Performance analysis of noncoherent direct-sequence spread-spectrum multiple-access (DS/SSMA) packet radio systems
Abstract
Most work on the characterization and performance analysis of direct-sequence spread-spectrum multiple-access (DS/SSMA) communications utilizes coherent correlation receivers. However, for certain applications, establishing phase synchronization is often difficult. Even if synchronization is possible, it may take too long. In addition, the hardware for coherent systems tends to be more complex than that of noncoherent systems; hence, noncoherent techniques which do not require phase information are often preferable. In this research, the performance of noncoherent DS/SSMA packet radio systems are studied. A characterization of the multiple-access interference without the ordinary Gaussian assumption is presented. We consider the case involving K users, each of which is assigned a set of randomly generated signature sequences. Each transmitter is assumed to have equal power, although the approach can accommodate the case of transmitters with unequal powers. The decision statistic is modeled as an inhomogeneous quadratic Gaussian random variable after appropriate conditioning. The dependence of the density function of the decision statistic on the length of the signature sequences is demonstrated. Furthermore, techniques are developed for the evaluation of the probability of data bit error and the probability of packet success (PPS) for the noncoherent DS/SSMA packet radio network employing error control coding. The model and the analysis account for the dependence which typically exists between error events from bit-to-bit within a packet. An equal phase equal delay (EPDA) representation of the moment generating function (MGF) of the system decision statistic is examined. This representation is shown to be asymptotic to the exact MGF using the Lebesque dominated convergence theorem. The EPDA representation is analytically tractable and results in a tremendous reduction in computational complexity and computation time at the expense of accuracy. The result is used to study the performance of the system; namely, the bit error probability and the PPS. The case in which all the interfering signals are in phase and chip alignment with the reference user's signal are also examined and it results in a worst case system performance. Numerical examples are given to illustrate the results. The analytical results are compared with results obtained from stochastic simulation which utilized the Importance Sampling (IS) technique.
Degree
Ph.D.
Advisors
Lehnert, Purdue University.
Subject Area
Electrical engineering
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