A thesis submitted in partial fulfillment of the requirement for the degree of Master of Engineering, School of Engineering and Technology

Thesis (M.Eng.) - Asian Institute of Technology,1992

This study is aimed at investigating the performance of a Hybrid Code Division Multiple Access I Carrier-Sense Multiple Access with Collision Detection Protocol [CDMA/CSMA-CD]. This hybrid protocol employs CDMA embedded in a carrier-sensing protocol with overload detection and is referred to as Carrier/Channel-load Sense Spread Spectrum with collision detection (CSSS/CD). This study concentrated on a one-persistent form of channel access. Depending on the channel access strategy, two different protocols, lP-CSSS/CD-1 and lP-CSSS/CD-M were identified. The network throughput was analysed for both of these protocols. The effect of bit errors, caused by multiuser interference, was also investigated for the 1 P-CSSS/CD-1 protocol with fixed length packets. With threshold approximations for the channel capacity, the network was modelled as a discrete-time semi Markov process. Results are presented showing the effects of network parameters on the throughput. These results are compared with the performance of lP-CSMA/CD [Ethernet] under the same operating conditions and it is shown that a real capacity gain over Ethernet is achieved with the spread-spectrum protocol. An additional advantage of the spread spectrum protocol is the low packet delay offered by the CDMA effect. System stability was evaluated using a general user model.