Ultra-Wideband - John Burnette -

What is UWB? Know since 60’s “Zero carrier” or “carrier free” Transmit short bursts Fraction of typical RF carrier wave Thus utlra wide band Difficult to determine carrier frequency

Frequency-domain behavior What is UWB? Cont’d Frequency Modulation 2.4 GHz Narrowband Communication 1 Time-domain behavior Frequency-domain behavior Impulse Modulation 3 10 GHz frequency Ultrawideband Communication time 1 (FCC Min=500Mhz) Communication that occupies more than 500 MHz of spectrum Communication with fractional bandwidth of more than 0.2

UWB Spectrum FCC allows spectrum overlap for UWB 1.6 1.9 2.4 Bluetooth, 802.11b Cordless Phones Microwave Ovens GPS PCS 5 802.11a -41 dBm/Mhz “Part 15 Limit” UWB Spectrum Frequency (Ghz) Emitted Signal Power 10.6 3.1 UWB can operate between 3.1 and 10 GHz as long as it stays below -41dBm

Good things about UWB 7.5 GHz of “free spectrum” in the US. The spectrum allocation for UWB overlays existing spectrum but the FCC power limitations are set to minimize interference with existing systems. High Data rates – under current regulations 500 Mbps at 10 feet.[1] Due to the short-pulse waveform of an UWB signal, they can be used to provide extremely high data rate performance in multi-user network applications. Also, when used for radar, these pulses provide a very fine range resolution and position measurement. Can function on simple CMOS transmitters so: Low cost – maybe whole radio can be digital with integrated antenna Ideal for battery powered devices “Moores Law Radio” – The data rate scales with the shorter pulse widths which are made increasingly faster by CMOS circuits

Good things cont’d When used for radar, these pulses provide a very fine range resolution and position measurement See through walls Imaging

And more… waves are relatively immune to multi-path cancellation When a strong reflected wave arrives partially or totally out of phase with the direct path signal thus canceling part of the signal—reduced amplitude at the receiver end. Therefore ideal for high-speed networked, mobile wireless applications. The signals are multiplexed in the time domain so protocols like TDMA can be used to implement this. UWB system is frequency adaptive. In other words, it can be positioned anywhere in the RF spectrum and still use its full bandwidth.

Good things about UWB cont’d

Low Energy Density Because of the short pulse duration, the signal can span the RF spectrum, and that at a low energy density. This makes the signal harder to detect by “unfriendly” receivers But Drawback A drawback of the LPD is that it may produce a “minimal interference to proximity systems and minimal RF health hazards Localization Sub-centimeter resolution using pulse leading edge detection passes through building blocks, walls, etc. (LOS not required) Difficult to intercept in traditional ways Low interference Very low spectral energy density

Early Implementation Take a wideband microwave antenna and use fast rise-time pulse excitations to generate the antennas “impulse” response (it is actually the antenna’s step response that is produced and radiated). Problem: generates a lot of unwanted, out-of-band radiation which can cause interference with other systems. Modern techniques create a UWB waveform through pulse shaping prior to actual transmission. This gives control to the engineers to prevent radiation into restricted bands, thus preserving safely and life systems.

Safety Concerns Safety-of-flight systems

UWB not perfect Since this is an RF technology it still has some of the same limitations that are inherent in RF systems. In designing a UWB system, address tradeoffs like signal-to-noise ratio versus bandwidth, range versus power levels. This technology isn’t the answer to everything. For example, high capacity optical fiber or optical wireless systems can still provide higher data rates, although these systems are much more expensive in both component cost and installation.

References http://www.timedomain.com http://www.palowireless.com/uwb/tutorials.asp Technical Issues in Ultra-Wideband Radar Systems Harold F. Engler, Jr. Chapter Two, Introduction to Ultra-Wideband Radar Systems, edited by James D. Taylor, CRC Press, 1995 http://www.aetherwire.com/CDROM/General/papers.html