08-01-2014, 12:38 PM
Ultra Wideband Technology for High Precision Ranging and Location
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Overview
Ultra Wideband (UWB) technology is typically defined as a wireless transmission scheme with a
bandwidth over 500 MHz, or occupying 20% or more of the carrier frequency.
UWB technology was initially made available in the 1980s, mainly for radar applications, due to the
wideband nature of the signal and its potential to provide very accurate ranging. More recently it
has become more attractive for low‐cost consumer applications involving either high speed
transmission or combined transmission and ranging capability. The technology was approved in 2002
by the Federal Communications Commission (FCC) for unlicensed use in the US. Subsequently, its
unlicensed use has been approved in Europe, Japan, Korea, and China.
Unlicensed use of UWB has sparked several years of intensive research resulting in the creation of
two standards groups, namely IEEE 802.15.3a TG and IEEE 802.15.4a TG, and an industry group, the
WiMedia Alliance.
Applications for Data Transmission, Ranging, and Location
In analyzing the main drivers for the development of UWB technology, we shall distinguish between
high rate/low range applications and low rate/ranging applications. In the first category, the main
application for UWB development is high bandwidth cable replacement for multimedia transmission.
This application is sometimes referred to as Wireless USB.
Market Perspective
UWB research has been very active for the last decade. This frantic activity has produced over 300
patents in UWB over last 30 years. Although major market players (e.g. Samsung, Nokia, Sony, LG,
Time Domain, Intel) accumulate a significant number of patents, innovation is widespread among a
much larger group of smaller companies, which is a typical situation of emerging technologies.
In the following we will continue distinguishing between high rate/low range UWB and low
rate/ranging UWB since the markets for target applications differ significantly.
low rate/ranging UWB
Low rate/ranging UWB has followed a slower pace both in standardization and in development of
equipment. It is based on modulated impulse technology, rather than OFDM technology, and it has
been finally standardized as IEEE 802.15.4a. Quite differently from the high rate application, in the
low rate/ranging arena, UWB still holds high promise due to its unmatched ranging capability.
Competing unlicensed technologies such as WiFi provide certain location capability based on
averaging of time of arrival timestamps, but its precision currently ranges from a few meters to a
few hundred meters. On similar environments, UWB can provide ranging accuracy in the order of
centimeters or less. In addition, the robustness of the UWB signal, which is underlay over a number
of licensed and unlicensed frequency bands, provides unmatched robustness to interference, which
is an important asset in critical safety applications.
Last years Ubisense, Zebra Enterprise Solutions and Time Domain have been commercializing precise
Real Time Location Systems (RLTS) based on non‐standard UWB technology. In adition, Decawave
have developed the first UWB transceiver IC that complies with the 802.15.4a standard. It will be in
mass production in 2011 and its main applications will be RLTS and ultra low power wireless
transceivers.
Performance
The ULAND® raw transmission rate is around 60 kbps, although the receiver skips frames due to non‐
real time operation, reducing the effective data rate. The data rate is limited by the transceiver
processing time and the size of the memory used in the FPGA, since the packets processing is done
offline. A real‐time processing implementation may be obtained implementing most of the receiver
processing on the FPGA. A maximum range up to 30m in line‐of‐sight (LOS) indoor conditions and a
root mean square error (RMSE) of the distance estimation under 50cm have been achieved. The
performance of the system regarding to the maximum range and ranging accuracy depends on the
detection algorithms used. Packet error rates lower than 0.3% have been achieved in ranges up to
25m, both indoors and outdoors.
These results have been obtained using energy detection algorithms. These algorithms do not
exploit all the benefits of the filter bank receiver. Therefore, this measurement campaign should be
understood as the lower bound of ULAND® performance. In fact, the resolution of the distance
measure is about 23cm. But in the other hand, all measurements show a promising standard
deviation (STD) lower than 30cm that can be improved with statistical averaging. As an example,
averaging five consecutive measures the maximum STD obtained is 13cm.