Adaptive Modulation Schemes for OFDM and SOQPSK Using Error Vector Magnitude (EVM) and Godard Dispersion

Abstract

In this paper, we develop a new approach which enables adaptation across two modulation schemes in the iNET standard: orthogonal frequency-division multiplexing (OFDM) and shaped-offset quadrature phased-shift keying (SOQPSK). We present the error vector magnitude (EVM) for OFDM and second-order Godard dispersion (D(²)) for SOQPSK as our link metrics that measure the degradation due to thermal noise and channel effects and then derive the mathematical relationship between these two metrics. This relationship enables us to utilize a set of empirically-derived rules that incorporate both modulation schemes.