CN101577692A - Channel estimating method of orthogonal frequency division multiplexing system and device thereof - Google Patents

Abstract

The invention discloses a channel estimation method and device for an orthogonal frequency division multiplexing system. The method includes: obtaining an initial channel time-domain impulse response; obtaining a channel time-domain impulse response corresponding to an effective multipath delay position in the initial channel time-domain impulse response, and generating a channel according to the effective multipath delay position An interference matrix; multiplying the inverse of the interference matrix by the channel time-domain impulse response corresponding to the multipath delay position to obtain a corrected channel time-domain impulse response; for the corrected channel time-domain impulse The response is Fourier transformed to obtain the channel frequency domain response estimate. The method and device of the present invention construct multipath interference, multiply the inverse of the interference matrix and the time-domain impulse response of the effective channel to suppress energy leakage, can effectively eliminate the energy leakage problem introduced by the virtual subcarrier, eliminate the floor effect, and improve Channel estimation accuracy, and the system complexity can be controlled by fast matrix algorithm.

Description

A Channel Estimation Method and Device for an Orthogonal Frequency Division Multiplexing System

technical field

The invention relates to the technical field of wireless mobile communication, in particular to a channel estimation method and device for an orthogonal frequency division multiplexing system.

Background technique

Orthogonal Frequency Division Multiplexing (OFDM) technology multiplexes high-speed data streams on different orthogonal sub-carriers after serial-to-parallel conversion, which improves spectral efficiency while reducing interference between data. Moreover, the subchannel corresponding to each subcarrier is a frequency flat fading channel, which effectively reduces intersymbol interference caused by multipath fading. At present, OFDM technology has been widely used in wireless local area networks, enhanced third-generation mobile communication systems, and so on.

In order to ensure the good performance of the OFDM system in the wireless mobile communication environment, the receiver needs to provide an estimate of the wireless fading channel as accurately as possible. Therefore, channel estimation is an indispensable and important link in OFDM system tether signal processing.

Fig. 1 shows a system schematic diagram of data transmission and reception in an OFDM system. As shown in Figure 1, at the sending end, the data undergoes channel coding, modulation, and space-time coding, and the generated signal and frequency-domain pilot signal are resource-mapped together, and then transmitted after IFFT transformation and framing processing. At the receiving end, after FFT transformation and pilot data separation, the separated pilot signal is used for channel estimation, and the separated data signal is subjected to space-time decoding according to the result of channel estimation, and then demodulated, channel decoded, etc. The operation restores the data sent.

In an actual OFDM system, in order to prevent the transmitted signal from being affected by the low-pass filter, some subcarriers at the edge of the bandwidth allocated by the system are usually reserved as virtual subcarriers. Since the pilot sequence falling within the range of the virtual carrier cannot provide channel information in the frequency domain, if the inverse Fourier transform is performed on the estimated value of the channel frequency domain response that loses part of the frequency domain information, the obtained time domain impulse response will be affected by Due to the impact of energy leakage, they interfere with each other, resulting in a decrease in channel estimation accuracy. Most of the existing channel estimation techniques do not consider the impact of energy leakage, and intercept a limited number of sampling points in the time domain, thus losing the effective time domain impulse response and causing the floor effect. Therefore, there is an urgent need for a method to effectively eliminate the influence of energy leakage to improve the channel estimation accuracy in practical systems.

Contents of the invention

A technical problem to be solved by the present invention is to provide a channel estimation method for an OFDM system, which can improve the channel estimation accuracy in the system.

The present invention provides a channel estimation method for an OFDM system, comprising: performing channel frequency domain response estimation on available pilots within the effective subcarrier range, performing Fourier inverse transform, and obtaining the initial channel time domain response obtain the channel time domain impulse response corresponding to the effective multipath delay position in the initial channel time domain impulse response, and generate an interference matrix according to the effective multipath delay position; combine the inverse sum of the interference matrix with the effective multipath time delay Multiply the channel time-domain impulse response corresponding to the delay position to obtain the corrected channel time-domain impulse response; perform Fourier transform on the corrected channel time-domain impulse response to obtain the channel frequency-domain response estimate.

According to an embodiment of the channel estimation method of the present invention, the method further determines the effective multipath delay position according to a preset effective path decision threshold. Wherein, the preset effective path judgment threshold Thr is:

$\mathrm{<span\; class="notranslate">\; Thr</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&rho;P</span>}\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; av</span>}}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; \&xi;</span>}$

Among them, ρ=J ₀ (2πf _D ΔmT _s ), T _s is the OFDM symbol period, f _D is the maximum Doppler frequency shift, ξ is the estimated signal-to-noise ratio, P is the pilot symbol power, and N _av is used to The number of OFDM symbols that need to be counted to calculate the decision threshold Thr.

According to an embodiment of the channel estimation method of the present invention, the interference matrix is generated according to the effective multipath delay position by the following formula:

in ${\mathrm{\&delta;}}_{i,j}(l_p,l_q)=W_N^{{\mathrm{\&beta;}}_{l_q,l_p}}\frac{\sin (\mathrm{\&pi;}(l_q-l_p+{\mathrm{\&alpha;}}_i)N_e/N)}{\sin (\mathrm{\&pi;}(l_q-l_p+{\mathrm{\&alpha;}}_i){\mathrm{D.}}_f/N)},$ $W_N^{{\mathrm{\&beta;}}_{l_q,l_p}}=\exp (-j2\mathrm{\&pi;}{\mathrm{\&beta;}}_{l_q,l_p}/N),$ l ₀ , l ₁ ,..., l _L'-1 is the effective multipath delay position, is the phase rotation factor of the time-domain impulse response of different transmitting antennas, α _i is the displacement factor of the time-domain impulse response of different transmitting antennas, N is the length of IFFT, N _e is the number of effective subcarriers, D _f is the frequency domain of the pilot symbol interval.

Further, for the OFDM system with frequency division multi-antenna pilot, ${\mathrm{\&beta;}}_{l_p,l_q}=l_{q}i-(l_q-l_p){\mathrm{D.}}_f/2,$ α _i =0; or, for an OFDM system with code division multi-antenna pilot, ${\mathrm{\&beta;}}_{l_p,l_q}=(l_q-l_p+{\mathrm{\&alpha;}}_i)/2,$ α _i =(i-1)K ₀ , D _f =1, where K ₀ is the distance on the time axis of the time-domain impulse responses of each transmitting antenna.

According to an embodiment of the channel estimation method of the present invention, the step of performing Fourier transform on the corrected channel time-domain impulse response to obtain the channel frequency-domain response estimation includes: adding 0 to the corrected channel time-domain impulse response so that The number of samples is extended to the system FFT/IFFT length N; the FFT transformation is performed on the extended channel time domain impulse response sequence to obtain the channel frequency domain response on each subcarrier.

Another technical problem to be solved by the present invention is to provide a channel estimation device for an OFDM system, which can improve the channel estimation accuracy in the system.

The present invention provides a channel estimation device for an OFDM system, including: an initial time-domain impulse response acquisition module, which is used to perform channel frequency-domain response estimation on available pilots located within the effective sub-carrier range, and for all The channel frequency domain response is estimated to perform Fourier inverse transform to obtain the initial channel time domain impulse response, and the initial channel time domain impulse response is sent; the effective time domain impulse response acquisition module is used to receive the initial channel time domain impulse response from the initial time domain The initial channel time domain impulse response of the impulse response acquisition module obtains the channel time domain impulse response corresponding to the effective multipath time delay position in the initial channel time domain impulse response, and sends the The time-domain impulse response of the channel corresponding to the position; the interference matrix acquisition module is used to generate an interference matrix according to the effective multipath delay position, and send the interference matrix; the time-domain impulse response correction module is used to receive information from the The channel time domain impulse response corresponding to the effective multipath delay position of the effective time domain impulse response acquisition module receives the interference matrix from the interference matrix acquisition module, and combines the inverse sum of the interference matrix with The channel time domain impulse response corresponding to the multipath time delay position is multiplied to obtain the corrected channel time domain impulse response, and the corrected channel time domain impulse response is sent; the frequency domain response estimation acquisition module uses After receiving the corrected channel time domain impulse response from the time domain impulse response correction module, performing Fourier transform on the corrected channel time domain impulse response to obtain the corrected channel frequency domain Response estimates.

Further, the channel estimation device further includes: an effective multipath delay location acquisition module, configured to determine the effective multipath delay location according to a preset effective path decision threshold, and send the effective multipath delay location; The effective time domain impulse response acquisition module is also used to receive the effective multipath time delay position from the effective multipath time delay position acquisition module; the interference matrix acquisition module is also used to receive the time delay from the effective multipath time The delay position acquires the effective multipath delay position of the module.

Further, the frequency domain response estimation acquisition module adds 0 to the corrected channel time domain impulse response to expand the number of samples to the system FFT/IFFT length N; performs FFT on the extended channel time domain impulse response sequence transform to obtain the corrected channel frequency domain response on each subcarrier.

The channel estimation method and device provided by the present invention, by constructing multipath interference, multiply the inverse of the interference matrix and the effective channel time-domain impulse response to suppress energy leakage, eliminate the floor effect, and improve the accuracy of channel estimation.

Description of drawings

Fig. 1 shows a schematic diagram of a system for data transmission and reception in an OFDM system;

Fig. 2 shows the flowchart of an embodiment of the channel estimation method of the OFDM system of the present invention;

Fig. 3 shows the flowchart of another embodiment of the channel estimation method of the OFDM system of the present invention;

Fig. 4 shows the block diagram of an embodiment of the channel estimation device of the OFDM system of the present invention;

Fig. 5 shows a block diagram of another embodiment of the channel estimation device of the OFDM system of the present invention.

Detailed ways

The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are illustrated. In the drawings, the same reference numerals denote the same or similar components or elements.

Fig. 2 shows a flowchart of an embodiment of the channel estimation method of the OFDM system of the present invention.

As shown in FIG. 2 , in step 202 , channel frequency domain response estimation is performed on the available pilots within the effective subcarrier range, and then inverse Fourier transform is performed to obtain an initial channel time domain impulse response. For example, channel frequency domain estimation can be performed on each pilot subcarrier based on the least squares or minimum mean square error criterion.

In step 204, the channel time domain impulse response corresponding to the effective multipath delay position in the initial channel time domain impulse response is obtained, and an interference matrix is generated according to the effective multipath delay position. The effective multipath position can be determined according to the preset effective path decision threshold; for a system with known channel multipath time delay, the effective multipath time delay position can be directly determined according to the known multipath time delay information. For a system with unknown channel multipath time delay, the method of retaining multipath also includes retaining the previous Lmax points, where Lmax is the maximum multipath time delay; or, according to the amplitude from large to small, retain L' points, L ' is an empirical value, which is different in different channel environments.

In step 206, the inverse of the interference matrix is multiplied by the channel time-domain impulse response corresponding to the position of the effective multipath time delay to obtain the corrected channel time-domain impulse response;

In step 208, Fourier transform is performed on the corrected channel time-domain impulse response to obtain a corrected channel frequency-domain response estimate.

Fig. 3 shows a flow chart of another embodiment of the channel estimation method of the OFDM system of the present invention.

As shown in FIG. 3 , in step 302, a signal is received, an FFT transform is performed on the received signal, and pilot symbols are separated from the received signal subjected to the FFT transform.

i，j分别表示第i根发送天线和第j根接收天线。In step 304, the channel frequency domain response estimate is obtained according to the least square or minimum mean square error criterion, and the initial time domain impulse response estimate is obtained after IFFT

i and j represent the i-th transmitting antenna and the j-th receiving antenna, respectively.

In step 306, according to the preset effective path decision threshold, search for effective multipath delay positions l ₀ , l ₁ , ..., l _L'-1 , and reserve the effective channel time corresponding to the effective multipath delay positions domain impulse response ${\tilde{h}}_{i,j}={[{\hat{h}}_{i,j}\left(l_0\right),{\hat{h}}_{i,j}\left(l_1\right),...{\hat{h}}_{i,j}\left(l_{L^{\&prime;}-1}\right)]}^T.$

In step 308, reconstruct the interference δ _i,j corresponding to each multipath delay according to the determined effective multipath delay position, and construct the interference matrix A _i,j :

为不同发送天线时域冲激响应的相位旋转因子，α_i为不同发送天线时域冲激响应的位移因子。根据不同的导频方式(例如，频分多天线导频、码分多天线导频)，这两个参数有所不同。in ${\mathrm{\&delta;}}_{i,j}(l_p,l_q)=W_N^{{\mathrm{\&beta;}}_{l_q,l_p}}\frac{\sin (\mathrm{\&pi;}(l_q-l_p+{\mathrm{\&alpha;}}_i)N_e/N)}{\sin (\mathrm{\&pi;}(l_q-l_p+{\mathrm{\&alpha;}}_i){\mathrm{D.}}_f/N)},$ $W_N^{{\mathrm{\&beta;}}_{l_q,l_p}}=\exp (-j2\mathrm{\&pi;}{\mathrm{\&beta;}}_{l_q,l_p}/N),$

is the phase rotation factor of the time-domain impulse response of different transmitting antennas, and α _i is the displacement factor of the time-domain impulse response of different transmitting antennas. These two parameters are different according to different pilot schemes (for example, frequency division multi-antenna pilot, code division multi-antenna pilot).

Multiply the effective channel time-domain impulse response by the inverse of the interference matrix Ai _,j ${\tilde{h}}_{i,j}={[{\hat{h}}_{i,j}\left(l_0\right),{\hat{h}}_{i,j}\left(l_1\right),...{\hat{h}}_{i,j}\left(l_{L^{\&prime;}-1}\right)]}^T,$ Get the corrected time-domain impulse response h _i,j :

${\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In step 310, add 0 to the modified time-domain impulse response h _i,j to N points, and then perform FFT transformation to obtain a modified channel frequency-domain response estimate.

According to an embodiment of the present invention, for a system with unknown channel multipath delay, the preset effective decision threshold Thr can be obtained according to the following formula:

$\mathrm{<span\; class="notranslate">\; Thr</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&rho;P</span>}\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; av</span>}}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; \&xi;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Among them, ρ=J ₀ (2πf _D ΔmT _s ), T _s is the OFDM symbol period, f _D is the maximum Doppler frequency shift, ξ is the estimated signal-to-noise ratio, P is the pilot symbol power, and N _av is used to The number of OFDM symbols that need to be counted to calculate the decision threshold Thr. According to the formula (3), the effective path is preserved for the initial channel time-domain impulse response:

${\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\left\{\begin{array}{cc}{\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>& {<span\; class="notranslate">\; |</span>{\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Greater\; Equal;</span>\mathrm{<span\; class="notranslate">\; Thr</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; else</span>}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

According to an embodiment of the present invention, for a system with unknown channel multipath time delay, an effective multipath time delay position is searched according to a preset decision threshold. In addition, multiple transmitting and receiving antenna pairs and multiple pilot symbols can be jointly counted to determine effective multipath delay positions l ₀ , l ₁ , . . . , l _L'-1 .

According to an embodiment of the present invention, for a system with channel multipath delay, the effective multipath delay positions l ₀ , l ₁ , ..., l _L' can be determined directly according to the known multipath delay information _-1 , and retain the time-domain impulse response corresponding to the effective multipath delay position:

${\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; [</span>{\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>{\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span>{\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; l</span>}}_{{\mathrm{<span\; class="notranslate">\; L</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; .</span>$

According to an embodiment of the present invention, the interference matrix A _i,j can be transformed into a complex conjugate symmetric matrix, and a more accurate time-domain impulse response of the channel can be solved by the Cholesky decomposition method, thereby reducing the computational complexity Effect.

It should be pointed out that the method of the present invention is applicable to OFDM communication systems of single transmission and single reception, single transmission and multiple reception, or multiple transmission and multiple reception.

The method of the present invention will be further described below through a specific application example.

In this application example, it is assumed that the length of the FFT/IFFT of the OFDM system is N, the number of effective subcarriers is N _e , and the number of virtual subcarriers is NN _e . The frequency domain signal Y _j [k] received on the jth antenna of the receiver is:

Y _j [k] = H _{j, i} [k] P _i [k] + V _j [k], k∈Ω _uc (5)

Among them, H _{j, i} [k] represents the channel frequency domain response from the i-th transmitting antenna to the j-th receiving antenna, P _i [k] is the pilot symbol of the i-th transmitting antenna, and Ω _uc is the effective subcarrier set .

Step 1: Perform channel frequency domain estimation based on the least squares or least mean square error criterion on each pilot subcarrier, and perform IFFT transformation to obtain the initial channel time domain impulse response

For the OFDM system with the frequency division multi-antenna pilot method, the subcarriers corresponding to each transmit antenna are divided by their respective pilot sequences to obtain the estimated value of the noisy channel frequency domain response of each transmit antenna:

${\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; \&Element;</span>{\mathrm{<span\; class="notranslate">\; \&Omega;</span>}}_{\mathrm{<span\; class="notranslate">\; uc</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

其中N为IFFT长度，D_f为导频符号频域间隔。for each transmit antenna Perform N/D _f -point IFFT transformation respectively to obtain the initial channel time-domain impulse response of each transmitting antenna

Among them, N is the length of IFFT, and D _f is the frequency domain interval of pilot symbols.

For the OFDM system of the code division multi-antenna pilot method, taking the exponential pilot as an example, the conjugate of the pilot symbol of the first transmit antenna is multiplied by the frequency domain signal Y _j [k] to obtain the noisy Accumulation of channel frequency domain response estimates:

$\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; ]</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; /</span>{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; ]</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;k</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; \&Element;</span>{\mathrm{<span\; class="notranslate">\; \&Omega;</span>}}_{\mathrm{<span\; class="notranslate">\; uc</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

进行N点IFFT变换，得到所有发送天线初始的信道时域冲激响应

各个发送天线的时域冲激响应在时间轴上互不重叠，其间距为K₀。For frequency domain signals

Perform N-point IFFT transformation to obtain the initial channel time-domain impulse response of all transmit antennas

The time-domain impulse responses of the transmitting antennas do not overlap each other on the time axis, and the distance between them is K ₀ .

The second step: set the effective path judgment threshold Thr according to the above formula (3), according to the above formula (4) from the initial channel time domain impulse response obtained in the first step Find effective multipath delay positions l ₀ , l ₁ , ..., l _L'-1 in , and reserve the time-domain impulse response corresponding to the effective multipath delay positions: ${\tilde{h}}_{i,j}={[{\hat{h}}_{i,j}\left(l_0\right),{\hat{h}}_{i,j}\left(l_1\right),...{\hat{h}}_{i,j}\left(l_{L^{\&prime;}-1}\right)]}^T.$ In order to improve the accuracy of multipath detection, the effective multipath time delay position can be determined through the joint statistics of multiple transmit antennas and multiple pilot symbols.

Step 3: Reconstruct the interference corresponding to each multipath delay according to the effective multipath delay position determined in the above steps ${\mathrm{\&delta;}}_{i,j}(l_p,l_q)=W_N^{{\mathrm{\&beta;}}_{l_q,l_p}}\sin (\mathrm{\&pi;}(l_q-l_p+{\mathrm{\&alpha;}}_i)N_e/N)/\sin (\mathrm{\&pi;}(l_q-l_p+{\mathrm{\&alpha;}}_i){\mathrm{D.}}_f/N).$

For different pilot modes, the interference δ _{i, j} is different. For example, for an OFDM system with frequency division multi-antenna pilot method, ${\mathrm{\&beta;}}_{l_p,l_q}=l_{q}i-(l_q-l_p){\mathrm{D.}}_f/2,$ α _i =0. For the OFDM system with code division multi-antenna pilot method, ${\mathrm{\&beta;}}_{l_p,l_q}=(l_q-l_p+{\mathrm{\&alpha;}}_i)/2,$ α _i =(i-1)K ₀ , D _f =1.

Then the interference matrix A _{i,j is constructed according to δ i, j} through the previous formula (1).

与干扰矩阵A_i，j的逆相乘(参见上面的公式(2))，以消除虚拟子载波引入的能量泄漏对信道估计造成的影响，得到更加准确的信道时域冲激响应h_i，j。The time-domain impulse response retained in the second step

Multiply with the inverse of the interference matrix A _{i, j} (see the above formula (2)), to eliminate the impact of the energy leakage introduced by the virtual subcarrier on the channel estimation, and obtain a more accurate channel time-domain impulse response h _{i, j} .

与

合并，新干扰矩阵

第(p，q)个元素为 ${\widetilde{\mathrm{\&delta;}}}_i(l_p,l_q)=W_N^{((l_q-l_p)D_f/2)}\sin (\mathrm{\&pi;}(l_q-l_p)N_e/N)/\sin (\mathrm{\&pi;}(l_q-l_p)D_f/N),$ 该干扰矩阵

为复共轭对称矩阵。可利用Cholesky分解求解方程组代替矩阵求逆，从而达到降低计算复杂度的效果。Preferably, A _{i, j} is transformed into a complex conjugate symmetric matrix. Taking the frequency division multi-antenna pilot method as an example, the

and

merged, new interference matrix

The (p,q)th element is ${\widetilde{\mathrm{\&delta;}}}_i(l_p,l_q)=W_N^{((l_q-l_p){\mathrm{D.}}_f/2)}\sin (\mathrm{\&pi;}(l_q-l_p)N_e/N)/\sin (\mathrm{\&pi;}(l_q-l_p){\mathrm{D.}}_f/N),$ The interference matrix

is a complex conjugate symmetric matrix. Cholesky decomposition can be used to solve equations instead of matrix inversion, so as to achieve the effect of reducing computational complexity.

Step 4: Estimating the channel time-domain impulse response obtained in the third step ${\stackrel{\&OverBar;}{h}}_{i,j}={[{\stackrel{\&OverBar;}{h}}_{i,j}\left(l_0\right),{\hat{h}}_{i,j}\left(l_1\right),...,{\hat{h}}_{i,j}\left(l_{L^{\&prime;}-1}\right)]}^T$ After adding 0 to N points, perform Fourier transform to obtain the corrected channel frequency domain response estimate.

Fig. 4 shows a block diagram of an embodiment of the channel estimation device of the OFDM system of the present invention. As shown in Figure 4, the channel estimation device includes an initial time domain impulse response acquisition module 41, an effective time domain impulse response acquisition module 42, an interference matrix acquisition module 43, a time domain impulse response correction module 44 and a frequency domain response estimation Get module 45. Among them, the initial time-domain impulse response acquisition module 41 is used to perform channel frequency-domain response estimation on the available pilots located in the effective subcarrier range, perform Fourier inverse transform on the channel frequency-domain response estimation, and obtain the initial channel time-domain impulse response send the obtained initial channel time-domain impulse response to the effective time-domain impulse response acquisition module 42. The effective time domain impulse response acquisition module 42 is used to receive the initial channel time domain impulse response from the initial time domain impulse response acquisition module 41, and obtain the initial channel time domain impulse response corresponding to the effective multipath delay position Channel time-domain impulse response, sending the channel time-domain impulse response corresponding to the position of effective multipath delay. The interference matrix acquisition module 43 is configured to generate an interference matrix according to the position of the effective multipath time delay, and send the interference matrix. The time domain impulse response correction module 44 is used to receive the channel time domain impulse response corresponding to the effective multipath delay position from the effective time domain impulse response acquisition module 42, and receive the interference matrix from the interference matrix acquisition module 43, Multiply the inverse of the interference matrix with the channel time domain impulse response corresponding to the effective multipath delay position to obtain the corrected channel time domain impulse response, and send the corrected channel time domain impulse response to the frequency domain response estimation Get module 45. The frequency domain response estimation acquisition module 45 is used to receive the corrected channel time domain impulse response from the time domain impulse response correction module 44, perform Fourier transform on the corrected channel time domain impulse response, and obtain the corrected The frequency domain response estimation of the channel.

Fig. 5 shows a block diagram of another embodiment of the channel estimation device of the OFDM system of the present invention. Compared with the channel estimation device in Fig. 4, the channel estimation device in Fig. 5 adds an effective multipath time delay position acquisition module 56, which is used to determine the effective multipath time delay position according to the preset effective path decision threshold, and sends the effective multipath time delay position to An effective time-domain impulse response acquisition module 42 and an interference matrix acquisition module 43 . The effective time domain impulse response obtaining module 43 receives the effective multipath time delay position from the effective multipath time delay position obtaining module 56 . The interference matrix acquiring module 43 acquires the effective multipath delay position of the module 56 from the effective multipath delay position. For other module descriptions, please refer to the descriptions of the corresponding modules in Fig. 4, and for the sake of brevity, no further description is given here.

Wherein, the preset effective path judgment threshold Thr adopted by the effective multipath time delay position acquisition module 56 in FIG. 5 is $\mathrm{Thr}=\mathrm{\&rho;P}\sqrt{2N_{\mathrm{av}}}/\mathrm{\&xi;}.$ Among them, ρ=J ₀ (2πf _D ΔmT _s ), T _s is the OFDM symbol period, f _D is the maximum Doppler frequency shift, ξ is the estimated signal-to-noise ratio, P is the pilot symbol power, and N _av is used to The number of OFDM symbols that need to be counted to calculate the decision threshold Thr.

According to an embodiment of the channel estimation device of the present invention, the effective multipath delay position acquisition module determines the effective multipath through joint statistics of multiple transceiver antenna pairs and multiple pilot symbols according to the preset effective path decision threshold Latency location. In addition, the interference matrix acquisition module generates the interference matrix A _i,j according to the effective multipath delay position through the above formula (1).

According to an embodiment of the channel estimation device of the present invention, the time-domain impulse response modification module transforms the interference matrix into a complex conjugate symmetric matrix, and calculates the inverse of the interference matrix by using a fast matrix inversion algorithm to reduce computational complexity.

According to an embodiment of the channel estimation device of the present invention, the frequency domain response estimation acquisition module adds 0 to the corrected channel time domain impulse response to expand the number of samples to the system FFT/IFFT length N; for the extended channel time domain impulse response The stimulus response sequence is subjected to FFT transformation to obtain the corrected channel frequency domain response on each subcarrier.

The method and device of the present invention construct multipath interference, multiply the inverse of the interference matrix and the time-domain impulse response of the effective channel to suppress energy leakage, are suitable for single-antenna and multi-antenna OFDM systems, and can be flexibly applied to existing or A system with unknown channel multipath delay information. This method can effectively eliminate the energy leakage problem introduced by the virtual subcarrier, eliminate the floor effect, improve the channel estimation accuracy, and control the system complexity through the fast matrix algorithm.

The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and changes will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to better explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention and design various embodiments with various modifications as are suited to the particular use.

Claims (11)

1. A channel estimation method for an orthogonal frequency division multiplexing system, comprising:

performing channel frequency domain response estimation on available pilot frequency in the effective subcarrier range, and performing inverse Fourier transform to obtain initial channel time domain impulse response;

obtaining channel time domain impulse response corresponding to effective multipath time delay position in the initial channel time domain impulse response, and generating an interference matrix according to the effective multipath time delay position;

multiplying the inverse of the interference matrix with the channel time domain impulse response corresponding to the effective multipath time delay position to obtain the corrected channel time domain impulse response;

and carrying out Fourier transform on the corrected channel time domain impulse response to obtain channel frequency domain response estimation.

2. The channel estimation method of the orthogonal frequency division multiplexing system as claimed in claim 1, further comprising the steps of:

and determining the effective multipath time delay position according to a preset effective path judgment threshold.

3. The channel estimation method of the ofdm system according to claim 2, wherein the preset effective path decision threshold Thr is:

<math> <mrow> <mi>Thr</mi> <mo>=</mo> <mi>&rho;P</mi> <msqrt> <msub> <mrow> <mn>2</mn> <mi>N</mi> </mrow> <mi>av</mi> </msub> </msqrt> <mo>/</mo> <mi>&xi;</mi> </mrow> </math>

where ρ ═ J₀(2πf_DΔmT_s) Ts is the OFDM symbol period, fD is the maximum doppler shift, ξ is the signal-to-noise ratio estimate, P is the pilot symbol power, and Nav is the number of OFDM symbols to be counted for calculating the decision threshold Thr.

4. The channel estimation method of orthogonal frequency division multiplexing system according to claim 2 or 3, wherein the step of determining the effective multipath delay position according to a preset effective path decision threshold comprises:

and determining the effective multipath time delay position through the joint statistics of a plurality of receiving and transmitting antenna pairs and a plurality of pilot symbols according to a preset effective path judgment threshold.

5. The channel estimation method of the ofdm system according to claim 1, wherein the interference matrix is generated according to the effective multipath delay position by the following formula:

wherein <math> <mrow> <msub> <mi>&delta;</mi> <mrow> <mi>i</mi> <mo>,</mo> <mi>j</mi> </mrow> </msub> <mrow> <mo>(</mo> <msub> <mi>l</mi> <mi>p</mi> </msub> <mo>,</mo> <msub> <mi>l</mi> <mi>q</mi> </msub> <mo>)</mo> </mrow> <mo>=</mo> <msubsup> <mi>W</mi> <mi>N</mi> <msub> <mi>&beta;</mi> <mrow> <msub> <mi>l</mi> <mi>q</mi> </msub> <mo>,</mo> <msub> <mi>l</mi> <mi>p</mi> </msub> </mrow> </msub> </msubsup> <mfrac> <mrow> <mi>sin</mi> <mrow> <mo>(</mo> <mi>&pi;</mi> <mrow> <mo>(</mo> <msub> <mi>l</mi> <mi>q</mi> </msub> <mo>-</mo> <msub> <mi>l</mi> <mi>p</mi> </msub> <mo>+</mo> <msub> <mi>&alpha;</mi> <mi>i</mi> </msub> <mo>)</mo> </mrow> <msub> <mi>N</mi> <mi>e</mi> </msub> <mo>/</mo> <mi>N</mi> <mo>)</mo> </mrow> </mrow> <mrow> <mi>sin</mi> <mrow> <mo>(</mo> <mi>&pi;</mi> <mrow> <mo>(</mo> <msub> <mi>l</mi> <mi>q</mi> </msub> <mo>-</mo> <msub> <mi>l</mi> <mi>p</mi> </msub> <mo>+</mo> <msub> <mi>&alpha;</mi> <mi>i</mi> </msub> <mo>)</mo> </mrow> <msub> <mi>D</mi> <mi>f</mi> </msub> <mo>/</mo> <mi>N</mi> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>,</mo> </mrow> </math> <math> <mrow> <msubsup> <mi>W</mi> <mi>N</mi> <msub> <mi>&beta;</mi> <mrow> <msub> <mi>l</mi> <mi>q</mi> </msub> <mo>,</mo> <msub> <mi>l</mi> <mi>p</mi> </msub> </mrow> </msub> </msubsup> <mo>=</mo> <mi>exp</mi> <mrow> <mo>(</mo> <mo>-</mo> <mi>j</mi> <mn>2</mn> <mi>&pi;</mi> <msub> <mi>&beta;</mi> <mrow> <msub> <mi>l</mi> <mi>q</mi> </msub> <mo>,</mo> <msub> <mi>l</mi> <mi>p</mi> </msub> </mrow> </msub> <mo>/</mo> <mi>N</mi> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </math> l₀，l₁，...，l_L’-1For the effective multi-path delay position in question,

phase rotation factor, alpha, for the time-domain impulse responses of different transmit antennas_iFor the displacement factors of the impulse response of different sending antennas time domain, N is the IFFT length, N_eIs the effective number of subcarriers, D_fIs a pilot symbol frequency domain interval.

6. The channel estimation method of the ofdm system according to claim 1, wherein the step of performing fourier transform on the modified channel time-domain impulse response to obtain the channel frequency-domain response estimate comprises:

compensating 0 for the corrected channel time domain impulse response to expand the number of sampling points to the system FFT/IFFT length N;

and performing FFT (fast Fourier transform) on the expanded channel time domain impulse response sequence to obtain channel frequency domain responses on each subcarrier.

7. A channel estimation apparatus for an orthogonal frequency division multiplexing system, comprising:

an initial time domain impulse response obtaining module, configured to perform channel frequency domain impulse response estimation on an available pilot frequency located in an effective subcarrier range, perform inverse fourier transform on the channel frequency domain impulse response estimation to obtain an initial channel time domain impulse response, and send the initial channel time domain impulse response;

an effective time domain impulse response obtaining module, configured to receive an initial channel time domain impulse response from the initial time domain impulse response obtaining module, obtain a channel time domain impulse response corresponding to an effective multipath time delay position in the initial channel time domain impulse response, and send a channel time domain impulse response corresponding to the effective multipath time delay position;

an interference matrix obtaining module, configured to generate an interference matrix according to the effective multipath delay position, and send the interference matrix;

a time domain impulse response modification module, configured to receive the channel time domain impulse response corresponding to the effective multipath time delay position from the effective time domain impulse response obtaining module, receive the interference matrix from the interference matrix obtaining module, multiply an inverse of the interference matrix with the channel time domain impulse response corresponding to the effective multipath time delay position to obtain a modified channel time domain impulse response, and send the modified channel time domain impulse response;

and the frequency domain response estimation obtaining module is used for receiving the corrected channel time domain impulse response from the time domain impulse response correcting module, and carrying out Fourier transform on the corrected channel time domain impulse response to obtain the corrected channel frequency domain response estimation.

8. The channel estimation device of the ofdm system according to claim 7, further comprising:

an effective multipath time delay position obtaining module, configured to determine the effective multipath time delay position according to a preset effective path decision threshold, and send the effective multipath time delay position;

the effective time domain impulse response obtaining module is further used for receiving the effective multipath time delay position from the effective multipath time delay position obtaining module; the interference matrix obtaining module is further configured to receive the effective multipath delay location from the effective multipath delay location obtaining module.

9. The channel estimation device of claim 8, wherein the effective multipath delay position obtaining module determines the effective multipath delay position according to a preset effective path decision threshold through joint statistics on a plurality of transceiving antenna pairs and a plurality of pilot symbols.

10. The apparatus of claim 7, wherein the interference matrix obtaining module generates the interference matrix according to the effective multipath delay position by the following formula:

wherein <math> <mrow> <msub> <mi>&delta;</mi> <mrow> <mi>i</mi> <mo>,</mo> <mi>j</mi> </mrow> </msub> <mrow> <mo>(</mo> <msub> <mi>l</mi> <mi>p</mi> </msub> <mo>,</mo> <msub> <mi>l</mi> <mi>q</mi> </msub> <mo>)</mo> </mrow> <mo>=</mo> <msubsup> <mi>W</mi> <mi>N</mi> <msub> <mi>&beta;</mi> <mrow> <msub> <mi>l</mi> <mi>q</mi> </msub> <mo>,</mo> <msub> <mi>l</mi> <mi>p</mi> </msub> </mrow> </msub> </msubsup> <mfrac> <mrow> <mi>sin</mi> <mrow> <mo>(</mo> <mi>&pi;</mi> <mrow> <mo>(</mo> <msub> <mi>l</mi> <mi>q</mi> </msub> <mo>-</mo> <msub> <mi>l</mi> <mi>p</mi> </msub> <mo>+</mo> <msub> <mi>&alpha;</mi> <mi>i</mi> </msub> <mo>)</mo> </mrow> <msub> <mi>N</mi> <mi>e</mi> </msub> <mo>/</mo> <mi>N</mi> <mo>)</mo> </mrow> </mrow> <mrow> <mi>sin</mi> <mrow> <mo>(</mo> <mi>&pi;</mi> <mrow> <mo>(</mo> <msub> <mi>l</mi> <mi>q</mi> </msub> <mo>-</mo> <msub> <mi>l</mi> <mi>p</mi> </msub> <mo>+</mo> <msub> <mi>&alpha;</mi> <mi>i</mi> </msub> <mo>)</mo> </mrow> <msub> <mi>D</mi> <mi>f</mi> </msub> <mo>/</mo> <mi>N</mi> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>,</mo> </mrow> </math> <math> <mrow> <msubsup> <mi>W</mi> <mi>N</mi> <msub> <mi>&beta;</mi> <mrow> <msub> <mi>l</mi> <mi>q</mi> </msub> <mo>,</mo> <msub> <mi>l</mi> <mi>p</mi> </msub> </mrow> </msub> </msubsup> <mo>=</mo> <mi>exp</mi> <mrow> <mo>(</mo> <mo>-</mo> <mi>j</mi> <mn>2</mn> <mi>&pi;</mi> <msub> <mi>&beta;</mi> <mrow> <msub> <mi>l</mi> <mi>q</mi> </msub> <mo>,</mo> <msub> <mi>l</mi> <mi>p</mi> </msub> </mrow> </msub> <mo>/</mo> <mi>N</mi> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </math> l₀，l₁，...，l_L’-1For the effective multi-path delay position in question,phase rotation factor, alpha, for the time-domain impulse responses of different transmit antennas_iFor the displacement factors of the impulse response of different sending antennas time domain, N is the IFFT length, N_eIs the effective number of subcarriers, D_fIs a pilot symbol frequency domain interval.

11. The channel estimation device of the ofdm system according to claim 7, wherein the frequency domain response estimation obtaining module complements 0 to the modified channel time domain impulse response to expand the number of sampling points to a system FFT/IFFT length N; and performing FFT (fast Fourier transform) on the expanded channel time domain impulse response sequence to obtain the corrected channel frequency domain response on each subcarrier.

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