Finding a closest match between wi-fi propagation measurements and models

In a series of papers by Sarkar and his team conducted radio propagation measurements to study the performance of Wi-Fi in terms of received signal strengths (RSS) in an obstructed office block. The goal of this paper is to find a closest match between the results obtained from propagation measurements and the theoretical models. The RSS measurement results are compared with the four selected propagation models (Free-space, Two-ray ground reflection, Shadowing path loss, and the overall Shadowing models). These models were selected based on their popularity and relevance to our study. Results obtained show that the overall shadowing model is the best-fit followed by the path loss Shadowing. We found about 94% and 99% matching with RSS measurement results for non-LOS and NLOS conditions, respectively. The analysis and research findings reported in this paper provide some insights into the deployment of indoor wireless systems

SPACE-TIME BEHAVIOR OF MILLIMETER WAVE CHANNEL AND DIRECTIONAL MEDIUM ACCESS CONTROL

An appropriate channel model is required to evaluate the performance of different physical (PHY) layer designs. However, there is no known space-time millimeter wave channel model that could benefit the use of directional antennas that is applicable in environments with lots of reflections such as residential or office. The millimeter wave signal strength is subject to temporal and spatial variations. The focus of the first part is the investigation of the characteristics of the millimeter wave propagation model. By analyzing measurement data of millimeter wave channels for indoor environments, space-time clusters are identified, and intercluster statistics for millimeter wave propagation are calculated. Correlation of the identified space-time clusters to the propagation environment is determined. In the second part, the effectiveness of the ray-tracing method in creating channel realizations in the intercluster and intracluster levels for millimeter wave indoor environments is validated. In the third part, a protocol to establish an optimal directional link between two nodes equipped with directional antennas is presented. The correctness of the protocol for different scenarios is illustrated using a ray-tracing tool. Then in the forth part, a Directional MAC (D-MAC) for supporting millimeter wave technology exploiting directional antennas is presented. The D-MAC is compatible with the current IEEE 802.15 MAC of WPAN, and it has backward compatibility to support devices which are not equipped with directional antennas. Finally, a directional neighbor discovery algorithm is presented which does not require time synchronization or any location information of communicating nodes. This means two nodes equipped with directional antennas can discover and communicate with each other through an established directional link as part of the D-MAC

First-passage-time problems in time-aware networks

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 183-194).First passage time or the first time that a stochastic process crosses a boundary is a random variable whose probability distribution is sought in engineering, statistics, finance, and other disciplines. The probability distribution of the first passage time has practical utility but is difficult to obtain because the values of the stochastic process at different times often constitute dependent random variables. As a result, most first-passage-time problems are still open and few of them are explicitly solved. In this thesis, we solve a large class of first-passage-time problems and demonstrate the applications of our solutions to networks that need to maintain common-time references. Motivated by rich applications of first passage time, we solve first-passage-time problems, which are divided into four categories according to the form of stochastic processes and the type of the boundaries. The four categories cover Brownian motion with quadratic drift and the boundary that consists of two constants; Brownian motion with polynomial drift of an arbitrary degree and the boundary that consists of two constants; multi-dimensional Brownian motion with polynomial drift and a class of boundaries that are characterized by open sets in the Euclidean space; and a discrete-time process with a class of correlations and the boundary that consists of one constant. These first-passage-time problems are challenging yet important for practical utility. The solutions to these first-passage-time problems range from an explicit expression to a bound of the first-passage-time distribution, reflecting the inherent difficulty in these first-passage-time problems. For Brownian motion with quadratic drift, the solution is explicit, consisting of elementary functions and functions that are characterized by Laplace transforms. For Brownian motion with polynomial drift of an arbitrary order, the solution involves analytical and numerical methods. For multi-dimensional Brownian motion, the solution is explicit for a certain shape of the boundary and is given by an upper bound and a lower bound for the other shapes. For the discrete-time process, the solution is explicit. The strength of our solutions is that they cover a large class of first-passage-time problems and are easy to use. The primary approach that allows us to solve these first-passage-time problems is transformation methodology. We apply various types of transformations, including transformation of probability measure, transformation of time, and integral transformation. Although these transformations are known, the combination of them in an appropriate order enables the solutions to previously-unsolved first-passage-time problems. We also discuss other problems that can be solved as consequences of the transformation methodology, including first-passage-time problems that involve a one-sided constant boundary, a moving boundary, and drifts such as logarithmic, exponential, sinusoidal, and square-root functions. A large class of first-passage-time problems confirms the utility of the transformation methodology. We demonstrate an application of the first-passage-time problems in the context of network synchronization. In the first setting that we consider, the first passage time is the first time that a network loses synchronization with a reference clock. At the first passage time, clocks in the network need to be calibrated. In the second setting, the first passage time represents the first time that a node achieves a correct synchronization of frames or packets. At the first passage time, a node in the network is able to process the packets that are transmitted as parts of the calibration. In both settings, we consider two performance metrics-the average and the outage-which succinctly summarize the first passage time. These metrics give insight, for example, into the amount of time for networks to lose synchronization as a function of key parameters such as noise in the clocks and the number of nodes in the network. Given the large class of first-passage-time problems being solved, we expect the thesis results to be useful in many disciplines where first-passage-time problems appear.by Watcharapan Suwansantisuk.Ph.D

Efficient approaches to robust and cooperative wireless network design

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 181-200).In wireless networks, relaying and user cooperation offer several attractive benefits such as higher throughput, better power efficiency, and larger coverage. As a result, cooperative networks are regarded as one of the most promising enabling technologies able to meet the increasingly high rate demands and quality of service requirements in wireless networks. In this dissertation, we investigate the efficient design of cooperative wireless networks from the perspectives of robust resource allocation, wideband communications, and energy efficiency. Given that the primary resource to be allocated is the relay node's transmission power, we propose robust and efficient relay power allocation algorithms when the global channel state information is subject to uncertainty. In addition, we propose practical algorithms that do not require frequent tracking of the global channel state information. This work reveals that ignoring global channel state information uncertainties and solving the relay power optimization problems often lead to poor performance, highlighting the importance of robust algorithm designs in practical wireless networks. Wideband cooperative networks allow for both higher data rate and higher resistance to interference. Since the gains achieved by using cooperation come at the cost of higher node complexity and substantial coordination overhead, it is important to study practical low-complexity signaling and receiver schemes suitable for wideband networks. In particular, we consider transmitted-reference signaling schemes and provide a unified performance analysis in terms of bit error rate. Since wideband networks are expected to coexist with many existing narrowband systems, it is important to characterize the effect of narrowband interference. We further extend the performance analysis of transmitted-reference signaling schemes to include the effect of narrowband interference..(cont) Finally, we conclude by studying the benefits of cooperation in a wireless sensor network, which aims at detecting the presence or absence of a certain physical phenomenon of interest using geographically dispersed sensor nodes. We propose a consensus flooding protocol and analyze its average energy consumption. We investigate the tradeoff between the detection reliability and the energy efficiency when nodes are allowed to cooperate. By addressing the above design challenges, this dissertation will be useful for obtaining insight into the theory and application of cooperative networks in future communication systemsby Tony Q.S. Quek.Ph.D

Optical generation of mm-wave signals for use in broadband radio over fiber systems

In future cellular radio networks Radio over Fiber (RoF) is a very attractive technology to deliver microwave and millimeter-wave signals containing broad band multimedia services to numerous base stations of the network. The radio signals are placed on an optical carrier and distributed by means of an optical fiber network to the base stations (BS). In the BS the optical signals heterodyne in a photodiode to produce the radio signals which are then sent via a wireless link to the mobile units (MU). The optical fiber network provides high frequency, wideband, low loss and a means of signal distribution immune to electromagnetic interference. In this thesis, different methods of electrooptical upconversion were investigated. The generation of an optical double-sideband with suppressed carrier (DSB-SC) signal is a straightforward method due to the fact that only one optical modulator driven at half the millimeter-wave frequency is required. One or both sidebands were ASK-modulated with baseband data rates of up to 10 Gbps. Optical single sideband modulation proves to be dispersion resilient as error free transmission was demonstrated after 53 km of single mode fiber transmission for data rates up to 10 Gbps. Wireless links up to 7 m were also demonstrated, proving the feasibility of this approach for broadband wireless inhouse access systems.Für zukünftige zellulare Funknetze ist „Radio over Fiber (RoF)“ eine sehr attraktive Technologie, um breitbandige Multimedia-Dienste mit Mikro- und Millimeterwellen zu übertragen. Die Funksignale werden dabei auf eine optische Trägerwelle aufmoduliert und mittels eines optischen Fasernetzes zu den Basisstationen (BS) verteilt. In den BS erfolgt die Überlagung der optischen Signale durch eine Fotodiode, um die Funksignale zu erzeugen. Diese werden dann über eine drahtlose Verbindung zu den beweglichen Multimedia-Endgeräten geschickt. Vorteile des optischen Fasernetzes sind Breitbandigkeit, geringe Dämpfung und eine gegenüber elektromagnetischen Störungen immune Signalverteilung. In dieser Arbeit werden verschiedene Methoden der elektrooptischen Aufwärtskonversion erforscht und die wichtigsten Eigenschaften dieser untersucht. Die Erzeugung eines optischen Zweiseitenbandsignales mit unterdrücktem Träger (DSB-SC) ist eine einfache Methode, da nur ein optischer Modulator, betrieben mit der halben elektrischen Trägerfrequenz, benötigt wird. Eine oder beide Seitenbänder konnten mit Bitraten bis zu 10 Gbps amplitudenmoduliert werden. Optische Einseitenbandmodulation ist extrem tolerant bezüglich der chromatischen Dispersion der Faser, wie die fehlerfreie Übertragung nach 53 km Glasfaser beweist. Drahtlose Links bis zu 7 m wurden realisiert und zeigen die Möglichkeit dieser Verfahren für breitbandige drahtlose Inhouse-Zugangssysteme