GPS World, January 2011
Vehicle Navigation RECEIVER DESIGN Aerial view of downtown Calgary from the southwest with test trajectory shown in red Dynamic Duo Combined GPS GLONASS Receivers in Urban Environments The impact of adding GLONASS to HS GPS is assessed using a software receiver operating in an actual urban canyon environment Results are compared with standard and high sensitivity GNSS receivers and show a significant improvement in the availability of position solutions when GLONASS is added An assisted high sensitivity receiver architecture is introduced which enables high fidelity signal measurements even in degraded environments Cillian ODriscoll Gérard Lachapelle and Mohamed Tamazin University of Calgary H igh sensitivity HS GNSS receivers have fl ourished in the last decade A variety of advances in signal processing techniques and technologies have led to a thousandfold decrease in the minimum useable signal power permitting use of GNSS in particular GPS in many environments where it was previously impossible Despite these recent advances the issue of availability remains in many scenarios there are simply too few satellites in view with detectable signals and a good geometry to compute a position solution Of course one way to improve this situation is to increase the number of satellites in view GLONASS has been undergoing an accelerated revitalization program of late such that there are currently more than 20 active GLONASS satellites on orbit The combined use of GPS and GLONASS in a high sensitivity receiver is a logical one providing a near two thirds increase in the number of satellites available for use The urban canyon environment is one in which the issue of signal availability is particularly important The presence of large buildings leads to frequent shadowing of signals which can only be overcome by increasing the number of satellites in the sky Even if suffi cient satellites are visible the geometric dilution of precision can often be large leading to large errors in position This work focuses on the advantages of using a combined GPS GLONASS receiver in comparison to a GPS only receiver in urban canyons The target application is location based services so only single frequency L1 operation is considered We collected and assessed vehicular kinematic data in a typical North American urban canyon using a commercially available high sensitivity GPS only receiver a commercial survey grade GPS GLONASS receiver and a stateof the art software receiver capable of processing both GPS and GLONASS www gpsworld com January 2011 GPS World 51
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