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In constant bit-rate timing transfer, the reference clocks which encode and reconstruct the service clock at origin and destination may be jittered. We present new, straightforward approaches to finding and visualizing jitter spectra in timing transfer for jittered destination and reference clocks, and confirm our results by simulation. Index Terms--Jitter, nonuniform sampling, sigma-delta modulator, synchronization, synchronous residual time stamp (SRTS).

We analyze the acquisition time performance of the distributed sample acquisition (DSA) scheme recently proposed for a fast DS/CDMA signal acquisition. To analyze the composite acquisition mechanism, we first define several acquisition-related probability parameters which can describe all the essential events in the DSA synchronization, along with the basic states that constitute the eventual DSA state transition diagram. Then, we construct the state transition diagram employing these basic states and the moment generating functions which are entirely based on the above defined probability parameters. Applying this state transition diagram and determining the acquisition-related parameters, we finally analyze the mean acquisition time performance of the DSA. Index Terms - Distributed sample acquisition, distributed sample scrambling, igniter sequence.

In this paper we investigate the tracking performance of two maximum-likelihood (ML)-oriented nondecision-aided (NDA) symbol synchronization algorithms, operating on a noisy M-PSK signal (M > 2) transmitted over a time-varying nonselective Rician fading channel. The first algorithm is nonchannel-aided (NCA): timing is acquired independently of the channel gain estimation. The second algorithm is channel-aided (CA): it makes use of (an estimate of) the instantaneous channel gain. As the channel gain estimator requires timing information, use of the CA algorithm implies that the timing and the channel gain must be acquired jointly. Both algorithms are suitable for fully digital implementation, and have a similar complexity. For [E.sub.s]/[N.sub.0] values of practical interest, we show that the NCA algorithm is to be preferred over the CA algorithm.

For frequency-hopped communication systems, the hop patterns of the transmitter and receiver must be closely aligned in time to prevent performance degradation. Coarse-time synchronization is achieved when this misalignment is reduced to less than one-half hop period. Fine-time synchronization reduces this error to typically a few percent of a hop period. For satellite uplinks, where several noncoherent MFSK user signals are combined by FDMA, each user's transmitter must be synchronized with the satellite receiver. Because of the long round-trip delay between the transmitter and receiver, accurate estimates of the time error are made at the receiver and sent to the user, who then uses the estimate to adjust the phase of the transmitter hop period. Several methods are described which lead to biased, consistent estimators for the fine-time synchronization error. These methods are based upon estimation of the second-order moments of the envelope-detected, match-filtered, received signal. The performance of these estimators is determined as a function of the Gaussian noise level and of the number of samples L used to form the estimate. The estimator mean and standard deviation are approximated by means of the central limit theorem. Solutions compare favorably with simulation results. Results for signal-to-noise ratios of 0, 5, and 10 dB and with L between 1 and 512 show that these estimators are superior to previously known methods.

The effect of the signal transition variation, due to the signal transition density, data asymmetry, and sinusoidal modulation, to the performance of the DTTL symbol synchronizer is addressed. These factors will affect the DTTL performance such as the clock jitter and the cycle slippage rate, and unnecessary system loss may result if the system parameters are not well selected. Given the background study in (1), this result can serve as an engineering design guideline for the DTTL in the context of the signal transition variation.