An introduction to WiMax

This article will help you understand how WiMax works and examines the role that it might play in environments looking to benefit from wireless mobility.

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Bob Friday

WiMax is a new standard being developed by the IEEE that focuses on solving the problems of point-to-multipoint broadband outdoor wireless networks. It has several possible applications, including last mile connectivity for homes and businesses and backhaul for wireless hot spots.

While WiMax has historically lacked the grassroots popularity of its cousin, Wi-Fi (i.e. 802.11), the standard is gaining significant traction from the high profile support it has received from the likes of Intel and other big name corporations. Supporters of the standard have some very lofty expectations for its potential. Intel, for example, stated that 802.16 is, "as important has the Internet itself" -- a technology that will enable up to 5 billion people to be connected over time.

Only time will tell if WiMax will live up to the expectations of its supporters. For the time being, it is important to understand how WiMax works and to examine the role that it might play in environments looking to benefit from wireless mobility.

The business case for WiMax
There are several business opportunities driving the development of WiMax. Some of these include:

 

  • WiMax provides a viable alternative to T1 as an access mechanism to small businesses. If WiMax lives up to its claims, a $20,000 base station could support up to 60 T1-equivalent connections, lowering the cost of broadband access by an order of magnitude.
  • WiMax can be a viable alternative to DSL and cable for broadband access to the home. Copying the trend of satellite TV, it provides a viable alternative to existing broadband solutions by leveraging wireless technology.
  • WiMax can be a reliable backhaul for Wi-Fi hotspots, especially in remote regions or countries that lack significant wired infrastructures over large areas.
  • Additionally, the WiMax standard is being evolved to work in mobile environments to make it competitive with 3G standards.

One element fueling the interest in developing the WiMax standard is the growing popularity of unlicensed bandwidth. While cellular operators are paying billions of dollars for bandwidth in 5 MHz chunks, unlicensed bands offer hundreds of MHz for free. As the cost of bandwidth is transferred to the end user, a cellular operator is forced to charge hundreds of dollars for thousands of minutes of monthly access. In contrast, WiMax is better suited for delivering unlimited usage of higher amounts of bandwidth, making broadband wireless networking much more economical than if it were delivered over a cellular infrastructure. So, while standards like WiMax and Wi-Fi are the technical enablers of wireless broadband, the unlicensed band is the physical enabler of the wireless broadband revolution.

The nuts and bolts of the standard
The original version of WiMax, known as 802.16, focused on delivering coverage in the 10 to 66 GHz band. A newer version, 802.16a, covers the 2 to 11 GHz spectrum. 802.16 and 802.16a both define a single carrier modulation scheme for line-of-sight links above 10 GHz. In addition, they define two flavors of OFDM for non-line-of-sight links below 11 GHz and Time Division Duplex (TDD) and Frequency Division Duplex ( FDD ) Medium Access Control protocols. The standard does not define specific quality of service (QOS) and scheduling algorithms, leaving room for flexibility among vendor implementations.

It is unclear exactly when the first WiMax products will be available, given all the different options. The best estimate is that WiMax products will be showing up on the market toward the end of 2004 and early 2005. Most likely the first WiMax products will conform to the 802.16a standard, operating in the 3.5 GHz and 10.5 GHz licensed spectrum internationally and 2.5 to 2.7 GHz licensed spectrum in the U.S., and in the 2.4GHz and 5.725-5.825GHz unlicensed spectrum worldwide.

WiMax, Wi-Fi, and the future of wireless
Unlike 802.11, WiMax was designed specifically for deployment in outdoor environments. This manifests itself in several ways. For one, WiMax has provisions at the physical layer for optimizing symbol rate. This makes it robust in the presence of increased delay spread, which is prevalent outdoors. In addition, WiMax does not use contention-based MAC protocol, such as CSMA. As a result, it is able to deliver more reliable QOS and per-client bandwidth assignments, which can become critical across longer distances.

Given the above, coupled with the fact that Wi-Fi is well on its way in terms of end user adoption and reduced cost metrics, it is likely that WiMax and Wi-Fi will coexist with one another. WiMax is poised to become the outdoor wireless network access of choice, with Wi-Fi being the prevalent indoor wireless network. As the adoption of wireless voice and data networks continues both indoors and outdoors, we can look forward to ubiquitous wireless coverage.

Quick technology comparison:

  WiFi
802.11
WiMax
802.16a
Mobile-Fi
802.20
Cellular
Speed 6 - 54 Mbps 70 Mpbs 16 Mbps 2 Mbps
Band Unlicensed Both Licensed Licensed
Coverage 50 - 1500 ft 2 - 30 miles 3 - 6 miles 1 - 3 miles

 


About the author:
Bob Friday is Co-Founder and Chief RF Scientist at Airespace.

This was first published in June 2004

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