CN101499817B - 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 a kind of S-CDMA and insert demodulation method and device in (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 receives 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 can different wave beam differences be come at receiving terminal.

In the prior art, user terminal adopts RAKE receiver to receive the signal that NodeB sends usually, and 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 multipath signal is become the favorable factor that can supply utilize, 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 basically 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 through 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 possibly in a certain time slot of a certain subframe, distribute did not send signal, and does not know in advance at the terminal.

3, some current common signal channels that are not directed against this terminal; Like physical access channel (FPACH; Fast Physical Access Channel) and other dedicated channels can adopt 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 at this terminal, when other user terminals during away from this terminal; These user terminal signals have diminished again to the interference at this terminal, and this terminal is before demodulation and do not know the situation of change of these interference.

4, joint detection algorithm also need comprise that this user's channel, common signal channel and other users' channel detects demodulation together with each code channel signal that receives in the current time slots.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 and the receiver in a kind of synchronous CDMA receiving system in a kind of synchronous CDMA receiving system, in order to eliminate the intersymbol interference that exists in the restituted signal.

Demodulation method in a kind of synchronous CDMA receiving system that the embodiment of the invention provides, this method comprises:

Receive the signal that signal transmitter sends, obtain receiving signal;

Utilize channel estimating tectonic system matrix, adopt least mean-square error piece linear equalization algorithm, and, estimate the transmission signal of said transmitter, obtain estimating to send signal through this sytem matrix and said reception signal;

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

The signal to noise ratio of utilizing the estimation after the despreading of each code channel to send each code channel of calculated signals, and judge according to the signal to noise ratio of each code channel whether self code channel is in state of activation;

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

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

Receive signal element, be used to receive the signal that signal transmitter sends, obtain receiving signal;

Estimate to send signal element, be used to utilize channel estimating tectonic system matrix, adopt least mean-square error piece linear equalization algorithm, and, estimate the transmission signal of said transmitter, obtain estimating to send signal through this sytem matrix and said reception signal;

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

The restituted signal unit is used to utilize the spreading code of said transmitter, signal is sent in the estimation of respective channel carry out despreading; When code channel is in state of activation, signal is sent in the estimation after the despreading carry out demodulation, obtain the restituted signal of respective channel.

The embodiment of the invention through receiving the signal that signal transmitter sends, obtains receiving signal; Utilize channel estimating tectonic system matrix, and, estimate the transmission signal of said transmitter, obtain estimating to send signal through this sytem matrix and said reception signal; Signal is sent in said estimation 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 sketch map that Fig. 2 provides for the embodiment of the invention;

Receiver structure sketch map 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 are sent from signal transmitter, and calculate reception 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 estimated vector that promptly is superimposed by the chip signal of sending to each code channel user.

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

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 preset threshold value, judge that this code channel is in state of activation, and, signal b is sent in the estimation after the despreading of each code channel carries out demodulation, obtain the restituted signal of each code channel; Otherwise, judging that this code channel is in unactivated state, signal b is sent in the estimation of giving up after the despreading of this code channel.

Be elaborated respectively in the face of above-mentioned steps down.

Step S101:

If the data that transmitter has sent 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 is through multipath channel h, and the reception signal that is obtained the terminal after being polluted by AWGN noise n is:

$e=s\⊗h+n$

Wherein

expression linear convolution computing.

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

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

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

If matrix

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 (signal is sent in the estimation that is each code channel) 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, each symbol data after the despreading that then this spreading code is corresponding 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:

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

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 through 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:

Receive signal element 31, be used to receive the signal that signal transmitter sends, obtain receiving signal.

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

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

Preferably, signal element 32 is sent in said estimation, adopts least mean-square error piece linear equalization algorithm, through said sytem matrix and said reception signal, estimates the transmission signal of said transmitter.

Preferably, said receiver also comprises:

Activate judging unit 34, be used for sending signal and judge whether corresponding code channel is in state of activation according to the estimation after the despreading of each code channel of said transmitter.

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

Preferably, said activation judging unit 34 comprises:

Threshold value unit 341 is used for being provided with 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 the transmission calculated signals of the estimation after the despreading of said 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 said 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, said activation threshold value is confirmed through emulation in said threshold value unit 341.

Preferably, said restituted signal unit 33 comprises:

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

Demodulating unit 332 is used for when code channel is in state of activation, signal is sent in the estimation after the despreading carry 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 through this scheme need not carry out complicated activation to other code channels 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, belong within the scope of claim of the present invention and equivalent technologies thereof if of the present invention these are revised with modification, then the present invention also is intended to comprise these changes and modification interior.

Claims (7)

1. the demodulation method in the synchronous CDMA receiving system is characterized in that this method comprises:

Receive the signal that signal transmitter sends, obtain receiving signal;

Utilize channel estimating tectonic system matrix, adopt least mean-square error piece linear equalization algorithm, and, estimate the transmission signal of said transmitter, obtain estimating to send signal through this sytem matrix and said reception signal;

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

The signal to noise ratio of utilizing the estimation after the despreading of each code channel to send each code channel of calculated signals, and judge according to the signal to noise ratio of each code channel whether self code channel is in state of activation;

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

2. method according to claim 1 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 said transmitter and comprises:

The activation threshold value of code channel is set in advance;

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

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

3. method according to claim 2 is characterized in that, said activation threshold value obtains through emulation.

4. the receiver in the synchronous CDMA receiving system is characterized in that this receiver comprises:

Receive signal element, be used to receive the signal that signal transmitter sends, obtain receiving signal;

Estimate to send signal element, be used to utilize channel estimating tectonic system matrix, adopt least mean-square error piece linear equalization algorithm, and, estimate the transmission signal of said transmitter, obtain estimating to send signal through this sytem matrix and said reception signal;

Activate judging unit, be used for sending signal and judge whether corresponding code channel is in state of activation according to the estimation after the despreading of each code channel of said transmitter;

The restituted signal unit is used to utilize the spreading code of said transmitter, signal is sent in the estimation of respective channel carry out despreading; When code channel is in state of activation, signal is sent in the estimation after the despreading carry out demodulation, obtain the restituted signal of respective channel.

5. receiver according to claim 4 is characterized in that, said activation judging unit comprises:

The threshold value unit is used for being provided with 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 the transmission calculated signals of the estimation after the despreading of said each code channel;

Whether identifying unit, the signal to noise ratio that is used to judge code channel be more than or equal to said 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.

6. receiver according to claim 5 is characterized in that, said activation threshold value is confirmed through emulation in said threshold value unit.

7. receiver according to claim 4 is characterized in that, said restituted signal unit comprises:

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

Demodulating unit is used for when code channel is in state of activation, signal is sent in the estimation after the despreading carry out demodulation, obtains the restituted signal of respective channel.

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