802.11n Morphs Into Spec For Home Video Stream
COLORADO SPRINGS, Colo. — When the IEEE first pondered antenna diversity for its 802.11n wireless LAN standard, the multiple-input/multiple-output antenna topology was seen as a general tool for increasing Internet data access to 500 Mbits/second--some 50 times that of 802.11b. But as draft silicon of 802.1n networks sampled in 2006, the focus had changed to a singular concentration on Internet Protocol TV (IPTV) and high-definition television video streams.
In a sense, the metamorphosis of 802.11n mirrors that of a shorter-range wireless technology, ultrawideband radio. After the IEEE 802.15.3a task group on UWB split up in acrimony last January, the promotional WiMedia Alliance group narrowed its focus to applications in which ultrawideband is a wireless replacement for the Universal Serial Bus. But more recently, "Certified Wireless USB" has taken a back seat to chip sets exploiting ultrawideband for in-home video distribution.
The two technologies are complementary. Since 802.11n must serve first duty as an access technology to broadband pipes, its hub-and-spoke LAN structure is designed for networking first. UWB, except when in the multipoint WiNet topology, is a serial file-sharing PAN with shorter range, but with data rates that can approach and sometimes exceed 1 Gbit/s. Both local- and personal-area networks are being optimized for video distribution in the home.
Some WLAN chip set developers even hope to repurpose OFDM media-access control and physical-layer chips, along with 4 x 5 antenna solutions, as a direct High Definition Multimedia Interface (HDMI) cable replacement. Amimon Inc. will demonstrate prototypes of this solution at next week's Consumer Electronics Show. Metalink has taken a slightly more conventional approach, using its WLANPlus chip set with enhanced quality-of-service (QoS) as a vehicle to improving HDTV distribution in the home, though not necessarily as an HDMI substitute.
For HDTV networks based on MIMO antennas, even the lower-speed 802.11b/g plays a role. In late 2005, Ruckus Networks Inc. went public with a MIMO-based access point that used 802.11b/g for video distribution in the home. In 2006, Ruckus extended its work with a residential gateway, and intends to upgrade its antenna diversity architecture for 802.11n support.
Ruckus' two proprietary concepts indicate where newcomer OEMs can add functionality with the first generation of 802.11n chips. Instead of relying solely on antenna spatial diversity, Ruckus adds beam-forming algorithms to adaptively choose the best RF paths in the home. It then adds routing-layer multicasting diversity, dubbed SmartCast, to make the best use of IPTV multicasting. In theory, combining MIMO and routing concepts in a new generation of 802.11n gateways will allow fast Internet Group Membership Protocol add and join operations, essential for fast "channel changing" in IPTV.
Broadcom Corp. and Atheros Communications Inc. raised eyebrows last January when they offered "draft" silicon for 802.11n, even though by year's end the IEEE working group had yet to finalize this standard. Almost as surprising as the early silicon for 802.11n was the fact that they emphasized consumer, rather than enterprise, applications on their Web sites.
Michael Hurlston, vice president and general manager of the home and wireless business unit at Broadcom, said that many security and quality-of service features for 802.11n can attract businesses seeking upgrades from b/g. Simple market dynamics, however, indicate that enterprise markets will be snowed under by potential retail and reseller markets for the digital home.
Home hobbyists have worked on distributing standard-definition 802.11g TV streams in the home, Hurlston said. The emerging 802.11n not only improves bandwidth and range, but also offers better forward error correction and QoS.
For Atheros, the better performance advantages of 5.7-GHz 802.11n and the limitations of using the 2.4-GHz band for the new standard, mean developers will quickly move the new WLAN standard into the higher unlicensed band. Broadcom executives are less certain of this. Hurlston said he thinks PC OEMs will ship dual-band versions of 802.11n with LAN on the motherboard, while retail home-router players will ship single-band 2.4-GHz products.
The wild card will be played by carriers, both cable TV and telephony, that may offer 802.11n in residential gateways. For the carriers, better TV performance may warrant 5.7-GHz platforms, Hurlston said.
Developers of both 802.11n and ultrawideband silicon agree that the technologies will coexist in the home. The question is where the two will meet and overlap. Rajeev Krishnamoorthy, founder and chief technology officer of UWB company Tzero Technologies Inc., said that 802.11n will always have an important role to play in access platforms like laptops, but that the access pipe into the home always will represent a bottleneck compared with the high-speed PAN responsible for carrying signals between media devices.
Some WLAN gateway makers developing 802.11n are bullish enough on the opportunities of antenna diversity to suggest that UWB's only role will be as a strict serial-interconnect replacement, particularly for Certified Wireless USB. Hurlston of Broadcom said that such a view ignores the gains UWB has made in non-USB apps, such as the wireless HDMI model Tzero and Analog Devices Inc. have developed.
"The key here is what goes inside the TV set. Ruckus and others working on the gateway side of 802.11 are betting on the integration of a module directly inside the TV. I haven't seen manufacturers leaping to this so far," Hurlston said. "On the other hand, UWB could go inside the TV or set-top box as an HDMI replacement, and there is already an interface model OEMs are familiar with. That kind of relationship between 802.11n and UWB seems much more likely."
