Graduation date: 1993

A distributed hash table (DHT) is a type of peer-to-peer (P2P) network that, like traditional hash tables, maps keys to values. Unlike traditional hash tables, however, the data is distributed across a network with each node being responsible for a particular range of keys. Numerous other DHTs have been presented and have become the cornerstone of wildly popular P2P file-sharing applications, such as BitTorrent. Each of these DHTs trades-off the number of pointers maintained per node with the overhead and lookup time; storing more pointers decreases the lookup time at the expense of increased overhead. A Grouped Hamming Network (GHN), the overlay network presented in this thesis, allows for the number of pointers per node to be any increasing function of n, P(n) = Ω(log n). The system presented assumes that nodes fail independently and uniformly at random with some probability q = 1 − p. Three different schemes for routing in a GHN are presented. For each routing scheme a theoretical estimate on the probability of failure is given and optimal configurations in terms of n and P(n) are given. Simulations of GHNs with various configurations indicate that the given estimates are indeed accurate for reasonable values of q and that the optimal configurations are accurate.

Bit-interleaved coded modulation with iterative decoding (BICM-ID)is a spectral efficient coded modulation technique to improve the performance of digital communication systems. It has been widely known that for fixed signal constellation, interleaver and error control code, signal mapping plays an important role in determining the error performance of a BICM-ID system. This thesis concentrates on signal mapping designs for BICM-ID systems. To this end, the distance criteria to find the best mapping in terms of the asymptotic performance are first analytically derived for different channel models. Such criteria are then used to find good mappings for various two-dimensional 8-ary constellations. The usefulness of the proposed mappings of 8-ary constellations is verified by both the error floor bound and simulation results. Moreover, new mappings are also proposed for BICM-ID systems employing the quadrature phase shift keying (QPSK) constellation. The new mappings are obtained by considering many QPSK symbols over a multiple symbol interval, which essentially creates hypercube constellations. Analytical and simulation results show that the use of the proposed mappings together with very simple convolutional codes can offer significant coding gains over the conventional BICM-ID systems for all the channel models considered. Such coding gains are achieved without any bandwidth nor power expansion and with a very small increase in the system complexity.

While mobile technologies and applications are rapidly and widely utilized and adopted in electronic commerce (E-commerce), it is extremely important to better understand the value creation, business model capability and core component capability in mobile commerce (M-commerce). In this study, we conduct the secondary data analysis and use a value shop model to analyze the innovation in technological knowledge, business model, and dynamic capability aspects used in Internet-enabled commerce (I-commerce) versus M-commerce. A set of critical dynamic capabilities for each innovation is then identified. These results provide great insight for practitioners and scholars for enhancing their understanding of M-commerce innovation, and provide guidelines to help practitioners adapt from I-commerce to M-commerce innovation.

Reliable communication in the hypercube with the safety vectors is discussed in this thesis. In the hypercube, the safety levels and the safety vectors, used to guide fault-tolerant routing, is a kind of limited global information based methods. The transmission cost of the safety vectors is O(n2) for each node. For increasing the probability of optimal routing, we attempt to increase the transmission cost for obtaining more information. We propose two methods with O(n3) transmission cost in each node, the enhanced safety vector and the spanning safety vector, to achieve the goal. We also propose the probabilistic safety vector which provides the probability of optimal routing for each node. Finally, our experiments show that the routing with the enhanced safety vector is more reliable than the safety vectors and the extended safety vectors, which were propose the probabilistic safety vector.

A distributed hash table (DHT) is a type of peer-to-peer (P2P) network that, like traditional hash tables, maps keys to values. Unlike traditional hash tables, however, the data is distributed across a network with each node being responsible for a particular range of keys. Numerous other DHTs have been presented and have become the cornerstone of wildly popular P2P file-sharing applications, such as BitTorrent. Each of these DHTs trades-off the number of pointers maintained per node with the overhead and lookup time; storing more pointers decreases the lookup time at the expense of increased overhead. A Grouped Hamming Network (GHN), the overlay network presented in this thesis, allows for the number of pointers per node to be any increasing function of n, P(n) = Ω(log n). The system presented assumes that nodes fail independently and uniformly at random with some probability q = 1 − p. Three different schemes for routing in a GHN are presented. For each routing scheme a theoretical estimate on the probability of failure is given and optimal configurations in terms of n and P(n) are given. Simulations of GHNs with various configurations indicate that the given estimates are indeed accurate for reasonable values of q and that the optimal configurations are accurate.

The hypercube is one of the most versatile and efficient networks yet discovered for parallel computation. It is well suited for both special-purpose and general-purpose tasks, and it can efficiently simulate many other networks of the same size. The size of subgraphs can be used to estimate the efficient communications of hypercube computer systems.The thesis investigates induced subgraphs of a hypercube, discusses sizes of subgraphs, and provides a formula to give bounds on the size of any subgraph of the hypercube.The concept of spanning graphs and line graphs is useful for studying properties of graphs. An MS WINDOWS based graphical system is developed which allows the creation and display of graphs and their spanning graphs, line graphs and super line graphs. / Department of Computer Science

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 90-92). Also available via the Internet.

The main focus of this thesis are hypercubes. In the first part, we introduce hypercubes, which form an interesting class of graphs that has practical uses in networks and distributed computing. Because of their varied applications, the thesis describes the graph-theory problems related to hypercubes such as searching for detour spanners, minimizing their maximal degree and finding multiple edge- disjoint spanners. It also overviews current results on selected hypercube problems and proposes a solution using a genetic algorithm. The genetic algorithm is designed, implemented and its performance is evaluated. The conclusion is that applying a genetic algorithm to some hypercube problems is a viable, but not the most effective method.

No