Konstanty Bialkowski

Generalized canonical correlation for passive multistatic radar detection

In this paper, we consider the problem of target detection in passive multistatic radar. In passive radar, we make use of illuminators of opportunity. As the illuminators are not under our direct control, the illuminating signal itself is unknown. We propose a signal model which reflects this. In deriving a maximum-likelihood estimator for the unknown parameters, including the illumination, we find that the maximum value of the likelihood is a monotonic function of the largest eigenvalue of the Gram matrix of the received signals. The generalised likelihood ratio test turns out to be equivalent to comparison of the largest eigenvalue against a threshold, so we propose its use as a target detection statistic. The proposed detector is similar to generalised canonical correlation in multivariate statistics. The benefit of using this statistic over others such as generalised variance is demonstrated through numerical simulations in the context of passive radar using DVB-T signals.

Design and Experimental Evaluation of a Non-Invasive Microwave Head Imaging System for Intracranial Haemorrhage Detection.

An intracranial haemorrhage is a life threatening medical emergency, yet only a fraction of the patients receive treatment in time, primarily due to the transport delay in accessing diagnostic equipment in hospitals such as Magnetic Resonance Imaging or Computed Tomography. A mono-static microwave head imaging system that can be carried in an ambulance for the detection and localization of intracranial haemorrhage is presented. The system employs a single ultra-wideband antenna as sensing element to transmit signals in low microwave frequencies towards the head and capture backscattered signals. The compact and low-profile antenna provides stable directional radiation patterns over the operating bandwidth in both near and far-fields. Numerical analysis of the head imaging system with a realistic head model in various situations is performed to realize the scattering mechanism of haemorrhage. A modified delay-and-summation back-projection algorithm, which includes effects of surface waves and a distance-dependent effective permittivity model, is proposed for signal and image post-processing. The efficacy of the automated head imaging system is evaluated using a 3D-printed human head phantom with frequency dispersive dielectric properties including emulated haemorrhages with different sizes located at different depths. Scattered signals are acquired with a compact transceiver in a mono-static circular scanning profile. The reconstructed images demonstrate that the system is capable of detecting haemorrhages as small as 1 cm3. While quantitative analyses reveal that the quality of images gradually degrades with the increase of the haemorrhage’s depth due to the reduction of signal penetration inside the head; rigorous statistical analysis suggests that substantial improvement in image quality can be obtained by increasing the data samples collected around the head. The proposed head imaging prototype along with the processing algorithm demonstrates its feasibility for potential use in ambulances as an effective and low cost diagnostic tool to assure timely triaging of intracranial hemorrhage patients.

Evaluations of MadWifi MAC layer rate control mechanisms

The 802.11 standards specify several transmission rates that can be used at the MAC layer protocol to adapt the transmission rate to channel conditions. Such dynamic adaptations can improve per-hop performance in Wireless Networks and therefore can have impact on the Quality of Service provided for communicating applications. In this paper we present a comprehensive evaluation of the performance of four rate control mechanisms used by the MadWifi driver in Linux: Onoe, AMRR, SampleRate and minstrel. The evaluation of these four rate control mechanisms was carried out in our platform for controllable and repeatable experiments.

Effect of line of sight propagation on capacity of an indoor MIMO system

In this paper the performance of a multiple input multiple output (MIMO) wireless communication system operating in an indoor environment, featuring both line of sight (LOS) and non-line of sight (NLOS) signal propagation, is assessed. In the model the scattering objects are assumed to be uniformly distributed in an area surrounding the transmitting and receiving array antennas. Mutual coupling effects in the arrays are treated in an exact manner. However interactions with scattering objects are taken into account via a single bounce approach. Computer simulations are carried out for the system capacity for varying inter-element spacing in the receiving array for assumed values of LOS/NLOS power fraction and signal to noise ratio (SNR).

Microwave System for the Early Stage Detection of Congestive Heart Failure

Fluid accumulation inside the lungs, known as cardiac pulmonary edema, is one of the main early symptoms of congestive heart failure (CHF). That accumulation causes significant changes in the electrical properties of the lung tissues, which in turn can be detected using microwave techniques. To that end, the design and implementation of an automated ultrahigh-frequency microwave-based system for CHF detection and monitoring is presented. The hardware of the system consists of a wideband folded antenna attached to a fully automated vertical scanning platform, compact microwave transceiver, and laptop. The system includes software in the form of operational control, signal processing, and visualizing algorithms. To detect CHF, the system is designed to vertically scan the rear side of the human torso in a monostatic radar approach. The collected data from the scanning is then visualized in the time domain using the inverse Fourier transform. These images show the intensity of the reflected signals from different parts of the torso. Using a differential based detection technique, a threshold is defined to differentiate between healthy and unhealthy cases. This paper includes details of developing the automated platform, designing the antenna with the required properties imposed by the system, developing a signal processing algorithm, and introducing differential detection technique besides investigating miscellaneous probable CHF cases.

A Wireless Sensor Node Architecture Using Remote Power Charging, for Interaction Applications

The wireless sensor node architecture proposed in this paper is optimized for use in a wireless interactive point, listen and see system. In particular, we focus on developing a wireless sensor node that can be remotely charged by harvesting microwave energy. The current system implementation allows a user to access information from a remote sensor via their mobile computing device. These sensors are limited in complexity due to the limited power available, and are cumbersome since manual intervention is required to replace its batteries. We propose a system where battery powered wireless sensor nodes can be recharged by harvesting energy from a microwave Radio Frequency (RF) signal source. The remote power charging module of the wireless sensor node architecture consisted of an antenna array and a rectification circuit. A prototype of the antenna array and rectification circuit of the remote power charging module for the wireless sensor node was constructed and is presented in this paper.

Feasibility of Using Wideband Microwave System for Non-Invasive Detection and Monitoring of Pulmonary Oedema.

Pulmonary oedema is a common manifestation of various fatal diseases that can be caused by cardiac or non-cardiac syndromes. The accumulated fluid has a considerably higher dielectric constant compared to lungs’ tissues, and can thus be detected using microwave techniques. Therefore, a non-invasive microwave system for the early detection of pulmonary oedema is presented. It employs a platform in the form of foam-based bed that contains two linear arrays of wideband antennas covering the band 0.7–1 GHz. The platform is designed such that during the tests, the subject lays on the bed with the back of the torso facing the antenna arrays. The antennas are controlled using a switching network that is connected to a compact network analyzer. A novel frequency-based imaging algorithm is used to process the recorded signals and generate an image of the torso showing any accumulated fluids in the lungs. The system is verified on an artificial torso phantom, and animal organs. As a feasibility study, preclinical tests are conducted on healthy subjects to determinate the type of obtained images, the statistics and threshold levels of their intensity to differentiate between healthy and unhealthy subjects.

Passive radar signal processing in single frequency networks

In this paper, we consider the problem of target detection in passive multistatic radar with multiple transmitters. Passive radar makes use of illuminators of opportunity, such as television and radio broadcast towers. As the illuminators do not cooperate with the receivers, the illuminating signal itself is unknown. The system considered is the DVB-T standard, which is often operated as part of single frequency network (SFN).

A signal strength based tag estimation technique for RFID systems

Radio frequency identification (RFID) is a wireless communication technology that provides automatic identification and data collection. In RFID systems with a large number of tags, many tags respond to the reader at the same time. Thus, enhanced anti-collision algorithms are required to have a fast multiple tag identification process. Anti-collision algorithms can be classified as probabilistic (eg. ALOHA based) algorithms and deterministic (tree based) algorithms. Better performance is achieved in all algorithms when accurate estimation of the number of tags is achieved. This paper presents a new method of estimating number of tags using signal strength properties. The simulated results show that our algorithm (efficiency 35%) significantly improves on existing estimation algorithms. That is 1% away from the perfect estimator and the theoretical optimum efficiency of slotted Aloha (36%).

2×2 MIMO Testbed for Dual 2.4GHz/5GHz Band

The paper describes a Multiple Input Multiple Output communication testbed for operation in a dual 2.4 GHz/5 GHz band, which is under development at the University of Queensland. This advanced testing equipment makes use of Field Programmable Gate Array technology for fast processing of the baseband signals. Its RF modules include commercially available RF transceiver chips and in-house developed antennas. Using a 100 Mbit Ethernet network connection and a Web browser, the estimated channel matrices and received and decoded signal constellations can be visualized in quasi realtime on a personal computer.