RF front-end considerations for SDR ultra-wideband communications systems

Abstract

he conventional design approach for T software-defined radio (SDR) receivers tends to minimize the RF analog frontend by transposing RF processing in the digital domain as much as possible. However, this approach is no longer appropriate for impulse ultra-wideband (UWB) applications because of bandwidth constraints and consequently the required sampling and processing frequencies as well as associated power consumption. For this reason, it is necessary to rethink the problem. In addition, UWB imposes specific constraints for features like low-cost designs and optimized run-time performance (i.e. low power consumption). The best way to address these issues is to perform fast and complex processing in an analog passive front end and provide the digital SDR part with reducedbandwidth signals. Hence, the following characteristics are required for the front end: ■ Passive analog frontend (low cost and low power consumption). ■ Easy-to-integrate. ■ Pre-processing that only extracts the necessary metrics (i.e. sufficiently informative statistics to solve essential questions such as detection and transmission issues). ■ Adequate bandwidth for low-cost analog-to-digital converter (ADC) and realistic digital processing speed. ■ Relaxed synchronization means. ■ Multiple usage of the same RF front-end output for several applications managed by SDR. ■ Multiband support for high data rates (each band having convenient characteristics for SDR capabilities) in a way that allows for parallelization of the subsequent digital processing. Thus, based on a non-coherent energy detector, an original demodulation scheme was designed and investigated for a multiband on-off keying modulation system. For this receiver, channel estimation constraints were relaxed and suitable signal processing schemes were developed with requisite hardware architecture derived. Only approximate delay spread and energy levels are needed, and the associated optimum demodulation turns out to be a non-trivial energetic threshold comparison. We have analytically computed the solution Figure 1. Non-coherent elementary receiver