CN1320788C - A time synchronization method for TD-SCDMA system - Google Patents

Abstract

The present invention relates to a time synchronization method in a communication system, particularly to a new time synchronization method realized by a 128-chip channel estimation sample drawing in a TD-SCDMA system. Each odd tap and relevant values of the previous tap and the next tap of communication channel response are obtained by two relevant devices. Whether a system is positive time synchronization error or a negative time synchronization error is judged by a decision unit by the relevant values, and the advancing, the delay or the immobility keeping of sample time is determined. In the method, the problem of the time synchronization error brought by a timing error existing in a matched filter (a root raised cosine filter) of a receiving terminal of the TD-SCDMA system is mainly solved, a false target is prevented, and intersymbol interference is reduced.

Description

Method for synchronizing time in a kind of TD-SCDMA system

Technical field:

The present invention relates to the method for synchronizing time in the communication system, particularly a kind of new method for synchronizing time that utilizes 128-chip channel estimating master drawing to realize in the TD-SCDMA system.

Background technology:

We know that TD-SCDMA system rule class is in the agreement of the 1.28Mcps of UMTS TDD, and the frame structure of TD-SCDMA and structure of time slot are as shown in Figure 1 and Figure 2.We illustrate midamble data forming process at following behavior example.

Suppose m _P=(m ₁, m ₂..., m _P) be basic Midamble sign indicating number, P=128, m _P=( _{m 1}, m ₂..., m _P) be the basic Midamble sign indicating number after the QPSK modulation, have so: m _i=(j) ⁱM _iTo all i=1 ..., P, $j=\sqrt{-1}.$ Make i _Max=L _m+ (K-1) W, L here _m=144, K can get 2,4,6,8,10,12,14,16}, usually K gets 8,

We construct $\underset{\‾}{m}=({\underset{\‾}{m}}_1,{\underset{\‾}{m}}_2,\·\·\·,{\underset{\‾}{m}}_{i_{\max }})=({\underset{\‾}{m}}_1,{\underset{\‾}{m}}_2,\·\·\·,{\underset{\‾}{m}}_{L_m+(K-1)W}),$ And m _i= m _I-PK the pairing Midamble sign indicating number of channel window is so ${\underset{\‾}{m}}^{\left(k\right)}=({\underset{\‾}{m}}_1^{\left(k\right)},{\underset{\‾}{m}}_2^{\left(k\right)},\·\·\·,{\underset{\‾}{m}}_{L_m}^{\left(k\right)})$ And ${\underset{\‾}{m}}_i^{\left(k\right)}={\underset{\‾}{m}}_{i+(K-k)W},$ L=1 ..., L _mAnd k=1 ..., K.

DEFAULT?mode：

Under this pattern, all ${\underset{\‾}{m}}^{\left(k\right)}=({\underset{\‾}{m}}_1^{\left(k\right)},{\underset{\‾}{m}}_2^{\left(k\right)},\·\·\·,{\underset{\‾}{m}}_{L_m}^{\left(k\right)}),$ K=1 ..., K may use, and they and code channel have corresponding relation.

COMMON?mode

Under this pattern ${\underset{\‾}{m}}^{\left(k\right)}=({\underset{\‾}{m}}_1^{\left(k\right)},{\underset{\‾}{m}}_2^{\left(k\right)},\·\·\·,{\underset{\‾}{m}}_{L_m}^{\left(k\right)}),$ K=1 ..., K has only needs to use, and it will be used by code channels all in this sub-district as identical midamble code.

Terminal at first resolves into two data blocks and a Midamble code block with the data that receive according to structure of time slot shown in Figure 3, again with the Midamble code block and the local relevant acquisition of Midamble sign indicating number channel estimating of regenerating that receive.

Provide the example of two channel estimating master drawings below, belong to DEFAULT and COMMON pattern respectively, wherein suppose K=8 under the DEFAULT pattern, and 4 channel windows activate.We suppose flat fading (having only a footpath) simultaneously.

It is that W is divided into K channel response window according to width that the channel impulse response estimation of 128-chip is come out back, is allocated to different code channels according to the TD mode of operation again and uses.Such as to the COMMON pattern, as Fig. 4 (a), 17-32 directly constitutes a channel window and uses for all code channels of this sub-district; And use for code channel 1 and 2 as first channel window among Fig. 4 (b) (1-16 footpath) under the DEFAULT pattern, and second channel window (17-32 footpath) uses for the 3rd and 4 code channels, and the rest may be inferred.

As mentioned above, the TD-SCDMA system is divided into K channel window with the channel that estimates and distributes to different code channel uses, can only there be the many warps of W bar at most in each channel window, when having synchronous error, a footpath originally is expanded into many footpaths with division, channel after expand this moment is many to be caused very big interference even causes bogus subscriber's appearance through probably going in other channel window, has greatly reduced the performance of system; Even many through also in this channel window after expanding, also can bring bigger intersymbol interference this moment.

With the DEFAULT pattern is example, and the channel response of Fig. 4 (b) is expanded into division shown in Figure 5 when the existence ± Tc/2 of system error.At this moment, channel carries out the branch timing will produce intersymbol interference Fig. 5 (a) and false target Fig. 5 (b), the expansion here many through being that matched filter (root raised cosine filter) by receiving terminal exists timing error to bring fully have stronger correlation by expanding the multipath that is brought between adjacent.

When there being negative time synchronization error (such as sampling in advance), shown in Fig. 5 (a), each odd tap of channel response that estimate this moment has stronger correlation with its next tap, and little with the correlation of its previous tap;

When there being positive time synchronization error (such as late samples), shown in Fig. 5 (b), each odd tap of channel response that estimate this moment is little with the correlation of its next tap, and incites somebody to action strong with the correlation of its previous tap;

Summary of the invention:

The objective of the invention is a kind of new method for synchronizing time that utilizes 128-chip channel estimating master drawing to realize in the TD-SCDMA system, there is time synchronization error that timing error brings in the matched filter (root raised cosine filter) that solves the receiving terminal of TD-SCDMA system, and may bring the technical problem of false target and big interference to system.

For solving the problems of the technologies described above, the present invention is achieved in that

Method for synchronizing time in a kind of TD-SCDMA system utilizes 128-chip channel estimating master drawing to carry out, and it is characterized in that: obtain the correlation of each odd tap of channel response with its last tap and next tap by two correlators; Utilizing this correlation is positive time synchronization error or negative time synchronization error by decision package judgement system, and the decision sampling time in advance, lag behind or keep motionless.

Utilize correlator to obtain correlation and carry out noise reduction process before earlier.

The inventive method utilizes 128-chip channel estimating master drawing to realize time synchronized in the TD-SCDMA system, for fear of false target occurring and reducing intersymbol interference.

Description of drawings:

Fig. 1 is a TD-SCDMA system subframe structure.

Among the figure: the shared chip number of each time slot is marked on the figure; TS0, DwPTS are constant to be descending; UpPTS, TS1 are constant to be up.

Fig. 2 is T0 in the TD-SCDMA system, T1 ..., the T6 structure of time slot.

Fig. 3 is a channel estimating part schematic diagram in the TD-SCDMA system.

Fig. 4 (a) and (b) are examples of two channel estimating, and time synchronized does not have error.

Channel response master drawing when Fig. 5 (a) and (b) are the life period synchronous error.

Fig. 6 is the schematic flow sheet of the inventive method.

Fig. 7 is the special case of a correlator in the inventive method.

Embodiment:

See also Fig. 6, it is the schematic flow sheet of the inventive method.As shown in the figure: the method for synchronizing time of this TD-SCDMA system, utilize 128-chip channel estimating master drawing to carry out, obtain the correlation of each odd tap of channel response by two correlators with its last tap and next tap; Utilizing this correlation is positive time synchronization error or negative time synchronization error by decision package judgement system, and the decision sampling time in advance, lag behind or keep motionless; Utilize correlator to obtain correlation and carry out noise reduction process before earlier.

Fig. 7 is a special case of correlator, wherein the real part of real (x) expression taking-up x.

We provide the false code of decision package simultaneously:

Suction parameter r ₁And r ₂, the outlet action is for shifting to an earlier date or lagging behind Time sample or the sampling time keeps motionless.

R＝0

L＝0

0 subframe of for N continuous

If r1 and r2 contrary sign and/r1/＞0.1﹠amp; / r2/＞0.1

if?r1＞r2

L＝L+1

if?r1＜r2

R＝R+1

end

end

if?R＞＝N

Sampling time hysteresis 1/8Tc carries out

elseif?L＞＝N

Sampling time shifts to an earlier date 1/8Tc and carries out

otherwise

Sampling time keeps motionless

end

Usually N0, N can not get into 1, and rock the easy like this front and back regularly of causing; The value that might as well get N0, N is 8 and 6, so just forms " ballot " mechanism, has guaranteed the stability of system synchronization.

To the TD-SCDMA receiver system of multiple sampling, the effect of this invention can be better.

Being preferred embodiment of the present invention only in sum, is not to be used for limiting practical range of the present invention.Be that all equivalences of doing according to the content of the present patent application claim change and modification, all should be technology category of the present invention.

Claims (2)

1, the method for synchronizing time in a kind of TD-SCDMA system utilizes 128-chip channel estimating master drawing to carry out, and it is characterized in that: obtain the correlation of each odd tap of channel response with its last tap and next tap by two correlators; Utilizing this correlation is positive time synchronization error or negative time synchronization error by decision package judgement system, and the decision sampling time in advance, lag behind or keep motionless.

2, the method for synchronizing time in the TD-SCDMA according to claim 1 system is characterized in that: utilize correlator to carry out noise reduction process earlier before obtaining correlation.

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