Certified Wireless USB and Ultra-wideband to the Rescue
Today's consumer demands a host of functionality from portable electronic devices. While wireless portable products can store significantly more video, photos and music than most PCs did just five years ago, this content creates a notorious drain on battery life and requires a new approach to wireless computing.
Just seven years ago, WiFi was just getting started and MP3 players were 16MB in size. Today there are Media Players out in the market that provide up to 8GB of flash memory, which can be easily filled with music alone. Movies and pictures move us above that mark quickly. Similarly for cameras, 2GB of SD flash memory is under $30, making it a standard add-on purchase. Consumers download, create, listen to, and watch more content -- often in cars, planes, airports and trains, or at home, in hotels, on vacation, at work and in the office. Consumers want to charge their devices once a week, but run them for 20 hours or more, the length of 2 transatlantic flights or a long vacation running their digital camera, or a week without recharging their media player for the commute.
Consumers also want the convenience of wireless for the same reasons that people reading this article might -- WiFi at home, a cell phone in their pocket, and a wireless phone at home. There are 3 reasons that Certified Wireless USB and Ultra-wideband will meet the needs of the typical consumer: 1) minimal power used to transfer content; 2) easy-to-use wireless standard based on learnings from USB/WiFi and Bluetooth, and 3) a strong standards program with certification logos.
Today, some cameras and phones use WiFi, but this drains batteries quickly in today's devices. The trick is to lower the power used for transmitting the data, by spreading the data over a wide band of frequencies, and then turn off the radio when not transmitting or receiving. Ultra-wideband (UWB) and Certified Wireless USB (CWUSB) are designed with these goals in mind. Ultra-wideband provides the wide frequency band at low power (see figure 1).
Figure 1: Ultra-wideband spreads the data over a wider range and uses less power.
CWUSB lets you schedule the transmissions, and shutdown between Tx/Rx times. As a result, compared to WiFi, a device consumes only about 5% of the power per Megabyte of data transferred. The CWUSB signaling rate is 480 Megabits per second (same as wired USB). In a worst-case scenario of software driver, protocol, firmware, and memory access overhead where throughput is about 100 Megabits per second, you can transfer all the photos off a 1GByte flash device in about 80 seconds. If we look at actual throughput on real WiFi networks running 802.11g, the best systems run at the rate of 20- 25 Megabits per second, which means the same transfer will take 400-500 seconds (see figure 2). This means the WiFi radio stays on for at least 4-5 times longer than a UWB radio. Battery life can be extended 5 times based on the transmission time, reducing the need to charge as often. CWUSB sends the data faster and shuts down, both during transmission and while in a suspend or keep-alive mode. The data is actually sent at lower power too, saving additional power. The challenges for chip designers are "how do I turn the radio off and on fast enough to take advantage of these savings and how do I design my protocol engine to drive the radio?"
Figure 2: Ultra-wideband offers faster throughput at 3 meters or less.
There are several ways to reduce the overall power consumption in a chip design in a standard CMOS process. Clock gating alone is insufficient because inactive gates still receive power and can still leak current. One solution, such as in Synopsys' DesignWare WiUSB Controller, is to build in two power rails. This allows power to be continuously delivered to a smaller group of keep-alive circuitry. The second rail allows power to be completely shut down to inactive or suspended circuitry. This eliminates power leakage which can be as high 50% at 65nm or smaller process geometries (footnote 1). In the past, mobile phone companies have avoided multiple power rails because of the additional area. The good news is that smaller geometry processes will overcome the area penalty and help these companies use multiple power rails to improve overall battery performance.
As consumers choose their devices based on reviews of battery performance, consumers also look for a logo showing interoperability. Because the USB-IF has extensive experience in getting USB standardized and interoperable, they will also be able to offer the same level of logo testing for CWUSB and UWB. This will include free interoperability plugfests, which take place 4 times a year, and independent 3rd party labs that will be able to provide certification. After a manufacturer goes through this testing, the USB-IF will authorize a Certified Wireless USB logo to be put on the product literature and packaging. The USB-IF will take responsibility for training retailers worldwide on the standards, to make sure that people on the showroom floor can explain why that logo is important and point consumers to the certified products. In this way, Certified Wireless USB will be promoted as an easy-to-use technology using the same infrastructure that made wired USB successful over the past several years.
As 2007 comes to a close you will see more logo certified products, like those from Dell and Lenovo laptops, as fully enabled Certified Wireless USB products. You will also see more products like the logo certified IOGear and D-Link products that will allow you to make existing USB products wireless. While product makers must focus on certification and interoperability testing, their power consumption will ultimately be determined by how the chip is designed. IP suppliers like Synopsys focus on all levels of design from design flow, to CMOS design, to PHY control. Readily available digital protocol engines sold as IP allow chip designers to drop CWUSB into their next design to reduce overall costs, while having confidence that the overall design will save power, area, and money for the end product. This means that product makers will have a full range of choices, from discrete chips to IP, for adding Certified Wireless USB to their end products. Consumers will soon be able to transfer their music, video, and pictures wirelessly and recharge their devices with less frequency than competing technologies.
(Footnote 1): Leakage Reference: http://vlsicad.ucsd.edu/leakage.htm