Analysis and comparison of Fractional Frequency Reuse schemes based on worst case Signal to Interference power Ratio in OFDMA uplink

Fractional Frequency Reuse (FFR) is an efficient interference mitigation technique for modern cellular networks due to its low complexity, low coordination requirements and resource allocation flexibility. This work considers the use of FFR in the cellular uplink (UL). We analyze the uplink worst case Signal to Interference power Ratio (SIR) for sectored FFR and compare its results with those of strict FFR and Soft FFR. A closed form expression is derived analytically for worst SIR and best inner radius. This analytical technique is utilized to configure a FFR solution for the TIL of Orthogonal Frequency Division Multiple Access (OFDMA) cellular systems. The analysis is performed using two-tiers cellular network with uniform user density and for three different cases of FFR, sectored FFR, Soft Frequency Reuse (SFR), and strict FFR with Frequency Reuse Factor (FRF)= 3 and FRF= 4. Also the effect of power control exponent on those FFR schemes is studied. The inner radius configuration depends on equalizing the worst SIR for both inner and outer edges of the cell. Numerical results show that sectored FFR without power control yields the highest SIR followed by strict FFR with FRF= 4. Power control exponent does not affect FFR with reuse three but strongly affects SFR and FRF= 4 as its increase reduces its SIR and inner radius. Sectored FFR without power control have the highest SE, hence sectored FFR highly balances the needs of interference reduction and resource efficiency but at the expense of increased system complexity.