EVM Analysis for Broadband OFDM Direct-Conversion Transmitters

Low-cost orthogonal frequency-division multiplexing (OFDM) direct-conversion transceivers suffer from signal degradation through the impairments of the analog front end, e.g., due to in-phase and quadrature (IQ) imbalance, phase noise, and nonlinear power amplifier (PA) effects. This paper analyzes joint performance degradation due to these key transmitter imperfections. Error vector magnitude (EVM) is chosen as the figure of merit, which is motivated by its frequent use in the standards for specifying transmitter requirements. In particular, we derive closed-form EVM expressions for the challenging problem of wideband OFDM transmitter design and validate the analysis through simulations. Based on the study, it is possible to conclude that EVM is governed by the memory effects associated with the PA and the reciprocal of the image rejection ratio (IRR), which is defined by the IQ modulator. We also demonstrated that intercarrier interference (ICI) due to the local oscillator phase noise shows an approximately frequency-flat response.