Relaying and scheduling in interference limited wireless networks

In this dissertation, we address two issues related to communication in interference-limited wireless networks. In the first part of the thesis, we study benefits of deploying inexpensive half-duplex relays in interference-limited cellular system. We study two relaying schemes in a downlink system, users sharing the same frequency band. In the first collaborative relaying scheme, relays help users after they decode the message intended for the user by a collaborative power addition scheme. We evaluate power savings and rate improvement for delivering a common rate for 90% of users in the system. We then consider power control at the base stations and relays in order to manage the interference. In both cases, the ability of relays to reduce the peak base station transmit power while delivering the baseline rate or alternately to increase the user rate is computed. When power control is employed, the peak power saving is 2.6 dB and the average total power in the system can be reduced by 3 dB. We also observe a 34% improvement over the baseline in the users’ common rate. In the second orthogonal relaying scheme, we study a simple scheme where the base station and relays transmit in orthogonal time slots. We find that the performance of the simple orthogonal relaying scheme comes very close to that of the collaborative power addition scheme. In the second part of the thesis, we consider a centralized spectrum server that coordinates the transmissions of a group of links sharing a common spectrum. Links employ on-off modulation with fixed transmit power when active. The rate obtained by an active link depends on the activity of all other links. With knowledge of the link gains in the network, the spectrum server schedules the on/off periods of the links so as to satisfy constraints on link fairness and efficiency. We then extend the centralized scheduling framework to multi-hop wireless networks with interfering links. A framework for cross-layer scheduling of end-to-end flows in a multi-hop wireless network with links sharing a common spectrum is presented. Given a set of known routes, the optimization framework can be used to find the flow on each route in order to maximize an objective function. The framework encompasses a variety of physical layer transmission schemes. The rates in the individual links are determined based on the transmission strategy employed. With the knowledge of the link rates in the network, the spectrum server schedules the rates on the links and flows on the sessions to maximize a utility function of the source rates. The schedules are a collection of time shared transmission modes (sets of active links).Ph.D.Includes abstractVitaIncludes bibliographical referencesby Chandrasekharan Rama