A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Time-Reversal Indoor Positioning System and Medium Access Control(2016) Wu, Zhung-Han; Liu, K.J. Ray; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With the rapid expansion of the wireless communication, there has been a rapid growth in the demand for the mobile traffic. Moreover, the wireless traffic not only expands in traffic volume but also in the diversity of applications and requirements with the rise of the Internet of Things (IoT) concept. The insatiable demand for both the traffic volume and the ever-expanding IoT applications poses a great challenge on the design of the next generation, i.e. the 5G, communication system. Time reversal (TR) technology has been proposed as a promising candidate for the 5G system with several promising characteristics, such as easy densification, asymmetric and heterogeneous design. TR system utilizes large bandwidth and observes detailed, location-specific channel impulse responses (CIR). With the detail CIR information, the TR system designs waveforms to concentrate transmitted energy to the intended users via the unique spatial temporal focusing effect. In this dissertation, we propose a TR indoor positioning system and medium access control design based on this unique effect. We begin by proposing the time reversal resonating strength (TRRS) to quantify the similarity between the location information embedded CIRs. The TR indoor positioning system identifies the unknown users by calculating the TRRS between the CIR of the unknown user and the CIRs in the database. We built the system prototype and are the first-ever to perform precise indoor positioning at 1 to 2 cm resolution in both line-of-sight and non-line-of-sight scenario using one pair of transmitter and receiver both equipped with a single antenna. Based on the positioning system, we propose an indoor tracking system by collecting CIRs at several regions of interest and track unknown users when they pass it. To facilitate deployment, we built a prototype to automate CIR collection and the experiments show that the system detects the users correctly with very low false alarm rate. In the second part, we design the medium access control scheme to maximize system sum rate and guarantee quality of service to the users in a downlink scenario. The system objective and constraints are transformed into a mixed integer quadratically constraint quadratic programming and can be solved efficiently. We then investigate rate adaptation scheme via selection of optimal backoff factors in TR system. The rate adaptation scheme effectively increases the system-wise performance and the fairness among users.Item Medium Access Control and Network Coding for Wireless Information Flows(2007-08-03) Sagduyu, Yalin Evren; Ephremides, Anthony; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation addresses the intertwined problems of medium access control (MAC) and network coding in ad hoc wireless networks. The emerging wireless network applications introduce new challenges that go beyond the classical understanding of wireline networks based on layered architecture and cooperation. Wireless networks involve strong interactions between MAC and network layers that need to be jointly specified in a cross-layer design framework with cooperative and non-cooperative users. For multi-hop wireless networks, we first rediscover the value of scheduled access at MAC layer through a detailed foray into the questions of throughput and energy consumption. We propose a distributed time-division mechanism to activate dynamic transmitter-receiver assignments and eliminate interference at non-intended receivers for throughput and energy-efficient resource allocation based on stable operation with arbitrary single-receiver MAC protocols. In addition to full cooperation, we consider competitive operation of selfish users with individual performance objectives of throughput, energy and delay. We follow a game-theoretic approach to evaluate the non-cooperative equilibrium strategies at MAC layer and discuss the coupling with physical layer through power and rate control. As a cross-layer extension to multi-hop operation, we analyze the non-cooperative operation of joint MAC and routing, and introduce cooperation stimulation mechanisms for packet forwarding. We also study the impact of malicious transmitters through a game formulation of denial of service attacks in random access and power-controlled MAC. As a new networking paradigm, network coding extends routing by allowing intermediate transmitters to code over the received packets. We introduce the adaptation of network coding to wireless environment in conjunction with MAC. We address new research problems that arise when network coding is cast in a cross-layer optimization framework with stable operation. We specify the maximum throughput and stability regions, and show the necessity of joint design of MAC and network coding for throughput and energy-efficient operation of cooperative or competitive users. Finally, we discuss the benefits of network coding for throughput stability in single-hop multicast communication over erasure channels. Deterministic and random coding schemes are introduced to optimize the stable throughput properties. The results extend our understanding of fundamental communication limits and trade-offs in wireless networks.