Electronic Design

UWB Seizes The USB Terrain... And That's Just The Start

Ultra-Wideband is changing the way we connect peripherals and home-entertainment equipment.

I would be worried if I were a USB cable manufacturer. The beginning of the end is here—maybe not a complete end, but one that would make me rethink my product strategy.

Ultra-Wideband (UWB) short-range wireless technology is now widely available, providing wireless connections between computers and their peripherals at a rate up to 400 Mbits/s. Be sure that wireless USB is just the beginning of its applications, because it offers data rates and other qualities competing wireless technologies simply can't achieve.

THE TECHNOLOGY AND ITS APPLICATIONS
UWB is a short-range technology because of its very low power restrictions ( 41.3 dBm/MHz) and very high frequency of operation (3.1 to 10.6 GHz). Maximum range is about 15 m at best, and that drops off to 10 m as the data rate rises to 110 Mbits/s. But UWB can still support very high-speed applications up to about 480 Mbits/s at 2 to 3 m. By far, it's the fastest short-range radio technology, even beating Wi-Fi 802.11n.

The basic WiMedia standard defines orthogonal frequency-division multiplexing (OFDM). It can operate in a group of three bands that are part of a 14-band spectrum spread over the 3.1- to 10.6-GHz range (Fig. 1). Each band is 528 MHz wide, meeting the Federal Communications Commission's definition of UWB. The bands are divided into five-band groups of three bands each, except band group 5, which only has two.

Each 528-MHz band is further divided into 128 channels, called tones or bins, each 4.125 MHz wide. Each channel is then individually modulated in parallel with a piece of the data to be transmitted, as called for in OFDM. UWB uses 100 of the channels for data, while the others are pilot, guard, or blank channels.

Most UWB products operate in the first band group using the first three lower bands from 3.168 to 4.952 GHz. While the U.S. can take advantage of all 14 bands, other countries restrict use to particular bands (see the table). Data rates are set at 53.3, 80, 106.7, 160, 200, 320, 400, and 480 Mbits/s. The range varies as the distance changes between the transmitter and receiver.

Quadrature phase-shift keying (QPSK) modulation is used at 200 Mbits/s and less. The upper data rates employ dual-carrier modulation (DCM), which maps two 100-bit data streams into two 16-point constellations similar to those in quadrature amplitude modulation (QAM). The data rate also varies based on the use of various forward error correction (FEC), time-domain spreading (TDS), and frequency-domain spreading (FDS) techniques, and it switches automatically as the environment changes.

The data is transmitted in packets and time-frequency multiplexed over the three adjacent bands in a band group. For example, the first packet would appear in the 3168- to 3696-MHz band 1, the next in the 3696- to 4224-MHz band 2, and the third in the 4224- to 4572MHz band 3. The sequence is then repeated. This technique improves the multipath and fading problems typical at these frequencies.

Newer UWB chip sets offer detect and avoid (DAA) technology, which senses other signals in the vicinity of the forthcoming transmission. If a signal is detected, DAAgreatly reduces the power of the UWB transmission to prevent any interference. DAA isn't required in the U.S., but it's a key part of UWB in Japan, Korea, Europe, and elsewhere. It's usually implemented by notching out parts of the spectrum where interference may occur. This is done by reducing transmit power in a group of the OFDM channels. Typically, power can be reduced by 15 dB or more.

KILLER APPS
What do you want to do with that kind of data rate in such a short range? Companies have searched for such a killer app since the beginning. At first, it was video home networking, but the limited range squelched it. Still, UWB probably is the best technology for transmitting video just because it's the fastest available—at least for now.

Short video connections between, say, a TV set and a DVD player will work. In other words, it would replace cable for video devices like HDTV sets, PVRs, set-top boxes, and even audio, plus all the other interconnects you need these days to implement the complete home entertainment center. Eliminating the cable mess is a great goal, and consumers will pay a little extra to do it.

That leads to UWB replacing cable between PCs and their peripherals—PC to printer, PC to external hard drive, PC to video monitor, and especially laptop to any peripheral, including mice, keyboards, and joysticks. Since most peripherals use USB, why not make it a wireless USB device? In fact, that's what UWB chip companies have done.

Most companies focus their initial efforts on creating a wireless USB standard in cooperation with the USB Implementer's Forum, which manages that standard. The wireless USB standard would then be built on top of the WiMedia radio technology standard. The standards are a good match because the USB interface can go to 480 Mbits/s. The standard speed for typical peripheral connections is 12 Mbits/s, while older versions were only good to 1.5 Mbits/s.

There are several ways to implement wireless USB. The ultimate goal is to embed wireless USB into every laptop, printer, and other computer device, leading to automatic linkup and function without cables. While a few early embedded wireless USB devices exist, like some Dell, Lenovo, and Toshiba laptops, initial implementation will be with UWB wireless USB dongles or adapters. Wireless USB hubs that accept four USB connections will also be popular (Fig. 2).

Many companies are looking at UWB as the newer and faster Bluetooth 3.0. With UWB as the new Bluetooth physical layer (PHY), Bluetooth can extend its reach into other products. The Bluetooth protocol stack is simply built on top of the WiMedia platform (Fig. 3).

A protocol adaption layer (PAL) interfaces the platform to the specific technology stack. PALs can be built to make the UWB PHY and media access controller (MAC) work with IEEE 1394, HDVI, and WiNet. For instance, WiNet is the WiMedia Alliance's own unique PAL for interfacing to Internet Protocol (IP) devices, including Ethernet.

Rumor has it that UWB will be adopted as a higher-speed option to work with the 802.15.4 personal-area-network (PAN) standard. Mesh networks based on 802.15.4 and ZigBee are inherently slow, as most sensor and control nets don't need the speed. But they're a great option for applications that may need a bit more speed. UWB is inherently low-power, so it's a good fit in mesh networks. UWB also may appear in cell phones to stream photos or video.

While the WiMedia Alliance and the USB Implementer's Forum developed the standards, the WiMedia specifications have been adopted by the European Computer Manufacturer's Association (ECMA) International as ECMA 368 and 369. In turn, it has become the International Standards Organization (ISO) standard.

PRODUCT PROFILES
Spun off from UWB pioneer Time Domain, Alereon now offers the AL5100 RF transceiver and the AL5300 MAC and baseband processor chips. Also, Alereon claims its AL4000-certified wireless USB chip set is the first RF chip set to cover the full 3.1- to 10.6-GHz band. This feature will make the chips a good fit for companies building products to comply with varying Asian and European frequency standards.

Artimi's A-150 UWB MAC chip works with several UWB RF transceivers. The chip's really low power consumption suits it for laptop and cell-phone applications. Artimi also has proposed a mesh network using UWB. This makes sense with UWB's short range, since mesh can greatly improve data rates by linking nodes over shorter distances. The mesh extends the overall range while maintaining data rate.

Blue7 Communications' Windeo Intelligent Array Radio two-chip set has all of the usual features and supports up to three antennas. This improves link reliability in non-line-of-sight (NLOS) environments. It also extends the range as well as provides an overall boost in data rate. Blue7 says the chip set can achieve a 106.7-Mbit/s rate at up to 20 m, which is well beyond the capability of most other chip sets.

Bluetooth chip leader CSR recently committed to the new Bluetooth UWB PHY. Though the company doesn't have a product yet, there's no doubt we can expect to see an advanced Bluetooth UWB chip set in the near future.

Focus Enhancements, which makes video decoder chips, is primarily interested in UWB for video applications. Its Telaria TT1013 UWB chip operates from 3.1 to 7.4 GHz. The radio and MAC baseband are in one chip, which can interface with almost anything. As a result, it can be used in all UWB applications, including wireless USB, digital cameras, and camcorders. It includes AES-128 encryption.

Intel was one of the early pioneers in the UWB movement. Today, its UWB Link 1480 MAC chip is WiMedia-compliant and useful in wireless USB applications.

NEC America's uPD720170 host controller is a good fit with other UWB chip sets. It enables the high-speed wireless transmission of data between PCs and peripherals such as printers, external hard drives, and digital cameras. It also will work in some consumer electronic devices. The chip supports the eight speed options of the UWB chips from 53.3 to 480 Mbits/s, as well as control, bulk, interrupt, and isochronous data transfers. Based on the WiMedia MAC and PHY, it can connect up to 32 devices simultaneously.

NXP Semiconductor's similar ISP3582 wireless USB device controller integrates directly into end systems at the board level. Designers can use it for the seamless replacement of wired USB in current systems instead of hub and dongle designs. Additionally, its small footprint will save space and components in embedded designs.

Pulse-Link, which has been involved with UWB from its earliest beginnings, developed impulse UWB. Its unique flavor of UWB, CWave, uses a continuous 4-GHz sinewave carrier that's modulated by binary phase-shift keying (BPSK) using a spread-spectrum-type exclusive OR (XOR) arrangement. Its raw data rate is 1.3 Gbytes/s.

With this arrangement, the overall signal bandwidth is from 2.7 to 5.3 GHz, or 2.6 GHz more than enough to be considered UWB. By adjusting the carrier frequency and the BPSK rate, the bandwidth can be set to just about anything in the 3.1- to 10.6GHz spectrum. Considering overhead, CWave is able to sustain a 400-Mbit/s throughput.

CWave can be used wirelessly, but Pulse-Link is promoting it as a cable technology. It's designed to operate over the installed base of cable TV coax in homes. Designers can use the CWave chips to create a complete home network that streams video and audio between devices. It supports IEEE 1394 and HDMI/DVI interfaces.

Realtek's RTU7105 single-chip CMOS solution supports the certified wireless USB device controller and the WiMedia logical link control protocol. It integrates the PAL, MAC, baseband controller, and RF transceiver, as well as USB 2.0 and SDIO interfaces. It also can operate over two of the UWB band groups, including the 3.168- to 4.752-GHz group and the 6.336- to 7.92-GHz group, suiting it for application in a wide range of international spectrum assignments.

Staccato Communications developed several iterations of its Ripcord chip set, the latest being its 3500 series single-chip UWB solution for wireless USB. Made with 110-nm CMOS, the chip includes the RF, digital baseband, MAC, memory, a 32-bit RISC processor, and an encryption engine. Its I/O interfaces include USB 2.0 host, USB 2.0 device, and SDIO 1.1.

Tzero Technologies' WiMedia-compliant TZ7000 series chip set incorporates a two-channel radio that brings MIMO to UWB. Called UltraMIMO, it increases link range and boosts link reliability in a multipath environment. It also enhances the through-wall performance, and helps to cancel interference.

With this feature, Tzero beats the usual speed-range specs for UWB, achieving a minimum of 106.7 Mbits/s at 20 m in a NLOS situation and 480 Mbits/s at more than 5 m. Tzero's ZeroWire TZC7200 focuses on video applications. In addition, the company offers an HDMI reference design.

WiQuest's WQST110/101 two-chip set meets all of the WiMedia specs and is certified for wireless USB. Its special coding scheme supports higher data rates from 558 Mbits/s to 1.037 Gbits/s. This proprietary mode gives you an extra blast of speed when you need it. The chips also incorporate the company's proprietary WiDV (Wireless Digital Video) technology.

Designed for various video applications, WiDV adds the processing engine, a security processor, a quality-of-service (QoS) manager, and a range of interfaces. You'll find a PAL on the WiMedia platform. In addition, its 5-to-1 video compression scheme transmits video over the 1-Gbit/s UWB link for improved video reproduction. MPEG2/4 and Motion JPEG use 40 to 60 to 1 compression, which results in reduced resolution.

With WiDV and the WiQuest chips, you can even create a wireless link between a PC or laptop and a video monitor. Toshiba is already doing that with its UWB gateway, which includes wireless video, mouse, keyboard, and UWB connections. New Dell, Lenovo, and Toshiba laptops embed WiQuest chip sets.

Wisair's WSR601 single-chip solution includes the RF PHY, the MAC, and a certified wireless USB subsystem. Applications include host and device wireless USB. The chip delivers 480 Mbits/s up to 8 m away and achieves 200 Mbits/s up to 20 m. Total average power consumption is 385 mW. Belkin, which manufactures Wi-Fi routers and gateways, implements the Wisair chip in its new wireless USB hub.

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