Multi-hop, or ad hoc, wireless networks use two or more wireless hops to convey information from a source to a destination. There are two distinct applications of multi-hop communication, with common features, but different applications.
- Mobile ad hoc networks (MANETS) A mobile ad hoc network consists of a group of mobile nodes that communicate without requiring a fixed wireless infrastructure. In contrast to conventional cellular systems, there is no master-slave relationship between nodes such as “base station to mobile users” in ad hoc networks. Communication between nodes is performed by direct connection or through multiple hop relays. Mobile ad hoc networks have several practical applications including battlefield communication, emergency first response, and public safety systems. Despite extensive research in networking, many challenges remain in the study of mobile ad hoc networks including development of multiple access protocols that exploit advanced physical layer technologies like MIMO, OFDM, and interference cancellation, analysis of the fundamental limits of mobile ad hoc network capacity, practical characterization of achievable throughputs taking into account network overheads.
- Multi-hop cellular networks Cellular systems conventionally employ single hops between mobile units and the base station. As cellular systems evolve from voice centric to data centric communication, edge-of-cell throughput is becoming a significant concern. This problem is accentuated in systems with higher carrier frequencies (more path loss) and larger bandwidth (larger noise power). A promising solution to the problem of improving coverage and throughput is the use of relays. Several different relay technologies are under intensive investigation including fixed relays (powered infrastructure equipment that is not connected to the network backbone), mobile relays (other users opportunistically agree to relay each others' packets), as well as mobile fixed relays (fixed relays that are mounted on buses or trains and thus moving). There has been extensive research on multi-hop cellular networks the last few years under the guise of relay networks or cooperative diversity. The use of relays, though, impacts almost every aspect of cellular system design and optimization including: scheduling, handoff, adaptive modulation, ARQ, and interference management. These topics are under intense investigation.
WSIL is actively researching many aspects of multi-hop wireless networks including both MANETs and cellular networks, from the perspectives of signal processing, networking, information theory, and prototyping. Click the links on the left for more detail about our projects.