CN1269325C - Channel estimation method for WCDMA communication system - Google Patents

Abstract

The present invention discloses a channel estimation method for a broadband code division multiple access system. Firstly, broadband spread spectrum signals input into an RAKE receiver are descrambled and de-spread; secondly, spread spectrum codes are used for de-spreading the broadband spread spectrum signals to respectively obtain a dedicated physical control channel and a dedicated physical data channel; thirdly, an initial channel estimation value is calculated, the channel estimation values Cem of window corresponding time are calculated by the arithmetic mean algorithm for continuous symbol strings of the dedicated physical control channel through decorrelation calculation; finally, the symbols of the dedicated physical data channel of m time of the CEm compensation window corresponding time and each of multipath compensation results are output to the maximal ratio merge module. The method of the present invention overcomes the defect that the channel estimation values can not reflect the channel characteristics so as to cause erroneous judgment ratios increase and bad performance under the condition of the deterioration of the channels existing in the prior art; the present invention can effectively increase the accuracy of the channel estimation so as to guarantee the high performance of a system under the environment of mobile communication and particular high speed mobile communication.

Description

The channel estimation methods that is used for Wideband Code Division Multiple Access (WCDMA) communication system

Technical field

The present invention relates to the channel estimation methods of wireless communication system, particularly relate to the channel estimation methods of a kind of Wideband Code Division Multiple Access (WCDMA) (WCDMA, Wide CDMA) communication system.

Background technology

Along with the fast development of mobile communication, people require also more and more higher to the quality of mobile communication and the type of service that provides thereof, and the proposition of 3G (Third Generation) Moblie and development have met people's this demand just, therefore get most of the attention.Wideband Code Division Multiple Access (WCDMA) (WCDMA, Wide CDMA) is a 3-G (Generation Three mobile communication system) standardization body (3 ^RdGeneration PartnershipProject, 3GPP) the Radio Transmission Technology of Ti Chuing (Radio TransmissionTechnology, RTT) scheme, it not only can provide high-quality voice service, and can provide and the similar multimedia service of fixed network.

As shown in Figure 1, in the WCDMA system, in order to improve uplink quality, (Dedicated Physical Control Channel has added the part frequency pilot sign in DPCCH), is used for channel estimating to carry out coherent detection at special physical controlling channel of upward.The emission of frequency pilot sign is discontinuous, according to different time slot formats, number of pilot symbols in each time slot is between 3 to 8, therefore, adopt which kind of method accurately to estimate the characteristic of channel of interior frequency pilot sign section of time slot and data symbol section correspondence, seem of crucial importance in the receptivity under the high-speed mobile environment improving receiver.

Channel estimation methods at present comparatively commonly used mainly contains following several: the average channel estimation methods of single time slot, based on the average weighted channel estimation methods of channel estimation methods, multi-slot (the Weighted Multi-Slot Averaging that simplifies Kalman's tracking filter, WMSA) and the iterative channel estimation technique (Iterative Channel Estimation, ICE).

The average channel estimation methods of single time slot is because frequency pilot sign is less, and therefore the effectively influence of filtering noise no matter be that performance is all relatively poor under low speed or high-speed mobile environment.Based on the channel estimation methods of simplifying Kalman's tracking filter is the former improvement, and performance makes moderate progress under the low speed mobile environment, but performance is still very poor under high-speed mobile environment.

The estimation procedure of the average weighted channel estimation methods of multi-slot (WMSA, Weighted Multi-SlotAveraging) is as follows: 1) utilize the average channel estimation methods of single time slot to obtain the channel estimation value of each time slot; 2), obtain the channel estimation value of current time slots with the estimated value weighted array of a plurality of time slots.Owing between a plurality of time slots, be weighted average, effectively filtering The noise, thereby under the situation of signal slow fading, this method can obtain good channel estimating performance, but deterioration along with channel, accelerate as translational speed, because estimated value can not reflect the characteristic of channel of different periods in the time slot well, thereby degradation.

Iterative channel estimates that (ICE) method is also having comparatively general application at present, it is 1384627 " a kind of channel estimation methods that is used for broadband CDMA system " that corresponding patent has publication number, its thinking is: earlier by multi-slot weighted average (WMSA) obtain each directly current time slots channel estimation value and to Dedicated Physical Control Channel (DPCCH, Dedicated PhysicalControl Channel) compensates, merge, result after being combined carries out hard decision, take out data segment symbol after the judgement as virtual pilot frequency and feedback the data segment symbol is carried out channel estimating again, be the raising precision, but this process iteration repeatedly.Because it is based on multi-slot weighted average (WMSA) method, to the channel estimating of data segment, the information that pilot portion is still only used in compensation, deterioration along with channel, the degradation of multi-slot weighted average (WMSA) method, the False Rate that merges the back hard decision increases, and this will cause the decreased performance of this method.

Summary of the invention

Purpose of the present invention is exactly that the situation lower channel estimated value in channel degradation that overcomes the prior art existence can't reflect the characteristic of channel, thereby the False Rate that causes increases, the shortcoming of degradation, in the hope of proposing the channel estimation accuracy of a kind of effective raising under mobile communication environment especially high-speed mobile communications environment, thereby guarantee high performance channel estimation methods.

For achieving the above object, the present invention proposes a kind of channel estimation methods that is used for broadband CDMA system, it is characterized in that, may further comprise the steps:

The first step: the wideband spread-spectrum signal to the input RAKE receiver carries out descrambling and de-spreading;

Second step: in a current and following time slot (hereinafter to be referred as " next time slot ") of Dedicated Physical Control Channel (DPCCH, Dedicated Physical Control Channel), take out frequency pilot sign according to known time slot format; To the frequency pilot sign that extracts, each frequency pilot sign and known pilot symbols are carried out the decorrelation computing, obtain the channel estimation value of each frequency pilot sign; Channel estimation value to all frequency pilot signs in each time slot is carried out arithmetic average, obtains the channel estimation value of each time slot;

The 3rd step: for pilot portion, adopt a moving window, if length of window is L, window covers the channel estimation value of the current pilot symbol in the current time slots and the channel estimation value of a historical L-1 symbol, the channel estimation value that had wherein both comprised the frequency pilot sign that obtains with desirable pilot tone decorrelation in the channel estimation value of historical symbol also comprises the channel estimation value (asking the method for the channel estimation value of non-frequency pilot sign to see step 5) of non-frequency pilot sign.Mean value in the window is the channel estimation value in the corresponding moment of window centre position or certain suitable moment, and this value also is the channel estimation value that DPDCH (Dedicated PhysicalData Channel) data were finally exported and be used for compensating to channel estimation module.Here the moment that certain is suitable is meant certain position of the middle deflection of window current time, mainly be that translational speed can be provided with a bigger L value when slow, can need the more data memory like this, for taking into account hardware resource, can proper timing of this consideration.Here with in the different window of prior art maximum both comprised pilot frequency information and also comprised non-pilot frequency information.Improved performance for estimating channel effectively.For non-frequency pilot sign, the mean value of channel estimation value of at first using the result of previous window and next time slot is as the channel estimation value of current sign, current sign is compensated, then the value after all multipath current sign compensation is done high specific and merge (MRC, Maximal RatioCombining), result after being combined does hard decision again, so just obtain current non-frequency pilot sign virtual desirable non-pilot tone (so-called virtual is meant original we do not know in advance, but we are according to other Given information, the value the when transmitting terminal that confidence level estimates it significantly sends).With this virtual value the non-frequency pilot sign of current reception is done the channel estimation value that the decorrelation computing just obtains current non-frequency pilot sign.Use the identical method of step 4 at last, obtain the channel estimation value of the corresponding moment of current window centre position or certain proper timing position.Here, equally have important different with prior art, this method has not only been used the pilot portion information of following time slot, current time slots even historical time slot, also use the information of the non-pilot portion that has estimated that comprises in the current window, further improved performance for estimating channel effectively.

The 4th step: with the channel estimation value of window output to the window centre position constantly or the DPDCH (Dedicated Physical Data Channel) of certain proper timing do compensation operation, data after the compensation merge all multipaths according to the algorithm that high specific merges, and the result who obtains gives decoding module.

Channel estimation methods of the present invention, compared with prior art, repeatedly make full use of the information of the non-pilot tone that has estimated, in limited moving window, utilized all utilizable information fully, improved the performance of channel estimation module effectively, significantly.The channel estimation methods that adopts invention to set forth, can obtain the channel estimation value of each character position in the time slot than prior art more accurately, can when channel fading is slow and fast, different changes in channel characteristics situations constantly in the time slot can both be reflected, thereby the receptivity of communication system can be improved greatly.Simulation result shows, no matter when translational speed was still fast slowly, the performance of the channel estimation methods that the present invention sets forth all was significantly improved than the channel estimating performance of prior art.

Description of drawings

Fig. 1 is the frame structure of WCDMA system uplink DPCH (DPCH, Dedicated PhysicalChannel);

Fig. 2 is existing multi-slot weighted average channel estimation methods schematic diagram.

Fig. 3 is that channel estimation methods of the present invention is implemented block diagram.

Fig. 4 is a channel estimation methods flow chart of the present invention.

Fig. 5 is an iterative algorithm flow chart in the channel estimation methods of the present invention.

Fig. 6 is a moving window arithmetic mean method schematic diagram in the channel estimation methods of the present invention.

Fig. 7 asks non-frequency pilot sign channel estimation value method schematic diagram in the channel estimation method of the present invention.

Embodiment

Be described in further detail below in conjunction with the enforcement of accompanying drawing to technical scheme, according to these accompanying drawings, the technical staff in same field can be easy to realize the present invention.

The present invention mainly be proposed a kind of WCDMA of being used for system uplink channel, based on the channel estimation methods of the moving window arithmetic average that makes full use of pilot tone and non-pilot frequency information, to improve the receptivity of communication system under mobile environment.

Fig. 1 is the frame structure of WCDMA system uplink DPCH (DPCH); In order to distinguish data field among the DPDCH and the data field among the DPCCH, the data field that identifies especially among the DPCCH is non-pilot field.

Fig. 2 is the schematic diagram of multi-slot weighted average channel estimation method of the prior art.In this concrete grammar, adopt multi-slot weighted average channel estimation methods to calculate the channel estimation value of time slot 2, detailed process is: earlier by each frequency pilot sign channel estimation value in the time slot is carried out the channel estimation value that arithmetic average obtains time slot 1,2,3 and 4 respectively, weights by each time slot correspondence among the figure are weighted between adjacent four time slots on average then, obtain the final channel estimation value of time slot 2, promptly

${\hat{E}}_2=({\mathrm{\&alpha;}}_2{\mathrm{<figure-callout\; id="1"\; label="E"\; filenames="C20031010398700171.png"\; state="\{\{state\}\}">E</figure-callout>}}_1+{\mathrm{\&alpha;}}_1{\mathrm{<figure-callout\; id="2"\; label="E"\; filenames="C20031010398700171.png"\; state="\{\{state\}\}">E</figure-callout>}}_2+{\mathrm{\&alpha;}}_1{E}_3+{\mathrm{\&alpha;}}_2{E}_4)/(2{\mathrm{\&alpha;}}_1+2{\mathrm{\&alpha;}}_2)$

In the formula

Be the final channel estimation value of time slot 2, E _i, α _iBe respectively the channel estimation value that on average obtains of each time slot arithmetic internal and the weights of each time slot correspondence when carrying out the multi-slot weighted average.The iterative channel estimation technique of the prior art is used exactly

Remove to compensate the non-pilot data in the time slot 2, obtain virtual known non-pilot data through high specific merging, hard decision then, again with despreading after DPCCH in non-frequency pilot sign do the decorrelation computing, obtain the channel estimation value of non-frequency pilot sign, thereby obtain the channel estimation value of all symbols of whole time slot 2, obtain the channel estimating of each time slot again through the multi-slot weighted average, this method is slightly better than common multi-slot weighted average method performance.

Fig. 3 is that channel estimation methods of the present invention is implemented block diagram, and this figure has illustrated the position of module in whole WCDMA RAKE receiver of the channel estimation methods of the present invention that will implement.In this example, the analog-signal transitions that AD converter 301 will be input to receiver is that digital signal is sent into descrambling and de-spreading module 304, each bar multipath scrambler that descrambling and de-spreading module 304 utilizes code tracking device 302 and code generator 303 to produce carries out descrambling and de-spreading to input signal, and each multipath signal behind the descrambling and de-spreading sent into its corresponding channel estimating and compensating module 305, channel estimating and compensating module 305 calculate the channel estimation value in the corresponding moment of each symbol of DPCCH respectively and dedicated channel DPDCH are compensated, each footpath signal after the compensation outputs to high specific merging module 306 and carries out the high specific merging, signal after will merging at last is input to and carries out deinterleaving and decoding in deinterleaving/decoder 307, obtains the primary signal of transmitting terminal emission.The position of the channel estimation methods that the present invention proposes in implementing block diagram is channel estimating and compensating module 305.

Fig. 4 is a channel estimation methods flow chart of the present invention, and this figure has illustrated the preparation that should be done before the channel estimation methods of the present invention that will implement, and the whereabouts of finishing the reprocessing result.

This logic flow starts from step 401, ends at step 404.

The wideband spread-spectrum signal of step 401 pair input RAKE receiver carries out descrambling and de-spreading.Because the signal that RAKE receiver receives all is to add expansion through scrambling, therefore need with the scrambler that responds earlier to its descrambling, be scrambler and received signal conjugate multiplication, with spreading code to its despreading, obtain DPCCH (Dedicated Physical Control Channel respectively, Dedicated Physical Control Channel) and DPDCH (Dedicated Physical Data Channel Dedicated Physical Data Channel), this is the preparation of later step, also has only the signal behind the descrambling and de-spreading can further make channel estimation process.

Order enters step 402, calculates channel estimation value.In a current and following time slot (hereinafter to be referred as " next time slot ") of Dedicated Physical Control Channel (DPCCH, Dedicated Physical Control Channel), take out frequency pilot sign according to known time slot format; To the frequency pilot sign that extracts, each frequency pilot sign and known pilot symbols are carried out the decorrelation computing, obtain the channel estimation value of each frequency pilot sign; Channel estimation value to all frequency pilot signs in each time slot is carried out arithmetic average, obtains the channel estimation value of each time slot.

Order enters step 403, for continuous DPCCH symbol string through the decorrelation computing, symbol ground moving window one by one, obtain the corresponding channel estimation value CEm constantly of window with the algorithm of arithmetic mean, this step is the core of this method, will do very concrete detailed description in Fig. 5.

Order enters step 404, with the corresponding m constantly of the 403 CEm backoff window that obtain DPDCH symbol constantly.Result after each multipath compensation exports to high specific and merges module.

Fig. 5 is an iterative algorithm flow chart in the channel estimation methods of the present invention, this figure detailed explanation the calculation process of channel estimation methods of the present invention.This figure is the core of the channel estimation methods that the present invention relates to, promptly how not only to utilize pilot tone but also utilize non-pilot frequency information to ask precise channels method of estimation by moving window, and Fig. 5 is the detail flowchart of this method, is the refinement of step 403.This logic flow starts from step 501, ends at step 512.

Step 501, all symbols of current time slots behind the descrambling and de-spreading that step 402 obtains and next time slot, from first sign-on of current time slots, till last symbol of current time slots, give step 502 symbol of a symbol, import next symbol again after the whole flow process of an experience Fig. 5.

Step 502, whether the current sign Sn that transports according to known time slot format (Slot Format) discriminating step 501 is first the non-frequency pilot sign in the current time slots, if step to step 506, steps to 503 if not.

Step 503 differentiates according to known time slot format whether current sign Sn is frequency pilot sign, if step to step 505.1, steps to step 507 if not.

Step 504 generates pilot frequency sequence according to known time slot format, uses for step 505.1.

Step 505 is done the decorrelation computing with the symbol and the known symbol (symbol that perhaps estimates) that receive, and decorrelation computing reality just multiplies each other, and promptly removes symbol.Wherein the known symbol of step 505.1 is the symbol of step 504 according to corresponding current location in the local sequence of pilot symbols that produces of known time slot format.And the known symbol in the step 505.2 is to pass through step 507,508,509,510 to estimate in fact, because generally speaking, the physical channel BER of DPCCH is relatively more following, and the symbol that estimates can be similar to as known symbol and be applied to the decorrelation computing.Step to step 511 after step 505 computing is intact.

Step 506, when receiving first non-frequency pilot sign, step 502 just steps to this step, this step is obtained all frequency pilot signs of next time slot from 402 output result, use again according to known time slot format and obtain known pilot sequence, frequency pilot sign to next time slot is done the decorrelation computing one by one, and the decorrelation calculated result is averaged just obtains CE then _Next-slotAt last CEnext-slot is preserved, because all will use it when estimating all non-frequency pilot signs.

Step 507, as shown in Figure 7, by CE _M-1And CE _Next-slotSimply average and obtain the pre-channel estimation value C ' n of current non-frequency pilot sign, i.e. C ' n=(CE _N-1+ CE _Next-slot)/2.CE wherein _M-1Be by previous symbol S _N-1The result that the whole flow process of process Fig. 5 obtains, and CE _Next-slotBe the result who tries to achieve in step 506.Fig. 7 is the schematic diagram of finding the solution the pre-channel estimation value of current non-frequency pilot sign, is that the figure of step 507 is set forth expression way.C ' n will be used for estimating the former symbol of Sn at transmitting terminal.

Step 508 is used the current non-frequency pilot sign S ' n after C ' n compensation Sn can arrive compensation.

Step 509, the method that the S ' n in all multipaths is merged with high specific merges the symbol S ' n-source after obtaining merging.

Step 510 is done hard decision to S ' n-source, ${\hat{S}}_{n-\mathrm{source}}=(S\text{'}n-\mathrm{soucrce}\&GreaterEqual;0)?1:-1,$ So

It is exactly the estimated value of the former symbol Sn-source of transmitting terminal.

Step 511 differentiates according to known time slot format whether current sign Sn is frequency pilot sign, receives 505.1 output result if selector switch points to the left side, and selector switch points to the right and receives 505.2 output result if not.

Step 512, as shown in Figure 6, moving window makes window cover Cn-L+i.....Cn, and the channel estimation value in the window is asked the arithmetic mean value, obtains the m final channel estimation value CEm constantly of window correspondence, promptly $\mathrm{CEm}=\frac{1}{L}\underset{i=1}{\overset{L}{\mathrm{\&Sigma;}}}{C}_{n-L+i},$ M＞=n-int (L-1)/2 wherein, int is downward round numbers, and L is a length of window, and L is according to the different value 6-60 of translational speed, and the slow more L value of speed can be big more, and L can estimate that the translational speed that obtains decides according to Doppler frequency deviation.M=n-int (L-1)/2 o'clock, time alignment during compensation, performance can be best, but for decline at a slow speed, when promptly L was bigger, therefore the hardware memory space that needs are bigger generally can get (n-int (L-1)/2, n) Zhong Jian a compromise value.CEm is a m final channel estimation value constantly, it will be used for DPDCH (Dedicated Physical Data Channel Dedicated Physical Data Channel) is done final compensation, compensation result can be given decoder for decoding behind MRC (Maximal RatioCombining, high specific merges).

Claims (3)

1, a kind of channel estimation methods that is used for broadband CDMA system is characterized in that, may further comprise the steps:

Step 1: the wideband spread-spectrum signal to the input RAKE receiver carries out descrambling and de-spreading, obtains Dedicated Physical Control Channel and Dedicated Physical Data Channel respectively;

Step 2: calculate channel estimation value: in the current of Dedicated Physical Control Channel and next time slot, take out frequency pilot sign according to known time slot format; To the frequency pilot sign that extracts, each frequency pilot sign and known pilot symbols are carried out the decorrelation computing, obtain the channel estimation value of each frequency pilot sign;

Step 3: in all symbol strings for the current time slots of continuous Dedicated Physical Control Channel through the decorrelation computing and next time slot, from first symbol of current time slots S1, till last symbol SL of current time slots, be total to L symbol, symbol ground moving window one by one, L is length of window, for the pilot tone in the current time slots, the pilot frequency sequence of learning according to time slot format carries out participating in the window arithmetic average after the decorrelation and obtains channel estimation value CEm; For the non-pilot tone of current time slots, first pilot average value CE with next time slot _Next-slotWith nearest channel estimation results CE _M-1Ask the pre-channel estimation value C ' n of average this non-frequency pilot sign of conduct, C ' n is carried out channel compensation and maximum ratio merging, according to the hard decision result after merging this non-pilot tone is carried out decorrelation then, the result after the decorrelation participates in the window arithmetic average and obtains channel estimation value CEm; Wherein subscript m is a channel estimation value index in time, and n is a Dedicated Physical Control Channel symbol index in time;

Step 4: with the corresponding m constantly of the channel estimation value CEm backoff window Dedicated Physical Data Channel symbol constantly that step 3 obtains, the result after each multipath compensation exports to high specific and merges module.

2, the channel estimation methods that is used for broadband CDMA system according to claim 1 is characterized in that, described step 3 specifically realizes by following steps:

In all symbols for the current time slots behind the descrambling and de-spreading and next time slot, from first symbol of current time slots S1, till last symbol SL of current time slots, enter following flow process a symbol of a symbol, previous symbol is imported next symbol after finishing whole flow process again;

Whether, be first non-frequency pilot sign in current time slots, subscript n is a Dedicated Physical Control Channel symbol index in time, if step to step (5), steps to step (2) if not according to known time slot format if (1) differentiating current sign Sn;

(2) differentiate according to known time slot format whether current sign Sn is frequency pilot sign,, step to step (6) if not if step to step (4);

(3) generate pilot frequency sequence according to known time slot format;

(4) symbol and the known symbol that receive are done the decorrelation computing, wherein known symbol is the symbol of step (3) according to corresponding current location in the local sequence of pilot symbols that produces of known time slot format;

(5) obtain all frequency pilot signs of next time slot, use according to known time slot format again and obtain known pilot sequence, the frequency pilot sign of next time slot is done the decorrelation computing one by one, the decorrelation calculated result is averaged obtains CE then _Next-slot, at last with CE _Next-slotPreservation is got up;

(6) by CE _M-1And CE _Next-slotSimply average and obtain the pre-channel estimation value C ' n of current non-frequency pilot sign, i.e. C ' n=(CE _M-1+ CE _Next-slot)/2; CE wherein _M-1Be the result who obtains through whole flow process by previous symbol Sn-1, CE _Next-slotBe the result who tries to achieve in step (5);

(7) use current non-frequency pilot sign S ' n after C ' n compensation Sn is compensated;

(8) method that the S ' n in all multipaths is merged with high specific merges the symbol S ' n-source after obtaining merging;

(9) S ' n-source is done hard decision, ${\hat{S}}_{n-\mathrm{soursce}}=(S\text{'}n-\mathrm{souscrce}\&GreaterEqual;0)$ 1:-1,

It is exactly the estimated value of the former symbol Sn-source of transmitting terminal;

(10) symbol that the non-frequency pilot sign Sn-source of the Dedicated Physical Control Channel that receives and step (9) are estimated Do the decorrelation computing;

(11) differentiate according to known time slot format whether current sign Sn is frequency pilot sign, if selector switch points to the output result of left side receiving step (4), selector switch points to the output result of the right receiving step (10) if not;

(12) ask the arithmetic mean value, obtain the m final channel estimation value CEm constantly of window correspondence, promptly $\mathrm{CEm}=\frac{1}{L}\underset{i=1}{\overset{L}{\mathrm{\&Sigma;}}}{C}_{n-L+i},$ M＞=n-int (L-1)/2 wherein, int is downward round numbers, i is an interim cyclic variable of asking average computation to use.

3, the channel estimation methods that is used for broadband CDMA system according to claim 2, it is characterized in that, in the described step (12), L is different and different according to translational speed, span is 6-60, the slow more L value of speed is big more, estimates that according to Doppler frequency deviation the translational speed that obtains decides.

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