Department of Computer Science and Engineering
Indian Institute of Technology, Guwahati
Assam India 781039
Tel: +91 9678980059 | Mail: email@example.com
We are currently exploring the concept of cognitive mesh networks for new research directions. A brief introduction:
"As radio spectrum usage paradigm moving from the traditional command-and-control allocation scheme to the open spectrum allocation & access scheme, wireless networks meet new opportunities and challenges. Accordingly, we introduce the concept of cognitive wireless mesh networking (CogMesh) and address the unique problems in such a dynamically networking environment. Basically, CogMesh is a self-organized distributed network architecture combining cognitive wireless access technologies (e.g. Cognitive Radio) with the mesh (ad-hoc) structure in order to provide an integrated & converged service platform over a wide range of heterogeneous networks. CogMesh is based on opportunistic spectrum access (OSA) and featured by self-organization, self-configuration, self-protecting and self-healing. Within the CogMesh framework, in order to achieve the OSA goal, we develope the "Cloud" based common control channel (CCC) selection scheme and the "Cluster" based networking formation techniques, which can be further extended to consensus based multiple rendezvous approach for "Cloud" and "Cluster" evolution in a dynamic manner."
The problem of hidden and exposed terminals are normally overlooked in case of basic wireless communications, due to the overhead associated with RTS/CTS based access mechanism. However, the problem of hidden and exposed terminals become severe for high speed wireless mesh network. Current development of IEEE 802.11n MIMO technology can support data rates upto approximately 600 Mbps. This works explores the problems of hidden and exposed terminals associated with high speed wireless mesh access, build over IEEE 802.11n MIMO and dual band communication technology, and tries to find out efficient solutions to mitigate the problem.Capacity Improvement, QoS, Multi-rate Adaptation and Opportunistic Forwarding in IEEE 802.11s Mesh Network
Current deployment of wireless community mesh networks and wireless municipal services using mesh connectivity utilizes single channel backbone mesh network to provide Internet connectivity to end users. IEEE 802.11s Wireless Mesh Network (WMN) is a promising technology to increase spatial reuse in a single channel mesh backbone using high gain directional antennas. However, for effective use of multi-interface multi-beam directional antennas in single channel environment, proper scheduling of interfaces and prioritization among different beams are required to minimize channel interference. Furthermore, the packet forwarding mechanism should co-operate with scheduling mechanism to improve network performance. This report provides current state of art for MAC layer channel access in single channel wireless mesh networks. It further discusses the motivation of using single channel directional antenna based communication in wireless mesh backbone for community and municipal wireless usage. The requirement of an efficient scheduling mechanism on the top of IEEE 802.11s standard is discussed with examples. Finally, the report provides the detail design and analysis for first contribution of the current research work - an efficient channel access and forwarding mechanism in IEEE 802.11s single channel directional wireless mesh network with single class traffic.
Quality of Service (QoS) is another important issue for community networks, both from the perspective of the service provider and the end-users. Different types of network traffic requires different amount of network resources for sustaining. For example, the voice traffic requires strict delay and bandwidth guarantee, whereas the video traffic requires minimum jitter (variation in end-to-end delay) support. Therefore, to support QoS assurance, the reservation of the network resources are required to be allocated dynamically based on the specific service requirements. Two types of service provisioning architectures have been incorporated in the Internet design - the integrated service architecture, and the differentiated service architecture. The integrated service architecture provides strict QoS requirements, however requires a centralized controller for the service provisioning. On the contrary, the differentiated service architecture provides minimum service guarantee, and can work in a distributed fashion. IEEE 802.11 is more preferable to the differentiated service architecture compared to the integrated service architecture, because of its inherent inability of centralized control. The IEEE 802.11e amendment over the basic standard supports service differentiation using Enhanced Distributed Channel Access (EDCA). Unlike EDCA, the mesh channel access protocol in IEEE 802.11s, called Mesh Coordinated Channel Access (MCCA), does not provide any service differentiation architecture. Designing efficient service differentiation technique over MCCA is challenging because the priority based flow reservation technique follows a non-convex function, which is hard to solve in a distributed environment.Topology control is a crucial aspect for the performance optimization in a multi-hop mesh architecture. IEEE 802.11s uses Mesh Peer Management (MPM) protocol to support the topology control in a mesh environment. Two neighbor mesh routers can not communicate directly until they establish a mesh peering using the MPM protocol. However, the standard MPM protocol supports fixed data rates only. On the other hand, most the physical layer technologies, like IEEE 802.11a/b/g/n support multiple physical data rates based on the modulation techniques. Different data rates can sustain at different channel conditions, measured in terms of the Signal to Noise Ratio (SNR). Lower data rates can sustain for lower SNR values, whereas higher data rates require high SNR value for correct decoding of the received signal. The current industry standard wireless access technologies support rate adaptation based on the physical layer channel conditions. On the contrary, IEEE 802.11s MPM uses a fixed data rate for peer establishment, therefore can not avail the advantages of the physical layer rate adaptation. This limits the performance of the IEEE 802.11s mesh technology to a fixed data rate support.
Topology control, channel access and forwarding are interdependent in the multi-hop mesh networks. As discussed, topology control requires the physical data rate information to establish peering among the neighbors. Selection of an optimal physical layer data rate depends on the network interference and the channel quality of the forwarding path. Conversely, channel access requires the topology information and the interference characteristics of the forwarding path. At the same time, forwarding should find out the path that provides maximum bandwidth based on the channel access information, and minimum end-to-end delay depending upon the topological connectivity. This interdependency makes the performance optimization aspects of a mesh network more challenging. Further, the forwarding path establishment in a mesh network faces several challenges. The proactive path selection mechanism finds out the optimum path before the actual routing requirements, and therefore may use the stale information for future decisions. As discussed earlier, traffic characteristics in a mesh network change arbitrarily with the variation of the number of mesh clients, and their individual traffic demands. In addition, wireless channel dynamics, like the signal blocking, fading, and the shadowing may result in a stale path information in case of the proactive selection. Conversely, the reactive path selection introduces extra network overhead by flooding control packets every time, before the data packets are required to be forwarded. IEEE 802.11s uses Hybrid Wireless Mesh Protocol (HWMP) for the forwarding path selection and maintenance, that is based on a combination of both the proactive and the reactive approaches. Therefore the shortcomings of the proactive path selection and the reactive path selection are inherent in HWMP protocol.