GPS World, March 2015

INNOVATION Algorithms Methods Where Are We Positioning in Challenging Environments Using Ultra Wideband Sensor Networks Zoltan Koppanyi Charles K Toth and Dorota A Grejner Brzezinska QUICK WHO WAS THE FIRST TO PREDICT THE EXISTENCE OF RADIO WAVES If you answered James Clerk Maxwell you are right If you didnt and have an electrical engineering or physics degree its back to school for you In the mid 1800s Maxwell developed the theory of electric and magnetic forces which is embodied in the group of four equations named after him This year marks the 150th anniversary of the publication of Maxwells paper A Dynamical INNOVATION INSIGHTS with Richard Langley Theory of the Electromagnetic Field in the Philosophical Transactions of the Royal Society of London Interestingly Maxwell used 20 equations to describe his theory but Oliver Lodge managed to boil them down to the four we are familiar with today Maxwells theory predicted the existence of radiating electromagnetic waves and that these waves could exist at any wavelength Maxwell had speculated that light must be a form of electromagnetic radiation In his 1865 paper he said This velocity of the waves is so nearly that of light that it seems we have strong reason to conclude that light itself including radiant heat and other radiations if any is an electromagnetic disturbance in the form of waves propagated through the electromagnetic field according to electromagnetic laws That electromagnetic waves with much longer wavelengths than those of light must be possible was conclusively demonstrated by Heinrich Hertz who between 1886 and 1889 built various apparatuses for transmitting and receiving electromagnetic waves with wavelengths of around 5 meters 60 MHz These waves were in fact radio waves Hertzs experiments conclusively proved the existence of electromagnetic waves traveling at the speed of light He also famously said I do not think that the wireless waves I have discovered will have any practical application How quickly he was proven wrong Beginning in 1894 Guglielmo Marconi demonstrated wireless communication over increasingly longer distances culminating in his bridging the Atlantic Ocean in 1901 or 1902 And as they say the rest is history Radio waves are used for data voice and image one way broadcasting and two way communications for remote control of systems and devices for radar including imaging and for positioning navigation and time transfer And signals can be produced over a wide range of frequencies from below 10 kHz to above 100 GHz Conventional radio transmissions use a variety of modulation techniques but most involve varying the amplitude frequency and or phase of a sinusoidal carrier wave But in the late 1960s it was shown that one could generate a signal as a sequence of very short pulses which results in the signal energy being spread over a large part of the radio spectrum Initially called pulse radio the technique has become known as impulse radio ultra wideband or just ultra wideband UWB for short and by the 1990s a variety of practical transmission and reception technologies had been developed The use of large transmission bandwidths offers a number of benefits including accurate ranging and that application in particular is being actively developed for positioning and navigation in environments that are challenging to GNSS such as indoors and built up areas In this months column we take a look at the work being carried out in this area by a team of researchers at The Ohio State University Innovation is a regular feature that discusses advances in GPS technology and its applications as well as the fundamentals of GPS positioning The column is coordinated by Richard Langley of the Department of Geodesy and Geomatics Engineering University of New Brunswick He welcomes comments and topic ideas To contact him see the Contributing Editors section on page 4 G NSS technology provides position navigation and timing PNT information with high accuracy and global coverage where line of sight between the satellites and receivers is assured This condition however is typically not satisfied indoors or in con ned environments Emerging safety military location based and personal navigation applications increasingly require consistent accuracy and availability comparable to that of GNSS but in indoor environments Most of the existing indoor positioning systems use narrowband radio frequency signals for location estimation such as Wi Fi or telecommunication based positioning including GSM and UMTS mobile telephone networks All these technologies require dedicated infrastructure and the narrowband RF systems are subject to jamming and multipath as well as loss of signal strength while propagating through walls In contrast using ultra wideband UWB signals can to some extent remediate those problems by offering better resistance against interference and multipath and they feature better signal penetration capability Due to these properties the use of UWB has the potential to support a broad range of applications such as radar throughwall imagery robust communication with high frequency and resistance to jamming Furthermore the impulse radio UWB IR UWB the subject of this article can be an efficient standalone technology or a component of positioning systems designed for multipath challenged con ned or indoor environments where GNSS signals are compromised IR UWB positioning can be useful in typical emergency response applications such as fires in large buildings dismounted soldiers in combat situations and emergency evacuations GPS World March 2015 www gpsworld com 44