Authors : Suman Kumar Dey; Bithi Nahar; Debbrota Kumar Ghuha; Rashdul Islam

Volume/Issue : Volume 10 - 2025, Issue 1 - January

Google Scholar : https://tinyurl.com/ybk5emyp

Scribd : https://tinyurl.com/2zchchvv

DOI : https://doi.org/10.5281/zenodo.14637043

Abstract : This study evaluates Underwater wireless spectral amplitude-coding optical code division multiple access (SAC-OCDMA) systems bit error rate (BER) performance when employing Modified Quadratic Congruence (MQC) codes as user address sequences. Balanced detection is utilized to mitigate multi-user interference (MUI), and use constant in-phase cross- correlation values of MQC codes. BER calculations consider phase-induced intensity noise (PIIN), shot noise, and thermal noise under varying optical signal power, link distances, inclination angles, and the number of concurrent users. The performance of photodiodes and avalanche photodiodes is compared, with the latter exhibiting enhanced sensitivity and noise characteristics, facilitating the detection of weaker signals across extended distances. The system's BER is examined across various seawater forms: pure seawater, clear ocean water, and coastal ocean water. The results indicate the optimal performance of avalanche photodiodes in pure seawater.

Keywords : BER Performance, Spectral Amplitude Coding (SAC), Underwater Wireless OCDMA, Modified Quadratic Congruence (MQC) Codes, Multi-user Interference (MUI), Photodiode, Avalanche Photodiode.

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