WiMAX summit: 'Standards-plus' could harm 802.16 roadmap

This week saw the WiMAX community gathered in force at the WiMAX Summit in Paris, France. It quickly emerged that the issue preoccupying both vendors and potential operators is the road to mobility and exactly how the transition to the forthcoming 802.l6e mobile standard will be achieved. With a key WiMAX Forum meeting to be held in the coming week in Spain, and 802.16e set to be ratified this year, it is essential to the uptake of the platform that the route to mobility is clarified as soon as possible.

All agree that 802.16 will be the platform with which WiMAX hits the big time. Most of the equipment majors are merely licensing fixed 802.16d (now renamed 802.16-2004) gear, while focusing their own development efforts on 'e'. That means that the chances for chipmakers to net the big OEM deals - with Alcatel, Nortel and the others - rely on the mobile standard. But there are two basic schools of thought among the chipmakers and their licensees as to their strategy in the interim.

The two WiMAX roadmaps

One is that there is a period of at least two years before 802.16e achieves volume, and that the upgrade path will be complex. That means the priority is to make 802.16-2004 as impressive as possible in order to drive short term sales and increase confidence in WiMAX. This will mean creating a so-called 'd+' technology that goes beyond the basic stipulations of the fixed standard, with a focus on aspects such as quality of service for voice and video, and portability with consumer grade subscriber equipment.

The other view is that the market needs to move to mobility more rapidly, by offering pre-standard networks that provide most of the functionality promised for 'e'. This strategy rests on the belief - or hope - that the mobile standard will come to market rapidly and that the leap from its predecessor will be a simple one.

Both points of view reflect that 802.16-2004, in its vanilla form, is fairly basic and will not, out of the box, deliver all the services and capabilities that have been marketed on its behalf. Either 'd+' or 'e' will be required to fill those gaps and make WiMAX an attractive platform outside the traditional broadband wireless niches such as backhaul and rural access, but these will bring the risks of non-standard extensions that kill interoperability, a trend that is already afflicting WiFi.

The main decision that will affect how painless is the shift from 802.16-2004 to 802.16e rests on the choice physical layer (PHY). The more complex the upgrade, the more important it is to create an attractive first generation platform - whether 'd+' or pre-standard mobile - that will justify investment in its own right and deliver returns before the upgrade process becomes necessary.

The PHY debate

The original IEEE/Forum plan was to use the same PHY for 'e' as for the fixed specification - OFDM 256 FFT. This would enable a simple, often software-based upgrade and would support interoperability of fixed and mobile base stations and customer premises equipment (CPE). The agreement last year to incorporate the Korean WiBro technology into the 802.16e process - a highly positive move in terms of international harmonization and technical knowhow - did however introduce the option of using the PHY favored by Samsung and LG. This is Scalable OFDMA, which claims better support for mobility by supporting sub-channelization and variation of the size of FFT according to bandwidth available. Despite its advantages, SOFDMA equipment would require hardware upgrades to base stations and would not be interoperable with legacy 802.16-2004 equipment, even in the same frequency band.