The emergence of the WiMax standards has spurred tremendous interest from operators seeking to deploy next-generation, high-performing, cost-effective broadband wireless networks. However, the availability of 802.16e and 802.16d as two different and incompatible iterations of the WiMax standards has in some cases added confusion to the operator's investment decisions.

WiMax refers to both the IEEE 802.16d and 802.16e standards, which support a variety of applications and network solutions. The WiMax label refers to a defined subset of technology specifications from the 802.16d and 802.16e standards called "profiles."

Often referred to as the mobile standard, 802.16e not only introduces mobility to broadband wireless specifications, but it also provides enhanced performance even in fixed and nomadic environments. Below I have outlined several reasons why 802.16e is the true future of WiMax [Which back Motorola's decision to skip d and go to e - Editor].

Not backward compatible
Operators seeking to make a WiMax investment must first recognise that 802.16e is not backward compatible with 802.16d. While some 802.16d vendors propose base station equipment with additional hardware complexity or software programmability to allow a switch to 802.16e, this will not impact any 802.16d end-user devices already deployed. These 802.16d end-user devices will not operate within an 802.16e network and the imperative for low-cost end-user devices makes it prohibitive to introduce additional hardware to attempt an upgrade to 802.16e compliance. Adding upgrade capability to the base station may also result in a large cost penalty.

Additionally, an operator who deploys 802.16d and then attempts to roll in 802.16e equipment at a later date will be disadvantaged by having to split the available licensed spectrum between the two technologies. Without a true upgrade path from 802.16d to 802.16e and the necessity to preserve spectrum to support network growth, 802.16e provides the best long-term protection for an operator's WiMax investments.

Lower cost
As the broadband wireless market continues to grow, the industry should expect to benefit from cost reductions enabled by volume deployments and economies of scale. Portable and mobile applications have a very strong track record for accelerating volume, therefore it is expected that mobile deployments of 802.16e will bring cost points down below solutions engineered solely for fixed applications using 802.16d.

Additionally, major chip set manufacturers have announced that 802.16e will be the premier standard for WiMax applications, pointing to a substantial embedded base of consumer products with 802.16e support. These same chip sets used in laptops and handhelds can be leveraged in the manufacturing of indoor- and outdoor-fixed customer premise equipment. It becomes quickly apparent that 802.16e offers the critical advantage of allowing the operator to ride a downward trending cost curve.

Scalable system bandwidth
With 802.16e, WiMax makes enhancements to the physical layer by employing Scalable Orthogonal Frequency Division Multiple Access (OFDMA). The ability to scale system bandwidth while maintaining constant symbol duration provides greater commonality in equipment components and offers operators the advantage of being able to deploy today and grow their system bandwidth tomorrow at a lower cost and reduced network impact.

Higher performance
While both 802.16d and 802.16e standards specify various requirements and optional techniques to enable a high-performing broadband wireless channel, IEEE 802.16e and the resultant WiMax profiles are expected to extend these requirements and options to guide vendors to further enhancements in capacity, coverage, power reduction, quality of service, and support for rich IP applications.

While 802.16d and 802.16e both support a variety of forward error correction techniques to increase the capacity of the broadband wireless system, the first generation of 802.16d products are not expected to implement such high-performing coding techniques. 802.16e products are anticipated to deliver such capabilities from the first shipments.

802.16e also provides sub-channelisation techniques to more efficiently manage the channel bandwidth among multiple end users. The base station uses sub-channelisation to optimise scheduling of multiple users having distinct spatial signatures. The various sub-channelisation schemes offered by 802.16e allow more efficient scheduling of users based on channel quality, priority, power and bandwidth allocation.

Power reduction
802.16e defines a series of sleep and idle mode power management functions to enable power conservation and preserve battery life for end-user devices. The mobility enhancements provided by the latest 802.16e amendment further enhance operation at vehicular speeds by providing improved support for inter-cell handoff, directed adjacent-cell measurement and sleep modes to support low-power mobile station operation.

Quality of service
802.16e introduces Extended Real-Time Polling Service, which allows 802.16e to manage traffic rates and transmission policies, as well as improve latency and jitter. The advantages afforded by the QOS techniques are especially important in the support of voice-over-IP applications.

802.16e also supports multicast and broadcast services. Single Frequency Network operation can be achieved using OFDMA for broadcast/multicast services, enabling very high data rate coverage at cell edge. Rich IP multimedia applications, such as IP TV, that make use of streaming video are greatly advantaged by multicast and broadcast capabilities to better manage bandwidth and content delivery.

Delays in certification and availability of 802.16d products, although they now are available, have significantly closed the gap before the emergence of the first 802.16e products. The first 802.16e products are expected to be available in Q2 2006 and follow with a long line of network and end-user equipment. Additionally, the industry can expect to see a significant base of consumer devices with embedded 802.16e chip sets provided by the major chip set manufacturers.

802.16d has all the appearances of being an interim technology with no true upgrade path to 802.16e. Operators should protect their early WiMax investments by selecting products based on the 802.16e standard. In addition to providing mobility for operators seeking to introduce mobile broadband applications, 802.16e will outperform 802.16d and benefit from economies of scale even for fixed applications.

Shamik Mukherjee is manager for WiMAX systems at Motorola. This article appeared in Computerworld