Precoding, Pilot Contamination and CSI Acquisition in Massive MIMO Systems: State of Art and Research Trends

Wireless communication is becoming increasingly important for micro economic indicators as the contribution of mobile broadband penetration to gross domestic product (GDP) growth is clearly established now. Developments in wireless technology like high bandwidth, low latency, resilience and reliability are further going to propel the economy. As we advance to long term evolution (LTE),5G, beyond 5G and 6G, massive multiple input multiple output (MIMO) systems become an integral part of technology development for addressing higher bandwidth requirements. With ultra-mobile broadband requirements of Industry 4.0 Internet of Things (IoT) applications, importance of 5G, beyond 5G, and 6G and hence massive MIMO systems becomes even more pressing. This paper presents a comprehensive review of three aspects precoding, pilot contamination and channel state acquisition of massive MIMO networks, its advancements and challenges while moving towards 6G wireless communication network. The paper highlights the paradigm shift brought by future wireless generation, characterized by enhanced energy efficiency, spectral efficiency, massive device connectivity, and higher frequency bands. The paper also explores its role in augmenting overall network performance via advanced techniques for signal processing. Considering the commercialization trajectory of MIMO technology and its integration into modern telecommunications, the paper highlights the ongoing research directions and future potential of massive MIMO networks gathering aspiring demands of 5G, beyond 5G and 6G wireless networks.