| Summary: | 博士 === 國立交通大學 === 資訊科學與工程研究所 === 103 === Due to no need for fixed infrastructures, wireless ad hoc networks can be flexibly deployed with low cost for various missions. However, without the help of infrastructures, connectivity is a major concern. The nonexistence of isolated nodes is a prerequisite of connectivity. Nodes are called isolated if they do not have links to other nodes. In a realistic system, nodes may become inactive due to internal breakdown or being in the sleeping state, and links may be down due to harsh environment or barriers between nodes. The inactive nodes and down links cannot take part in routing/relaying and thus may affect the connectivity. We study the connectivity of wireless ad hoc networks that are composed of unreliable nodes and links by investigating the distribution of the number of isolated nodes.
Furthermore, many theoretical studies on network connectivity were based on disk graph model. The disk graph model sometimes is criticized for simplifying wireless channels too much to depict the behaviors of wireless networks. Most previous analytic works were not based on practical channel models. We study this problem using a generic probabilistic channel model that can capture the behaviors of the most widely used channel models. We derive the expected number of isolated nodes and further prove that their distribution asymptotically follows a Poisson distribution.
Deliverability is also a fundamental requirement in wireless ad hoc and sensor works. Without fixed infrastructures, virtual backbones are constructed and maintained for routing packets to deliver more efficiently. Relative neighborhood graphs (RNGs) are widely used to construct planar virtual backbones. However, most previous works assumed underlying networks are connected, or implicitly assumed the transmission radius can be arbitrarily increased if necessary. In addition, in order to locally construct virtual backbones, only part of structures will be constructed. This could increase the dilation factor and cause more energy consumption. By investigating the largest RNG edge length, we show that complete RNGs can be locally constructed with high probability by using only 1-hop information if the transmission radius is properly set.
In grid routing, the plane is tessellated into equal-sized square cells. If communication parties are in the same cell, packets can be transmitted directly; otherwise, packets are forwarded to routing neighbors that are in cells closer to destination cells. As a greedy strategy, grid routing suffers the existence of local minima at which no neighbor nodes exist for relaying packets. To guarantee deliverability, we investigate two vital parameters of grid routing, called the grid size and the transmission radius. We shall eliminate the probability of existence of local minima by simply setting a proper grid size and a proper transmission radius.
In addition to theoretical analysis, we study applications using inertial sensors. Inertial measurement units (IMUs) are widely used in various applications. We focus on the applications in positioning and navigation. We propose two applications using inertial sensors. The first application is a motion tracking system, called g-sensor constellations, in which only g-sensors but no direction sensors are used. The second is a personal navigation system for handheld devices, which is an integration of a pedestrian tracking system for handheld devices and GPS. It provides the position information with high precision.
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