On the Design of RD-MIMO: Spatial Multiplexing Versus Opportunistic Transmission Schemes

In this work, we focus on the implementation of reconfigurable distributed multiple-input multiple-output (RD-MIMO) schemes in practical communication environment. Considering RD-MIMO schemes, we raise an original research question, i.e., under what scenario whether we should recruit-then-transmit to multiple mobile receivers simultaneously or just recruit-then-transmit to one best selected mobile receiver. To address this question, we design a spatial multiplexing RD-MIMO (SM-RD-MIMO) scheme and an opportunistic RD-MIMO (O-RD-MIMO) scheme for the scenario of multiuser communication and that of one single best user communication, respectively. Aiming at the practical implementation of the RD-MIMO schemes, we choose zero-forcing (ZF) and maximal ratio transmitting (MRT) as beamforming strategies for the SM-RD-MIMO scheme and the O-RD-MIMO scheme, respectively. To evaluate the performance of the proposed schemes, we formulate sum rate maximization problems and solve the formulated problems analytically under some specific network settings. Through analytical and numerical examples, we show that the SM-RD-MIMO scheme outperforms the O-RD-MIMO scheme at moderate and high transmit signal-to-noise ratio (SNR) regimes, and vice versa at low transmit SNR regime. In addition, via numerical results, we provide a new finding that the ZF precoding under dynamic transmit power threshold-based per transmitter power constraint (PTPC) gives the same performance as that of the ZF precoding under sum power constraint (SPC).