ITC/USA 2008 Conference Proceedings / The Forty-Fourth Annual International Telemetering Conference and Technical Exhibition / October 27-30, 2008 / Town and Country Resort & Convention Center, San Diego, California / UUV homing and docking and UAV collision avoidance are two seemingly separate research topics for different applications. Upon close examination, these two are a pair of dual problems, with interesting correspondences and commonality. In this paper, we present the theoretical analysis, signal processing, and the field experiments of these two algorithms in UAV and UUV applications in homing and docking as well as collision avoidance.

Random access schemes are primarily used for data transmission in the uplink of cellular networks. Every user in a random access network is programmed to follow a predetermined transmit control policy that is designed to achieve optimal network performance. This approach, however, is not very efficient in cellular networks where channel conditions vary from time to time. Employing a fixed transmission policy may not guarantee optimal performance. To alleviate this problem, recently, channel aware random access schemes have been proposed wherein information available at the physical (PHY) layer is utilized at the higher layers to maximize network throughput. Such a cross-layer approach naturally has its share of challenges and problems. The objective of the proposed research is to study the effect of multicarrier diversity on channel aware random access schemes. First, we describe two generic random access schemes - channel aware multicarrier random access (CAMCRA) and no selection random access (NS-RA) for multicarrier networks. The former is based on judicious carrier selection and exploits multicarrier diversity while the latter does not perform carrier selection. For illustration purposes, we consider the well-known Aloha protocol and study the effect of channel state imperfection on the overall network throughput. We show that networks employing the NS-RA scheme are extremely sensitive to channel measurement errors. More precisely, the asymptotic average throughput of the NS-RA scheme under uncertain channel conditions is zero. The CAMCRA scheme, however, is very robust to channel estimation errors and maintains the same order of throughput.

The Best PhD Thesis in the Faculties of Dentistry, Engineering, Medicine and Science (University of Hong Kong), Li Ka Shing Prize,2007-2008 / published_or_final_version / Computer Science / Doctoral / Doctor of Philosophy

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This thesis presents an investigation into the problems of exploration, map building and collision free navigation for intelligent autonomous mobile robots. The project began with an extensive review of currently available literature in the field of mobile robot research, which included intelligent control techniques and their application. It became clear that there was scope for further development with regard to map building and exploration in new and unstructured environments. Animals have an innate propensity to exhibit such abilities, and so the analogous use of artificial neural networks instead of actual neural systems was examined for use as a method of robot mapping. A simulated behaviour based mobile robot was used in conjunction with a growing cell structure neural network to map out new environments. When using the direct application of this algorithm, topological irregularities were observed to be the direct result of correlations within the input data stream. A modification to this basic system was shown to correct the problem, but further developments would be required to produce a generic solution. The mapping algorithms gained through this approach, although more similar to biological systems, are computationally inefficient in comparison to the methods which were subsequently developed. A novel mapping method was proposed based on the robot creating new location vectors, or nodes, when it exceeded a distance threshold from its mapped area. Network parameters were developed to monitor the state of growth of the network and aid the robot search process. In simulation, the combination of the novel mapping and search process were shown to be able to construct maps which could be subsequently used for collision free navigation. To develop greater insights into the control problem and to validate the simulation work the control structures were ported to a prototype mobile robot. The mobile robot was of circular construction, with a synchro-drive wheel configuration, and was equipped with eight ultrasonic distance sensors and an odometric positioning system. It was self-sufficient, incorporating all its power and computational resources. The experiments observed the effects of odometric drift and demonstrated methods of re-correction which were shown to be effective. Both the novel mapping method, and a new algorithm based on an exhaustive mesh search, were shown to be able to explore different environments and subsequently achieve collision free navigation. This was shown in all cases by monitoring the estimates in the positional error which remained within fixed bounds.

RFID technology has attracted much attention due to its wide range of applications, such as inventory control and object tracking. Passive RFID tags are battery-less, mobile and lack intercommunication. Hence, they require a central node (the reader) to power them up, organize their replies, and read their data. In the last decade, several proposals have targeted the channel efficiency in RFID systems to improve time and power efficiencies. While such proposals achieve significant performance improvements, they are limited by the backscattering half-duplex channel in which the reader has to wait for the tag to finish its reply (even if the reply is corrupt or redundant). In this thesis, the Modulation Silencing Mechanism (MSM) is proposed as a novel full-duplex-like communication over half-duplex RFID links. With a simple additional circuit at the tag and upgraded software algorithms at the reader, the reader is capable of terminating the tag's non-useful transmissions. Consequently, we propose three schemes that utilize MSM in key application domains where the tag-reader transaction contains a considerable amount of non-useful transmissions. MSM is utilized to enhance tag identification, tag count estimation and tag authentication. First, we propose a Modulation Silencing Anti-collision (MSA) scheme that targets collision time reduction in time slotted anti-collision protocols. In MSA, the time requirements of state of the art identification protocols are significantly reduced. Moreover, we establish a backward compatibility procedure for proper identification of legacy and MSM-enabled tags. Secondly, a Variance- Modulation Silencing Estimation (VMSE) scheme is proposed to increase tag estimation accuracy and to minimize overall estimation time. Variance-to-mean ratio estimator is proposed to determine the most accurate tag count estimate. VMSE combines both, the accuracy of the variance-to-mean ratio estimator and the time efficiency of MSM and delivers rapid, accurate, and anonymous tag estimation that outperform recent estimation schemes for small and large scale tag deployment. Finally, we propose Unique Hash Sequence Authentication (UHSA) scheme for efficient tag authentication. The UHSA is based on hashed key prefetching algorithm at the reader augmented by the MSM circuitry at the tag. UHSA scheme provides higher time efficiency and robustness against tracking and compromising attacks. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2013-04-30 12:38:44.0