Increasing SDR receiver dynamic range by ADC diversity
Nowadays, most radio implementations are based on software-defined radio (SDR) technologies. The capabilities of digital signal processing enable new applications like low power wide area networks (LPWAN), which are expected to play a decisive role in the upcoming Internet of Things. Centralized gateways, usually realized in an SDR architecture, are used to connect many thousands of objects to the internet. Due to the high variance of the received signal level, a high dynamic range is required for the SDR receiver front-end. In current receiver architectures, the dynamic range is mainly limited by the analog-to-digital converter (ADC). Several techniques have been proposed to extend the dynamic range by stacking multiple ADCs and driving them with different gain factors. Correlation of quantization noise was identified as key parameter to determine the dynamic range enhancement. This paper compares the proposed techniques and extends existing analysis tools for the use of arbitrary gain factors. Additionally, the influence of further noise sources like thermal noise and jitter are taken into account. The theoretical considerations are supported by simulations and measurements using a real LPWAN SDR implementation.