How to Build a WiMAX Network

Overview

The latest technology buzz is WiMAX wireless networks. We have heard many things about this wonderful new long haul wireless technology that it almost seems as though you are just a phone call away from having yours' designed and installed. Well before you start assuming things like we all do, we thought as engineers and network architects we would share personal experiences and the experiences of collections from around the world, in a manner that is direct, helpful, educational, and certainly reality based. This is a backpocket Primer for anyone now dealing with the implementation of a WiMAX network.

First, there are several misconceptions surrounding WiMAX that need to be cleared up so that the business aspects and engineering basis have a common understanding.

Secondly, the people who make the various decisions within your organizations need to understand that there are differences between a private network and an interoperable network strategy. This minority difference does exist and requires a plan which considers the final transition aspects, if considered now, to easily provide a lower cost upgrade to a true interoperable network, now incorporating diverse vendor equipment.

Finally, while WiMAX has been out internationally for several years, it is very new to the United States, only a few months old, with very little training and education available to those who have the responsibility to build these systems or those who will make the financial and technical decisions to have these systems built for them as part of their long haul wireless strategy.

Our experiences and the experiences of our colleges are offered here as contributions as well as tying these in the standards and certification authorities all meant to provide a reality based quick reference education for anyone in the throws of how to build a WiMAX network.

Primer

WiMAX is a standard designed for fixed broadband wireless access featuring a controllable base station, that connets subscriber stations not to each other but to various public networks, such as the Internet, linked to that base station. The acronym means "worldwide interoperability for microwave access" or (WiMAX).

WiMAX, as a standards initiative, is based on a "set of profiles" supporting a wide range of frequencies (up to 66GHz) with channel sizes (1.25MHz to 20MHz) and applications (LOS and NLOS), and finally PTP and PTMP. The WiMAX profiles narrow the scope of 802.16 to focus on first service specific configurations. The IEEE titled the specification 802.16 and released it December 2002. The profiles addressed in that "profiles release" are 802.16-2004 (old d) and 802.16e as presented further down.

The WIMAX forum was formed eight months earlier in April 2002 to support, promote and certify compatibility and interoperability of devices based on the 802.16 specification, and to develop such devices for the marketplace. Founding Members of the organization include Airspan, Alvarion, Analog Devices, Aperto Networks, Ensemble Communications, Fujitsu, Intel, Nokia, OFDM Forum, Proxim, and Wi-LAN.

WiMAX is the IEEE 802.16 Point-to-Multipoint broadband wireless access standard for systems in the stated frequency ranges. WiMAX will initially provide fixed fixed, portable and ever, mobile wireless broadband connectivity. To that end there are two standards (802.16d (new -2004) and 802.16e respectively) although they will both perform similar functions because they must be interoperable. One clearly is a fixed solution and the other a mobile solution that must still communicate with a fixed solution. So one of the first considerations is wherever you want to build out a mobile or fixed network. In many cases you would have already considered your target market segments, spectrum availability, regulatory constraints and your deployment need.

Which One do I Need?

Generally speaking, the current 802.16-2004 (originally 802.16d) fixed network products are less complex than 802.16e mobile network systems because; they can be used in a wider range of unlicensed bands, they offer a faster time-to-market, and in many cases a higher throughput than 802.16e equipment. On the other hand, there is better support for mobility and a wider range of terminal form factors advantages of 802.16e equipment.

It's certainly a consideration but no matter what you chose the migration paths to move in either direction are easily achieved through overlay networks, software upgradeable base stations, dual mode devices and dual mode base stations. This consideration assures you are not stuck in one mode or the wrong mode and that your initial investment is protected. Makes the CTO and CEO happy.

WiMAX base stations transmit up to 30 miles, but because it is a cell-based topology, would yield a more typical range of 3 to 5 miles. WiMAX systems can deliver a capacity of up to 75 Mbps per channel, for fixed and portable access applications. This is sufficient bandwidth to simultaneously support hundreds of businesses with T-1 speed connectivity and thousands of residences with DSL speed connectivity as we have seen.

WiMAX technology will be incorporated in portable computers and PDAs expected in late 2006 and early 2007, allowing for urban areas and cities to become "MetroZones", the new buzz word, for portable outdoor broadband wireless access. In addition, Wireless service providers and telecommunication equipment industries are embracing WiMAX technology because of its tremendous cost advantages to provide that last-mile connectivity to large parts of the world that are too expensive to serve with wired technologies requiring all that trenching.

Security

Due to the security issues with WEP in the 802.11 Wi-Fi arenas, the standards bodies took no chances with WiMAX, and wisely prioritized security from the sunset. Base station designers went to work to secure a dedicated high performance security processor. The WiMAX security standard requires that all traffic be encrypted with CCMP (which is Counter Mode with Cipher Block Chaining Message Authentication Code Protocol).

According to the WiMAX forum, the group's aim is for end-to-end authentication. WiMAX uses PKM-EAP (Extensible Authentication Protocol), which relates to the TLS standard following public key cryptography. Having addressed this level of security from the start provides an excellent reference point to add multi-level security options as well, if your implementation requires an MLS approach. Secure (blacker) implementations would require such an approach.

What is Released?

The first certification release for 802.16-2004 fixed is out there already and includes products from certified vendors with two profiles in the 3.5GHz and the 5.8GHz bands supporting fixed and nomadic access. The profiles for 802.16e mobile are not available nor released as of this writing but are expected to be in the ranges of 2.3GHz to 2.5GHz when officially released. WiMAX profiles based on 802.16-2004 are better suited to fixed applications that use directional antennas because OFDM is inherently less complex than SOFDMA used in the mobile application. As a results, 802.16-2004 networks will be deployed much faster and at a lower cost. Our experiences are with these released systems in the US and around the world in ground applications, mobile military, public safety and maritime applications.

Planning for WIMAX

Companies, cities or projects in maritime or ground systems in the US that have decided to or are considering building and operating a WiMAX network will have a few important issues to consider. The initial spectrum for WiMAX in the USA is unlicensed spectrum in the 5GHz range. Given this spectrum is open it will have inherent interference issues and decisions which will require attention. There are many ways of overlapping issues. The answers come from a proper site selection, following your RF survey training and from the actual selected equipment. So, the planning and site survey results remain the key to your confident success.

Summary

WiMAX provides optimized solutions for fixed, nomadic, portable and mobile broadband wireless access. There are two flavors in various release and implementation modes. The first is 802.16-2004 WiMAX with two initial frequency profiles – the 3.5GHz and the 5.8GHz bands supporting fixed and nomadic access in LOS and NLOS environments now. The other flavor is 802.16e WiMAX with expected profiles in the 2.3GHz and 2.5GHz ranges optimized for dynamic mobile radio channels supporting hands-ff and roaming –arriving by 2007. Another exciting technology for all of us. Have fun!
an extended version of this Primer is presented in our OnLine-CTO e-magazine.
Contact Gina Smith at onlinecto@networkanatomy.com

Source by Douglas Linman

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