Towards a reliable parallel redundant WLAN black channel

Abstract

WLAN according to standard IEEE 802.11 is widely regarded unsuitable as communication channel for real-time and safety applications. Non-determinism and interference liability leads to packet loss, exceeded and variable latency times due to retransmissions. This work proposes a method that compensates such consequences of stochastic channel fading by the parallel operation of diverse wireless channels, applying frequency and space diversity techniques. A fault-tolerant wireless “black channel” is achieved that is able to fulfill soft real-time availability plus providing redundancy. This is realized with standard WLAN components and the “Parallel Redundancy Protocol” (PRP) according to IEC 62439-3. Reliability and performance characteristics are derived from measurements on an experimental setup with SafetyNET p nodes.