According to the WiMax Forum:
“WiMAX is a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to wired broadband like cable and DSL. WiMAX provides fixed, nomadic, portable and, soon, mobile wireless broadband connectivity without the need for direct line-of-sight with a base station. In a typical cell radius deployment of three to ten kilometers, WiMAX Forum Certified systems can be ex- pected to deliver capacity of up to 40 Mbps per channel, for fixed and portable ac- cess applications.
“This is enough bandwidth to simultaneously support hundreds of businesses with T- 1 speed connectivity and thousands of residences with DSL speed connectivity. Mo- bile network deployments are expected to provide up to 15 Mbps of capacity within a typical cell radius deployment of up to three kilometers. It is expected that WiMAX technology will be incorporated in notebook computers and PDAs by 2007, allowing for urban areas and cities to become ‘metro zones’ for portable outdoor broadband wireless access.”
You must understand a few aspects of WiMax; the first is the concept of being fixed line of sight (LOS) or non-LOS (mobile). In non-LOS, mobile doesn’t mean mobile in the sense that most of us think. WiMax mobility is more like the ability to travel and then set up shop temporarily. When you are done, you pack up and move on. A few service providers use this technology to provide end-user access as an alternative to DSL or cable modem. Your signal range in this Non-LOS scenario is about 3 to 4 miles, and data rates are adver- tised at around 30 Mbps, but you can expect less—closer to 15 Mbps.
Other service providers are targeting business customers in a fixed LOS WiMax deploy- ment in which the topology most closely resembles that of a traditional T1, being a point- to-point type of topology and providing backhaul or backbone services. This fixed LOS advertises 30 to 70 Mbps throughput, but you can expect around 40 Mbps.
As the IEEE standardizes WiMax technology, it has progressed from the original 802.16 to 802.16a, c, d, and finally 802.16e.
As mentioned, the WiMax defines last-mile access. Figure 8-6 shows a sample topology in which subscribers have a point-to-point connection back to a service provider and from there have access to the public Internet.
WiMax operates on the 10- to 66-GHz frequency band, so it doesn’t interfere with 802.11 LANs. So why is it discussed in this section? The school of thought here is that, with some planning, a device acting as a gateway can be deployed offering 802.11 LAN access with 802.16 last-mile access or upstream access to a service provider, thus removing the need for wires. The question of how feasible this is lies in the hands of the vendors devel- oping the products and the standards committees ensuring interoperability. Some vendors, however, have tested this technology in lab environments with much success.
Other Types of Interference
Other types of interference can occur in the same frequency ranges. These devices might not be the most obvious, but they should be considered. They can include the following:
- Microwaves (operate at 1 to 40 GHz)
- Wireless X11 cameras (operate at 2.4 GHz)
- Radar systems (operate at 2 to 4 GHz for moderate-range surveillance, terminal traffic control, and long-range weather and at 4 to 8 GHz for long-range tracking and air- borne weather systems)
- Motion sensors (operate at 2.4 GHz)
- Fluorescent lighting (operates at 20000 Hz or higher)
- Game controllers and adapters (usually operate at 2.5 GHz)
When dealing with wireless deployments, you can use tools to determine signal strength and coverage, but just knowing about these additional sources of interference will save you some time in determining where to place APs and clients.
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