Analysis of Relay-Assisted OFDMA Cellular Systems with Different Frequency Reuse Techniques

摘要

Co-channel interference (CCI) degrades performance of cellular networks. Therefore, this paper addresses CCI problem in relay-assisted (R-A) orthogonal frequency division multiple access cellular systems. Analytical treatments are conducted. The network performance improvements through reducing CCI effects are evaluated using different four interference mitigation models. These models represent R-A strict fractional frequency reuse (FFR) technique with frequency reuse factor (FRF) 3, R-A strict FFR technique with FRF 4, R-A sectored FFR technique and R-A soft frequency reuse (SFR) technique. Each model contains two different configurations for further network performance improvement. The first configuration assumes three relay stations (RSs) per cell (RPC) while the other one proposes 6 RPC. The best RSs locations in terms of SIR are proposed. Moreover, closed-form expressions for worst cases CEU's SIR, cell centre user's SIR and inner radius are implemented. These expressions are used to compare different models using various performance evaluation metrics. The results demonstrate that the two configurations in R-A sectored FFR and R-A strict FFR models provide equal CEU's SIR. The reason of this result can be attributed to applying equal power transmission strategy. Moreover, the two configurations of R-A SFR network attain different CEU's SIR values. This result can be accredited to the SFR power control factor. The work outcomes attain much higher CEU's SIR improvement. Therefore, the outage probability is decreased. Thus, more users can be covered by the network. Accordingly, the total network cost is reduced. So, this treatment improves the network performance while keeping lower network cost.