Error Vector Magnitude as a Figure of Merit for CDMA Receiver Design

Standards for modern digital CDMA communication systems specify limits on the error vector magnitude (EVM) of the transmitted signal at the transmitter, whereas performance at the receiver is characterized by the bit error rate (BER). Traditionally, RF receiver specification defines limits on amplitudeand phase ripple over a certain bandwidth, IP3, IQ-mismatch, DC-offset, etc. Unfortunately, these parameters lack an obvious relation to BER. In this paper, we show that the EVM offers remarkable advantages when used as a conceptual figure of merit to characterize the distortions caused by the elements of the receiver’s RF frontend. The use of the EVM as a parameter for the optimization of the RF receiver and for the description of the RF-BB (radio frequencybaseband) interface leads to a simple design process and avoids over-specification. For CDMA systems, we give an explicit relation between the EVM and the BER. Furthermore, the benefits of using the EVM in RF receiver design are illustrated by examples and verified by simulations.