Original URL: http://www.theregister.co.uk/2006/10/18/precertified_mobile_wimax/

802.16 momentum shadowed by platform trade-offs

Large players waiting for wave two

By Wireless Watch

Posted in Data Networking, 18th October 2006 13:38 GMT

Officially, 802.16e - or Mobile WiMAX as the vendors insist on calling it, even though its greatest advantage is that it spans fixed and mobile operations - is almost with us.

The standard is frozen, many of the forum's profiles are close to completion, certification testing is supposed to start towards the end of the year, two plugfests have been held, and suppliers are showing off their pre-certified equipment.

Traditional WiMAX suppliers like Alvarion and Aperto showcased their 802.16e-compliant wares alongside the grander statements of Motorola, Alcatel and Nortel.

However, this is all eerily reminiscent of the early days of 802.16d fixed WiMAX equipment, when there was a phony war between various so-called WiMAX systems as the market waited for certification testing to begin and "real" WiMAX products to hit the streets.

Now there is the same situation and the same dilemmas for buyers - namely, should they buy a first generation 802.16e system, non-certified or, even at the turn of the year, only supporting the limited first wave of the standard; grab the most developed, if least future-proof option and enter the market early with enhanced 802.16d systems; or wait for the second wave of 802.16e products, which will feature key additions like MIMO and, driven by large vendor roll-outs, should see significant price competition, but which could be unavailable for another year?

Announcements like Sprint's of its 802.16e plans have given credibility to the standard and increased operator willingness to invest, but for those that want to start to build out before mid-2007, the choices are all sub-optimal, certainly if the service provider is planning mobile multimedia offerings and so really needs to take advantage of second wave characteristics like MIMO combined with beamforming to gain the best cost of delivery and functionality.

For those who opt for pre-certified or first wave 802.16e, there will be few choices that include both MIMO and beamforming, for instance. Many of the large vendors, while talking up their homegrown 802.16e wares, will actually wait until wave two to launch these, and in the meantime will continue to rely on OEM deals, a halfway house that will not lead to rapid price erosion (Nortel, for instance, will ship its MIMO enabled WiMAX in the third quarter of next year, and until then continues to offer Airspan's systems).

Without MIMO and beamforming, it is hard to achieve key operator objectives such as effective indoor penetration without the need for very dense base station build-out. Early indoor devices have been disappointing in this respect, a factor that may have led to the scaling back of Airspan's flagship project with Japan's Yozan.

Some vendors are starting to implement these technologies even before wave two, often at the behest of a sought-after customer - SR Telecom has shipped products with indoor coverage using its own adaptive antenna technologies, partly to keep hold of its large Telefonica contract for wireless access in Spain.

The 'd-plus'agenda

But with pre-certified 802.16e immature, there is still some space for the somewhat sidelined "d-plus" agenda, which involves enhancing the fixed standard to support nomadic applications and other advances, to provide a stopgap that, for operators with no urgent requirement to offer mobile services, could last for some years.

While Aperto claims to have transferred its whole PacketMAX architecture to 802.16e, allowing for a software upgrade since both systems are in TDD spectrum only, other vendors cannot offer a smooth migration between their two products - especially if the first one is in FDD spectrum, since the FDD version of 802.16e is at least a year away. This may incentivise Alvarion and others, despite their strong mobile product plans, to extend the life of the "d" market for as long as possible.

By contrast, those with no legacy in fixed WiMAX - from small players like Adaptix, which is leaping straight into OFDMA, to giants like Motorola - wish to accelerate the "e" agenda and end the "d" distraction forever.

At the recent plugfest, however, there were tests of the "ETG mode", which extends 802.16d into laptops and other applications and supports improved interoperability between "d" and "e" CPEs.

Some chipmakers, notably WaveSat, have staked their short term business on this approach, arguing that "d" is proven and will support most operators' business models for some years to come; others, like Sequans, offer ETG as an option but regard it as "swimming against the tide" towards 802.16e being the only important WiMAX platform.

The momentum behind 802.16e combined with the wait for most tier one vendors' products actually to hit the market - Motorola and Alcatel being likely exceptions - should play into the hands of the equipment makers that have focused on new antenna techniques from the start and have always looked towards a mobile agenda.

With NextNet now part of Motorola, the chief representative is Navini, which showed off its Smart WiMAX offering in Boston. This does combine MIMO and beamforming, the latter technology something that Navini has pioneered in the embryonic mobile broadband sector with its proprietary Ripwave architecture, which now has a migration path to WiMAX, embodied in the hybrid Ripwave MX system.

Navini is taking orders for Smart WiMAX but has not announced a commercial release date yet - however, it is likely to be ahead of official wave two in order to gain a headstart on larger competitors.

Certainly, support for these two technologies, preferably in combination, will be the hallmark of 802.16e, even though they are only optional in the largely WiBro-oriented wave one of the standard.

Nortel, like Navini, sees this as its differentiator. Peter MacKinnon, general manager of the WiMAX-focused Nortel LG joint venture, said Nortel has seven years of research in OFDM and MIMO and the intellectual property and patents to back this up. "We're coming out from day one with MIMO, while our competitors are doing adaptive array," MacKinnon said. "We’re starting out with a second generation product so we won't have the product maturity issues others will face."

Nortel is avoiding the two-tiered technology path of most vendors, which are starting with adaptive antenna system (AAS) and beamforming and later incorporating MIMO. But others will soon catch up. Motorola will incorporate MIMO in its Diversity base stations late in the year and Alcatel will soon ship a software defined base station that will support MIMO next year with a software upgrade.

A year from now should, if the forum keeps on track, see wave two testing and the availability of many of these promised systems, which many believe will be the first "true WiMAX". Rather as the 3G community now refers to HSxPA as "true 3G" - finally delivering the operator promises that UMTS failed to do - the 802.16e world will likely wait a product generation to achieve a technology that delivers what carriers really want.

In the meantime, however, many operators want to start moving this year, and will have to balance their time to market pressures against a variety of technical trade-offs and migration headaches, whichever first generation system they choose.

Antenna technologies

Beamforming and MIMO are both multiple antenna technologies that differ mainly in how they use those antennas to create a connection to the end device.

AAS and beamforming systems use multiple antennas to create a single beam aimed at a particular device. That single beam provides a stronger signal and a higher capacity link to the individual user. MIMO, however, uses its multiple antennas (usually two, three or four at either end) to create multiple parallel beams, each of which finds its way to corresponding antennas on the device.

Multiple signals hitting multiple antennas means more capacity, and signal processing software sorts out the individual transmissions, simulating a single high capacity transmission back to the base station.

The typical criticism of beamforming is that it does not support high mobility. While the base station can easily steer the beam to follow individual users throughout the cell, it isn't easily adaptable for high mobility cases, particularly when a user is moving between base stations.

MIMO also helps in dense urban environments as it can take advantage of multipath effects as signals bounce off buildings on their way to the device.

Companies such as Navini and chipmaker Beceem see the two technologies as complementary and will focus on systems that switch between the two schemes as a user moves throughout the network, constantly optimising the configuration of the device as signal conditions change.

Copyright © 2006, Wireless Watch

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