14 DAY TRIAL // The 802.11n 100Mbps wireless LAN standard is nearing completion, and it seems that the IEEE working group is preparing for the launch of a new 1Gbps WLAN standard project, or, to put it in other words, gigabit Wi-Fi. A Very High Throughput (VHT) Study Group was formed last year for the exploration of the possibility of making 802.11 WLAN standard support gigabit capacity. There are two frequency bands the group focuses on, namely a high-frequency 60GHz, fit for relatively short ranges, and under-6GHz band for the same ranges as those of the current WLANs in the 5GHz band, 802.11a and 11n.
“The basic idea right now, and that's subject to change, is that the 'maximum mandatory mode' on a single link would be [at least] 500Mbps,” says Tushar Moorti, director of systems architecture for chipmaker Broadcom's WLAN Business Unit. “But the further requirement is that [an access point] device that supports VHT would be able to sustain multiple links, so the aggregate would be over 1Gbps.”
Today's WLAN products developed on the draft 2 802.11n standard can offer throughput of 130Mbps to 150Mbps and, in rare cases, of even 170Mbps. “I think we'll see a [VHT] standard in two years, and WLAN products with more than 1 gigabit per second within three years,” says Craig Mathias, principal for wireless consultancy Farpoint Group. “That is absolutely phenomenal.” The study group has been finalizing a proposal for the creation of a new task group to work further on crafting a standard. Still, it has to be accepted by the 802.11 Working Group, which oversees the entire WLAN standard.
“It's the next-generation technology for wireless LAN, in the same sense that 11n was the follow-on to 11a/b/g,” says Broadcom's Moorti. One version of the IEEE proposal projects the completion target date of the standard somewhere in the 2012-13 timeframe. Although it may sound optimistic, there are a lot of big players that have been active in the group, including Atheros, Broadcom, Intel, Marvell, Motorola, and Nortel.
The proposal states that VHT “will allow a corporate or home user to roam from high-throughput dense cells to wider area networks in a seamless manner, while maintaining full support for the installed base security, management, diagnostics and backbone infrastructure.” Also, VHT will be compatible with existing and emerging 802.11 standards, including 11i for security, and 11s for mesh networking.
Vendors like BridgeWave and DragonWave already offer gigabit wireless Ethernet radios, yet they are used mainly for point-to-point links over several miles, and for backhauling cellular traffic, and not for building wireless LANs. The high-capacity wireless links in the 60GHz band came into the spotlight earlier this year at the Consumer Electronics Show in Las Vegas, as there were some wireless products, built on SiBeam's multigigabit wireless chip, capable of streaming up to 4Gbps at up to 30 feet.
The speed boost will be achieved through parallelized data transmissions
Little is known on why the VHT group has been taking into consideration the two frequency bands, yet Moorti says that the possibility that the group would propose the standard for both of them exists, since they might be seen as complementary.
“At this point, we're not sure whether or not the 60GHz band will provide enough range to support enterprise WLANs, but it is certainly worth exploring,” says Ajit Jha, WLAN Product Manager at Proxim Wireless. “The 6GHz band is also worth exploring, since it provides the key benefit of backwards compatibility with existing 802.11 a/b/g/n WLANs.”
Although the 60GHz band has a lot of unused spectrum available and VHT considers it well-suited for very-high-speed, the signal would have difficulties in penetrating walls or other obstacles because of the high frequency. That would cause applications to span short distances like one or two rooms at home or the office. “It used to require all kinds of exotic silicon, but now you can do this in CMOS,” says Mathias. “But because of the problem of radio propagation, you have to be very directional, and you need sophisticated antenna arrays.”
According to Moorti, “The under-6GHz band is about multi-user technology to improve overall network performance.” He also says that there is less available spectrum on the under-6GHz band, which forces VHT advocates to look for different methods of boosting throughput beyond 11n, ranging from advanced digital processing to more mature antenna technology.
The parallelization of data transmissions between a VHT access point and its associated clients is one technique taken into consideration. According to Moorti, current access points share limited throughput and work in a serial manner with associated clients. The serial transmission would limit the possibilities of a VHT access point supporting 500Mbps as well. “[But] if you can parallelize those guys, and send to them at the same time, each user gets the full 500Mbps,” Moorti says. “All the traffic would flow at the full rate.”
According to InfoWorld, the VHT Study Group and the 802.15.3c task group have already been talking about this issue. The 802.15.3c task group works on wireless personal-area networks, and has an eye on the 60GHz band as well. While some consider the discussion a possible conflict, Moorti sees it as an attempt to work on resolving possible issues likely to appear from the coexistence of the two technologies. “From what I understand, things are progressing,” he says. “I don't see any problems that would prevent either group from moving forward.”