QoS multicast routing and causal ordered group communications in cognitive radio networks

Abstract

With the development of wireless communications, wireless networks become more and more popular in our lives. However, there exist some problems in the usage of spectrum. On one hand, there has not much unlicensed spectrum left. On the other hand, the utilization of the licensed spectrum is very low. Such problems seriously block the further development of wireless communications. Fortunately, cognitive radio technology can reduce the unbalance of the spectrum usage. That is because cognitive radio is able to capture or sense the idle spectrum information from its radio environment and accesses such idle spectrum without interfering with the licensed user. Cognitive radio networks have received a lot of attentions in recent years because they can exploit the existing wireless spectrum opportunistically and improve the spectral efficiency. In such networks, the secondary users equipped with cognitive radio can sense and access the "spectrum hole" unoccupied by the primary user. Since nodes have different surrounding environment in cognitive radio networks, the secondary users have different available spectrum bands or channels. This heterogeneous characteristic introduces additional complexities to communications in cognitive radio networks. Based on the heterogeneous characteristic, we address the issue of QoS multicast routing and the issue of supporting causal ordered group communication in cognitive radio networks. The major work and contributions can be summarized as follows. (1) Discuss the issues of QoS multicast routing and transmission scheduling in cognitive radio ad hoc networks. The problem of our concern is: given a cognitive radio network and a QoS multicast request, how to set up a multicast connection so that the total bandwidth consumption of the multicast is minimized while the QoS requirements are met. The QoS requirements contain the delay and bandwidth in this thesis. In order to solve the problem, we propose a four-way handshake and distributed protocol which consists of tree construction and transmission scheduling. To minimize the bandwidth consumption, we introduce an auxiliary graph to represent timeslot assignment in the network. The transmission scheduling problem is then transformed into the minimal set cover problem and a heuristic method is proposed to it. Extensive simulations are conducted to show that our proposed method performs well in reducing the total bandwidth consumption of the multicast tree. Additionally, our method has high success rate. (2) Further discuss the issues of QoS multicast routing in cognitive radio ad hoc networks and propose two methods to solve it. One is a two-phase method. In this method, we first employ a minimal spanning tree based algorithm to construct a multicast tree, and then use a transmission scheduling algorithm to reserve timeslots for each non leaf nodes such that the bandwidth consumption of the tree is minimized. The other is an integrated method that considers the multicast routing together with slot reservation. It starts with the destinations which are considered as the subtrees, and merges the subtrees to a single tree towards the direction of the source. Extensive simulations are conducted to show that the two methods perform much better than the shortest path tree based two-phase method in reducing the total bandwidth consumption of the multicast tree. Besides, the two methods have higher success rate. (3) Discuss the causal ordering group communication in cognitive radio ad hoc networks. Different from the previous work, we discuss the causal ordering at the network layer. The problem of our concern is: given a group communication request in a cognitive radio ad hoc network, how to set up the connection so that the causal ordering of the group communication can be preserved, and the bandwidth consumption of the communication is minimized. We propose a non-core group routing method to solve it. In the method, we first construct a multicast tree for the communication, and then assign slots for all tree links. It is proved that the method can preserve the causal ordering of messages without extra communication overhead nor the latency for delivering messages. Simulations are conducted to show that compared with the core based tree based method, our method requires less bandwidth consumption of the group communication, and has higher success rate.

Date of Award	3 Oct 2011
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Xiaohua JIA (Supervisor)