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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. [ABSTRACT FROM PUBLISHER]

In recent years, it has become common consensus that independent consideration of communication layers often turns out to be inadequate in terms of providing the desired quality of service (QoS) and power efficiency in wireless networks. The need for a synergistic, cross-layer design framework has already been identified. In that respect, our work constitutes an important step towards a better understanding of the cross-layer paradigm by simultaneously targeting both the power efficiency and the end-to-end QoS in multi-hop wireless networks. More specifically, we address the joint problem of power control and scheduling with the objective of minimizing the total transmit power subject to the end-to-end bandwidth guarantees and the bit error rate constraints of each communication session. After identifying the inherent difficulty of the problem, we propose two classes of heuristic algorithms that rely on graph theory principles as well as on derived metrics such as effective interference. The first heuristic follows a top-down design strategy by solving the schedule feasibility problem as the initial step and then targeting the total power efficiency. On the other hand, the second heuristic follows a bottom-up approach that schedules one wireless link at a time by greedily filling up the available time slots. The simulation results reveal valuable insights about the performance of each strategy. The top-down design strategy turns out to address power efficiency issues better, whereas the bottom-up design strategy with a properly selected cost function for link scheduling shows better performance in finding a feasible solution, namely one that satisfies both the QoS and the transmit power constraints. Our results also illustrate the impact of routing decisions on the feasibility and the power efficiency of multi-hop wireless networks through employing different routing criteria in the experiments [ABSTRACT FROM PUBLISHER]