Performance Evaluation of MC-CDMA over Hybrid Satellite/Underwater Acoustic Channel

Underwater communication is one of the most researched fields in literature. Low-powered underwater devices such as diving sensors, Unmanned or Autonomous Underwater Vehicles, (UUVs) or (AUVs), surface buoys etc. are incapable of carrying data to longer distances. Hence, hybrid satellite/ underwater communication system is proposed in literature, to support wide overseas coverage for ubiquitous availability of data. In this paper, the performance analysis of full load & overload Multicarrier (MC)-CDMA transmission scheme over hybrid Satellite/ Underwater Acoustic (UWA) channel is presented. For full load case Walsh-Hadamard (WH) & Carrier Interferometry (CI) spread codes are employed, and for overload case Pseudo Orthogonal (PO)-CI code set in addition to CI codes are used. The analytic expressions for the code cross-correlation terms, and hence the Multiple Access Interference (MAI) terms are derived for overloaded MC-CDMA system, and compared with its fully loaded counterpart. Later it is shown that, the BER performance of overloaded system over UWA channel illustrates worse performance than over narrowband satellite channel due to higher code cross-correlation and large delay spread. Finally, from the simulation results, the BER performance of PO-CI spread (overloaded) MC-CDMA is observed to be slightly degraded than CI spread (full-load) MC-CDMA. Thus, a tradeoff is established between the achievable system capacity and the error performance. Hence for the increased network capacity or better error performance, PO-CI/MC-CDMA or CI/ MC-CDMA respectively, stems out to be the suitable candidates, for hybrid satellite/underwater acoustic communications.