Tradeoffs Between Wireless Communication and Computation in Closed-loop Implantable Devices

This paper discusses general tradeoffs between wireless communication and computation in closed-loop implantable medical devices for neurological applications. Closed-loop devices enable neural monitoring, automated diagnostics and treatment of neurological disorders. Several topologies for the loop are discussed, including within the implant, as well as implemented with a wearable, handheld or stationary processor. Common wireless communication data rate and range requirements and algorithmic computational requirements are summarized. As a case study, a 0.13 mu m CMOS neurostimulator SoC for closed-loop treatment of intractable epilepsy is presented. Its triple-band radio with a 1m 230Mbps pulse-radio, a 2m 46Mbps pulse-radio 2, and a 10m 1.2Mbps FSK radio provides a versatile transcutaneous interface. The in-implant processor has constrained computational resources which results in a limited detection performance - seizure detection sensitivity of 87%. A higher-performance signal processing algorithm implemented on a stationary device within a loop enhances the seizure detection performance which was improved to a sensitivity of 98% with three times fewer false alarms. This comes at the cost of an increased wireless transmitter power budget, if communicated directly. These results illustrate a fundamental tradeoff between the communication and computation in closed-loop electronic therapies for neurological disorders.