Part Two: UWB Definition & Advantages 3
Copyright 2012 Time Domain
Brief Description of Time Domain’s UWB Technology
Ultra Wideband (UWB) is a short duration, pulsed RF technology that achieves the highest possible
bandwidth at the lowest possible center frequency. The technology can be used for communications,
radar
1
, and ranging/location applications.
In contrast with spread spectrum radio technologies that achieve a few 100s of kilohertz (kHz) to 10s of
megahertz (MHz) of bandwidth, UWB signals are spread over a few gigahertz (GHz), achieving relative
bandwidths of 25-100%.
UWB systems achieve this bandwidth by transmitting an impulse-like waveform. Such waveforms are
inherently broadband. In fact, Fourier analysis teaches us that an ideal impulse (i.e., a waveform of a
given amplitude and infinitesimally short duration) would provide infinite bandwidth. As a result,
transmissions are quite unlike traditional RF modulated sine waves. Instead they resemble a train of
pulses. An example of an individual UWB pulse is shown in Figure 1.
0 1 2 3 4 5 6
7
8
-40
-30
-20
-10
0
dB
3.1
5.3
Frequency, GHz
-1000 -500 0 500 1000
-1
-0.5
0
0.5
1
t, pico seconds
Fig. 1: UWB waveform shown in time domain (at left) and frequency domain (at right)
While most UWB providers use some version of this waveform, there are several different approaches
to implementing UWB systems. Some companies transmit waveforms infrequently and use relatively
high energy pulses. Others send low energy pulses hundreds of millions of times per second. While a
few systems incorporate some level of coherent signal processing, most are non-coherent.
Time Domain relies on low duty cycle transmissions, with coherent signal processing and typical
repetition rates of 10 MHz. These UWB transmissions normally consist of a packet of between several
thousand and a few hundred thousand coherently transmitted pulses. Because the transmissions are
coherent, the signal energy can be spread over multiple pulses, thereby increasing the energy per bit
and consequently the signal to noise ratio (SNR).
Independent communications channels are established by pseudo-randomly encoding the phase,
position, and/or repetition rate of the pulse train. Data can be added to the transmissions by further
modulating either the phase and/or position of the pulses. The pseudo-random code and data are
typically applied not to individual pulses but to blocks of many pulses. This approach has been
implemented in the PulsON 400 (P400) family of Ranging and Communications Modules (RCM) and
Monostatic Radar Modules (MRM). This family currently includes the P400 andP410 devices. These
