Ultra Wideband Radio (UWB) Hanbiao Wang EE206A Spring 2001

What’s UWB? zBasically impulses of extremely short duration, 10s pico-sec to nano-sec zDefinition: radio signals with a fractional bandwidth  larger than 25% where f L and f H are the frequencies measured at the –10 dB emission points

Applications z Communication z Tracking z Radar Traditional sine wavesUWB coherent pulses

Advantages in Communication z+ Very High Data Rate yBecause extremely narrow pulse width (a few nano-seconds) allows very small pulse repetion interval (10s nano-sec), UWB could easily reach a very high data rate (100s Mbps).

Advantages cont’ z+ Immunity to Multipath Fading yWith the relatively small ratio of pulse width over the pulse repetition interval (0.01~0.1), the direct path has come and gone before the reflected path arrives and little cancellation occurs. yGood for indoor or in-building use

Advantages cont’ z+ Very Low Transmision Power yAccording to TimeDomain.com, a transmission power of only 50 micro-watt is needed for commercial communication application, it’s just 10^-4 of a cell phone. yExpected application in communication is short-ranged.

Advantages cont’ z+ Inherent Encryption yBecause very low transmission power and ultra wide transmission bandwidth, the resultant spectral density is very low. Thus UWB has a very low detection probability. y“Time Hopped” channel coding makes it random noise-like.

Advantages cont’ z+ Immunity to Hostile Jamming yBecause UWB has inherent encryption, it’s difficult to determine whether UWB transmission is on or not. Thus, it’s difficult for the hostile one to decide whether to apply jamming or not. yBecause UWB has ultra wide transmission bandwidth, jamming won’t work even if the hostile one know UWB transmission is on.

Concern in Communication z? Interference to Existing Radio Communication or Sensing Systems yTheoretically, UWB will cause little interference because of low spectral density and noise-like signature. yNTIA conducted comprehensive tests on the potential for interference of UWB to both non-GPS and GPS systems. yhttp://sss-mag.com/uwb.html

Interference to Non-GPS zFeasible between about 3.1 and GHz at heights of about 2 meters with some operating constraints. zBelow 3.1 GHz, "widespread, dense uses will be hard to accommodate” zEvaluation limited from 400 MHz to approximately 6.0 GHz. Potential impact of higher frequency unknown. Announced On 31 January, 2001

Interference to GPS zObjective: "to define the maximum allowable UWB equivalent isotropically radiated power (EIRP) levels... compared to the emission levels derived from the limits specified for unintentional radiators in C.F.R., Title 47, Part to assess the applicability of the Part 15 limits to UWB devices.” Announced on 28 February 2001

Interference to GPS cont’ zGiven a requisite 6 dB margin for GPS acquisition performance, the NTIA demonstrated that a 20 MHz (pulse repetition frequency) dithered UWB transmission must be at least 33.3 dB down from existing Part 15 levels (41.6 dB down for non-dithered emissions) in order to not interfere with GPS.

Interference to GPS cont’ zPulse dithering, while making the UWB signal appear more "noise like", had a less than 10 dB advantage. This advantage was completely "lost when a multiple of as few as 3 of these UWB signals with equivalent power levels at the GPS receiver input are considered in aggregation."

Interference to GPS cont’ z"When multiple noise-like UWB signals with equivalent power levels at the GPS receiver input are considered, the effective aggregate signal level in the receiver IF bandwidth is determined by adding the average power of each of the UWB signals." zAggregate effects are indeed unimportant

Inplementation Challenges zUWB transmitters require precise pulse shaping to produce the required spectrum and maximize the antenna's emission. zUWB antennas are better described and designed in time domain than in frequency domain, in terms of convolution of signals with the antenna’s impulse response.

Advantages in Localization and Tracking zAdvanced time resolution results in very high geo-location accuracy, which is good for localization zVery narrow pulse width result in multipath fading resistance, which is good for tracking

FCC Regulatory Process zNotice of Inquiry issued in August 1998 zNotice of Proposed Rule Making issued on 14 June 2000 zRequested comment on the first set of NTIA test reports for UWB interference to non-GPS systems (FCC Public Notice DA ) issued on 24 January 2001

Conclusion zUWB may survive and prosper with high probability zUWB can’t completely replace existing wireless systems.