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Thesis (Ph. D.)--Johns Hopkins University, 1922. / Biographical notes. "Reprinted from the Physical review, s. s., vol. xx, no. 5, November, 1922."

In this thesis, we analyze the performance of heterogeneous wireless communication systems that are composed of Optical Wireless Communication (OWC) and Radio Frequency (RF) systems. OWC systems further include long range outdoor Free Space Optical (FSO) systems and short range indoor Visible Light Communication (VLC) systems. Hybrid FSO/RF systems have emerged as a promising solution for high data rate wireless transmissions. Various transmission schemes including switch-over and soft-switching had been presented for hybrid FSO/RF systems. To overcome the drawbacks of existing schemes, we present a new transmission strategy for hybrid FSO/RF systems exploring an adaptive combining technology. This new strategy shows an improved outage performance. Typically, when the transmitter and the receiver are provided with channel state information, the transmission schemes can be adaptively designed allowing the channel to be used more efficiently. We present two new joint adaptive transmission schemes for hybrid FSO/RF systems. The first one is joint adaptive modulation and adaptive combining scheme which improves the spectral efficiency of hybrid FSO/RF systems. The other one is joint power adaptation and adaptive combining scheme which improves the throughput and the outage performance of hybrid FSO/RF systems. We accurately evaluate the performance of both schemes. FSO technology can be used effectively in multiuser scenarios to support Point-to-Multi-Point (P2MP) networks. In P2MP networks, FSO links are used for data transmission from a central location to multiple users. In this thesis, we present a new P2MP network based on hybrid FSO/RF transmission system. A common backup RF link is used by the central station for data transmission to any user in case of the failure of its corresponding FSO link. Based on a Markov Chain formulation, we study the performance of the resulting system. P2MP Hybrid FSO/RF network achieves considerable performance improvement over the P2MP FSO-only network. In VLC, Light Emitting Diode (LED) is used for the purpose of simultaneous illumination and data communication at high data rate. However, the light originating from a LED source is naturally confined to a small area and is susceptible to blockages. Hybrid VLC/RF systems have been emerged as a promising solution to provide enhanced communication coverage. We introduce a new dual-hop VLC/RF system with energy harvesting relay to extend the coverage of indoor wireless system based on VLC. The second-hop RF transmission uses the harvested energy over the first-hop VLC transmission. In this thesis, we propose two different approaches for energy harvesting at the relay terminal. In the first approach, the relay harvests light energy from different artificial light sources and sunlight entering the room. In this approach, we propose a novel statistical model for the harvested electrical power and analyze the probability of data packet loss. In the second approach, the relay harvests energy from the VLC link by extracting the direct current component of the received optical signal. In this approach, we investigate the optimal design of the hybrid VLC/RF system in terms of data rate maximization. In both cases, we present extensive numerical examples to define important design guide lines for VLC/RF systems. / Graduate

Using communication signals for radar applications has been a major area of research in radar engineering. In the recent years, due to the widely available wireless signals, a new area of research called commensal radars has emerged. Commensal radars use available wireless Radio Frequency (RF) signals to detect and track targets of interest. This is achieved by placing two antennas, one towards the transmitting base station and the other towards the surveillance area. The signal received by these two antennas are correlated to determine the location and velocity of the target. When a signal passes through a channel, it reflects off the obstacles within its path. These reflections usually degrade quality of the signal and cause interference to the telecommunication systems. To mitigate the effects of the channel on a signal these systems transmit a known bit sequence within each frame. Our goal, with this thesis, is to design and implement a working prototype of a novel architecture for the commensal radar system, which uses these known bit sequences to extract the channel information and determine events of interest. The major novelties of the system are as follows. Firstly, this system will be built upon existing communication systems using Software Defined Radio (SDR) technology. Secondly, this design eliminates the need for a reference antenna, which reduces the cost of the system and creates an opportunity to make the system portable. We name this system Communication-Sensing (CommSense). Since, our plan is to use Global System for Mobile Communication (GSM) as the parent system for the prototype development, we decide to update the name to GSM based Communication-Sensing (GSM-CommSense) system. This thesis begins with theoretical analysis of the feasibility of the GSM-CommSense system. First of all, we perform a link budget analysis to determine the power requirements for the system. Then we calculate the ambiguity function and Cram´er-Rao Lower Bound (CRLB) for a two-path received signal model. With encouraging theoretical results, we design a prototype of the system that can capture real GSM base station broadcast signals. After the design of the GSMCommSense system, we capture channel data from multiple locations with varying environmental conditions. The aim for this set of experiment is to be able to distinguish between different environmental conditions. Then, we performed statistical analysis on the data by means of Probability Density Function (PDF) fitting, a goodness-of-fit test called chi-square test and a clustering algorithm called Principal Components Analysis (PCA). We have presented the results from each analysis and discussed them in detail. Upon, receiving positive results in each step we have decided to move towards using learning algorithms to categorise the data captured by the system. We have compared two widely accepted supervised learning algorithms, called Support Vector Machines (SVM) and Multi-Layer Perceptron (MLP). The results showed that with the current hardware capabilities of the system and the amount of data available per GSM frame, the performance of SVM is better than MLP. Thus, we have used SVM to classify two events of detection and classification across a wall. We have presented our findings and discussed the results in detail. We conclude our current work and provide scope for future work in development and analysis of the GSM-CommSense system.

Thesis (M. Eng.)--Memorial University of Newfoundland, 1999. / Bibliography: leaves 83-88.

Nowadays, identification of fake data is an elaboratechallenge that calls for the use of machine learning techniques.This is due to the huge amount of data and its complexity makesthe differences indistinguishable even for the trained eye. In thisproject we use the MATLAB wlanTGnChannel System objectto simulate multipath fading channels that are comparable toreal impulse response measurements made by Ericsson AB of anindoor8×8MIMO (Multiple Input Multiple Output) system.We use an SVM classifier to compare the eigenvalues of theircorrelation covariance matrices, obtaining an accuracy of 84%.Comparing their power delay profiles (PDPs) happens to bea classification task of low complexity due to time resolutionlimitation in the real measurements. We suggest that the proposedMATLAB model strongly differs from the real data we have beenprovided with. / Nu för tiden så är identifiering av fejkad data en svår utmaning som ofta kräver maskininlärningstekniker. Detta beror på den stora mängden data och att komplexiteten i datat gör att skillnaderna kan vara svår att se även för ett tränat öga. I det här projektet använder vi oss av MATLABs systemobjekt wlanTGnChannel för att simulera flervägs fädningskanaler som kan jämföras med riktiga impulssvarsmätningar gjorda av Ericsson AB av ett innomhus 8 X 8 MIMO(Multiple Input Multiple Output) system. Vi använde en SVM (stödvektormaskins) klassificerare för att jämföra egenvärdena av deras korrelationskovariansmatriser, vilket erhåller en noggranhet på 84%. Att jämföra deras power delay profiles (PDP) råkar vara ett klassificeringsproblem av låg svårighetsgrad på grund av tidsupplösningsbegränsningar för de riktiga mätningarna. Vi vill påstå att den tilltänkta MATLAB- modellen aviker mycket från den givna datan. / Kandidatexjobb i elektroteknik 2020, KTH, Stockholm

LOW power operation for wireless radio receivers has been gaining importance lately on account of the recent spurt of growth in the usage of ubiquitous embedded mobile devices. These devices are becoming relevant in all domains of human influence. In most cases battery life for these devices continue to be an us-age bottleneck as energy storage techniques have not kept pace with the growing demand of such mobile computing devices. Many applications of these radios have limitations on recharge cycle, i.e. the radio needs to last out of a battery for long duration. This will specially be true for sensor network applications and for im-plantable medical devices. The search for low power wireless receivers has become quite advanced with a plethora of techniques, ranging from circuit to architecture to system level approaches being formulated as part of standard design procedures. However the next level of optimization towards “Smart” receiver systems has been gaining credence and may prove to be the next challenge in receiver design and de-velopment. We aim to proceed further on this journey by proposing Power Scalable Wireless Receivers (PSRX) which have the capability to respond to instantaneous performance requirements to lower power even further. Traditionally low power receivers were designed for worst-case input conditions, namely low signal and high interference, leading to large dynamic range of operation which directly im-pacts the power consumption. We propose to take into account the variation in performance required out of the receiver, under varying Signal and Interference conditions, to trade-off power. We have analyzed, designed and implemented a Power Scalable Receiver tar-geted towards low data-rate receivers which can work for Zigbee or Bluetooth Low Energy (BLE) type standards. Each block of such a receiver system was evaluated for performance-power trade-offs leading to identification of tuning/control knobs at the circuit architecture level of the receiver blocks. Then we developed an usage algorithm for finding power optimal operational settings for the tuning knobs, while guaranteeing receiver reception performance in terms of Bit-Error-Rate (BER). We have proposed and demonstrated a novel signal measurement system to gen-erate digitized estimates of signal and interference strength in the received signal, called Received Signal Quality Indicator (RSQI). We achieve a RSQI average energy consumption of 8.1nJ with a peak energy consumption of 9.4nJ which is quite low compared to the packet reception energy consumption for low power receivers, and will be substantially lower than the energy savings which will be achieved from a power scalable receiver employing a RSQI. The full PSRX system was fabricated in UMC 130nm RF-CMOS process to test out our concepts and to formally quantify the power savings achieved by following the design methodology. The test chip occupied an area of 2.7mm2 with a peak power consumption of 5.5mW for the receiver chain and 18mW for the complete PSRX. We were able to meet the receiver performance requirements for Zigbee standard and achieved about 5X power savings for the range of input condition variations.