Analysis of a Phase-shift Technique for Inter-modulation Cancellation Proposed for 2-Carrier QPSK Systems

In communication systems, amplifiers introduce distortions due to a nonlinear input-output power characteristic, known as the amplitude modulation to amplitude modulation (AM/AM conversion), and a nonlinear input power-output phase characteristic known as the amplitude modulation to phase modulation (AM/PM conversion). When a signal composed of more than one carrier is applied to such a system, integer multiples of main frequencies are added/subtracted to form unwanted frequency components known as inter-modulation distortion (IMD). These components have a degradation effect on the performance of the system concerned. Various baseband, IF, and RF techniques have been proposed to combat this. These techniques usually result in minimizing non-linear distortion effects and hence improving the performance of communication systems. In this paper a phase-shift technique is proposed to completely suppress selected IMD products