Si-Ming Pan

Acquisition time distribution for spread-spectrum receivers

Serial search spread-spectrum code acquisition is analyzed. A modified flow graph is presented. It permits the use of a generalized lock strategy and allows the false alarm time to be treated as a random variable. The distribution of acquisition time is obtained directly by using an extended generalization of Bernoulli trials. Compared to recent work which uses a fixed penalty false alarm time, the analysis is more general and requires fewer assumptions and approximations. The analysis is suitable for both single dwell and multidwell systems. Examples are presented to show the effect on the acquisition time distribution of sequence length and normalized detection threshold. >

Statistical distribution of PCM framing times

The authors evaluate a robust framing technique which incorporates sufficient memory to simultaneously evaluate all bits in a candidate synchronizing codeword. Three performance measures are identified and the distribution function and mean value are developed in closed form for each measure. Predicted search and maintenance time distributions have been verified by measurements on a laboratory model. The authors present graphs of search time distributions which illustrate the effect of system parameters and variations in the channel error rate. >

A unified time-domain analysis of serial search with application to spread spectrum receivers

The paper presents a time-domain approach to the analysis of the code phase acquisition process in direct sequence spread spectrum receivers. This approach is suitable for a variety of search and verification/lock strategies. The time-domain approach is more direct than the unified z transform-domain approach and permits computation of the acquisition time distribution. The paper also provides equations for calculating the mean acquisition time under various search and verification/lock strategies. The usefulness of the approach is demonstrated by application to a specific nontrivial case of practical significance.

An offset-Z search strategy for spread spectrum systems

A new Z search method is proposed which can significantly improve mean acquisition time when compared with the best previous Z search strategy. The codephase search starts from a position offset from centre of a range which has been determined from a priori information. The proposed search method includes previous Z search strategies as special cases. The distribution and mean of acquisition time have been developed for the proposed search strategies. With minimum mean acquisition time as objective, optimization of the starting position offset has been investigated.

Acquisition time distribution for Z search strategies in spread spectrum receivers

An analysis of the acquisition process for Z serial-search direct-sequence spread spectrum receivers is presented. Using strictly time-domain techniques, equations for the acquisition time probability density function and mean are derived. Probabilities for small acquisition time may be calculated exactly, while larger times require Gaussian approximation to reduce computation time. The analysis brings out the effect of various factors that contribute to acquisition time. The results are suitable for use in the design of receivers which incorporate Z search and utilize a priori information about the code pulse. The method is illustrated by providing acquisition time distribution graphs. The technique known as broken-center/Z search provides the best performance among the various Z strategies.<<ETX>>

Statistical distribution of PN acquisition time in direct-sequence spread spectrum receivers

A method developed to analyze the acquisition process of a direct-sequence spread-spectrum receiver is described. The system is represented by a simplified flow graph. Equations of the mean and probability distribution of acquisition time are developed based on this model. Typical distributions are presented.<<ETX>>

An offset Z search strategy for spread spectrum systems

A novel Z search method is proposed in which the search is started at a position in the code phase uncertainty region which is offset from center. Using the unified time-domain approach developed by A. Polydoros and C. L. Weber (1984) the distribution and mean of the acquisition time have been obtained for the offset Z search strategy. Based on the mean acquisition time, the optimum offset of the Z search has been studied. The proposed method can improve mean acquisition by as much as 30% when compared with the best previous Z search strategy. The search pattern is optimized by a simple adjustment of the offset parameter.<<ETX>>

A unified time-domain analysis for serial search in spread spectrum receivers

The authors present a time-domain approach to analyze the code acquisition process in spread spectrum receivers. The approach is suitable for single-dwell and multi-dwell systems with various Z search and expanding window strategies. Compared to the unified Z-domain approach, the time-domain approach is more direct and permits computation of the distribution and mean of the acquisition time for a variety of search/verification/lock strategies.<<ETX>>

Single and dual multi-dwell synchronization for a direct-sequence spread spectrum receiver

Investigates factors affecting the coarse synchronization performance of a multi-dwell circuit for direct sequence spread spectrum receivers. The influence of the search/verification/lock (SVL) strategy, detector threshold and dwell time on the speed of acquisition is analyzed. For a selected multi-dwell SVL strategy, the mean, variance and distribution of the acquisition time are presented for several values of the detector threshold. A system design example is presented which demonstrates the high sensitivity to detector threshold. Two dual multi-dwell circuits that reduce the acquisition time are presented. The first approach searches two mutually exclusive areas, while the other searches the full region in opposite directions. It is shown that there is little difference in performance between these dual multi-dwell circuits.