Performance analysis of CSMA/CD‐PS systems

Abstract

Recently, the interest in wireless LANs has been increasing. For wireless LANs, light and simple terminals are desirable, and random access protocols such as CSMA and CDMA are preferable. In order to improve the performance of these protocols, some variations have been proposed. Among them is the CSMA/CD‐PS (Carrier Sense Multiple Access with Collision Detection and Packet Segmentation) protocol, in which a message to be transmitted is divided into several packet segments separated by short intervals to enable sensing the channel state. In this paper we analyze the performance of CSMA/CD‐PS systems and derive the Laplace–Stieltjes transform (LST) of the probability distribution function (PDF) of the message interdeparture time and that of the PDF of the message response time. We note that the analysis of the LSTs of the PDFs of performance measures is important, because in communication systems, the output process of each sub‐system may form the input process to another one and that in order to evaluate the performance of communication systems more accurately, we need the stochastic characteristics of relevant output processes. Through LSTs, we can calculate not only averages but also higher moments of performance measures such as coefficients of variation. As for the analysis, we first define the state of the system and observe it at those epochs just after the end of successful/unsuccessful message transmissions. Then we derive the state transition probability matrix and obtain the state probability distribution. Secondly we analyze the interdeparture time and response time distribution of the system to obtain their LSTs. We also present some numerical results for the channel utilization, the average and the coefficient of variation of the interdeparture time, and the average and the coefficient of variation of the message response time.