CN104539562A - MIMO-OFDM wideband HF channel estimation method - Google Patents

MIMO-OFDM wideband HF channel estimation method Download PDF

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Publication number
CN104539562A
CN104539562A CN201410605918.9A CN201410605918A CN104539562A CN 104539562 A CN104539562 A CN 104539562A CN 201410605918 A CN201410605918 A CN 201410605918A CN 104539562 A CN104539562 A CN 104539562A
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channel
pilot
ofdm
signal
estimation
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Inventor
唐宏
粟根花
夏小霞
李兆玉
韦世红
杨浩澜
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Chongqing University of Post and Telecommunications
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Chongqing University of Post and Telecommunications
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Abstract

The invention asks for protecting an MIMO-OFDM (Multi-Input Multi-Output Orthogonal Frequency Division Multiplexing) wideband HF channel estimation method. The method comprises the following steps: designing a comb-type pilot frame structure format according to the characteristics of a wideband HF channel to determine the insertion position of a pilot; acquiring channel impulse response on the pilot position by taking a least square method as an estimation criterion through an observation sample of an MIMO-OFDM pilot signal; performing filtering through wavelet transform, tracking the maximal value of the wavelet transform on each scale, finding out a signal portion, and filtering noise to increase the accuracy of channel estimation, wherein for a signal mixed with Gaussian white noise, the amplitude of the wavelet transform decreases along with the increase of a wavelet decomposition scale; and acquiring the channel frequency domain response of a full band by adopting an interpolation algorithm based on transform domain zero padding. The method is low in computation complexity, and high in error estimation performance.

Description

Based on the HF wideband channel method of estimation of multi-I/O OFDM
Technical field
The present invention relates to the channel estimation methods of wireless communication field, specifically based on the channel estimation methods of broadband shortwave MIMO-OFDM system.
Background technology
Short wave communication refers to the radio communication carried out in frequency range 1.5M-30MHz (wavelength 10m-200m) scope.This frequency range comprise short-wave band (3M-30MHz) and part medium-wave band (1.5M-3MHz), therefore short wave communication be otherwise known as high frequency (High Frequency, HF) communication.Due to shortwave propagation distance, thus its once become in, the major wireless communications means of telecommunication.The advantages such as meanwhile, it is low that short wave communication has again cost, and equipment is simple, and communication mode is flexible, the good and strong security of survivability, are therefore widely used in fields such as military affairs, meteorology, aviation and rescue and relief works.
Modern short wave communication is with " broadband high-speed " for principal character, and it belongs to wireless communication field, and channel circumstance is complicated severe.Owing to being carry out bounce transmission information by ionosphere in shortwave transmission, and the Rapid Variable Design of the regular rapid movement in ionosphere and reflector height, the length of propagation path can be made constantly to change, thus cause Doppler frequency shift, the phenomenons such as doppler spread.Shortwave also there will be multi-hop phenomenon in transmitting procedure, and this phenomenon can cause multipath effect, thus it is more complicated that shortwave is transmitted.Therefore, modeling is accurately carried out to short wave channel and to work out the channel estimation methods of a set of applicable shortwave particularly important to the research of following short wave communication.
OFDM (OFDM) technology is a kind of parallel multi-carrier modulation technology, its be by coding after converting serial data streams be parallel data stream, then equally spaced N number of subcarrier in frequency is adopted to modulate parallel data respectively, send after the signal plus of the N number of subcarrier after modulation more simultaneously, the sub-fraction of a frequency spectrum busy channel bandwidth of each like this symbol, therefore, the demand of spectral bandwidth is little, in addition, OFDM technology also effectively can resist multidiameter delay, and its mitigating frequency-selective fading ability is also very strong.MIMO (multiple-input and multiple-output) system is improved the capacity of system channel, significantly improved by the gain of space multiplexing technique by system, under the prerequisite ensureing low error rate, constantly realizes high efficiency transmission.MIMO-OFDM wireless communication system combines the two advantage effectively, therefore, the research that MIMO-OFDM system channel is estimated at wireless communication field in occupation of critical role.
The channel estimating of MIMO-OFDM system roughly can be divided three classes according to the difference of method: blind Channel Estimation, semi-blind channel estimation and based on the non-blind Channel Estimation having ginseng.Blind Channel Estimation and semi-blind channel estimation because of convergence rate slow, algorithm is complicated, and operand is large, uses relatively less.But not blind Channel Estimation is the estimation carried out based on frequency pilot sign or training sequence due to it, method comparison is simple, and that uses in practical application is more extensive.Non-blind channel estimation technique is broadly divided into least square method (LS), LMSE method (MMSE), linear minimum mean-squared error method (LMMSE).Wherein least square method algorithm complex is low, is easy to realize, but LS channel estimating belongs to unbiased esti-mator, so affected by noise comparatively large, for actual environment, is unlikelyly draw channel statistics information more accurately.The algorithm for estimating of least mean-square error (MMSE) criterion has good inhibitory action for inter-sub-carrier interference and white Gaussian noise, so MMSE algorithm for estimating is more excellent than the performance of LS algorithm for estimating, but MMSE algorithm needs to carry out matrix inversion operation, when the number of subcarriers N of system increases, the operand of matrix can become very large.Engineering is difficult to realize.Linear minimum mean-squared error channel estimating effect is better, but calculating process also relates to the calculating of large moment matrix and covariance, and the complexity of therefore computing is also comparatively large, and the part can getting low order is similar to.
Summary of the invention
For above deficiency of the prior art, the object of the present invention is to provide a kind of HF wideband channel method of estimation reducing the complexity of channel estimating, technical scheme of the present invention is as follows: a kind of HF wideband channel method of estimation based on multi-I/O OFDM, and it comprises the following steps:
101, at transmitting terminal, according to the parameter index of HF wideband channel channel, design one and adapt to the Comb Pilot of fast channel and determine the insertion position of Comb Pilot, the Comb Pilot designed is inserted the position determined, sent by antenna;
102, design in advance, pilot data is extracted from each antenna receiving terminal, the pilot data extracted is delivered to successively the channel estimator designed and produce pilot signal, and by described bank of filters, filtering is carried out to pilot signal, pilot signal data after output filtering, then utilize least square method to calculate sampling of data value when pilot frequency locations virgin carrier channel estimates frequency domain, obtain transmitting accept antenna between domain samples value;
103, each transmitting is accepted antenna between the domain samples value that obtains adopt discrete fourier DFT converter technique to transform in transform domain, by wavelet transformation designing filter, in the transform domain as illustrated low-pass filtering is carried out to signal, and then carry out zero padding in transform domain, again the time domain sequences after zero padding is carried out inverse discrete Fourier transform IDFT conversion, obtain the channel response at all sub-carrier positions places;
104, finally will estimate channel response gives signal processing unit after each reception antenna in step 103, the short wave channel completing whole multi-input multi-output orthogonal frequency division multiplexing system be estimated.
Further, in step 101, HF wideband channel model adopts Watterson channel model, and simplified model h (t) of broadband shortwave Watterson model can be expressed as follows:
Wherein, a kfor the relative amplitude of path k; L is number of path; f dkfor Doppler frequency shift; for initial phase; τ kfor the relative path time delay on the k of path; δ is impulse function; T is the time.
Further, the frequency interval D of pilots insertion f:
τ in formula maxfor the maximum delay of channel response is expanded, T sit is a multi-I/O OFDM symbol period not comprising Cyclic Prefix.
Further, channel estimator designs according to LS least square method, and suppose that sending signal is X, channel response is H, and the signal received is Y, and noise jamming is σ, then channel model is:
Y=XH+σ
Then obtain LS channel estimating frequency domain response for:
H ^ LS = X - 1 Y = X - 1 ( XH + σ ) = H + X - 1 σ
Wherein for the estimated value of Comb Pilot after the channel response estimated, for estimating to obtain
Domain channel response.
Further, in step 103, receiving terminal time domain channel estimated value is:
h ^ ls , k = h k + n k x k
Wherein, for the channel estimation value on a kth carrier frequency, h kfor the true response of channel, for the interference that noise is introduced, Wavelet Denoising Method process is as follows:
Wherein c k, nthe coefficient of low frequency part after decomposing, d k, nbe the coefficient of HFS after decomposing, l span is the element number of sequence, and n is the n-th element in sequence, be scaling function, the HFS decomposed out is noise section, and low frequency part is signal section.
Advantage of the present invention and beneficial effect as follows:
Present invention employs broadband shortwave Watterson simplified model, the complexity of the channel estimating greatly reduced, Comb Pilot frame structure is adopted to follow the tracks of channel, relatively be applicable to changing short wave channel faster, adopt zero padding interpolation algorithm in transform domain, filtering is carried out, to obtain channel estimating more accurately by the thought of wavelet transformation.
Accompanying drawing explanation
Fig. 1 is the broadband shortwave MIMO-OFDM system model figure according to one embodiment of the present invention;
Fig. 2 interpolation of the present invention and filtering flow chart;
Fig. 3 channel estimating flow chart.
Embodiment
The invention will be further elaborated to provide an infinite embodiment below in conjunction with accompanying drawing.But should be appreciated that, these describe just example, and do not really want to limit the scope of the invention.In addition, in the following description, the description to known features and technology is eliminated, to avoid unnecessarily obscuring concept of the present invention.
A preferred embodiment of the present invention is: see Fig. 1, and a kind of MIMO-OFDM HF wideband channel method of estimation, is characterized in that: according to characteristics design Comb Pilot frame structure format of HF wideband channel, namely determine the insertion position of pilot tone; Utilizing the observation sample of MIMO-OFDM pilot signal, take least square method as the channel impulse response that estimation criterion obtains pilot frequency locations place; Utilize wavelet transformation to carry out filtering, aliasing the increase of signal along with wavelet decomposition scales of white Gaussian noise, the amplitude of wavelet transformation can reduce thereupon, follow the tracks of the maximum of the wavelet transformation under each yardstick, find out signal section, filtering noise, thus improve the precision of channel estimating.Computation complexity of the present invention is low, and evaluated error is functional; The interpolation algorithm based on transform domain zero padding is adopted to obtain the channel frequency domain response of full frequency band.Specific implementation step is:
(1) in the actual conditions of transmitting terminal according to HF wideband channel, the Comb Pilot designed is inserted relevant position accurately;
(2) pilot data is extracted from each reception antenna end, all pilot datas are delivered to successively in the channel estimator designed, by the bank of filters designed, filtering is carried out to signal, export pilot signal data, then utilize least square method to calculate pilot frequency locations virgin carrier channel and estimate frequency domain data sample value;
(3) by each transmitting-accept antenna between the domain samples value that obtains carry out DFT and transform in " transform domain " of this algorithm definition, by wavelet transformation thought designing filter, in the transform domain as illustrated filtering is carried out to signal, and then carry out zero padding in transform domain, and then the time domain sequences after zero padding is carried out IDFT conversion, obtain the channel response at all sub-carrier positions places.
(4) finally will estimate channel response gives signal processing unit after each reception antenna, complete the equilibrium of whole MIMO-OFDM system, empty time decoding or closed loop transmission function.In above-mentioned steps (1), broadband shortwave Watterson simplified model is as follows:
Wherein, a kfor the relative amplitude of path k; L is number of path; f dkfor Doppler frequency shift; for initial phase; τ kfor the relative path time delay on the k of path; δ is impulse function; T is the time.
In above-mentioned steps (1), pilots insertion frequency interval meets:
D f ≤ T s τ max
τ maxfor the maximum delay of channel response is expanded, T sit is a MIMO-OFDM symbol period not comprising Cyclic Prefix.
The signal received is carried out common filtering, deliver to DFT unit and deliver to DFT unit, counting of DFT is equal with the number of MIMO-OFDM subcarrier, then the data after DFT are carried out least-squares estimation respectively, obtained estimated value is carried out interpolation processing, interpolation of the present invention is transform domain zero padding interpolation algorithm, wherein, in transform domain first to data by carrying out wavelet filtering, again zero padding is carried out to data after elimination HFS, length after zero padding should equal the number of whole subcarrier, then IDFT conversion is carried out, obtain all subcarrier responses.
The design of the wavelet transform filter designed in the present invention can adopt the thought of repeatedly decomposing.The process of Wavelet Denoising Method is as follows:
Wherein c k, nthe coefficient of low frequency part after decomposing, d k, nit is the coefficient of HFS after decomposing.L span is the element number of sequence, and n is the n-th element in sequence. be scaling function.The HFS decomposed out is noise section, and low frequency part is signal section, so, by HFS filtering after above formula decomposes.
After entering wavelet filtering, carry out transform domain zero padding, if N is whole number of sub carrier wave, N pfor number of sub carrier wave, LS channel estimating frequency domain response carry out DFT conversion, obtain right in transform domain carry out zero padding, again do the IDFT conversion of N point, transform domain formula is as follows:
G ^ P ( p ) = Σ k = 0 N P - 1 H ^ P ( k ) exp ( - j 2 π N P kp ) , 0 ≤ p ≤ N P - 1
G ^ N ( q ) = G ^ P ( q ) 0 ≤ q ≤ N P - 1 0 N P - 1 ≤ q ≤ N - 1
H ^ N ( k ) = Σ q = 0 N - 1 G ^ N ( q ) exp ( - j 2 π N qk ) , 0 ≤ k ≤ N - 1
Wherein k represents frequency domain label, and p, q represent transform domain symbol. namely all subcarrier responses are represented.
As shown in Figure 1, Bit data pending is flowed through constellation point and becomes modulated signal, then carry out MIMO and be encoded into multiple signals, each road signal carries out OFDM modulation again, and modulation signal is launched after digital-to-analogue conversion and intermediate frequency Modulation, through short wave channel, receiver Received signal strength, acknowledge(ment) signal is carried out OFDM demodulation, and then every road signal carries out MIMO decoding and constellation point, obtains transmitted signal.
As shown in Figure 2, N is made in pilot subchannel response p(pilot sub-carrier number) puts DFT conversion, carries out filtering, filtering noise, then zero padding in transform domain, is then N (whole sub-carrier number) and puts IDFT conversion, obtain all subcarrier responses.
As shown in Figure 3, be flow chart of the present invention;
These embodiments are interpreted as only being not used in for illustration of the present invention limiting the scope of the invention above.After the content of reading record of the present invention, technical staff can make various changes or modifications the present invention, and these equivalence changes and modification fall into the inventive method claim limited range equally.

Claims (5)

1., based on a HF wideband channel method of estimation for multi-I/O OFDM, it is characterized in that: comprise the following steps:
101, at transmitting terminal, according to the parameter index of HF wideband channel channel, design one and adapt to the Comb Pilot of fast channel and determine the insertion position of Comb Pilot, the Comb Pilot designed is inserted the position determined, sent by antenna;
102, design in advance, pilot data is extracted from each antenna receiving terminal, the pilot data extracted is delivered to successively the channel estimator designed and produce pilot signal, and by described bank of filters, filtering is carried out to pilot signal, pilot signal data after output filtering, then utilize least square method to calculate sampling of data value when pilot frequency locations virgin carrier channel estimates frequency domain, obtain transmitting accept antenna between domain samples value;
103, each transmitting is accepted antenna between the domain samples value that obtains adopt discrete fourier DFT converter technique to transform in transform domain, by wavelet transformation designing filter, in the transform domain as illustrated low-pass filtering is carried out to signal, and then carry out zero padding in transform domain, again the time domain sequences after zero padding is carried out inverse discrete Fourier transform IDFT conversion, obtain the channel response at all sub-carrier positions places;
104, finally will estimate channel response gives signal processing unit after each reception antenna in step 103, the short wave channel completing whole multi-input multi-output orthogonal frequency division multiplexing system be estimated.
2. a kind of HF wideband channel method of estimation based on multi-I/O OFDM according to claim 1, it is characterized in that: in step 101, HF wideband channel model adopts Watterson channel model, and simplified model h (t) of broadband shortwave Watterson model can be expressed as follows:
Wherein, a kfor the relative amplitude of path k; L is number of path; f dkfor Doppler frequency shift; for just
Beginning phase place; τ kfor the relative path time delay on the k of path; δ is impulse function; T is the time.
3. the HF wideband channel method of estimation based on multi-I/O OFDM according to claim 1, is characterized in that: the frequency interval D of pilots insertion f:
τ in formula maxfor the maximum delay of channel response is expanded, T sbe one and do not comprise circulation
The multi-I/O OFDM symbol period of prefix.
4. the HF wideband channel method of estimation based on multi-I/O OFDM according to claim 1, it is characterized in that: channel estimator designs according to LS least square method, suppose that sending signal is X, channel response is H, the signal received is Y, noise jamming is σ, then channel model is:
Y=XH+σ
Then obtain LS channel estimating frequency domain response for:
H ^ LS = X - 1 Y = X - 1 ( XH + σ ) = H + X - 1 σ
Wherein for the estimated value of Comb Pilot after the channel response estimated, for estimating the domain channel response obtained.
5. the HF wideband channel method of estimation based on multi-I/O OFDM according to claim 1, is characterized in that: in step 103, receiving terminal time domain channel estimated value is:
h ^ ls , k = h k + n k x k
Wherein, for the channel estimation value on a kth carrier frequency, h kfor the true response of channel, for the interference that noise is introduced, Wavelet Denoising Method process is as follows:
Wherein c k, nthe coefficient of low frequency part after decomposing, d k, nbe the coefficient of HFS after decomposing, l span is the element number of sequence, and n is the n-th element in sequence, be scaling function, the HFS decomposed out is noise section, and low frequency part is signal section.
CN201410605918.9A 2014-10-30 2014-10-30 MIMO-OFDM wideband HF channel estimation method Pending CN104539562A (en)

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CN109041214A (en) * 2018-08-20 2018-12-18 深圳大学 A kind of mobile location method and system

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