Distributed base station architectures represent the new trend that operators follow in order to resolve cost, performance and efficiency challenges when deploying 4G networks. Main components of such architectures are multimode radios capable of operating according to GSM, HSPA, WiMAX and LTE standards, known as remote radio heads (RRH). The key feature of remote radio heads is the extended software configurability which enables the deployment of more flexible and energy-efficient radio solutions. This paper describes a modern multi-mode radio system reference architecture and the major digital building blocks that when combined together enable multi-mode and more power efficient operation. It concentrates on blocks which can efficiently run multi-rate digital signal processing and blocks that increase radio power efficiency by linearizing the power amplifier output stage. The importance of a digital predistortion (DPD) block is emphasized and an adaptive polynomial approach based on cartesian to polar conversion is then proposed. Such radio architecture has successfully been implemented on a low-cost FPGA family meeting the WiMAX/LTE spectrum and Error Vector Magnitude (EVM) requirements.
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