Block-Diagonalization Applied in Multi-User Massive MIMO

One of the main areas of research for the next generation of mobile communications (5G) is the concept of Massive MIMO, which implies using base stations that employ a considerably larger number of antennas than the classic MIMO systems (tens or even hundreds of antennas). The challenges become increasingly difficult when it comes to dealing with multiple mobile stations (MU-MIMO system) sharing the same time-frequency resource. This paper treats the downlink direction case. In a hypothetical system implementation in which the base station (BS) applies a classical "point-to-point" MIMO precoding method the mobile stations have to make use of a collaborative detection method, where each mobile station is required to share its received signals as well as channel information to all others. In order to avoid the need of a collaborative detection scheme, the BS needs to apply a precoding scheme that is capable of eliminating inter-user interference: each user should receive only its own signals and not the ones intended for the other users. This paper investigates the scalability of the Block Diagonalization MU-MIMO digital precoding scheme in a multi-user Massive MIMO system.