Capacity analysis of a peripheral nerve using modulated compound action potential pulses

Artificial neural stimulation of a peripheral nerve can create an in-body data communications channel. We propose the stimulation of a peripheral nerve using energy-harvesting arrays of nanodevices, embedded in biocompatible tissue patches. The resulting extracellular compound action potential (CAP) pulse can provide a data bit-stream for communicating with an embedded receiver. Our objective is to determine the maximum achievable transmission range of a CAP along a nerve and the maximum sustainable bit rate. We model the generation of a CAP and then compute the reduction in amplitude and the spreading of the pulse with propagation distance. The channel capacity is calculated for ON-OFF keying (OOK) and digital pulse interval modulation. We show that the transmission range depends on the number and diameters of the activated neurons contributing to the CAP amplitude and width. Our modulation analysis demonstrates the effects of attenuation, background noise, the neural refractory period, and pulse broadening on the achievable bit rate. We show how a maximum OOK bit rate of 200 bit/s can be sustained over transmission distances greater than 100 mm. The proposed approach provides a low bit rate, unidirectional asynchronous transmission system that could, for example, deliver simple instructions to an embedded drug-delivery system.