On the impact of receiver RX filters on EDGE EVM measurements

Contemporary GSM networks use a modulation technique known as Gaussian minimum shift keying, GMSK, while EDGE (enhanced data rates for GSM evolution) utilizes eight phase shift keying, 8-PSK. 8-PSK operates in the same 200 kHz GSM bandwidth supporting three times higher data rates while permitting the coexistence of EDGE and GSM services (see Mashhour, A., 1999). The QPSK mapping technique converts the binary information into phase information, representing a specific location on the Fresnel plane. Noise and the nonlinear behavior of semiconductor devices can alter the location of recovered data on the Fresnel plane. To examine this dependency, one can employ the error vector magnitude (EVM) concept. ETSI (see "Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular Systems", 1995) introduces five intersymbol interference (ISI) symbols to the processed signal. These complicate the hardware implementation as well as the interpretation of the recovered data when achieved by different methods. This article considers the influence of noise and AM-AM and AM-PM distortion on EVM measurement by comparing three receiver RX-filter architectures, based on the zero forcing filter principle, a zero forcing filter combined with matched filtering principle and ETSI measurement protocol.