A practical approach to production test of UWB devices: Part 1
Adam Smith, Verigy -- Test & Measurement World, 12/7/2007 10:33:00 AM
As consumers demand that traditionally wired products “cut the cord” and move into the wireless era, technologies are emerging to meet that demand. One such technology is ultra-wideband (UWB). UWB allows for communication rates that can be applied in household products that, for example, transmit wireless video or support wireless USB 2.0.
The emergence of this technology, however, creates several challenges—both economic and technological. On the economics side, the addition of the UWB communication interface must not add significant cost to the consumer product. Regarding technology, UWB has some unique attributes that can make testing these devices in high-volume production very challenging. In particular, as the ultra-wideband name implies, the modulation bandwidth that the device employs is an order of magnitude larger than even the latest wireless LAN (Wi-Fi) devices. Because UWB technology has some non-traditional test requirements, it is very difficult to approach UWB devices entirely with a traditional production test strategy. This article will explore those challenges to show that there are ways to meet device manufacturers' test requirements using a mixture of familiar test techniques combined with some design-for-test (DFT) creativity in order to minimize the test cost per device. While there are some daunting challenges in the testing of this technology, a test solution can be found on readily available production testers, without a need for specialized test equipment.
What is ultra-wideband?
The term ultra-wideband (UWB) describes an unlicensed radio technology that occupies channel bandwidths of greater than 500 MHz (Ref. 1). UWB’s channel bandwidth is a major departure from existing narrowband and wideband wireless standards. Narrowband technologies such as those employed in 1G/2G/2.5G mobile phones, generally occupy less than 2 MHz, where wideband technologies such as 3G mobile phones and wireless LAN (Wi-Fi) generally occupy 3 MHz to 40 MHz. UWB technology provides a personal area network (PAN) at high communication rates over short distances. It can provide PAN coverage in many of the same applications as Bluetooth and Wi-Fi, however, at much greater data rates.
This ultra-high speed, short-range RF technology has application uses in many of the household consumer appliances, such DVDs, digital TV set-top boxes, digital TVs, PCs, and printers. In addition, UWB shares its technical roots with radar technology and has possible application usage in the collision-avoidance automotive space as well as penetrating radar, which can be useful in law enforcement.
Why is there so much excitement around UWB?
The portability of PC technology in smart-phone and other mobile devices is putting the ability to manage a significant amount of data in the consumer’s pockets (music, photos, email, file-sharing, etc.). The need for fast and efficient transmission of that data between mobile devices, even faster than Wi-Fi, is driving a requirement for a wireless path to do so.
What does “ultra” wide bandwidth allow? There is a relationship due to Shannon’s law (Ref. 2) between the data rate, bandwidth of the signal, and signal to noise ratio (SNR) that is dictated by
C = BW*log2(1 + SNR)
where C is channel capacity in bits per second, BW is channel bandwidth in hertz, and SNR is the signal to noise ratio.
The major implications of this equation are that increasing the data transmission rate of a signal can be accomplished either by increasing the occupied bandwidth, the SNR, or both. SNR can loosely be correlated to transmitted power, or more importantly, battery consumption in the case of mobile applications. UWB seeks to operate in a small signal to noise environment to minimize power consumption. Because of the ultra-high bandwidth, UWB allows for an efficient use of mobile power while still achieving a very high rate of data transmission.
There are several other advantages to UWB technology. First, the energy in a transmitted UWB signal is spread out in such a large bandwidth; the signal is unlikely to interfere with another communication system because the signal power at a specific frequency is seen as noise to the other system. Likewise, a UWB receiver accepts such a wide bandwidth that a powerful narrowband signal is unlikely to interfere, because most of the transmitted information will be outside of the interfering signal.
In addition, since the transmitted power of UWB is so small, it is a mobile-friendly technology that consumes little power—significantly less power than Wi-Fi. The down-side to the lower power—combined with the physical nature of higher frequency signals—is short range of operability, which makes UWB suited for a personal network rather than a wide network.
The market adoption of UWB
While the application usage of UWB looks to be various, UWB’s primary market challenge is the adoption of a common standard. A task group was assembled to define the UWB standard, which was identified as the IEEE 802.15.3a working group. Initially, there were two competing approaches to UWB, both of which are backed by large companies. The technology suffered a setback in early 2006 when the task group could not come to an agreement on the standard’s definition, and voted to disband (Ref. 3).
Competing standards
One of the competing factions in UWB was the MBOA Alliance, which proposed a multi-band orthogonal frequency division multiplexing (OFDM) approach to UWB. This method divides the entire bandwidth into smaller parallel sections; it borrows largely from the same techniques used in WLAN’s 802.11a/g. This technique has the advantage of being more robust in a noisier environment, maintaining a high rate of data transmission. In addition, the technique allows for scalability and the coexistence with other OFDM systems like Wi-Fi. The counter approach to MBOA proposed for UWB is a direct-sequence approach, which instead of breaking the spectrum into pieces, utilizes the entire band. This approach works by sending billions of pulses across the transmitted spectrum. While this technique is also fairly robust against interfering signals emitted from other transmission sources, its primary advantage is that it is a simpler approach in its implementation (Ref. 1).
The lack of adoption of a single standard for UWB is affecting its adoption in the consumer marketplace. Initially, UWB intended to be the primary technology in wireless video applications. Digital TV requires approximately 50-Mbps digital transmission rate for standard-definition television. Even though Wi-Fi is currently capable of 54-Mbps data rates (802.11a/g), the effective data rate is actually closer to 35 Mbps due to overhead in the protocol. However, Wi-Fi is now rolling out devices capable of up to 100-Mbps data rates through the 802.11n standard, which has the added advantage of backwards compatibility to devices that utilize the very popular 802.11g Wi-Fi standard.
UWB’s commercial outlook
The longer that UWB takes to reach a standard implementation, the more difficult it will be to find commercial success. Because Wi-Fi is making quick strides in the wireless-video application space, UWB is looking to find a “killer application.” One likely candidate is wireless USB, where the required data rate is up to 480 Mbps, which far exceeds the roadmap of Wi-Fi. In addition, USB applications are generally in extremely close proximity to each other (less than three meters), which also fits well with the UWB requirements. A working group, the WiMedia Alliance (www.wimedia.org), is attempting to standardize a wireless USB interface based on UWB technology. WiMedia’s approach offers some technical advantages in this application space which allow multiple radios to operate in a highly dense environment.
UWB could replace most of the USB cables between the PC, mouse, keyboard, printer, scanner, external storage media, mobile phone, and portable music player. It would also be a common network interface between all of these peripherals, which would be a significant improvement over the wireless keyboard and mouse products available today in the desktop market. It would allow interoperability between devices much in the same way that Bluetooth revolutionized the hands-free audio device interoperability between different head-set and automobile manufacturers.
Because there is synergy between UWB and Bluetooth applications, the Bluetooth taskforce is evaluating the possibilities of an UWB and Bluetooth convergence. The benefit of this would be to add functionality to a mobile device, such as the mobile phone, and would not require an additional wireless radio device—the UWB radio would effectively replace the Bluetooth radio.
Another application that requires a solution is wireless HDTV. However, even at the maximum proposed 480 Mbps data rate of UWB, it cannot address the 1.3 Gbps requirement of HDTV.
The consumer market is ready for a high-speed PAN solution. It seems only a matter of time before UWB serves the market. The unknown is the degree of success UWB will have while Wi-Fi continues its rapid growth.
Ed. note: This article is part 1 of a 3-part series. Part 2 discusses test challenges and how they will evolve over the three phases of UWB rollout. Part 3 covers test-cost targets, native testing, and DFT strategies.
REFERENCES
1. Kolic, Rafael, “An introduction to Ultra Wideband (UWB) wireless,” deviceforge.com, 2004, www.deviceforge.com/articles/AT8171287040.html.
2. Wilson, James M, “Ultra-Wideband/a Disruptive Technology?” Intel, 2002, www.intel.com/technology/comms/uwb/download/Ultra-Wideband_Technology.pdf.
3. “Semiconductor Application Markets Report,” 2006 edition, www.researchandmarkets.com.
Adam Smith is a business development engineer at Verigy. He has 10 years of ATE industry experience, focused on RF/microwave device test technology. Adam holds a Bachelor of Science in Electrical Engineering from Cal Poly, San Luis Obispo. He can be reached at adam.smith@verigy.com.
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