109 results about "Ofdm channel estimation" patented technology

Multiple Transmit Multiple Receive Orthogonal Frequency Division Multiplexing (‘OFDM’) comprising generating bit streams and corresponding sets of N frequency domain carrier amplitudes ({tilde over (s)}(kN+j), 0≦j≦N−1) modulated as OFDM symbols subsequently to be transmitted from a transmitter, where k is the OFDM symbol number and j indicates the corresponding OFDM carrier number. Affix information is inserted at the transmitter into guard intervals between consecutive time domain OFDM symbols and are used at the receiver to estimate the Channel Impulse Response (H_lm) of the transmission channels, the estimated Channel Impulse Response (Ĥ_lm) being used to demodulate the bit streams in the signals received at the receiver. The affix information is known to the receiver, as well as to the transmitter, and is mathematically equivalent to a vector (c_D) that is common to the time domain OFDM symbols multiplied by at least first weighting factors (α_k) that are different for one time domain OFDM symbol (k) than for another and second weighting factors (w_i(k)) that enable one of the transmit antenna means (i) to be distinguished from another.

Systems and methods for estimating channel response in the presence of interference. Interference and/or noise present on received training symbols is estimated. Based on the measured noise and/or interference, a weighting among training symbols is developed. Channel response is then estimated based on a weighted least squares procedure.

The invention discloses a sparse OFDM channel estimation method based on a generalized orthogonal matching tracking algorithm. The method comprises the following steps: step one, translating a channelestimation problem into a problem for reconstructing original signal based on the compressed sensing theory; step two, designing a measurement matrix; and step three, reconstructing the original signal by using the generalized orthogonal matching tracking method so as to finish the channel estimation. The sparse OFDM channel estimation method based on the generalized orthogonal matching trackingalgorithm in the compressed sensing disclosed by the invention comprises the steps of translating the channel estimation problem into the problem for reconstructing original signal based on the compressed sensing theory, designing the measurement matrix and reconstructing the original signal by using the generalized orthogonal matching tracking algorithm. The operation complexity, namely the running time, are greatly reduced, the impulse response of the channel is precisely estimated, the system performance of the OFDM sparse channel estimation is improved so as to improve the signal demodulation quality, and the method has high application value.

The invention discloses a novel OFDM signal channel estimation combination ICI self elimination method. The sending end pilot frequency design adopts a cluster type pilot frequency OFDM structure with the ICI estimation function. The receiving end is processed according to the following steps: a, converting proceeding FFT of an OFDM sign to a frequency domain, taking out the pilot frequency, and carrying out ICI elimination signal channel estimation; b, carrying out counter modulation after using the signal channel estimation in the first step for coarse balancing; c, using the signal channelestimation in the first step for time domain linear continuous sign signal channel estimation; d, calculating ICI signal channel matrixes through cyclic convolution by using a time domain pulse response structure in the third step, and obtaining ICI interference matrixes; and e, carrying out ICI elimination through combining counter modulation signals in the second step and ICI interference matrixes in the fourth step, and making the judgment after the secondary balancing. The invention solves the problem of influence on OFDM by interference between carrier waves under the condition of lineartime change signal channels, and improves the frequency spectrum utilization rate and the system performance.

Methods, apparatuses, and systems for improved channel estimation in an Orthogonal Frequency Division Multiplexing (OFDM) system are discussed. In one example discussed herein, joint two-dimensional Minimum Mean-Square Error (2D-MMSE) channel estimation is performed on any Resource Element (REs) containing a reference signal in a Resource Block (RB), one-dimensional Minimum Mean-Square Error (1D-MMSE) channel estimation is performed in the frequency domain on each OFDM symbol in the RB, and then channel estimation is performed in the time domain on each frequency sub-carrier in the RB. In another example discussed herein, Power Delay Profiles (PDPs) and/or frequency correlations are calculated using minimax optimization and then stored in a Look-Up Table (LUT) indexed by estimated Signal to Noise Ratio (SNR) and the estimated maximum delay spread. A portable device could use such an LUT in MMSE calculations.

The invention discloses an OFDM sparse channel estimation method based on adaptive compressed sensing. The method comprises the following steps of step (1), modeling an OFDM channel estimation problemas a compressed sensing signal reconstruction problem; and step (2), solving the compressed sensing signal reconstruction problem by utilizing an adaptive compressed sensing channel estimation algorithm, and estimating an OFDM sparse channel. The method has the advantages that the OFDM sparse channel can be quickly estimated under a condition that the OFDM system channel sparsity is unknown; andcompared with an OFDM sparse channel estimation method based on an existing sparsity adaptive algorithm, the OFDM sparse channel estimation method based on the algorithm has lower channel estimation mean square error, lower system error bit rate and shorter estimation time.

This invention provides one simple and effective training sequence design scheme in the MIMO-OFDM system with several antenna, which comprises front frequency structure and comb frequency structure to make each antenna frequency position crossed to remove the interference between each antenna, wherein, the front frequency structure scheme is suitable for slow declining channel and the comb frequency finding structure scheme is suitable form rapid declining channel. The invention also provides one MIMO-OFDM channel computation method based on the ML method to apply the method into the above two structures.

The invention discloses an OFDM channel estimation method for de-noising which is based on wavelet unbiased risk threshold value, which relates to the technical field of communication, the purpose of the invention is that the problem that an LS method is easy to be influenced by noise under the condition without channel information is effectively solved. The realizing process of the method comprises first, obtaining channel frequency response which contains noise according to the LS channel estimation method which is on the basis of an OFDM system which is based on pilot frequency, second, doing inverse discrete Fourier transform for the channel frequency response which is obtained and to get channel time-domain impulse response which contains noise, third, de-noising the channel time-domain impulse response the method for de-noising which is based on wavelet unbiased risk threshold value, and getting channel time-domain impulse response after de-noising, fourth, doing inverse discrete Fourier transform for the channel time-domain impulse response after de-noising, and getting frequency domain response of channel, and compensating the received signals by the channel time-domain impulse response after de-noising. The method can be used in OFDM channel estimation techniques under various multi-path channels.

A frequency domain diversity DVB receiver device includes multiple antenna ports for receiving radio signals, and radio signal processing circuits connected to the antenna ports that convert the received radio signals into digital samples. The digital samples from the different antenna ports time-share a front-end processor which processes the digital samples to provide time-domain symbols. The time-domain symbols are stored in time-domain symbol buffers according to which of the antenna ports the time-domain symbols are received. A fast fourier transform circuit then retrieves the time-domain symbols and converts them frequency-domain symbols, which are then stored one or more frequency-domain symbol buffers according to the antenna ports the corresponding radio signals are received. A diversity processor which combines the frequency-domain symbols from the frequency-domain symbol buffers.

Channel estimation for high mobility OFDM channels is achieved by identifying a set of channel path delays from an OFDM symbol stream including carrier data, inter-channel interference noise and channel noise; determining the average channel impulse response for the identified set of channel path delays in each symbol; generating a path delay curvature for each channel path delay in each symbol based on stored average channel impulse responses for the identified channel path delays; estimating the carrier data in the symbols in the OFDM symbol stream in the presence of inter-channel interference noise and channel noise from the OFDM symbol steam and the average impulse responses for the identified channel path delays; reconstructing the inter-channel interference noise in response to the path delay curvature, the identified set of channel path delays and estimated carrier data to produce a symbol stream of carrier data and channel noise with suppressed inter-channel interference noise.

The invention discloses an MIMO-OFDM channel estimation method considering same frequency interference. The method comprises the following steps that 1), an observation sample of MIMO-OFDM pilot signals is utilized, an estimation criterion of the least square method is based, and then initial estimation of a channel impulse response is obtained; 2), the initial estimation of the channel impulse response is utilized, a residual error estimation method is based, and then an initial estimation value of an interference covariance matrix is obtained; 3), the initial estimation value of the interference covariance matrix is utilized, Cholesky decomposition and time domain 'low-pass filtering' are based, and then an improved estimation value of the interference covariance matrix is obtained; 4), the improved estimation value of the interference covariance matrix is utilized, a maximum likelihood estimation method is based, and then an improved estimation value of the channel impulse response and an improved estimation value of the channel frequency response are obtained. The MIMO-OFDM channel estimation method considering the same frequency interference is low in computation complexity and good in estimation error performance, and the performance gain is larger as the number of antennas is increased.

FBMC (Filter Bank Multicarrier) is a special carrier communication mode. Being different from OFDM (Orthogonal frequency division multiplexing), subcarriers of the FBMC are not orthogonal to one another, so that intersymbol interference and inter-carrier interference naturally exist. A traditional OFDM channel estimation method is built on the basis of no intersymbol interference and inter-carrier interference, thereof, to carry out accurate channel estimation, the interference of surrounding symbols to a pilot symbol must be eliminated, and surrounding interference factors are definite under a certain filter bank structure and a prototype filter design. An auxiliary pilot method is such a method that an auxiliary pilot is placed nearby the position of an actual pilot, the value of the auxiliary pilot is determined by virtue of the values of the surrounding symbols and the corresponding interference factors, and the interference of the surrounding symbols to the pilot position is eliminated by virtue of the auxiliary pilot, so as to carry out accurate channel estimation.

The OFDM channel estimation and Inter-Carrier Interference (ICI) cancellation method uses a few pilots within Orthogonal Frequency Division Multiplexing (OFDM) systems in general, and mobile OFDM systems in particular. The frequency domain channel is estimated using an eigenvalue based model reduction technique with high accuracy. A Minimum Mean Square Error (MMSE) based Finite Impulse Response (FIR) equalizer is then used to obtain an ICI free estimate of the transmitted signal.

The invention provides a TDS-OFDM (Time Domain Synchronous-Orthogonal Frequency Division Multiplexing) channel estimation equalization method. The TDS-OFDM channel estimation equalization method comprises receiving and storing information frames and extracting a frame header and the data portion of the current information frame and a frame header of the next information frame; processing the data portion of the current information frame so as to obtain data time domain signals, wherein the trailing interference of the frame header of the current information frame in the data time domain signals is eliminated; performing estimation on a channel which is corresponding to the data portion of the current information frame so as to obtain the frequency domain response of the channel; performing the frequency domain equalization on the time domain signals through the frequency domain response so as to obtain a data symbol sequence. The TDS-OFDM channel estimation equalization method can be applied to the large doppler range and a rapid time-varying channel and is suitable for ultra-high-speed mobile application scenarios. The invention also provides a TDS-OFDM channel estimation equalization system.

The invention discloses an OFDM (Orthogonal Frequency Division Multiplexing) channel estimation method and device. The method comprises the following steps of: extracting pilot frequency information to obtain a channel estimation time domain shock response value containing a noise pilot frequency site; extracting a real part and an imaginary part of the channel estimation time domain shock response value containing the noise pilot frequency site; respectively carrying out wavelet denoising on the real part and the imaginary part of the channel estimation time domain shock response value containing the noise pilot frequency site; and combining the real part and the imaginary part of the wavelet denoised channel estimation time domain shock response value containing the noise pilot frequency site to obtain a denoised channel estimation time domain shock response value. The invention has the advantages of improving the anti-noise capacity of OFDM channel estimation, effectively reducing the error rate of the system, estimating a channel parameter with a high precision and improving the integral performance of the system.

The invention discloses a sparse MIMO-OFDM channel estimation method based on a space-time correlation of a channel. Channel frequency domain responses of different transmit-receive antenna to a pilot frequency in a received OFDM symbol are estimated; the channel frequency domain responses of the different transmit-receive antenna to the estimated pilot frequency are arranged according to a certain rule into a matrix; the matrix is processed through the super-resolution algorithm so that the multipath time delay number of the channel can be acquired; the matrix is processed according to the acquired multipath time delay number, so that multipath time delays of the channel are acquired; multipath gain corresponding to a time delay is acquired according to the acquired multipath time delays and the acquired matrix of the channel; a channel frequency domain response to a subcarrier at data is acquired according to the acquired multipath time delays and the acquired gain. In this way, the problem that the number of required pilot frequencies increases along with the number of antenna in the channel estimation process in a current MIMO-OFDM system is solved; meanwhile, the space-time correlation of the channel is used for further improving channel estimation accuracy, remarkably reducing system pilot frequency spending, and improving spectrum efficiency.

The invention discloses a short wave OFDM (orthogonal frequency division multiplexing) channel estimating method in narrow band interference. The method includes the steps: firstly, estimating an initial estimation value of a pilot frequency in a channel by the aid of an LS (list scheduling) algorithm, then performing a primary noise filtration for the initial estimation value by the aid of DFT (discrete Fourier transformation) channel estimation algorithm principle, namely, the length of a circulation prefix code is larger than channel impact response, filtering noise except a circulation prefix by the aid of a method that an estimation value larger than the length of the circulation prefix code is reset zero, finally, performing a secondary noise filtration for the initial estimation value by leading in a threshold value, acquiring a final estimation value at the pilot frequency by performing zero setting for signals smaller than the threshold value and keeping invariable for the portions larger than the threshold value, then performing interpolation for pilot frequency estimation according to interpolation modes to obtain estimation of the whole channel, and performing DFT for channel estimation of a time domain to obtain channel estimation of a frequency domain. The channel estimation perform is improved, the pilot frequency is of a comb-like pilot frequency structure, and rapid fading of short wave signals is effectively restrained.