Efficiency-Enhanced Dual-Input Transmitter Using Over-the-Air Combination for MIMO Systems

In this article, a dual-input transmitter (Tx) architecture with dual-power amplifier (PA) dual antennas is presented for multiple-input multiple-output (MIMO) systems. The baseband signal is split into two data streams with different peak-to-average power ratios (PAPRs) in the time domain, which are transmitted independently and recombined at the receiver antenna to boost Tx efficiency. An optimal PAPR and power-level configuration strategy is established, which is a constant threshold separation algorithm (CTSA), based on an efficiency prediction method and the distribution of modulation signals (MSs). In CTSA, the PAPR of the separated signal is correlated with the power level. Furthermore, a dynamic threshold separation algorithm (DTSA) is proposed to expand the solution space of the separated signal by decoupling the power from the PAPR of signals using an amplitude control factor. In addition, the spatial adjacent channel power ratio (ACPR) is utilized to evaluate the pollution to other systems in space by bandwidth expansion caused by signal separation. In DTSA, the optimal configuration strategy of PAPR and power under spatial ACPR constraints can be obtained. The Tx architecture is verified at 3.5 GHz with three different spatial ACPR requirements. For an MS with 8.4-dB PAPR, the optimal average efficiency of the Tx can be improved by 1.2 $\times$ compared with a uniform linear array (ULA) with 58% saturation efficiency of PAs. At the desired receptive end, the EVM and ACPR of the recombined signal achieve below $-$ 33 and $-$ 45 dBc, respectively, after linearization.