Wireless media access control for highly mobile information servers: simulation and performance evaluation

Innovations of modern digital radio technology has enabled many large mobile and distributed information systems, such as inventory tracking systems, to provide readily accessible voice and data services to end users despite mobility of data servers. These systems often contain components that are equipped with radio frequency identification (RFID) tags and interrogators for wireless connectivity. However, there are usually large number of these tagged items in these systems that are highly mobile. The wireless connections among them are also prone to failure. In this paper, we evaluate and compare the performance of two RF tag data access protocols in a single channel per cell implementation: slotted ALOHA Time Division Multiple Access (slotted ALOHA/TDMA) and Direct Sequence Code Division Multiple Access (DS/CDMA).We use a discrete event simulation model to study the impact of these protocols on data service under a diversity of highly mobile operating conditions. Mobile conditions are captured separately by various levels of burst error, uplink and downlink disconnections, and tag population. The results show that performance of DS/CDMA dominates in all mobile conditions. In the most general cases, DS/CDMA outperforms slotted ALOHA/TDMA by 1.5 times faster message time. DS/CDMA is particularly superior in the case of pure uplink disconnections. For burst error and pure downlink disconnections, DS/CDMA renders as much as 2.0 times and 4.5 times faster message time respectively.

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