By Jim Geier
July 17, 2003
There are lots of companies today wanting to deploy wireless connectivity over larger areas, such as cities and rural areas, as an alternative to using copper and fiber-based solutions. Wireless is certainly less expensive to install and support in most cases, especially in locations where it’s cost prohibitive to install physical media or right-of-way issues persist.
The problem, however, is that there have not been effective, standards-based solutions for implementing wireless networks within metropolitan-sized areas. Traditionally, companies install proprietary or 802.11 equipment for wireless connectivity over areas outside the confines of a building. Proprietary systems are great for meeting performance and security requirements; however, they tend to be more expensive and a bit risky in terms of long-term support. They also lack interoperability, something that end users demand.
The use of 802.11-based hardware for metropolitan-sized networks decreases costs, but 802.11 has performance limitations when supporting larger numbers of users needing guaranteed bandwidth. In addition, RF interference is often a significant problem with 802.11 when covering large areas due to license free operation. A competitor may install an 802.11 network which interferes with yours, and users will suffer due to sporadic, poor performance. There’s really nothing you can do about that because there are no legal grounds to remedy the situation.
802.16 to the Rescue
The IEEE 802 group initiated the IEEE 802.16 Working Group to create standards for broadband wireless access in order to offer a high speed/capacity, low cost, and a scalable solution to extend fiber optic backbones. The first IEEE 802.16 standard, published in April 2002, defines the WirelessMAN Air Interface for wireless MANs. These systems are meant to provide network access to homes, small businesses, and commercial buildings as an alternative to traditional wired connections.
If you want the long range wireless for your needs in the near term, forget it, 802.16 won’t work for you — there are no products yet.
Several companies, such as Airspan Networks, Alvarion, Intel, Nokia, Proxim and Wi-LAN — all members of WiMax, an industry group backing 802.16 — are in the process of developing 802.16 products, but they won’t be available until mid-2004. That’s almost a year away, so your decision should depend on the urgency of installing the system and whether or not you feel that mid-2004 is a solid date. As we all know, product release dates tend to slip, especially for products using new standards and technologies.
With wireless base station equipment targeted at under $20,000, 802.16 can economically serve up to 60 customers with T-1 speed connections. That’s really attractive to the typical WISP that’s short on cash. In addition, 802.16 can provide a feasible backhaul for connecting wireless LAN hotspots together.
802.16 in Operation
802.16 supports point-to-multipoint architecture in the 10-66 GHz range, transmitting at data rates up to 120Mbps. At those frequencies, transmission requires line-of-sight, and roofs of buildings provide the best mounting locations for base and subscriber stations. The base station connects to a wired backbone and can transmit wirelessly up to 30 miles to a large number of stationary subscriber stations, possibly hundreds.
To accommodate non-line-of-sight access over lower frequencies, IEEE published 802.16a in January 2003, which includes support for mesh architecture. 802.16a operates in the licensed and unlicensed frequencies between 2GHz and 11GHz using orthogonal frequency division multiplexing (OFDM), which is similar to 802.11a and 802.11g.
The 802.16 medium access control (MAC) layer supports many different physical layer specifications, both licensed and unlicensed. Through the 802.16 MAC, every base station dynamically distributes uplink and downlink bandwidth to subscriber stations using time-division multiple access (TDMA). This is a dramatic difference from the 802.11 MAC, with current implementations operating through the use of carrier sensing mechanisms that don’t provide effective bandwidth control over the radio link.
Mobility is Coming
The next step for the 802.16 working group is to add portability and mobility to the standard. In March 2002, the working group began the 802.16e Study Group on Mobile Broadband Wireless Access. This group will address many different mobility issues, including providing connectivity to moving vehicles within a base station’s sector.