A low power software-defined-radio baseband processor for the Internet of Things

In this paper, we define a configurable Software Defined Radio (SDR) baseband processor design for the Internet of Things (IoT). We analyzed the fundamental algorithms in communications systems on IoT devices to enable a microarchitecture design that supports many IoT standards and custom nonstandard communications. Based on this analysis, we propose a custom SIMD execution model coupled with a scalar unit. We introduce several architectural optimizations to this design: streaming registers, variable bit width datapath, dedicated ALUs for critical kernels, and an optimized flexible reduction network. We employ voltage scaling and clock gating to further reduce the power, while more than a 100% time margin has been reserved for reliable operation in the near-threshold region. Together our architectural enhancements lead to a 71× power reduction compared to a classic general purpose SDR SIMD architecture. Our IoT SDR datapath has sub-mW power consumption based on SPICE simulation, and is placed and routed to fit within an area of 0.074mm2 in a 28nm process. We implemented several essential elementary signal processing kernels and combined them to demonstrate two end-to-end upper bound systems, 802.15.4-OQPSK and Bluetooth Low Energy. Our full SDR baseband system consists of a configurable SIMD with a control plane MCU and memory. For comparison, the best commercial wireless transceiver consumes 23.8mW for the entire wireless system (digital/RF/ analog). We show that our digital system power is below 2mW, in other words only 8% of the total system power. The wireless system is dominated by RF/analog power comsumption, thus the price of flexibility that SDR affords is small. We believe this work is unique in demonstrating the value of baseband SDR in the low power IoT domain.