The 802.16a Standard WiMAX

WiMAX – Not just another standard

Broadband wireless access provides more capacity at lower cost than DSL or cable for extending the fibre networks and supporting multimedia and fast internet applications in the enterprise or home. But it has been held back by the lack of a standard, so that solutions have been based on proprietary, single-vendor efforts. Standardization through the IEEE 802.16 specification raises the potential to:

  • Stall wired broadband and make wireless the key platform of the future
  • Extend the range of Wi-Fi so that the myth of ubiquitous wireless can become a reality
  • Provide an alternative or complement to 3G
  • Provide an economically viable communications infrastructure for developing countries and mobile blackspot regions in developed nations

Markets for WiMAX

The greatest media excitement about WiMAX has centred on its potential mobility and its role as a backhaul or even replacement for public Wi-Fi. However, its initial raison d’etre and still its primary focus is on broadband fixed wireless access for homes and businesses. This sector is populated by a horde of mainly American niche players with expensive equipment using various versions of smart antennas, OFDM and sometimes mesh to provide often effective alternatives to wired communications. ArrayComm, Alvarion, IPWireless, Navini and Beamreach are high profile names, though the majority of these specialists will refocus their products around WiMAX in the coming year

Business users Only 5 percent of commercial structures worldwide are served by fibre networks, the main method for the largest enterprises to access broadband, multimedia data services. In the wired world, these networks are extended to the business or residence via cable or DSL, both expensive options because of the infrastructure changes required. DSL typically operates at 128Kbps to 1.5Mbps and slower on the upstream.

Enterprises can use WiMAX instead of T1 for about 10 percent of the cost, while SMEs can be offered fractional T1 services. Base stations will cost under $20,000 and support 60 enterprise customers with T1-class connections. Last mile to the home A low cost alternative could end the wars between the cable and ADSL operators and really make the broadband home revolution happen.

Hotspots

Wi-Fi hotspot operators may be able to build a spot for a few thousand dollars’ worth of equipment, but then they need to anchor it to the public network, and this is normally done with expensive T1 or DSL. WiMAX backhaul could significantly reduce hotspot costs, although there is also the potential for Wi-Fi to be bypassed altogether by WiMAX ‘hotzones’.

Remote regions

The most lucrative market for the proprietary BWA vendors has been remote regions, especially in developing countries but also in rural areas of the US, where there is no wired or cellular infrastructure nor the will or cash to invest in building it. The main alternative to BWA in this market is satellite. Still early in its lifecycle – and potentially a powerful technology to integrate with WiMAX – satellite has severe limitations of upstream bandwidth, spectrum availability and also suffers from high latency.

China

One of the most potentially lucrative markets for remote region BWA is, of course, China, and discussions have been held between the Chinese government and IEEE with a view to making 802.16 the Chinese national standard for fixed broadband wireless access at 3.5GHz. Chinese operators are already rolling out WiMAX base stations even before standard, low cost silicon is ready, and Alvarion recently supplied this type of equipment to China Unicom for a network covering, initially, six cities.

Background and 802.16

Although the 802.16 project started as far back as 1998, the body of work was done in 2000 - 2003 in an open consensus process. The aim was to make broadband wireless access more widely and cheaply available through a standard for wireless metropolitan area networks.

The overall vision for 802.16 is that carriers would set up base stations connected to a public network. Each base station would support hundreds of fixed subscriber stations, probably mounted on rooftops. The base stations would then use the standard's medium access control layer (MAC) - a common interface that makes the networks interoperable - to nearly instantaneously allocate uplink and downlink bandwidth to subscribers according to their needs.

802.16 MANs could also anchor 802.11 hotspots, which serve as wireless local area networks (LANs), as well as servicing end users directly. With the mobile standard, users will be able to use the WMAN base station to communicate via handsets as they move within the 50 mile range.

The first version of the standard, 802.16, was published in April 2002 and addressed fixed, line of sight connections for the ‘first mile/last mile’ link. It focused on efficient use of various licensed frequencies in the 10-66GHz bandwidth. 802.16 standards have never taken a lowest common denominator approach. Unlike Wi-Fi, few proprietary vendors of equivalent equipment can outdo the performance of WiMAX. It offers the highest performance broadband , technology except for broadcast and, on the wired side, MMDS, and is on a level with satellite. Although, even with the upcoming mobile version of standard, WiMAX cannot be as wide area as 2G/3G, it delivers far higher rates and, with sufficiently widespread deployment, could significantly cut into the usage of cellular networks in many areas.

The next version of the standard, 802.16a, published in April 2003, is the one that has really kick-started WiMAX into being adopted as the dominant wireless broadband technology. This is also for fixed wireless but extends the range of WiMAX from 31 to 50 miles and operates in the low frequency 2-11GHz spectrum and so can be adopted by unlicensed operators. It uses point-to-multipoint or (optionally) mesh topologies and does not require line of sight. Specifically, it uses licensed bands at 3.5GHz and 10.5GHz internationally and 2.5-2.7GHz in the US; and unlicensed 2.4GHz and 5.725-5.825GHz.

An important aspect of 802.16x is that it defines a MAC (media access control) layer that supports multiple physical layer (PHY) specifications. This is critical to allow equipment makers to differentiate their offerings – for instance with novel approaches to smart antenna use – without becoming non-interoperable; and to customize the equipment for the frequency band in use.