  Supporting real-time communications over Wireless networks (WSNs) is a tough
challenge, due to packet collisions and the non-determinism of common channel
access schemes like CSMA/CA. Real-time WSN communication is even more
problematic in the general case of multi-hop mesh networks. For this reason,
many real-time WSN solutions are limited to simple topologies, such as star
networks. We propose a real-time multi-hop WSN MAC protocol built atop the IEEE
802.15.4 physical layer. By relying on precise clock synchronization and
constructive interference-based flooding, the proposed MAC builds a centralized
TDMA schedule, supporting multi-hop mesh networks. The real-time multi-hop
communication model is connection-oriented, sing guaranteed time slots, and
enables point-to-point communications also with redundant paths. The protocol
has been implemented in simulation using OMNeT++, and the performance has been
verified in a real-world deployment using Wandstem WSN nodes.
