Ultra wideband

Ultra-wideband (also UWB, and ultra-wide-band, ultra-wide band, etc.) usually refers to a radio modulation technique based on transmitting very-short-duration pulses, often of duration of only nanoseconds or less, whereby the occupied bandwidth goes to very large values. Ultra-wide-band may also be used to refer to anything with a very large bandwidth (e.g.: a type of sampling rate in the Speex speech codec). This article discusses the meaning in radio communications.

There are two major methods used to modulate waveforms: Time-modulated pulse-position modulation and bi-phase-modulated pulse-amplitude modulation[1]. By long-established practice, the radio modulation technique, UWB, is considered to occupy a fractional bandwidth of 20% or greater, or a bandwidth of 250 MHz or more, of spectrum. The U.S. Federal Communications Commission (FCC) restricts UWB to fractional bandwidth of 20% or greater, or bandwidths of 500 MHz or more (not 250 MHz). In December 2004 the FCC effectively eliminated this minimum bandwidth requirement as to the 5925-7250 MHz and 16.2-17.7 GHz frequency bands.

The processing gain of UWB, defined as the ratio of occupied bandwidth relative to the modulation bandwidth, is similar to spread spectrum for transmission. However, UWB is only typically able to benefit from processing gain during transmission. Reception of UWB is usually based on time-correlation of pulses, and the receiving benefits of processing gain possible with spread spectrum are not usually realized in practice.

In February 2002 the FCC approved a spectral mask for operation of UWB devices. The major part of it lies between 3.1 and 10.6 GHz with allowed effective isotropically radiated power (EIRP) of -41.3dBm/MHz. It has been proposed that impulse radio systems (that transmit very narrow pulses) are good candidates to satisfy these constraints. OFDM-based technologies also meet FCC requirements. In March 2005 the FCC granted a waiver that benefits both so-called multiband OFDM (MB-OFDM), which "hops" an OFDM signal from one band to another, and gated direct sequence ultra-wideband (DS-UWB), which occupies a much wider swatch of spectrum but switches on and off while in operation. The waiver allows both technologies to take their measurements for compliance with the -41.3dBm/MHz limit in their normal operating mode -- i.e., with the hopping or gating turned on. The practical effect is to boost the useful operating power by several dB.

Ultra-wideband or UWB is a developing communication technology that delivers very high speed network data exchange rates across relatively short distances with a low power source. Although the connection speed decreases quickly as a function of distance, UWB has the potential to replace the cables that currently connect devices.

UWB can potentially deliver data faster than 1 Gigabit per second. It operates in low frequencies that no other technology utilizes. This reduces interference and power requirements. This might make traditional wired LANs and WANS obsolete.

However, UWB suffers from synchronization requirements due to the very low Duty cycle pulses employed. There are also a number of competing standards which makes commercial UWB products unlikely.

See also: Wireless | Network | Bandwidth | Fat-Pipe | Wideband

External links:

• The Ultra-Wideband Radio Laboratory at the University of Southern California has many publications including "Low noise amplifier design for ultra-wideband radio" by Jongrit Lerdworatawee, Won Namgoong, 2003