126 results about "Sampling frequency offset" patented technology

The invention provides a method for precisely estimating a large frequency offset of a DFT-s-OFDM (Direct Fourier Transformer Spread Orthogonal Frequency Division Multiplexing) system. The method comprises the following steps of synchronizing SC-OFMA (Single-Carrier Orthogonal Frequency Division Multiplexing) symbols; performing frequency offset estimation by utilization of a synchronized cyclic prefix CP and a data section tail part Tail so as to obtain a small frequency offset, and compensating the small frequency offset on a receiving signal; performing automatic RB (Resource Block) detection after removing the carrier leakage from the compensated receiving signal, and distributing sub carriers according to frequency domain RB so as to obtain a large frequency offset; generating a DMRS (Demodulation Reference Signal) local reference signal for a time slot under an unknown time slot number according to receiver DMRS symbols; obtaining a precise frequency offset according to an average phase difference of two DMRS symbols in one sub carrier, and obtaining a large frequency offset estimation range. According to the method for precisely estimating the large frequency offset of the DFT-s-OFDM system, the inter-symbol interference and the inter-sub carrier interference can be conquered, and the frequency offset estimation on signals is realized under the condition of unnecessarily knowing signal resource block allocation and sub frame sequence number in advance, so that the frequency offset range is enlarged, and the precision of the estimation result is improved.

A technique to determine sampling frequency offset (SFO) phase shift and perform channel estimation for symbols of a signal communicated across a multiple-input-multiple-output (MIMO) communication channel, in which preambles utilized for channel estimation are sent over more than one time block. Because the transmission of preambles used for channel estimation are sent over multiple time blocks, a SFO phase shift that is linear across tones of an OFDM signal is experienced between preambles of the two time blocks. Upon detection of the SFO phase shift, a weighting matrix used for channel estimation is modified to account for the SFO phase shift, in order to perform the channel estimation with correction for the SFO phase shift.

The invention relates to a method for combined compensating the sampling frequency bias and the carrier wave frequency bias, used in the orthogonal frequency division multiplexing system, and a relative device, wherein based on the phase bias of pilot sub carrier wave, the invention uses the weight least square method and another two simplify methods to estimate the slope and intercept of phase bias curvature of sub carrier wave, whose weight is decided by the increment function or signal/noise ratio of pilot channel; compensates the phase bias of data sub carrier wave via the estimated phase bias curvature; and supports the accurate estimated value of FFT window drift based on the curvature slop, to adjust the position of FFT window by FFT window controller, to compensate the sampling frequency bias; then based on the curvature intercept, supports the estimated value of carrier wave frequency bias, to feedback and compensate the carrier wave frequency bias. The invention can improve the compensate accuracy of sampling frequency bias and carrier wave frequency bias under multi-path condition.

A method for tracking carrier frequency and sampling frequency offsets in an OFDM wireless communication system comprises: (a) detecting data received from the transmitter using a first signal, and tracking a phase offset caused by the carrier frequency offset using the detected received data; (b) detecting the data received from the transmitter using the first signal, and tracking the phase offset caused by the sampling frequency offset using the detected received data; (c) compensating for the phase offset caused by the carrier frequency offset between the transmitter and the receiver according to the phase offset tracked in (a); and (d) compensating for the phase offset caused by the sampling frequency offset between the transmitter and the receiver according to the phase offset tracked in (b).

Synchronization method for a multi-carrier transceiver using a filter bank, for example a cosine modulated filter bank, a wavelet packet filter bank or a complex modulated filter bank, the transceiver comprising a transmitter (100) and a receiver (300) able to communicate with each other over a communication channel (200), the method comprising the following steps: sending a periodic and coded training sequence over the communication channel (200) with the transmitter (100), determining in the receiver (300) time alignment information from the received training sequence, performing a coarse synchronization of the receiver (300) to said transmitter (100) using said time alignment information, sending modulated data (1) in data mode over the communication channel (200) with the transmitter (100), pilot signals being multiplexed into said data (1), tracking sampling frequency offset and phase jitter within the receiver (300) using the pilot signals, performing the continuous synchronization of the transceiver with the help of the tracking information determined in the step of tracking. The invention also relates to a multi-carrier transceiver, consisting of a transmitter (100) and a receiver (300), able to perform this synchronization method.

A technique for improving the performance of OFDM (Orthogonal Frequency Division Multiplexing) systems addresses the Sampling Frequency Offset (SFO) estimation and correction problems of conventional techniques and provides improved performance in a wide range of operating conditions. The technique teaches a correction scheme that uses known pilots in each OFDM symbol to estimate slope of phase error and subsequently calculate the correction factor for each of the sub-carriers in the associated OFDM symbol. The present subject matter further teaches an averaging slope estimates over a window of predetermined number of OFDM symbols to average out noise and get a refined correction factor. In addition, the present technique teaches tracking rate of growth of slope across OFDM symbols to estimate SFO, which can be used for the timing error correction in the time domain.

The invention relates to a method for quickly synchronizing OFDM sampling frequencies with a high carrier number. The method includes the steps that (S1) a pilot frequency symbol is inserted into a sending end, (S2) sampling frequency offset precorrection is carried out on the current symbol by means of a capture estimated value of a previous signal, (S3) a pilot frequency phase difference of corresponding bits is obtained, (S4) sampling frequency offset capture value estimation of the current symbol is carried out through the pilot frequency phase difference, and a current symbol capture value and the previous symbol capture estimated value are summed to obtain a new estimated value, (S6) when the new capture value is larger than a set capture value, sampling frequency offset correction output is carried out on the current symbol by means of the capture estimated value of the current symbol on the basis of a frequency domain correction method, a precorrection signal in the step (S2) is output when the new capture value is smaller than the set capture threshold, and the step from (S2) to (S4) are repeated when a next symbol is updated into the current symbol. By means of the method, real-time high-precision sampling frequency offset correction can be carried out on each OFDM symbol.

The invention designs a downlink sampling frequency offset estimation and compensation method for a low-earth-orbit satellite multi-carrier communication system, and belongs to the field of wireless communication. A downlink refers to a transmission link which is transmitted by a gateway station, forwarded by a satellite and received by a user terminal. The specific method comprises the followingsteps that: a gateway station estimates downlink common Doppler sampling frequency offset based on ephemeris, and pre-compensates a downlink transmitting signal by using a downlink common Doppler sampling frequency offset estimation value and changing the sampling frequency of a sampling crystal oscillator or using a resampling digital filter; and a user terminal estimates a downlink residual sampling frequency offset by using the downlink synchronization signal and a segmentation correlation algorithm, and compensates a downlink receiving signal in a frequency domain by using a downlink residual sampling frequency offset estimation value. The downlink sampling frequency offset can be compensated with lower complexity and higher precision under the condition that the user terminal has noephemeris and only the gateway station has ephemeris, and the demodulation requirement of multi-carrier communication under the large sampling frequency offset of a low-earth-orbit satellite is met.

The invention aims at the problem of desynchrony of a transceiver oscillator of a multiband orthogonal frequency division multiplexing (OFDM) ultra wideband communication system, and provides a method for tracking the carrier frequency on the basis of a time-domain technology. A time-domain or frequency-domain type data symbol and a time-domain expansion symbol are utilized to estimate a first band frequency offset, a second band frequency offset and a third band frequency offset are derived after the filtering of a loop, the estimated values of the three frequency offsets are respectively input into a triple-path phase accumulator and an exponential function (exp) generator to form a triple-path compensating structure, a time-frequency code controls a feedback signal to be multiplied with the data in a time domain or a frequency domain and a forward path in a time division way, and accordingly, the frequency offset compensation is realized. The method does not need to use additional pilot frequency subcarriers, is beneficial to saving frequency spectrum, and can simultaneously realize better tracking performance than that of a traditional pilot frequency assistant method, the high precision estimation and compensation of small frequency offsets are realized, the desynchrony of the transceiver oscillator is made up, the system performance is guaranteed, and the method can be widely applied in multiband OFDM wireless communication systems which adopt a time-domain expansion diversity technology.

Method and apparatus for achieving high precision sampling recovery at a relatively low sampling rate. The apparatus includes: a sampling rate conversion module for converting the sampling rate of a received signal to an required sampling rate; a time domain impulse response estimation module for estimating a time domain impulse response of a transmission channel according to data output by the sampling rate conversion module; a high order interpolation module for performing high order interpolation to one or more selected transmission paths after obtaining the time domain impulse response; and a sampling error information extraction module for extracting sampling phase offset information and sampling frequency offset information based on interpolation results and drifts in two consecutive interpolation results of the high order interpolation step. The apparatus is capable of realizing fast high precision locking of sampling phase and correction of sampling frequency offset at a relatively low sampling rate.

The invention discloses device and method for sampling frequency offset estimation and compensation, particularly device and method for executing the calculation of phase difference by mathematical linear method to reduce the application of the multiplier and the storage circuit thereof in the sampling frequency offset estimation and compensation. In a preferable embodiment, the method comprises the following steps: receiving signals by employing a sampling frequency offset estimation circuit, then calculating the phase value of each signal, capturing pilots in the signals, calculating the phase difference by subtracting the received singles from the pilots after several symbol delays, further storing the phase difference by employing a phase difference storing circuit, calculating the phase difference between two neighbor symbols by employing the accumulation and the least error sum of squares circuit, calculating the estimated value of sampling frequency offset of the communication system according to the phase difference, and applying the estimated value to compensate the sampling frequency offset.

Systems and methods for canceling carrier frequency offset (CFO) and sampling frequency offset (SFO) in a radio receive chain are disclosed. In one embodiment, a method is disclosed, comprising: receiving a sub-frame via a radio receive chain in a time domain; performing per-user filtering on the sub-frame to obtain a signal for a particular user; obtaining a CFO correction signal; adding the CFO correction signal in the time domain to perform a CFO correction step on the signal for the particular user; performing an FFT on the output of the CFO correction step to obtain samples in a frequency domain; adding an SFO correction signal in the frequency domain to perform an SFO correction to the output of FFT step; and demodulating the output of SFO correction step, thereby performing CFO and SFO correction while reducing inter-carrier interference (ICI).

A system and method for detecting a sampling clock offset of an analog-to-digital converter used to digitize an analog image signal. A method comprises buffering samples of an analog image signal, computing a value of an autocorrelation function using the buffered samples and a delayed version of the buffered samples, and repeating the computing a value for delays in a range of delays. The method also comprises computing a sampling frequency offset from the values of the autocorrelation function and changing a sampling frequency using the sampling frequency offset.

A sampling frequency offset (SFO) estimation method for use in a digital receiver to estimate a correct SFO is disclosed. The method for estimating the SFO in the digital receiver includes the steps of (a) receiving an estimated phase, and comparing a magnitude of the estimated phase with that of a predetermined standard deviation; (b) if the magnitude of the estimated phase is greater than that of the predetermined standard deviation, compulsorily setting the estimated phase to zero, and storing the estimated phase of zero; and (c) calculating an SFO value using the stored phase. Therefore, the method performs zero-forcing on a phase overshoot caused by a ghost, such that a correct SFO can be estimated in the tracking mode.

A fast clock recovery system with a large dynamic range based on a voltage-controlled crystal oscillator, the clock recovery system is placed before a carrier synchronization loop, and includes: an analog-to-digital conversion ADC, a shaping filter, a timing error detector TED, Loop filter LF, control signal generator CSG, voltage controlled crystal oscillator VCXO, among which TED calculates the phase detection error signal P value according to the output data of the shaping filter, and then performs two consecutive phase detection error signal P values. Differential processing, multiply the multiplication factor and the differential processing result, and send the multiplication result to the loop filter LF until the sampling frequency offset is captured, and finally send the phase detection error signal P value to the loop filter LF to achieve Sampling frequency offset tracking. After continuous correction of the loop, the oscillation frequency of the VCXO is finally locked with the sampling clock of the transmitter to realize clock recovery. The invention has the advantages of wide dynamic range and fast clock recovery.

The invention provides a method and device for timing synchronization of burst signals in satellite communication. The method includes: performing sliding window calculation on a received burst signal to obtain a position of a maximum value in calculation results; performing position filtering on the acquired position of the maximum value to obtain a filtering position with a fraction bit; using an integer bit of the filtering position as an initial position to perform fetching on the burst signal; and using the fraction bit of the filtering position as a fraction position of an interpolation position, performing interpolation filtering on all sample value point data, and thus obtaining reconstruction data of each sample value point at an optimal sampling point. The method provided by the invention performs processing on the burst signal, including maximum value acquisition, position filtering, fetching and interpolation filtering, in the burst signal with a short unique word or without a unique word, can rapidly and accurately realize timing synchronization of a receiver and the burst signal and track a sampling frequency offset caused by instability of a timing device of a terminal and high-speed movement of the terminal, and the method provided by the invention is suitable for timing synchronization and timing tracking of receivers of various communication systems adopting a burst mode to transmit.

The invention relates to an automatic frequency control method of a spread spectrum communication system under the condition of large frequency offset. The carrier frequency offset correction cannot be finished through an automatic frequency control loop under the condition of the large frequency offset by the current method. The method comprises the following steps: firstly respectively and circularly dispreading I/Q chip baseband data after spectrum displacement; implementing delay conjugate cross-product frequency discrimination for adjacent tick data after being circularly dispread; transmitting frequency discrimination output to a digital controlled oscillator through a loop filter and then adjusting the local carrier frequency; and finally utilizing a frequency discrimination result transmitted by the loop filter to analyze variance and judge the convergence state of the loop. With the adoption of the automatic frequency control method of the invention, the carrier frequency offset can be accurately, quickly and reliably corrected, and correction range of the carrier frequency offset is large, and the automatic frequency control method is suitable for the spread spectrum communication system in a quadrature amplitude modulation mode.

A sampling frequency offset estimation apparatus of an orthogonal frequency division multiplexing (OFDM) system according to an aspect of the invention may include: a first differential operation unit performing complex conjugate multiplication of scattered pilots of complex symbols subjected to a fast Fourier transform (FFT) in an OFDM receiver; an interpolation unit repeating an operation of obtaining a median complex symbol between two consecutive symbols among complex symbols having first phase difference information from the first differential operation unit by a predetermined number; a second differential operation unit performing complex conjugate multiplication of two consecutive median complex symbols among median complex symbols from the interpolation unit; and a sampling frequency offset estimation unit estimating sampling frequency offset using complex symbols having second phase difference information from the second differential operation unit.

The present invention discloses a combined tracking method for timing deviation and sampling frequency offset, which is suitable for a digital mobile multimedia broadcasting system. The method comprises the steps of: according to channel impulse response information obtained by estimation, firstly estimating timing deviation for OFDM symbols and determining timing adjusting information for the next time slot; and then estimating sampling frequency offset according to the position information of the strongest path in the channel impulse response and the timing adjusting information for the last time slot, thereby realizing the combined adjusting of the timing deviation and the sampling frequency offset. The combined tracking method of the invention can not only track a symbol timing error brought by multipath distribution characteristic of a transmission channel, but also track and correct the sampling frequency offset brought by the inconsistency between two local oscillators for transmitting and receiving terminals; stable operation can also be realized even in the time division working mode of a receiver and the receiver can stably work by flexibly changing the estimation size of the sampling frequency offset according to the length of the time division working time of the receiver.