How we love the Universal Serial Bus, at least those of us who remember the days of the serial and parallel cables. Jettisoning forever all that mucking about with IRQs and other technical arcana, USB allowed users to easily attach and detach printers, digital cameras, disk drives, memory “sticks” and other devices.

Now the folks that shepherd USB, the USB Implementers Forum (http://www.usb.org/), have presented the specifications for doing USB wirelessly. Soon, all those thin USB cables on your desk, lying about like snakes on hot pavement, could be sent packing as well.

The Intent of Wireless USB

The forum is designing Wireless USB (WUSB) for those devices for which a WiFi connection would be overkill, either for power consumption or just because such devices don’t need a full-fledged network address. The designers of WUSB figure that there are dozens of gadgets around the home, from printers to wireless monitors, that could benefit. Wireless personal area networking, or WPAN, is the buzzphrase coined for such collections.

Of course, Bluetooth (http://www.bluetooth.com/) has offered wireless connectivity for several years now, with middling success at best. The word on Bluetooth? It’s too complicated to set up, and too few device makers included the option in their products. However, thanks to the pretty much universal success of USB, WUSB may succeed in a mass market way where Bluetooth faltered.

“The USB brand is fairly well recognized by consumers, so we think that Wireless USB will be adapted pretty quickly,” said Jim Robillard, director of product marketing for Alereon Inc., one of a number of fabless semiconductor companies hoping for a bright future in providing WUSB chips to equipment manufacturers.

Where is Linux in all of this? Some preliminary work has been done to put the WUSB references in the Linux kernel. But when the wireless devices start hitting the virtual shelves of PriceWatch.com, will the Linux home user be able to plug-and-play? Old-timers remember the slow adoption of USB in Linux when USB started making its way into computers a decade ago. In many cases, it was the Linux community that had to write the USB drivers for devices, not the manufacturers.

But that was a long time ago, when Linux was nowhere near as pervasive. The dirty little secret these days is that, in the hardware world, Linux has fast become the operating system of choice for driver development. No longer will companies have to port their drivers to Linux. They were written in Linux.

Untether Your World

Although it’s been in development for a few years, Wireless USB only enjoyed its debutante’s ball this past May. That’s when the USB Implementers Forum published the Wireless USB Specification (http://www.usb.org/developers/wusb/docs/WUSBSpec_r10.pdf), a document that illustrates how Wireless USB should work and what manufacturers have to do to get on the bus, so to speak.

By then, of course, WUSB already had some powerful backers. In the spring of 2004, a number of companies, including Agere Systems, Hewlett-Packard, Intel, Microsoft, NEC, Philips Semiconductors, and Samsung Electronics, banded together to form the Wireless USB Promoter Group,

You should start seeing the first WUSB devices by the end of this year or early in 2006, according to Jeff Ravencraft, chairman of the USB Implementers Forum. Roughly speaking, you’ll see two kinds of WUSB products: those for your host (your computer) and stand-alone devices that come with WUSB built-in.

The former group will come first. To outfit existing computers with WUSB powers, manufacturers will start offering dongles, or host wire adapters that plug into a computer USB port. These dongles will act like WiFi access points, collecting signals from devices. You’ll also see device wire adapters, which you can place somewhere in your office and plug in all of your wire-based USB devices. The adapter then transmits data wirelessly across the room.

Then, sometime in 2006 and 2007, you should see the makers of cameras, cell phones, and music players start to incorporate WUSB into their wares. Alereon, for instance, expects to start shipping chipsets for device makers by late 2006, complete with tiny antennas 27 millimeters long and 3 millimeters thick. The company is also planning on introducing a WUSB card that can fit into a standard Flash memory slot.

Ultra Wideband

Despite the recent hoopla, the work on Wireless USB has been at least a few years in the making. What kicked off WUSB was actually an seemingly unrelated event, namely the 2002 approval by the U.S. Federal Communications Commission (FCC) of some spectrum space — nine gigahertz to be exact, from 3.1 GHz up to 10.6 GHz — for a new type of radio transmission type called Ultra Wideband (UWB).

UWB is different from almost every other type of radio transmission technique. Regular radio signals are usually modulated onto sine-shaped waves. UWB has no such carriers. Instead, UWB signals are a steady stream of small pulses of energy. A signal is transmitted by altering the expected cadence of the pulses. UWB gets its name from the fact the pulses are spread out over a wide frequency. This approach may be different, but it offers some serious throughput. Most UWB device makers claim to have achieved transfer rates of up to 480 megabits per second (Mbps) in working prototypes.

While fast, UWB devices have a limited range. When ratified in 2002, the FCC had one stipulation: UWB devices had to keep their transmissions under- 41 dBm, because other types of wireless communications (maritime radio navigation, satellite communications, and so on) also used portions of this radio space. This meant that UWB devices had to operate under the noise floor of these other devices, which in turn limited the output to about 10 meters, or about 30 feet, according to Robillard. Chip-makers could provide the guts for devices that could transmit at multi-gigabit rates, but only over short distances.

As it happened, this was perfect for the keepers of the USB standards, who were allready searching for a way to do USB wirelessly. USB was originally created as a universal cabled connection pathway for peripheral devices, designed to replace parallel, serial and PS/2 conduits. Since its introduction, USB has achieved near universal acceptance, counting over two billion implementations. The latest version of wired USB, USB version 2, achieves a throughput of 480 Mbps.

“We knew that consumers had a lot of high data-rate content. All the devices that they were using were storage devices: the cell phone, camera, the camcorder, the PDA. They are all storing large amounts of content and users want to move that content quickly,” Ravencraft said. “For high-data rate wireless personal area networks, UWB was a perfect fit.”

To be specific, WUSB does not use traditional UWB. A lot of companies, such as Robillard’s Alereon augmented UWB with the Orthogonal Frequency Division Multiplexing (OFDM) modulation method, or Multiband OFDM, which is also used by WiFi. OFDM is not pure UWB in that it divides up the frequency into 128 sub-bands. The benefits to this approach is that the signals can be tweaked for each country, Robillard said. (In the U.S. the transmission range will be between 3.1 to 5.7 Ghz). You can “sculpt to your transmit spectrum,” Robillard said.

Another advantage OFDM supposedly carries is that it requires less processing power than raw UWB. UWB, in general, has excellent power conservation qualities, but an OFDM unit can draw as little as 300 mW, a thousandfold decrease from WiFi power requirements, Robillard said. Such a small appetite is good news for mobile devices living off tiny batteries.

Robillard said that OFDM uses even less power than even raw UWB, thanks to the fact to the fact that the signal is converted to digital early in its acquisition. However, UWB purists, notably the members of the UWB Forum, also claim that their approach uses less power than OFDM, since their approach — also in the milliwatt range — does not require digital conversion at all. (This micro-feud takes an another interesting dimension: the Bluetooth Special Interest Group has decreed it will use the UWB as its radio carrier, while the USB Implementers Forum has put its weight behind OFDM.)

Linux and the Specs

When it comes to adoption by the computer industry, WUSB has one huge advantage: it can use a lot of what has already been developed for USB itself. The WUSB format plans to use the same architecture as the USB format itself.

“The USB drivers available today — the storage class, the video device class, the audio class— those driver classes will look virtually the same,” Ravencraft said.

For end users, a WUSB device should act exactly like a USB device, except that you actually do not have to plug it in.

Although you can attach multiple USB devices to computer, USB itself is not like a standard bus, one with multiple devices competing for resources on one channel (like say ATA). Rather, the topology resembles a tree, in which devices are connected to a hub in point-to-point fashion, according to the book Linux Device Drivers, Third Edition (O’Reilly Media, Inc.) written by Jonathan Corbet, Greg Kroah-Hartman, and Alessandro Rubini.

In this setup, the host adapter, usually in the desktop computer itself, does all the heavy lifting, Robillard said. The device’s USB driver is rather simple; the host adapter coordinates the traffic between all the devices, granting each device the permission to send data. The Linux kernel has a subsystem, called the USB Core, to do most of the interface work.

Like its wired cousin, WUSB runs on a hub and spoke model. A WUSB host can logically connect up to 127 devices and will communicate with each of them via polling. To connect, a device sends a message to the host at pre-specified time, carrying an authentication number and security keys. The host then assigns the end device a unique address.

Many other aspects to Wireless USB are identical to USB. Bandwidth allocation is one of them, as is the format for piping the data. In fact, WUSB was designed to be backward compatible, meaning you could plug your older USB devices into a device adapter and have the data traverse the wireless portion unimpeded.

Hot to Trot

When it was launched, USB was celebrated for being hot-pluggable, meaning you didn’t have to reboot your computer merely to get it to recognize a device. And WUSB, of course, will do even better in this regard. It will have to: devices, buried in their owners’ pockets, will enter and leave rooms all the time. Both the host and the device have protocols to detach the device from the network, and the host has the prerogative to drop a device if it doesn’t respond in a set period of time. A device can only connect to one USB host at anyone time, forming a master-slave-like relationship.

To maintain security, WUSB will also work very much like USB itself, in that “Connection-level security between devices will ensure that the appropriate device is associated and authenticated before operation of the device is permitted,” wrote Rafael Kolic, a technology marketing manager in Intel’s Corporate Technology Group, in a white paper about the topic (http://www.deviceforge.com/articles/AT9015145687.html).

One thing that WUSB doesn’t do is power up devices. Tease apart a USB cable and you’ll find four wires, two for signals and two for power. Needless to say, you can’t power up or charge a device via Wireless USB.

Work to be Done

Though much of the heavy lifting has been done by the USB folks, don’t be fooled: much work still must be done to prepare Linux for WUSB. While Wireless USB will be transparent in many ways to Linux, some aspects will need attention, either by device drivers or by the kernel itself, including variable transfer speeds, authentication, and packet sizes.

That work is still to be done.

“It is pretty quiet right now, mostly because the community has just the specification and not prototype hardware,” said William Weinberg, an open source architecture specialist for Open Source Development Labs, which coordinates the development of Linux kernel. “Typically, the way development proceeds with any subsystem is with something that actually runs. That is especially true for Linux.”

Some preliminary work has been done. In June, developer David Brownell posted a set of declarations on the Linux USB developer’s (http://marc.theaimsgroup.com/). The declarations described new requests, descriptors, and bitfields. Brownell’s patch has been rolled into the 2.6.13 tree of the Linux kernel.

The patch “teaches Linux about the various new descriptors and host-visible messages that will be involved,” wrote Linux developer David Brownell on the list. Kroah-Hartman clarified by email that the patch added the proper #defines and structures to the kernel USB header file. The patch paves the way for someone else to come along and provide the USB support for the Linux kernel. (Rumor has it that at least one company is writing a Linux host adapter driver, though it is keeping the work under wraps until the official unveiling).

On the device side, Linux drivers should be easier to come by, since many device makers now use Linux as the primary platform for developing device drivers.

“As the device manufacturers do their[ development] internally, they’re increasingly using Linux as part of their process,” Weinberg said. Alereon, for instance, uses Linux for development. The company provides with its chipsets a software developer’s kit with a device driver, associated utilities and example code, all for Linux. The device driver code is code itself Native C and is agnostic “as possible” when it comes to operating system and processor architecture.

“Our native development is Linux, so we will have Linux drivers right out of the box,” Robillard said.

Permanent Link

Courtsey :  Joab Jackson

Comments (1)

bruce gemberling said:

WUSB pronunciation So will this acronym be pronounced "woozby"...That would be awesome!!!

February 03, 2010 | url

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