channel is in state of activation.

S105, when the signal to noise ratio of certain code channel during more than or equal to default threshold value, judge that this code channel is in state of activation, and, the estimation after the despreading of each code channel is sent signal b carries out demodulation, obtain the restituted signal of each code channel; Otherwise, judge that this code channel is in unactivated state, the estimation of giving up after the despreading of this code channel sends signal b.

Below above-mentioned steps is elaborated respectively.

Step S101:

If transmitter has sent the data of K code channel in current time slots, each Q chip of code channel spread spectrum code length (chip) sends N symbol.

If the symbol data of k code channel is: b ^(k) _j, j=0 ..., N-1, k=0 ..., K-1, wherein j is-symbol data number.

If the sequence of the spreading code that k code channel uses and the product of scrambler is c ^(k) _i, i=0 ..., Q-1.

Then the spread-spectrum signal on k code channel is:

s ^(k) _(j*Q+i)＝b ^(k) _j·c ^(k) _i，k＝0，…，K-1，j＝0，…，N-1，i＝0，…，Q-1

The composite signal of the data of K code channel is: $s=\underset{k=0}{\overset{K-1}{\mathrm{\Σ}}}{s}^{\left(k\right)}.$

S is through multipath channel h, and the received signal that is obtained terminal after being polluted by AWGN noise n is:

$e=s\⊗h+n$

Wherein

The computing of expression linear convolution.

Step S102:

If the maximum multipath delay spread of channel is no more than W chip in the current time slots, then channel h can be expressed as h _i, i=0 ..., W-1.

If the noise power of estimated channel h is in the current time slots

If the chip number on the data field is L, then satisfy L=NQ.

The sytem matrix A of the capable L of structure L+W-1 row then obtains system equation by least mean-square error (MMSE) criterion and is as shown in Figure 2:

$(A^H\·A+{\mathrm{\σ}}_n^2\·I)\·d=A^H\·e$

Wherein, the d estimated vector that the chip signal that sends to each code channel user is superimposed of serving as reasons, I is a unit matrix, A ^HAssociate matrix for A.

If matrix $R=(A^H\·A+{\mathrm{\σ}}_n^2\·I),$ Because the conjugate symmetry matter of matrix R can think that R equals the associate matrix H of a lower triangular matrix H and H ^HProduct, matrix R is carried out Qiao Luosiji (Cholesky) decomposes and to obtain lower triangular matrix H, that is: R=HH ^H, H wherein ^HBe the associate matrix of H, obviously H ^HBe upper triangular matrix.

Then system equation is:

H·H ^H·d＝A ^H·e

Hz=A solves an equation ^HE obtains z.

H solves an equation ^HD=z obtains estimated vector d, and its each component (estimation that is each code channel sends signal) is d _i, i=0 ..., L-1.

In the prior art, when the tectonic system matrix, considered despreading simultaneously, this makes sytem matrix bigger, causes calculation of complex, and exists channel to activate the problem that detects.And the embodiment of the invention is not considered despreading when the tectonic system matrix, only according to dissemination channel model construction sytem matrix, utilize sytem matrix to handle to received signal after, carry out de-spreading operation again, this makes sytem matrix smaller, calculates simple.

Step S103:

If the sequence of the product of this terminal use's spreading code and scrambler is c ^(k) _j, j=0 ..., Q-1, then each symbol data after the despreading of this spreading code correspondence is estimated as ${b^{\left(k\right)}}_i=\underset{j=0}{\overset{Q-1}{\mathrm{\Σ}}}(d_{i\·Q+j}\·{c^{{\left(k\right)}^{*}}}_j),i=0,\·\·\·,N-1.$

Step S104:

Signal to noise ratio is after calculating the demodulation on this code channel:

${\mathrm{SNR}}^{\left(k\right)}=\frac{{\left|E\left(\left|{b^{\left(k\right)}}_i\right|\right)\right|}^2}{E\left({|\left|{b^{\left(k\right)}}_i\right|-\left|E\left(\left|{b^{\left(k\right)}}_i\right|\right)\right||}^2\right)}$

Wherein, E () is that mathematic expectaion (mean value) is calculated.

Preestablish the activation thresholding SNR_threshold of code channel, if SNR ^(k)SIR_threshold or SNR ^(k)=SIR_threshold has then thought this code channel activating; Otherwise, think that this code channel does not activate, and gives up each symbol data of this code channel of estimating.

Wherein, activating thresholding SNR_threshold can obtain by emulation.

Step S105:

When judging that code channel is in state of activation, utilize maximum-likelihood criterion to b ^(k) _i, i=0 ..., N-1 adjudicates one by one, obtains demodulated symbols value v ^(k) _i, i=0 ..., N-1, the i.e. restituted signal of this code channel.

Introduce the device that the embodiment of the invention provides below.

Referring to Fig. 3, the receiver in a kind of synchronous CDMA receiving system that the embodiment of the invention provides comprises:

Received signal unit 31 is used for the signal that the received signal transmitter sends, and obtains received signal.

Estimate to send signal element 32, be used to utilize channel estimating tectonic system matrix, and, estimate the transmission signal of described transmitter, obtain estimating to send signal by this sytem matrix and described received signal.

Restituted signal unit 33 is used for that described estimation is sent signal and carries out despread-and-demodulation, obtains restituted signal.

Preferably, described estimation sends signal element 32, adopts least mean-square error piece linear equalization algorithm, by described sytem matrix and described received signal, estimates the transmission signal of described transmitter.

Preferably, described receiver also comprises:

Activate judging unit 34, be used for estimation according to each code channel of described transmitter and send signal and judge whether corresponding code channel is in state of activation.

Then described restituted signal unit 33 when code channel is in state of activation, sends signal to the estimation of this code channel and carries out despread-and-demodulation, obtains the restituted signal of this code channel.

Preferably, described activation judging unit 34 comprises:

Thresholding system unit 341 is used to set in advance the activation threshold value of code channel.

Signal to noise ratio unit 342 is used for the signal to noise ratio according to the corresponding code channel of estimation transmission calculated signals of described each code channel.

Whether identifying unit 343, the signal to noise ratio that is used to judge code channel be more than or equal to described activation threshold value, if judge that then this code channel is in state of activation; Otherwise, judge that this code channel is in unactivated state.

Preferably, described activation threshold value is determined by emulation in described threshold value unit 341.

Preferably, described restituted signal unit 33 comprises:

Despread unit 331 is used to utilize the spreading code of described transmitter, the estimation of respective channel is sent signal carry out despreading.

Demodulating unit 332 is used for that the estimation after the despreading is sent signal and carries out demodulation, obtains the restituted signal of respective channel.

In sum, after the embodiment of the invention is utilized channel estimating tectonic system matrix A, carry out the be eliminated estimation of transmitter of intersymbol interference of MMSE_BLE equilibrium earlier and send signal d, with spreading code d is carried out the demodulation of matched filtering integration again and obtain corresponding despread signal; And, utilize despreading after signal to noise ratio judge whether code channel is in state of activation.Make that by this scheme not needing that other code channels are carried out complicated activation detects, realize separating timing to the MMSE_BLE of iterative solution equation equalization algorithm after adopting Cholesky to decompose forward direction iterative solution Fang Cheng, sytem matrix adopts the channel estimating structure, matrix dimension is reduced, greatly reduce amount of calculation, also lack than the existing amount of calculation of joint detection algorithm when only detecting a code channel; And, eliminated ISI and MAI that the multipath transmission brings.

Obviously, those skilled in the art can carry out various changes and modification to the present invention and not break away from the spirit and scope of the present invention.Like this, if of the present invention these are revised and modification belongs within the scope of claim of the present invention and equivalent technologies thereof, then the present invention also is intended to comprise these changes and modification interior.

Claims (12)

1, the demodulation method in a kind of synchronous CDMA receiving system is characterized in that, this method comprises:

The signal that the received signal transmitter sends obtains received signal;

Utilize channel estimating tectonic system matrix, and, estimate the transmission signal of described transmitter, obtain estimating to send signal by this sytem matrix and described received signal;

Described estimation is sent signal carry out despread-and-demodulation, obtain restituted signal.

2, method according to claim 1 is characterized in that, adopts least mean-square error piece linear equalization algorithm, by described sytem matrix and described received signal, estimates the transmission signal of described transmitter.

3, method according to claim 1 is characterized in that, this method also comprises:

Send signal according to the estimation of each code channel of described transmitter and judge whether corresponding code channel is in state of activation;

When code channel is in state of activation, the estimation of this code channel is sent signal carry out demodulation, obtain the restituted signal of this code channel.

4, method according to claim 3 is characterized in that, sends the step that signal judges whether corresponding code channel is in state of activation according to the estimation of each code channel of described transmitter and comprises:

Set in advance the activation threshold value of code channel;

Send the signal to noise ratio of the corresponding code channel of calculated signals according to the estimation of described each code channel;

If the signal to noise ratio of code channel during more than or equal to described activation threshold value, judges that then this code channel is in state of activation; Otherwise, judge that this code channel is in unactivated state.

5, method according to claim 4 is characterized in that, described activation threshold value obtains by emulation.

6, method according to claim 1 is characterized in that, described estimation is sent signal carry out despread-and-demodulation, and the step that obtains restituted signal comprises:

Utilize the spreading code of described transmitter, the estimation of respective channel is sent signal carry out despreading;

Estimation after the despreading is sent signal carry out demodulation, obtain the restituted signal of respective channel.

7, the receiver in a kind of synchronous CDMA receiving system is characterized in that, this receiver comprises:

The received signal unit is used for the signal that the received signal transmitter sends, and obtains received signal;

Estimate to send signal element, be used to utilize channel estimating tectonic system matrix, and, estimate the transmission signal of described transmitter, obtain estimating to send signal by this sytem matrix and described received signal;

The restituted signal unit is used for that described estimation is sent signal and carries out despread-and-demodulation, obtains restituted signal.

8, receiver according to claim 7 is characterized in that, described estimation sends signal element, adopts least mean-square error piece linear equalization algorithm, by described sytem matrix and described received signal, estimates the transmission signal of described transmitter.

9, receiver according to claim 7 is characterized in that, this receiver also comprises:

Activate judging unit, be used for estimation according to each code channel of described transmitter and send signal and judge whether corresponding code channel is in state of activation;

Described restituted signal unit when code channel is in state of activation, sends signal to the estimation of this code channel and carries out despread-and-demodulation, obtains the restituted signal of this code channel.

10, receiver according to claim 9 is characterized in that, described activation judging unit comprises:

Thresholding system unit is used to set in advance the activation threshold value of code channel;

The signal to noise ratio unit is used for the signal to noise ratio according to the corresponding code channel of estimation transmission calculated signals of described each code channel;

Whether identifying unit, the signal to noise ratio that is used to judge code channel be more than or equal to described activation threshold value, if judge that then this code channel is in state of activation; Otherwise, judge that this code channel is in unactivated state.

11, receiver according to claim 10 is characterized in that, described activation threshold value is determined by emulation in described threshold value unit.

12, receiver according to claim 7 is characterized in that, described restituted signal unit comprises:

Despread unit is used to utilize the spreading code of described transmitter, the estimation of respective channel is sent signal carry out despreading;

Demodulating unit is used for that the estimation after the despreading is sent signal and carries out demodulation, obtains the restituted signal of respective channel.

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