Load-Modulated Single-RF MIMO Transmission for Spatially Multiplexed QAM Signals

Today, MIMO has become an indispensable scheme for providing significant spectral efficiency in wireless communication and for future wireless system, recently, it goes to two extremes: massive MIMO and single-RF MIMO. This paper, which is put in the latter, utilizes load-modulated arrays with only reactance loads for single-RF transmission of spatially multiplexed QAM signals. To alleviate the need for iterative processes while considering mutual coupling in the compact antenna, we present a novel design methodology for the loading network, which enables the exact computation of the three reactance loads per antenna element and also the perfect matching to the source with the opportunity to select appropriate analog tunable loads. We verify the design methodology by comparing the calculated values for some key parameters with the values from the circuit simulation. In addition, as an evaluation of the proposed architecture, we perform the bit error rate (BER) comparison which shows that our scheme with ideal loading is comparable to the conventional MIMO.