| This thesis is about deployment strategies for 4G cellular networks using fixed relays. We argue that while relays will surely be an essential component of future 4G systems, their indiscriminate use is an inefficient way to allocate the limited radio resources available. The most efficient method to allocate the radio license is when the number of relays is minimized, while still achieving the desired coverage objectives. Thus, the focus of this work is to determine the optimal number and locations of fixed radio relay stations forming multi-hop links, such a way the right balance between achieving the functional requirements and assigning minimum resources is achieved. Under the assumption of using orthogonal channels for the intermediate hops, and using the spectral efficiency as a metric, it is shown that the optimal relay locations are at equal intervals along the straight line between source and destination. The Multi-Hop Criterion (MHC) to determine in which conditions a single-hop fixed radio link can be efficiently (from a spectral efficiency perspective) replaced with a chain of (multi-hop) links is introduced. Since a routing method is required to take advantage of any multi-hop architecture over a two-dimensional array of relays, four routing algorithms are devised and compared: direct single hop to destination, multi-hop using shortest possible hops, multi-hop using MEC to decide the number of hops, and exhaustive search for the route with smallest cost. Through computer simulations it is shown that the routing algorithm based on the MHC always achieves a spectral efficiency performance which is close to or equals the optimal (exhaustive search), outperforming both "single-hop" and "short-hops" schemes. |
