CN104378318A - Broadband satellite mobile communication channel estimation improved method based on power judgment - Google Patents

Abstract

The invention discloses a broadband satellite mobile communication channel estimation improved method based on power judgment. The declination character of a broadband satellite mobile communication channel is fully utilized, a traditional DFT conversion estimation algorithm, a power judgment estimation algorithm and a time domain zero fill interpolation algorithm are combined, gradual boosting is carried out, the channel estimation precision of the broadband satellite mobile communication system is effectively improved, and the communication performance is improved. Meanwhile, according to the method, calculation is easy, after the power threshold value is determined, it is only needed to carry out M times of threshold value comparing, the channel response estimation value can be obtained, the FFT can be adopted for the corresponding DFT conversion, and therefore complexity is reduced, and hardware achievement is facilitated.

Description

A kind of broadband satellite mobile telecommunication channel based on power judgement estimates the method improved

Technical field

The present invention relates to broadband satellite moving communicating field, especially a kind of broadband satellite mobile telecommunication channel based on power judgement estimates the method improved.

Background technology

At present, along with growing with each passing day of global roaming and high-speed wideband demand, the research of broadband satellite mobile communication system is also launched step by step.OFDM technology relies on data transmission capabilities, the efficiently availability of frequency spectrum and the good anti-multipath performance of its high speed, becomes one of core transmission technology in 4G mobile communication system.Therefore, the broadband satellite mobile communication system based on OFDM has good researching value and development prospect.

There is multipath effect, Doppler frequency shift and shade and cover in broadband satellite mobile channel, ofdm signal will be caused to produce inter-sub-carrier interference and intersymbol interference, have a strong impact on the reliability of Signal transmissions.Therefore, only have receiver to estimate the information of channel accurately, just can carry out correct data demodulates, usually use the channel estimation methods based on pilot tone.

Based in the channel estimation method of pilot tone, because broadband satellite mobile channel scattering path is less, effective tap energies mainly concentrates on direct path, and the algorithm for estimating based on DFT conversion is more applicable.But this algorithm does not effectively suppress the noise in protection interval, and the effective tap outside protection interval is also removed by zero setting, and therefore estimated performance is not good.For this problem, there is following several innovatory algorithm at present: 1, based on the algorithm for estimating of the thought proposition discriminant analysis of noise cluster, utilize the thresholding constantly updated to obtain the feature of effective tap; 2, a low pass filter is added in the transform domain as illustrated by high-frequency noise filtering; 3, time domain estimated value is utilized to calculate channel correlation matrix and noise variance, and in frequency domain least mean-square error (Minimum Mean SquareError, MMSE) algorithm for estimating.These innovatory algorithm strengthen the suppression to effective tap external noise, improve channel estimating performance, but to increase algorithm complex for cost, and under broadband satellite mobile channel environment, the performance of some innovatory algorithm is not even as traditional algorithm.

Summary of the invention

Technical problem to be solved by this invention is, provide a kind of broadband satellite mobile telecommunication channel based on power judgement to estimate the method improved, algorithm complex is low, is easy to hardware implementing.

For solving the problems of the technologies described above, the invention provides a kind of method that broadband satellite mobile telecommunication channel based on power judgement is estimated to improve, comprising the steps:

(1) traditional LS algorithm is utilized to obtain pilot tone place channel estimation value

(2) being transformed to time domain by IDFT is m represents the number of every symbol pilot tone;

(3) performance number of each time point is calculated and by the limit calculation power threshold P to effective tap number _h;

(4) performance number of each time point is compared with power threshold, obtain new time domain channel estimated value ${\hat{h}}_{p,\mathrm{PLS}}={[{\hat{h}}_{\mathrm{PLS},0},{\hat{h}}_{\mathrm{PLS},1},\&CenterDot;\&CenterDot;\&CenterDot;,{\hat{h}}_{\mathrm{PLS},M-1}]}^T$ For ${\hat{h}}_{\mathrm{PLS},n}=\left\{\begin{array}{cc}\begin{array}{c}{\hat{h}}_{\mathrm{LS},n},{\left|{\hat{h}}_{\mathrm{LS},n}\right|}^2>P_h\\ 0,{\left|{\hat{h}}_{\mathrm{LS},n}\right|}^2<P_h\end{array}& n=\mathrm{0,1},\&CenterDot;\&CenterDot;\&CenterDot;,M-1.\end{array}\right.$

(5) to utilize in signal processing time domain zero padding to be again equivalent to and carry out the principle of interpolation to recover the complete channel frequency response at subcarrier place at frequency domain, after zero padding, the time domain impulse response sequence of channel is:

${\hat{h}}_n=\left\{\begin{array}{cc}{\hat{h}}_{n,\mathrm{PLS}}& n=\mathrm{0,1},\&CenterDot;\&CenterDot;\&CenterDot;,M-1\\ 0& n=M,M+1,\&CenterDot;\&CenterDot;\&CenterDot;,N-1\end{array}\right.$

Then to the time domain impulse response sequence of complete channel do DFT conversion, be namely equivalent to and done interpolation at frequency domain, obtain complete channel frequency domain response value for $\begin{array}{cc}{\hat{H}}_k=\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{\hat{h}}_n{e}^{-j2\mathrm{\&pi;nk}/N}& k=\mathrm{0,1},\&CenterDot;\&CenterDot;\&CenterDot;,N-1.\end{array}$

Beneficial effect of the present invention is: make full use of broadband satellite mobile channel fading characteristic, associating conventional DFT conversion algorithm for estimating, power judgement algorithm for estimating and time domain zero padding interpolation algorithm, iterative method, effectively raise precision of channel estimation in broadband satellite mobile communication system, improve communication performance; The present invention simultaneously calculates simply, only need carry out M subthreshold and compare, can obtain channel response estimated value after power threshold is determined, corresponding DFT conversion can adopt fast algorithm FFT, and therefore complexity reduces, and is easy to hardware implementing.

Accompanying drawing explanation

Fig. 1 is the satellite communication system structure chart that the present invention is based on OFDM.

Fig. 2 is Improvement of estimation algorithm schematic diagram of the present invention.

Fig. 3 is that the mean square error of LS, QLS, PLS, PLS_ZP of the present invention tetra-kinds of channel estimation method parameter Estimation compares simulation result figure.

Fig. 4 is that different channels algorithm for estimating performance of BER of the present invention compares simulation result figure.

Embodiment

As shown in Figure 1, branch road above represents transmitting portion on star, and branch road below represents ground station reception part.At transmitting terminal, first data source completes chnnel coding, intertexture, sign map and serioparallel exchange, and after insertion pilot tone, frequency domain data X (k) is through inverse fast Fourier transform IFFT, obtain time domain data s (n), wherein k, n=0,1,2...N-1, N represent sub-carrier number; After adding cyclic prefix CP, parallel-serial conversion, digital to analog conversion and up-conversion, signal enters satellite channel and transmits.Raw information is recovered by the inverse process of transmitting terminal and channel estimation technique at receiving terminal.

As shown in Figure 2, be estimation innovatory algorithm of the present invention.First, on the basis based on DFT algorithm for estimating, for broadband satellite mobile channel multipath tap is less and energy mainly concentrates on the feature on direct path, effective tap number is limited, determine suitable power threshold, thus avoid threshold value in conventional threshold values algorithm and be difficult to the problem determined; Secondly, after power threshold is determined, analyze each tap, therefore protect in interval and protect the noise outside interval to be obtained for effective suppression, performance is obviously better than traditional algorithm for estimating based on DFT conversion; Finally, when after the estimated value obtaining pilot tone place, utilize the principle of time domain zero padding equivalent frequency domain interpolation to improve former frequency domain interpolation algorithm, take full advantage of all pilot frequency informations estimated, for traditional frequency domain interpolation algorithm, there is better estimated performance.

Estimate that innovatory algorithm comprises the steps:

(1) traditional LS algorithm is utilized to obtain pilot tone place channel estimation value

(2) being transformed to time domain by IDFT is m represents the number of every symbol pilot tone;

(3) performance number of each time point is calculated and by the limit calculation power threshold P to effective tap number _h;

(4) performance number of each time point is compared with power threshold, obtain new time domain channel estimated value ${\hat{h}}_{p,\mathrm{PLS}}={[{\hat{h}}_{\mathrm{PLS},0},{\hat{h}}_{\mathrm{PLS},1},\&CenterDot;\&CenterDot;\&CenterDot;,{\hat{h}}_{\mathrm{PLS},M-1}]}^T$ For ${\hat{h}}_{\mathrm{PLS},n}=\left\{\begin{array}{cc}\begin{array}{c}{\hat{h}}_{\mathrm{LS},n},{\left|{\hat{h}}_{\mathrm{LS},n}\right|}^2>P_h\\ 0,{\left|{\hat{h}}_{\mathrm{LS},n}\right|}^2<P_h\end{array}& n=\mathrm{0,1},\&CenterDot;\&CenterDot;\&CenterDot;,M-1.\end{array}\right.$

(5) to utilize in signal processing time domain zero padding to be again equivalent to and carry out the principle of interpolation to recover the complete channel frequency response at subcarrier place at frequency domain, after zero padding, the time domain impulse response sequence of channel is:

${\hat{h}}_n=\left\{\begin{array}{cc}{\hat{h}}_{n,\mathrm{PLS}}& n=\mathrm{0,1},\&CenterDot;\&CenterDot;\&CenterDot;,M-1\\ 0& n=M,M+1,\&CenterDot;\&CenterDot;\&CenterDot;,N-1\end{array}\right.$

Then to the time domain impulse response sequence of complete channel do DFT conversion, be namely equivalent to and done interpolation at frequency domain, obtain complete channel frequency domain response value for $\begin{array}{cc}{\hat{H}}_k=\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{\hat{h}}_n{e}^{-j2\mathrm{\&pi;nk}/N}& k=\mathrm{0,1},\&CenterDot;\&CenterDot;\&CenterDot;,N-1.\end{array}$

As shown in Figure 3 and Figure 4; deemed-to-satisfy4 emulation by MATLAB of the present invention carries out analysis and evaluation; in emulation, model of communication system adopts structure chart as shown in Figure 1, and design parameter is set to: system bandwidth is 20MHz, 4 sampling frequencies; carrier number N is 1024; channel is 5 footpaths and maximum multipath time delay is 6.85 μ s, and maximum doppler frequency is 100Hz, and multi-carrier modulation scheme is QPSK; protection gap length is 256, and adjacent pilot frequencies is spaced apart 8.

In order to better verify the superiority of algorithm of the present invention, the traditional LS algorithm of contrast simulation, tradition based in the algorithm for estimating PLS based on power judgement in the algorithm QLS of DFT conversion, the present invention, the present invention based on the algorithm for estimating of power judgement in conjunction with the mean square deviation of time domain zero padding interpolation algorithm PLS_ZP these four kinds of algorithms and performance of BER curve.As can be seen from simulation result, the innovatory algorithm based on power judgement that the present invention proposes all has good performance under low signal-to-noise ratio and high s/n ratio environment, effectively can reduce the bit error rate of receiving terminal, improve the communication performance of system.Under low signal-to-noise ratio environment, compared with traditional LS algorithm, the mean square deviation performance of parameter Estimation of the present invention improves 6dB nearly.In addition the present invention is in conjunction with time domain zero padding interpolation algorithm, take full advantage of all pilot frequency informations estimated, the good channel that reacted, in do not had in the same time correlation, makes performance of BER other three kinds of algorithms relative improve a lot, especially more obvious under high s/n ratio.

Although the present invention illustrates with regard to preferred implementation and describes, only it will be understood by those of skill in the art that otherwise exceed claim limited range of the present invention, variations and modifications can be carried out to the present invention.

Claims (1)

1., based on the method that the broadband satellite mobile telecommunication channel estimation of power judgement improves, it is characterized in that, comprise the steps:

(1) traditional LS algorithm is utilized to obtain pilot tone place channel estimation value

(2) being transformed to time domain by IDFT is m represents the number of every symbol pilot tone;

(3) performance number of each time point is calculated and by the limit calculation power threshold P to effective tap number _h;

(4) performance number of each time point is compared with power threshold, obtain new time domain channel estimated value for n=0,1 ..., M-1;

(5) to utilize in signal processing time domain zero padding to be again equivalent to and carry out the principle of interpolation to recover the complete channel frequency response at subcarrier place at frequency domain, after zero padding, the time domain impulse response sequence of channel is:

Then to the time domain impulse response sequence of complete channel do DFT conversion, be namely equivalent to and done interpolation at frequency domain, obtain complete channel frequency domain response value for k=0,1 ..., N-1.