Description
The use of frequency division duplex (FDD) communication in a multihop wireless network partitions the nodes in two operating modes (or genders), depending on the frequency bands used for the transmission and reception. Since the FDD nodes of the same gender, located in a 1-hop neighborhood, cannot communicate with each other, it can limit the availability of communication links between the neighboring nodes and leads to network partitioning. Therefore, the operating mode of these nodes should be selected such that every node can establish links with its 1-hop neighbors. The multihop network of static FDD nodes is modeled as a graph, and a novel, distributed bipartite graph coloring scheme, for mode selection of FDD nodes is designed. Unlike the existing graph coloring schemes, which use the entire network topology and yet do not ensure network connectivity, this scheme requires only the local information of the 1-hop neighborhood of each node in a distributed manner. The proposed mode selection algorithm ensures that every FDD node can establish the communication links with approximately half of its 1-hop neighbors for omni as well as directional communication, without introducing any disconnected node. This mode selection algorithm has lower computational complexity and provides robust network connectivity, which would help in fault tolerance and establishing stable routes in the network. Next, a novel, distributed, low-complexity mode reassignment (MR) scheme is designed for maintaining connectivity among the mobile FDD nodes in a decentralized, multihop wireless network. Since it is not practical to know the complete topology of such a network in real-time, the proposed scheme is fully distributed, relies only on the local node information, and is applied only on those nodes whose connectivity drops below a threshold. Besides maintaining a desired value of connectivity degree for each node at all time steps, the proposed MR scheme minimizes the impact of mode change on the existing links and ongoing data transmissions. A Kalman filter based node mobility prediction and link failure prediction scheme is designed to select the best candidate nodes for mode change. Several novel measurements are introduced to evaluate the performance of our MR scheme. The optimality and error control bounds of the proposed MR scheme show that it consistently increases the nodes’ connectivity degree (achieves optimal connectivity for most nodes) while requiring a low number of nodes undergoing the mode change at each MR round. This MR scheme has low computational complexity and would help in establishing stable routes in a mobile network. Next, a mobile wireless ad-hoc network equipped with full-duplex nodes is considered. The full-duplex capability can be provided either by transmitting and receiving data simultaneously in a given frequency band by canceling the self-interference or can be provided by utilizing two separate frequency channels for transmission and reception at the same time in the FDD node. In either case, the full-duplex capability allows the formation of bidirectional routes, where every forward and reverse route between a source and destination pair completely overlaps. These completely overlapped bidirectional routes can support efficient transmission of bidirectional flows between a pair of source and destination nodes. In this dissertation, a novel routing protocol, called as bidirectional AOMDV (BAOMDV) is proposed, that discovers multiple, link-disjoint, bidirectional routes in the network, to make efficient use of full-duplex nodes. This routing protocol overcomes the limitations of existing AOMDV based protocols in finding the bidirectional routes. Additionally, the effect of route break in the presence of multiple active routes among source and destination pairs is considered and a novel bidirectional local route repair scheme called BAOMDV-LR is proposed in this dissertation. This scheme is capable of locally repairing routes formed based on the proposed BAOMDV protocols while preserving the link-disjoint and bidirectional nature of the routes, and can avoid the expensive route discovery procedure in the mobile ad-hoc networks. The scheme helps to maintain multiple active bidirectional routes for longer duration and reduce the need for frequent route discovery. The proposed BAOMDV-LR scheme is able to increase the overall network performance especially at higher data rates, and node speeds.
