Evaluation and characterization of a reduced-bandwidth sampling system for predistorting broadband E-Band communication links

Abstract

Today’s communication link modulation formats, such as 5G New Radio or wideband Code Division Multiple Access (CDMA), require highly linear Radio Frequency (RF) front-ends to allow for sufficient bandwidth and efficient transmissions. Power Amplifiers (PAs) are the communication link’s predominant nonlinear component. To avoid nonlinear behavior, PAs have to be operated in back-off in terms of PA input power. However, limiting the PA’s input power reduces the available bandwidth and leads to PA inefficiency. If PA’s linear amplification region would be higher, efficiency could be improved. One approach to compensate for PA nonlinearity is Digital Predistortion (DP). However, broadband DP puts high demands on the Analog-to-Digital Converters (ADCs) in terms of sampling rate. Therefore, costly broadband ADCs are required. To address this issue, the Institute of Robust Power Semiconductor Systems (Institut für Robuste Leistungshalbleitersysteme, ILH) developed a low-cost Printed Circuit Board (PCB) that claims to be suitable for sampling 2.5GHz baseband signals and therefore allowing for DP. This is achieved by downconverting and by sampling the broadband input signal in individual and narrowband frequency windows using a frequency mixer. In this study, it was investigated, whether the new PCB is capable of downconverting and sampling of 2.5GHz bandwidths for a satellite communication link. During testing, it was found that the hardware is not capable of sampling broadband signals due to a missing filter. Nevertheless, it was possible to sample a bandwidth of 700MHz by adding filters manually. This implies, that the concept of sampling a broadband signal using low-cost components works. However, in this thesis only the PCB and its sampling capabilities were examined and no DP was performed. Future studies might successfully develop and verify DP using low-cost, broadband downconverting and sampling PCBs. Such PCBs could be beneficial in predistorting broadband satellite communication links.