802.16 momentum shadowed by platform trade-offs

Large players waiting for wave two

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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