48 results about "Symbol timing offset" patented technology

The invention provides a synchronous processing method based on new CMMB (China Mobile Multimedia Broadcasting) synchronous signals. The CMMB synchronous signals comprise first training sequences and second training sequences; the first training sequences comprise CAZAC (Constant Amplitude Zero Auto Correlation) sequences, and the second training sequences comprise PN (Pseudo-Noise) sequences; in the synchronous processing method, the CAZAC sequences are utilized to achieve coarse symbol timing offset estimation and decimal frequency offset coarse estimation; the PN sequences are utilized to achieve the estimation of strongest path time delay in multipath, and the multipath is taken as coarse symbol timing positioning; the CAZAC sequences and the PN sequences are utilized to achieve the integer frequency offset estimation; the fast Fourier transform (FFT) is performed on the PN sequences to achieve the channel response estimation so as to estimate a first path time delay and achieve the fine symbol timing position estimation; and a maximum likelihood (ML) criterion is utilized to process the PN sequences in the second training sequences to obtain the decimal frequency offset fine estimation. The synchronous processing method can effectively improve the synchronous accuracy and can achieve better synchronization performance in the mobile communication environment with low signal-to-noise ratio.

The invention relates to a synchronization and channel response estimation method which is applicable to an OFDM system, the technical proposal is as follows: a maximum likelihood criterion ML-based cost function for the symbol timing synchronization, the carrier frequency synchronization and the channel parameter joint estimation is proposed by using an OFDM system model under a frequency selective fading channel and against the requirements on the accuracy of the transmission of high-quality information of the next generation of wireless communication system and the existing OFDM wireless communication system. A system architecture and a strategy of joint estimation symbols of timing offset Theta, carrier frequency offset Epsilon and channel impulse response h are derived from the cost function. The method comprises the following steps of carrying out the coarse synchronization and the channel response estimation and carrying out the fine synchronization and the calculation of a channel estimated value. The method can realize the balance between the calculation precision and the calculation complexity, increase or reduce the times of the iteration of the fine synchronization according to an actual system, reduce the interference during the wireless transmission, further improve the reliability of the system and improve the availability of the system.

The invention provides a synchronized method of an orthogonal frequency division multiplexing (OFDM) system. The invention discloses an associated synchronized method of frame synchronization, carrier frequency synchronization and sampling clock synchronization. Carrier frequency offset estimation, channel estimation and fine estimation of symbol timing offset are performed again after sampling clock offset correction is finished, thereby avoiding influences of sampling clock offset on the carrier frequency offset estimation, the channel estimation and the fine estimation of the symbol timing offset, compensating phase deflection caused by the residual carrier frequency offset and the sampling clock offset simultaneously, greatly improving the synchronized performance, and meeting the demands of a high-order modulated system. In addition, due to aiming at a low time-varying channel, the channel estimation is required to be performed once only, thereby reliving the complexity of the system.

A method includes determining a number of observations. Each observation occurs at an observation time and corresponds to one of a number of received frequency multiplexed training symbols. The method also includes determining a number of roots of a first polynomial equation that is a function of a variable corresponding to frequency offset errors of carrier frequencies of the training symbols. Constants in the first polynomial equation are determined using at least the observations. The roots of the variable correspond to possible frequency offset errors. Based on at least the observations, the possible frequency offset errors, and possible symbol timing offset errors of the observation times of the training symbols, a number of estimated channel responses are determined corresponding to the training symbols. The method includes using a second polynomial equation that is a function of at least the estimated channel responses, the possible frequency offset errors, and the possible symbol timing offset errors, determining at least a resultant frequency offset error and a resultant symbol timing offset error. The method further includes using the resultant frequency offset error and resultant symbol timing offset error in order to receive at least one frequency multiplexed data symbol.

A method includes converting a received time domain digital signal to a corresponding frequency domain digital signal, calculating phase angles of tones of at least one symbol of the frequency domain digital signal when a symbol timing offset exists, and calculating at least one differential phase offset (DPO). A DPO is the difference between two consecutive gaps, a gap being the difference between the phase angle of a tone of the symbol of the frequency domain digital signal when the timing offset of the symbol exists and a correct phase angle of the tone of the symbol of the frequency domain digital signal. The method estimates the symbol timing offset with at least one DPO.

A computer-implemented system and method for blind demodulation of an offset QPSK input signal, involving repeatedly performing a set of operations, including: (a) applying a phase correction to the input signal based on an estimate of a carrier phase offset of the input signal to obtain a first modified signal; (b) shifting a quadrature component of the first modified signal by half a symbol period relative to an inphase component to obtain a second modified signal; (c) extracting a first sequence of symbols from the second modified signal, where the extraction includes estimating a symbol timing offset from the second modified signal; (d) performing hard-decision demodulation on the first sequence of symbols to obtain a second sequence of reference symbols; (e) computing a phase difference between the first sequence of symbols and second sequence of reference symbols; and (f) updating the carrier phase offset estimate using the phase difference.

A method for estimating a symbol timing offset in an Orthogonal Frequency Division Multiplexing (OFDM) communication system is disclosed. The method includes detecting a channel impulse response within one Fast Fourier Transform (FFT) duration; and estimating a symbol timing offset taking the detected channel impulse response into account. The symbol timing offset estimation includes calculating a channel delay duration depending on the detected channel impulse response; and estimating the symbol timing offset such that the channel impulse response is detected within a guard interval, taking into account the calculated channel delay duration and the guard interval existing in the one FFT duration.

A carrier phase and symbol timing recovery circuit and method may be used for robust synchronization in a broadcasting ATSC receiving system. Carrier phase and symbol timing offsets may be simultaneously adjusted by using redundancy information contained in an ATSC signal spectrum. A desired sampling time instant and carrier phase offset for synchronization may be simultaneously obtained due to correlation between carrier phase and symbol timing detectors.

A method and an apparatus for estimating a symbol timing offset in an Orthogonal Frequency Division Multiplexing (OFDM) based communication system are provided. A Carrier to Interference Ratio (CIR) of an Reference Signal (RS) is acquired using received pilot signals. The RS CIR includes power information on channel components of the RS. A CIR of a Secondary Synchronization Channel (S-SCH) is acquired using the received pilot signals. The S-SCH CIR includes power information on channel components of the S-SCH. Unnecessary channel components are suppressed from the RS CIR using the S-SCH CIR. Real channel components of the RS remain. An observation window is set having a predetermined duration for windowing the real channel components of the RS. A first arriving channel component is searched for within the observation window. A start point of data is estimated using the first arriving channel component.

Disclosed herein are a Bluetooth signal receiving device and a Bluetooth Smart receiving method. The Bluetooth signal receiving device includes a frequency shift demodulator circuit, a sampler circuit, a training bit pattern discriminator circuit, and a symbol timing offset compensation circuit. The frequency shift demodulator circuit generates a baseband signal by performing frequency shift modulation on a received signal. The sampler circuit samples the baseband signal based on a symbol timing, and generates a plurality of series of bit streams based on sampled values. The training bit pattern discriminator circuit determines whether the plurality of series of bit streams generated by the sampler circuit satisfies a training bit pattern condition. The symbol timing offset compensation circuit compensates the symbol timing of the baseband signal based on a measured error metric as an effective error metric if the plurality of series of bit streams satisfies the training bit pattern condition.

A system and method for reducing implementation complexity for estimation of a Carrier Frequency Offset (CFO) and a Symbol Timing Offset (STO) for an input signal for spectrally shaped multiple communication standards. The system is implemented by replacing multiplier with shifters. The system includes a CFO estimation block, a STO estimation block, and a band extraction block that extracts a lower band edge and an upper band edge of the input signal. The STO estimation block includes (i) a sample error generation block that computes a sampling timing error value, and (ii) a Phase Lock Loop block that estimates a frequency error and a phase error corresponding to the sampling timing error value. The CFO estimation block includes (i) a carrier offset error generation block that generates a carrier offset error value, and (ii) a leaky average block for performing a filter operation.

A radio transmission system based on a frequency divisional multiplexing method is described, comprising an improved method for estimating symbol timing offset and frequency timing offset. The receiver estimates the symbol timing offset based of a block of received symbols based on a cyclic prefix and suffix.

A ATSC compliant digital television (DTV) receiver. including an image rejection filter, an interpolator, a numerically controlled oscillator (NCO), a matched filter unit, a frequency converter, and a DC remover. The image rejection filter removes (filters out) an unwanted image signal and an adjacent channel's interference signal from a first intermediate frequency (IF) signal sampled at a first sampling frequency. The interpolator resamples (at a second sampling frequency) a signal output from the image rejection filter and compensates for a predetermined symbol timing offset in response to a first control signal, thereby outputting a second IF signal. The NCO down converts the second IF signal and simultaneously compensates for a predetermined carrier offset in response to a second control signal, thereby outputting a first complex signal. The matched filter unit receives the first complex signal and filters the first complex signal, thereby outputting a second complex signal. The frequency converter generates a third complex signal having a double side band from the second complex signal output from the matched filter unit. The DC remover removes (filters out) a pilot signal from a DC signal included in the third complex signal output from the frequency converter.

An orthogonal frequency division multiplex (OFDM) receiving system for changing a fast Fourier transform (FFT) window period using a guard interval, and a method for the same are provided. The method includes extracting scattered pilots, which are inserted into a symbol at intervals of predetermined samples, from a received OFDM signal, estimating a symbol timing offset using the extracted scattered pilots and setting a symbol timing synchronization point in the data transmission interval, and adding samples in a predetermined interval in the data transmission interval to samples in an interval obtained by subtracting a predetermined length from the useful symbol interval starting from the symbol timing synchronization point and performing FFT with respect to the result of addition. Accordingly, symbol timing synchronization and channel equalization can be accurately performed without having ISI even when a symbol start point is not correctly decided under a multi-channel (or a Rayleigh channel) or a pre-ghost channel environment.

The invention provides a method for estimating noise based on signal elimination. The method comprises the following steps of: receiving a signal sequence and carrying out fast fourier transform (FFT) to obtain a frequency domain sequence; carrying out symbol timing offset estimate on the transformed frequency domain sequence; obtaining the sampling value of optimum sampling points by an interpolation algorithm; calculating the average value of the optimum sampling values of multiple repeated sequences, and normalizing to a standard value; and calculating noise in the sequences and calculating a signal-to-noise ratio. The invention correspondingly provides a system for estimating noise based on signal elimination. The method and the system, provides by the invention are helpful in quickly obtaining accurate signal-to-noise ratio.

A symbol timing recovering apparatus of an orthogonal frequency division multiplexing (OFDM) receiver includes a unit for detecting a symbol timing offset from an OFDM signal; a unit for multiplying a first symbol timing offset by a first weighting factor and a second symbol timing offset by a second weighting factor, and adding and outputting the products; a unit for detecting an inter-symbol interference and a sampling offset value of the OFDM signal due to the channel, based on the outputs from the factor computing unit; a unit for adjusting a window timing of the symbol of the OFDM signal based on the inter-symbol interference; and an interpolator for correcting the sampling timing of the OFDM signal based on the sampling offset value.

Disclosed are a method and apparatus for estimating symbol timing in a non-synchronized OFDM system. The present invention includes synchronizing a frame of a received signal, estimating the symbol timing of each symbol of the frame based on the synchronization, compensating for the symbol timing using a phase difference attributable to a Symbol Timing Offset (STO), variably changing within a Cyclic Prefix (CP) interval due to the frequency offset of a sampling clock and thermal noise, and performing channel equalization using a preamble based on output including corrected phase rotation.

A system and method involve receiving a plurality of samples of at least one orthogonal frequency division multiplex (OFDM) signal, the samples containing at least one complete OFDM symbol including data samples and a cyclic prefix, using an initial symbol timing offset (STO) estimate to initialize an N×1 vector of occupation probabilities α, where Nis the number of sub-carriers of the OFDM signal, and, for each subsequent set m of OFDM samples received containing at least one complete OFDM symbol, determining a STO estimate from a set of candidate STO estimates, updating the vector of occupation probabilities α, and determining a final STO estimate. The final STO estimate is used to determine a carrier frequency offset and may be determined using the STO estimate with the highest occupation probability.

The invention is concerned with the symbol timing migration method in the radio communications system, which the method includes: to confirm the channel frequency response of the opposite known pilot frequency point of each of the received symbol; to conduct combining to each of the symbol to form the perfect pilot frequency; to complete combination of each of the symbol and to obtain the timing migration value of the symbol by using the channel frequency response value constructs the frequency response of the channel.

This invention relates to methods for determining symbol timing shift for a received signal, comprising the steps of: demodulating a received signal; removing a phase reference sequence from the demodulated signal to generate a channel frequency response; converting said channel frequency response to the time domain to generate a channel impulse response; determining a detection threshold; determining a first path and a last path as a function of the detection threshold; and calculating a timing shift as a function of the first path and the last path.