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Communication options
This section aims at reviewing the main communication mechanisms, potential candidates to build the Human Intranet. Wireless communication techniques are widely spread due to the number of connected objects continuously increasing. Are including in this category the following communication protocols: Bluetooth, BLE (Bluetooth Low Energy), WiFi (Wireless Fidelity), and ZigBee. All of the above are very similar as they are IEEE standards, operating in the same ISM frequency band of 2400 MHz (and 5 GHz for WiFi). They are extremely popular as their frequency of operation is unlicensed worldwide. WiFi communication standard is however excluded from review as it is not widely deployed for BAN and PAN applications due to its protocol overhead and associated power consumption, and higher output power. Wifi is more capable than the others in terms of data rate and covered range to the cost of higher power consumption and radiated power. Classic RF communication propagates through the air enabling on-body and off-body communications.
It offers a communication range up to 10m, data rates up to 10’s of megabit per second (3 Mbit/s for Bluetooth), and an output power rarely exceeding 10 dBm [28, 29]. Those protocols rely on narrowband communication with multiple channels available within the allocated bandwidth. Bluetooth offers 79 communication channels with a frequency-hoping spread spectrum, allowing the radio to switch channel during the transmission. It permits multiple devices to co-exist while homogenizing the bandwidth occupation. A lower power Bluetooth version has been created, BLE (Bluetooth Low Energy), to reduce the energy cost and overall communication delay [30]. The number of channels has been reduced to 40, including three broadcast dedicating ones, allowing better traffic handling and coexistence with other protocols such as WiFi. The maximum data rate has been reduced down to 1 Mbit/s. BLE also embeds an advertising/scanning capability allowing two nodes to trigger a data exchange while optimizing the power consumption. Contention techniques, such random advertising time offset or backoff strategy are implemented.
In [30], the authors propose a BLE extension to improve BLE’s efficiency for deployments with a large number of nodes. The need for this extension relies on the fact that above 5 scanning devices listening for a tag’s advertising message, the probability of success (to establish the link) starts decreasing significantly. Additional listening time can improve those results, granting more time for the different nodes to communicate and avoid a collision. Above 9 scanning nodes, the probability of communication success within a 5s-window after the advertising drops below 70%. Those results are the consequence of the limited number of advertising channels, in combination with a consequent number of nodes intending to communicate. While Bluetooth and BLE are offering great advantages in terms of off-body range, data rate, power consumption, and widely spread communication mechanism, its limitations regarding the communication latency due to node density could be problematic for building the Human Intranet.
Body Coupled Communication State of the Art
Body Coupled Communication (BCC) consists of using the human body as a communication medium, carrying the signal, and associated data. The three mains BCC mechanisms are Galvanic, Magnetic Resonance, and Capacitive coupling. They are introduced with their principle, as well as a few relevant examples of modeling and implementation from the state-of-the-art within this section.
Magnetic Coupling
Magnetic Body Coupled Communication (M-BCC) consists of at least a coil on the transmitter’s(Tx) end. When a current flows through the inductor, a magnetic field is generated. On the receiver’s (Rx) side, two configurations can be observed. Either the considered subject must interact with its environment by touching dedicated spots, electrically closing the Rx loop which senses the current induced from Tx [6]. This configuration is depicted in figure 2.5(a). The other option relies on a second coil on the Rx side converting the generated magnetic field into a current [7, 8], as pictured in figure 2.5(b).
The single-coil configuration, regardless of the number of potential applications, does not suit very well within the framework of the Human Intranet due to its infrastructure requirements and immobility. On the other hand, the double-inductor approach makes this communication fully wearable. To improve the channel characteristics and lower the impact of the wearer surroundings, M-BCC should operate with a quasi-static magnetic field. A magnetic field is considered magnetostatic if the equation (2.1) is satisfied [6, 8]. d << c 2f where d is the distance between both coils, c the speed of light, and f the frequency of operation.
Consequently, a frequency in the megahertz range is usually considered. The coil size is chosen accordingly, a 6.73 cm square in shape inductor with a maximum operating frequency of 20 MHz is reported in [8]. Their measurement results are presented in figure 2.6 over frequency for a range of 1m. One can observe the tight relationship between the skin-coil separation distance and the attenuation: the greater is the separation distance, the more important is the path loss. Therefore, M-BCC is sensitive to the coil movement relative to the human body. This point was also highlighted in [7] for inductors wrapped around a limb. To maximize energy efficiency, the frequency of excitation is chosen such as it corresponds to the resonance frequency. Body motion could detune the coil, making the system operating off-resonance, reducing the efficiency, the covered range, and increasing the attenuation.
Table of contents :
Abstract
Résumé
Acknowledgments
List of Figures
List of Tables
Acronyms
1 Introduction
1.1 Research Context & Human Intranet Concept
1.1.1 Research Context
1.1.2 The Human Intranet Concept
1.1.2.1 Overview
1.1.2.2 Requirements
1.2 Thesis Purpose and Main Contributions
1.2.1 Thesis Objective
1.2.2 Main contributions
1.3 Manuscript Structure
2 State of the Art
2.1 Communication options
2.2 Body Coupled Communication State of the Art
2.2.1 Magnetic Coupling
2.2.2 Galvanic Coupling
2.2.3 Capacitive Coupling
2.2.4 Comparison and preferred solution
2.3 Conclusion
3 Body Coupled Communication
3.1 Theoretical Analysis
3.1.1 Small Dipole Behavior in Free Space
3.1.2 Small Dipole Behavior on a Conductive Surface
3.1.3 Theoretical Model Applied to C-BCC
3.2 Electromagnetic Simulations
3.2.1 Simulated Model
3.2.2 In Free Space
3.2.3 On Phantom
3.2.4 Wrap-up
3.3 Channel Characterization
3.3.1 Electrode Implementation and VNA measurements
3.3.1.1 Electrode design and sizing
3.3.1.2 In Free Space
3.3.1.3 On Body
3.3.2 Prototype Implementation and In-Context System Measurements
3.3.2.1 Battery Powered Prototype BoM and Operating Mode
3.3.2.2 Measurements in Free Space
3.3.2.3 Measurements on Phantom
3.3.2.4 Measurements on Body
3.3.3 Wrap-up
3.4 Proposed Channel Model and Operating Frequency
3.4.1 Channel Model
3.4.2 Operating Frequency
3.4.3 Wrap-up
3.5 Comparison with Other solutions
3.5.1 Reference scenario
3.5.2 Compared technologies
3.5.3 Results
3.5.4 Conclusion on compared technologies
3.6 Conclusion
4 Network Topology
4.1 Network Architecture
4.1.1 Topologies, reliability and Quality of Service (QoS)
4.1.2 Human Intranet Skeleton
4.1.3 Wrap-up
4.2 Communication protocol
4.2.1 WBAN IEEE 802.15.6 and WPAN IEEE 802.15.4
4.2.2 Wake-up Receiver and Duty Cycle Approach
4.2.3 Wrap-up
4.3 Heartbeat-based Synchronization and Communication Protocol
4.3.1 Synchronization principle
4.3.2 Deployment principle
4.3.3 Human Intranet Communication protocol
4.3.4 Wrap-up
4.4 Conclusion
5 System Level Simulation
5.1 System Architecture Model and Non-Idealities
5.1.1 Heartbeat Detector
5.1.2 Timer
5.1.2.1 Oscillator Frequency Offset and Counter Granularity
5.1.2.2 Oscillator Frequency Drift
5.1.2.3 Oscillator Accumulated Random Jitter
5.1.3 Transmitter and Receiver
5.1.4 Synchronization Margin
5.1.5 Wrap-up
5.2 Metrics
5.2.1 Latency and additional synchronization time
5.2.2 System Power Consumption
5.2.3 Channel Availability
5.2.4 Wrap-up
5.3 Simulations and Comparison with Duty-Cycled Receivers
5.3.1 Heartbeat-Based System Level Simulations
5.3.2 Duty-Cycled Approach
5.3.3 Comparison
5.3.3.1 Channel Availability Comparison
5.3.3.2 System Power Consumption Comparison
5.3.3.3 Communication latency
5.4 Conclusion
Wireless Hub for the Human Intranet
6 Conclusion and Future Work
6.1 Conclusion
6.2 Future Work
Bibliography
