EVM Degradation in LTE Systems by RF Filtering

This report presents the results of an investigation into the EVM rise experienced by an LTE signal as it passes through an RF band pass filter of the type found in the front end of a typical cellular Node B.

Section 2 defines the meaning of EVM for LTE signals, as set out in the 3GPP standard. A method is also presented for estimating the EVM performance of RF filters based on their measured S-parameters.

Section 3 describes an experimental test bench that was used to perform a variety of LTE EVM measurements on an RF filter having high levels of amplitude, phase and group delay ripple across its pass band.

Section 4 presents a number of screenshots from the LTE test bench, showing the RF spectra of some typical LTE signals, and the results screen of the Vector Signal Analyzer that was used for measuring EVM.

Sections 5 & 6 present the experimental results of EVM testing on an RF filter using both downlink and uplink signals respectively, under a range of different conditions.

The final section of the report presents some concluding remarks about the lessons learned in the course of this investigation.