Mitigating multi-path fading in a mobile mesh network Marcos A.M. Vieira ⇑ , Matthew E. Taylor, Prateek Tandon, Manish Jain, Ramesh Govindan, Gaurav S. Sukhatme, Milind Tambe Department of Computer Science, University of Southern California, Los Angeles, CA, United States article info Article history: Available online xxxx Keywords: Mobile and wireless ad-hoc networks Multi-path fading Complex environments Distributed optimization Experimental and prototype results abstract By using robots as routers, a team of networked robots can provide a communication substrate to establish a wireless mesh network. The mobile mesh network can autonomously optimize its configuration, increasing performance. One of the main sources of radio signal fading in such a network is multi-path propagation, which can be mitigated by moving the senders or the receivers on the distance of the order of a wavelength. In this paper, we measure the performance gain when robots are allowed to make such small movements and find that it may be as much as 270%. Our main contribution is the design of a system that allows robots to cooperate and improve the real-world network throughput via a practical solution. We model the problem of which robots to move as a distributed constraint optimi- zation problem (DCOP). Our study includes four local metrics to estimate global throughput. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction With advances in processor, memory, sensing, actuation, and radio technology, it is possible to assemble novel sys- tems using off-the-shelf components. A good example is a robot with navigation capabilities, and an on-board proces- sor with wireless communication capabilities. Among its many uses, such a robot can be used as a router in a mobile wireless mesh network. In such a network, a team of robots can provide a communication substrate for a collection of clients. Such a mobile wireless mesh network can have applica- tions in various settings. In an infrastructure-less settings, it can be used to form a connection backbone, such as in the LANdroids project [1], where the goal is enable soldiers to communicate even in dense urban settings. A mobile wireless network network can also be quickly and autonomously deployed in urban search and rescue efforts, allowing searchers to communicate even when no other infrastructure exists: thus, small robots could venture where humans cannot, to search for survivors of earth- quakes, collapsed mines and other disasters. Unlike a static, manually deployed mesh network, the dynamism in the network allows nodes to move and re- organize the network, to achieve optimize or improve cover- age, performance, or other such objectives. In this paper, we leverage this mobility to consider a specific kind of perfor- mance improvement. Our work is motivated the observa- tion that one of the main sources of radio signal fading in urban settings is multi-path propagation. Multi-path occurs when a transmitted signal takes more than one path to a receiver, causing the signals to interfere. The central obser- vation of our paper is that robots can actively reduce multi- path effects by making small movements (or micro-motion). By avoiding deep fades, robotics routers can increase network throughput, enabling applications with higher bandwidth requirements, or improving user satisfaction in general. Thus, in this paper we explore two questions. First, is it possible to improve the overall network throughput of a mo- bile mesh network by using (possibly coordinated) robotic micro-motion? Second, how would one design an on-line system that performed this optimization autonomously? 1570-8705/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.adhoc.2011.01.014 ⇑ Corresponding author. Tel.: +55 31 3409 5860. E-mail addresses: mvieira@usc.edu (M.A.M. Vieira), taylorm@usc.edu (M.E. Taylor), tandonp@usc.edu (P. Tandon), manishja@usc.edu (M. Jain), ramesh@usc.edu (R. Govindan), gaurav@usc.edu (G.S. Sukhatme), tambe@usc.edu (M. Tambe). Ad Hoc Networks xxx (2011) xxx–xxx Contents lists available at ScienceDirect Ad Hoc Networks journal homepage: www.elsevier.com/locate/adhoc Please cite this article in press as: M.A.M. Vieira et al., Mitigating multi-path fading in a mobile mesh network, Ad Hoc Netw. (2011), doi:10.1016/j.adhoc.2011.01.014