Channel Adaptive Real-Time MAC Protocols for a Two-Level Heterogeneous Wireless Network

Wireless technology is becoming an attractive mode of communication for real-time applications in typical settings such as in an industrial setup because of the tremendous advantages it is capable of offering. However, the high bit error rate characteristics of wireless channel due to conditions like attenuation, noise, fading and interference seriously impact the timeliness and guarantees that need to be provided for realtime traffic. Existing wireless protocols either do not adapt well to the 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 scheduling messages in a 2-level hierarchical wireless industrial network taking into account the time-varying channel condition. Our objective is to minimize the loss rate of messages using the slot exchange protocol[9] that actively combats the erroneous channel conditions and maximize the channel utilization by enabling parallel transmissions in a collision-free manner. Unfortunately, these two goals have inherent conflicts in shared medium wireless networks. We propose a distributed protocol, called the Adaptive protocol that arbitrates between these two design criteria in order to resolve the inherent conflict between them. Through simulation studies, we show that the proposed Adaptive protocol achieves significant improvement in deadline miss ratio compared to the baseline protocols that exploit complete parallelism and full exchange, for a wide range of channel conditions.