Rival wireless home nets square off at cable show

By
EE Times
(05/06/02, 10:23:22 AM EDT)

PARIS Will cable operators looking to field wireless home networking features opt for the established 802.11b standard, for which silicon prices are rapidly declining, or the emerging 802.11a, which offers higher data rates and operates on a cleaner, 5-GHz frequency? That's what wireless chip and set-top vendors hope to divine as they gather in New Orleans Monday (May 6) for the National Cable Television Association's Cable 2002 show.

Philips Semiconductors and partner Pace Micro Technology (West Yorkshire, U.K.) will show a low-cost 802.11b-based solution for distributing multiple video streams in the home. On the other side of the debate, Magis Networks Inc. (San Diego) will demonstrate a 5-GHz home network that uses 802.11a to simultaneously transmit HDTV and Internet signals .

Among the considerations for service providers are the quality of the distributed video, the imperviousness of the radio technology to interference, system cost and bandwidth availability.

Radios designed to 802.11b transmit at 2.4 GHz and send data at up to 11 Mbits/second using direct-sequence spread-spectrum modulation; 802.11a radios transmit at 5 GHz and send data at up to 54 Mbits/s using orthogonal frequency-division multiplexing. The latter is seen as suitable for bandwidth-hungry applications, while 802.11b is gaining ground as a wireless Ethernet standard for data.

Managing the bandwidth

Eager to exploit off-the-shelf 802.11b chips, Philips developed an 802.11b-based home networking system using a proprietary "transrating" algorithm that incorporates video post-processing capabilities to help manage the available bandwidth, according to the company.

MPEG-2 video streams coming into a house via cable or a satellite at a variable bit rate 3 to 7 Mbits/s with an occasional 15-Mbit/s burst at peaks would be transrated to a constant 2.5-Mbit/s video stream. Handling the transrating task would be a home media center based on Philips' Nexperia dual MIPS- and VLIW-processor platform.

The media center can wirelessly distribute two live video streams, compressed to 2.5 Mbits/s, to two TVs. A third TV in the same household could pull yet another video stream from the media center's hard drive. At each TV, a thin client with a minimum MPEG-2 decoding capability would be installed.

Mark Samuel, set-top marketing director at Philips Semiconductors, said Pace and Philips spent five month to vet the system. Pace engineers wirelessly ran video signals over five walls, at a 100-foot distance, in the presence of several microwave ovens and cordless phones, all operating simultaneously on the same, 2.4-GHz band as the 802.11b home media center. "We tweaked our transrating algorithms further" after reviewing the test results, he said.

Philips thus claims the technology overcomes 802.11b's limited bandwidth and susceptibility to interference at the crowded 2.4-GHz frequency.

'Clear' choice

Magis, for its part, sidestepped bandwidth availability and interference issues by pursuing an 802.11a-based system that operates in a 5-GHz frequency, which experiences less interference than the 2.4-GHz band. Its silicon solution for the Air5 network is also based on the HiperLAN2 and Wireless 1394 standards. "While the 5-GHz band is rated at 54 Mbits/s, our Air5 technology supports up to 40-Mbit/s actual throughput," said Pete Fowler, executive vice president of Magis. "In a real-world home environment, you might have a channel or two of SDTV at 6 Mbits/s or HDTV at 19.6 Mbits/s, plus some data at 1 to 3 Mbits/s, all running simultaneously." Air5, he said, "could support all of these applications simultaneously, and more."

The Air5 network preserves quality-of-service as carried over 1394 and provides a seamless interface to the transport stream, Fowler said. And "Magis has developed algorithms and techniques to handle QoS required for delivery of real-time video as is necessary for wireless distribution of broadband cable and satellite services in the home," he said. Magis hopes to leverage strategic partnerships with such companies as Motorola, Hitachi, Panasonic and Sanyo all investors in the startup to see its technology evolve into a market leader in wireless networking.

Magis doesn't believe 802.11b can cut it in the home environment, Fowler said: "Although 802.11b is rated at 11 Mbits/s, its actual throughput is around 5 Mbits/s," he said. "It also uses the very noisy 2.4-GHz band, which it shares with microwaves, baby monitors, cordless phones, etc. Put a video stream into that environment with some data, and noise performance is going to take a significant hit."

Distance is also a concern. Motorola has told Magis that a home requires generous bandwidth and an operating range of 150 feet, Fowler said. "We are currently demonstrating HDTV at up to 250 feet," he said. "I'm not sure how far 802.11b can send video."

Philips Semiconductors argues that its solution reduces a video stream to a lower data rate and thereby combats 802.11b's low bandwidth. But Magis' Fowler countered that such an approach "would increase cost and decrease the quality of video."

Philips nonetheless argues that its single-chip Nexperia solution with dual MIPS and TriMedia cores is becoming a standard, cost-effective platform for set-tops. "Many cable operators thought wireless home networking as a product concept for 2004, but after going through our demos, they were surprised to see the maturity and [low] cost of our technology," said Philips' Samuel. "You can build this by using existing silicon, today."

The difference in the bill of material for wireless chips based on 802.11a and 802.11b last year was about $40. Philips predicts the gap will narrow to about $12 in 2003 or 2004. But that "difference is still significant for consumer products," Samuel said.

Magis declined to comment on the BOM for its 802.11a chip set. "We have not publicly released this information yet," Fowler said.