Energy-Efficient Synchronous CDMA for Multiple Channel Access in Internet of Bodies

This paper introduces an energy-efficient code-division multiple access (CDMA) architecture for wearable devices for the Internet of Bodies (IoB), which is an emerging data communication framework for connected sensor nodes around the human body. To address the challenge of simultaneous data transmission from multiple transmitters, which often leads to interference, we propose the adoption of standard-basis based CDMA encoding and decoding, which has higher energy efficiencies than the traditional Walsh code-based implementation. We also present a novel architecture for body-worn sensor nodes and data aggregators, where both the sensor nodes and the aggregator possess transceiver functionalities for (1) transmitting data from the sensors to the aggregator, and (2) sending clock synchronization information from the aggregator to the nodes. Acknowledging the synchronization requirements of CDMA, a Clock Data Recovery Circuit (CDR) module is integrated within the body-worn nodes. Experimental results with iCE40 wearable FPGAs, under the assumption of synchronized clocks, validate the effectiveness of CDMA encoding and decoding with 4 sensor nodes. The overall energy efficiency for the sensor node with circuit-level simulations using a standard 65nm process is found to be only 62 pJ/bit (> 3× better than literature) at 1 Mbps.