A Dynamic Backoff Window Scheme for Machine-Type Communications in Cyber-Physical Systems

A cyber-physical system (CPS) requires a time-bounded communication process for real-time interaction between the digital world and the physical world so that they can form a tight loop. Using the machine-type communication (MTC) protocol for a large-scale CPS is a good solution. However, the MTC protocol uses a random access (RA) mechanism to solve the radio resource contention problem, but that inevitably causes access delays especially in scenarios when there is a large number of MTC devices. To meet CPS requirement and address this problem, we propose a dynamic backoff window adjustment (DBA) algorithm for a pull-based RA process that can appropriately distribute the failed MTC devices engaged in the backoff window, so as to expedite their contention retrial time interval and achieve increased success probability. Simulation results showed that the DBA algorithm significantly increases the success probability of MTC devices contending for RA, and as well, shortens the mean access delay of the MTC devices. In comparison to the standard RA backoff scheme and a novel dynamic backoff (DB) scheme, the DBA algorithm proved to be more effective and suitable for the CPS to the best of our knowledge.