PERFORMANCES OF DS SSMA COMMUNICATIONS WITH MPSK SIGNALING AND COMPLEX SIGNATURE SEQUENCES/

In this paper, we study a direct-sequence spread-spectrum multiple-acc ess (DS/SSMA) communication system with M-ary phase-shift-keyed (MPSK) signaling. Users in the system employ complex signature sequences, wh ich are modeled as deterministic sequences. We present upper and lower bounds for the probability of bit error (p.b.e.) of a reference trans mission. First, the conditional p.b.e. given the multiple-user interfe rence (MUI) is obtained. Then, the conditioning is removed by averagin g over the discretized probability density function (p.d.f.) of the MU I. 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 deri ved in this paper. Arbitrarily tight bounds can be obtained at the cos t of increased computation. Numerical results are presented for comple x 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 assume d, 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 av ailable signature sequences is greatly enlarged.