Performance Analysis of the MIMO Receiver with Inter-Cell Interference and Imperfect Channel State Information in LTE-Advanced System

Abstract

Long Term Evolution-Advanced (LTE-Advanced) was adopted by International Telecommunication Union-Radiocommunication Sector (ITU-R) as the fourth-generation wireless communications system in January 2012. LTE-Advanced supports Multiple-Input Multiple-Output (MIMO), which uses multiple transmit and receive antennas to improve frequency efficiency, and Orthogonal Frequency-Division Multiple Access (OFDMA) to provide high flexibility in resource allocation for the downlink. A MIMO receiver may suffer performance degradation due to imperfect Channel State Information (CSI) and, depending on the cellular communication infrastructure, OFDMA may experience Inter-Cell Interference (ICI), which can lead to fatal performance degradation of User Equipments (UEs) located in cell edge regions. In this dissertation, we quantitatively analyze the impact of imperfect CSI on the Bit Error Rate (BER) performance and that of ICI by use of OFDMA, and consequently propose a new Fractional Frequency Reuse (FFR) algorithm which improves user throughput. Imperfect CSI causes channel estimation error and interference resulting from channel change between channel estimation events; all of these lead to the lowering of Signal-to-Interference-and-Noise Ratio (SINR) in the MIMO receiver and eventual performance degradation. A performance analysis must consider all of these factors. To this end, we consider a MIMO Zero-Forcing (ZF) receiver with simple structure for deriving the SINR, reflecting the effects of channel estimation error and interference, and then we develop BER expressions for M-ary Phase Shift Keying (M-PSK) and M-ary Quadrature Amplitude Modulation (M-QAM) in the most generalized Nakagami-m fading model to finally identify the results brought about by imperfect CSI. Imperfect CSI is mainly seen in UEs in cell edge regions, resulting partly from increased ICI from adjacent cells under OFDMA. Thus, we propose a new FFR algorithm seeking to improve cell edge and lower 5-percentile user throughputs under ICI in OFDMA. The proposed algorithm divides the full frequency band into six sub-bands and applies the Wrap-Around technique to deploy each frequency sub-band, mitigating ICI from adjacent cells. The proposed algorithm slightly lowers cell center user throughput, but it reduces the complexity of resource utilization and improves cell edge user throughput because the same allocation logic is applied to all cell regions. For the final step, we design and implement a System Level Simulator (SLS) based on LTE-Advanced system for performance analysis on the synthetic impacts of imperfect CSI and ICI. The SLS applies a packet scheduler, several MIMO modes and feedback types defined by the Third Generation Partnership Project (3GPP), and is implemented in a way that simulates the real-world environment, assuming a two-tier, 19-cell configuration. With such a model, we apply the MIMO ZF receiver having imperfect CSI and the proposed FFR algorithm. Finally, we comparatively analyze performance to prove that the user throughput is improved in LTE-Advanced system. The SLS implemented in this dissertation can further be used to locate some unexpected problems in advance when developing techniques intended for International Mobile Telecommunications-Advanced (IMT-Advanced), consequently reducing the development schedule and enhancing their performance. The findings of this research are expected to be useful reference data for improving system reliability and equity in resource allocation.