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Because of its high data rate performance, low power requirements and low cost, ultrawideband (UWB) is increasingly garnering the industry's attention. Like many wireless technologies, its origin stems from work done for the U.S. government. These days though, rather than radar and other government-based communications applications, it's being eyed as a solution to the market demand for high-speed wireless and precision radar/positioning applications, such as mobile and home theater products, as well as enterprise/office solutions for high-definition television (HDTVs), media blasters and laptops. In early 2005, Freescale Semiconductor even demonstrated a UWB-enabled cell phone.

While there is no denying the technology's potential, it is not without its limitations — namely that UWB has a short range. Thanks to a wave of events earlier this year, primarily the dissolution of the IEEE 802.15.3a task group, which oversaw the formation of the UWB standard, some confusion exists over the technology's direction. Despite these setbacks, UWB technology is going strong with two approaches for implementing it (direct-sequence UWB (DS-UWB) and multiband orthogonal frequency-division multiplexing (MBOFDM) UWB) and UWB-enabled products making their way to market (see the related article, “A Tale of Two UWB Approaches”). There's also been a development from a wireless standard organization that promises to give UWB an extra boost. What do these developments mean for the future of UWB wireless technology? Let's take a closer look.

UWB technology transmits ultra low-power radio signals with short electrical pulses, often in the picosecond (1/1000th of a nanosecond) range, across all frequencies at once. The short time duration of the UWB waveform gives it unique properties. In communications, for example, UWB pulses can be used to provide extremely high data-rate performance in multi-user network applications. Additionally, the waveforms are relatively immune to multipath cancellation effects in mobile and in-building environments. Consequently, UWB systems are suited for high-speed, mobile wireless applications.

Other specific advantages include:

• Low system complexity and low cost. Because of its inherent RF simplicity, UWB systems are highly frequency adaptive. This enables them to be positioned anywhere within the RF spectrum and avoid interference to existing services, while fully using the available spectrum.

• Because of its low power requirements, UWB is difficult to detect and difficult to regulate.

• Since it spans the entire frequency spectrum, licensed and unlicensed, it can be used indoors and underground.

• It features simpler, higher-performance RF-to-digital conversion techniques than narrowband radios, making it suitable for battery-powered devices and mobile applications such as RFID tagging, warehouse sensor networks, and unwiring the enterprise desktop.

Despite its enviable benefits, UWB technology has its disadvantages. Because of its high data rates it is limited to a short range. And, like all RF wireless technologies, trade offs are required in terms of signal-to-noise ratio (SNR) vs. bandwidth, and range vs. peak and average power levels. Additionally, while the technology is expected to empower a range of applications it is by no means the answer for all wireless applications.

Whether based on DS-UWB or MB-OFDM, UWB-enabled solutions are making their way to market. Solutions range from chipsets and hubs, to intellectual property (IP) and test and measurement solutions. Here's a look at some of the solutions available:

• Cable-free USB solutions. Powered by Freescale's UWB chipset based on DS-UWB and the ExtremeUSB solution from Icron Technologies Corporation, cable-free USB is intended to enable a zero-install wireless USB solution. It supports USB 1.1 and USB 2.0 devices, giving users a “plug and play” experience right out of the box. Two early adopters of cable-free USB are Belkin Corporation and Gefen.

  Belkin offers a cable-free USB hub and dongle, which allows users to place their laptop anywhere in the room while maintaining wireless access to USB devices, such as printers, scanners, hard drives and MP3 players.

  Gefen's wireless USB extender uses small sender and receiver units connected to the computer and the extended USB device. By plugging the receiver into the USB port on the target device, an instant wireless connection is achieved. No USB cables are needed to deliver data from the sender to the receiver, which can be connected to the camera, keyboard, printer or USB 2.0 device up to 30 feet from the computer.

• Certified Wireless USB. Certified Wireless from the USB-IF supports robust high-speed wireless connectivity and is based on the MB-OFDM ultrawideband (UWB) radio platform. Its performance is targeted at 480 Mbps at three meters and 110 Mbps at 10 meters. Some recent Certified Wireless USB solutions include:

1. The Ripcord family of single-chip, all-CMOS solutions, from Staccato Communications.

2. A UWB PHY module for the Intel Certified Wireless USB peripheral development kit (PDK) from Wisair.

3. A DesignWare wireless USB device controller IP, from Synopsys, which provides designers with a high-bandwidth WiUSB IP core for SoC integration.

4. The high bandwidth, real-time TDS6000 series oscilloscopes and TDSUWB software application from Tektronix that allows users to measure and analyze Certified Wireless USB signals.

5. The wireless USB Explorer 300 protocol analyzer from Ellisys.

One of the more interesting things to occur with UWB this year was its selection by the Bluetooth SIG for integration with current Bluetooth wireless technology. The organization selected MB-OFDM as the technology it will use to help create a high-speed, high data rate option of Bluetooth to meet the high-speed demands of synchronizing and transferring large amounts of data as well as enabling high-quality video and audio applications for portable devices, multimedia projectors and TV sets.

This Bluetooth/UWB combination offers a number of benefits, especially for the mobile market. As Tom Houy, vice president of Strategic Marketing, Americas, for Cambridge Silicon Radio (CSR), explained, “When it comes to mobile devices, like phones, MP3 players or PDAs, power is king. In standby mode, Bluetooth uses about one-twentieth the power of UWB and UWB, when transmitting, has excellent power per bit utilization. As a result, the two make a perfect mobile solution.”

The Bluetooth SIG and WiMedia Alliance are working together to ensure that the combined high-speed solution is optimized for mobile devices with low power consumption. It will feature low cost, ad-hoc networking, built-in security features and the ability to integrate into mobile devices. Both organizations are working to help MB-OFDM UWB achieve global regulatory acceptance by developing a high-speed, high data rate Bluetooth solution that uses the unlicensed radio spectrum above 6 GHz.

These steps are not that surprising for the Bluetooth standard. As Michael Foley, Bluetooth SIG executive director pointed out, “Consumers were introduced to Bluetooth with the headset or hands-free use case. Now we are seeing a large interest in wireless streaming of stereo audio. The next step would be streaming high-def video. Current Bluetooth technology doesn't offer the throughput to support this application. This is one of the reasons we have teamed with the WiMedia Alliance to offer a high-speed Bluetooth option. Using UWB from the WiMedia Alliance, the high-speed version of Bluetooth technology will allow for 100 Mbps at the same range consumers have become accustomed to: 30 feet. This faster option will offer the same low-power consumption Bluetooth technology is known for, which makes it a natural for battery-operated mobile devices.”

The combined Bluetooth technology/UWB chipsets are expected to be available by the end of 2007 with products on the shelf by 2008 (Figure 1). These chips will likely go into computers and devices where high data rate may be required.

UWB is an emerging wireless technology that holds great potential for use in high-speed, low-power and low-cost applications. With the IEEE 802.15.3 task group no longer driving UWB standardization, the market will have to decide which UWB variant — DS UWB or MB-OFDM — it prefers. The availability of viable solutions based on either technology is sure to help move this debate along quickly; as is the selection of MB-OFDM by the Bluetooth SIG.

The lack of an official IEEE 802.15.3a UWB standard has left the decision of which UWB technology to adopt up to the market. Currently, there are two approaches to implementing UWB technology. These include direct-sequence UWB (DS-UWB), which is promoted by the UWB Forum, and multiband orthogonal frequency-division multiplexing (MB-OFDM) UWB, which is promoted by WiMedia Alliance. Which one of these approaches prevails in the market will be determined by good old-fashioned competition. Here's a bit of information on what each approach entails.

Using a combination of a single-carrier spread-spectrum design and wide coherent bandwidth, DS-UWB transmits data by pulses of energy generated at very high rates: in excess of 1 billion pulses per second. It supports data rates of 28, 55, 110, 220, 500, 660 and 1320 Mbps via a fixed chip rate and variable-length spreading code words. Its key advantages include: quality of service (QoS), high data rates that scale to 1 Gbps and more, low cost, and long battery life. In addition, it provides low-fading, optimal interference characteristics, inherent frequency diversity, precision ranging capabilities, and has a total transmit power of about 1/10 mW across its entire signal bandwidth.

In contrast, MB-OFDM transmits data simultaneously over multiple, accurately spaced, carrier frequencies. Each frequency band is 528 MHz wide. It employs the quadrature phase-shift keying (QPSK) modulation technique and operates between 3 GHz and 5 GHz, with optional modes that extend to 10.6 GHz. MB-OFDM features high spectral flexibility plus resilience to RF interference and multipath effects. Additionally, because the MB-OFDM transceiver architecture requires just a single analog receive chain, relatively low-resolution ADCs and DACs, and limited internal precision in the digital baseband, it meets the low-cost requirement of today's consumer products.