CN1165185C - Pilot and data combined channel estimation method in code division multiple address system and its device - Google Patents

Abstract

The present invention relates to a pilot frequency and data combined channel estimation method in a code division multiple address system, which is characterized in that two-stage treatment is adopted in the present invention; on the basis of traditional PSAM channel estimation, one-time temporary hard decision is carried out to a rake combined output result, and then, data obtained in the hard decision are modulated again; the signal demodulation operation of received data corresponding to data segments in all time slots is carried out by utilizing the data, and the data sequence and demodulated data in delayed pilot frequency segments are used jointly so as to obtain a data sequence which is similar to continuous pilot frequency; then, the channel estimation method of the continuous pilot frequency (sliding average and adaptive filtering) is utilized, and finally, secondary estimation which has more accurate data code elements is obtained.

Description

Pilot tone and data combined channel estimation method and device thereof in the code division multiple access system

Technical field

The present invention relates in code division multiple access (CDMA) system pilot tone and data combined channel estimation method and device thereof at mobile fading channel.

Background technology

Under mobile communication environment, transmitting to be subjected to the influence of multipath fading, and its concrete manifestation mode arrives receiver for transmitting by a plurality of object reflections, diffraction and refraction with different time-delays, gain and phase place.A high performance receiver must carry out coherent reception to transmitting, and its purpose is exactly to eliminate the influence of channel to transmitting.In CDMA Cellular System, transmitting, what pass through is a frequency selective fading channels, but a favorable factor is that each distinguishable multipath can effectively be separated in received signal, optimum receiver equivalence merges for a plurality of multipath signals with independent flat fading channel (or the non-selective channel of frequency) characteristic being carried out high specific, and promptly coherent rake (RAKE) receives.Like this, compensation and the diversity receiving technology problem of frequency-selective channel equalization problem with regard to being reduced to the non-selective channel of a plurality of frequencies.Under the slow fading channel condition, receiver can be finished receiving function preferably, but, when mobile station speed is accelerated and when the raising of carrier frequency and the channel rapid fading that causes, mobile channel is not only all being introduced very strong random disturbances to transmitting on the amplitude but also on phase place, in this case, the impulse response of obtaining channel becomes very difficult, and common coherent detection technology is difficult to realize.

At present, a kind of channel estimating that comparatively generally adopts and compensation technique are based on channel and intercept technology (ChannelSounding).And channel intercepts technology and can be divided into two classes, and a class is based on the Pilottone technology, i.e. continuous pilot technology, as shown in Figure 1; One class is based on PSAM (PilotSymbolAidedMethod) technology, i.e. time-multiplexed pilot technology, as shown in Figure 2.

Suppose a single user system.Transmit is (0,1) equally distributed random bit stream, and through quadriphase PSK (QPSK) modulation, the sequence of data symbols that obtains is placed in the time slot sequence, each time slot comprises Nd data code element, Np pilot frequency code element is attached to the beginning of each time slot, and this data structure is seen Fig. 2.

The length T of each time slot _Slot(N _p+ N _d) T.The T here is the cycle of quadriphase PSK (QPSK) code element.If suppose multipath channel be by the L road can decompose propagate the footpath (l=0,1 ..., L-1) to form, the signal that then receives can be expressed as:

$r\left(t\right)=\underset{l=0}{\overset{L-1}{\mathrm{\Σ}}}{a}_l\left(t\right)s(t-{\mathrm{\τ}}_l)+n\left(t\right)---\left(1\right)$

Wherein, n (t) is a background noise, can be considered additivity Gauss white noise, and its one-sided power spectrum density is ND; Al (t) and τ l then are l footpath complex channel gain and time-delay; S (t) is corresponding transmitting baseband signal.Can establish $E\left[\underset{l=0}{\overset{L-1}{\mathrm{\Σ}}}{\left|a_l\left(t\right)\right|}^2\right]=2S,$ S is the average power of received signal.The expression formula of s (t) is:

s(t)＝p(t)d(t) (2)

P in the formula (t) is the frequency spreading wave function, and d (t) is quadriphase PSK (QPSK) modulating data waveform, and it has comprised pilot signal and data-signal.C (k) is that random binary is propagated sequence, φ (q) ∈ { (2m+1) π/4; M=0-3 is the phase modulation of quadriphase PSK (QPSK).Tc represents chip period, and u (t) is a unit function.

Adopted the PSAM technology in the WCDMA system at present, the CDMA2000 up link has also adopted similar techniques, this technology is carried out channel estimating by periodically insert pilot frequency code element in data bit flow, its essence is equivalent to obtain by known pilot frequency code element the estimation of channel fading process sampled point, obtains the data symbol channel parameter corresponding by the correlated channels algorithm for estimating again.When rate of fading is low, interpolation class channel estimation method (single phase channel estimation methods) based on the PSAM technology can provide estimated performance preferably, and the realization technology is simple, the key of this technology is how to utilize the channel fading coefficient interpolation of known pilot symbols to draw unknown data symbols channel fading coefficient, the design of interpolation algorithm just.At present, the interpolation method that comparatively generally adopts has Gauss interpolation (zeroth order, single order, second order), multi-slot weighted average (WMSA) and other interpolation methods.

Specific implementation process such as Fig. 3 of said method, the separable footpath of each after despreading data r ₁(k) ... r ₂(k), r for example ₁(k) and r _L(k) (be assumed to be two footpaths) and be sent to pilot/data branching unit 101,102 respectively, carry out the shunt of pilot tone and data segment and handle,

Pilot data r along separate routes _{P, 1}(k) and r _{P, L}(k) be sent to channel estimating unit 103,104 respectively and carry out the estimation of the channel parameter of data segment (comprising phase place, amplitude), as noted above all kinds of interpolation algorithms of the channel estimation methods of Cai Yonging wherein, and the data segment data r along separate routes _{D, 1}(k) and r _{D, L}(k) then multiply each other with the conjugate of corresponding channel estimating parameter through corresponding delay unit 109,110

This step carries out in multiplier unit 105,106.Afterwards, can obtain of the estimation of each footpath about data

And then each footpath data is carried out high specific merge in adder unit 107, the data that obtain are carried out soft-decision output through soft judge unit 108.This mode is traditional Rake (RAKE) receive mode, and independent process is carried out in each footpath respectively, and then carries out the high specific merging, merges output and enters follow-up decoded portion.

In interpolation class channel estimating (single phase channel estimation methods) method of above-mentioned prior art, only utilized the interior and corresponding observation data of pilot frequency code element of each time slot in the actual reception signal based on pilot symbol assisted modulation (PSAM).Under the slow fading channel situation, because the interior channel variation of time slot is little, can utilize the channel information of pilot to carry out interpolation, obtain the channel information of data segment.But if the travelling carriage fast moving causes channel variation to be accelerated, the method for then utilizing the pilot channel information to carry out interpolation purely can not recover the channel information of data segment fully.

When utilizing in the time slot the pairing observation data of data symbols, because data symbols itself is unknown, therefore the initial estimation of formation data symbols earlier utilizes this estimation to carry out a new iteration as known quantity again, finally converges to point of safes.In the flat fading channel estimation problem, often adopt an iteration just can reach comparatively satisfied result, such structure is exactly so-called decision-feedback technology.Said method could obtain preferable performance by sufficiently high initial symbol judgement accuracy to satisfy certain condition of convergence usually.

Summary of the invention

Partial channel knowledge is extracted in a kind of employing that the objective of the invention is to propose for the defective that overcomes above prior art from the observation data that receives corresponding time slot data symbols section, and unite use by certain mode with the channel information of pilot, thereby obtain the more channel information of horn of plenty, estimate and try to achieve under the fading channel situation more precise channels, and can adapt to pilot tone and data combined channel estimation method in a kind of code division multiple access system of fading channel situation of faster variation.

Realize that technical scheme of the present invention is: pilot tone and data combined channel estimation method in a kind of code division multiple access system the steps include: that the channel information of data symbols section correspondence in a, elder generation's each time slot to received signal forms initial estimation; B, utilize this estimation to carry out a new iteration again as known quantity; Be characterized in, also comprise the channel estimating of second stage, the steps include:

C, on the basis of above-mentioned channel estimation methods, with each footpath received signal and respective channels initial estimate conjugate multiplication, try to achieve estimated value of each footpath data symbols, carry out Rake again and merge, the result carries out once hard decision temporarily to its output;

D, hard decision data is carried out multiple phase shift keying modulation more again, and utilize reception data the write to number modulation operations of these data data segment correspondence in each footpath time slot;

E, the data sequence that obtains after the corresponding time-multiplexed pilot section of the data sequence number of the writing to modulation that obtains after the data segment number of the writing to modulation is united use, obtain the data sequence of continuous pilot;

F, the continuous pilot of utilizing the e step to produce are carried out channel estimating by moving average, adaptive filter method, obtain more accurate secondary estimated value, again each is directly received data and respective channels secondary estimated value conjugate multiplication, carry out Rake then and merge, soft-decision output.

A kind of device of realizing pilot tone and data aggregate channel estimating in the code division multiple access system comprises corresponding multipath input, a plurality of modules of working simultaneously, and the corresponding module in each footpath has:

The pilot/data branching unit is used for the data in each the separable footpath after the despreading are carried out the shunt processing of pilot tone and data segment;

First delay unit is connected with the output of described pilot/data branching unit;

First channel estimating unit is connected with the output of described pilot/data branching unit, is used for the pilot data after the shunt is carried out the phase place of channel parameter of data segment and the first estimation of amplitude;

First multiplier is connected with first delay unit in this footpath and the output of first channel estimating unit respectively, is used for that data after the time-delay and corresponding channel estimating parameter are carried out conjugate and multiplies each other, and obtains the first estimated value of this footpath about data;

First adder is connected with the output of each footpath first multiplier, is used for that each footpath data is carried out high specific in this first adder unit and merges;

Be characterized in, also comprise:

Second delay unit, the 3rd delay unit, described second delay unit is connected with the output of this footpath pilot/data branching unit, and described the 3rd delay unit is connected with the output of second delay unit;

The interim hard decision of symbol unit is connected with the output of first adder, is used for the data that obtain after merging through high specific are carried out interim hard decision output;

Modulating unit is connected with the output of the interim hard decision of symbol unit, is used for the result of hard decision is modulated;

Second multiplier is connected with the output of modulating unit, second delay unit, with the code element that regenerates with carry out conjugate multiplication through the data in the reception data segment of second delay unit;

The time-division combiner unit is connected with the output of each footpath second multiplier, is used for the channel fading information with the frequency pilot sign correspondence is merged;

Low pass filter is connected with the output of the time-division combiner unit in this footpath, and it adopts the channel estimation methods under the continuous pilot system, adds through relevant, obtains the valuation second time of the channel fading coefficient of data segment code element correspondence;

The 3rd multiplier is connected with the output of low pass filter, is used for the channel estimation results second time data segment data corresponding with each footpath are carried out conjugate multiplication;

Second adder is connected with each footpath the 3rd multiplier output, is used for that each channel estimation results of directly exporting is carried out high specific for the second time and merges;

The soft-decision output unit is connected with the output of second adder, and the result carries out soft-decision to output.

Because the present invention has adopted above technical scheme, utilize the decision-feedback technology to obtain utilizing the combined channel of pilot tone and data to estimate, on the structure that multipath channel is estimated, significant change is arranged than traditional method, it estimates to have added one deck processing unit again on the structure in traditional multipath channel, many processing in a stage, make channel estimating not only under the situation of slow fading, make moderate progress, and can adapt to variation than fast fading channel, obtain estimating comparatively accurately, thereby improve the error rate.

Description of drawings

Be further to understand feature of the present invention, performance, existing with the following Examples and accompanying drawing be explained in detail.

Fig. 1 is the continuous pilot frame structure;

Fig. 2 is the time-multiplexed pilot frame structure;

Fig. 3 is that prior art is estimated structured flowchart based on PSAM interpolation class algorithm multipath channel;

Fig. 4 is that prior art is based on PSAM two stages channel estimating structured flowchart;

Fig. 5 is the concrete device block diagram of the present invention in the WCDMA system;

Fig. 6 (a), Fig. 6 (b), Fig. 6 (c) be the present invention's two stages channel estimation methods with common interpolation class channel estimating at different signal to noise ratios and fading rate curve chart.

Embodiment

See also accompanying drawing.

The present invention is on the basis of traditional PSA M channel estimating, RAKE (Rake) is merged the output result carry out once interim hard decision, then the hard decision data that obtains is modulated again again, and utilize these data to the reception data number of the writing to modulation operations of data segment correspondence in each footpath time slot, because it is lower than Dan Jing that multipath merges the later data hard decision error rate, can think and receive the data sequence ratio that comprises channel information that obtains after the data number of the writing to modulation operations drew channel estimation value originally by the pilot tone interpolation accuracy height, the data aggregate of the pilot number of the writing to modulation after this data sequence and the time-delay is used, obtained the data sequence of similar continuous pilot, utilize the channel estimation methods (moving average of continuous pilot again, adaptive-filtering), thereby the secondary that obtains data symbols channel information in the time slot is estimated, finally obtains the more accurate secondary of data symbols and estimates.The embodiment of this method principle sees also Fig. 4, the data r in the separable footpath of each after the despreading ₁(k) ... r ₂(k), r for example ₁(k) and r _L(k) two paths of signals adopts conventional channel method of estimation 50 to carry out the conventional channel estimation, does time- delay 51,52 simultaneously respectively; On the basis of above-mentioned channel estimation methods, Rake (RAKE) merged 53 output result and carry out once interim hard decision 54; Hard decision data is carried out multiple phase shift keying (MPSK) modulation more again, and utilize these data that the reception data of data segment correspondence in each footpath time slot are carried out signal and go modulation operations; The data sequence that obtains after the corresponding time-multiplexed pilot section of the data sequence number of the writing to modulation that obtains after the data segment number of the writing to modulation is united use, obtained the data sequence of similar continuous pilot; Utilize the continuous pilot that produces to carry out combined channel and estimate 55, obtain more accurate secondary and estimate soft-decision output 56 by moving average, adaptive filter method.

Fig. 5 is the block diagram of concrete device of the present invention; A kind of device that is used to realize said method comprises corresponding multipath input, a plurality of modules of working simultaneously.Present embodiment is two footpath inputs, and this corresponding module in two footpaths has: pilot/data branching unit 201,202; First delay unit 401,402 that is connected with the output of each pilot/data branching unit 201,202 and first channel estimating unit 203,204 respectively; First multiplier 205,206 that is connected with the output of first delay unit and first channel estimating unit respectively; The first adder 207 that is connected with the output of each footpath first multiplier; Second delay unit 403,404, the 3rd delay unit 405,406 that are connected with the output of each footpath pilot/data branching unit, described second delay unit 403,404 is connected with the output of each footpath pilot/data branching unit respectively, and the output of second delay unit that described the 3rd delay unit is corresponding with each connects; The interim hard decision of the symbol unit 208 that is connected with the output of first adder 207; The modulating unit 503 that is connected with the output of the interim hard decision of symbol unit; Second multiplier 501,502 that the output with each second delay unit that is connected with the output of this modulating unit respectively is connected; The time-division combiner unit 209,210 that is connected with the output of each footpath second multiplier; The low pass filter 300,301 that is connected with the output of each time-division combiner unit; The 3rd multiplier 302,303 that is connected with the output of low pass filter; The output signal of the 3rd delay unit that each footpath is connected with second delay unit also is connected with the 3rd multiplier simultaneously, and the signal of exporting from each footpath the 3rd multiplier is input to second adder 304, outputs to 305 outputs of soft-decision output unit again.

The separable multipath data of after the despreading each r ₁(k) ... r ₂(k), r for example ₁(k) and r _L(k) be sent to pilot/data branching unit 201,202 respectively, carry out the shunt of pilot tone and data segment and handle, along separate routes the pilot data r after _{P, 1}(k) and r _{P, L}(k) be sent to phase place and the first estimation of amplitude, the pilot data r after the shunt in addition that first channel estimating unit 203,204 is carried out the channel parameter of data segment respectively _{D, 1}(k) and r _{D, L}(k), carry out conjugate by first multiplier unit 205,206 and corresponding channel estimating parameter again and multiply each other respectively through the time-delay of first delay unit 401,402 Obtain of the first estimation of each footpath about data

And then each footpath data is carried out high specific merge in first adder unit 207, the data that obtain are carried out interim hard decision output through symbol interim judgement unit 208, output result to hard decision carries out quadriphase PSK (QPSK) modulation again in modulator unit 503 then, the code element that utilization regenerates with through second delay unit 403,404 reception data segment data are at second multiplier unit 501, the signal that conjugate multiplication obtains modulating in 502, the channel information that obtains so again will be than channel estimating unit 203,204 values that obtain are more near actual conditions.Deciliter unit 210 when the pilot data is along separate routes also delivered to respectively, 209, at time-division combiner unit 210, in 209, their channel fading information with the frequency pilot sign correspondence is merged, constitute the form of similar continuous pilot signal, again with this " continuous pilot signal " in low pass filter unit 300, adopt the channel estimation methods (moving average method under the continuous pilot system in 301, adaptive-filtering), add through relevant, improve signal to noise ratio, obtain the valuation second time of the channel fading coefficient of data segment code element correspondence, then with corresponding data segment data in channel estimation results and each footpath at second multiplier unit 302,303 conjugate multiplication, value of each footpath output 304 is carried out high specific and is merged in the second adder unit, carry out soft-decision output by 305 pairs of output of soft-decision output unit result, and offer follow-up decoded portion.In this embodiment, as can be seen,, can obtain more precise channels estimation, receive the error rate thereby improve by using two stage channel estimation methods.Fig. 6 be the present invention's two stages channel estimation methods with common interpolation class channel estimating at different signal to noise ratios and fading rate curve chart.Suppose to transmit and propagate three separable footpaths of experience constant power, abscissa Eb/NO is the ratio of every bit signal average power with the noise power in wherein each bar propagation footpath, ordinate is the error rate, curve when Fig. 6 (a) expression Doppler frequency is 120Hz, curve when Fig. 6 (b) expression Doppler frequency is 360Hz, the curve when Fig. 6 (c) expression Doppler frequency is 480Hz.As seen from Figure 6, the hardware resource that the processing links that is increased consumes is also little, but the processing gain that obtains can reach one more than the dB.

The present invention is applicable to the CDMA Cellular System that adopts the PSAM technology.

Claims (2)

1, pilot tone and data combined channel estimation method in a kind of code division multiple access system the steps include: that the channel information of data symbols section correspondence in a, elder generation's each time slot to received signal forms initial estimation; B, utilize this estimation to carry out a new iteration again as known quantity; It is characterized in that, also comprise the channel estimating of second stage, the steps include:

C, on the basis of above-mentioned channel estimation methods, with each footpath received signal and respective channels initial estimate conjugate multiplication, try to achieve estimated value of each footpath data symbols, carry out Rake again and merge, the result carries out once hard decision temporarily to its output;

D, hard decision data is carried out multiple phase shift keying modulation more again, and utilize reception data the write to number modulation operations of these data data segment correspondence in each footpath time slot;

E, the data sequence that obtains after the corresponding time-multiplexed pilot section of the data sequence number of the writing to modulation that obtains after the data segment number of the writing to modulation is united use, obtain the data sequence of continuous pilot;

F, the continuous pilot of utilizing the e step to produce are carried out channel estimating by moving average, adaptive filter method, obtain more accurate secondary estimated value, again each is directly received data and respective channels secondary estimated value conjugate multiplication, carry out Rake then and merge, soft-decision output.

2, a kind of device of realizing pilot tone and data aggregate channel estimating in the code division multiple access system comprises corresponding each footpath input, a plurality of modules of working simultaneously, and the corresponding module in each footpath has:

The pilot/data branching unit is used for the data in each the separable footpath after the despreading are carried out the shunt processing of pilot tone and data segment;

First delay unit is connected with the output of described pilot/data branching unit;

First channel estimating unit is connected with the output of described pilot/data branching unit, is used for the pilot data after the shunt is carried out the phase place of channel parameter of data segment and the first estimation of amplitude;

First multiplier is connected with first delay unit in this footpath and the output of first channel estimating unit respectively, is used for that data after the time-delay and corresponding channel estimating parameter are carried out conjugate and multiplies each other, and obtains the first estimated value of this footpath about data;

First adder is connected with the output of each footpath first multiplier, is used for that each footpath data is carried out high specific in this first adder unit and merges;

It is characterized in that, also comprise:

Second delay unit, the 3rd delay unit, described second delay unit is connected with the output of this footpath pilot/data branching unit, and described the 3rd delay unit is connected with the output of second delay unit;

The interim hard decision of symbol unit is connected with the output of first adder, is used for the data that obtain after merging through high specific are carried out interim hard decision output;

Modulating unit is connected with the output of the interim hard decision of symbol unit, is used for the result of hard decision is modulated;

Second multiplier is connected with the output of modulating unit, second delay unit, with the code element that regenerates with carry out conjugate multiplication through the data in the reception data segment of second delay unit;

The time-division combiner unit is connected with the output of each footpath second multiplier, is used for the channel fading information with the frequency pilot sign correspondence is merged;

Low pass filter is connected with the output of the time-division combiner unit in this footpath, and it adopts the channel estimation methods under the continuous pilot system, adds through relevant, obtains the valuation second time of the channel fading coefficient of data segment code element correspondence;

The 3rd multiplier is connected with the output of low pass filter, is used for the channel estimation results second time data segment data corresponding with each footpath are carried out conjugate multiplication;

Second adder is connected with each footpath the 3rd multiplier output, is used for that each channel estimation results of directly exporting is carried out high specific for the second time and merges;

The soft-decision output unit is connected with the output of second adder, and the result carries out soft-decision to output.

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