L-3 Communications Titan Corporation

Wi-lan Inc.

L-3 Services, Inc.

John Wiss

Timothy Leo Gallagher

Yair Bourlas

Sheldon I Gilbert

Frederick Wales Price

Blaine Clifford Readler

Stephen C Pollmann

Pranesh Sinha

Sharon Akler

Eli Arviv

Yuhui Marie Ren

Omer Acikel

Timothy Lyle Blalock

Ell Arviv

Apparatus, system and method for synchronizing one or more clocks across a communication link. A slave clock may be synchronized to a master clock by means of a synchronization signal sent from the master to the slave clock side of the link. The synchronization signal may be an expected signal pattern sent at intervals expected by the slave side. The slave clock may correlate received signals with a representation of the expected synchronization signal to produce a correlation sample sequence at a first sample rate which is related as n times the slave clock rate. The synchronization signal receipt time indicated by the correlation sample sequence may be refined by interpolating the correlation sample sequence around a best correlation sample to locate a best interpolation at an interpolation resolution smaller than the sample resolution. The best interpolation may in turn be further refined by estimating between interpolator outputs adjacent to the best interpolation output. The synchronization signal receipt time thus determined is compared to the expected time based upon the slave clock, which is adjusted until the times match. After initialization, all slave clock errors are preferably accumulated to prevent long-term slip between the slave and master clocks. Formerly independent master and slave clocks synchronized across the communication link constitute a noncommon clock which may be compared on each side of the link to secondary independent clocks, and the secondary independent clocks may then be separately synchronized by adjusting one to have the same difference from its local noncommon clock as the secondary clock on the other side of the link has from its local noncommon clock.

Synchronizing clocks across a communication link

A communication signal including a plurality of bursts that individually include a plurality of data symbols is processed by both interleaving diversity and duplication diversity prior to transmission in order to preserve the content of the signal when the signal is corrupted by interference during transmission of the signal. A received communication signal having a plurality of bursts that individually include a plurality of data symbols which have been processed for transmission by interleaving diversity is processed to recover the content of the signal when the signal is corrupted by interference during transmission of the signal. Upon determining that the received communication signal may have been corrupted by interference during transmission, the received signal is processed by inserting erasure symbols into a deinterleaver prior to deinterleaving of the data symbols. The erasure symbols are necessary for recovering the content of the transmitted interleaved data symbols.

Preserving the content of a communication signal corrupted by interference during transmission

A slave clock may be synchronized to a master clock by means of a synchronization signal sent from the master to the slave clock side of the link. The synchronization signal may be an expected signal pattern sent at intervals expected by the slave side. The slave clock may correlate received signals with a representation of the expected synchronization signal to produce a correlation sample sequence at a first sample rate which is related as n times the slave clock rate. A best interpolation may in turn be further refined by estimating between interpolator outputs adjacent to the best interpolation output. The synchronization signal receipt time thus determined is compared to the expected time based upon the slave clock, which is adjusted until the times match. The best interpolation may in turn be further refined by estimating between interpolator outputs adjacent to the best interpolation output.

A receiver, which is adapted for demodulating signal carriers at variable frequencies to provide received signals at a plurality of different received frequencies, is calibrated to compensate for a frequency-dependent imbalance in the amplitude and/or the quadrature phase of analog in-phase (I) and quadrature (Q) received-signal components that have passed through receiver circuit paths that may cause such imbalance. I-channel and Q-channel Rx-correction coefficients for each of a plurality of different calibration frequencies are estimated and stored in a lookup table. Rx-correction coefficients for a calibration frequency or frequencies that are the same as or closest to the received frequency or frequencies are accessed from the lookup table and combined with digital I and Q components of received signals that have been provided by analog-to-digital conversion of analog I and Q components of received signals that have passed through the imbalance-causing receiver circuit paths upon demodulation at the received frequency.

Receiver and transmitter calibration to compensate for frequency dependent I/Q imbalance

A carrier frequency in a filtered received M-ary phase-shift keyed (MPSK) modulated signal having in-phase and quadrature components is detected by processing the filtered received signal to remove modulation components and thereby generate a test signal at the carrier frequency; processing the test signal to provide an amplitude spectrum of samples at different test frequencies; and processing the amplitude spectrum to detect the carrier frequency in accordance with the test frequency at which there is a test statistic of the highest magnitude. The magnitude of the test statistic is determined by processing a signal statistic in relation to a noise statistic. The signal statistic is the amplitude of the largest-amplitude sample. The filtered received signal is processed to provide approximate values of the modulus of the received signal and the phase of the received signal; and the approximate modulus and phase values are processed to generate the test signal.

Carrier frequency detection for signal acquisition

The preambles of narrow band signals and DSSS signals are prepared for compatible detection. The preamble is encoded by encoding a sequence of identical preamble blocks with sequentially corresponding code elements of a preamble encoding sequence. Each of the identical preamble blocks has the same predetermined pattern of code elements. When the signal is a DSSS signal, the preamble is a spread preamble in which each of the blocks has a number of code elements corresponding to a spread-factor multiple of the number of code elements in a block of an unspread preamble for a narrow band signal. The preambles of both types of received signals are detected by processing a metric representing detected coherent energy with a metric representing detected noncoherent energy, after first determining that the detected noncoherent energy is greater than the average energy of the received signal.

Compatible preparation and detection of preambles of direct sequence spread spectrum (DSSS) and narrow band signals

The tracking of the phase of a received signal having a known preamble is accomplished by the steps of: initializing a phase-locked loop in accordance with estimated phase parameters, which are generated during an estimation interval by processing samples of the known preamble; delaying the preamble; generating phase error parameters by processing samples of the delayed preamble; and training the phase locked loop by tracking the phase-tracked signal in accordance with the tracking error parameters during a training interval after the estimation interval. The timing of the sampling is likewise trained in a closed timing loop in accordance with timing error parameters generated during the training interval after the timing loop has been initialized by estimated timing parameters generated during the estimation interval. The duration of the delay of the preamble is one-half the duration of the estimation interval.

Tracking the phase of a received signal

One or more clocks are synchronized across a communication link using a synchronization signal sent from a master to a slave clock. The synchronization signal may be an expected signal pattern sent at intervals expected by the slave. The slave clock may correlate received signals with a representation of the expected synchronization signal to produce a correlation sample sequence at a first sample rate. The synchronization signal receipt time is compared to the expected time and the slave clock is adjusted until the times match. Master and slave clocks synchronized across the communication link constitute a noncommon clock which may be compared on each side of the link to secondary independent clocks. The secondary independent clocks may be separately synchronized by adjusting one to have the same difference from its local noncommon clock as the secondary clock on the other side of the link has from its local noncommon clock.

The signal-to-noise ratio of a demodulated received signal is estimated by measuring the error vector magnitude (EVM) of the demodulated signal; and processing the measured EVM in combination with a correction term to estimate the signal-to-noise ratio of the demodulated signal. The correction term is a polynomial function of the measured EVM. The signal-to-noise ratio is estimated in accordance with the formula: wherein {circumflex over (&#x3bc;)}is the measured EVM based on the mean of a Rayleigh density of EVM measurements; and C is the correction term.

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Carlsbad, CA, United States of America

John Wiss