Industry Compliant Wireless Power and Data Transfer Module Towards Ensuring Battery Denial of Service Protection

Abstract

The field of active implantable medical devices (IMDs) has made huge steps forward in the last years. IMDs are used today for the treatment of previously untreatable conditions as well as the continuous monitoring of the health of patients. The field, where active IMDs have been the most successful, is the field of neurological conditions, on which traditional medicine such as the intake of pills has very limited effect. In order to take full advantage of the possibilities offered by the IMDs it is vital to have communication between them and the external world. In this way, the treatment method provided by the IMD can be configured and optimized for each separate individual, achieving the best possible results. Moreover, the state of the device itself can be assessed and therefore possible flaws in its operation can be detected and corrected. Finally, in case of monitoring the patient’s health condition communication is also vital.
However, this communication between the external world and the implanted device also introduces the possibility for someone, that possesses the required expertise and skills, to hack the device. The hacker can possibly “eavesdrop” the communication channel in order to extract information regarding the patient or even act in order to change parameters of the device and the therapy it provides, possibly causing harm to the patient. One way for hackers to disrupt the normal operation of the IMD is to drain its power source, namely the battery of the device, an attack that is named battery denial of service (BDoS) attack. One of the easiest ways to achieve such an attack is to make the device commit valuable power resources in order to run the authentication protocols continuously, by non-stop requesting for access. In this thesis, we try to tackle this problem by creating an analog circuit module that can act as an add-on to commercial IMDs that will have the task of authenticating the user that is trying to communicate with the IMD by making use of harvested wireless energy that is required for the communication. In this way, we expect to relieve the IMDs from spending time and resources on the authentication process. To that end, we designed and created an analog experimental prototype that employs both wireless power transfer and data communication, by simply making use of off-the-shelf components. The goal of this experimental prototype is to identify further challenges that can arise in a so called zero power defence scenario.
To that end we implement a system that makes use of near-field resonant inductive coupling as a wireless power transfer method and is able to provide some mW of power across distances of up to 2cm, an amount of power that is sufficient to drive a microcontroller that can execute a low power security protocol in order to authenticate the entity trying to access the receiver. In addition to that, it can achieve a downlink data rate of 200kbit/s using amplitude shift keying modulation and an uplink data rate of 1kbit/s by making use of passive load shift keying modulation. This system is a unique implementation, since it constitutes the only solution that implements a highly asymmetrical bidirectional link by making use of ASK and LSK modulation and has a completely wirelessly powered receiver. Moreover, since this implementation was achieved with simple off-the-shelf components, there is a large margin of improvement in terms of size and efficiency if such a system was to be designed as an ASIC.