257 results about "Channel frequency response" patented technology

Multi-drop communications channels can have significantly deep notches in their frequency response causing a corresponding limitation of the effective data transmission rate. A special time-ordered coding method is described which results in the emitted spectrum of the data stream transmitted into the channel having a notch at the same frequency as the notch in the channel frequency response, permitting channel receivers to successfully decode the transmitted data stream. The described coding method may be applied at various multiples of the channel notch frequency to support different throughput rates, and may be combined with other coding techniques such as group or vector signaling codes.

A receiver for recovering data from a symbol of signal samples generated in accordance with Orthogonal Frequency Division Multiplexing is described. The symbol may be a COFDM symbol in accordance with the DVB-T standard, and includes pilot carrier signals for use in estimating channel conditions. The receiver includes a pilot assisted channel estimator comprising a pilot extractor operable to extract the pilot carrier signals from the signal samples and to generate from the extracted pilots samples of the channel frequency response or channel transfer function estimate. The channel frequency response generator is operable to compare the extracted pilot carrier signals with a predetermined version of the pilot carrier signals. The pilot assisted channel estimator includes a frequency dimension interpolation filter operable to interpolate the pilot-derived samples of the channel frequency response in the frequency dimension, and a filter controller. The frequency response of the frequency interpolation filter has a pass bandwidth, which is adjustable, and the filter controller is operable to adjust the bandwidth of the frequency interpolation filter to the effect of reducing noise in the channel frequency response estimate. The use of an adjustable pass bandwidth for a frequency domain interpolation filter can advantageously be used to reduce noise in the channel impulse response estimate by enabling an appropriate selection of the bandwidth of the frequency domain interpolation filter according to the particular current characteristics of the channel impulse response.

A receiver for recovering data from a received symbol of signal samples generated in accordance with Orthogonal Frequency Division Multiplexing (OFDM) includes a pilot assisted channel estimator operable to generate an estimate of a transmission channel through which the received OFDM symbol has passed. The OFDM symbol includes pilot signals provided at different sub-carrier locations for each of a set of OFDM symbols, the sub-carrier locations of the pilot signals being repeated for subsequent sets of symbols. The pilot assisted channel estimator comprises a pilot extractor, a time interpolation filter controller and an adaptive bandwidth interpolation filter. The channel assisted channel estimator is operable to extract the pilot carrier signals from the signal samples, and to generate an estimate of a sample of the channel frequency response for each pilot signal in the received OFDM symbol, by comparing the extracted pilot carrier signals with predetermined versions of the pilot carriers. The adaptive bandwidth time interpolation filter is operable to interpolate the samples of the channel frequency response derived from pilot carrier signals at corresponding sub-carrier locations within temporally separated OFDM symbols to generate an interpolated version of the channel frequency response estimate. The time interpolation filter controller is operable to generate an estimate of a rate of change of the channel frequency response with time and to adapt a pass bandwidth of the time interpolation filter in accordance with the determined rate of change of the channel. As such, there is an increased likelihood of correctly recovering data conveyed by the OFDM symbol.

The invention discloses a signal channel training method based on a beacon frame, which includes: performing initial synchronous search for the beacon frame and computing initial estimation of frequency offset of a sampling clock after access terminal equipment is powered on; starting tracking estimation and compensation of frequency offset of the sampling clock based on initial estimation of frequency offset of the sampling clock; estimating in-band narrow-band interference and computing the coefficient of a notching filter according to the frequency point position of the in-band narrow-band interference; performing second power control processing for digital baseband signals processed by means of low-pass filtering and notching filtering; starting coarse carrier frequency offset estimation and compensation; starting fine carrier frequency offset estimation and compensation; starting signal channel frequency response estimation; and leading a receiver to enter a signal channel condition tracking state. The invention further discloses a signal channel training receiver device based on the beacon frame. The success probability of synchronous detection for the beacon frame can be increased, and signal channel estimation precision can also be improved.

Time-varying and frequency-selective channels in an orthogonal frequency division multiplexing (OFDM) network are estimated by first storing, in a buffer at a receiver, a received signal corresponding to a set of pilot tones of a set of OFDM symbols, wherein the pilot tones are predetermined and inserted in frequency subcarriers and time slots of the OFDM symbol. A covariance matrix of the received signal is estimated. A diagonal matrix is estimated based on the covariance matrix and a variance of noise in the received signal. The diagonal matrix indicates delays of non-zero paths in a time domain. A channel impulse response (CIR) for each OFDM symbol is estimated using the diagonal matrix, and the received signal. Then, the CIR is transformed to the frequency domain to obtain the channel frequency response (CFR).

The present invention provides a channel estimation method for a Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing system, characterized by comprising steps of: for each of a plurality of receiving antennas of said Orthogonal Frequency Division Multiplexing system, calculating a channel impulse response sequence and a channel frequency response sequence for a channel between said receiving antenna and each transmitting antenna by using a pilot sequence received by said receiving antenna; wherein said pilot sequence is a comb pilot sequence, and the pilot symbols, to which each of said transmitting antennas corresponds, are located in the same position in frequency domain and separated from one another in time domain. The present invention further provides a corresponding mobile communication system. The pilot sequence of the present invention may be used in a wireless channel with a relatively high moving speed. The present invention considers the impact of virtual sub-carriers in a Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing system, and possesses relatively high performance and relatively low complexity.

The invention discloses a transform domain quadratic estimation method uniting weighted threshold de-noising and balanced decision. The method comprises the following steps: step 1), uniting a superimposed training sequence and a harmonic sequence and generating a sending sequence; step 2), in an OFDM (Orthogonal Frequency Division Multiplexing) baseband system, through an estimation method of an LS channel of the superimposed training sequence, obtaining coarse estimation of a channel frequency response; step 3), performing amplitude phase compensation on the coarse estimation of the channel frequency response, adding a window function with a width of M and performing DCT (Discrete Cosine Transformation) of an M point, performing low-pass filtering, time domain de-noising and sequence zero padding extension processing on the obtained sequence, performing N point IDCT (Inverse Discrete Cosine Transform), window removing and secondary amplitude phase compensation on an extended N point sequence, as the following formula, and obtaining the following formula; step 4), performing balanced decision on the obtained result and obtaining the following formula, repeating M point DCT, low-pass filtering, time domain de-noising, interpolation zero padding and N point IDCT, and obtaining a final estimation of a frequency domain response, as the following formula. The transform domain quadratic estimation method uniting the weighted threshold de-noising and the balanced decision provided by the invention eliminates the influence of a data sequence and the training sequence on the channel estimation performance, improves the performance of the existing LS (Least Squares) channel estimation, and has lower implementation complexity.

The transfer function of the communication channel in a mud pulse telemetry system is determined by sending a known signal through the channel and spectral analysis of the received signal. The known signal may be a chirp signal or a stepped frequency signal. Based on the determined transfer function, operating parameters of the pulser are adjusted.

Disclosed is a radio communication device, and more particularly to a method for estimating a channel and compensating for error occurring in the estimation procedure, for a device for performing a frequency domain signal processing, such as Orthogonal Frequency Division Multiplexing (OFDM) The channel estimation method in a radio communication system includes the steps of: transforming a received OFDM signal into a frequency domain; estimating a channel frequency response (CFR) value from a result value obtained through the transformation by using a pilot signal; transforming the estimated CFR value into a time domain through an extended Inverse Fast Fourier Transform scheme, and detecting a channel impulse response (CIR) value; detecting a delay path position of a channel; modifying a non-ideal autocorrelation function; and compensating the estimated CIR value for error, through use of the detected delay path position and the non-ideal autocorrelation function.

The invention discloses an OFDM (Orthogonal Frequency Division Multiplexing) pilot scheme design and channel estimation method. The method comprises the following steps: pilot symbols are uniformly inserted into data frames of an OFDM system to obtain a pilot pattern, the frequency response of the channel at the pilot position is calculated according to the pilot pattern to obtain the sampling sequence of the channel frequency response information, and modified orthogonal matching tracking channel estimation is carried out according to the sampling sequence of the channel frequency response information and part of discrete Fourier matrices. By adopting the method provided by the invention, the channel estimation algorithm complexity is greatly reduced while the pilot density is greatly lowered, the channel estimation accuracy is improved, and accordingly, the efficient, low-complexity and accurate channel estimation is realized.

The invention belongs to the technical field of wireless communication and particularly relates to a channel estimation and IQ (In-phase Quadrature) imbalance united compensation method in a wireless communication system which is influenced by in-phase orthogonal two-way imbalanced interferences. The channel estimation and IQ imbalance united compensation method comprises the following steps of performing constraint on ranges of IQ imbalanced parameters; constructing objective functions; obtaining coordinate values of an optimal solution; working out an optimal parameter for IQ imbalance; recovering ideal CFR (Channel Frequency Response); and performing compensation on the IQ imbalance and achieving the channel estimation and correction of the IQ imbalance.

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.

The invention discloses an information transmission method for lowering peak to average power ratio of an OFDM system signal. In the method of the invention, after being coded, weaved, modulated and performed with serial/parallel conversion, the input bit stream is adjacently cut into a plurality of mutually disjoint frequency domain subsequences; each subsequence is inserted with pilot frequency as required; parts of transmission sequences are used for lowering the peak to average power ratio without transmitting a phase rotation factor to a receiving end. At the receiving end, the received signal is performed with serial/parallel conversion, DFT and parallel/serial conversion and is cut into a frequency domain signal subsequence according to the same mode with a receiver end; pilot frequency contained in the subsequence is utilized for the channel estimation of the subsequence; the multiplied phase rotation factor serves as one part of channel frequency response so as to restore frequency domain data in the subsequence; the frequency domain ratio data are combined into one sequence; and an output bit stream is obtained after demodulating, deinterlearing and decoding. The invention eliminates the influence of sideband information on the frequency spectrum utilization ratio and signal transmission rate.

The invention belongs to the field of underwater sound communication, and particularly relates to a channel estimation method for reducing gaussian noise and interpolation error in channel estimation. The channel estimation method for underwater sound orthogonal frequency division multiplexing comprises the following steps that (1) channel frequency response estimation is obtained through the channel estimation method based on a least square method; (2) noise reduction is carried out on the pilot frequency response estimation through a wavelet noise reduction method to obtain the channel frequency response subjected to noise reduction; (3) the channel frequency response of a data sub-carrier is obtained by carrying out a discrete Fourier transform interpolation method on the channel frequency response subjected to noise reduction; and (4) the received data is balanced through the channel frequency response of the data sub-carrier, the balanced data is encoded and re-modulated, comb-shaped pilot frequency is converted into block-type pilot frequency, and the received data is judged, fed back and balanced through a block-shape minimum mean square error channel balancing method. According to the channel estimation method for underwater sound orthogonal frequency division multiplexing, the impact of the channel noise on channel estimation and the interpolation error are reduced, and the judging performance and the channel estimation precision are improved.

A wiener interpolation method based on time domain SNR estimation includes the steps of acquiring a channel frequency response of a pilot subcarrier; utilizing two cascade interpolation filters to acquire the channel frequency response of a data subcarrier; utilizing a stored interpolation result to carry through frequency domain equalization of single tap on the data received on the data subcarrier. The performance of the wiener interpolation method estimated by the real time flatness SNR of the invention is very close to the performance under a situation estimated by an ideal SNR and is extremely better than the system of the method by adopting line interpolation. Furthermore, by adopting a method for storing the parameters of an interpolation filter in advance, the matrix inversion with large calculating amount can be avoided, thereby greatly simplifying the realizing complexity of a receiver.

A method an apparatus for providing channel state information in a receiver are described. In the method, direct channel state information may be generated based on a calculated error signal, and indirect channel state information may be generated based on a magnitude of a channel frequency response. A channel state selection control signal is generated based on the calculated error signal and magnitude of the channel frequency response. One of the direct channel state information and indirect channel state information may be output based on a logic state of the channel state selection control signal.

The invention discloses a method for channel estimation in a broadband wireless mobile communication system and a channel estimator. The method comprises the following steps: 1) pilot channel estimation is carried out by adopting a given algorithm to each pilot symbol in a plurality of pilot symbols transmitted by the channels, in pilot subcarriers within the usable subcarrier range, boundary value reprocessing is carried out to virtual pilot falling into the high frequency virtual subcarrier range so as to obtain the channel frequency response estimation of equal-interval pilot subcarrier position in a plurality of pilot symbols; 2) reverse Fourier transform is carried out to the channel frequency response estimation of the equal-interval pilot subcarrier position in a plurality of pilot symbols, so as to obtain time-domain channel impulse response estimation of a plurality of pilot symbols, and the time-domain channel impulse response estimation of the data symbol is obtained by adopting the given algorithm; and 3) after zero value insertion processing is carried out to a plurality of pilot symbols and the obtained time-domain channel impulse response estimation of the data symbol, the channel estimation result can be obtained by adopting the Fourier transform. The invention improves the accuracy and the robustness of the channel estimation.

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.

The invention relates to a channel estimation method for a dual-antenna generalized multi-carrier system, wherein, according to a time-frequency structure of frame data stipulated by a system, a pilot subcarrier is assigned according to the position of a special subband, while a null carrier is assigned by a non-special subband. During the transmission of frame data, the pilot orthogonality of two transmitting antennas are rationally designed under the condition of slow channel time variation, two pilot blocks in one frame are used to jointly make a channel estimation to make the channel estimation problem to convert into the solution of a linear equation group, a channel frequency response estimation value at the position of the special subband can be obtained through the linear treatment, the position of the non-special subband is not estimated, thus the pilot resource is saved, and other frequency-division multiplexing access multi-user systems are easy to be reached, ie. orthogonal frequency division multiplexing access system and single-carrier frequency division multiplexing access system.

The present invention relates to a method for gaining channel quality information at a base station of a multi-carrier radio communication system having a plurality of orthogonal frequency sub-carriers. According to the present invention, the method comprises the steps of: measuring a Channel Frequency Response at a user terminal of said multi-carrier radio communication channel; extracting samples of said Channel Frequency Response represented in the frequency domain at a predefined oversampling factor; sending said samples on a signaling channel from said user terminal to said base station; performing a windowing operation on the received samples in the time domain; determining a channel quality information for each of said sub-carriers on a representation in the frequency domain of said received samples after windowing operation.