4653 results about "Frequency offset" patented technology

A pipelined digital data receiver for a cable TV headend which is capable of receiving DOCSIS 1.0 or 1.1 or advanced PHY TDMA or SCDMA bursts having programmable symbol rates and programmable modulation types as well as a host of other burst parameters such at Trellis code modulation on or off, scrambling on or off, various values for Reed-Solomon T number and codeword length. The receiver has an RF section to filter and digitize incoming RF signals. It also has an input section to detect impulse noise and do match filtering and despread SCDMA bursts. A timing recovery section recovers the symbol clock and detects the start of bursts and collisions. A rotational amplifier and equalizer calculate and track gain, phase and frequency offsets and correct symbols and calculates equalization coefficients. A decoder section decodes TCM and non TCM bursts, and a Reed-Solomon decoder section reconstructs RS codewords and uses them to error correct the payload data.

A system and method for synchronizing a local clock to a reference clock using a linear model of the error between the local clock and the reference clock is disclosed. In one embodiment, a direct smoothing process is used in conjunction with the linear model to estimate a frequency offset by which the frequency of an oscillator of the local clock is adjusted. Also disclosed herein is a phased-lock loop (PLL) adapted to synchronize a local clock with a reference clock using the direct smoothing process, as well as a system implementing the PLL for timing the playout of data received from a transmitter.

Timing synchronization between base stations of uncoordinated communication networks includes obtaining timing synchronization information from one base station, and adjusting a clock of the other station in response to the synchronization information. The timing synchronization information can be identified from a strongest synchronization signal from nearby uncoordinated base stations. The timing synchronization can accommodate clock offsets and frequency offsets.

A system and method are described for compensating for frequency and phase offsets in a multiple antenna system (MAS) with multi-user (MU) transmissions (“MU-MAS”). For example, a method according to one embodiment of the invention comprises: transmitting a training signal from each antenna of a base station to one or each of a plurality of wireless client devices, one or each of the client devices analyzing each training signal to generate frequency offset compensation data, and receiving the frequency offset compensation data at the base station; computing MU-MAS precoder weights based on the frequency offset compensation data to pre-cancel the frequency offset at the transmitter; precoding training signal using the MU-MAS precoder weights to generate precoded training signals for each antenna of the base station; transmitting the precoded training signal from each antenna of a base station to each of a plurality of wireless client devices, each of the client devices analyzing each training signal to generate channel characterization data, and receiving the channel characterization data at the base station; computing a plurality of MU-MAS precoder weights based on the channel characterization data, the MU-MAS precoder weights calculated to pre-cancel frequency and phase offset and/or inter-user interference; precoding data using the MU-MAS precoder weights to generate precoded data signals for each antenna of the base station; and transmitting the precoded data signals through each antenna of the base station to each respective client device.

A transmitter is provided having transmission methods that minimize the power needed to ensure reliable reception in a coverage area. In one aspect, data that requires re-transmission as acknowledged mode data is re-transmitted when the power level of the transmission link is higher than a pre-determined level set for reliable reception. The data rate of the re-transmitted data is set according to the difference in the actual power and the pre-determined level. In a second aspect, two transmitting antennae are used to transmit the same signals with a frequency off-set. The frequency off set can be used to determine the phase of the signals being received at the receiver, so that a phase off-set can be introduced to optimise the effect of interference at the receiver.

Systems and methods for receiving an OFDM preamble without knowledge of channel characteristics are provided. An OFDM preamble signal with frequency shifted cyclic extensions is received. Taken together the cyclic extensions form a frequency shifted version of the OFDM preamble signal. Frequency offsets and timing offsets are estimated and corrected in an efficient manner using a simple concatenation approach in the time domain, followed by a summation of the OFDM preamble signal and the concatenation after a transformation of the OFDM preamble and the concatenation into the frequency domain. Phase errors in the frequency domain are estimated and corrected after FFT transformations of the received signals. A valid preamble is detected and additional parameters for receiving subsequently transmitted OFDM symbols in a channel are extracted from the OFDM preamble. The methods are computationally efficient and robust. Receiver implementations for performing the methods in a DVB receiver are disclosed.

Methods and systems for processing communication signals in an Orthogonal Frequency Division Multiple Access (OFDMA)-Passive Optical Network (PON) are disclosed. An optical carrier at a wavelength generated at an optical line terminal (OLT) may be reused by optical network units (ONUs) in the network for upstream transmission of data signals to the OLT. In addition, each ONU may perform carrier suppression to avoid broadband beating noise resulting from the simultaneous transmission of upstream data signals on the same wavelength. Further, the optical source at the OLT used to generate the optical carrier may be reused as a local oscillator for coherent detection of received upstream signals to minimize any frequency offsets.

A digital receiver, that may be used to receive VSB/QAM digital television signals, includes an adaptive fine carrier recovery circuit that compensates for deviations in the carrier frequency or phase. The carrier recovery circuit de-rotates a signal including phase errors. Estimations of phase errors are filtered using a filter whose gain and bandwidth are adjusted adaptively. This allows the carrier recovery circuit to track phase/frequency offset without introducing significant jitter. In one embodiment, the receiver includes a DFE, and the adaptive carrier recovery circuit mitigates instability that might be associated with the DFE.

A direct sequence spread spectrum receiver samples an incoming signal and stores the sample in memory. Prior to sampling and storage, the incoming signal is translated to an IF signal. Also prior to storage, the IF signal is corrected for a frequency offset signal. The frequency offset may be caused by many sources, Doppler shift or local oscillator error, for example. Once the signal is corrected for the frequency offset, the signal sample is stored in memory. The signal sample is read from memory as necessary to process the signal. Such a receiver is useful in global positioning satellite (GPS) signal processing where the incoming signal contains several satellite transmissions encoded with CDMA encoding.

A novel antenna system for receiving transmissions in the VHF and UHF frequency bands particularly suitable as a miniaturized antenna for UHF reception, such as of digital video broadcasting transmissions. The antenna system utilizes a combination of three techniques including (1) the use of dialect loading using a high dielectric constant ceramic substrate; (2) an antenna dielectrically loaded and tuned to a significantly higher frequency than desired; and (3) use of a tuning circuit to compensate for the frequency offset of the antenna thereby shifting the resonant frequency to cover the entire band. The antenna is intentionally designed to be too small to radiate at the frequency of interest. The antenna element is then ‘forced’ to be tuned to the desired lower frequency using passive (or active) reactive components as part of a tuning circuit. Multi-band operation is achieved by providing a bypass switch to connect the antenna element either to (1) a first receiver without the tuning circuit (i.e. high frequency tuning) or (2) a second receiver with the tuning circuit (i.e. low frequency tuning).

The present invention includes novel techniques, apparatus, and systems for optical WDM communications. Various wavelocker apparatus and methods are disclosed that measure the frequency offsets between signal lasers and reference lasers. The measured offsets are used to adjust the signal laser frequencies to meet their target frequencies. The absolute accuracy of the reference laser frequency is improved by measuring the absorption of the reference laser by a gas cell with known fixed absorption lines versus the reference laser frequency. Apparatus and methods are disclosed to cover scenarios in which the reference laser polarization is aligned with the signal lasers, as well as those in which the reference laser polarization is not aligned with the signal lasers. The wavelocker apparatus may or may not be located at the same network site as the signal lasers.

A method and apparatus for detecting and synchronising packets of data with a repeated sequence as a pilot symbol received by a communications system are provided. The method and apparatus include receiving data, detecting a packet within the received data, producing an estimate of the time-varying frequency offset of the received data, estimating the start of the packet of the received data, estimating the time-varying phase offset of the received data and estimating the time-varying time offset of the received data. Methods for assessing each one of the time-varying frequency offset, the time-varying phase offset, the time-varying time offset and the start of packet are also provided.

In a cellular mobile telecommunications system the position of a mobile station can be estimated in terms of its bearing and range from a cell site. A multi-element direction finding antenna at the cell site receives signals from the mobile station and a receiver circuit estimates the bearing using the relative phase of signals received at different antenna elements and estimates the range by measuring round trip delay of signals to and from the mobile station. Motion of the mobile station can introduce errors into the bearing estimate due to frequency offset and frequency spread when element sampling is non-simultaneous. Compensation for these errors is introduced by using signal samples successively received at the same antenna element to estimate Doppler frequency offset and spread. It is necessary to ensure accurate calibration of the direction finding antenna and the receiver circuit. This is done by injecting calibration signals into the circuit near the antenna or into the antenna itself from a near field probe. Other aspects of calibration, such as antenna position, are calibrated using a remote beacon. A beacon emulating a mobile station but at a fixed, known location, or a beacon at an adjacent cell site may be used.

This disclosure describes methods and systems for stationary user detection in a hybrid location system. In some embodiments, the method for determining whether a satellite enabled device is stationary by measuring the Doppler frequency of received satellite signals can include acquiring satellite measurements from at least two satellites, wherein the satellite measurements include Doppler frequency measurements, acquiring a rough estimate of location of the satellite enabled device and calculating an internal frequency offset of satellite enabled device.

A DTV receiver includes a tuner, an information detector, a demodulator, and a channel equalizer. The tuner receives a broadcast signal including valid data in which a known data sequence is periodically repeated. The information detector detects location information of the known data sequence and a coarse frequency offset value of the broadcast signal. The demodulator demodulates the broadcast signal by estimating a fine frequency offset value using the detected location information and by compensating a frequency offset of the broadcast signal using the course and fine frequency offset values. Finally, the channel equalizer compensates channel distortion of the demodulated signal using the detected location information.

A digital television (DTV) receiving system includes an information detector, a resampler, a timing recovery unit, and a carrier recovery unit. The information detector detects a known data sequence which is periodically inserted in a digital television (DTV) signal received from a DTV transmitting system. The resampler resamples the DTV signal at a predetermined resampling rate. The timing recovery unit performs timing recovery on the DTV signal by detecting a timing error from the resampled DTV signal using the detected known data sequence. The carrier recovery unit performs carrier recovery on the resampled DTV signal by estimating a frequency offset value of the resampled DTV signal using the detected known data sequence.

A digital television (DTV) receiving system includes an information detector, a timing recovery unit, a carrier recovery unit, and a phase compensation unit. The information detector detects position information of a known data sequence periodically repeated in a DTV signal and estimates an initial frequency offset value. The timing recovery unit performs timing recovery on the DTV signal by detecting timing error information from the DTV signal using the position information. The carrier recovery unit performs carrier recovery on the DTV signal using the position information. The phase compensation unit compensates a phase offset of the DTV signal using the position information.