Adaptive Suppression of Interfering Signals in Communication Systems

• Main Author: Pelteku, Altin E.
• Other Authors: Donald Richard Brown III, Committee Member
• Format: Others
• Published: Digital WPI 2013
• Subjects: interference suppression; adaptable RF front end; signal to interference ratio; blocking; differential amplifier; common mode rejection ratio; low noise amplifier; mixed-mode s-parameters; amplitude and phase mismatches; differential noise figure; third order intercept point; noise figure measurement; intermodulation distortion; harmonic balance; combline filter; dielectric filter; reflection type phase shifter; voltage variable attenuator
• Online Access: https://digitalcommons.wpi.edu/etd-dissertations/138; https://digitalcommons.wpi.edu/cgi/viewcontent.cgi?article=1137&context=etd-dissertations

The growth in the number of wireless devices and applications underscores the need for characterizing and mitigating interference induced problems such as distortion and blocking. A typical interference scenario involves the detection of a small amplitude signal of interest (SOI) in the presence of a large amplitude interfering signal; it is desirable to attenuate the interfering signal while preserving the integrity of SOI and an appropriate dynamic range. If the frequency of the interfering signal varies or is unknown, an adaptive notch function must be applied in order to maintain adequate attenuation. This work explores the performance space of a phase cancellation technique used in implementing the desired notch function for communication systems in the 1-3 GHz frequency range. A system level model constructed with MATLAB and related simulation results assist in building the theoretical foundation for setting performance bounds on the implemented solution and deriving hardware specifications for the RF notch subsystem devices. Simulations and measurements are presented for a Low Noise Amplifer (LNA), voltage variable attenuators, bandpass filters and phase shifters. Ultimately, full system tests provide a measure of merit for this work as well as invaluable lessons learned. The emphasis of this project is the on-wafer LNA measurements, dependence of IC system performance on mismatches and overall system performance tests. Where possible, predictions are plotted alongside measured data. The reasonable match between the two validates system and component models and more than compensates for the painstaking modeling efforts. Most importantly, using the signal to interferer ratio (SIR) as a figure of merit, experimental results demonstrate up to 58 dB of SIR improvement. This number represents a remarkable advancement in interference rejection at RF or microwave frequencies.