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In this paper, the throughput performance of the Code Shift Keying Spread Spectrum Multiple Access (CSK/SSMA) ALOHA system which combines the ALOHA system with CSK using nonorthogonal sequences is analyzed by non-perfect capture. The throughput performance of the CSK/SSMA ALOHA system with nonorthogonal sequences is evaluated when varying the number of concatenations because the nonorthogonal sequences are constructed by concatenating Mcon orthogonal sequences. Moreover, the effect of Channel Load Sensing Protocol (CLSP) is examined. Consequently, the throughput performance varies according to Mcon and the throughput performance improves considerably by using CLSP.

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In this paper, turbo-coded on-off keying (OOK) with differential detection is proposed. The proposed system constitutes the standard turbo code with OOK modulation, differential encoding and a delay detection technique. The purpose of using the differential encoding system is to suppress the influence of background noise in an optical wireless channel (OWC). OOK systems use the threshold detection method to determine the data. In optical intensity modulation/direct detection (IM/DD) systems, disturbances in the channel such as background noise and scintillation make it more difficult to decide the threshold value. Hence, in order to deal with the degradation in the quality of communication due to background noise, a turbo-coded OOK system with differential encoding and delay detection is proposed. The bit error rate (BER) performance of the proposed system is analyzed through computer simulation of an OWC in the presence of background noise, scintillation and avalanche photodiode (APD) noise. In terms of the BER performance, the results of this study show that the proposed system outperforms the conventional turbo-coded OOK system by 2.0 [dBm] at BER=10 −5 .