http://ieeexplore.ieee.org TOC Alert for Publication# 50 2013 May 16 31 12 1845 1855 2293 $M$-ary overlapping pulse-position modulation ($M$-OPPM) scheme is adopted and each user is assigned two orthogonal code sequences to represent these two levels. The code sequences are selected from a minimum cross-correlation code set. The bit error rate (BER) of the proposed system is derived, taking into account the effects of phase-induced intensity noise, shot noise, and thermal noise in addition to the multiple-access interference. The BER performance of this system is compared to other systems adopting $M$-PPM and OOK schemes under same pulsewidth constraints. Our results reveal that, while keeping the BER well below a prescribed threshold, the proposed $M$ -OPPM SAC-OCDMA system achieves higher transmission rate as compared to both $M$-PPM and OOK SAC-OCDMA systems under same constraints. Specifically the transmission rate of a single user of the proposed system can be increased by about 34.44% as compared to traditional systems.]]> 31 12 1856 1866 3088 31 12 1867 1876 2070 31 12 1877 1883 1561 31 12 1884 1889 821