Intersil, Silicon Wave sample combo Bluetooth/WLAN solution

By
EE Times
(04/19/02, 12:31:17 PM EDT)

MANHASSET, N.Y. Intersil Corp. and Silicon Wave Inc. are ready to demonstrate the first radio transceiver circuitry that supports both IEEE 802.11b wireless LANs and Bluetooth communications. The four-piece chip set enables the seemingly simultaneous operation of both networks without mutual interference.

The Blue802 chip set, to be demonstrated at the Network+Interop conference in Las Vegas in early May, is the result of a co-development deal the companies signed over two years ago. It is comprised of Intersil's Prism 3 direct-conversion 802.11b radio chip, baseband and media-access controller (MAC), and Silicon Wave's direct-conversion Bluetooth radio modem and baseband processor. The solution essentially adds a transparent layer of software between the two companies' circuitry at the MAC layer to prevent interference. Both radios are laid side by side on a Mini-PCI card and share an antenna and switch.

Seemingly simultaneous

"We've developed an [software] interface that allows collaborative, real-time transmit and receive control," said Ken Sherman, senior product manager at Silicon Wave. "It's at the MAC layer, so we can present to the notebook PC user simultaneous operation, while we're in reality preventing simultaneous transmission. So we can optimize the throughput for both Bluetooth and 802.11b." Blue802 gets over 90 percent of the specified performance for each air interface, Sherman said.

Blue802 was to be demonstrated by Microsoft Corp.'s vice president of platforms Jim Allchin at the Windows Hardware Engineering Conference in Seattle on Tuesday (April 16), but the Washington State Convention & Trade Center's network went down before the simultaneous operation could be shown.

The Intersil-Silicon Wave implementation lands ahead of the combo solution of Mobilian Corp., which has promised to deliver an 802.11b/Bluetooth solution. Mobilian plans to sample its combo device in May, and to be in production by year's end, according to Frank Hanzlik, the company's vice president of marketing. Pricing has yet to be determined.

Intersil and Silicon Wave are sampling Blue802 today to key customers and will go into full production in August. The cost will be the sum of the companies' separate direct-conversion chip sets. Intersil's Prism 3 currently costs $30. Silicon Wave did not present its pricing information by press time.

Mobilian opts for integration

The Mobilian and Intersil/Silicon Wave designs differ in terms of integration. Mobilian is developing a fully integrated solution that supports simultaneous operation of 802.11b and Bluetooth, and at a lower price and smaller footprint than separate solutions, the company said.

To support simultaneous operation as opposed to the MAC-layer switching of the Intersil/Silicon Wave solution Mobilian took a systems approach to its SimOp radio architecture, Hanzlik said. "From the start we built the Bluetooth and Wi-Fi [802.11b] front-ends, baseband and MAC with coexistence in mind. Both operate at the same time, and along with our integration, this makes us unique." Hanzlik said. SimOp's MAC, physical-layer and antenna design involve eight patents, he said.

The MAC techniques allow SimOp to intelligently manage traffic between the Bluetooth and Wi-Fi radios, while PHY-layer techniques manage the self-jamming and adjacent channel-interference issues, Hanzlik said.

But SimOp's simultaneous radio operation involves some risks, according to Jim Zyren, marketing manager at Intersil. "When co-located, there's a possibility of one radio overloading the radio front-end of the other, thereby eliminating any selectivity," he said. "When Bluetooth is at 20 dB, it can overload the 802.11b front-end, which is why we opted for a time-division duplex implementation."

Even advanced techniques, such as adaptive frequency hopping, don't help when the radios are co-located, Zyren said. Many standards bodies are pushing adaptive frequency hopping as the best solution for the 802.11b/Bluetooth coexistence problem that has plagued designers of radios in the 2.45-GHz ISM band. However, the Federal Communications Commission has yet to approve that method, Zyren said.

Another approach to a combo 802.11b/Bluetooth solution employs a driver-swapping scheme, but that approach has "too large a degree of abstraction from the traffic in the air interface and the MAC," said Tim Godfrey, strategic marketing manager at Intersil. Described by IBM Corp., the approach "requires the packet to go through queuing, scheduling and timing issues before it gets sent out, so you can't properly coordinate the sent traffic [between the two radios]," he said.

'Tried and tested'

Though the 802.11b and Bluetooth radios do not operate simultaneously in the Intersil/Silicon Wave solution, "the Blue802 does use two tried and tested radios, both of which have been passed by their respective qualifying standards," said Navin Sabharwal, director of residential and networking technologies and Allied Business Intelligence Inc. (Oyster Bay, N.Y.)., "This means a lot for OEMs who are looking to get off the ground quickly with combo solutions."

The Mobilian solution, on the other hand, offers "higher and more elegant integration and probably lower cost, but will have to worry about standards compliance," Sabharwal said. "[Blue802] may not be the cheapest solution in the world, but it's a good first-generation solution with next-generation versions promising higher integration."

The Blue802 implementation gives default priority to 802.11b, according to Silicon Wave's Sherman. "When the 802.11b connection is at full speed, however, and Bluetooth wants priority, Bluetooth can request priority. We call this 'Blue802 bandwidth on demand.' "

In addition, said Sherman, the switch matrix that allows the Bluetooth antenna to share one of two diversity antennas in a notebook PC allows an OEM to add Bluetooth capability via a Blue802 Mini-PCI card without re-spinning a design. "Those antennas offer better performance too, as they're typically up in the corners of the screen, instead of burying a third antenna [for Bluetooth] down in the notebook," he said.

Blue802 requires nothing of a PC's operating system apart from the Bluetooth support that Microsoft has promised by summer, Sherman said. "Bluetooth has a standard interface between the chip set and stack via the HCI [host controller interface]," he said. "In addition, Silicon Wave's radio was selected by Microsoft as the 'golden' unit for Windows interoperability testing."