Theoretical analysis of the trade-off between power efficiency and linearity for power amplifiers in carrier aggregated systems.

Abstract

The bandwidth and data rate gains achieved by carrier aggregation led to its evolution through LTE releases R10 (LTE-Advanced) to R15 (5G NR). However, the aggregation of multiple OFDM and SC-FDMA signals suffer from high Peak-to-Average-Power-Ratio (PAPR), which in turn affects the High Power Amplifier (HPA) by inducing non-linearities and causing deterioration in the power efficiency, in band and out of band distortions. However, there exists a fundamental trade-off between power efficiency and linearity in the High Power Amplifier. This complicates the design of a high performing system on both aspects. This thesis serves to present a Carrier Aggregated OFDM system that combines PAPR reduction with Digital Predistortion to achieve a good trade-off between efficiency and linearity. Towards meeting this goal, we thus follow a three step process where we first analyze and reduce the PAPR of the CA-OFDM system by deriving the probability distribution of PAPR in CA-OFDM systems and proposing a new PAPR reduction method. Then we study existing linearization techniques and apply the well-known technique of Digital Predistortion (DPD). Finally, we combine the proposed PAPR reduction method with DPD to study the overall system performance. Our obtained results indicate that combining PAPR reduction and Digital Predistortion enhances the performance of the system in terms of lowering the Adjacent Channel Power Ratio and reducing the needed Input backoff thus increasing the power efficiency.