Asymmetric Decomposition of Single Carrier QAM for Efficiency Enhancement of PAs

This study presents a polarization-division multiplexing (PDM) of asymmetric decomposed quadrature amplitude modulation (QAM) in a single carrier to enhance the power amplifier (PA) efficiency in the presence of cross-polarization interference (XPI). A high-order QAM is decomposed into two asymmetric low-order QAMs which will be subjected to PDM, and they are amplified using separate PAs to enhance efficiency while having a reduced peak-to-average power ratio (PAPR). Since XPI induces degradation in error vector magnitude (EVM) within PDM, a technique for recovering the EVM, enabled by the asymmetric decomposition, is proposed and applied. When the scale parameters $\alpha $ and $\beta $ are optimized, the proposed system yields an average dc power reduction ratio of 54%/67%/72% while it becomes 40%/52%/51% for the nonoptimized scale parameter ( $\alpha=\beta $ = 1) compared with the original 16/64/256 QAM, respectively. In addition, a prototype system is fabricated to validate the feasibility of the proposed approach. The dc power consumption of PAs in both systems is measured, and the symbol error rates (SERs) are estimated based on the measured EVM. With the nonoptimized scale parameter, the fabricated system achieves a dc power reduction ratio of 32.5%/43%/43.4% compared with the original 16/64/256 QAM, respectively, while exhibiting improved SER.