Opportunistic Scheduling and Routing in Wireless Networks

A centralized dynamic, opportunistic scheduling decision has to be made by a Base station (BS) to fair share the resources, based on the current channel gains signaled by the mobiles. But the mobiles can be non-cooperative, they may signal erroneously to improve their own utilities. We first study the case of efficient scheduling (which gives least priority to fairness) via Signaling Game. We find that this game admits only babbling equilibria at which the BS ignores the signals from mobiles. We then propose various approaches to enforce truthful signaling. We obtain a stochastic approximation based robust scheduling policy, that combines estimation and control. We further identify other equilibria that involve non-truthful signaling. The scheduling policy that gives priority to fairness can not be studied using a Signaling game. Nevertheless, using general non-cooperative game theoretic framework, we show that there exists only Nash Equilibrium (NE), which resemble the babbling equilibria. However, as the priority to fairness increases the existing fair schedulers become increasingly robust against non-cooperation. We then propose robust fair schedulers which induce truth revealing NE as is done in the case of efficient schedulers.

In wireless networks with limited connectivity, data routing becomes a challenging task. Users demanding data transfers can tolerate delays and this fact is utilized to design effective routing solutions, utilizing the contact opportunities that arise because of the mobility patterns of the elements of the network. These are called Delay Tolerant Networks (DTNs). In one such example, message is spread across the contacted (relay) users and it spreads like epidemics till it reaches the destination. The epidemics should be generated in a controlled manner so as to optimize performance. Successful delivery probability of a message within a given deadline is one such performance and it often takes the form of the expectation of the exponent of some integral cost. We identify a general framework from optimal control in finance, known as risk sensitive control, which allows us to handle this multiplicative cost and obtain solutions to several novel control problems in DTNs. New optimal control problems which consider the effect of wireless propagation path loss factor and the power constraints at the source and or the destination are proposed for DTNs. The possibility of non-threshold type optimal policies is established for some of the control problems.

Alternatively, a BS is placed in a moving object (for example a Bus circulating in the area) to facilitate data transfer. We study one such system, ferry based wireless local area network (FWLAN), using the results of polling systems. Not much theory is available for the polling system that can model FWLANs as these need systems with continuum of arrivals. We first obtain the stationary workload performance of continuous polling systems via discretization approach and apply the results to study FWLANs.

Brief Biodata: Kavitha obtained her B.E. degree in Electronics from UVCE, Bangalore in 1994 and the M.Sc (Engg) and Ph.D. degrees respectively from the Departments of EE and ECE, Indian Institute of Science (IISc), Bangalore in 2002 and 2007. From 1994-2000, she was involved in the design and development of GPS, CDMA and Voice band modems at Accord Software and Systems, Bangalore. She was an NBHM (National Board for Higher Mathematics) post doctoral fellow at Tata Institute of Fundamental Research (TIFR), Bangalore, during 2007-08. From 2008 onwards, she has been a post doctoral researcher with MAESTRO, INRIA, Sophia Antipolis, France and LIA, University of Avignon, France.