Efficient Power Division Multiplexing in MIMO Systems

For the physical (PHY) layer in the 5th generation (5G) networks, there may be only time division multiplexing (TDM) and orthogonal frequency division multiplexing (OFDM) as candidates to serve multiple information flows via a single wireless link. Such two multiplexing schemes require the timing/ frequency synchronizations strictly, which is not suitable for power division based medium access control (MAC) protocols, i.e., non-orthogonal multiple access (NOMA). To address this, associating with multiple-input multiple-output (MIMO) techniques, a power division multiplexing (PDM) scheme is proposed as an alternative option to MIMO-TDM/MIMO-OFDM. The proposed MIMO-PDM directly utilizes the division of transmit power to replace the conventional time-slot/sub-band for the different information flows. Thus, it owns high compatibility with NOMA which is a promising multiple access protocol in 5G. With regarding the quality of service (QoS) required by the information flows, this paper derives the optimum power division of MIMO-PDM in conditions of multiple-input single-output (MISO), single-input multiple-output (SIMO), and MIMO, respectively. Additionally, we study the optimum pre- and post-coding of MIMO when serving arbitrary number of information flows. The proposed optimization algorithms of MIMO-PDM own reasonable computational complexity which is not higher than the classic water-filling algorithms. Consequently, the proposed MIMO-PDM could efficiently achieve the optimum performance as well as ensure the QoS of multiple information flows.