Studies on the Viability of Cellular Multihop Networks with Fixed Relays

Abstract: The use of low cost fixed wireless relays has been proposed as a way to deploy high data-rate networks at an affordable cost. During the last decade, significant academic and industrial research has been dedicated to relays. Protocol architectures for cellular-relaying networks are currently considered for standardization as part of both IEEE 802.16 and 3GPP. Various relaying techniques have successfully been commercialized over the years. This dissertation concentrates on the particular case of large scale use of low cost relays, for which focus is put on signal processing and radio resource allocation, rather than on antenna and radio frequency (RF) design, or on network planning. A key question is how low relay cost is low enough for a relaying architecture to be viable from an economic point of view? We develop a framework for evaluating the viability of relaying solutions. The framework is based on a comparison between the relaying architectures and traditional single-hop cellular architectures. This comparative analysis is done from an operator perspective, and is formulated as a network-dimensioning problem. The associated investment decisions are based on financial measures (cost or profit) and taken under technical constraints (throughput, coverage, etc.).First, we consider a large number of traditional dimensioning scenarios, in which the radio network is design for a predefined traffic demand and target quality of service level. We show that the use of low cost relays can indeed be viable, but that the cost savings vary strongly from case to case and often are only modest. Due to the half-duplex nature of the low cost relays, these relays are best suited for providing coverage to guaranteed data-rates, at low end-to-end spectral efficiency, and in environments with strong shadow fading. The type of environment and the placement of relays are more important than the specific protocols and algorithms used in the network. Therefore, traditional network planning remains an essential and challenging task, which is unlikely to be replaced by large-scale (unplanned) use of relays.Second, we suggest a new direction of research in which the viability of relays is judged considering the entire life cycle of a radio network. We give several examples in which the temporary use of relays is economically viable, especially if the service uptake is slow or the uncertainty about the future demand is high. This is particularly relevant if the last-mile cost of a network is dominated by the backhaul transmission cost, and if relaying is implemented as a feature of an access point, rather than as a new device type.