In [1], we showed that the minimum probability p^0 for which pairwise enabling is an optimal group testing algorithm under an unbounded Bernoulli arrival sequence model satisfies 0.430

Recently we have developed a class of media access control algorithms for different types of Local Area Networks. A common feature of these LAN algorithms is that they represent various strategies by which the processors in the LAN can simulate the availability of a centralized packet transport facility, but whose service incorporates a particular type of change over time known as 'moving sever' overhead. First we describe the operation of moving server systems in general, for both First-Come - First-Served and Head-of-the-Line orders of service, together with an approach for their delay analysis in which we transform the moving server queueing system into a conventional queueing system having proportional waiting times. Then we describe how the various LAN algorithms may be obtained from the ideal moving server system, and how a significant component of their performance characteristics is determined by the performance characteristics of that ideal system. Finally, we evaluate the compatibility of such LAN algorithms with separable queueing network models of distributed systems by computing the interdeparture time distribution for M/M/1 in the presence of moving server overhead. Although it is not exponential, except in the limits of low server utilization or low overhead, the interdeparture time distribution is a weighted sum of exponential terms with a coefficient of variation not much smaller than unity. Thus, we conjecture that a service centre with moving server overhead could be used to represent one of these LAN algorithms in a product form queueing network model of a distributed system without introducing significant approximation errors.

Time-based secure localization protocols allow a group of mutually trusted entities called verifiers to cooperatively determine the location of an untrusted and possibly malicious stranger entity called the prover. Many applications associate certain privileges with the true physical location of an entity, therefore there is an incentive for a prover to claim a more "valuable" location, different from its true location. A well known threat to time-based localization protocols is distance fraud where a malicious prover misrepresents its location by intentionally changing its response time across a series of bilateral dialogues with individual verifiers. To address this threat, secure localization protocols must use a technique called "simultaneous multilateration".

A recently introduced protocol used simultaneous challenges by multiple verifiers, over separate RF channels, to defend against distance fraud. The authors also claimed that simultaneous multilateration by using simultaneous challenges, is optimal in the sense of achieving the maximal security that can be provided by any time-based localization protocol. In the first part of this thesis, we show that the structure of this newly proposed protocol is unnecessary, and significantly more complex than existing protocols. We propose a new protocol named Elliptical Multilateration (EM) that does not use simultaneous challenges. Instead, our EM protocol achieves simultaneity in multilateration by using multiple passive receivers to observe the prover's response. Our EM protocol requires fewer resources, provides commensurate security against distance fraud, and is inherently more accurate.

The second part of this thesis focuses on the issues related to practical implementation of time-based localization protocols. Most existing works focus on cryptographic aspects of time-based secure localization protocols. We found that the existing literature does not

address the issues that arise when these time-based protocols are implemented on real systems. For example, many authors have designed protocols based on single-bit exchanges (which is non-conformant with standard networking protocols and hardware, and extremely difficult to implement), ignore inevitable measurement errors etc. In this thesis, we show that the amount and magnitude of measurement errors depend largely on the structure of a protocol, and differ significantly across the known localization protocols. We investigate whether measurements can be made with sufficient accuracy to achieve localization on the order of a few meters. To the best of our knowledge, this thesis is the first work that attempts to analyze measurement error in practical realization of different localization protocols. The factors influencing the measurement errors, which are highlighted in this thesis, are significant and cannot be ignored.

We show that taking into account the significance of message structure and the factors influencing the measurement error, can lead to new protocols that are no worse in terms of security, need fewer message exchanges, and achieve better accuracy in comparison to existing time-based localization protocols.