Pages: pp. 16-18
Since the approval of the original IEEE 802.11 standard in 1997 and the increased use of the resulting Wi-Fi technology over the years, interest in wireless networking has grown rapidly.
As is the case with other networking technologies, Wi-Fi users have sought faster IEEE 802.11 versions with longer transmission ranges. Industry observers say higher data rates are particularly important for new consumer offerings such as high-definition television.
Because of this, users have eagerly awaited IEEE 802.11n, which promises higher speeds and longer ranges than earlier Wi-Fi versions, which the " Major Wi-Fi Flavors" sidebar addresses.
However, the technology has had a rocky standardization process. As is so often the case, two groups of vendors squared off over whose 802.11n approach would become the standard and thereby yield revenue and potential market dominance to the winner.
Recently, though, the two sides have moved toward a compromise. However, there are still some unresolved issues, and the IEEE 802.11 Wireless Local Area Networks (WLAN) Working Group still hasn't approved the new technology as a standard.
Nonetheless, Wi-Fi vendors are releasing prestandard 802.11n products. According to senior analyst Gemma Tedesco with market research firm In-Stat, this has raised concerns that the products won't be compatible with either one another or the final IEEE standard. This could yield competing versions of the technology and products that won't work together and that won't perform as promised.
Despite this, industry analysts are bullish about 802.11n's future.
For example, 802.11n chipsets, which will represent only 3.6 percent of global WLAN chipset unit sales this year, will represent 20 percent next year, predicted Tedesco.
In 2004, the 802.11 WLAN Working Group formed Task Group N (TGn) to develop IEEE 802.11n as a faster, longer-range Wi-Fi version.
An 802.11n system is made up of all or some of the following elements: radios, transceivers, antennas, analog-to-digital converters, and a signal processor. The system feeds the signals to the processor, which then delivers the data transmission to the network.
802.11n adds multiple-in, multiple-out (MIMO) technology—explained in Figure 1—to the earlier 802.11g technology. As is the case with its predecessor, the new Wi-Fi operates in the 2.4-GHz frequency range. It is backward compatible with 802.11b and g.
Figure 1 IEEE 802.11n adds MIMO to the earlier 802.11g technology to improve its transmission speed and range. MIMO takes advantage of multipath interference, which occurs when transmitted signals bounce off objects and create reflected signals (in red) that take multiple paths to their destination. MIMO systems use multiple receiving and sending antennas that can fit on an add-on card. The system resolves the multiple data flows so that it can use the multipath channels as additional data paths, rather than just redundant carriers of the original signal.
The technology uses MIMO to improve its transmission speed and range. MIMO takes advantage of what has been one of radio communication's oldest problems, multipath interference. This occurs when transmitted signals bounce off objects and create reflected signals that take multiple paths to their destination.
With standard antennas, the signals arrive out of phase and then interfere with and cancel out one another. MIMO systems use multiple receiving and sending antennas that can fit on a Wi-Fi add-on card.
By resolving data from the multiple flows, MIMO can use the multipath channels as additional data paths, rather than just redundant carriers of the original signal, thereby increasing bandwidth and transmission range, explained Intel engineer James Wilson.
The receiving system processes the multiple data flows and puts them in the proper order.
Moreover, 802.11n can bond two or more of MIMO's 20-MHz channels together to create even more bandwidth. Thus, 802.11n has a theoretical maximum throughput of 600 Mbits per second and a transmission range of up to 50 meters.
For security, 802.11n relies on earlier technologies such as the 802.11i-based Wi-Fi Protected Access.
802.11n is implemented on its own processor. Atheros Communications, Broadcom, and Marvell are already making 802.11n chipsets, and Intel plans to release a draft 802.11n processor that will become part of next year's Santa Rosa chipset for the fourth-generation Centrino notebook architecture.
Belkin, Buffalo Technology, D-Link, Linksys, and Netgear plan to use 802.11n chips in equipment such as routers, access points, and network interface cards (NICs).
According to In-Stat's Tedesco, vendors see the technology being used initially in PCs and laptops, whose owners have proven willing to spend more for additional bandwidth, rather than in consumer electronics such as PC-based home-entertainment systems.
However, this could change as 802.11n costs fall, according to Rolf De Vegt, MIMO vendor Airgo's senior director of business development.
As has been the case with many other important technologies, the development of an IEEE 802.11n standard has been a difficult process, featuring a battle between industry groups.
TGnSynch, which disbanded in 2005 in favor of the Enhanced Wireless Consortium (EWC), was an industry group that included Atheros, Intel, Nortel Networks, Panasonic, Philips Electronics, Qualcomm, Samsung, and Sony.
The group supported the use of MIMO in the 2.4- or 5-GHz frequency range, with two 20-MHz channels bonded together to form a 40-MHz channel that would increase bandwidth to 600 Mbps.
The World-Wide Spectrum Efficiency (WWiSE) group, which also disbanded last year, included Broadcom, Conexant Systems, Motorola, STMicroelectronics, and Texas Instruments, and was led by Airgo Networks.
WWiSE contended that 802.11n should be based on 2x2 MIMO, which entails two transmitters and two antennas operating in a single 20- or 40-MHz channel, with no bonding, in the 2.4- or 5-GHz frequency ranges.
The group also advocated adding spatial-division multiplexing as a way to split up multiple transmission streams by sending them to different antennas.
WWiSE said this approach would be backward compatible with more Wi-Fi versions, not interfere with existing 802.11 LANs, and yield data rates up to 540 Mbps.
Because the approach is based on technology that Airgo is already using, proponents said it is mature and could be turned into a standard immediately, enabling vendors to get products to market sooner.
Faced with the inability to reach agreement in separate groups, TGnSynch and WWiSE disbanded. Various members—including Atheros, Broadcom, Intel, and Marvell—then formed the EWC so that they could work out their differences and reach a compromise enabling users to select features of either approach in many cases, according to Atheros chief technology officer Bill McFarland.
Proponents of two other 802.11n proposals—one from Mitsubishi and Motorola and one from Qualcomm—have abandoned their efforts and joined the EWC.
The 802.11 Working Group recently voted on the EWC's compromise approach but only about 46 percent of the voters approved the draft, far short of the 75 percent required for approval.
The opposition was led by WWiSE leader Airgo, which has long shipped MIMO equipment. Airgo, which has not joined the EWC, continues to support its own approach and, as an early vendor of the technology, has a strong influence over some other vendors, including Atheros and Jungo.
One major source of disagreement is over 802.11n's 40-MHz channels. Airgo claims that the EWC's plan to bond two 20-MHz channels will cause interference with existing Wi-Fi networks, explained company CEO Greg Raleigh.
"A new vote on the standard may not occur soon because the IEEE's TGn is dealing with 12,000 comments on the draft proposal," said Broadcom media relations manager Heather Roberts.
"Although there remains a fair amount of work to do on the specification, we expect official ratification in the second half of 2007," she added.
However, said Atheros' McFarland, the TGn won't issue a second draft until November and thus won't be able to distribute the mail ballot until January 2007, meaning 802.11n might not become a standard until early 2008.
Numerous vendors are already shipping prestandard 802.11n products. For example, according to In-Stat, Belkin, Buffalo, D-Link, Linksys, and Netgear have shipped about 300,000 routers, client NICs, and access points—powered by Atheros, Broadcom, and Marvell chipsets—all based on the IEEE's current 802.11n draft.
Vendors hope to begin making money from the technology now and stake out a strong market position for the future, said Craig Mathias, principal with the Farpoint Group, a wireless-technology advisory firm.
Roger Entner, vice president of wireless telecommunications for market research firm Ovum, expressed concern that the prestandard products might not conform to the final standard and thus will be incompatible with subsequent products that do.
However, McFarland contends the final standard won't differ significantly from the current draft. Moreover, he added, vendors could easily bring products into compliance with the final standard via firmware upgrades.
Some prestandard 802.11n products can reach the technology's promised bandwidth and range when used with equipment, such as access points and NICs, from the same vendor. Performance can suffer with equipment from different companies, though, because vendors don't have to implement the draft standard in exactly the same way.
For example, eWeek Labs analyst Andrew Garcia said he recently found that communications between a Belkin NIC running an Atheros 802.11n chip and a Buffalo router running a Broadcom chip occurred only at 70 to 90 Mbps.
Proponents say that 802.11n's predicted real-world speeds of 100 Mbps, the same as Fast Ethernet, eventually will make it attractive for office and in-home networks.
However, said In-Stat's Tedesco, 802.11n's main challenge is the lack of a standard, caused by vendor infighting.
Farpoint's Mathias said many vendors are happy with the current situation. Companies offering prestandard 802.11n products want their technologies to win in the marketplace before the IEEE can adopt a standard that might differ from their approaches, he explained.
And because 802.11n product sales are already growing rapidly, Mathias noted, there is no pressure on vendors to agree on a standard.
Still, he added, the IEEE will adopt a standard eventually, at which point 802.11n will dominate the Wi-Fi marketplace. "With the technology's performance advantages," he said, "802.11a, b, and g will disappear."
"802.11n is the future," said Tedesco, "and eventually, all product segments will shift to this standard."
The three major commercial Wi-Fi standards thus far have been IEEE 802.11 a, b, and g.
In 1999, the IEEE approved 802.11b, which operates in the 2.4-GHz frequency range and offers maximum data rates of 11 Mbits per second and a transmission range of 30 meters.
802.11a, approved the same year, works in the 5-GHz frequency range and provides maximum data rates of 54 Mbps and a transmission range of 30 meters.
Ratified in 2003, 802.11g operates in the 2.4-GHz frequency range (making it backward compatible with 802.11b) and offers maximum data rates of 54 Mbps and a transmission range of 30 meters.