Secret Key Generation Based on AoA Estimation for Low SNR Conditions

In the context of physical layer security, a physical layer characteristic is used as a common source of randomness to generate the secret key. Therefore an accurate estimation of this characteristic is the core for reliable secret key generation. Estimation of almost all the existing physical layer characteristic suffer dramatically at low signal to noise (SNR) levels. In this paper, we propose a novel secret key generation algorithm that is based on the estimated angle of arrival (AoA) between the two legitimate nodes. Our algorithm has an outstanding performance at very low SNR levels. Our algorithm can exploit either the Azimuth AoA to generate the secret key or both the Azimuth and Elevation angles to generate the secret key. Exploiting a second common source of randomness adds an extra degree of freedom to the performance of our algorithm. We compare the performance of our algorithm to the algorithm that uses the most commonly used characteristics of the physical layer which are channel amplitude and phase. We show that our algorithm has a very low bit mismatch rate (BMR) at very low SNR when both channel amplitude and phase based algorithm fail to achieve an acceptable BMR

Vibration Energy Harvesting in Wireless Sensor Networks (WSNs) for Structural Health Monitoring (SHM)

Harvesting of vibration energy from the ambient environment, such as vibrations experienced by bridges due to vehicle movements, wind, earthquakes, has become an essential area of study by many scientists aiming to design new systems which can improve self-powered network sensors in wireless sensor networks (WSN), thus providing a more efficient system that does not require the human involvement. One of the essential components of WSN systems is the sensor node. It is used to continuously send/receive information to monitor a certain behavior targeted by the application; for example, to monitor bridge infrastructure's health. Sometimes, sensors are programmed and adjusted to send useful data for monitoring 24 hours a day, seven days a week. This configuration harms the sensors' batteries and shortens their lives, since sending/receiving data consumes power and leads to the reduction of the batteries' voltage levels. Due to this fact, energy harvesting is critical to maintaining long-term batteries that can recharge themselves from the available ambient harvested energy and eliminate the need for human involvement in replacing or recharging them in their specified locations in the network. Recent structural health monitoring systems (SHM), in civil infrastructure environments, have focused heavily on the use of wireless sensor networks (WSNs) due to their efficient use of wireless sensor nodes. Such nodes can be fixed onto any part of the infrastructure, such as bridges, to collect data remotely for monitoring and further processing. However, the drawback of using such sensor networks relies mainly on the finite life-time of their batteries. Due to this problem, the concept of harvesting energy from the ambient environment became more important. Ensuring efficient battery usage would have a great benefit in maximizing overall systems functionality time and ensures efficient use of natural energy resources like solar, wind and vibration energies. This work aims to study the feasibility of using a piezoelectric vibration energy harvester to extend overall battery life using a single, external, super-capacitor component which is serving as a storage unit for the harvested energy. The methodology followed in this work states the general direction of the flow of energy in a sensor node which can be summarized into the following: 1-Piezoelectric Vibration Energy Harvester: This module was used to convert mechanical energy of the vibrations from the ambient environment to electrical energy. 2-Energy Harvesting Circuit: This circuit is responsible for the power conditioning, enabling the circuit to output energy to the sensors under certain threshold criteria. 3-Energy Storage: This the super-capacitor served to store harvested energy. 4-Energy Management Scheme: The scheme proposed by this work under the energy requirements and constraints of the sensor nodes in order to conserve batteries voltage level to extend sensors' batteries lives. 5-Wireless Sensors Nodes: Each sensor node type has specific energy requirements that must be recognized so that it can be adequately powered and turned on using the harvested energy. The main contribution of this work is a proposal of an energy management scheme which ensures that the harvested energy being provided to the harvester circuit must be greater than the energy output that is going to be consumed by the sensor. This proposed scheme has proved the feasibility of using impact vibrations for efficient energy harvesting and subsequently increase the battery life time needed to turn on the wireless sensor nodes. Furthermore, as a future direction of work, to increase the amount of harvested energy, hybrid power sources can be explored by combining more than one energy source from the ambient environment, such as solar and vibration energy.qscienc

Unleashing the secure potential of the wireless physical layer: Secret key generation methods

AbstractWithin the paradigm of physical layer security, a physical layer characteristic is used as a common source of randomness to generate the secret key. This key is then used to encrypt the data to hide information from eavesdroppers. In this paper, we survey the most recent common sources of randomness used to generate the secret key. We present the steps used to extract the secret key from the estimated common source of randomness. We describe the metrics used to evaluate the strength of the generated key. We follow that with a qualitative comparison between different common sources of randomness along with a proposed new direction which capitalizes on hybridization of sources of randomness. We conclude by a discussion about current open research problems in secret key generation

Robust Secret Key Extraction from Channel Secondary Random Process

The vast majority of existing secret key generation protocols exploit the inherent randomness of the wireless channel as a common source of randomness. However, independent noise added at the receivers of the legitimate nodes affect the reciprocity of the channel. In this paper, we propose a new simple technique to generate the secret key that mitigates the effect of noise. Specifically, we exploit the estimated channel to generate a secondary random process (SRP) that is common between the two legitimate nodes. We compare the estimated channel gain and phase to a preset threshold. The moving differences between the locations at which the estimated channel gain and phase exceed the threshold are the realization of our SRP. We study the properties of our generated SRP and derive a closed form expression for the probability mass function of the realizations of our SRP. We simulate an orthogonal frequency division multiplexing (OFDM) system and show that our proposed technique provides a drastic improvement in the key bit mismatch rate (BMR) between the legitimate nodes when compared to the techniques that exploit the estimated channel gain or phase directly. In addition to that, the secret key generated through our technique is longer than that generated by conventional techniques. Moreover, we compute the conditional probabilities used to estimate the secret key capacity