Gill R. Tsouri

On Increasing Network Lifetime in Body Area Networks Using Global Routing with Energy Consumption Balancing

Global routing protocols in wireless body area networks are considered. Global routing is augmented with a novel link cost function designed to balance energy consumption across the network. The result is a substantial increase in network lifetime at the expense of a marginal increase in energy per bit. Network maintenance requirements are reduced as well, since balancing energy consumption means all batteries need to be serviced at the same time and less frequently. The proposed routing protocol is evaluated using a hardware experimental setup comprising multiple nodes and an access point. The setup is used to assess network architectures, including an on-body access point and an off-body access point with varying number of antennas. Real-time experiments are conducted in indoor environments to assess performance gains. In addition, the setup is used to record channel attenuation data which are then processed in extensive computer simulations providing insight on the effect of protocol parameters on performance. Results demonstrate efficient balancing of energy consumption across all nodes, an average increase of up to 40% in network lifetime corresponding to a modest average increase of 0.4 dB in energy per bit, and a cutoff effect on required transmission power to achieve reliable connectivity.

Constrained independent component analysis approach to nonobtrusive pulse rate measurements

Nonobtrusive pulse rate measurement using a webcam is considered. We demonstrate how state-of-the-art algorithms based on independent component analysis suffer from a sorting problem which hinders their performance, and propose a novel algorithm based on constrained independent component analysis to improve performance. We present how the proposed algorithm extracts a photoplethysmography signal and resolves the sorting problem. In addition, we perform a comparative study between the proposed algorithm and state-of-the-art algorithms over 45 video streams using a finger probe oxymeter for reference measurements. The proposed algorithm provides improved accuracy: the root mean square error is decreased from 20.6 and 9.5 beats per minute (bpm) for existing algorithms to 3.5 bpm for the proposed algorithm. An error of 3.5 bpm is within the inaccuracy expected from the reference measurements. This implies that the proposed algorithm provided performance of equal accuracy to the finger probe oximeter.

Establishing secure measurement matrix for compressed sensing using wireless physical layer security

The simple structure of compressed sensing allows its use not only for low-complexity compression but also for low-complexity encryption. Augmenting compressed sensing to secure information is based on using the sensing matrix as a symmetric encryption key. This imposes the requirement that the key is either preinstalled before deployment or is agreed over some secure communication channel. Both options are problematic when considering a wireless network comprised of nodes with limited resources that could be compromised. This paper proposes an encryption framework where the sensing matrix is established using wireless physical layer security and linear feedback shift register with corresponding m-sequences. Using a Rician fading channel, it is shown that the proposed framework generates valid compressed sensing matrices while preventing access from an eavesdropper in close proximity to one of the legitimate participants.

Securing OFDM over wireless time-varying channels using subcarrier overloading with joint signal constellations

A method of overloading subcarriers by multiple transmitters to secure OFDM in wireless time-varying channels is proposed and analyzed. The method is based on reverse piloting, superposition modulation, and joint decoding. It makes use of channel randomness, reciprocity, and fast decorrelation in space to secure OFDM with low overheads on encryption, decryption, and key distribution. These properties make it a good alternative to traditional software-based information security algorithms in systems where the costs associated with such algorithms are an implementation obstacle. A necessary and sufficient condition for achieving information theoretic security in accordance with channel and system parameters is derived. Security by complexity is assessed for cases where the condition for information theoretic security is not satisfied. In addition, practical means for implementing the method are derived including generating robust joint constellations, decoding data with low complexity, and mitigating the effects of imperfections due to mobility, power control errors, and synchronization errors.

Low-Power Body Sensor Network for Wireless ECG Based on Relaying of Creeping Waves at 2.4GHz

A wireless communication platform for ECG operating in the unlicensed 2.4-2.4835GHz band is proposed and analyzed. The platform uses relaying of creeping waves to drastically reduce sensor transmission power while maintaining reliable performance. A point to point link budget is designed based on the creeping wave component of the propagating signal. The link budget is then integrated into a body sensor network design. System management details are presented and discussed. Performance metrics including scalability of the system and network lifetime are evaluated. The proposed design is shown to achieve a dramatic 1.5x105 increase in battery life for mobile scenarios compared to a reference system without relaying. In addition, it is shown that the design may scale to support applications that demand higher data rates than ECG.

An Investigation Into Relaying of Creeping Waves for Reliable Low-Power Body Sensor Networking

We investigate the use of relaying of creeping waves in the industrial scientific medical frequency bands of 434 MHz, 915 MHz, and 2.4 GHz. The investigation includes generic analysis and experimental setups. For generic analysis, a link budget model is derived based solely on the creeping wave component of the transmitted signal while marginalizing for other effects, such as reflections from the surrounding environment. Closed-form expressions of the gains in network lifetime and energy per bit are derived for a system covering the entire body using relays compared to a reference system offering the same level of reliability without relaying. The experimental setups are used to gather measurements in the 2.4-GHz band with a body sensor network development platform in a nonreflective open-space environment and in a reflective residential environment. The measurements are used to validate the link budget model and evaluate performance of practical systems. Analysis and experimentation demonstrate that relaying of creeping waves offers considerable performance gains in all frequency bands. For example, using a single relay on either side of the body in 2.4 GHz can potentially increase network-lifetime times 40 and decrease energy per bit by 48 dB. Part of this potential is achieved in experimental setups where relaying was shown to increase network lifetime times 13, decrease energy per bit by 13 dB and provide the ability to compensate for a wider fading margin.

Patient-Specific 12-Lead ECG Reconstruction From Sparse Electrodes Using Independent Component Analysis

We propose and evaluate a method of 12-lead electrocardiogram (ECG) reconstruction from a three-lead set. The method makes use of independent component analysis and results in adaptive patient-specific transforms. The required calibration process is short and makes use of a single beat. We apply the method to two sets of leads: leads I, II, V2 and the Frank XYZ leads. Performance is evaluated via percent correlation calculations between reconstructed and original leads from a publicly available database of 549 ECG recordings. Results depict percent correlation exceeding 96% for almost all leads. Adaptability of the methods transform is shown to compensate for changes in signal propagation conditions due to breathing, resulting in reduced variance of reconstruction accuracy across beats. This implies that the method is robust to changes that occur after the time of calibration. Accurate and adaptive reconstruction has the potential to augment the clinical significance of wireless ECG systems since the number of sensor nodes placed on the body is limited and the subject could be mobile.

Threshold Constraints on Symmetric Key Extraction from Rician Fading Estimates

Symmetric key establishment using reciprocal quantization of channel estimates in wireless Rician fading environments is considered. The quantization bits from channel-phase and channel-amplitude are treated as the output of a random number generator. We determine threshold constraints on the required minimal distance of the legitimate communicating parties from a passive eavesdropper, and determine threshold constraints on maximal key establishing rates. The analysis makes use of widely accepted statistical test suites applied to the generated bit streams along with a lemma we define and prove. For distance analysis, the minimal required distance from the eavesdropper to maintain perfect secrecy during key establishment is derived. For key establishing rates, the maximal rates are derived while ensuring the generated bits streams pass the statistical test suites. The work results in generic and clear threshold requirements on distance and rates as function of the Rician factor and quantization bit for any transmission frequency. Clear thresholds are useful for systems operating in a-priori known or estimated propagation environments. In addition, we address the effect of imperfect channel reciprocity on key agreement. Results show practical systems can operate under reciprocal and secure conditions, and that channel-phase estimates perform better than channel-amplitude estimates.

On the benefits of alternative color spaces for noncontact heart rate measurements using standard red-green-blue cameras

Abstract. Existing video plethysmography methods use standard red-green-blue (sRGB) video recordings of the facial region to estimate heart pulse rate without making contact with the person being monitored. Methods achieving high estimation accuracy require considerable signal-processing power and result in significant processing latency. High processing power and latency are limiting factors when real-time pulse rate estimation is required or when the sensing platform has no access to high processing power. We investigate the use of alternative color spaces derived from sRGB video recordings as a fast light-weight alternative to pulse rate estimation. We consider seven color spaces and compare their performance with state-of-the-art algorithms that use independent component analysis. The comparison is performed over a dataset of 41 video recordings from subjects of varying skin tone and age. Results indicate that the hue channel provides better estimation accuracy using extremely low computation power and with practically no latency.

Reverse piloting protocol for securing time varying wireless channels

We consider single-tone pilot based burst transmission over slow time varying flat fading wireless channels with no line of sight. We propose a reverse pilot signaling protocol, based on sending the pilot signal from the receiver to the transmitter instead of from the transmitter to the receiver and on channel tracking at the receiver. We show that the channel performs automatic symbol level encryption analogous to a shift cipher. We derive explicit relationships between channel and system parameters which guarantee secure transmission of the entire data burst for given channel conditions, and depict them for Rayleigh fading. The proposed protocol exhibits high key generating rates, and no overheads on key distribution, enciphering and deciphering. Its security strength increases with mobility. These properties make it a good candidate for mobile wireless systems where bandwidth and power resources are scarce, such as mobile wireless sensor networks and mobile ad-hoc networks.