Hybrid pulse interval modulation-code-division multiple-access for optical wireless communications.

The work in this thesis investigates the properties of the IR diffuse wireless link with regard to: the use of sets of signature sequences with good message separation properties (hence providing low BER), the suitability of a hPIM-CDMA scheme for the IR diffuse wireless systems under the constraint of eye safety regulations (i.e. when all users are transmitting simultaneously), the quality of message separation due to multipath propagation. The suitability of current DS-CDMA systems using other modulation techniques are also investigated and compared with hPIM-CDMA for the performances in power efficiency, data throughput enhancement and error rate.A new algorithm has also been proposed for generating large sets of (n,3,1,1)OOC practically with reduced computation time. The algorithm introduces five conditions that are well refined and help in speeding up the code construction process. Results for elapsed computation times for constructing the codes using the proposed algorithm are compared with theory and show a significant achievement. The models for hPIM-CDMA and hPPM-CDMA systems, which were based on passive devices only, were also studied. The technique used in hPIM-CDMA, which uses a variable and shorter symbol duration, to achieve higher data throughput is presented in detail. An in-depth analysis of the BER performance was presented and results obtained show that a lower BER and higher data throughput can be achieved. A corrected BER expression for the hPPM-CDMA was presented and the justification for this detailed. The analyses also show that for DS-CDMA systems using certain sets of signature sequences, the BER performance cannot be approximated by a Gaussian function.