We present an ultra low power MAC designed for battery-operated subcutaneous implants. Our MAC protocol addresses special communication needs of medical implants like latency, emergency messaging, priority etc., while maintaining an extremely low power-consumption profile. The paper presents the design choices made for a practical cardiac intra-body network and exploits the inherent asymmetries of the network to reduce power consumption. We present a new scheme for deriving analytically the power-optimised TDMA frame parameters like beacon interval and discuss a hardware solution to manage synchronisation overhead. Equations for deriving the duty-cycling efficiency are presented and the packet error rate is calculated for the in-body wireless channel. Our results and simulations show that our protocol is several times more efficient than the state of the art ultra low power protocols. Thus, we illustrate and validate our solution for a very real use case: cardiac networks. However, our new methodology can be applied for any Body Area Network. In this sense, our paper presents a ‘universal’ solution.

Since the release of spectrum by FCC in 2002 the UWB standard has undergone some significant changes, the most important being the elimination of full bandwidth (FBW) peak power constraint. Under new regulation, while the concept of average power (-41.25 dBm/MHz) remains the same, the new regulation adds the notion of a peak power density (PPD) limitation. In our recent work, we proposed a new model to compute the in-body path loss for standards lying beyond the 2.4GHz band and thereby demonstrated the feasibility of UWB for biomedical implants. In this paper we extend that work and show that in light of the aforementioned revision of UWB standard, we can leverage the PPD provision to enable longer ranges for low data rate applications such as most in- and on-body medical-implants.

Medical implants operate on a tight power budget and have very low latency communication requirements. To reduce power consumption, medical implants typically contain an additional radio, called wakeup receiver (WURX). WURX is an ultra low power receiver and it monitors the channel for “start of communication” command. To further scale down the power consumption, WURX is heavily duty cycled which causes latency and in turn adversely affects the alarm situations where immediate communication is required. This paper proposes a new scheme i.e. use of UWB as “wake up transmitter”(WUTX) radio in medical implants. We show that the new scheme enables the implant to initiate communication under alarm situations, with very low latency with the base-station, a key improvement which was thus far not possible with the conventional WURX enabled medical implant radios. We carry out a power and link budget analysis of this UWB-TX to show that the proposed scheme imposes a very low energy overhead and permits operation inside human tissue.

This paper presents an ultra low power MAC designed for in-body implant network. We show how an in-body implant network, has its own unique set of requirements (priority, latency, throughput etc.) which are not addressed by generic BAN(body area network) protocols which are designed assuming identical sensors. By choosing a particular use case, we demonstrate how we can exploit disparities inherent in a typical implanted BAN to enable ultra low power operation which also meets other (often) competing requirements. We present a new MAC scheme, which allows ultra low power operation by handling the nodes in accordance to their power and latency requirements. We present a new scheme for deriving analytically the power-optimised TDMA frame parameters like beacon interval and discuss solutions to manage synchronisation overhead. Equations for deriving the duty-cycling efficiency are presented and the packet error rate is calculated for the in-body wireless channel. Our results and simulations show that the protocol outperforms best of reported MACs and for low data rate sensors (typical of BAN) our MAC allows close to standby limit power consumption.

Medical implants are battery-powered, and have very stringent power consumption requirements. Devices like pacemakers consume few tens of microamps and last for well over 7-8 years. RF technologies are increasingly enabling communication and configuration of these medical implants. The Federal Communications Commission (FCC) has allocated a dedicated spectrum for operation of medical devices, the Medical Implant Communication System (MICS). This spectrum is in the range of 402-405 MHz and has suitable propagation characteristics through human tissues. Other narrow band low power standards (ZigBee) also exist and are used for on-body applications. The disadvantage of all these narrow-band standards is that their receivers require power hungry components like VCO, PLL and ADCs. Moreover, their power consumption does not scale down with data rates. Ultra wide band (UWB), in its simplest form, Impulse Radio (IR), is a promising low complexity standard. IR-UWB is the natural choice for low-power and low-data rate sensor nodes since for IR-UWB power scales down with low data rate. An UWB-IR transmitter is simple to design and power consumption and complexity are more on the receiver side. Hence, in applications like pacemakers and defibrillators, where the external base station has less stringent power requirements, UWB-IR becomes an option worth studying. Unfortunately, while UWB has been investigated for on-body medical implants no study has been done yet to show the feasibility of UWB for in-body medical implants. We look at the feasibility of UWB signals when they propagate inside human body. We present a MATLAB model for the path loss inside human body tissues for different distances and frequencies in the UWB range, starting with the theoretical background and going on to the complete model. Our results show that despite significant attenuation inside human tissue, UWB signals can be a promising low power.

Today's medical implants communicate with each other over radio, typically using standards such as MICS. However, in order to reduce power consumption and improve datarates, we need to explore better standards. Ultra wide band radios (UWB) are known to be low power. While studies on UWB radios for on-body implants exists, no study exists which explains the effect of UWB for in-body medical implants. This paper shows that Ultra wideband (UWB) can be a feasible solution for in-body medical implants in certain cases. We present a model to compute path loss inside human body tissues, for frequencies in the UWB standard, a study that has not been done so far. Furthermore, we extend this model to include reflection losses. We will show from our study that UWB is an excellent option for short-distance inter-implant communication and combined in- and on-body communications.