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Meet W-USB...The Next Generation of Wireless Interconnect

Fri, 05/28/2004 - 6:17am

The homes of tomorrow will be digital, wireless, and wideband. And both wireless USB and Ultra Wideband technologies will have a large role.

By Rafael Kolic

In the digital home of the not-too-distant future, it is expected that people will be sharing photos, music, video, data, and voice among networked consumer electronics, PCs, and mobile devices throughout the home and even remotely. For example, users will be able to stream video content from a PC or consumer electronics device — such as a camcorder, DVD player or personal video recorder — to a flat screen HDTV display without the use of any wires.

A leading candidate for enabling this capability is called UWB. This is a wireless technology designed for short range, WPANs. This year, UWB is making the transition from laboratories to standardization, a key step toward the development of real-world products.

Recent industry achievements with UWB range from researchers showing proof-of-concept demos, formation of a SIG (Special Interest Groups) to define the Phy and MAC, and demonstrating the worlds first multi-band OFDM silicon. In the U.S., the Federal Communications Commission has mandated that UWB radio transmission can legally operate in the range from 3.1 GHz to 10.6 GHz, at a transmit power of – 41dBm/MHz. Japanese regulators have issued the first UWB experimental license allowing the operation of a UWB transmitter in Japan.

The Common UWB Radio Platform

In the forefront of UWB technology development is the concept of a UWB radio spanning many different applications and industries. This concept, which has been coined the "Common UWB Radio Platform," creates the first high-speed wireless interconnects. UWB technology offers a combination of performance and ease of use unparalleled by other interconnect options available today.

The UWB radio, along with the convergence layer, becomes the underlying transport mechanism for a variety of applications, of which some are currently only wired. Some of the more notable applications that would operate on top of the Common UWB Radio Platform would be USB, IEEE 1394, and UPnP.

UWB is defined by the PHY and MAC layers, which represent the radio portion. These layers are being addressed by the IEEE as well as the Multiband OFDM Alliance, an industry group with more than 120 participants supporting a common technical proposal for UWB. On top of the MAC is the convergence layer, which is being addressed by WiMedia Alliance, an industry association formed to promote personal-area range wireless connectivity and interoperability among multimedia devices. On top of the convergence layer are the applications, such as WUSB, Wireless 1394, and UPnP.

W-USB is expected to be the first application to run on Ultra Wideband radio. Ultra Wideband can be thought of as replacing the physical wire on which USB runs today. Presently, wired USB has significant market segment share as the cable interconnect of choice for the PC platform. But the need for the cable itself points to convenience and usability challenges for users. By unleashing peripheral devices from the PC while still providing the performance users have come to expect from wired USB connections, UWB promises to gain significant volume in the PC peripheral interconnect market segment.

Usage Scenarios

Digital Home - Requirements for the digital home include high speed data transfer for multimedia content, short range connectivity for transfer to other devices, low power consumption due to limited battery capacity, and low complexity and cost due to market pricing pressures and alternative wired connectivity options. Playback of video from a camcorder to an HDTV is one scenario. Another model is the ability to view photos from the user's digital still camera on a larger display. UWB allows for high data throughput with low power consumption for distances less than 10 meters — about 30 feet, very applicable to digital home requirements. The fastest data rate over UWB is now an impressive 480 Mb/s.

Consumer Electronics - The consumer electronics environment will have high expectations for performance. Many consumer usage models will center on demanding streaming media distribution using compression algorithms. Typical video delivery with standard SDTV/DVD can consume between 3 to 7 Mb/s, while HDTV can require between 19 to 24 Mb/s. A point distribution technology like Wireless USB with its projected effective bandwidth of 480 Mb/s could manage multiple 20+ Mb/s streams. Host buffering could enable a network backbone to effectively distribute content to all distribution hosts, enhancing the quality experience for all users. The Wireless USB specification will be an effective way to ensure both convenience and quality of service meets typical consumer entertainment expectations.

Business and Office - Connectivity issues and other inconveniences of wired connections can hurt productivity and slow the adoption of new devices within the work environment. Users of mobile computers and PDAs particularly face connection challenges as they move from place to place and want to use printers and other devices. W-USB could simplify their lives while providing a time-saving, high-speed connection that enhances productivity in the office environment. With W-USB, for example, a worker could simply approach the nearest printer or multi-function device and print the needed documents. This would alleviate many of the hassles today involved in adding a printer and finding it among multiple network printers.

A Closer Look at the Technology

A UWB transmitter works by sending billions of pulses across a very wide spectrum of frequency several GHz in bandwidth. The corresponding receiver then translates the pulses into data by listening for a familiar pulse sequence sent by the transmitter. Specifically, UWB is defined as any radio technology having a spectrum that occupies a bandwidth greater than 20% of the center frequency, or a bandwidth of at least 500 MHz.

UWB can take the form of either a single-band approach or a multi-band approach. The multi-band OFDM approach allows for good coexistence with narrowband systems such as 802.11a, adaptation to different regulatory environments, future scalability and backward compatibility.

With the multi-band OFDM approach, the available spectrum of 7.5 GHz is divided into several 528 MHz bands. This allows the selective implementation of bands at certain frequency ranges while leaving other parts of the spectrum unused. The dynamic ability of the radio to operate in certain areas of the spectrum is important because it can adapt to regulatory constraints imposed by governments around the world.

The band plan for the MBOA proposal has five logical band groups (see Figure 1). Band group 1, which contains the first three bands, is mandatory for all UWB devices and radios. Multiple groups of bands enable multiple modes of operation for MultiBand OFDM devices. In the current MultiBand OFDM Alliance's proposal, bands 1-3 are used for Mode 1 devices (mandatory mode), while the other remaining band groups (2-5) are optional. There are up to four time-frequency codes per channel, thus allowing for a total of 18 piconets with the current MBOA proposal. In addition, the proposal also allows flexibility to avoid band group 2 when and if U-NII (Unlicensed-National Information Infrastructure) interference, such as from 802.11a, is present.


Figure 1. Multiband OFDM Frequency Band Plan

OFDM Modulation

The information transmitted on each band is modulated using OFDM. OFDM distributes the data over a large number of carriers that are spaced apart at precise frequencies. This spacing provides the orthogonality in this technique, which prevents the demodulators from seeing frequencies other than their own. The benefits of OFDM are high spectral efficiency, resiliency to RF interference and lower multi-path distortion.

By using OFDM modulation techniques coupled with multi-banding, it becomes easier to collect multi-path energy using a single RF chain and allows the receiver to deal with narrowband interference without having to sacrifice sub-bands or data rate. These advantages relate to the ability to turn-off individual tones and also easily recover damaged tones through the use of forward error correction coding, bit interleaving, and other techniques.".

Wireless USB Technology Requirements

Topology - The fundamental relationship in W-USB is the "hub-and-spoke" topology, as shown in Figure 2. The host initiates all the data traffic among the devices connected to it, allotting time slots and data bandwidth to each device connected. These relationships are referred to as clusters. The connections are point-to-point and directed between the W-USB host and W-USB device. The main difference here from wired USB case is that there are no hubs present in the connection topology. The W-USB host can logically connect to a maximum of 127 wireless USB devices.


Figure 2. W-USB topology

W-USB clusters coexist within an overlapping spatial environment with minimum interference, thus allowing for a number of other W-USB clusters to be present within the same radio cell. In addition to providing wireless connectivity, W-USB is planned to be backwards compatible with wired USB and provide bridging to wired USB devices and host. A method will be required to enable the exchange of data between clusters or devices not related to the same host. This method may be a second level connection between two hosts (i.e. a network) or some method of transferring data between two clusters not managed by the same host.

W-USB implementations are expected to follow the wired USB connectivity models as closely as possible to reduce development time. A dual-role model would enable a device to also provide limited host capabilities. This model would allow mobile devices to access services with a central host supporting the services (i.e. printers and viewers). It would also allow devices to access data outside an existing cluster to which they are currently connected, by creating a second cluster as a limited host.

Performance - W-USB performance, at launch, must provide adequate bandwidth to meet the requirements of a typical user experience with wired connections. The 480 Mb/s initial target bandwidth is comparable to the current wired hi-speed USB standard. With 480 Mb/s as the initial target, the W-USB specification will allow for generation steps of data throughput. The specification intends for W-USB to operate as a wire replacement with targeted usage models for cluster connectivity to the host and device-to-device connectivity at less than 10 meters.

Radio System Power - Radio system power (power used only by the radio) will be expected to meet the most stringent requirements, particularly where mobile and handheld battery life is important. A typical iPAQ PDA uses between 250 and 400 mW without a radio connection. Cellular phones typically use 200 mW to 300 mW with the primary WAN radio. Adding a W-USB radio should not increase power requirements such that battery life would be reduced more than by existing wireless technologies employed today. Battery-powered operation requires reasonable battery life — three to five days for highly mobile devices and several months for intermittently used devices like remote controls. W-USB based on MBOA radio will strive to meet this standard. The power target for W-USB radio is expected to be between under 250mW at introduction and will drive shortly thereafter to a target of 100mW over time.

Power Management - Creative power management techniques can be used to preserve battery life. The radio, for instance, could sleep when possible and listen to wake on request. Power could also be conserved by stopping power draining operations during idle periods.

Summary

Researchers and engineers are working to deploy UWB technology in the near future. Device manufacturers in the PC, mobile, and consumer electronics industries will have the opportunity to choose UWB as a physical layer and will be able to take advantage of the low power and high bandwidth this technology provides. In particular, the Common UWB Radio Platform will be a critical step in enabling advanced communications. Of the various applications expected to run on Ultra Wideband radio, W-USB is considered by many to be the most likely candidate for early implementation.

About the author
Rafael Kolic is a technology marketing manager in the Communications Technology Lab, part of Intel's Corporate Technology Group. Since joining Intel in 2000, he has worked on a number of projects involving Ultra-Wideband, USB 2.0, UPnP*, and several other technologies. Kolic has also performed research in the area of power electronics. He holds an M.E. in electrical engineering and a B.S. in electrical and computer engineering from the University of Florida.

Glossary of Acronyms

DVD - Digital Video Disk/Digital Versatile Disk
HDTV - High-Definition Television
MAC - Media Access Control
OFDM - Orthogonal Frequency-Division Multiplexing
PAN - Personal Area Network
PC - Personal Computer
PDA - Personal Digital Assistant
PHY - Physical Layer
SDTV - Standard Definition Television
UPNP - Universal Plug-and-Play
USB - Universal Serial Bus
UWB - Ultra Wideband
W-USB - Wireless USB
WAN - Wireless Area Network
WPAN - Wireless Personal Area Network

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