Towards Ultra-Low Power OFDMA Downlink Demodulation.

OFDMA downlink design allowing parallel processing OFDM subcarriers is adopted by a number of commercial wireless standards such as LTE, 5G, and 802.11ax. However, the widespread adoption of OFDMA downlink on low-end IoT devices is stymied due to the existing digital receiver framework's ≈100mW power consumption, which is mainly incurred by LO+mixer, ADC, and complex digital processing. In this paper, we present an ultra-low-power OFDMA downlink demodulation design, which achieves ≈100 μW receiving power. Our basic idea is to transform the current digital demodulation approach into the analog one based on filtering, which avoids those power-hungry components. We achieve this by proposing a series of novel RF front-end hardware designs: 1) a μ W-level two-stage mixing scheme that enables adjustable and precise subcarrier filtering, 2) a quartz crystal-based filter circuit incurring negligible insertion loss, and 3) a passive phase-to-envelope conversion technique enabling low-power non-coherent phase demodulation. We build a prototype to verify the proposed schemes. Experimental and IC simulation results show that: our new design can achieve 130 -- 1500 times power savings depending on the number of subcarriers that need to be processed in parallel, compared with the traditional all-digital design.