Channel Adaptive Real-Time Medium Access Control protocols for Industrial Wireless Networks
Balasubramanian, Kavitha (2007) Channel Adaptive Real-Time Medium Access Control protocols for Industrial Wireless Networks. Masters thesis, Iowa State University.
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Wireless technology is increasingly finding its way into industrial communication because of the tremendous advantages it is capable of offering. However, the high bit error rate characteristics of wireless channel due to conditions, such as attenuation, noise, channel fading and interference seriously impact the timeliness and reliability guarantee that need to be provided for real-time traffic. Existing wireless protocols either do not adapt well to erroneous channel conditions or do not provide real-time guarantees. The goal of our work is to design and evaluate novel real-time MAC (Medium Access Control) protocols for combined scheduling of periodic and aperiodic messages taking into account the time-varying channel condition. Our first contribution is the design of a combined scheduling algorithm that exploits both spatial and temporal diversity of the wireless channel through "exchange of slots" among nodes, to effectively mitigate bursty channel error conditions. Simulation results show that the proposed algorithm achieves significant improvements in message success ratio compared to baseline protocols under a wide range of traffic and channel conditions. The second contribution assumes a two-level hierarchical network in which nodes are grouped into clusters and the communication occurs within each cluster and across clusters. The goal is to maximize the schedulability of intra- and inter-cluster periodic and aperiodic messages with deadline guarantees. In this context, we propose an Adaptive protocol that maximizes the channel utilization by enabling parallel transmissions in a collision-free manner, in conjunction with the use of the slot-exchange technique to actively combat the erroneous channel conditions. Through simulation studies, we show that the proposed Adaptive protocol achieves significant improvement in packet loss performance compared to the baseline protocols that exploit complete parallelism and full exchange, for a wide range of channel conditions. The future work includes: (i) Formulation of the MAC scheduling problem to a n- level hierarchical network and developing novel scheduling algorithms (ii) Extending the scheduling problem to account for node mobility and developing mobility-aware MAC protocols.
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