Alliance Defines New MAC For UWB Networks

An industry alliance has forged a new media-access controller for ultrawideband networks that proponents said will meet the myriad needs of the PC, consumer electronics and mobile markets.

Details of the new MAC were thrashed out during a five-day session of the Multiband-OFDM Alliance (MBOA) led by Intel Corp. and Texas Instruments Inc. In doing so, the group has effectively rejected the IEEE 802.15.3 MAC, which the IEEE 802.15.3a task group has stipulated as the controller of choice for whichever physical layer that group eventually defines.

The move further complicates the efforts of the task group, which is currently deadlocked in its search for a suitable physical layer (PHY) that would reach rates of 480 Mbits/s at 1 meter, or 110 Mbits/s at up to 10 meters. The dispute pits MBOA against a group the includes Motorola, CRL, decaWave and Oki Semiconductor which is promoting a direct-sequence UWB (DS-UWB) proposal.

While each side continues to back the standards process, both continue to work in parallel to independently bring their respective technologies to market. To that end, MBOA formed its own special interest group in late January.

However, EE Times has learned that the DS-UWB group will announce next Monday (March 22) that it has formed a competing umbrella group. Initially to be called the "DS-UWB Forum," the new group will instead now be known as the "UWB Forum." The name reflects the inclusion of the recently defined common signaling mode (CSM) in Motorola's latest proposal. Forum details - along with a Web site - will be disclosed next week after the IEEE 802 plenary session in Orlando, Fla.The new MBOA MAC, while deviating substantially from the 802.15.3 version, was deemed necessary by the alliance. According to Kursat Kimyacioglu, director of wireless business development for business line connectivity at Philips Semiconductor, the new MAC "will solve all the mobility and CE requirements and issues as well as [the needs of] all the isochronous and asynchronous applications and related issues for UWB systems."

Kimyacioglu added that PC and mobile requirements will also be met, particularly with respect to mesh networking and the management of piconets.

The MAC combines proposals made by Philips, Sony and Alereon, and was unanimously approved by 54 participants representing 24 companies. According to Kimyacioglu, the MAC allows for the reservation of timeslots for 802.15.3-like time-division multiple access for high priority connections requiring determinism while assigning contention-based, best-effort access periods.

A key requirement for the MAC is decentralization, along with the notion that every node will announce its connections and with whom its exchanging data. "So every node is fully aware of what's going on with every other node in the network, which will reduce reconnect time and latencies," said Kimyacioglu.

"There are certain features the 802.3 MAC doesn't have, mostly mobility centric such as mesh and roaming and the ability to handle dynamically varying environments," he added. With the new MAC, service will be continued "as the data has multiple paths so as paths or nodes fail, data can be rerouted," he said.Along with facilitating roaming and reducing dropped connections, the mesh capability also provides a spatial frequency reuse capability "so devices that are out of range of each other can communicate independently," Kimyacioglu added.

The MBOA MAC's piconet structure, combined with its decentralized resource-handling ability has other advantages, according to Steve Turner, UWB business development manager for Dallas-based TI's consumer networking business unit. "If you do get into situations of mobility from one piconet to the next, the MAC's ability to allocate resources makes it much easier to get the resources you need, so you can, for example, get access to unused bandwidth to reduce your latency."

Motorola objects

Martin Rofheart, Motorola's director of UWB operations (Vienna, Va.), disputed MBOA's claims about the .15.3 MAC. "That MAC is already proven to be suited to CE A/V applications, with low latency, full QoS and support for multiple users," he said. The controller has "been through simulations and now it's been implemented. It's mature and proven."

"We're disappointed to hear they're walking away from it [.15.3 MAC]," added John Barr, Motorola's director of standards realization. "We're here [in Orlando] to discuss an alternate PHY for the 802.15 MAC. That's the PAR [project authorization request] and that's the only thing that's going to come out of this group."MAC development is expected to track PHY development, and sample by year's end with products expected during the first quarter of 2005.

For MAC developers with products complying with 802.15.3, it's back to the drawing board. "Many believe they can take their existing .15.3 MACs and leverage the hardware portion and do a lot of it in firmware," said MBOA spokesman Mark Fidler, senior engineer scientist at the Imaging and Printing Systems division of Hewlett-Packard. "However, there are aspects that will be similar, but it's probably far enough of a deviation that it's questionable whether you can make these changes and implement them on the same 15.3 MAC."