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Design of a hybrid multirate asynchronous O-CDMA system: performance, spectral efficiency, and throughput analyses

The multiple-code (MC) and multicode-keying (MK) schemes were recently proposed to support multirate multimedia services in asynchronous optical code-division multiple-access (O-CDMA) systems. A user in the MC scheme simultaneously conveys multiple codewords to represent the transmission of multiple data bits of 1. While the MK scheme only transmits one codeword at a time, each codeword represents a symbol (of multiple data bits of 0 and 1). In this paper, a hybrid multirate asynchronous O-CDMA system model that comprises the conventional single-rate scheme and these two multirate schemes is studied. The bit error probability (BEP), spectral efficiency (SE), and throughput of the proposed hybrid systemare formulated. The conditions and combinations of simultaneous users from these three schemes that can optimize the system's BEP, SE, and throughput are investigated. Finally, the new analytical models are validated with numerical examples and computer simulations.