802.16: The Future in Last Mile Wireless Connectivity

Monday Aug 18th 2003 by Beth Cohen

802.16 promises to deliver true broadband speed wirelessly, but when will products be available and how important a role should the so-called WiMAX standard play in your future network plans? Join Beth Cohen and Debbie Deutsch as they take an in-depth look at the wonderful world of WiMAX.

Imagine having DSL- or T1-speed communications access for all your office locations, not just in office parks or urban centers. Would you like to provide metropolitan area broadband-speed links for all your staff, without leasing expensive circuits or installing costly fiber? As a home user, would you like to have a wireless broadband alternative to DSL and cable modems? The new IEEE 802.16 standard promises to deliver all of this and more.

802.16, the latest entry in the wireless networking technology pantheon, is an up and coming serious contender as a wireless alternative to DSL, cable modem, leased lines, and other broadband network access technologies. Intel has already pledged to develop a silicon product based on the 802.16 standard, and it claims equipment based on its chips will have a range of up to 30 miles and the ability to transfer data, voice, and video at speeds of up to 70 Mbps.

And while 802.16 products will not be widely available for at least another year or so, the standard itself should play an important role in your future network plans. 802.16 has the potential to slash your long-haul network/internet access costs and allow you to deploy a broadband mesh connecting all your sites in a region, which could reduce the requirement for leasing circuits or fiber, enable data center consolidation, and generate additional cost savings. With that in mind, it's important to get up to speed with the development of the various 802.16 standards.

Broadband Wireless Access

The telecommunications companies have made huge capital investments over many years to support POTS (plain old telephone service). In a regulated environment, Ma Bell was assured of a reasonable return on its investment. These days, building the “last mile” of fiber connectivity to an office park or city neighborhood can be highly speculative with an enormous up-front investment required before a carrier can expect to collect any revenue.

In contrast, broadband wireless has the potential to vastly reduce the initial investment and risk. Because customer premises equipment is a significant portion of the cost of wireless deployment, deferring that investment until the carrier signs up the customers can be a great advantage. Like a cell phone network, the carrier would pre-install base station transceivers on towers, poles, church steeples, or other high, fixed platforms. Unlike a cellular network, the customer’s transceiver normally is stationary, typically located on a roof — not unlike a satellite dish installation.

Because conventional “last mile” connectivity remains so expensive, the idea to use wireless technology instead is hardly new. The FCC auctioned bandwidth for something called Local Multipoint Distribution Service (LMDS) back in 1998 and 1999. The key selling points behind LMDS, 802.16, and related technologies are that they have the potential to be deployed far faster, less expensively, and more flexibly than similar wireline installations.

However, despite the benefits of broadband wireless access, you might have noticed that it is not yet readily available. This can be explained in part by the implosion of the data networking industry during the economic downturn, but another factor preventing widespread deployment is that until recently there has been no single, well-accepted standard for broadband wireless access. The growing success and popularity of 802.11 has turned the spotlight on 802.16 at just the time when it has passed a number of significant standards milestones.

Page 2: IEEE 802.16 Progress

IEEE 802.16 Progress

Work on 802.16 started in July 1999. Four years into its mission, the IEEE 802.16 Working Group on Broadband Wireless Access has delivered a base and three follow-on standards.

  • IEEE 802.16 (“Air Interface for Fixed Broadband Wireless Access Systems”) was approved in December 2001. This standard is for wireless MANs operating at frequencies between 10 and 66 GHz.

  • IEEE 802.16.2, published in 2001, specifies a “recommended practice” to address the operation of multiple, different broadband systems in the 10-66 GHz frequency range.

  • In January of this year, the IEEE approved an amendment to 802.16, called 802.16a, which adds to the original standard operation in licensed and unlicensed frequency bands from 2-11 GHz.

  • 802.16c, which was approved in December 2002, is aimed at improving interoperability by specifying system profiles in the 10-66 GHz range.

The IEEE is not resting after all this work. Authorization for the development of a new amendment known as 802.16e, which would extend the standard to cover “combined fixed and mobile operation in licensed bands” (2-6 GHz), was approved in December 2002.

Other Wireless Broadband Standards

802.16 is not the only wireless broadband standard in the pipeline, and the IEEE is not the only industry group working on new standards for broadband wireless data services. Parallel to 802.16, the IEEE has also created a new working group, 802.20, which is charged with “the physical and medium access control layers of an air interface for interoperable mobile broadband wireless access systems that operate in licensed bands below 3.5 GHz.” 802.20's technical goal is to “optimize IP-based data transport, target peak data rates per user at over 1 Mbit/sec, and support vehicular mobility up to 250 km/hour.”

Meanwhile, the ETSI (the European Telecommunications Standards Institute) project BRAN (Broadband Radio Access Networks) has been creating two standards that are roughly parallel to IEEE 802.16 and 802.16a. HIPERACCESS covers frequencies above 11 GHz. While work on HIPERACCESS began before 802.16, it was approved after 802.16. HIPERMAN is for frequencies below 11 GHz. The two standards bodies cooperate to a certain extent.

Think of the vast opportunities that these new wireless technologies would open for carriers. Service providers could offer broadband wireless data connectivity as ubiquitous as cell phone connectivity, without the need to co-market hotspots. They could even extend it to moving targets like cars, RVs, and trains.

Which technology will providers adopt for the future? Could 802.16 and PDAs eventually replace cellular technology and handsets for wireless telephone service? The answers will depend on many factors, including which standard is translated into readily available products first as well as continuing advances in battery technology.

Page 3: The Importance of Frequency Bands

The Importance of Frequency Bands

Compared with LMDS, 802.16 is a next-generation technology that operates over greater distances, provides more bandwidth, takes advantage of a broader range of frequencies, and supports a greater variety of deployment architectures, including non-line-of-sight operation — a very significant advantage. 802.16 is nominally specified to operate over a 50 km radius and support channels ranging up to the tens of megabits.

No single 802.16-compliant product will operate over the entire 2-66 GHz frequency range. In fact, that frequency range represents most of the radio communications spectrum. So, why has the IEEE defined 802.16 so broadly? The reasons are a combination of physics, regulatory issues, and user requirements.

Radio signal propagation depends on its frequency. The lower frequencies in the 802.16a standard do not require line-of-sight to work. Easing the requirement for line-of-sight between transmitter and receiver widens the range of feasible product offerings. For example, the roof of your home may be too low for line-of-sight service to work, but a non-line-of-sight implementation would enable carriers to deliver wireless broadband directly to consumers.

Vendors of wireless products are very sensitive to regulations. In the US, the FCC is responsible for the allocation of all radio frequency bands. Other countries have their own equivalent regulatory authorities. In addition to defining how the frequency spectrum is divided into bands and prescribing their usage, the FCC also specifies if a license is required to transmit on a particular band. It may also limit the power of a transmission.

The regulations are designed to minimize interference and maximize the overall utilization and usefulness of the spectrum. The ability to purchase a license for a particular piece of spectrum assures a carrier that there will be no signal interference from other carriers.

Wireless networks deployed by carriers operate at a frequency and power level that allows the signal to cover a wide region. Wireless devices intended to operate inside an enterprise would use an unlicensed frequency band and power level designated for short-distance communications. While the lack of a license requirement allows the enterprise to avoid delays and costly paperwork, there is a chance of interference from other kinds of devices that emit (intentionally or not) at the same frequency. Microwave ovens which emit over a broad spectrum are well known offenders, while 2.4 GHz wireless telephone handsets may also cause problems.

Because of the decision to define 802.16 to operate across such a broad frequency range and in many different countries, the standard supports a variety of physical layers. For example, for 10-66 GHz line-of-sight operation, the base station uses Time Division Multiplexing (TDM). This technique allocates timeslots on a single frequency to address each customer’s receiver separately as a way to share the bandwidth. Upstream customers transmit back to the base station using Time Division Multiple Access. The standard defines two choices: either the base station and customer transceiver use the same frequency, or they operate at different frequencies. Operating the equipment at different frequencies enables synchronous transmission in both directions.

Compared with line-sight-operation, 802.16 non-line-of-sight operations must be able to cope with harder technical problems at the physical layer, such as multipath propagation of radio signals as they bounce off buildings and other large objects, which can cause problems similar to the effect of acoustical echoes.

Unlike fiber or copper cable technologies, 802.16 deployments must deal with changeable environmental factors. Rain can interfere with reception. The 802.16 specification includes radio link control to establish initial parameters when links come up as well as to alter them as conditions change. Just as cell phones adjust their power consumption in relation to their proximity to a base station, 802.16 equipment will continue to monitor link quality after initialization and will adjust transmission parameters accordingly.

Page 4: Are We There Yet?

Are We There Yet?

The WiMAX (Wireless Interoperability Microwave Access) industry consortium’s charter is to promote the “deployment of broadband wireless access networks by using a global standard and certifying interoperability of products and technologies.” With industry leaders such as Intel and Nokia among its members, it stands foursquare behind 802.16. To promote interoperability, WiMAX is developing system profiles of supported features and testing procedures for standards conformance and interoperability.

However, with the availability of products still a year or more away, and standards work on enhancements ongoing, it is hard to predict at this point exactly how successful 802.16 will be, what products will be coming on the market, and when significant deployment will begin. One possibility is that it will become a technology of choice in the carrier market; however, it is hard to judge what 802.16's role in the enterprise will be. Will its use be limited to broadband access, or will it be used for more?

As it is, wireless is one of the more active areas in network technology investment and product development. If the timing is right, when the economy picks up, 802.16 could be in the sweet spot for an infusion of investment and innovation. In our next article, we will discuss in greater detail how the 802.16 technology actually works and compare its potential for success with the already popular 802.11 standard.

Technical References

A Technical Overview of 802.16: 802.16 Tutorial
802.16 Technical Specifications: IEEE 802.16's Published Standards and Drafts
IEEE 802.16 Working Group: "802.16"
WiMAX Industry Association: WiMAX Forum

Beth Cohen is president of Luth Computer Specialists, Inc., a consulting practice specializing in IT infrastructure for smaller companies. She has been in the trenches supporting company IT infrastructure for over 20 years in a number of different fields, including architecture, construction, engineering, software, telecommunications, and research. She is currently consulting, teaching college IT courses, and writing a book about IT for the small enterprise.

Debbie Deutsch is a principal of Beech Tree Associates, a data networking and information assurance consultancy. She is a data networking industry veteran with 25 years experience as a technologist, product manager, and consultant, including contributing to the development of the X.500 series of standards and managing certificate-signing and certificate management system products. Her expertise spans wired and wireless technologies for Enterprise, Carrier, and DoD markets.

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