IJCSNS International Journal of Computer Science and Network Security, VOL.7 No.1, January 2007 365 Manuscript received January 5, 2007. Manuscript revised January 25, 2007. Performance Analysis of Wireless Control Area Networks Sofiene DRIDI, Oussama KALLEL, Salem HASNAOUI SYSCOM Laboratory, National School of Engineering of Tunis TUNISIA Summary It is widely known that Control Area Networks (CAN) are used in real-time, distributed and parallel processing which cover manufacture plants, humanoid robots, networking fields, etc. Where wireless conditions are encountered it is convenient, as we will demonstrate later, to continue the exchange of CAN frames within a baptized Wireless CAN (WCAN). While we define the WCAN, we adopted the RTS/CTS scheme to gain access to the medium in a first step and the exchange of ordinary CAN frames in a second step [1, 2, 3]. The latency time is the most important factor to consider when evaluating a control network. The latency incurred in message delivery has not been a metric to be optimized. So in the second part of this paper, we compute the throughput-latency time couple that would guarantee a maximum throughput and a minimum latency time in the case of wireless communications, precisely in WCAN. This work represents our real contribution by introducing the WCAN concept for the first time, by the correct definition of WCAN frames, by the evaluation of parameters boundaries of WCAN, and by the calculation of the latency time and its coupling to the throughput, according the medium access scheme. Key words: WCAN protocol, RTS/CTS Media Reservation Mechanism, Throughput - Latency time Analysis. 1. Introduction CAN networks, called Controller Area Networks, can be used in the framework of real-time distributed industrial applications. Such applications cover manufactures, the distributed and parallel processing systems in industrial and networking fields, etc. CAN networks guarantee sufficently short time latency and it has been shown that these systems exceed in performance token-based ones. Access to the medium in wired CAN is shared based. It respects the CSMA/CA scheme which is “Arbitration on Message Priority” and “bit-wise Contention” technique. This technique, along with the mecahnism of detecting and correcting errors, gives high performance to the protocol CAN to be adopted for real-time applications where multiple access are applied. Unfortunately, the features of wired CAN cannot be adopted as they are without modification in the wireless case. Thus, we adopt the use of RTS/CTS (Request To Send/Clear To Send) mechanism along with the binary exponential backoff algorithm to gain access to the medium in first step and to exchange ordinary CAN frames in a second step. Thus, in the second section, we describe the key WCAN concepts, essentially the RTS/CTS scheme used to reserve the medium. In the third section, we evaluate the WCAN throughput. The key parameter which affects directly the throughput is the payload [1]. It is sufficient to increase the WCAN payload to join the WLAN performances. The improvements, in modifying the other parameters in physical and MAC sublayers, are negligible. However, the most important factor to consider when evaluating a control network is the end-to-end time delay between sensors, controllers, and actuators. The correct operation of a control system depends on the timeliness of the data coming over the network, and thus, a control network should be able to guarantee message delivery within a bounded transmission time. So, in the fourth section, we evaluate the latency time. After analysis, we deduce that when we increase the payload, the latency time along with the throughput increases respectively. A second work, exposed in the fifth section, consists in computing the throughput-latency time couple that would guarantee a maximum throughput and a minimum latency time in the case of WCAN. In the sixth section, we resume some important conclusions that can be taken as guidelines when designing a WCAN. 2. Overview of WCAN This section presents briefly the WCAN as presented for the first time in the paper [1]. Both in WLAN and wired CAN, access to the medium is share-based and respects the CSMA/CA scheme which is a listen before talk access mechanism. So the medium access control used in CAN MAC sublayer can be used as MAC protocol for fix and mobile industrial Wireless based CAN protocol. However, depending on the CAN frame format, some modifications should be done in the wireless case. In fact, due to the absence of network terminator impedances, a station is unable to transmit and listen for collisions. The hidden problem, when every station may not necessarily hear all other stations is a second deep problem. The RTS/CTS mechanism is proposed to exactly resolve the problems cited above and it is considered as a “second carrier sensing” mechanism, often called a “virtual carrier sensing technique”[7]. In