High Order QAM Performance Under Phase and Amplitude Distortions

Abstract

High Order QAM such as 512QAM, 1024QAM along with mm-wave transmission is one of the strong candidates for next generation wireless networks. However, due to nonlinearities of RF devices the performance of higher order QAM may be hampered and restrict the transmission rate. As observed in many studies in the literature, outermost constellation points are usually more adversely affected by these impairments. In our previous work, we analyzed this effect by using the Rapp model. Namely, only amplitude distortion on the constellation points was taken into account, where in-phase and quadrature distortions originating from the model can be assumed as independent. In this work, in addition to amplitude distortion, we add phase distortion to the system by using the Saleh model and adding phase distortion prevents us to assume that in-phase and quadrature parts of the distortions are independent according to our observations. In this work, focusing on non-uniform EVM values of each QAM symbol we evaluate achievable rates by considering correlation between in-phase and quadrature distortions. Moreover, we propose a receiver that considers correlation between the in-phase distortion and the quadrature distortion and the unequal EVM distribution by assessing each symbol’s distortion. The performance of the receiver is compared with that of other two receivers.