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Interest in Smart Antenna Technology for wireless communication systems has increased in the recent years as a promising technique to improve the performance of cellular mobile systems. Considerable amount of research is being conducted to improve the performance of the system in terms of increasing the capacity and range. We discuss the different types of Smart Antenna systems using switched beam and adaptive antenna array techniques and describe how they can be used to implement in different multiple access schemes in wireless communications. A smart antenna's ability to simultaneously resolve simultaneous transmissions on the same channel is exploited to help expedite the process of random access. Intended for bursty data traffic, a random access Medium Access Control (MAC) protocol seeks to insure an orderly sequencing of packets from the various mobile stations onto the shared channel with minimum time lost to collisions. When applied to cellular radio systems, a MAC protocol must also cope with the various impairments suffered on the radio link such as multi-path fading, shadowing, and co-channel interference from other mobiles.This thesis proposes to upgrade the performance of a class of random access protocols for wireless digital networks with smart antennas operating in the presence of Rayleigh slowly fading multipath transmission channels. The capture model assumed is a threshold model based on the signal to noise ratio, while the MAC protocol deployed is the two-cell random access algorithm, in a network environment where nodes are equipped with adaptive array smart antennas. The deployed protocol relies on the ability of the antenna to deploy Direction of Arrival (DoA) algorithms, to identify the direction of transmitters and to subsequently beam-form accordingly for Signal- to Interference and Noise Ratio (SINR) maximization. The performance of the protocol is evaluated using analytical modeling as well as detailed simulations in Matlab, where we demonstrate the benefits of using smart antennas.

For many communication applications with time constraints (e.g., transmission of packetized voice messages), a critical performance measure is the percentage of messages which are transmitted within a given amount of time after their generation at the transmitting station. In this talk we present a random access algorithm (RAA) suitable for time-constrained applications. Performance analysis demonstrates that significant message delay improvement is attained, at the expense of minimal traffic loss. We also consider the case of noisy channels. The noise effect appears at erroneously observed channel feedback. Error sensitivity analysis shows that the proposed random access algorithm is insensitive to feedback channel errors. Window Random Access Algorithms (RAAs) are considered next. These algorithms constitute an important subclass of Multiple Access Algorithms (MAAs); they are distributive and they attain high throughput and low delays by controlling the number of simultaneously transmitting users. Theses. (FR)