Energy-Efficient Relay Deployment in Cellular Systems Using Fractional Frequency Reuse Scheme

In cellular systems, the relaying technique is used for increasing service coverage, system capacity, and cell- edge user throughput at a relatively low cost. However, the introduction of relay stations (RSs) leads to a more complex intra-cell and inter-cell interference problem between the base station (BS) and RSs. The fractional frequency reuse (FFR) is one of the most simple and efficient (thus, practical) techniques to solve this problem. To heighten the performance of cellular systems with the relaying/FFR combination, the deployment (i.e., the positioning) of RSs should be managed carefully. In this paper, we focus on energy efficiency (EE) as a performance index, which is quantified as the number of bits that can be transmitted per unit of energy consumption. We first derive the EE as a function of the distance between BS and RS. Then, we find out the optimal distance using optimization approach. Based on the numerical results, we provide a guideline in the deployment of RSs.