Interference considerations in MIMO-based cellular systems

Cimini, LeonardIn this thesis, we consider MIMO-based intra-tier interference in single-tier cellular systems, and inter-tier interference in two-tier femtocellular systems. In single-tier cellular systems, intra-tier interference is a major limiting factor on performance. To mitigate this intra-tier interference, a scheduling algorithm is developed in the presence of an uncertain interference environment. Due to the limited knowledge about the interference, a "margin" is applied in estimating the transmission rate, that is, a backoff from the achievable rate in the previous packet transmission. This algorithm is overly conservative; so, the performance is not satisfying, especially in channels where the fading is relatively uncorrelated from packet to packet. It is diffcult to obtain good performance without knowledge of the interference. For two-tier femtocelular systems, the introduction of femtocells into existing macrocellular systems has the potential to significantly improve the coverage and capacity of these networks. However, the inter-tier interference caused to macrocellular users due to femtocellular transmissions is also a big challenge. In this thesis, the efficacy of applying beamforming (BF) with nulling at the femtocellular base stations (FBSs) is studied in order to mitigate the interference to macrocellular users. The performance of other transmission modes, such as no beamforming and transmit beamforming, are compared with beamforming with nulling, for both macrocellular and microcellular propagation scenarios. Simulation results demonstrate the effectiveness of beamforming with nulling for introducing femtocells with minimal effect on the macrocellular (microcellular) user.University of Delaware, Department of Electrical and Computer EngineeringM.S