Challenges in multi-hop networks

Wireless multi-hop networks have generated a lot of interest in the recent past due to their many potential applications. Examples of such networks are sensor, ad hoc, and mesh networks. These networks bring a lot of new challenges; some are linked to the wireless physical layer, some to the end-devices, and some to the multi-hop characteristic. A wireless channel is usually characterized by its broadcast nature, strong path loss, time varying fading and shadowing. Many wireless devices have limited battery and processing power. Multi-hopping implies the existence of many geographically distributed devices that share the wireless medium which creates the needs for efficient MAC and routing protocols to mitigate interference and take full advantage of spatial reuse. The complexity and time-varying attributes of the wireless channel seem to call for cross-layer integration, i.e., the need for the higher layers of the protocol stack to take into account the characteristics of the physical layer. In spite of a vast amount of research on multi-hop networks in the past few years, many fundamental challenges have not been answered. This presentation will ask fundamental questions on 3 of these challenges and bring some elements of response. The first challenge is the design of a fair and efficient MAC protocol. Another one is to find the right level of cross-layer interactions to design schemes that are more efficient while maintaining the robustness and the usability of the system. Another challenge is to understand the fundamental limits of multi-hop networks in realistic scenarios