We study a direct-sequence spread-spectrum multiple-access (DS/SSMA) communication system with M-ary phase-shift-keyed (MPSK) signaling. Users in the system employ complex signature sequences, which are modeled as deterministic sequences. We present upper and lower bounds for the probability of bit error (p.b.e.) of a reference transmission. First, the conditional p.b.e., given the multiple-user interference (MUI), is obtained. Then, the conditioning is removed by averaging over the discretized probability density function (p.d.f.) of the MUI. The result is an upper (or lower) bound when the discretized p.d.f. is a shifted-high (or shifted-low) version of a sectioned p.d.f. This process requires the two-dimensional p.d.f. of the MUI, which is derived. Arbitrarily tight bounds can be obtained at the cost of increased computation. Numerical results are presented for complex FZC and near optimal 4-phase sequences, as well as real binary Gold sequences, for BPSK, 4-PSK, and 8-PSK. Gray code bit mapping is assumed, although the analysis can be applied to other bit mappings. Results show that complex sequences can yield better performance than binary sequences in MPSK signaling. Using complex sequences, the number of available signature sequences is greatly enlarged.>

Studies sequential acquisition schemes of m-sequences, based on the sequential probability ratio test (SPRT) and a truncated SPRT (TSPRT), with noncoherent demodulation. Most reported results on sequential acquisition schemes assume that independent samples are available for the decision process. The assumption of independent and identically distributed (i.i.d.) samples requires the integrator in the receiver to be reset periodically. This introduces loss in the effective signal-to-noise ratio, degrading the performance. In the present paper, on the contrary, the authors' two sequential schemes use continuous integration. It can be shown that the likelihood ratio is monotonic; consequently, the tests can be easily implemented in realtime. Methods are proposed for designing the decision thresholds to achieve the desired false-alarm and miss probabilities. Performances of the proposed schemes are obtained and they suggest that the TSPRT is more desirable. The effect of slowly-varying channel fading is also investigated. Results show that fading does not affect the false alarm probabilities, but it can drastically reduce the probability of detecting the alignment of the two PN sequences, especially when the fading is severe.>

Direct-detection optical code-division multiple-access (CDMA) communication systems with avalanche photodiode (APD) photodetectors are investigated. A Chernoff upper bound, modified Chernoff upper bound, and Gaussian approximation on the probability of bit error are presented for general APDs and arbitrary

A unified performance analysis of direct-sequence spread-spectrum multiple-access (DS/SSMA) communications with deterministic complex signature sequences is presented. The probability density function (PDF) of the multiple-user interference is determined. Using a round-down and round-up procedure on the PDF, arbitrarily tight lower and upper bounds on the probability of bit error (PBE) are obtained. Results based on the Gaussian approximation method are also presented. It is shown that complex sequences can yield better PBE performance than binary sequences. Using complex sequences, the number of signature sequences that have good auto- and cross-correlation properties is greatly enlarged. New users employing complex or binary signature sequences can be added to existing systems with graceful performance degradation.>

Time-hopping and frequency-hopping multiple-access (TH/FHMA) packet communication systems are proposed and investigated. In TH/FHMA communication systems, a message packet is encoded into several subpackets via a Reed-Solomon error correcting code. The subpackets are transmitted over the channel using time-hopping and frequency-hopping patterns. It is assumed that the channel is noiseless and the side information is perfect so that all subpacket collisions can be correctly detected. Slot-synchronous and totally asynchronous TH/FHMA systems are analyzed in detail, and they are shown to have excellent throughputs at small packet erasure rates. Various time-hopping techniques which significantly reduce the multiple-access interference are developed.>

Time-hopping patterns can be constructed from simple difference sets. By studying such constructions, it has been proven that whenever n-2, n-1, or n+1 is a prime power, then time-hopping patterns that have n terms can be constructed and are of length less than n/sup 2/. By computation it is shown that such patterns can have length less than n/sup 2/-n/sup 1.44/ for all n>

In this paper, we investigate the performance of a nearoptimum receiver in a frequency-hopped multiple-access (FHMA) differential phase-shift-keyed (DPSK) spread-spectrum communication system. We obtain upper bounds on the bit error rates (BER's) for the chipsynchronous system and the chip-asynchronous system in the presence of a single interfering signal which interferes in one time-chip. We also obtain upper bounds on the BER for the chip-synchronous system with multiple-user interference, for the special case where each time-chip has at most one interfering signal of the same power as the desired signal. We find that, for the chip-synchronous system, the upper bound on the BER when one time-chip has two interfering signals is larger than the upper bound on the BER when each of the two time-chips has a single interfering signal. We also discuss system performance for a large number of simultaneous users, and examine the additive white Gaussian noise (AWGN) approximation for the multiple-user interference. Finally, results for the chip-synchronous system with single interference in one time-chip over a Rayleigh fading channel are presented.