Relays in Cellular Networks: A Simplified Cost-Benefit Analysis

In contemporary cellular systems, end users near cell edges experience inferior data rates; this is because of falling signal strength and increased interference from neighboring cells. Low-cost relays have been proposed to provide near-equitable data rates to all users throughout a cellular region. We investigate the cost-performance trade-off resulting from the use of such relays, in a simplified setting of uniformly placed relays. Using the normalized spectral efficiency as our performance criterion, we derive expressions for the optimal relay density for street and hexagonal grid uniform deployments. For these layouts, we show that, for a given frequency reuse scheme in a given propagation environment, the optimal value of relay density is a function of the ratio of the average cost of a relay station to that of the base station. This theoretical result, in our simplified setting, allows us to infer a practical strategy for the deployment of relays. An alternate way to increase data rates in cellular networks is to use the conventional one-hop system but with a reduced cell size, resulting in an increase in the number of base stations. We show that the relay station to base station cost ratio determines whether or not such a conventional one-hop system is preferred over a multi-hop cellular network.