Browsing by Subject "Wireless Networks"
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Item Distributed Linear Combination Estimators for Localization Based on Received Signal Strength(2013-12-05) Chen, Wei-YuLocating the position of a radio frequency device is indispensable in many wireless applications. The most famous method is the Global Positioning System (GPS), which uses trilateration with satellites, is generally unavailable for indoor devices and expensive for large networks. Therefore, this dissertation aims to develop and discuss accurate, fast, low-cost, energy-efficient, and robust localization algorithms especially based on the received signal strength (RSS). This dissertation proposes a distributed and iterative estimator by linearly combining location estimates from maximum likelihood based range estimates. In non- cooperative cases where unknown-location (blindfolded) devices only utilize the in- formation from known-location devices (anchors), each combining weight is proportional to the reciprocal of the estimated distance squared between the blindfolded node and an anchor. The numerical simulations demonstrate that the proposed LC estimator has similar error behaviors to the maximum likelihood estimator (MLE) and fewer computations under various topologies and noisy wireless environments. If the parameters for the RSS model are unknown, they are estimated by the least square and/or maximum likelihood methods. The accuracy difference of the linear combination estimators by estimated and perfect parameters is acceptable and decreasing as more anchors are deployed. In cooperative localization, a blindfolded node uses information from not only anchors but also other blindfolded nodes. The combining weight is now proportional to the reciprocal of the estimated distance squared and the transmitter?s positioning error. After being mainly compared with the distributed maximum likelihood estimator by coordinate descent method and the distributed weighted-multidimensional scaling (dwMDS) method, the LC estimator performs well in accuracy, computation time, and the use of wireless transmissions under various topologies, connectivities, and noisy environments. Moreover, the estimation error is clipped by upper and lower bounds. The drawback is that the convergence is not guaranteed, although non-convergent cases rarely happen. For the connectivity issue, placing more nodes with smaller transmitting ranges results in fewer connected nodes and less power consumption. However, to improve localization of an existing system, the relative costs of node and consumed power must be considered to determine the lowest cost system. Finally, the density of blindfolded nodes is two to three times to the density of anchors to achieve the same accuracy.Item Multicast networks : capacity, algorithms, and implementation(2011-12) Abdel Hadi, Ahmed Mohamed; Gerstlauer, Andreas, 1970-; Vishwanath, Sriram; Valvano, Jonathan; Vikalo, Haris; Akella, Maruthi; Bovik, AlanIn this dissertation, we investigate the capacity and performance of wireless networks with an emphasis on multicast traffic. The defining characteristic of a multicast network is a network where a number of different destinations all require the information generated by a single source. The models that we explore differ in the nature of the nodes from all-mobile case where all nodes are mobile to hybrid case where some nodes are mobile and some are static. We investigate different performance measure for these wireless multicast networks: upper bounds, capacity scaling laws, and achievable rates. The understanding of these measures for such networks helps in the development of efficient algorithms for operating these networks. In addition, we study the practical realization of algorithms for real-time streaming of rich multimedia content in the context of mobile wireless networks for embedded and cyberphysical systems. Our initial work is in the context of unicast and multiple unicast systems over an autonomous aerial vehicle (AAV) network. Bandwidth requirements and stringent delay constraints of real-time video streaming, paired with limitations on computational complexity and power consumptions imposed by the underlying implementation platform, make cross-layer and cross-domain co-design approaches a necessity. In this dissertation, we propose a novel, low-complexity rate-distortion optimized (RDO) protocol specifically targeted at video streaming over mobile embedded networks. First, we test the performance of our RDO algorithm on simulation models developed for aerial mobility of multiple wirelessly communicating AAVs. Second, we test the performance of our RDO algorithm and other proposed adaptive algorithms on a real network of AAVs and present a comparative study between these different algorithms. Note that generalizing these algorithms to multicast settings is relatively straightforward and thus is not highlighted to a great degree in this thesis.Item Reliable Downlink Scheduling for Wireless Networks with Real-Time and Non-Real Time Clients(2014-08-05) Jain, AbhishekIn this thesis, we studied the problem of designing a down link scheduling policy to serve multiple types of clients from a base station in a time-varying wireless network. An ideal scheduling policy is fair among the clients, provides reliability to the clients, achieves high system throughput and prevents strategic clients from choosing incorrect means. The existing scheduling policies fail to achieve one or more of these features. The Proportional Fair scheduling policy for example, fails to provide reliability to the real time clients, while Round Robin policy provides reliability to the clients but fails to achieve high system throughput in a time-varying wireless network. Apart from these policies, there are scheduling policies which prioritize clients based on their delay requirements. Here, a client with lower priority may choose incorrect means like claiming false types of flows to obtain a better performance. A non-real time client may pretend to be a real time client if doing so, which might aid it to achieve better performance in terms of average throughput. We proposed a new scheduling policy that is not only proportionally fair but also provides reliability to the mixture of real time and non-real time clients over a shared wireless channel. Our proposed policy aims to serve clients with different service requirements and provides best service to the clients which furnish true information about their service requirements; the client claiming false service requirements is penalized with the reduced performance. We theoretically demonstrate the effectiveness of the algorithm by considering uniform distribution of service rates of all the clients. We then provide extensive simulation results of our scheduling policy under the fast fading Rayleigh model to show that this policy can be easily extended in wireless networks. We also show that our policy outperforms existing policies in providing better reliability to the clients and unlike other common policies, our policy degrades the performance of a client that chooses incorrect means.