WiMAX in a Wi-Fi Mesh Network

Mesh topology is not supported by existing IEEE's wireless LAN standards but it becomes popular as city-wide (municipal) Wi-Fi network deployment gains more supporters day after day. In a mesh network, each node (i.e. base station or access point) connects to several neighboring nodes and on to a mesh gateway (i.e. a base station that aggregates the mesh network traffic and routes it to the Internet). Since each node has many routes to a mesh gateway, mesh network is very reliable. But mesh network is more complex to manage and poses interference challenge especially for operation in a license-exempt band such as in Wi-Fi case.

Picture. Mesh Network with Wi-Fi and/or WiMAX
WiMAX can work on all layers of a municipal mesh network (hotzone/metro zone).

By examining current Wi-Fi mesh network architecture, basically there are three layers. These are mesh access handling user access to a mesh node, mesh transport interconnecting mesh nodes and routing traffic to mesh gateways, and backhaul connecting a mesh gateway to an Internet PoP (Point of Presence) or other content gateways.

Backhauls for mesh Wi-Fi networks are provided using various wired and wireless solutions, i.e. fiber optic, leased line, DSL, and proprietary point-to-point (PTP) or point-to-multipoint (PMP) radio including some pre-WiMAX equipment. A wireless backhaul - specifically WiMAX - enables flexible placement of a mesh gateway node anywhere in the network, therefore it doesn't have to be located in a telco's CO or close to a fiber/DSL termination point. The portable WiMAX equipment (Base Station) also allows fast installation and easy relocation. Moreover, WiMAX was designed for outstanding performance in NLOS environment, typical in metro area with many high rise buildings. WiMAX also can operate either on licensed or unlicensed band, giving more options for operator/ISP/municipality in addressing various interference conditions and users' requirements.

The mesh transport layer provides the interconnection between mesh nodes. There is a project in the IEEE to standardize Wi-Fi as an intra-mesh transport solution, but the work is still in progress. The current established Wi-Fi solution uses proprietary technology developed by each vendor which might cause interoperability issues in the future. WiMAX can naturally replace Wi-Fi in this layer, interconnecting mesh nodes using standard equipment based on the IEEE 802.16-2004 or 802.16e which includes support for optional mesh topology. Besides, WiMAX has built-in QoS support and is optimized for longer distance (WiMAX is a wireless MAN while Wi-Fi is a wireless LAN) .

For mesh access layer, at present users connect using their Wi-Fi-enabled laptops, PDAs, or smart phones. WiMAX integration into such portable/mobile devices is still in its early stage of development. However, in several months/years to come one may expect the emergence of dual-mode Wi-Fi/WiMAX devices and network adapters (NIC, PC card, PCI Express) which can connect automatically to any available network with the best signal.