Using Two, More, or a Massive Number of Antennas

This chapter talks about the benefits, and also the challenges, when the transmission and reception are supported by more than one antenna. If the distance between two antennas is at least half a wavelength, then the small scale fading at these antennas can be considered uncorrelated. The chapter introduces the concept of spatial multiplexing or communication through multiple spatial channels, which is possible in a multiple input multiple output channel (MIMO) setup, where both the transmitter and the receiver have multiple antennas. It discusses the concept of spatial multiplexing or communication through multiple spatial channels, and the basic ideas of massive MIMO, a disruptive concept inspired by the asymptotic properties of large antenna arrays. The use of multiple antennas and digital beamforming through precoding allow Bastian to apply space division multiple access (SDMA). Spectrum sharing by SDMA is critically dependent on information of the dynamically changing channel coefficients.