Ultra wideband
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Ultra-wideband (also UWB, and ultra-wide-band, ultra-wide band, etc.) usually refers to a radio communications 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.
UWB is a wireless communication technology fundamentally different from all other radio frequency communications. It is unique in that it achieves wireless communications without using an RF carrier. Instead it uses modulated high frequency low energy pulses of less than one nanosecond in duration.
Since the actual transmission is physically a wavelet, some authorities consider it to be true wavelet-modulated radio.
There are two major methods used to modulate waveforms: Time-modulated pulse-position modulation and bi-phase-modulated pulse-amplitude modulation[1] (http://www.kuroda.elec.keio.ac.jp/pdf/kuroda/2003/2003_19.pdf). By long-established practice, 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. Additionally, UWB has difficult-to-realise synchronization requirements (for semiconductor companies) due to the very low Duty cycle pulses employed.
ON 14th February 2002 [FCC15 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 (from the middle of S band through to the middle of X band) with allowed effective isotropically radiated power (EIRP) of -41.3 dBm/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 -41.3 dBm/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 wireless network data exchange rates (up to 800 Mb/s) across relatively short distances (less than 10 m) with a low-power source (UWB operates at low energy - reducing interference and power requirements). Although the connection speed decreases quickly as a function of distance, wireless UWB has the potential to replace the cables that currently connect devices.
UWB can also use mains-wiring, co-ax cable or twisted-pair cables to communicate - with potential deliver data faster than 1 gigabit per second. Recently, both Bluetooth and USB stakeholders have expressed an interest in using UWB at the core of their next-generation standards.
There are a number of competing standards which makes universally compatible UWB products problematic in the short-term.
See also
External links
- The Ultra-Wideband Radio Laboratory at the University of Southern California (http://ultra.usc.edu/New_Site/) has many publications including "Low noise amplifier design for ultra-wideband radio" (http://ultra.usc.edu/New_Site/papers/lna.pdf) by Jongrit Lerdworatawee, Won Namgoong, 2003de:Ultra Breitband Technologie