| Ad Hoc multicast is an efficient technology for group communications in scenarios where no infrastructure exists or, if it existed, it can no longer be accessed. Providing reliable and robust multicast in an ad hoc wireless environment, however, is very challenging due to mobility, interference, and unpredictable radio channel. In such a disruptive environment, conventional links, networks, and transport protocols fail to operate properly---a significant fraction of the packets are received in error and/or are lost. To overcome these problems, researchers have exploited cross-layer and diversity techniques. Using cross-layer feedback, Physical and Link layer measurements assist in finding more reliable routes. Likewise, multi-path diversity increases packet reliability and route robustness. This thesis aims at improving reliability and robustness in wireless ad hoc multicast by leveraging cross-layer interactions between network and lower layers, and by exploiting diversity schemes, e.g., spatial, temporal, and spectrum. The contribution of the thesis is three-fold. First, we develop cross-layer ad hoc multicast protocols which support reliability, QoS, congestion control, and delay tolerant network communications. Next, we implement and investigate various diversity schemes. We compare network and erasure coding performance via simulation and develop a MANET routing protocol that combines multipath routing (spatial diversity) and network coding (temporal diversity). Moreover, we design a new MANET multicast protocol, called MIMO-CAST, that uses a new Physical layer technology, namely, the Multiple Input Multiple Output (MIMO) antenna system. Last, we develop a software Thin Layer that combines cross-layer interaction and diversity. The layer is kept thin by the fact that it does not itself provide diversity techniques---these are implemented by specific layers, e.g., multipath routing in Network layer and multi-channel scheduling in MAC and PHY layers. It only includes a temporal diversity module, e.g., network coding as well as network control and management. The Thin Layer intelligently controls and manages the various diversity options via cross-layer interaction. We show that the Thin Layer yields significant performance improvements in various mobile ad hoc scenarios exploiting cross-layer and diversity schemes. |
