Smart RF signal processing for advanced transmitters: From theory to practice

Multi-band multi-standard Base Stations (BS) are believed to be one promising solution to manage the coexistence of different technological standards (e.g. 2G/3G/4G) with reasonable installation and operation costs. Except for multi-technology baseband (BB) units and multi-band/broadband RF-frontends e.g. antenna and Power Amplifier (PA), the realization of such BSs requires sophisticated cooperation between digital BB and analog components to reduce frontend costs and to enhance energy efficiency, flexibility and transmission quality. Such a concept is called “Smart RF”. In this paper, we investigate the prototype implementation of practical digital signal processing techniques for performance enhancement of the RF-frontends and analog BB components in multi-band multi-standard transmitters. These techniques include the digital compensations of I/Q-imbalance, modulator (MOD) DC-offset and PA nonlinearity. A prototype platform is described where realtime impairment compensation circuits are implemented. Practical implementation issues incl. complexity and synchronization are discussed. Finally, experimental measurements are presented, which verify the effectiveness of the implemented Smart RF techniques.