Vendors not waiting for 802.11n
Extending the speed and range of Wi-Fi to allow Ethernet-like wireless services that span several office floors with less infrastructure and maintenance costs is nirvana for existing wireless local area network, or WLAN, users — especially public-safety users looking for cost-effective and reliable WLAN equipment.
That’s the notion behind development of the next generation of 802.11 technology, known as 802.11n, which proposes to boost Wi-Fi’s data rate from its official 56 Mb/s in the 802.11g standard to real throughput of 100 Mb/s or more.
Ratification of 802.11n isn’t expected until late 2006, but vendors aren’t waiting. They have begun offering products that tout the benefits of multiple-input/multiple-output, or MIMO, smart antenna technology that increases data speeds, range and reliability of Wi-Fi networks.
Belkin introduced what it calls “pre-N” routers and adapters in December, while Linksys, Netgear and D-Link also have announced similar products. Vendors say customers want this capability today, and Wi-Fi competition demands it — despite the fact that pre-standard products pose an inherent risk for early technology adopters in terms of quality and interoperability.
“MIMO has been adopted more rapidly than any other 802.11 product — faster than 802.11g, b or a,” said David Borison, director of product manufacturing for Wi-Fi chip provider Airgo, which supplies its True MIMO chips to a number of vendors, including Belkin. The semiconductor company says it shipped 3 million chips based on True MIMO and has garnered a 3% market share by volume in the last six months.
For public-safety users looking to deploy 802.11-compliant equipment in the 4.9 GHz band, which was set aside by the FCC for exclusive use by first responders, MIMO is enticing because it promises to make Wi-Fi technology more cost-effective for wide-area deployment. Existing Wi-Fi technologies are designed to serve only a localized environment because of their propagation limitations. MIMO also has the potential to combat interference problems posed when all licensed public-safety entities within a region begin consuming all of the available frequency channels.
But herein lies the counterbalance to MIMO’s benefits: Wi-Fi vendors and chipmakers have their own definitions of what MIMO is, which threatens to tarnish the value proposition of the future 802.11n standard.
The Wi-Fi MIMO market has separated into different technology camps. For instance, Belkin and Linksys offer MIMO products based on Airgo’s chips and its spatial multiplexing technology, and Netgear is incorporating both Airgo’s chips and additional smart antenna technology, known as sectorized antennas, from Video54. However, D-Link is using chips from competitor Atheros Communications, which is incorporating beam-forming smart antenna technology.
Airgo, whose CEO Greg Raleigh invented MIMO, claims the technology generally requires the use of multiple antennas on both sides of a communications link to simultaneously transmit several data streams through the same channel. But the key to real MIMO is its ability to do spatial multiplexing — which allows for the transmission of multiple distinct data streams over multiple radios in the same frequency at the same time. In essence, spatial multiplexing creates multiple parallel independent channels from a base station to the device and recognizes the unique codes of these independent paths. Knowing the individual path code allows them to be used as independent parallel highways, carrying much more data than a single link and effectively doubling data throughput. Spatial multiplexing will be a mandatory element in the 802.11n standard.
“What has happened as a result of our success and market share is that some competitors are on the defense, offering what they call MIMO products, but in reality they aren’t,” Borison said.
Ira Brodsky, president of Datacomm Research, agrees. He believes MIMO technology based on spatial multiplexing is perhaps the biggest development to impact the wireless industry.
“Airgo is multiplying capacity, and that is a big difference from smart antenna schemes, which provide incremental improvements,” he said. “MIMO is a paradigm shift, both technically and in the mindset of the telecom world. A lot of these companies just don’t fully get that yet.”
For Atheros, it’s a matter of how narrow the view of MIMO is. “There are some folks who have a very narrow definition of MIMO,” said Jeff Gilbert, director of algorithms and architecture for Atheros. “What MIMO stands for is multiple input/multiple output, meaning you use multiple radios on the same channel. MIMO itself can encompass several different types of techniques.”
Atheros offers a chipset that uses four antennas and two radios that send data over two transceivers simultaneously. The difference is that the two radios transmit the same data stream simultaneously to extend the range of a signal but not the throughput speed. This beam-forming technique is being proposed as an optional element to the 802.11n standard.
Gilbert argues that spatial multiplexing is only useful when the 802.11n standard is complete because compliant devices will be able to turn off the multiplexing mode and act as a standard device when communicating with a legacy 802.11a, g or b device. Beam forming can extend the range of legacy equipment, he said.
“The advantage of this MIMO is that it’s fully standards-compatible. It doesn’t change what you’re sending over the air, but it can work on only one side of the link so that we can use our MIMO products on legacy devices and still give performance to those devices,” Gilbert said.
However, Borison said Airgo has shown that spatial multiplexing can benefit legacy devices. MIMO can accomplish a 20% to 30% increase in throughput and range when talking to legacy devices.
“What we’ve done is build on top of the standard. It’s like 802.11g/a on steroids,” he said.
The earliest the Institute of Electrical & Electronics Engineers could ratify the 802.11n standard is the second half of 2006 with interoperability testing and Wi-Fi certification following in 2007. Two competing proposals are coming from TGn Sync, which includes Atheros and large vendors such as Cisco Systems, Nokia and Nortel, and the World Wide Spectrum Efficiency group, whose members include Airgo, Texas Instruments and Broadcom.
Last fall, the Wi-Fi Alliance warned against pre-N products, saying it would not certify data rate enhancement features based on 802.11n until the standard is ratified.
“Vendors took advantage of unsuspecting buyers when they touted pre-standard technology for 802.11g that later did not meet the standard,” said Ken Dulaney, wireless analyst with Gartner. “Left unchecked, the industry is unfortunately poised to repeat itself with 802.11n.”
However, John Yunker, president of Byte Level Research, sees pre-standardized 802.11n equipment as a sign of a healthy industry.
“There is a definite need for 802.11n products today,” he said. “Although standardization is beneficial, equipment tends to become commoditized very rapidly. If vendors can beat the standard and get some sales with some decent margins, I don’t think that’s bad at all.”
In addition, vendors are signing their own death warrants if they don’t offer pre-802.11n products, say analysts. Broadcom ruled the 802.11g market largely by introducing products based on the draft version of the standard that the company called “54g” months before 802.11g was accepted.
TGn Sync Consortium
Members include: Atheros, Cisco, Samsung, Nortel, Intel, Sony and Qualcomm.
Key Features of TGn Sync Proposal
- MIMO spatial division multiplexing to support 315 Mb/s reliably with two antennas, up to 630 Mb/s with larger systems.
- Scalable architecture for different spatial stream (2 to 4) and spectrum configurations (10, 20, 40 MHz).
- Seamless interoperability between 802.11a/b/g and new modes of operation.
- Timed receive mode switching and multiple receiver addressing to reduce power for battery-operated devices.
- Flexible architecture offering product compliance for all major regulatory domains while preserving interoperability.
World Wide Spectrum Efficiency Consortium
Members include: Airgo, Broadcom, Motorola, Nokia, NTT and ST Microelectronics.
Key features of the combined WWiSE proposal:
- Mandatory use of the approved, pre-existing, worldwide 20 MHz Wi-Fi channel width.
- Enhanced MIMO technology that enables a maximum data rate of 135 Mb/s in the minimum mandatory 2×2 configuration and a single 20 MHz to keep implementation costs low.
- Mandatory modes affording backward-compatibility and interoperability with existing Wi-Fi devices in the 5 GHz and 2.4 GHz bands to ensure strong support of legacy deployments.
- Rates up to 540 Mb/s, accomplished with a 4×4 MIMO structure and optional 40 MHz channel width (where permissible by regulatory bodies).
- Provisions for advanced features that improve data rate and range such as beam-forming and closed loop methods.