USB

USB Hits the Airwaves

Craig Szydlowski and John Blyler

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Figure 1: The WiRanger wireless USB 2.0 hub from Icron Technologies.

USB is getting a facelift through several initiatives that will provide greater freedom and convenience for connecting all types of devices. Already the most successful interface in PC history __ with more than three billion USB-enabled devices shipped worldwide in 2008, according to In-Stat __ new wireless and connectivity capabilities will help USB stay in the mainstream. Most new technologies have been in development for several years, but products are finally hitting store shelves. USB solution providers are predicting these advances will increase USB adoption in consumer electronics devices, further boosting USB volumes.

Several technologies target wireless personal area networking (WPAN) and feature either high data rates or lower power consumption, including wireless USB and low-rate WPAN. Wireless USB provides the same functionality and speed as high-speed USB 2.0, but without the cable. Low-rate WPAN provides wireless connectivity for cost-sensitive, battery-operated devices with modest data transmission requirements.

ExtremeUSB, developed by Icron Technologies, extends USB connections well beyond the standard desktop range of five meters and can be used with standard 802.11g radios. For those interested in connecting peripherals to each other without an intervening PC, USB On-The-Go enables point-topoint connections between peripherals that must share data, such as mobile phones, printers, and cameras.

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Figure 2: Wireless protocol standards spectrums. (source: Synopsys Inc.)

Cutting the Cord
Wireless USB is a new high-rate WPAN technology based on “ultra-wideband,” or UWB, radio technology. It lets devices exchange files at rates up to 480Mbps at short range (typically three meters or less), matching the speed of wired USB 2.0. Wireless USB preserves the functionality of wired USB and provides enhanced support for streaming-media consumer electronics devices and peripherals. Networks will also operate over a ten-meter range with a reduced data rate of 110Mbps.

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Figure 3: USB On-The-Go applications. (source: www.usb.org)

This technology can help tidy up the office environment by eliminating cables between PCs, printers, cameras, MP3 players, and external storage devices, such as high-density drives. Since many device types already have wired USB connections, developers can leverage software stacks as they migrate their products to wireless USB. In the future, users can discard their collection of diverse USB cables.

The home entertainment center is accumulating myriad devices and a tangle of wires between them. Although many consumer electronics are USB-enabled, such as HDTVs, game consoles, and personal video recorders, a lack of plug-n-play capability plagues stationary components. Some emerging product categories, like the entertainment PC, could gain better traction if device manufacturers embraced standard data connectivity such as wireless USB.

The wireless USB certification process is well underway, and companies are announcing their solutions. Realtek, for example, launched RTU7105, a singlechip, all-CMOS solution supporting Certified Wireless USB Device Controller and WiMedia Logical Link Control Protocol functionality. The chip integrates protocol adaptation layers, a media access controller, a baseband processor, RF transceivers, and USB2.0 and SDIO interfaces.

Laptops are being unveiled that support wireless USB, such as the ThinkPad T61p from Lenovo, which supports ultrawideband technology with an optional add-in card.

Long Range Wireless USB
ExtremeUSB was developed to enable USB devices in industrial and commercial environments where operational requirements, such as connections hundreds of meters long, exceed those of the typical desktop PC. It is fully USB compliant and is the only USB Implementers Forum approved extension solution.

The WiRanger is the world’s first wireless USB 2.0 hub, combining Icron’s patented ExtremeUSB technology and an industry standard 802.11g radio, as shown in Figure 1. The WiRanger Hub enables wireless connection of USB devices including printers, scanners, isochronous web cams, hard drives, and MP3 players.

Low-Power Wireless Options
Two wireless technologies, Wibree and ZigBee/IEEE are competing to provide low-rate WPAN solutions in a space that has been dominated by Bluetooth. They target battery-operated devices, such as mobile phones and pagers, that share relatively small amounts of data with other devices. As with Bluetooth, these emerging wireless technologies are creating new opportunities for USB dongles needed by PCs, printers, and perhaps home entertainment systems.

Several years ago, the Nokia-led Wibree Forum announced it was merging with the Bluetooth Special Interest Group (SIG), the body that oversees the wireless standard. Wibree is a Nokia-developed ultra-low-power wireless technology used for networking highly portable devices. Like Bluetooth, it operates in the 2.4GHz band, connecting devices within a tenmeter range with a data rate of 1Mbps. Some view Wibree and Bluetooth as complementary technologies: Wibree exchanges small packets of data and control information, and Bluetooth is well-suited for streaming and data-intensive applications such as file transfer. Bluetooth is widely used in phones, but Wibree may be a better solution for the smaller devices around the phone such as watches, wireless keyboards, and gaming and sports sensors.

ZigBee is a specification for a suite of high-level communication protocols using small, low-power digital radios based on the IEEE 802.15.4 standard with data rates of 250Kbps, 40Kbps, and 20Kbps. The ZigBee 1.0 specification was ratified on December 14, 2004, and is available to members of the ZigBee Alliance.

Data Rate and Distance
Developers of wireless technologies must be content with the tradeoff between data rate and distance for their target applications. In Figure 2, UWB and IEEE 802.15.4/ZigBee are compared to other wireless technologies. UWB supports the highest data rate, but distances are limited to three to ten meters. IEEE 802.15.4/ZigBee has a relatively short range and small data rate due to its use of simpler, lower-power radios that minimize power consumption.

USB On-the-Go
The USB Implementers Forum added a supplement to the standard USB 2.0 that supports point-to-point connectivity between peripheral devices called USB On-the-Go (OTG). This enhancement eases the development of user-friendly features in mobile devices, such as letting a camera communicate directly to a printer instead of using a PC as an intermediary. Other use models are shown in Figure 3.

To maintain backward compatibility to prior USB standards, OTG still maintains host and peripheral roles. When two peripherals are communicating, one will be the host and the other the peripheral, initially defined by how they are cabled together. Some OTG devices can switch roles through the host negotiation protocol without changing the cabling.

Products supporting OTG are available, including the Atmel AT90USB device, a high-end, eight-bit AVR microcontroller. It addresses embedded applications requiring USB connectivity in host and function modes. The AT90USB microcontroller also complies with the USB OTG standard, allowing dual-role devices in applications operating as either host or peripheral.

USB 3.0?
With designs well underway for the next-generation, highspeed USB specification known as Superspeed USB 3.0, users in the near future can look forward to products with gigabyte data rates.

With a faster USB link, some interesting use models could emerge. In his blog, Jeffrey Foerster of Intel writes, “Looking to the future, though, there are two primary applications of interest which could drive the need for higher-andhigher throughputs, namely wireless video cable replacement and rapid largefile download. In addition to video, the other application driving the need for high-throughput radios is rapid large file ‘synch-n-go’. How long would you wait to download an HD movie from a kiosk to your laptop or handset before getting on an airplane (a 20 GByte HD movie takes about 27 minutes at 100 Mbps and only 32 seconds at 5 Gbps speeds)? As the patience of consumers continues to shrink, having the ability to download large files quickly becomes more important.”

Craig Szydlowski is a writer specializing in business and technology. He has over 20 years of engineering and marketing experience with embedded and communications systems at Intel, IBM and Siemens.

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