Self-Organizing Mechanisms and QoS-Guaranteed Scheduling Algorithms in Wireless Ad Hoc Networks

• Main Authors: Chih-Cheng Tseng, 曾志成
• Other Authors: 陳光禎
• Format: Others
• Language: en_US
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/69294967434836510195

博士 === 國立臺灣大學 === 電信工程學研究所 === 95 === Since nodes in the wireless ad hoc networks are mobile and powered by the bat-teries, for prolonging the communication duration of the nodes, the transmission power is required to be minimized to conserve the limited battery life. In addition, since there is no fixed infrastructure, for the wireless ad hoc networks to be applicable, the wireless ad hoc networks are required to be connected. Unfortunately, these two requirements are against each other. In order to control the network topology in a power-efficient manner, we in-vestigate the relationships between the length of the transmission range, the size of the service area and the connectivity of the wireless ad hoc networks in this thesis. By deriv-ing the probability of isolated node, we obtain the minimum transmission range and the maximum size of the service area that are required to maintain the connectivity of the wireless ad hoc networks. Next, we propose a generalized (N,B) model to investigate the impact of B boundary nodes (i.e. nodes with only one neighbor) on the network connec-tivity, the equivalent service area and the average node degree of a wireless ad hoc net-work with N nodes. Due to nodes are randomly deployed, the distances between nodes are also random. By using the 2-dimensional Euclidean space, we derive three distance related probability distributions: the distribution of the distance to the k-th nearest neighbor, the distribution of the distance between two randomly selected nodes and the joint distribution of the distances between nodes and a randomly selected reference node. With these three probability distributions, the optimal transmission range to deploy a power-efficiently connected wireless ad hoc network in the ideal environment, the formu-lation of the node degree in the shadow fading environment and the network connectivity both in the ideal and shadow fading environments are studied. Next, we study the prob-lem to organize the (N,B) connected wireless ad hoc networks into a cluster-based net-work architecture in which the total number of generated cluster is reduced. By examin-ing the clusters generated by the well known ID-based and Degree-based clustering algo-rithms, we find that most of the clusters that have only one member (i.e. orphan cluster) are generated by boundary nodes. This inspires us to reduce the total number of generated clusters by minimizing the number of orphan clusters that are generated by boundary nodes. By making the only neighbor of a boundary node (i.e. critical node) with the high-est priority to be a clusterhead, the numbers of orphan clusters that are generated by boundary nodes are minimized by the proposed Boundary-First Cluster-Minimized (BFCM) based clustering algorithm. Thus, the total number of generated clusters is also reduced. To further reduce the number of generated cluster, we modify the Quine-McCluskey (QM) algorithm that is originally used in the minimization of a Boolean func-tion with multiple variables in the logic design. Instead of using the physical node degree to be the weighting value, the proposed Modified QM (MQM) clustering algorithm se-lects nodes with the highest logical node degree among its one-hop neighbors to be clus-terheads. The simulation results show that the MQM clustering algorithm generates the minimum number of clusters if compared to the Degree-based and the BFCM-Degree clustering algorithms. The cost for this improvement is the decrease of the order of gate-way node. The impacts of the shadow fading effects on the network clustering are also studied. Finally, we study the problem to provide QoS-guaranteed multimedia services to the wireless ad hoc networks. We first study the single hop scenario and a QoS-guaranteed wireless access protocol, namly the Priority Polling with Reservation (PPR) protocol, is proposed to provide the jitter and delay constraints for CBR and VBR sources. Then, based on multi-cluster network architectures, relative synchronization among clus-ters and the rendezvous windows at the gateway nodes, we design a layer-integrated QoS-guaranteed multihop scheduling algorithm. We analyze the delays and jitters of the CBR and VBR sources suffered at each hop and the end-to-end delays for each intra-cluster and inter-cluster connection. The obtained delays and jitters are then used to be the connection admission control criterion. We show that the proposed multihop schedul-ing algorithm schedules multimedia connections in a preset non-preempted service prior-ity without violating the requested QoS requirements.