On the Use of Reciprocal Filter against WiFi Packets for Passive Radar

This paper aims at a critical review of the signal processing scheme used in WiFi-based passive radar in order to limit its complexity and enhance its suitability for short range civilian applications. To this purpose the exploitation of a reciprocal filtering strategy is investigated as an alternative to conventional matched filtering at the range compression stage. Along with the well-known advantage of a remarkable sidelobes control capability for the resulting range-Doppler response, the use of a reciprocal filter is shown to provide additional benefits for the specific sensor subject of this study. Specifically, it allows to streamline the disturbance cancellation stage and to implement a unified signal processing architecture which is capable to handle the different modulation schemes typically adopted in WiFi transmissions. Appropriate adjustments are also proposed to the theoretical reciprocal filter in order to cope with the inherent loss in term of signal-to-noise power ratio. The effectiveness of the revised signal processing scheme encompassing the reciprocal filtering strategy is proved against both simulated and experimental datasets

A spatial diversity scheme for fixed point indoor wireless communication

The ease with which indoor wireless systems can be installed has become their main selling feature. A desirable application for wireless systems is the transmission of compressed digital music in an indoor shopping mall environment. The indoor environment, with its many walls and highly reflective surfaces, has a high level of multipath. High levels of slowly changing multipath can cause deep fades, and therefore reduce the reliability of the system. The proper use of multiple receiving elements is one way to mitigate the deep fades caused by multipath. The main objective of this thesis is to study a simple and cost effective approach to combining the signals from several receiving elements. A novel diversity combining approach using 2 receiving elements is presented. The novel diversity combining approach consists of periodically changing the phase of one of the two received signals. A set of simulations was developed to study the effectiveness of the novel diversity combining method in mitigating deep multipath fades. The relative performances of two different implementations of the diversity combining were compared to a baseline test case that did not include diversity combining. In both of the simulated implementations, the diversity combining approach proved to be an effective means of mitigating the multipath fading phenomenon. A proof-of-concept, bench-top hardware prototype was also developed. The transmitter and receiver were implemented in Field Programmable Gate Arrays (FPGAs). The laboratory testing of the hardware successfully illustrated the feasibility of the proof-of-concept system

Superimposed training low probability of detection underwater communications

This paper proposes a superimposed training method for low probability of detection underwater acoustic communications. A long pilot sequence was superimposed to the message for equalization and synchronization purposes. A fast Hadamard transform (FHT) estimated the channel impulse response and compressed the pilot energy. A Wiener filter performed equalization. The interference signal was removed using hyperslice cancellation by coordinate zeroing. An inverse FHT decompressed the remaining sequence energy and the message was retrieved. Results from a shallow water experiment presented bit error rates <10-2 for signal-to-noise ratios <-8 dB.info:eu-repo/semantics/publishedVersio

Passive radar based on WiFi transmissions: signal processing schemes and experimental results

Aim of this work is to study innovative techniques and processing strategies for a new passive sensor for short range surveillance. The principle of work of the sensor will be based on the passive radar principle, and WiFi transmissions - which usually provide Internet access within local areas - will be exploited by the passive sensor to detect, localize and classify targets

Passive radar based on WiFi transmissions: signal processing schemes and experimental results

Aim of this work is to study innovative techniques and processing strategies for a new passive sensor for short range surveillance. The principle of work of the sensor will be based on the passive radar principle, and WiFi transmissions - which usually provide Internet access within local areas - will be exploited by the passive sensor to detect, localize and classify targets

Advanced signal processing techniques for WiFi-based Passive Radar for short-range surveillance

In this work, advanced signal processing techniques for a Passive Radar (PR) based on WiFi transmissions are considered. The possibility to exploit such a ubiquitous and accessible source is shown to be an appropriate choice for the detection, localization and imaging of vehicles, people and aircrafts within short ranges in both outdoor and indoor environments

MedLAN: Compact mobile computing system for wireless information access in emergency hospital wards

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.As the need for faster, safer and more efficient healthcare delivery increases, medical consultants seek new ways of implementing a high quality telemedical system, using innovative technology. Until today, teleconsultation (the most common application of Telemedicine) was performed by transferring the patient from the Accidents and Emergency ward, to a specially equipped room, or by moving large and heavy machinery to the place where the patient resided. Both these solutions were unpractical, uneconomical and potentially dangerous. At the same time wireless networks became increasingly useful in point-of-care areas such as hospitals, because of their ease of use, low cost of installation and increased flexibility. This thesis presents an integrated system called MedLAN dedicated for use inside the A&E hospital wards. Its purpose is to wirelessly support high-quality live video, audio, high-resolution still images and networks support from anywhere there is WLAN coverage. It is capable of transmitting all of the above to a consultant residing either inside or outside the hospital, or even to an external place, thorough the use of the Internet. To implement that, it makes use of the existing IEEE 802.11b wireless technology. Initially, this thesis demonstrates that for specific scenarios (such as when using WLANs), DICOM specifications should be adjusted to accommodate for the reduced WLAN bandwidth. Near lossless compression has been used to send still images through the WLANs and the results have been evaluated by a number of consultants to decide whether they retain their diagnostic value. The thesis further suggests improvements on the existing 802.11b protocol. In particular, as the typical hospital environment suffers from heavy RF reflections, it suggests that an alternative method of modulation (OFDM) can be embedded in the 802.11b hardware to reduce the multipath effect, increase the throughput and thus the video quality sent by the MedLAN system. Finally, realising that the trust between a patient and a doctor is fundamental this thesis proposes a series of simple actions aiming at securing the MedLAN system. Additionally, a concrete security system is suggested, that encapsulates the existing WEP security protocol, over IPSec

Analysis of Ultra Wide Band (UWB) Technology for an Indoor Geolocation and Physiological Monitoring System

The goal of this research is to analyze the utility of UWB for indoor geolocation and to evaluate a prototype system, which will send information detailing a person’s position and physiological status to a command center. In a real world environment, geolocation and physiological status information needs to be sent to a command and control center that may be located several miles away from the operational environment. This research analyzes and characterizes the UWB signal in the various operational environments associated with indoor geolocation. Additionally, typical usage scenarios for the interaction between UWB and other devices are also tested and evaluated

Chirp-rate quasi-orthogonality based DSSS-CDMA system for underwater acoustic channel

Abstract(#br)Underwater network node positioning is a key supporting technology for underwater networks. Generally, nodes at known locations (anchor nodes) are used to transmit location information to the node to be located, and the node to be located performs location calculation according to the arrival time of the received information, which requires multiple access communication between the anchor nodes and the node to be located. In order to reduce the multiple access interference (MAI) and distinguish the information of different anchor nodes, it is necessary to study the underwater multiple access method. The GPS positioning system uses direct sequence spread spectrum code division multiple access(DSSS-CDMA) technology, and the positioning satellite transmits a signal formed by the BPSK modulation by transmitting a pseudo-random sequence (PN sequence) to the binary code sequence corresponding to the navigation message to the user equipment to be located. The underwater acoustic (UWA) channel has a complex multipath structure and Doppler effect, which causes a large interference to the communication system. Compared with narrowband communication, spread spectrum communication has a strong anti-interference ability, and can maintain the reliability of the communication system in the UWA channel. Based on this, this paper proposes a quasi-orthogonal Chirp-rate based DSSS-CDMA method under UWA channel, and carries out simulation analysis and experimental verification