156 results about "Residual frequency offset" patented technology

A receiving system and a method of processing broadcast signals in the receiving system are disclosed. The receiving system includes a tuner, a known sequence detector, a carrier recovery unit, a baseband processor, and a channel equalizer. The tuner receives a broadcast signal of a passband including a data group. Herein, the data group comprises mobile service data, a plurality of known data sequences, and signaling data. The known sequence detector estimates an initial frequency offset and detects a position of each known data sequence based on the known data sequence having the first data pattern. The carrier recovery unit acquires an initial frequency synchronization using the initial frequency offset estimated by the known sequence detector and estimates a residual frequency offset based upon the known data sequences having the second data pattern so as to perform carrier recovery. The baseband processor performs complex multiplication between the received broadcast signal and an output of the carrier recovery unit, thereby converting the passband broadcast signal to a baseband broadcast signal.

The invention provides a frequency offset estimation method for high-dynamic large-frequency-offset burst signals. The estimation method comprises burst frame capturing, estimation and correction of Doppler changing rate, basic frequency offset estimation, and Doppler frequency offset estimation, a burst signal frame is formed by a pilot frequency segment and a data segment, and a receiver employs the pilot frequency segment to realize frequency offset estimation. Firstly, the burst frame capturing is realized via a threshold comparison method; then the segmentation of pilot frequency data is realized, a DFT-assistant hierarchical iteration method is employed to estimate the Doppler changing rate, and the estimation value of the Doppler changing rate is used for dynamic compensation of the pilot frequency segment; later, DFT-assistant basic frequency offset estimation of signals after dynamic correction is realized; and finally, the estimation value of the Doppler changing rate and the basic frequency offset estimation value are combined to estimate the frequency offset of each symbol in the burst signal frame. According to the frequency offset estimation method, the data segment is compensated by the adoption of the frequency offset estimation result so that the data segment has small frequency changing rate and residual frequency offset, and bit synchronization, frame synchronization, and carrier synchronization can be realized.

Disclosed is a wireless communication apparatus which synthesize signals received from a plurality of antennas to separate the signals into synthesis signals of a plurality of logical channels. The apparatus has a first phase corrector correcting a phase of a reception signal by estimating an amount of phase correction by a frequency offset of each reception signal from the plurality of antennas; a synthesizer synthesizing reception signals after phase correction by the first phase corrector to separate the reception signals into synthesis signals of a plurality of logical channels; and a second phase corrector correcting a phase of a synthesis signal by estimating an amount of phase correction by a residual frequency offset after phase correction by the first phase corrector based on the synthesis signal synthesized by the synthesizer.

Signal processing methods and apparatus which incorporate I / Q imbalance compensation based on most likely estimates of the I / Q imbalance between the I and Q components of a baseband signal are disclosed. In accordance with at least one disclosed embodiment of the invention, most likely estimates of the common phase error may also be used to compensate the initial channel estimates to further improve receiver performance. Though applicable to any multicarrier OFDM communications system, the disclosed methods and apparatus may be conveniently implemented in IEEE 802.11a, IEEE 802.11g, or 802.16a compliant wireless communications systems to reduce the effects of imbalanced I / Q components of baseband signals recovered from inbound RF signals, as well as counter residual frequency offset and phase noise potentially present in such baseband signals.

An apparatus for compensating for a frequency offset and a channel variation, includes: a frequency offset compensation unit estimating the frequency offset of receptions signals received via reception ends based on a final metric value of the reception signals, and a compensator compensating for the frequency offset of the receptions signals based on the estimated frequency offset; Fast Fourier Transformers (FFTs) converting reception signals having the compensated frequency offset into frequency domain reception signals; and a frequency offset and channel variation compensation unit estimating channel coefficients of signals output from the FFTs by sub carriers, compensating for a residual frequency offset and a channel variation of the reception signals from the FFTs based on pilot signals and the estimated channel coefficients, and detecting signals transmitted from transmission ends based on the reception signals having the compensated residual frequency offset and channel variation and the estimated channel coefficients.

The invention relates to a novel methodology and apparatus for clock-offset compensation and common-phase offset correction in Frequency Division Multiplixing based wireless local area network (WLAN) environment, such as an Orthogonal Frequency Division Multiplexing (OFDM) environment. A curve fit, such as a threshold-based, least mean squares (LMS) fit of phase of the pilot sub-carriers in each OFDM symbol is used to estimate and counteract the rotation of the data sub-carriers due to residual frequency offset, low frequency phase noise, and clock offset. The invention is particularly well suited to wireless channels with multipath where pilots typically undergo frequency-selective fading. The thresholding LMS is implemented in a hardware-efficient manner, offering cost advantages over a weighted-LMS alternative. Additionally, the invention uses a unique phase-feedback architecture to eliminate the effects of phase wrapping, and avoid the need to refine channel estimates during packet reception.

A method for tracking a residual frequency offset for a single carrier-frequency domain equalizer system includes: determining a pilot from the data and known pilot data, adding the determined pilot to the leading part of the data, copying a part of the frame of the data after a block and adding it before the block, and generating a preamble to construct one frame; eliminating a cyclic prefix, processing signals per an FFT block, extracting the preamble, and performing an initial channel estimation; updating a channel estimation, performing channel compensation, receiving a pilot, calculating an average phase of all the pilots in one FFT block, updating the channel estimation, performing an IFFT operation, extracting data, and recovering the original digital signal from the data.

An apparatus for compensating for a frequency offset and a channel variation, includes: a frequency offset compensation unit estimating the frequency offset of receptions signals received via reception ends based on a final metric value of the reception signals, and a compensator compensating for the frequency offset of the receptions signals based on the estimated frequency offset; Fast Fourier Transformers (FFTs) converting reception signals having the compensated frequency offset into frequency domain reception signals; and a frequency offset and channel variation compensation unit estimating channel coefficients of signals output from the FFTs by sub carriers, compensating for a residual frequency offset and a channel variation of the reception signals from the FFTs based on pilot signals and the estimated channel coefficients, and detecting signals transmitted from transmission ends based on the reception signals having the compensated residual frequency offset and channel variation and the estimated channel coefficients.

A communications receiver is provided that includes a first and second compensators 64 and 68, a pilot tracker 60, and a demodulator 66. The first compensator 64 is operable to adjust an input signal based on both a coarse frequency offset and a fine frequency offset to produce an adjusted input signal. The pilot tracker 60 determines an estimated residual frequency offset based on at least a portion of the adjusted input signal. The demodulator 66 determines at least a first symbol sequence and a second symbol sequence based on the adjusted input signal. The second compensator 68 is operable to adjust the first symbol sequence and the second symbol sequence based on the estimate residual frequency offset.

The present invention provides frequency correction method and device. It contains Utilizing receiving all cell signal frequency offset estimation, uniform proceeding calibration to received carrier frequency, independent estimating each cell signal residual frequency offset, through feed forward frequency correction ensuring each cell signal demodulation and detection performance; also through coherence length shorter cell searching, fast selecting demodulation cell participate carrier frequency calibrating signal generation and residual frequency offset forward correcting, quick adjusting carrier frequency in switching or cell updating, to make it more approaching most strong service cell transmission frequency, ensuring metric switching or cell updating accuracy, reducing up-down going transmitted signal power, system interference; cell searching to obtain higher SNR cell, measuring CPICH signal intensity.

Disclosed is a method for compensating for a residual frequency offset in an orthogonal frequency division multiplexing system comprising the steps of: a) performing a fast fourier transform for an input signal to convert the input signal into a serial signal; b) detecting signal power of the serial signal to control the passthrough a signal greater than a predetermined critical value; c) selecting each section of a quadrant for each passed signal; d) estimating a phase error in each section of the quadrant for one orthogonal frequency division multiplexing symbol with respect to the selected section of the quadrant; and e) frequency-oscillating a signal based on the estimated phase error, generating the input signal by multiplying an oscillated signal by a band-passed signal, and then returning to step a).

The invention relates to a novel estimation method for an orthogonal frequency-division multiplexing receiving channel combining a time domain and a frequency domain. The method comprises the following steps that (1) frame structural design is carried out on a sending end, wherein leader characters for channel estimation and pilot frequency insertion are set at the sending end; (2) time domain channel estimation balancing is carried out at a receiving end, wherein the time domain channel estimation balancing is carried out by using the leader characters; (3) frequency domain channel estimation balancing is carried out, and residual frequency offset is corrected, wherein the frequency domain channel estimation balancing is carried out by using pilot frequency information. Through the method, sent information amount is improved, influences of noise can be restricted better, and performance of a system is improved; when the frequency domain channel estimation balancing is carried out by using pilot frequencies, division channel balancing is achieved by using multiplication channel balancing, resources are saved, and calculating time is reduced when hardware is achieved; the channel estimation balancing can be achieved correctly under a low SNR and multiple channels, and the novel estimation method for the orthogonal frequency-division multiplexing receiving channel combining the time domain and the frequency domain has strong application adaptability.

Improved decision directed adaptation and decision feedback equalizers are provided in a block coded digital communication system. The performance of a receiver is significantly improved by allowing the decision feedback equalizer to perform time-tracking and residual frequency offset compensation during the data portion of a frame. This is accomplished by capitalizing on the inherent correlation among the chips of a code word in a block coded digital communication system to identify certain instances where more reliable symbol estimates can be derived from a sliced chip without introduction the delay inherent in decoding. As the more reliable symbol estimates are fed back into the chip slicer, the total efficiency of the decision feedback equalizer is improved and the more reliable symbol estimates can be used to replace older content in the feedback filter to further improve the accuracy of the modified slicer input and further decrease the effects of error propagation by the decision feedback equalizer.

The invention discloses a frequency offset estimation method in a DVB-T2 system. The method includes using a P1 symbol which is generated in a receiver again, relating the P1 symbol with a received signal and reducing the range of residual frequency offset; using time domain information of pilot frequency of a P2 symbol to be related with the received signal, and estimating an integral frequency offset; using the time domain information of the pilot frequency of the P2 symbol to be related with the received signal, and estimating fractional frequency offsets; calculating the fractional frequency offsets for many times and obtaining an average value of the fractional frequency offsets for improvement of accuracy. Due to the fact that multiple fractional frequency offsets are calculated and the average value is obtained, the accuracy of estimation is improved. The method avoids relative complex calculation in a 16K and 32K mode of the integral frequency offset, and improves detection speed and estimation precision of the integral frequency offset.

The invention provides a multi-stage framework based OQPSK signal big-frequency-offset carrier synchronization method. The multi-stage framework based OQPSK signal big-frequency-offset carrier synchronization method comprises the steps of performing rough estimation of a carrier frequency by utilizing an iterative time delay multiplication forward frequency estimation method so as to realize rapid locking of the carrier; realizing synchronous estimation of a carrier phase and bit information by adopting a joint estimation method of combining carrier synchronization with bit synchronization for residual frequency offset phase positions; and eliminating 180-degree integral multiple ambiguity problem of the carrier phase by using an unwinding and unfolding method, and realizing precise estimation of the carrier phase by adopting an automatic sliding window accumulation method. The problem of mutual interference between carrier phase synchronization and clock synchronization in existing OQPSK modulation is solved, big-frequency offset rapid capture of the carrier frequency is realized at the same time, and extremely small phase jitter exists after the capture.

The invention relates to a novel methodology and apparatus for clock-offset compensation and common-phase offset correction in Frequency Division Multiplexing based wireless local area network (WLAN) environment, such as an Orthogonal Frequency Division Multiplexing (OFDM) environment. A curve fit, such as a threshold-based, least mean squares (LMS) fit of phase of the pilot sub-carriers in each OFDM symbol is used to estimate and counteract the rotation of the data sub-carriers due to residual frequency offset, low frequency phase noise, and clock offset. The invention is particularly well suited to wireless channels with multipath where pilots typically undergo frequency-selective fading. The thresholding LMS is implemented in a hardware-efficient manner, offering cost advantages over a weighted-LMS alternative. Additionally, the invention uses a unique phase-feedback architecture to eliminate the effects of phase wrapping, and avoid the need to refine channel estimates during packet reception.

The invention provides an OFDM-IM system frequency offset estimation method. The method comprises the steps of S1, using a two-step method to perform preliminary frequency offset compensation on a receiving signal that is subjected to non-uniform frequency offset: 1, resampling and down-converting; and 2, performing unified compensation on the residual frequency offset (epsilon), wherein the sum of energy for using null sub-carriers used in the sub-step 2 is used as a cost function, a preliminary estimated value of the epsilon is acquired via one-dimensional search, and preliminary compensation is performed; S2, estimating a non-activated sub-carrier position in an OFDM-IM system by using the preliminarily compensated signal; and S3, endowing each estimated sub-carrier with a certain weight, adding the energy of the estimated sub-carriers into the cost function according to the different weights, performing the one-dimensional search on the epsilon to acquire a final estimated value ofthe epsilon, and performing compensation once more. According to the method provided by the invention, the sub-carriers using the OFDM-IM are partially activated. It means that the energy of the non-activated sub-carriers can still be used besides the preliminarily set null sub-carriers. Therefore, the estimation of Doppler frequency shift is optimized by using the non-activated sub-carriers.

The invention provides a method and a device for processing uplink frequency offset of a communication system. The method at a base station side comprises the following steps: demodulating a random access message sent by a terminal, obtaining an initial Doppler frequency offset of the terminal and sending the initial Doppler frequency offset to the terminal; receiving an uplink sub-frame signal sent by the terminal, estimating a Doppler residual frequency offset of the terminal in the uplink, obtaining a frequency adjustment amount according to the Doppler residual frequency offset and transmitting the Doppler residual frequency offset to the terminal. The method on the terminal side comprises the following steps: receiving the initial Doppler frequency offset transmitted by the base station, obtaining the initial transmission frequency of the uplink and transmitting the uplink sub-frame signal according to the initial transmission frequency and the initial Doppler frequency offset ofthe downlink; receiving the frequency adjustment amount transmitted by the receiving base station, and obtaining the transmission frequency of the next uplink according to the frequency adjustment amount. By compensating the uplink at the terminal, the invention reduces the pressure of frequency offset estimation at the base station side to the maximum extent, and can improve the demodulation performance of the base station.

The invention discloses an auxiliary synchronizing channel transmission method of full-area multi-beam satellite LTE. The method includes a time frequency structure of an S-SCH and a sub-carrier mapping mode of a frequency domain SSS sequence, sixth and seventh OFDM symbols of the S-SCH in the number zero time slot and the number ten time slot in a time domain, and seventy-two sub-carriers of the S-SCH in the center of a system downlink transmitting bandwidth in a frequency domain, wherein DC sub-carriers are not included. According to the method, interference of S-SCHs of different satellites in a full-area multi-beam satellite LTE system is avoided, the cell search performance is improved, and quick cell searching is achieved. Meanwhile, by means of the S-SCH transmission scheme, estimation of residual frequency offset is convenient to achieve.

A method of determining a residual frequency offset between a transmitter and a receiver in a transmission of data via a communication channel, is described, wherein the message is transmitted from the transmitter to the receiver via the communication channel and the message comprises at least one short preamble (201), at least one long preamble (202) and user data (203). The at least one long preamble (202) comprises residual frequency offset determination information based on which the residual frequency offset is determined.

A residual frequency offset compensation apparatus is provided. The residual frequency offset compensation apparatus includes: a basic phase offset compensation unit compensating input symbols using a previously stored basic phase offset and generating first symbols; a phase shift calculation unit calculating a phase shift value of each of a predetermined number of the first symbols using first detection symbols and the first symbols, the first detection symbols being generated by detecting the first symbols; a phase shift compensation unit compensating the first symbols based on an average of the phase shift values; and a basic phase offset update unit updating the basic phase offset based on the phase shift values.

A method and apparatus for processing a radio frequency signal. The method includes compensating a digital in-phase signal and a digital quadrature signal for any imbalance; converting the compensated digital in-phase signal and the compensated digital quadrature signal into a frequency domain digital OFDM symbol; generating a plurality of channel estimates, wherein each channel estimate corresponds to an estimate of the channel for a corresponding sub-carrier of the frequency domain digital OFDM symbol; and generating (i) a most likely estimate of the imbalance between the digital in-phase signal and the digital quadrature signal and (ii) a most likely estimate of a common phase error in the plurality of channel estimates. The most likely estimate of the imbalance is used to compensate the digital in-phase signal and the digital quadrature signal, and the most likely estimate of the common phase error is used to compensate the plurality of channel estimates.

Improved performance, particularly gain in signal-to-noise ratio (SNR), in high-bandwidth Orthogonal Frequency Division Multiplexing (OFDM) receivers, software and systems is achieved by compensating channel estimates not only for carrier frequency offset and phase noise, but also for interference caused by sample phase jitter. At high bandwidths, e.g., using 256 quadrature amplitude modulation (QAM) symbol constellation, significant SNR improvement is gained by determining and applying a corresponding compensation to each data sub-carrier channel, the compensation preferably including a term that increases linearly with the sub-carrier index.

The invention relates to a method and a sytem for estimating residual fractional frequency offset. The method comprises the following steps: residual frequency offset computing, Doppler estimation and accumulation; according to the difference of a dispersed pilot frequency module value and a dispersed pilot frequency phase angle, obtaining a residual frequency offset estimation value of maximum and minimum borders so as to eliminate a distortion point and a phase spill point caused by a dynamic multi-path channel; during the catching state of the Doppler estimation, reducing a border value through adding a decay factor in each time slot; judging whether to unlock according to the frequency offset border update quantity wherein the decay is not carried out under a locked state; and during the accumulation, accumulating OFDM symbols and the output of the each-time Doppler estimation to be compensated to a time domain end. In the residual fractional frequency offset estimation method disclosed by the invention, the processing of the Doppler frequency offset is increased, the influence of the Doppler frequency offset to a system is reduced, therefore, the residual fractional frequency offset in the dynamic multi-path channel can be accurately estimated, and the accuracy of the residual fractional frequency offset estimation and the stability of the system are improved.

A residual frequency offset (RFO) compensation method and a compensation system of a multi-carrier communication system is disclosed. The compensatory method of present invention includes two phase-computation steps. The first phase-computation step processes a phase variation of an OFDM data symbol each time to obtain a RFO estimation for compensating a demodulation carrier. The second-phase computation processes a plurality of OFDM data symbols each time to obtain a RFO estimation for compensating the demodulation carrier. The compensation system of the present invention includes: a Discrete Fourier Transformation (DFT) unit for performing DFT on receiving OFDM packages; a phase variation detector connecting to the DFT unit for detecting phase variations of a plurality of OFDM data symbols; and a residual frequency offset compensator connecting to the phase variation detector, which generates the desired RFO estimations in accordance with the phase variations of the plurality of OFDM data symbols and the compensation method of the present invention.

The invention discloses an outer radiation source radar direct wave suppression method being suitable for WiFi. The outer radiation source radar direct wave suppression method being suitable for WiFiincludes the steps: by means of a least square channel estimation algorithm and an FIR filter, obtaining each subcarrier channel estimation value, and extracting each subcarrier channel estimation phase; by means of a pilot signal, extracting the residual frequency offset phase, and combined with each subcarrier channel estimation phase, obtaining the residual phase of each subcarrier channel; performing one time of curve fitting by means of each subcarrier residual phase to estimate fractional times of delay of the direct wave; through three times of batten interpolation and fractional timesof delay displacement of the direct wave, obtaining a reference signal after correction of time delay; and suppressing the direct wave of the monitoring signal by means of an expansion cancellation batch processing algorithm. Compared with the prior art, the outer radiation source radar direct wave suppression method being suitable for WiFi can improve the direct wave suppression performance of the monitoring channel, is conductive to target detection of a radar system, and is simple in the implementation method.

A technique to provide frequency offset estimation for packets transmitted during a service period allocated strictly for designated source and destination devices. The destination device obtains coarse and fine frequency offset estimation from the short and long preambles. A residual frequency offset is tracked for the data blocks and combined with the coarse and fine frequency offset to obtain a total frequency offset to apply to the data blocks. The total frequency offset value at the end of the first packet is saved and, instead of again estimating the coarse and fine frequency offset values with the short and long preambles of the second packet, the saved total frequency offset value is used as the initialization value to add to the residual frequency offset in the second packet. The saved offset value at the end of each packet becomes the initialization value for the subsequent packet.

A method of determining a residual frequency offset between a transmitter and a receiver in a transmission of data via a communication channel, is described, wherein the message is transmitted from the transmitter to the receiver via the communication channel and the message comprises at least one short preamble (201), at least one long preamble (202) and user data (203). The at least one long preamble (202) comprises residual frequency offset determination information based on which the residual frequency offset is determined.

The invention discloses a synchronous equalizing method in a high speed data transmission system. The method comprises the steps of: step 1, estimating and compensating a large frequency offset of a digital baseband signal; step 2, performing timing synchronization to the signal, the large frequency offset of which is compensated; locating an optimal sampling time; step 3, performing carrier synchronization by using a decision directed algorithm to realize residual carrier frequency offset estimation; before feeding carrier frequency offset information back to a timing synchronization module, realizing residual frequency offset compensation correction; and step 4, performing adaptive blind broadband balance to the synchronized signal by using a CAM (Constant Modulus Algorithm). By adoption of the method provided by the technical scheme of the invention, the bit error rate and the demodulation loss are reduced.