EVM Simulation and Analysis Techniques

Abstract

EVM (Error Vector Magnitude) is used as the metric for transmitter signal quality compliance in many modern communication systems. Examples include IS-54/IS-136, GSM/EDGE, 3GPP-WCDMA, and 802.11a/b/g wireless LAN commercial standards. MUOS (Mobile User Objective System) [1][3] is an example of a next generation military communications system leveraging the commercial use of this metric. Both engineering analysis and simulation were used to develop the EVM specification for MUOS. The approach is described in this paper. All major aspects of a transmitter physical layer system were studied, including the impact of distortions due to modulator imbalances, phase noise, non-linear amplifiers, spurs, and non-ideal filtering. For illustrative purposes, specific data values for individual distortions are taken from the TDRSS [4] and WGSS [5] transmitter systems, published in open literature to represent performance typical of a transponding satellite using an 8PSK [4][5] waveform. Matlab simulation results are compared to analytical predictions for a generic transmitter system, validating the technical approach used in MUOS. The resulting transmitter signal distortion is translated from EVM to Ec/No degradation for determination of end-to-end link performance. Practical issues on EVM laboratory measurements and the diagnostic value of EVM are also addressed.