Performance enhancement of spectral-amplitude-coding optical CDMA using pulse-position modulation

TLDR

Spectral‑amplitude‑coding optical CDMA systems suffer from interference between incoherent sources. The study analyzes this interference limit for a balanced receiver and proposes pulse‑position modulation coding to surpass it. A simple, robust PPM decoding structure is introduced, and the overall PPM‑OCDMA system performance is analytically evaluated. The PPM‑OCDMA system outperforms the original when the number of simultaneous users approaches or exceeds the PPM word length, achieving up to a 100 % increase in spectral efficiency for a word length of two without altering signaling rate, data rate, or BER.

Abstract

Spectral-amplitude-coding optical code-division multiple-access (OCDMA) systems are limited by interference between incoherent sources. A detailed analysis of this limit for a system with a balanced receiver is presented. Additional pulse-position modulation (PPM) coding is proposed as a method to improve the system performance beyond this limit. A simple and robust PPM decoding structure is proposed, and the performance analysis of the whole PPM-OCDMA system is presented. The interference-limited performance of the PPM-OCDMA system is found to be superior to that of the original system when the number of simultaneous users is of the order of the PPM word length or larger. In particular, for a PPM word length of two, an increase in spectral efficiency of up to 100% is possible with no change in the signaling rate, data rate, or bit-error rate (BER).