CN1304255A - Pilot and data combined channel estimation method in code division multiple address system and its device - Google Patents
Pilot and data combined channel estimation method in code division multiple address system and its device Download PDFInfo
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Abstract
The present inventino is characterized by adopting two-stage processing method, including the following steps: on the basis of traditional PSAM channel estimation, making one temporary hard decision for RAKE merged output result; remodulating the obtained hard decision data, and utilizing said data to make signal demodulation operation of received data correspondent to data fields being in all the time slots, then jointly using said data sequence and time-delayed pilot section demodulated data to obtain the data sequence similar to continuous pilot frequency, then utilizing channel estimation method of continuous pilot frequency (sliding average and adaptive filtering) to finally obtain more accurate secondary estimation of data code element.
Description
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.
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 (1=0,1 ..., L-1) to form, the signal that then receives can be expressed as:
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 the 1st footpath complex channel gain and time-delays; S (t) is corresponding transmitting baseband signal.Can establish
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 multipath data of each after despreading 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 path about data
And then each path 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 path 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.
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, try to achieve the modulation value of writing to of each footpath data symbols, carry out Rake (RAKE) again and merge, the result carries out once interim hard decision to its output;
D, 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;
E, the pilot number of the writing to modulating data after the data sequence that obtains after the data segment number of the writing to modulation and the time-delay is united use, obtained the data sequence of similar 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 and estimate, again each are directly received data and write to modulate and Rake (RAKE) merging soft-decision output.
A kind of device that is used to realize said method, comprise corresponding multipath input, a plurality of modules of working simultaneously, the module of each path correspondence has: a pilot/data branching unit, delay unit and the channel estimating unit that is connected with the output of this pilot/data branching unit respectively, the multiplier that is connected with the output of delay unit and channel estimating unit, the adder that is connected with the output of each road multiplier, be characterized in, also comprise: second delay unit that is connected with the output of each road pilot/data branching unit, the 3rd delay unit, the interim hard decision of the symbol unit that is connected with the output of adder, the modulating unit that is connected with the output of the interim hard decision of symbol unit, second multiplier that the output with each second delay unit that is connected with the output of this modulating unit is connected, the time-division combiner unit that is connected with the output of each road second multiplier, the low pass filter that is connected with the output of each time-division combiner unit, the 3rd multiplier that is connected with the output of low pass filter, the output signal of the 3rd delay unit that each road is connected with second delay unit also is connected with the 3rd multiplier simultaneously, be input to second adder from the signal of each road the 3rd multiplier output, output to the output of soft-decision output unit again;
The separable multipath data of after the despreading each are sent to the pilot/data branching unit respectively, carrying out the shunt of pilot tone and data segment handles, pilot data along separate routes is sent to channel estimating unit respectively and carries out the phase place of channel parameter of data segment and the first estimation of amplitude, then respectively through multiplying each other with the conjugate of corresponding channel estimating parameter by first multiplier unit again behind first delay unit, obtain of the first estimation of each path about data, and then each path data is carried out high specific merge in adder unit, the data that obtain are carried out interim hard decision output through symbol interim judgement unit, output result to hard decision carries out multiple phase shift keying (MPSK) modulation again in modulator unit then, the code element that utilization regenerates with through the reception data segment data signal that conjugate multiplication obtains modulating in second multiplier unit of second delay unit, in the time-division combiner unit, their channel fading information with the frequency pilot sign correspondence is merged, constitute the form of similar continuous pilot signal, again this " continuous pilot signal " adopted the channel estimation methods under the continuous pilot system in low pass filter unit, add through relevant, 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 in the second multiplier unit conjugate multiplication, the value of each footpath output is carried out high specific and is merged in the second adder unit, by the soft-decision output unit output result is carried out soft-decision 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.
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.
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 that the reception data of data segment correspondence in each footpath time slot are carried out signal and go modulation operations, because it is lower than Dan Jing that multipath merges the later data hard decision error rate, can think that receiving data carries out the data sequence that comprises channel information that signal goes to obtain after the modulation operations than the accuracy height that drew channel estimation value originally by the pilot tone interpolation, 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 separable multipath data of each after despreading r
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; With the data sequence that obtains after going to modulate with go modulating data to unite use by the pilot of delaying time after 51,52, 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 the inputs of two paths, the module of this two paths correspondence has: pilot/data branching unit 201,202, respectively with each pilot/data branching unit 201, the delay unit 401 that 202 output connects, 402 and channel estimating unit 203,204, the multiplier 205 that is connected with the output of delay unit and channel estimating unit respectively, 206, the adder 207 that is connected with the output of each road multiplier, second delay unit 403 that is connected with the output of each road pilot/data branching unit, 404, the 3rd delay unit 405,406, the interim hard decision of the symbol unit 208 that is connected with the output of adder 207, the modulating unit 503 that is connected with the output of the interim hard decision of symbol unit, second multiplier 501 that the output with each second delay unit that is connected with the output of this modulating unit respectively is connected, 502, the time-division combiner unit 209 that is connected with the output of each road second multiplier, 210, the low pass filter 300 that is connected with the output of each time-division combiner unit, 301, the 3rd multiplier 302 that is connected with the output of low pass filter, 303, the output signal of the 3rd delay unit that each road is connected with second delay unit also is connected with the 3rd multiplier simultaneously, be input to second adder 304 from the signal of each road the 3rd multiplier output, output 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 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 path about data
And then each path data is carried out high specific merge in 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 the second multiplier unit 50l, 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/N0 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, try to achieve the modulation value of writing to of each footpath data symbols, carry out Rake again and merge, the result carries out once interim hard decision to its output;
D, hard decision data is carried out multiple phase shift keying 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;
E, the pilot number of the writing to modulating data after the data sequence that obtains after the data segment number of the writing to modulation and the time-delay is united use, obtained the data sequence of similar 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 and estimate, again each are directly received data and write to modulate and the Rake merging soft-decision output.
2, a kind of device that is used to realize the described method of claim 1, comprise corresponding multipath input, a plurality of modules of working simultaneously, the module of each path correspondence has: a pilot/data branching unit, delay unit and the channel estimating unit that is connected with the output of this pilot/data branching unit respectively, the multiplier that is connected with the output of delay unit and channel estimating unit, the adder that is connected with the output of each road multiplier, it is characterized in that, also comprise: second delay unit that is connected with the output of each road pilot/data branching unit, the 3rd delay unit, the interim hard decision of the symbol unit that is connected with the output of adder, the modulating unit that is connected with the output of the interim hard decision of symbol unit, second multiplier that the output with each second delay unit that is connected with the output of this modulating unit is connected, the time-division combiner unit that is connected with the output of each road second multiplier, the low pass filter that is connected with the output of each time-division combiner unit, the 3rd multiplier that is connected with the output of low pass filter, the output signal of the 3rd delay unit that each road is connected with second delay unit also is connected with the 3rd multiplier simultaneously, be input to second adder from the signal of each road the 3rd multiplier output, output to the output of soft-decision output unit again;
The separable multipath data of after the despreading each are sent to the pilot/data branching unit respectively, carrying out the shunt of pilot tone and data segment handles, pilot data along separate routes is sent to channel estimating unit respectively and carries out the phase place of channel parameter of data segment and the first estimation of amplitude, then respectively through multiplying each other with the conjugate of corresponding channel estimating parameter by first multiplier unit again behind first delay unit, obtain of the first estimation of each path about data, and then each path data is carried out high specific merge in adder unit, the data that obtain are carried out interim hard decision output through symbol interim judgement unit, output result to hard decision carries out the multiple phase shift keying modulation again in modulator unit then, the code element that utilization regenerates with through the reception data segment data signal that conjugate multiplication obtains modulating in second multiplier unit of second delay unit, in the time-division combiner unit, their channel fading information with the frequency pilot sign correspondence is merged, constitute the form of similar continuous pilot signal, again this " continuous pilot signal " adopted the channel estimation methods under the continuous pilot system in low pass filter unit, add through relevant, 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 in the second multiplier unit conjugate multiplication, the value of each footpath output is carried out high specific and is merged in the second adder unit, by the soft-decision output unit output result is carried out soft-decision output.
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2004066528A1 (en) * | 2003-01-21 | 2004-08-05 | Da Tang Mobile Communications Equipment Co., Ltd. | Channel estimating method for multi-set of code in slotted cdma system |
| CN100435499C (en) * | 2002-06-10 | 2008-11-19 | 北京邮电大学 | Channel estimation method for wide-band CDMA system |
| CN102104561A (en) * | 2009-12-16 | 2011-06-22 | 中国移动通信集团公司 | Receiving method and device based on overlap cut frequency-domain equalization algorithm |
| WO2017076326A1 (en) * | 2015-11-06 | 2017-05-11 | 中兴通讯股份有限公司 | Transmission method and device for pilot signals in multicarrier system |
| CN107852269A (en) * | 2015-08-07 | 2018-03-27 | 华为技术有限公司 | The method and apparatus for transmitting data |
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2000
- 2000-01-10 CN CNB00111431XA patent/CN1165185C/en not_active Expired - Fee Related
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN100435499C (en) * | 2002-06-10 | 2008-11-19 | 北京邮电大学 | Channel estimation method for wide-band CDMA system |
| WO2004066528A1 (en) * | 2003-01-21 | 2004-08-05 | Da Tang Mobile Communications Equipment Co., Ltd. | Channel estimating method for multi-set of code in slotted cdma system |
| US7433387B2 (en) | 2003-01-21 | 2008-10-07 | Da Tang Mobile Communications Equipment Co., Ltd. | Multiple code-set channel estimation method in time-slotted CDMA system |
| CN102104561A (en) * | 2009-12-16 | 2011-06-22 | 中国移动通信集团公司 | Receiving method and device based on overlap cut frequency-domain equalization algorithm |
| CN102104561B (en) * | 2009-12-16 | 2014-04-09 | 中国移动通信集团公司 | Receiving method and device based on overlap cut frequency-domain equalization algorithm |
| CN107852269A (en) * | 2015-08-07 | 2018-03-27 | 华为技术有限公司 | The method and apparatus for transmitting data |
| CN107852269B (en) * | 2015-08-07 | 2020-02-14 | 华为技术有限公司 | Method and device for transmitting data |
| WO2017076326A1 (en) * | 2015-11-06 | 2017-05-11 | 中兴通讯股份有限公司 | Transmission method and device for pilot signals in multicarrier system |
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