Spectral Efficiency Enhancement in Uplink Cell-free Massive MIMO System over Fading Channel

Abstract

The advancement of technology has produced huge changes in modern wireless communication systems. This rapid growth of technology has brought high data rates, low costs, and reliable transmission across active users. The current cellular massive multiple-input multiple-output (MIMO) system is better at connecting user equipment (UE), offering substantial capacity, and delivering high data rates within specific cells. However, these systems grapple with signal interference issues, particularly at cell edges, which can be problematic for mobile users. To address the interference challenges inherent in cellular massive MIMO, a cell-free massive MIMO system has emerged. Unlike current cellular massive MIMO systems, it does not rely on predefined cell boundaries; instead, it utilizes an array of distributed antennas to concurrently serve multiple users. This innovative technology has substantial promise for the evolution of wireless communication networks, including the development of beyond fifth-generation (B5G) wireless communication. In the uplink of a cell-free massive MIMO system, multiple UEs generate interference across various combining schemes. To mitigate this interference and enhance system performance, this thesis has proposed a hybrid decoding technique using partial minimum mean square error (P-MMSE) combining and dynamic cooperative cluster (DCC) with successive interference cancellation (SIC) technique, to reduce interference and increase the spectral efficiency (SE) of the cell-free massive MIMO systems over the Rayleigh fading channel. The proposed decoding uses the received signal at the central processing unit (CPU) to maximize the desired signal by minimizing the interference for a given UE. The proposed method improved the sum SE by 6.347% for 200 APs, 5 antennas per access point (AP), and 60 UEs compared to the P-MMSE. Additionally, the SE, bit error rate (BER), and number of complex multiplications also improved compared to existing techniques in the presence of interferences