G. Enrico Santagati

Sonar Inside Your Body: Prototyping Ultrasonic Intra-body Sensor Networks

Biomedical systems of implanted miniaturized sensors and actuators interconnected into an intra-body area network could enable revolutionary healthcare and clinical applications. Given the well-understood limitations of radio frequency (RF) propagation in the human body, in our previous work we investigated the use of ultrasonic waves as an alternative physical carrier of information [1], and proposed Ultrasonic WideBand (UsWB), an ultrasonic multipath-resilient integrated physical and medium access control (MAC) layer protocol [2]. In this paper, we discuss the design and implementation of a software-defined testbed architecture for ultrasonic intra-body area networks, and propose the first experimental demonstration of the feasibility of ultrasonic communications in biological tissues. We first discuss in detail our FPGA-based prototype implementation of UsWB. We then demonstrate how the prototype can flexibly trade performance off for power consumption, and achieve, for bit error rates (BER) no higher than 10-6, either (i) high-data rate transmissions up to 700 kbit/s at a transmit power of -14 dBm (≈ 40 μW), or (ii) low-data rate and lower-power transmissions down to -21dBm (≈ 8μW) at 70kbit/s. Finally, we show how the UsWB MAC protocol allows multiple transmitter-receiver pairs to coexist and dynamically adapt the transmission rate according to channel and interference conditions to maximize throughput while satisfying predefined reliability constraints.

Medium access control and rate adaptation for ultrasonic intrabody sensor networks

The use of wirelessly internetworked miniaturized biomedical devices is promising a significant leap forward in medical treatment of many pervasive diseases. Recognizing the limitations of traditional radio-frequency wireless communications in interconnecting devices within the human body, in this paper, we propose for the first time to develop network protocols for implantable devices based on ultrasonic transmissions. We start off by assessing the theoretical feasibility of using ultrasonic waves in human tissues and by deriving an accurate channel model for ultrasonic intrabody communications. Then, we propose a new ultrasonic transmission and multiple access technique, which we refer to as Ultrasonic WideBand (UsWB). UsWB is based on the idea of transmitting information bits spread over very short pulses following a time-hopping pattern. The short impulse duration results in limited reflection and scattering effects, and the low duty cycle reduces the impact of thermal and mechanical effects, which may be detrimental for human health. We then develop a multiple access technique with distributed control to enable efficient simultaneous access by mutually interfering devices based on minimal and localized information exchange and on measurements at the receiver only. Finally, we demonstrate the performance of UsWB through a multiscale simulator that models the proposed communication system at the acoustic wave level, at the physical (bit) level, and at the network (packet) level. We also validate the simulation results by comparing them to experimental results obtained with a software-defined testbed.

Distributed MAC and rate adaptation for ultrasonically networked implantable sensors

The use of miniaturized biomedical devices implanted in the human body and wirelessly internetworked is promising a significant leap forward in medical treatment of many pervasive diseases. Recognizing the well-understood limitations of traditional radio-frequency wireless communications in interconnecting devices within the human body, in this paper we propose to develop network protocols for implantable devices based on ultrasonic transmissions. We start off by assessing the feasibility of using ultrasonic propagation in human body tissues and by deriving an accurate channel model for ultrasonic intra-body communications. Then, we propose a new ultrasonic transmission and multiple access technique, which we refer to as Ultrasonic WideBand (UsWB). UsWB is based on the idea of transmitting information bits spread over very short pulses following a time-hopping pattern. The short impulse duration results in limited reflection and scattering effects, and its low duty cycle reduces the thermal and mechanical effects, which are detrimental for human health. We then develop a multiple access technique with distributed control to enable efficient simultaneous access by interfering devices based on minimal and localized information exchange and on measurements at the receiver only. Finally, we demonstrate the performance of UsWB through a multi-scale simulator that models the proposed communication system at the acoustic wave level, at the physical (bit) level, and at the network (packet) level.

U-Wear: Software-Defined Ultrasonic Networking for Wearable Devices

Wearable medical sensing devices with wireless capabilities have become the cornerstone of many revolutionary digital health applications that promise to predict and treat major diseases by acquiring and processing health information. Existing wireless wearable devices are connected through radio frequency (RF) electromagnetic wave carriers based on standards such as Bluetooth or WiFi. However, these solutions tend to almost-blindly scale down traditional wireless technologies to the body environment, with little or no attention to the peculiar characteristics of the human body and the severe privacy and security requirements of patients. We contend that this is not the only possible approach, and we present U-Wear, the first networking framework for wearable medical devices based on ultrasonic communications. U-Wear encloses a set of physical, data link and network layer functionalities that can flexibly adapt to application and system requirements to efficiently distribute information between ultrasonic wearable devices. U-Wear also offers reconfiguration functionalities at the application layer to provide a flexible platform to develop medical applications. We design two prototypes that implement U-Wear and operate in the near-ultrasonic frequency range using commercial-off-the-shelf (COTS) speakers and microphones. Despite the limited bandwidth, i.e., about 2 kHz, and COTS audio hardware components not optimized for operating at high frequency, our prototypes (i) achieve data rates up to 2.76 kbit/s with bit-error-rate lower than 10-5 using a transmission power of 20 mW; (ii) enable multiple nodes to share the medium; and (iii) implement reconfigurable data processing to extract medical parameters from sensors with high accuracy.

Design of A Software-defined Underwater Acoustic Modem with Real-time Physical Layer Adaptation Capabilities

This article describes the design of a custom software-defined modem with adaptive physical layer for underwater acoustic (UWA) communications. The modem consists of a commercial software-defined radio (SDR) interfaced with a wideband acoustic transducer through amplifying circuitry. With this custom-built platform, we focus on the unique physical layer challenges of the underwater acoustic channel to demonstrate the benefits of real-time adaptation in such rapidly varying environments. We first focus on an Orthogonal-Frequency-Division-Multiplexing (OFDM) transmission scheme. In particular, for the forward link, we consider and implement a high-data rate Zero-Padded OFDM (ZP--OFDM) physical layer with a superimposed convolutional error-correction coding scheme. ZP--OFDM offers high re-configurability in terms of number of OFDM subcarriers, modulation type (e.g., BPSK, QPSK), and error-correction coding rate. Real-time adaptation at the transmitter is achieved through a robust feedback link based on a binary chirp spread-spectrum modulation (B-CSS). We demonstrate that joint real-time adaptation of system parameters such as modulation constellation and channel coding rate leads to significant data rate increase under preset bit-error-rate (BER) constraints. Moreover, in the same context, we present for the first time a seamless switch of our SDR transmitter between different signaling technologies such as OFDM and direct-sequence spread-spectrum (DS-SS).

Modeling signal propagation in nanomachine-to-neuron communications

Abstract Nanomachine communications are a promising paradigm for the large applications which can be envisaged especially in the medical field. As an example, many widespread neurological diseases such as Alzheimer and/or paralysis are associated to bad neuronal communication or to interruption of the pulse propagation across the nervous system due to irreversible damages across a human body area. In this context, nanomachines can be integrated into a neuronal network system to restore biological communications. To this purpose, a preliminary step is modeling all the phases of the communication among neurons through a block scheme where input/output relationships at each block are characterized in terms of transfer functions, gain and delay. In order to make the characterization realistic, we also consider the possibility to have multiple inputs along the surface of a neuron cell. The communication perspective being used can be useful to design nanomachines compatible with biological structures and able to interact with biological systems.

SEANet: A Software-Defined Acoustic Networking Framework for Reconfigurable Underwater Networking

As of today, Underwater Acoustic Networks (UANs) are heavily dependent on commercially available acoustic modems. While commercial modems are often able to support specific applications, they are typically not flexible enough to satisfy the requirements of next-generation UANs, which need to be able to adapt their communication and networking protocols in real-time based on the environmental and application conditions. To address these needs, we present SEANet (Software-dEfined Acoustic Networking), a modular, evolving software-defined framework for UAN devices that offers the necessary flexibility to adapt and satisfy different application and system requirements through a well-defined set of functionalities at the physical, data-link, network, and application layers of the networking protocol stack. SEANet is based on a structured modular architecture that enables real-time reconfiguration at different layers, provides a flexible platform for the deployment of new protocol designs and enhancements, and ensures software portability for platform independence. Moreover, we present a prototype of a low-cost, fully reconfigurable underwater sensing platform that implements the SEANet framework, and discuss performance evaluation results from water tank tests.

Opto-ultrasonic communications in wireless body area nanonetworks

Wirelessly interconnected nanorobots, i.e., engineered devices of sizes ranging from one to a few hundred nanometers, are promising revolutionary diagnostic and therapeutic medical applications that could enhance the treatment of major diseases. Each nanorobot is usually designed to perform a set of basic tasks such as sensing and actuation. A dense wireless network of nano-devices, i.e., a nanonetwork, could potentially accomplish new and more complex functionalities, e.g., in-vivo monitoring or adaptive drug-delivery, thus enabling revolutionary nanomedicine applications. Several innovative communication paradigms to enable nanonetworks have been proposed in the last few years, including electromagnetic communications in the terahertz band, or molecular and neural communications. In this paper, we propose and discuss an alternative approach based on establishing intra-body opto-ultrasonic communications among nanorobots. Opto-ultrasonic communications are based on the optoacoustic effect, which enables the generation of high-frequency acoustic waves by irradiating the medium with electromagnetic energy in the optical frequency range. We first discuss the fundamentals of nanoscale opto-ultrasonic communications in biological tissues, and then we model the generation, propagation, and detection of opto-ultrasonic waves.

Characterization of molecular communications among implantable biomedical neuro-inspired nanodevices

Abstract In the next future nanodevices are expected to be implanted in the human body and communicate with each other as well as with biological entities, e.g. neuronal cells, thus opening new frontiers for disease treatment, especially in neurological therapy and for drug delivery. Moreover, considering that these nanoscale devices will be small in size, will have limitations in terms of energy consumption and processing and will be injected into a biological system, they will be not able to use traditional electromagnetic or acoustic communications paradigms: rather, they will employ communication schemes similar to those used by neuronal cells and based on molecule exchange. With respect to this, a theoretical work is required to identify the information bounds for nanoscale neuronal communications. In previous papers, achievable information rates of active and passive transport in molecular communication systems have been investigated in the hypothesis of considering two nanodevices which exchange information through molecules released by a transmitter and diffused according to a Brownian motion or using molecular motors. Stochasticity in the diffusion process of these molecules causes noise in the communication among these nanodevices. In this paper we address the derivation of information bounds by introducing a realistic neuron-like communication model which takes into account interactions among nanodevices that can be implanted in the human body and, like neurons, can be simultaneously connected through thousands of synapses. In particular, an accurate characterization of the communication channel is derived and the estimation of the capacity bounds is achieved.

High data rate ultrasonic communications for wireless intra-body networks

It is well known that electromagnetic radio-frequency (RF) waves that are the basis of most commercial wireless technologies are largely unsuitable to interconnect deeply implanted medical devices. RF waves are in fact absorbed by aqueous biological tissues and prone to malicious jamming attacks or to environmental interference from pervasively deployed RF communication systems; moreover, they pose a potential safety hazard when exposure of tissues is prolonged and at high power. While existing wireless technologies can satisfy the requirements of some specific applications, the root challenge of enabling networked intra-body miniaturized sensors and actuators that communicate through body tissues is largely unaddressed. Considering these limitations, this article proposes a high data rate ultrasonic communication scheme for wireless intra-body networks. The proposed scheme can enable various applications that require high sampling rates such as neural data recording or monitoring of the digestive tract through endoscopic pills. The proposed scheme is based on Orthogonal Frequency-Division Multiplexing (OFDM), which is proven to be robust against frequency-selective channels with relatively long delay spreads like the intra-body ultrasonic channel. The proposed scheme is implemented in a prototype ultrasonic software-radio and demonstrated to achieve data rates up to 28.12 Mbit/s through synthetic phantoms mimicking the ultrasonic propagation characteristics of biological tissues.