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Beyond WiMAX certification: What to look for in an advanced network

Posted: 28 Dec 2007 ?? ?Print Version ?Bookmark and Share

Keywords:WiMAX Forum? WiMAX certification? VoIP? time domain duplexing?

By Elvis Tucker
Aperto Systems

Not all WiMAX-compliant systems will be created equally.

The WiMAX Forum defines the profiles that any WiMAX-compliant broadband wireless access systems must support in order to achieve inter-operability. But while inter-operability is an important goal for any WIMAX-compliant system, it will not ensure optimization.

While the new WiMAX Forum-certified products are expected to have higher levels of performance over the pre-WiMAX single carrier systems, it is equally clear that some WiMAX systems will perform better than others!especially in critical areas.

What are the key performance differentiators that will set apart the WiMAX Fiat from the WiMAX Ferrari?

Many believe that quality of service, scalability, manageability and maintenance top the list. As operators gear up to address the mass market WiMAX opportunity, some features can emerge as critical to their success and should be kept in mind when one is out "kicking the tires" of a prospective WiMAX system.

Here are several features worthy of consideration when comparing WiMAX systems.

Quality of Service
The WIMAX standard specifies that a compliant system should support QoS. However, specific algorithms for achieving QoS suitable for multimedia service differentiation and enterprise level service agreements are not specified by the standard.

Considering the growing popularity of VoIP in developed markets and exploding demand for voice services in emerging markets, many believe that voice services may emerge as the "killer app" for WiMAX.

Advanced WiMAX systems will allow operators to tune the system for the unique characteristics of voice (low latency and jitter)!delivering toll quality while simultaneously satisfying the bandwidth hungry data and streaming media applications. WiMAX systems implemented with leading edge QoS features will offer a distinctive advantage to operators intending to offer voice, data and multi-media services.

Link optimization
Similar to QoS, WIMAX does not specify the algorithms that make the most effective use of the wireless link. In WiMAX parlance, this is commonly referred to as dynamic link adaptation!adjusting the modulation parameters "on the fly" for subscriber link optimization.

System vendors with proven experience in developing link adaptation algorithms can leverage this experience into their WiMAX compliant systems. WiMAX network operators should look for systems that automatically tune the link on a per subscriber basis during dynamic RF conditions.

Duplexing mode
For many small and large operators, radio spectrum is a precious and scarce resource. Therefore, it is critically important to use it efficiently and cost effectively.

WiMAX systems based on Time Domain Duplexing (TDD) frame structure are becoming highly preferred (versus FDD based systems) because of their ability to more specifically tuned for the application and spectrum efficiency.

For example, most data traffic tends to be asymmetrical in nature, with the aggregate downlink traffic always exceeding the aggregate upstream traffic!TDD systems can assign more bandwidth in the downlink direction. Advanced TDD systems will dynamically adjust and synchronize the bandwidth allocation for hundreds of subscribers according to application traffic requirements.

For an operator to maximize the revenue opportunity of WiMAX, it is important to deploy systems that scale effectively. This means not only supporting a large number of subscribers at the base station but also classifying and delivering their traffic to the network according to their revenue potential.

For example, two subscribers both using a voice service do not necessarily represent the same impact on the operator's bottom line!one subscriber may have a consumer/SoHo service plan, while perhaps the other has a higher cost business level plan.

WiMAX systems supporting these requirements should support hundreds of subscribers per wireless sector and thousands of service flows differentiating subscribers and services being used. This level of support is non-trivial. Advanced WiMAX systems will use MAC level enhancements!beyond those as prescribed by the WiMAX standard!to reduce contention, reduce latency and improve capacity in the sector.

Another key differentiator will be found in the WiMAX solutions that incorporate enhanced security features. WIMAX-compliance prescribes security to be an optional feature, and even when security is supported, it requires only DES-based encryption.

The WiMAX systems that support both DES and AES will have a distinctive advantage. Enabling the use of a combination of encryption suites in a sector will make it possible to use different encryption keys for different service flows to the same CPE.

This will allow service providers to offer different layers of security for different traffic types. For example, it will enable service providers the ability to provide maximum security to financial data, but little or no encryption for general web browsing.

Open standards design
As WiMAX moves toward open standards to drive interoperability upward and cost downward, operators should seek to leverage this paradigm shift on the hardware infrastructure side, as well as the subscriber side of the wireless link.

Advanced Telecommunications Computing Architecture (ATCA) is quickly becoming the de-facto standard for high performance telco-grade systems providing next generation enhancements in reliability, availability and serviceability.

WiMAX systems that use open standards hardware designs will offer greater flexibility to the operator in scaling and evolving its WiMAX offering. Advanced TCA-based systems enable vendors to accelerate new feature development, expand solution offering, and simplify third party technology collaboration versus proprietary hardware systems.

These advantages should translate into time to market, time to revenue and cost improvements for the WiMAX operator.

Moving ahead
While WiMAX certification is an important industry milestone, certification by itself is only a baseline. WiMAX service providers should look under the hoods of the various WiMAX systems to see which ones can deliver the innovative and differentiated WiMAX features required to successfully address the burgeoning WiMAX opportunity.

About the author
Elvis Tucker
is the director of solutions and alliances at Aperto Networks.

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