Ultra-wide band (UWB) for the portable Internet

Ultra-wide band is one of the most anticipated radio-frequency technologies because it can transmit data at very high speeds by sending the transmission over a wide range of frequencies at very low power levels. Home networking and other shortrange, high-bandwidth applications are some of the promising uses of UWB. Much like small FM radio transmitters that broadcast within a few feet to a car radio from a portable MP3 player, UWB could make use of the spectrum in a small area to increase connectivity, without interfering with the spectrum owner’s operation. UWB communication devices can be used to distribute services via wireless such as phone, cable, and computer networking throughout a building or home.

UWB technology has been used for some time in ground-penetrating radar applications and is now being developed for new types of imaging systems that would enable fire and rescue personnel to locate persons hidden behind a wall or under debris in crises or rescue situations. UWB imaging devices also could be used to improve the safety of the construction and home repair industries by locating steel reinforcement bars in concrete, or wall studs, electrical wiring and pipes hidden inside walls. UWB devices could improve automotive safety with collision avoidance systems (http://www.uwb.org/faqs.html).

One striking element of UWB communications is the ability to communicate below the noise floor, often referred to as “underlay” (see Figure 1). All electronic devices produce radiation at various frequencies, whether they are intentional radiators or not. This means that as long as there are electronic devices, there will always be at least some level of interference, commonly referred to as the noise floor. Engineers build licensed devices that must be able to withstand low levels of interference; that is they must be able to send and receive signals above the noise floor (see box: "Comparing underlays to a quiet house").

By employing a wide range of frequencies, UWB allows for effective transmission through objects, including walls and the ground. UWB can penetrate dense obstacles that would severely hamper communication using traditional higher-powered, narrow band radio waves. Its signals penetrate dense objects, rather than bounce off them. This is especially important for radio applications that suffer from multipath problems. Multipath is a type of signal distortion that occurs when the original signal, and a reflected signal arrive at different times, “confusing” the receiving radio. One good example of multipath is when a car radio’s reception deteriorates at a stoplight but pulling the car a metre forward improves the signal. The signal deteriorates momentarily because the radio is receiving the original signal, as well as a slightly late echo that essentially cancel each other out. Moving slightly can remove the “echo” and the radio plays normally again.

UWB uses a different method of transmitting data than typical radios. Traditional radio technologies use various carrier waves to send data information. The carrier wave is tuned to a specific frequency and the data is superimposed on the wave by adjusting either its frequency or amplitude. Typical examples would be FM and AM radio. UWB is different because, unlike the carrier example of FM and AM radio, it instead uses very fast pulses to represent the zeros and ones of digital communication.

UWB offers the potential to increase spectrum efficiency drastically. The key decision for policy-makers is whether this technology will work as advertised. Governments around the world are starting to formulate UWB policies, as the benefits of UWB could potentially be very large. The technology operates under a wide swath of licensed and unlicensed frequencies and many current licensees are following its development very closely. This is not surprising, as many licensees have been sceptical over fears that an “unproven technology” will cause problems in the bands they have paid for.

UWB may fundamentally change the way spectrum authorities look at spectrum rights. In the United States, for example, the Federal Communications Commission (FCC) is taking ultra-wide band very seriously and approved a low-powered version of the technology in February 2002. Initially, there had been concerns that UWB signals would interfere with the GPS navigation system. But after extensive testing, FCC found that UWB would not cause significant disruption at low power levels. FCC took a cautious approach to UWB, limiting the range of the technology to roughly 30 feet, close enough for home networking indoors. If systems in development work as planned, FCC had mentioned that it would be willing to increase the power limits in the initial ruling.

For its part, the International Telecommunication Union has been conducting technical studies through a Task Group of its Radiocommunication Sector (ITU–R) to examine ways in which UWB can coexist with other radiocommunication services. These studies are expected to be completed during 2004.

The role of UWB in the portable Internet will likely be similar to other wireless LAN technologies. It will bridge the gap between a very fast, wired connection and a multitude of devices inside a home. Examples include the streaming of high-definition television (HDTV) signals throughout a house for all televisions and computers. UWB may also be used as a wire replacement between DVD players and television sets, due to its high speeds and robust connectivity. Once the technology has advanced, it may be possible to use UWB technologies at higher power levels, allowing for outdoor use.