CN100388639C - Multi-path time-delay estimating method for direct spread-spectrum CDMA system - Google Patents

Abstract

The present invention relates to a multi-path time-delay estimating method of a direct spread-spectrum CDMA system. Firstly, different time delay relations of a baseband signal and a known scrambling code and pilot are formed; after an amplitude time delay contour is obtained, a Mexico straw hat function and an amplitude time delay contour form a relation again; a maximum peak is searched in the obtained wave shape to be used as the time delay of a path; then, the amplitude time delay contour component of the path is minus from the original data; then, the Mexico straw hat function and the updated data form a relation again; a next path is found, and the circulation proceeds until all paths are found. Due to the time-frequency characteristics of the Mexico straw hat function, the processing of the present invention can greatly eliminate the influence of the amplitude time delay contour, which is caused by noise; simultaneously, the mutual influence of two adjacent paths can also be eliminated, and the accuracy of the time delay estimation of each path is improved.

Description

A kind of multipath delay method of estimation of Direct-Spread code division multiple access system

Technical field

The present invention relates in the wireless mobile communications field multipath delay estimation approach in the Direct-Spread code division multiple access system, more specifically relate in the WCDMA system, how accurately to estimate multidiameter delay.

Background technology

In the third generation mobile system, because wireless channel is quite wide, use spread spectrum and code division multiple access, a plurality of users can use identical channel.Utilize direct spreading sequence, information symbol is represented by chip sequence.In the wireless interface receiving end, be correlated with the recovering information symbol with chip sequence.Radio wave is along the different propagated between launch site and the reception place, thereby for each signal that is sent out, what receiver received is not single signal, but a plurality of reproducing signals of different delayed time and different amplitudes, these signals are called as multipath signal.For more effective with communicate by letter reliably, adopt Rake receiver to come harvest energy from different multipath signals, can reduce noise greatly, improve the energy of signal.The relevant method of Rake receiver utilization detects the signal in each footpath, obtains its time delay, and each signal is directly carried out demodulation and merging.

Because in radio communication, what travelling carriage might not stop moves, wireless channel changes in time, and multidiameter delay can change in time, therefore needs constantly to estimate the time delay in each bar footpath.United States Patent (USP) " MOBILEDEMODULATOR ARCHITECTURE FOR A SPREAD SPECTURUM MULTIPLE ACCESSCOMMUNICATION SYSTEM " (U.S. Patent number: 5,764,687) propose present normally used peak value detection method, used the pilot signal in the Dedicated Physical Control Channel to estimate multidiameter delay.Do different delay relevant with known scrambler with pilot signal with the baseband signal that receives, obtain a correlation function.When relevant time-delay was identical with the time-delay in footpath, a peak value will appear in correlation function, and correlation function is with respect to the peak value symmetry.In the correlation function waveform, seek the time delay that the pairing time delay of peak value is exactly each footpath.

The waveform of correlation function reduces symmetrically around its peak value, as shown in Figure 1.But because noise effect, particularly when noise ratio was big, its waveform peak might be offset, as shown in Figure 2.Another kind of situation is adjacent closer the time when two footpaths, just might cause correlation function to change owing to the stack of signal, and the peak value appearance is offset.Fig. 3 represents that exactly two footpaths are adjacent when closer, and peak value and waveform all change, and skew has taken place the peak value in strong footpath, and the peak value in weak footpath disappears.

For first kind of situation, existing technology does not provide the method for solution.For second kind of situation, Chinese patent " method and apparatus that in direct sequence spread spectrum communication system, is used for Multipath Time Delay Estimation " (application number: 99802134.2) propose after detecting the time delay of most powerful path, from correlation function, remove the correlated components in this footpath, and then from correlation function, look for next peak value, just can solve the problem of adjacent footpath phase mutual interference.But as can be seen from Figure 3, because peak value and waveform change, the time-delay in article one footpath of finding is just not right, removes the correlated components in this footpath and will bring bigger deviation from correlation function, and the time-delay in the adjacent footpath that obtains like this is just more impossible correct.

Summary of the invention

The objective of the invention is to propose a kind of time delay estimation approach of under wireless multipath channel situation, accurately carrying out each footpath, thereby can improve the signal energy that receives, reach than higher signal to noise ratio.

In this programme, the same in prior art, use the pilot signal in the Dedicated Physical Control Channel to estimate, at first baseband signal is done the relevant of different delay with known scrambler and pilot tone, obtain a correlation function, we be referred to as the magnitude time delay profile (Amplitude Delay Profile, ADP).After obtaining the magnitude time delay profile, with Mexico straw hat function M (t), t=0 ..., 2L+1 and magnitude time delay profile carry out a correlations again, seek the time delay of peak-peak as a footpath from the waveform that obtains.From former data, deduct the magnitude time delay profile component in this footpath then, again with Mexico's straw hat function with upgrade after data carry out relevantly again, find next bar footpath, and circulation goes down, up to finding all footpaths.

Because the time-frequency characteristic that Mexico's straw hat function has, processing of the present invention just can be eliminated the influence of noise to the magnitude time delay profile greatly, can also eliminate interacting between the adjacent footpath simultaneously, improves the precision that each footpath time delay is estimated.

Description of drawings

Fig. 1 is the single footpath magnitude time delay profile diagram when not having noise;

Fig. 2 is the single footpath magnitude time delay profile diagram when having noise;

Fig. 3 has the adjacent magnitude time delay profile diagram when closer in two footpaths;

Fig. 4 is the structure chart of Rake receiver;

Fig. 5 is the structure chart of searcher;

Fig. 6 is the structure chart of magnitude time delay profile (ADP) correlator;

Fig. 7 is typical Mexico straw hat function and its Fourier transform figure;

Fig. 8 be noise exist situation place an order the footpath Mexico's straw hat functional dependence design sketch;

Fig. 9 is Mexico's straw hat functional dependence design sketch under two adjacent nearer situations in footpath;

Figure 10 is the relevant effect figure that removes a footpath back magnitude time delay profile and Mexico's straw hat function.

Embodiment

Be described in further detail below in conjunction with the enforcement of accompanying drawing technical scheme.

At a Direct-Spread code division multiple access system, generally be to realize synchronously with pilot signal.Pilot signal is the important component part of Dedicated Control Channel (DPCCH), knows in advance at receiving terminal under the situation of pilot signal and the scrambler that uses and searches for multipath.The mechanism of Rake (RAKE) receiver as shown in Figure 4, baseband signal is delivered to respectively in searcher 401 and M the demodulator 403.Searcher 401 is searched multipath from baseband signal, look for the time delay of each multipath, offers each demodulator 403 respectively.Demodulator 403 carries out the demodulation of data according to each the footpath time delay that obtains, and demodulation result is delivered to path combiner 402 merges, and exports then.It is quite important to RAKE receiver that each footpath time-delay accurately is provided, otherwise can not demodulate correct data.And because the time-varying characteristics of wireless channel need searcher constantly to upgrade the time-delay in each footpath.

We suppose has time-delay to be T in the multipath channel ₁, T ₂..., T _NThe N paths, (M≤N), M demodulator are used for this strongest M paths of demodulation and RAKE receiver uses searcher to record the strongest M paths.The structure of searcher 401 as shown in Figure 5, it is that scrambler and the pilot tone of 2L+1 done the relevant of different delay t that baseband signal is at first delivered in the magnitude time delay profile correlator (ADP) 411 with known length, obtain a correlation function, we are referred to as magnitude time delay profile A (t).Detailed process as shown in Figure 6, baseband signal is at first sent delayer 4111, and signal amplitude is delayed time.Signal is sent into relevant module 4112 and 4113 then, and signal is carried out relevant treatment.Send into the relevant die lifter 4114 that adds up subsequently, be correlated with and add up, and complex signal is got its mould value, thereby obtain the magnitude time delay profile.

For the n footpath, as time delay t=T _nThe time, a peak value can appear in the magnitude time delay profile.The way of prior art is exactly to find out the time-delay of M bar most powerful path by the method for seeking magnitude time delay profile peak value, delivers to and carries out demodulation in the demodulator.But when noise ratio is bigger, because interference of noise might cause magnitude time delay profile peak value to change, as shown in Figure 2.Another kind of situation is when many footpath time-delays are more approaching, the phase mutual interference causes peak value separately to change, Fig. 3 just represent two footpath time-delays relatively near the time to the influence of magnitude time delay profile, skew has taken place in the peak value of most powerful path, and the peak value in weak footpath has disappeared.Therefore in these cases, directly from the magnitude time delay profile, look for the method for peak value to tend to cause the time-delay of finding inaccurate.

The present invention is the magnitude time delay profile A (t) from 411 outputs of magnitude time delay profile correlator, is input to distribution correlator 412, does further relevant.This correlations is not to use pilot tone and the scrambler of 2L+1, but adopts Mexico straw hat function M (t), t=0 ..., it is relevant with the input signal work that 2L+1 comes, and obtains correlation function C (t).Correlation function C (t) is sent into peak value selector 413, find peak-peak c _{Max_1}Time delay t with correspondence ₁Time delay t wherein ₁It is exactly the time delay of most powerful path.

Mexico's straw hat function is the second dervative of Gaussian function, and this function is used to the multi-scale morphology of computer vision the earliest.Normalized Mexico straw hat function is

$M\left(t\right)=\frac{2}{{\mathrm{\&pi;}}^{1/4}\sqrt{3\mathrm{\&sigma;}}}(1-\frac{{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="C20041004177500091.png"\; state="\{\{state\}\}">t</figure-callout>}}^2}{{\mathrm{\&sigma;}}^2})\exp \left(\frac{{-\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="C20041004177500091.png"\; state="\{\{state\}\}">t</figure-callout>}}^2}{2{\mathrm{\&sigma;}}^2}\right)$

Its Fourier transform is

$\hat{M}\left(w\right)=\frac{\sqrt{8}{\mathrm{\&sigma;}}^{5/2}{\mathrm{\&pi;}}^{1/4}}{\sqrt{3}}{w}^3\exp \left(\frac{{-\mathrm{\&sigma;}}^2{w}^2}{2}\right)$

Fig. 7 represents Mexico's straw hat function and the Fourier transform thereof when σ=1, and as can be seen from the figure this function has bandpass characteristics on frequency domain.Magnitude time delay profile and this functional dependence just are equivalent to through a band pass filter, so just not only can remove the noise of low frequency and high frequency, stack causes between the adjacent footpath direct current and low frequency component can also be eliminated, therefore also just interfering with each other between the adjacent footpath can be eliminated.This function can be seen from Fig. 8 suppressing The noise, can eliminate The noise greatly after being correlated with, and helps finding footpath time-delay accurately.Fig. 9 represents is to use Mexico's straw hat function can eliminate phase mutual interference between the adjacent footpath, observe the waveform that magnitude time delay profile and Mexico's straw hat functional dependence obtain, the peak value in the more intense footpath 1 of the peak value on its left side and signal alignment as can be seen, the peak in the footpath 2 that the peak on its right and signal are more weak only differs 1 unit.Therefore the time-delay of most powerful path was done in result's peak-peak position after we can adopt and be correlated with.

In order further to eliminate the interference between adjacent each footpath, after finding a footpath, from former amplitude time-delay profile, deduct the magnitude time delay profile component in this footpath.The magnitude time delay profile component in this footpath is exactly correlation and single footpath exemplary amplitude time-delay profile function A in this footpath _{Sin gle}(t) product, subtracter 414 is realized this function.Magnitude time delay profile A (t), peak-peak c _{Max_1}Time delay t with correspondence ₁All be admitted in the subtracter 414, the magnitude time delay profile component that detects the footpath is removed from the magnitude time delay profile, obtain new magnitude time delay profile A _New(t):

A _new(t)＝A _old(t)-c _{max_1}*A _sin?gle(t-t ₁)

Here single footpath exemplary amplitude time-delay profile function of using can be to obtain from reality, such as obtaining under the situation that very high signal interference ratio is set, also can be similar to Gaussian Profile.Because the footpath that detects earlier all is that signal Hen is strong, it also is maximum to the influence in adjacent other footpaths, and the accuracy that helps detecting is in the back removed in its influence from the magnitude time delay profile function.

With new magnitude time delay profile, promptly remove the magnitude time delay profile A that has detected the footpath influence _New(t) deliver to distribution correlator 415, do relevantly again, be used for obtaining new correlation function C (t), therefrom find next peak value c again with Mexico straw hat function _{Max_2}Time delay t with correspondence ₂Shown in Figure 10 is exactly removes the magnitude time delay profile after the component that detects footpath 1 and the correlated results of Mexico's straw hat function, and the peak in the position of correlated results peak value and footpath 2 is consistent as can be seen, so just can guarantee to detect the accuracy of directly delaying time.Circulation is gone down like this, up to detecting M bar footpath, promptly finds the time delay (t of M bar most powerful path ₁, t ₂..., t _M).

Claims (3)

1. the multipath delay method of estimation of a Direct-Spread code division multiple access system, it is characterized in that: this method may further comprise the steps:

1.1 baseband signal is input in the magnitude time delay profile correlator and does the relevant of different delayed time with known scrambler and pilot tone, obtains magnitude time delay profile A (t);

1.2 carry out a correlations again with Mexico's straw hat function and magnitude time delay profile, from the waveform that obtains, seek the time delay of peak-peak as a footpath; From former data, deduct the magnitude time delay profile component in this footpath then, again with Mexico's straw hat function with upgrade after data carry out relevantly again, find next bar footpath; Circulation is gone down successively, up to finding all footpaths.

2. the multipath delay method of estimation of the described Direct-Spread code division multiple access system of claim 1 is characterized in that, described step 1.2 comprises:

2.1 deliver in the distribution correlator magnitude time delay profile A (t) and Mexico straw hat function M (t), t=0 ..., 2L+1 is correlated with, and obtains correlation function C (t);

2.2 correlation function C (t) is sent into a peak value selector, finds first peak-peak c _{Max_1}Time delay t with correspondence ₁, the time delay t that finds ₁It is exactly the time delay of most powerful path;

2.3 with magnitude time delay profile A (t), the peak-peak c that finds _{Max_1}Time delay t with correspondence ₁All be admitted in another subtracter, the magnitude time delay profile component that detects the footpath is removed from the magnitude time delay profile, obtain new magnitude time delay profile A _New(t):

A _New(t)=A _Old(t)-c _{Max_1}* A _Single(t-t ₁); Wherein, A _Old(t) be former amplitude time-delay profile, A _Single(t) be single footpath exemplary amplitude time-delay profile function;

2.4 the new magnitude time delay profile A that will find _New(t) send in another distribution correlator, obtain new correlation function C (t), deliver to another peak value selector again, find new peak-peak c _{Max_2}Time delay t with correspondence ₂

2.5 according to the method for step 2.3 and 2.4, up to the time delay (t that finds M bar most powerful path ₁, t ₂..., t _M) till.

3. the multipath delay method of estimation of the described Direct-Spread code division multiple access system of claim 1 is characterized in that, described step 1.1 comprises: baseband signal is at first sent delayer, and signal amplitude is delayed time; Signal is sent into relevant module then, and signal is carried out relevant treatment with scrambler, pilot tone respectively; Send into the relevant die lifter that adds up subsequently, be correlated with and add up, and complex signal is got its mould value, thereby obtain the magnitude time delay profile.

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