ISBN 9783843924252

978-3-8439-2425-2, Reihe Elektrotechnik

Alessio Farabegoli
Digital Predistortion and Crest Factor Reduction Architectures for Mobile Radio Handset Transmitters

211 Seiten, Dissertation Universität Erlangen-Nürnberg (2015), Softcover, B5

Zusammenfassung / Abstract

Modern 3G and 4G communication standards utilise signals with high spectral efficiency and complex modulation schemes. The high Peak-to-Average Power Ratios (PAPRs) achieved by High Speed Packet Access (HSPA) and Long-Term Evolution (LTE) signals strongly reduce the efficiency of Power Amplifiers (PAs), which are themselves key elements in the transceivers. Several techniques, e.g. average power tracking or dynamic load-line modulation have been investigated in an attempt to simultaneously improve PA linearity and efficiency. Baseband digital processing techniques are also good candidates: the use of cost-effective components, benefitting from Moore’s law and from high flexibility, makes them an optimum solution for improved mobile PA performance. Digital Predistortion (DPD) and Crest Factor Reduction (CFR) are concepts that follow this approach. DPD extends the PA linear output power by counteracting its distortions, thus the PA efficiency arises. By contrast, CFR decreases the dynamic range of the baseband signal by introducing distortions. This leads to a reduced peak power, which translates to lower RF stress and chip area. The scope of this work is to develop enhanced architectures which can improve the trade-off between adaptation capability, low complexity and high performance that limit today the usage of CFR and DPD in cellular transmitters. The state of the art is improved by the following three main steps: 1. a high precision PA model is developed to allow a fast optimisation and verification of new concepts. 2. novel CFR and DPD techniques are derived without interlinking them showing that the current state of the art applicable to mobile transmitters can be improved with concepts focused on the cellular case of study. 3. a complete analysis of combined CFR and DPD architectures is investigated to understand the operation of this type of system, which has been known to present contradictory results. A novel concept for a joint architecture based on an optimisation technique is developed for finding the optimum compromise between linearity, efficiency and reduced PAPR, by utilising the EVM and ACLR performance margins. The capabilities of the concepts presented here are confirmed using a PA module for mobile communications, working in the high frequency bands (1900-2100 MHz) and manufactured with Gallium-Arsenide (GaAs) technology.