Fractional frequency reuse to enhance down link performance in MU Massive MIMO

Abstract

In Multi User (MU) Massive MIMO Base Station is provided with large number of antennas to serve number of single antenna user terminals. It offers several benefits over conventional MIMO and takes the advantage of multipath propagation by sending and receiving multiple data signals in same time-frequency resource which increases the throughput, coverage, and reliability. Massive MIMO, averages out the small scale fading and thermal noise. This averaging is done as the number of BS antennas increases without limit (M ≫ K). One of the limiting factor for the performance of Massive MIMO system is pilot contamination. Reuse of the orthogonal pilot sequences in adjacent cells cause pilot contamination. Pilot contamination causes poor channel estimation at the BS and degrades the performance of the system. The proposed scheme improves the performance of downlink by optimized allocation of pilot sequences and using fractional frequency reuse factor (1/N). All the available pilot signals are equally divided among the cells as per the cluster size (N = 1, 3, 7). In the proposed scheme orthogonal pilot signal is transmitted by each user terminal to get the Channel State Information (CSI) to estimate the channel. SIR and terminal capacity for the downlink are calculated for the given number of user terminals using linear precoding (Matched Filter and Zero Forcing) schemes which are the function of the estimated channel and the pilot transmission power (ρ p ). It is observed that there is significant improvement in Pilot Signal to Interference Plus Noise (PSINR), SIR and terminal capacity by reducing fractional frequency reuse factor i.e. (N = 1, 3, 7).