High-Definition Video over Wi-Fi
Wireless chips could soon manage a gigabit of data per second.
Several next-generation wireless schemes, including WiMax, 4G cellular technology, and others that explore previously untapped parts of the radio spectrum, promise faster, better connectivity through the air. But these standards still face business and technological challenges. In the midst of all this, a startup called Quantenna plans to improve wireless connectivity simply by supercharging Wi-Fi. With this goal in mind, the company, based in Sunnyvale, CA, will release chip sets in the coming months that can handle a gigabit of data per second over Wi-Fi–enough to stream high-definition video and other content over short distances.
“In my experience,” says company CTO Andrea Goldsmith, who is also a professor at Stanford University, “you can’t have a successful wireless company unless you’re standards based.”In other words, Goldsmith believes that it will be a lot easier to roll out technology that is compatible with Wi-Fi than with chips that use relatively uncharted frequencies. (See “High-Def Is in the Air.”) The reason is simple economics: fewer companies may be willing to embrace an unproven technology rather than a well-established one.
Quantenna’s chips use a specific Wi-Fi standard called 802.11n. (See “Faster, Farther Wi-Fi.”) Among other things, 802.11n allows up to four antennas to be used to transmit data, and four to receive it. Compared with Wi-Fi chips with a 2x2 antenna scheme–the most common type on the market today–Quantenna’s chips are twice as powerful, Goldsmith says. “For the same data rates and same applications, you can go twice the distance.”
But it is the specific way in which Quantenna’s multiple antennas work that set them apart from existing Wi-Fi technology: the antennas form a direct wireless link between enabled devices, using a technique called beam forming. Unlike traditional radios that send and receive data in all directions, a beam-forming radio locates a receiver and concentrates the signal into narrow paths for each data stream. When this sort of wireless link is formed, data can be transmitted at much faster rates. It could wirelessly connect components of home theaters, streaming high-definition content between, for example, a DVD player and a television. Currently, beam-forming technology is used in wireless chips that operate at between 60 and 100 gigahertz–far beyond the 5- and 2.5-gigahertz frequencies used by Wi-Fi.
Beam forming at Wi-Fi frequencies couldn’t happen without the 4x4 antenna scheme , says Goldsmith. This is because antennas don’t just send and receive data: they can also adapt to the channel characteristics and avoid interference. In fact, if there are two data streams, in a 4x4 antenna, then there will be extra antennas to optimize the beam’s path and to correct for disruption. “Having four antennas allows you to mitigate the impact of interference and point the beam in the optimal directions,” Goldsmith says.
Beam forming is not new, but Goldsmith and her engineers faced new challenges in ensuring that the technology would comply with the Wi-Fi standard. For one thing, they had to make sure that the chip would adjust its power levels at the antennas receiving the data quickly enough–within four microseconds, as dictated by the standard–when it went from standard Wi-Fi mode to beam-forming mode. Without giving details, Goldsmith says that her team developed algorithms that were able to handle the power adjustment more rapidly.
Other tricks include developing beam-forming algorithms to manage all the environmental information, and making sure that the connection can be corrected quickly enough when interference is detected, so that there’s no lag in wireless speed.”Beam forming is indeed a good way of improving capacity,” says Jan Rabaey, a professor of electrical engineering and computer sciences at the University of California, Berkeley. “It’s definitely something that will happen.”
Rabaey notes, however, that antennas operating at Wi-Fi frequencies must be separated by centimeters, due to the properties of the frequencies used, which imposes a lower limit on the size of the antenna arrays that can be used. Still, he suspects that this sort of chip could eventually find its way into laptops and even PDAs, if the chips can be engineered to fit.
To start with, Quantenna plans to focus on getting its chips in base stations and flat-screen televisions, considered the next big frontier in wireless. The company is working with traditional home-networking vendors, says Goldsmith, and its products will be available in Asian markets in the coming months.
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