Next generation wireless networks are expected to provide high data rate and satisfy the Quality-of-Service (QoS) constraints of the users. A significant component of achieving these goals is to increase the effi ciency of wireless networks by either optimizing current architectures or exploring new technologies which achieve that. The latter includes revisiting technologies which were previously proposed, but due to a multitude of reasons were ignored at that time. One such technology is relaying which was initially proposed in the latter half of the 1960s and then was revived in the early 2000s. In this dissertation, we study relaying in conjunction with resource allocation to increase the effi ciency of wireless networks. In this regard, we differentiate between conventional relaying and relaying with buffers. Conventional relaying is traditional relaying where the relay forwards the signal it received immediately. On the other hand, in relaying with buffers or buffer-aided relaying as it is called, the relay can store received data in its buffer and forward it later on. This gives the benefit of taking advantage of good channel conditions as the relay can only transmit when the channel conditions are good. The dissertation starts with conventional relaying and considers the problem of minimizing the total consumed power while maintaining system QoS. After upper bounding the system performance, more practical algorithms which require reduced feedback overhead are explored. Buffer-aided relaying is then considered and the joint user-and-hop scheduler is introduced which exploits multi-user diversity (MUD) and 5 multi-hop diversity (MHD) gains together in dual-hop broadcast channels. Next joint user-and-hop scheduling is extended to the shared relay channel where two source-destination pairs share a single relay. The benefits of buffer-aided relaying in the bidirectional relay channel utilizing network coding are then explored. Finally, a new transmission protocol for overlay cognitive radios is derived. This protocol utilizes relays with buffers, requires only causal knowledge of the primary's message at the secondary and incentivizes the primary to cooperate with the secondary and share its codebook.

京都大学 / 0048 / 新制・課程博士 / 博士(生命科学) / 甲第19143号 / 生博第326号 / 新制||生||43(附属図書館) / 32094 / 京都大学大学院生命科学研究科高次生命科学専攻 / (主査)教授 渡邉 大, 教授 影山 龍一郎, 教授 渡邊 直樹 / 学位規則第4条第1項該当 / Doctor of Philosophy in Life Sciences / Kyoto University / DFAM

Wireless sensor networks (WSNs) are systems of resource-constrained sensor nodes (SNs), distributed throughout a sensor field. Energy limitations persist due to the wireless nature of SNs and an interest in minimizing the cost and physical footprint of SNs. Due to the resource-constrained nature of SNs, much WSN research has focused on energy-efficient communication algorithms. Communication algorithms are necessary for energy-efficient data transmission between SNs and the transmission of data collected by SNs to a base station. A popular algorithm known as Low-Energy Adaptive Clustering Hierarchy (LEACH) achieves more energy-efficient communication by organizing SNs into clusters for localized communication. When SNs are mobile, the energy efficiency of LEACH is degraded because of geographic dispersion of SN clusters. This thesis proposes LEACH-Centered Cluster-head (LEACH-CCH), a clustering algorithm aimed at improving WSN lifetime in cases of stationary and mobile sensor nodes. Mobile sensor network applications are explored including vehicle-to-infrastructure communication networks.

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Bluetooth™ is an emerging short-range RF wireless voice and data communication technology expected to spread widely in a couple of years. The open specification technology eliminates the need for cables to connect mobile phones, portable computers and countless other devices to each other from all different manufacturers. This thesis provides an overview of the emerging Bluetooth™ technology and investigates the performance of Bluetooth™ data networks in various network topologies simulated from actual usage scenarios. Using a typical office environment, the study examines the probability and effects of Co-Channel interference as Bluetooth™ ad-hoc networks are formed in adjacent offices. A computer aided simulation tool, MATLAB simulates a low to highly dense interfering Bluetooth™ environment which provides the parameters to evaluate the bluetooth co-channel interference and performance. Several metrics are identified to predict Bluetooth™ performance in a piconet after a collision has occurred: data through put, the probability of frequency collision, transmitter - receiver distance, and power received. Next, to predict Bluetooth performance we also need to define what constitutes a lost packet. Finally, a Bluetooth™ network simulation is developed to measure the metrics, given occurrence of the lost packets. / Master of Science

The analysis of radio wave propagation is a crucial part in designing an efficient wireless communication system. The Geographic Information System (GIS) can be incorporated into this procedure because most of the factors in radio wave propagation are geographic features. In this research, a commercial wireless planning software is tested in a field driving test carried out in Montgomery County, VA. The performance of current wireless planning software is evaluated based on field measurement. The received signal strength data collected during this driving test are then analyzed in a GIS environment in a statistical approach. The effects of local geographic features are modeled in GIS by appropriate spatial analyses. / Master of Science

A Geographic Information System (GIS) viewshed is the result of a function that determines, given a terrain model, which areas on a map can be seen from a given point(s), line or area. In the communications industry, this function has been used to model radio wave coverages and to site transceiver towers for cellular phones. However, there are errors involved with this function and, without the requisite data, it cannot account for building heights that may affect visibility in urban areas. This paper examines the ability to accurately show line-of-sight (LOS) radio wave coverages in order to establish the viability of replacing existing field methods with GIS viewshed analysis. An origin point capable of supporting a line-of-sight radio wave transmitter was chosen from within the Virginia Tech campus study area. A viewshed analysis was performed with ESRI's ArcView GIS, using this site as the observation point and a 30-meter resolution Digital Elevation Model (DEM) from the US Geological Survey. To check the accuracy of the viewshed, we transmitted at 27.5 GHz, a LOS frequency that has properties common in the wireless telecommunications industry. We also transmitted at 900 MHz from the same point to provide a comparison of the 27.5 GHz frequency to a non-line-of-sight radio wave.The data was recorded and then entered into the GIS where the visibility attribute of each point was compared to the viewshed's prediction of visibility. After this comparison, footprints and heights of campus buildings were included in the model, by adding them to the ground heights of the DEM. Another viewshed analysis was performed using the same origin site and the new building height DEM as the elevation grid. This second viewshed was compared with the recorded visibility attribute and signal strength data. The use of more complete surface data was shown to have a more positive correlation with the recorded data than the previous model. The comparison of these two viewsheds demonstrated how well the viewshed function can represent real-world visibility and showed that the accuracy of the viewshed function is dependent on the accuracy of the elevation model. The signal strength attribute enabled us to create a communications viewshed, or 'commshed'. The commshed consists of all data points that received a signal strong enough to carry data. The building viewshed and commshed were then compared to see to what degree the 27.5 GHz frequency deviates from true line-of-sight paths. There were slightly fewer points in the commshed than points 'in view' in the viewshed model due to the frequency's small wavelength and the lack of vegetation data in the elevation grid. However, when a power margin is added to the transmitter strength in order to overcome unpredictable conditions, the commshed's predictive accuracy increases as well. This means that for LOS radio systems running under normal operating conditions, the viewshed is an excellent predictor of receiving areas. A 900 MHz commshed was also created so that we could study the relationship between a line-of-sight radio wave and a wave that is not blocked by structures. This comparison showed that, as expected, a viewshed is a better predictor of LOS radio waves than non-LOS waves. The data sets and analysis presented here should help communications companies ascertain the best way to incorporate GIS and the viewshed function into their wave coverage mapping and tower siting processes. / Master of Science

This thesis proposes a system architecture for a high-data rate mobile Local Multipoint Distribution Service (LMDS) Network. Its goal is to provide a workable "strawman" design that can serve as a basis for further research. The architecture is designed to offer broadband services to train commuters via LMDS. The thesis provides a broad overview of system aspects, such as Doppler shift, modulation selection, and error correction coding. These parameters and others are important in providing a robust design. This thesis discusses a set of criteria that seek the best approach in terms of economical feasibility, throughput capabilities, design complexity, data routing, and robustness in serving multiple mobile units simultaneously. These criteria are examined through link budget analysis, layout designs, and throughput efficiency. System throughput specifications are calculated for services, such as web browsing, email, ftp, and voice services to 100 train commuters. The information rate was 134.4 Mbps. The information rate plus overhead, which includes routing, bit and framing synchronization, and error correction coding, was approximately 201.51 Mbps. Using Carson's rule, the total required bandwidth for downstream transmissions was approximately 263 MHz. This throughput requirement was a criterion in selecting the appropriate system architecture. Three approaches were evaluated: LMDS Infostations, Tower Sites, and Infostations/Tower Sites. Infostations are low-powered wireless cells designed to offer individual pockets of high bandwidth connectivity for broadband services. Tower Sites use switched antenna beams to offer continuous services to train commuters. The hybrid solution, Infostations/Tower Sites, offers continuous services with increased power requirements and increased base stations separation when compared to the Infostation approach. Link budgets were examined for the Infostations and Tower Site approach. The initial required power for the Infostation was 1 mW. A 42.4 dB Eb/No link margin was computed using the Friis equation. The initial required power for the Tower Site approach was 500 mW. A 10.2 dB Eb/No link margin was computed with this approach. Tradeoffs with the non-fixed parameters were made to vary the link margins. An economically feasible number of required units were also determined. Approximately 3,000 low-powered Infostations would be needed to offer continuous service. Only 93 Tower Sites would be required and 4*93 Tower Site/Infostation units would be needed to supply continuous, seamless services over a 230-miles coverage area. The LMDS Tower Site was chosen to be the most suitable approach because of its robustness in meeting the pre-defined criteria. / Master of Science

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