Navini heads Smart Alliance to promote beamformed MIMO

By Caroline Gabriel, Research director, Rethink Research Associates LTD,

Web site: www.rethinkresearch.biz

If Mobile WiMAX is to maintain the momentum of its market head start on other OFDM-based technologies like LTE, it has to make its price/performance case as quickly and convincingly as possible, to win operator trust before they have any real pre-4G alternatives. One of its problems in achieving this is being confined for now – in its official profiles at least – to spectrum above 2GHz, which have range and penetration challenges. This makes techniques to boost spectral efficiency vital to prove WiMAX’ case, and one of the most important has been a combination of MIMO smart antenna arrays and beamforming. The cheerleader for this approach, Navini, has just announced a $330m acquisition by Cisco, and will no doubt use the weight of its soon-to-be parent to promote the ‘beamformed MIMO’ cause still further. In the meantime, the start-up is also looking to punch above its weight by enlisting some allies to its cause, forming the Smart Antenna RF Test Alliance (Smart) with chipmakers Fujitsu, Runcom and Beceem, to support beamforming and beamformed MIMO, as outlined in wave two of the WiMAX 802.16e standard.

MIMO improves capacity and signal strength with the use of parallel antennas and complex algorithms, while beamforming enhances range and quality by concentrating the strength of the signal in one desired direction instead of wasting much of it in a 360-degree dispersion pattern. Navini’s VP of product management, Sai Subramanian, claims the combination doubles capacity and coverage compared to ‘vanilla’ 802.16e systems, such as those being certified for wave one of the WiMAX Forum’s specifications. The main objectives of Smart, like most industry alliances, are to raise awareness of the technology; encourage interoperability; and create sufficient economies of scale that a broad range of attractive and affordable subscriber units can be assured.

The new Alliance plans to publish a system performance baseline for the mandatory smart antenna features adopted in 802.l6e wave two, and will work on interoperability between the devices of its current and future members. This highlights one of the key trends in wireless – for groups of suppliers with a common interest to work together on interoperability testing long before this becomes a reality in the official certification bodies’ processes, which are increasingly looking too slow for the speed of change of the wireless market. Conformance and interoperability certification of wave two WiMAX equipment will not begin in the WiMAX Forum test labs until well into 2008.

All four founders of the Smart Alliance have made a strong commitment to beamforming, usually in combination with MIMO. Navini leads the beamforming task group within the WiMAX Forum’s Certification Working Group and has 27 patents awarded or pending in this area; Beceem was the first subscriber unit chipmaker to offer a commercial 802.16e terminal chipset supporting the wave two smart antenna feature set; Fujitsu recently participated in the first multivendor interoperability demonstration of beamformed MIMO with Navini; and Israel’s Runcom has also made firm pledges to support the technologies in its CPE chipsets.

Smart Alliance members will collaborate implementation guidelines to optimize performance, and open their field testing labs to other members for performance interoperability testing. Test results will be shared.

Navini has been making headway in recent months with its claims that beamforming plus MIMO is a superior approach to MIMO alone, and more large vendors are showing an interest in the combination, especially amid calls from some large operators, like AT&T, to move to a more stringent set of specifications – in effect a ‘wave three’ – that would almost certainly include larger MIMO arrays and beams.

Some vendors, notably Nortel, have been less enthusiastic about beamforming, claiming it is an unsuitable technology for high mobility or dense urban environments. Nortel is a pioneer in MIMO, and stakes much of its technical differentiation in WiMAX on the platform. Last year it entered into a philosophical debate with Navini over whether beamforming was necessary too, but now even the Canadian giant seems to be taking a more flexible view. It is also leading the field with the Collaborative MIMO technique, an option in 802.16e wave two, but potentially an important want to improve uplink performance. It enables a wave two system to interface with non-MIMO devices and still take advantage of multiple paths. While standard MIMO focuses on sending multiple signals from the device across the same frequency, giving the user increased capacity or redundancy, Collaborative MIMO allows two separate devices to transmit different signals over the same frequency, so that the base station can support twice the number of devices/users. “Some carriers are more interested in the number of subscribers they can support with MIMO than they are in bandwidth to the individual subscriber,” said the company.

10/05/2007 05:24:00 PM