09 August 2011
60GHz band emerges as a complement to wifi
The emergence of smartphones and tablet computers alongside digital cameras, tvs and laptops means most interactions will soon be between devices, rather than between a device and the internet. Looking to enable these links, the Wireless Gigabit standard is being aimed as a broad interface that will support key computing and consumer electronics protocols without the need for cabling.
Wireless Gigabit (WiGig) is a 60GHz point to point complement to wifi that will enable data to be transmitted at up to 7Gbit/s. And, by mapping the functionality of key interfaces over the air, the standard will support USB, PCI Express, DisplayPort, HDMI and SDIO. WiGig is being standardised by the IEEE as 802.11ad.
However, wifi continues to evolve. IEEE802.11n can support four spatial streams at up to 600Mbit/s, while the next wifi standard – IEEE802.11ac –will support 1Gbit/s.
WiGig supports wifi and point to point interfaces at 60GHz, but will also be implemented in dual band designs with 5GHz wifi and in tri band radios that add 2.4GHz wifi. People will communicate with the internet using wifi, but will shift to 60GHz WiGig when it comes to inter device communication, claimed Ali Sadri, chairman and president of the Wireless Gigabit Alliance.
While the 60GHz band has been chosen partly because it is the next available license free band after 5GHz, the band is unlicensed because it attenuates radio signals heavily. Mark Grodzinsky, vp of marketing at WiGig start up Wilocity, said: "Because of absorption, you lose 15dB of gain over a kilometre." But this characteristic is useful in enabling multiple local high speed links. "WiGig at 60GHz has a 5x [user] density improvement over wifi at 5GHz," said Sadri.
The reach is several metres only if the 60GHz signal in transmitted in all directions, as with wifi. Using beamsteering however, the radio signal can be focused in a particular direction, boosting the range to match 5GHz wifi, said Sadri. And since a 60GHz signal's wavelength is 5mm, beamsteering can be supported with an antenna array: 16 or more 2 x 2mm antennas take up the same space as one wifi antenna.
Wilocity has demonstrated two WiGig devices sharing a table and operating in the same channel. "There was negligible interference between the two," said Grodzinsky. "They happened to be set up pointing in different directions but co channel interference was very low."
WiGig also consumes five times less energy per bit than wifi, according to the WiGig Alliance. Sadri claims that, for handheld devices, a WiGig chipset can consume as little as 500mW when transmitting at 2Gbit/s.
These high data rates are a direct result of the amount of frequency available at 60GHz. For 2.4GHz wifi, 80MHz of spectrum is available, separated in 20 and 40MHz bands. WiGig divides the spectrum – 57 to 64GHz – into four channels, each effectively 1.7GHz wide (see fig 1).
Wider channels means a simpler modulation scheme can be used compared to wifi. IEEE802.11n uses 64 QAM (quadrature amplitude modulation) to cram data within the channels. In contrast, WiGig uses 16 QAM. "This is much less complicated and you get 7Gbit/s," said Grodzinsky. "There is no black magic when it comes to pure speed; it just translates from the amount of spectrum you have available."
A WiGig chip comprises two functional blocks: a media access controller (MAC) and the physical layer (PHY).
The PHY supports two modulation schemes: orthogonal frequency division multiplexing (OFDM) and a single carrier scheme. The single carrier, suited to lower power applications, achieves a data rate up to 4.6Gbit/s, while OFDM enables 7Gbit/s.
"The MAC protocol has specifications for network management, packet flow, beam refinement and congestion avoidance," said Craig Ochikubo, general manager of Broadcom's wireless personal area networking division.
WiGig also includes protocol adaptation layers (see fig 2) that run on the MAC and implement the various interfaces – PCI Express, the display interfaces HDMI and DisplayPort, usb and SDIO. "You've got WiGig over the air, but encapsulated in the data, you can have HDMI packets, for example," said Grodzinsky.
Wilocity has partnered with Qualcomm Atheros to develop a wifi/WiGig tri band solution. Wilocity's 60GHz silicon works alongside Qualcomm Atheros' wifi ic. "On a half mini card – the traditional wifi product that goes into a notebook or a pc – you'll see the Atheros chip operating at 2.4 and 5GHz – that does 802.11n and Bluetooth – and you'll see the Wilocity chip that does 60GHz," said Grodzinsky.
Wilocity has a 60GHz radio module alongside its ic, whereas Qualcomm Atheros' design is a single chip that integrates the rf and baseband. But Wilocity sees no reason why future WiGig designs will not integrate the two radio standards on chip.
One challenge highlighted by Grodzinsky with a tri band design is ensuring a fast handover when a user moves out of range of a 60GHz link and reverts to wifi. "In order for this to be a useful technology, you want to make sure it [the handover] is transparent to the user when you are moving from 60GHz," said Grodzinsky. Since applications such as video transfers are sensitive to latency, the session transfer must occur within milliseconds, he said.
The first joint product is being aimed at the notebook and tablet devices. "For customers, it is just swapping one half mini card [with 802.11n] for another [802.11n and WiGig]," said Srinivas Pattamatta, senior product marketing manager at Qualcomm Atheros. "Regardless of whether it is one or two chips, they regard it [wifi and WiGig] as a swappable solution."
Qualcomm Atheros and Wilocity expect first product samples imminently, with production samples available by year end. Product shipment is expected from mid 2012. The joint design will operate at up to 4.6Gbit/s, says Grodzinsky. The speed is based on overall system design considerations involving complexity, power consumption and cost tradeoffs.
Broadcom has yet to detail its plans, but says it has ongoing WiGig developments. "One key application is wireless docking, which will enable a device to connect wirelessly to, and use, a high definition display," said Ochikubo. "As computing platforms become lighter and thinner, they drive the need for separate wireless docks with the same interfaces and capabilities of bulky computing machines used today for content creation."
Sadri expects a variety of uses for WiGig. "Anything that wifi cannot do today, that is what WiGig will do first." But he also sees an eventual role for WiGig for internet access, for example providing internet access to users in crowded venues such as conference halls.
Meanwhile, version 1.1 of the WiGig specification is now with the IEEE. "The IEEE, either at this meeting or the next, will go to sponsor ballot," said Grodzinsky. "That is a much higher level of maturity than even 802.11n was at before we started certifying and shipping product."
As for when WiGig will become a high volume market, Sadri looks at how long it has taken 802.11n since certification. "It will take a further three years – 2015," he said.