927 results about "Carrier frequency offset" patented technology

Disclosed is a method, a computer program product and a device that includes a receiver for receiving a downlink signal transmitted into a cell. The receiver is operable to obtain time, carrier frequency and cell-specific preamble synchronization to the received signal and includes a plurality of synchronization units that include a first detector to detect a frame boundary using preamble delay correlation; a second detector to detect the frame boundary with greater precision using a conjugate symmetry property over a region identified by the first detector; a cyclic prefix correlator to resolve symbol boundary repetition; an estimator, using the cyclic prefix, to estimate and correct a fractional carrier frequency offset; an operator to perform a Fast Fourier Transform of an identified preamble symbol and a frequency domain cross-correlator to identify cell-specific preamble sequences and an integer frequency offset in sub-carrier spacing. The transmitted signal may be a downlink signal transmitted into the cell from a base station that is compatible with IEEE 802.16e (WiMAX).

A method of wireless transmission for estimating the carrier frequency offset in a base station of a received transmission from a user equipment (UE) accessing a radio access network. The method time de-multiplexes selected symbols of a received sub-frame, computes the frequency-domain symbols received from each antenna through an FFT, de-maps the UEs selected sub-carriers for each antenna, computes metrics associated to a carrier frequency offset hypothesis spanning a searched frequency offset window, repeats these steps on subsequent received sub-frames from the UE over an estimation interval duration, non-coherently accumulates the computed metrics and selects the carrier frequency offset hypothesis with largest accumulated metric amplitude.

A communications system includes a multiple-input / multiple-output (MIMO) architecture for high capacity switched mesh networks. The MIMO architecture has a plurality of radio frequency chains. One of the plurality of radio frequency chains is configured to apply a first frequency offset to a base frequency of an output signal to generate a first transmitting frequency; and another of the plurality of radio frequency chains being configured to apply a second frequency offset to the base frequency to generate a second transmitting frequency. The system uses the carrier frequency offset to lock the clock of the master subsystem to the clock of the slave subsystem, thereby enabling bandwidth expansion to be employed on the MIMO data streams.

A method and system for communication of information in OFDM format are disclosed. The method employs multi-symbol encapsulation (MSE), wherein multiple OFDM symbols are grouped together in cyclic frames having a single cyclic guard portion, for example a cyclic prefix, with multiple OFDM symbols sandwiched between each two consecutive cyclic guard portions. All OFDM symbols of one frame are equalized together at the receiver in a frequency domain using a single DFT / IDFT operation sequence. Embodiments of the MSE OFDM system are disclosed enabling high bandwidth efficiency, high tolerance to carrier frequency offset and low peak-to-average power ratio.

An Orthogonal Frequency Division Multiplexing (OFDM) receiver that employs N second-order phase-lock loops sharing a common integrator (where N is the number of pilots in the system). The N second order phase-lock loops track out independent pilot phase rotations to facilitate the constructive averaging of the pilots' phase information. At the same time, by sharing a common integrator, the OFDM receiver takes advantage of noise averaging over multiple pilots to obtain a cleaner frequency offset estimation. The OFDM receiver may also compensate for FFT window drift by calculating a phase difference between a selected pair of pilots and tracking the rate of change of the calculated phase difference over time. The calculated phase difference is used to control the position of an upstream FFT window after a predetermined phase difference threshold is exceeded. The tracked rate of change is used to continuously adjust the phase of downstream equalizer taps.

A hybrid carrier frequency offset estimator that uses data-aided and non-data-aided signal processing techniques to produce multiple candidates for the carrier frequency offset within a return channel receiver in a DVB-RCS system using turbo coding and quadrature phase shift keying (QPSK) data modulation. In this system, the invention is employed to estimate signal distortion caused by carrier frequency offset so that this particular source of signal distortion can be removed to improve the ability of the receiver to maintain synchronization in low signal-to-noise conditions. This, in turn, allows the receiver to meet the DVB-RCS performance target, measured in terms of packet loss ratio, in low signal-to-noise ratio conditions and in particular for burst-mode data transmission with a short data packet size.

The present disclosure provides a method of carrier phase error removal associated with an optical communication signal. The method includes estimating and removing a first phase angle associated with an information signal using coarse phase recovery, the information symbol being associated with a digital signal, the digital signal representing the optical communication signal; estimating a carrier frequency offset between a receiver light source and a transmitter light source by using the estimated first phase angle, the carrier frequency offset being associated with the information signal; removing carrier phase error associated with the carrier frequency offset; and estimating and removing a second phase angle associated with the information signal, the estimated second phase angle being based on the estimated first phase angle and the estimated carrier frequency offset.

Disclosed is an apparatus and method for compensating for frequency offset in a wireless communication system using an OFDM system which can compensate for phase change due to carrier frequency offset and sampling frequency offset of data carried on subcarriers. The apparatus includes an FFT window adjustment unit for receiving sampling data when a packet is received, setting a start point of a FFT window at a start point of long training symbols and adjusting a position of the FFT window according to an input window adjustment value, an FFT unit for receiving an output of the FFT window adjustment unit, transforming time-domain symbols into frequency-domain symbols and calculating FFT coefficients, a channel estimation unit for receiving the coefficients from the FFT unit, estimating a channel state and outputting a value for compensating for an estimated value, a channel compensation unit for compensating for the frequency-domain symbols using the output of the channel estimation unit and a phase error tracking and correction unit for receiving an output of the channel compensation unit, detecting a sampling frequency offset and a phase change of a carrier signal and outputting the window adjustment value to the FFT window adjustment unit.

A receiver and a method for receiving a signal comprising a carrier modulated with a known training sequence is described in which an estimate a carrier frequency offset is obtained from an autocorrelation signal by autocorrelation of the part of the received signal containing a known training sequence. The received signal is compensated with the frequency offset obtained to form a compensated received signal, and a timing reference for the received signal is obtained by cross-correlation of the compensated received signal with a known training sequence.

Disclosed is a method, a computer program product and a device that includes a receiver for receiving a downlink signal transmitted into a cell. The receiver is operable to obtain time, carrier frequency and cell-specific preamble synchronization to the received signal and includes a plurality of synchronization units that include a first detector to detect a frame boundary using preamble delay correlation; a second detector to detect the frame boundary with greater precision using a conjugate symmetry property over a region identified by the first detector; a cyclic prefix correlator to resolve symbol boundary repetition; an estimator, using the cyclic prefix, to estimate and correct a fractional carrier frequency offset; an operator to perform a Fast Fourier Transform of an identified preamble symbol and a frequency domain cross-correlator to identify cell-specific preamble sequences and an integer frequency offset in sub-carrier spacing. The transmitted signal may be a downlink signal transmitted into the cell from a base station that is compatible with IEEE 802.16e (WiMAX).

A system and method estimates symbol timing of long training symbols and coarse carrier frequency offset in an orthogonal frequency division multiplexing receiver of a wireless local area network. The system and method estimates the symbol timing and coarse carrier frequency offset during short training symbols of a preamble of a data packet. Fine carrier frequency offset is estimated during long training symbols. Channel estimates during a data portion of the data packet are adapted.

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.

A system and method are provided for carrier frequency offset (CFO) and Doppler frequency estimation and correction for Orthogonal Frequency-Division Multiple Access (OFDMA) and Single Carrier-Frequency-Division Multiple Access (SC-FDMA) signals in a wireless communications receiver. The receiver is capable of accepting a plurality of multicarrier signals transmitted simultaneously from a plurality of transmitters, with overlapping carrier frequencies and orthogonal reference signals. For each multicarrier signal, a channel estimate is performed and the channel is equalized. Then, a frequency offset is estimated between the transmit carrier frequency of each multicarrier signal and a receiver local oscillator frequency using either the phase rotation of data constellations as a function of time or the phase rotation of channel estimates as a function of time. The receiver supplies the CFO / Doppler frequency estimates and corrects the equalized symbols prior to demodulation.

A method for estimating symbol timing of a guard interval in an orthogonal frequency division multiplexing receiver of a wireless local area network comprises receiving a preamble including a plurality of short training symbols; sampling said short training symbols of said preamble at a first rate; correlating a first short training symbol with a second short training symbol that is adjacent to said first short training symbol and generating a correlation signal; normalizing said correlation signal to generate a normalized correlation signal; and calculating a mean absolute difference of said normalized correlation signal.

A device for signal synchronization in a communication system, the device comprising a first detector configured to perform a first sliding correlation for a received signal and a pseudo-random noise (PN) sequence to obtain information on symbol timing, a second detector configured to identify a fractional carrier frequency offset (FCFO) using the information on symbol timing and the cyclic extension property of the PN guard interval (GI), a first multiplier configured to provide a first product by multiplying the received signal with the FCFO, and a third detector comprising a set of second multipliers configured to provide a set of second products by multiplying the first product with each of a set of phases related to integral carrier frequency offsets (ICFOs), a set of sliding correlators each being configured to perform a second sliding correlation for the PN sequence and one of the set of the second products, the set of sliding correlators providing a set of peak values, and a peak detector configured to identify an ICFO by detecting an index number of a maximal value among the set of peak values.

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 system and corresponding method for the concurrent operation of multiple radar systems on a common frequency and in the same geographical area includes a waveform generator that specifies certain operating parameters for the transmitted radar pulses. In a first instance, the carrier frequency can include an offset for each radar system. In a second instance, complementary codes can be used for the radar pulses such that each radar system operates with a unique code for substantially reducing the cross-talk between the radar systems. In another instance, both carrier frequency offset and complementary coded waveforms can be used to increase the number of radar systems that operate concurrently. Carrier frequency offset can also be used to combat range-wrap by using different carrier frequencies for adjacent radar pulses.

A symbol detector for an OFDM receiver determines the correlation of corresponding samples of at least two received preamble symbol samples, one of the samples delayed a predetermined duration with respect to the other; determines a timing metric based on the correlation results; detects multiple peaks in the timing metric; indicates a symbol detection based on the multiple peaks detected in the timing metric; and gets a refined CFO estimation using averaging the phase information across these multiple peaks.

An apparatus and method for carrier frequency synchronization in an Orthogonal Frequency Division Multiplexing (OFDM) system are provided for correcting an initial carrier frequency offset in the OFDM system. A metric generator for frequency estimation performs a first accumulation process for a value computed by multiplying a Phase Reference Symbol (PRS) generated from a reception stage by a Fast Fourier Transform (FFT) output signal for an OFDM symbol in a PRS position within a frame, acquires a differential symbol from a product of adjacent FFT output symbols, performs a second accumulation process for a real part extracted from the differential symbol, and outputs a metric value for the frequency estimation. A maximal value-related index generator compares metric values for initial frequency estimation within a predetermined frequency offset estimation range, and selects and outputs a maximal metric value as a frequency offset estimate.

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.

Provided are a method and apparatus for uplink carrier frequency synchronization and antenna weight vector estimation in an Orthogonal Frequency Division Multiple Access System (OFDMA) having a smart antenna. The inventive method comprises the steps of receiving and storing training symbols in the time domain transmitted to estimate an antenna weight vector during a training symbol transmission interval; estimating carrier frequency offsets using training symbols in the frequency domain that are obtained by performing a Fast Fourier Transformation (FFT) algorithm with respect to the training symbols received during the training symbol transmission interval; compensating the stored training symbols in the time domain based on the estimated carrier frequency offsets; and estimating an antenna weight vector using training symbols in the frequency domain that are obtained by applying an FFT algorithm with respect to the training symbols in the time domain derived by compensating the carrier frequency offsets during the training symbol transmission interval.

While a clock generated by a built-in clock generator is used as a reference signal for determining a carrier frequency of a transmit signal, carrier frequency synchronization is achieved between base stations. A base station device is configured to perform wireless communication with a terminal device. In the base station device, accuracy of a carrier frequency of an OFDM signal is affected by accuracy of a clock frequency generated by a built-in clock generator 18. The base station device receives an OFDM signal transmitted from another base station device while transmission to the terminal device is stopped, estimates a carrier frequency offset of the OFDM signal, and corrects a carrier frequency of an OFDM signal to be transmitted to the terminal device.

Methods and apparatus for estimating and correcting carrier frequency offsets in a bust multi-tone receiver are described. Course and fine carrier frequency estimates are generated from the signal's preamble. Decision directed carrier frequency offset estimates are then generated from the signal field and data fields of the multi-tone signal. Frequency error estimates are generated for each tone of the signal and combined using a weighted average to generate the frequency error estimate used to perform the correction operation. Error estimates corresponding to noisy data tones are weighted less then estimates corresponding to less noisy data tones. In cases of low SNR frequency error estimates corresponding to pilots are weighted by an extra amount as compared to error estimates corresponding to tones used to transmit data symbols. During times of high SNR error estimates corresponding to pilot tones are weighted in the same manner as error estimates corresponding to data tones.

A method and apparatus for signal acquisition in an OFDM receiver relies on a preamble training sequence to synchronize the receiver in time (e.g. determining the start of a frame) and in frequency (carrier frequency offset compensation). The preamble training sequence has a periodic structure and the method and apparatus perform a cross-correlation technique using a matched filter to achieve time synchronization and / or frequency synchronization and / or channel estimation, the latter being especially useful in multi-antenna receivers for diversity combining purposes. Many advantages derive from performing at least two and preferably all three operations jointly, in terms of latency, hardware complexity, and length of training sequence required to achieve satisfactory convergence on all counts. The periodicity of the training sequence is exploited to reduce considerably the main filter complexity and optionally dynamically adjust carrier offset compensation throughout the filtering process, thus improving the quality of all final estimates (carrier frequency offset, time synchronization, and channel).

A receiver and a method for receiving a signal including a carrier modulated with a known training sequence is described in which an estimate a carrier frequency offset is obtained from an autocorrelation signal by autocorrelation of the part of the received signal containing a known training sequence. The received signal is compensated with the frequency offset obtained to form a compensated received signal, and a timing reference for the received signal is obtained by cross-correlation of the compensated received signal with a known training sequence.

An UKF based channel and carrier wave frequency shift estimation method in OFDM system is applied in the technique field of wireless transmission. Said channel estimation method starts from a frequency domain, to get cursory estimated values at pilot channels firstly by using a LS method, and then to get accurate estimated values by utilizing path capturing method and UKF method in time domain. According to the UKF based carrier wave frequency shift estimation method in OFDM system in accordance with the present invention, wave frequency shift is estimated in time domain through UKF filtering method, and then ICI is eliminated through carrier wave frequency shift correction. Aiming at OFDM system in which disturbances between sub-carriers exist and which passes through time-varying wireless channel, the present invention further provides an UKF based channel and carrier wave frequency combination estimation method which is capable of eliminating ICI and improving veracity of channel estimation and exhibits excellent astringency and robustness by utilizing specific pilot frequency structure and convolutional change forms of a matrix.

A technique to determine carrier frequency offset (CFO) 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 CFO phase shift that is flat across tones of an OFDM signal is experienced between preambles of the two time blocks. Upon detection of the CFO phase shift, a weighting matrix used for channel estimation is modified to account for the CFO phase shift, in order to perform the channel estimation with correction for the CFO phase shift.

The invention discloses a method for estimating pulse noise in an OFDM (Orthogonal Frequency Domain Multiplexing) underwater acoustic communication system. At a receiving end, sparse estimation is performed on pulse noise on an OFDM signal in an underwater acoustic channel transmission process according to a frequency domain signal subjected to redundant Doppler frequency shift compensation, and frequency offset compensation is performed on the frequency domain signal subjected to the redundant Doppler frequency shift compensation with void subcarriers. Under the consideration of mutual interference between the pulse noise and a carrier frequency offset in underwater acoustic communication, compensation of the carrier frequency offset is added in an iteration process while the pulse noise is estimated with all subcarriers and a posteriori distribution under a framework of conventional sparse Bayesian learning, and the frequency domain signal subjected to the redundant Doppler frequency shift compensation and a measurement diagonal matrix for estimating the pulse noise are updated continuously in order to lower influences between the two types of interference. Moreover, the pulse noise is estimated by full utilization of all the subcarriers in the method, so that the spectrum efficiency and the performance of the communication system are improved.

The present invention relates to an apparatus and method for estimating and compensating for a time offset and a carrier frequency offset in a Multiple Input Multiple Output (MIMO) communication system that supports Orthogonal Frequency Division Multiplexing (OFDM) or Orthogonal Frequency Division Multiplexing Access (OFDMA). According to the present invention, a phase difference of pilot signals of the same transmitting antenna, which are received through receiving antennas, is calculated. An arc tangent operation is then carried out on the phase difference of the pilot signals to calculate a time offset linear phase and / or a carrier frequency offset linear phase. Further, a time offset compensation value and / or a carrier frequency offset compensation value are found by employing the time offset linear phase and / or the carrier frequency offset linear phase. A time offset and / or a carrier frequency offset with respect to pilots and data are compensated for by employing the time offset compensation value and / or the carrier frequency offset compensation value.

An embodiment of the present invention includes a method for generating a training sequence for joint frame synchronization and carrier frequency offset estimation and a communication system and method using the training sequence. In one embodiment, the training sequence includes a first training symbol and a second training symbol of equal-length, but without a cyclic prefix (CP). One embodiment of the method for generating the training sequence includes generating the first training symbol randomly according to a method for generating normal data symbols; subdividing the generated first training symbol logically into M sub-blocks with equal-length, wherein the structure characteristic M is a natural number larger than or equal to 1 and less than or equal to N; and copying the M sub-blocks in an reverse order to form the second training symbol, which together with the first training symbol constitute the training sequence.