Reliable multicast and broadcast services in relay-based emergency communications

Having reliable communications during large-scale emergency situations is of paramount importance in today´s world. In particular, broadcasting critical information to both survivors and rescue teams (shelter locations, details of the disaster, regional map information, etc.) is an important component of emergency communications. Since the regular communication channels typically become non-operational in large-scale disasters, a temporary communication infrastructure is needed. Relay networks (e.g., those currently being standardized under IEEE 802.16j) are suitable for such situations in which relay stations may be conveniently positioned in the disaster area in order to expand the coverage of base stations and improve communication reliability. In this article we review the multicast and broadcast services (MBS) mechanism in the current IEEE 802.16j baseline document, which achieves macrodiversity through simultaneous transmissions of the base station and relay stations to the mobile stations. We discuss how it can be used for emergency communications, and propose two different techniques for improving the reliability of MBS in relay networks. Improvements in packet error rate performance are demonstrated through some computer simulations.