On Relay-assisted Cellular Networks

Cellular operators are developing low-cost relays to improve the coverage and capacity of next generation cellular networks. Deploying low cost relays reduces the infrastructure cost of setting up new base stations in order to support the rapidly growing number of subscribers. In this thesis, we present methods to design the system architecture and efficient protocols to achieve maximum benefit from the introduction of cellular relays. We focus on three of these issuesrelay placement for coverage extension, capacity improvement with relays and relay automatic repeat request (ARQ) protocols. The first problem considered is relay placement for maximum extension of the cell radius. Increase in cell radius helps reduce infrastructure cost of deploying more base stations to support the rapidly growing number of subscribers. We define the notion effective radius of the cell in terms of the probability of correct decoding at a point, and determine the optimal relay position which maximizes the effective cell radius. We also analyze the multicell scenario, by taking into account inter-cell interference and present an iterative algorithm to determine the relay positions. Apart from coverage extension, cellular relays also improve the cell capacity. This is because mobile stations get the advantage of diversity due to two possible signal paths one directly from the base station, and another via a relay. Thus, incoming calls experience lower blocking probability. We present a novel approach to determine the downlink Erlang capacity of the cell. Then, we extend this idea to evaluate the Erlang capacity for relayassisted cellular networks, and demonstrate how a capacity improvement takes place. Lastly, we analysis ARQ protocols for relay-assisted cellular networks. We demonstrate that major packet loss takes place during handover in the hop-by-hop ARQ protocol. We present a novel channel and handover model and use it to quantify this packet loss. Then, we propose modifications to hop-by-hop ARQ which reduce the packet loss during handover, at the cost of an increase in queueing delay. Time delay analysis is performed to show that the increase in queueing delay is negligible.