Future Multi-User MIMO Systems: A Discussion

Wireless communication technology is evolving at a fast pace to meet requirements of emerging applications, such as ultra-high resolution video, cloud computing, internet of things, etc. For example, it took only 2 years for cellular systems to evolve from LTE to LTE-A, delivering a 10 × increase in data rates. Almost at the same time that the first LTE-A service was launched, people are talking about next-generation (5G) wireless communication systems [3]. The coming 5G communication aims to connect tens of billions of devices with some reaching several gigabit-per-second data rates and milliseconds service latency. On the other hand, bandwidth is a scare resource, demanding revolution in wireless communication technologies to achieve these aggressive targets. Technologies being discussed include small-cell networks [7], millimeter wave communication [14], interference cancellation (e.g., full-duplex transmission [2]), advanced waveforms [6] (e.g., Generalized Frequency Division Multiplexing, Universal Filtered Multi-carrier, Filter-Bank based Multi-Carrier, Bi-orthogonal Frequency Division Multiplexing), Massive MIMO [4, 16], etc. Among those, Massive MIMO has been widely accepted, both in academia and industry, as one of the promising candidates for 5G. 3GPP is developing 3D channel models for this new MIMO technique. Studies for the Time-division duplexing (TDD) Massive MIMO have been initiated for 3GPP Release 13. In this chapter, we will focus on the Massive MIMO technology, discussing its basic concepts, state-of-the-art research progress, key signal processing in the digital baseband, as well as new challenges for designing reconfigurable architectures for its baseband implementation.