Some studies on Wirless Mesh Net Works (WMNS)

Abstract

Wireless Mesh Networks is a new exciting technology that is anticipated to resolve the limitations and to significantly improve the performance of adhoc networks ,wireless local area networks(WLANS),wireless personal area networks(WPANS), and wireless metropolitan area networks(WMANs).Wireless Mesh Network is a decentralized networking technology that is currently being adapted to connect peer-to-peer clients and large-scale backbone networks. It will deliver wireless services for a large variety of applications in personal, local, campus, and metropolitan areas. Wireless Mesh Networks (WMNs) consist of mesh routers and mesh clients, where mesh routers have minimal mobility and form the backbone of WMNs. They provide network access for both mesh and conventional clients. Mesh routers have bridging and gateway functionality that in turn helps in the integration of WMNs with other existing networks such as internet, cellular, IEEE 802.15, IEEE 802.16, sensor networks , etc. However mesh clients can be either stationary or mobile and form a client mesh network among themselves and with mesh routers. In WMNs, nodes are comprised of mesh routers and mesh clients. Each node operates not only as a host but also as a router, forwarding packets on behalf of other nodes that may not be within direct wireless transmission range of their destinations. A WMN is dynamically self-organized and self-configured, with the nodes in the network automatically establishing and maintaining mesh connectivity among themselves (creating, in effect, an ad hoc network). This feature brings many advantages to WMNs such as low up-front cost, easy network maintenance, robustness, and reliable service coverage. Conventional nodes (e.g., desktops, laptops, PDAs, Pocket PCs, phones, etc.) equipped with wireless network interface cards (NICs) can connect directly to wireless mesh routers. Customers without wireless NICs can access WMNs by connecting to wireless mesh routers through, for example, Ethernet. Thus, WMNs will greatly help the users to be always-on-line anywhere anytime. Moreover, the gateway/bridge functionalities in mesh routers enable the integration of WMNs with various existing wireless networks such as cellular, wireless sensor, wireless-fidelity (Wi-Fi), worldwide inter-operability for microwave access (Wi MAX), Wi Media networks. Consequently, through an integrated WMN, the users of existing network can be provided with otherwise impossible services of these networks. WMN is a promising wireless technology for numerous applications, e.g., broadband home networking, community and neighbourhood networks, enterprise networking, building automation, etc. It is gaining significant attention as a possible way for cash strapped Internet service providers (ISPs), carriers, and others to roll out robust and reliable wireless broadband service access in a way that needs minimal up-front investments. With the capability of self-organization and self-configuration, WMNs can be deployed incrementally, one node at a time, as needed. Mesh networks provide a number of applications. For example in difficult environments such as emergency situations, tunnels, oil rigs, battlefield surveillance, high speed mobile video applications on board public transport or real time racing car telemetry. Some current applications are: 1. U.S. military forces are now using wireless mesh networking to connect their computers, mainly ruggedized laptops, in field operations. 2. Electric meters now being deployed on residences transfer their readings from one to another and eventually to the central office for billing without the need for human meter readers or the need to connect the meters with cables. 3. The laptops in the one laptop per child program use wireless mesh networking to enable students to exchange files and get on the Internet even though they lack wired or cell phone or other physical connections in their area. 4. Broadband home networking. 5. Community and neighbourhood networking. 6. Enterprise networking. 7. Metropolitan area networks. 8. Transportation systems 9. Building automation 10. Health and medical systems. 11. Security surveillance systems 12. P2P Communications However, to make a WMN be all it can be, considerable research efforts are still needed. For example, the available MAC and routing protocols applied to WMNs do not have enough scalability; the throughput drops significantly as the number of nodes or hops in a WMN increases. Similar problems exist in other networking protocols. Also a number of research challenges remain in all protocol layers. Consequently, all existing protocols from the application layer to transport, network MAC, and physical layers need to be enhanced or re-invented. Researchers have started to revisit the protocol design of existing wireless networks, especially of IEEE 802.11 networks, ad hoc networks, and wireless sensor networks, from the perspective of WMNs. Industrial standards groups are also actively working on new specifications for mesh networking. For example, IEEE 802.11, IEEE 802.15, and IEEE 802.16 all have established sub-working groups to focus on new standards for WMNs. New modulation schemes need to be developed in order to achieve higher transmission rate. For e.g., new wideband transmission schemes other than OFDM and UWB are needed. Advanced antenna processing including directional, smart and multiple antenna technologies is further investigated, since their complexity and cost are still too high for wide commercialization. Several other efforts are needed in fields like flexible spectrum management, cross layer design etc