GPS World - January 2008 - (Page 32)

SYSTEM DESIGN & TEST | Receiver Design be identical with and without the LNA if the C/N0 is kept constant. Conversely, any signiﬁcant diﬀerences in measured performance may indicate inadequate end-to-end gain, the presence of measurable interference in the vicinity of the RF chain, or both. Static, Moving. All the tests described above are normally performed with a static scenario, since this typically results in the best receiver performance and it is reasonable to expect that manufacturers’ data sheet numbers are derived this way. It is also informative, however, to perform all the tests described here with a moving scenario, since the behavior of a receiver’s tracking loops can change signiﬁcantly with dynamics. In particular, some high-sensitivity receivers are known to employ a “pinning” mode, in which tracking sensitivity is increased by adjusting the receiver’s loop characteristics on-the-ﬂy when the receiver detects that it is stationary. Unfortunately, the choice of motion trajectories is entirely arbitrary. Aside from the “racetrack” scenario described in the 3GPP speciﬁcations for assisted GPS testing, there has been no standard trajectory proposed for dynamic testing to date. To this end, we propose a simple circular trajectory as a starting point for dynamic measurements. is trajectory has several beneﬁts: First, the symmetry of a circular path means that the eﬀects of signal power transitions are not dependent on a par- ticular location in the trajectory, and are therefore insensitive to timing. Second, the constant two-dimensional acceleration ensures that receivers are tested beyond the point where simple linear position propagation (which is a form of “dead reckoning”) could be used in the navigation ﬁlter to improve receiver performance. is, in other words, is a more stringent test. Absent other speciﬁc requirements, reasonable parameters for the circular trajectory are radius = 500 meters, tangential velocity = 10 meters/second. In any case, the almanac initialization period described in the tests above should be performed before circular motion is initiated, ensuring the initialization runs to completion successfully. Constellation, Calibration, TTFF. As noted in the description of the acquisition and reacquisition tests, the statistical nature of TTFF testing makes it challenging to obtain results with high statistical conﬁdence. Speciﬁcally, the TTFF depends on two separate (but related) processes: how long it takes to identify at least four satellites in the RF signal, and how long it takes to decode enough navigation data from all four satellites to get a ﬁx. Each number is important in its own right: in the case of assisted GPS (or in cases where recent good data is stored in memory), navigation data is already provided, so TTFF is entirely dependent on ﬁnding the signals (that is, the ﬁrst process). By comparison, in the case of standalone GPS, ArtechHouse.com—Your Destination for the Latest GNSS Know-How Just-Published Titles at an Exclusive 15% GPS World Discount Principles of GNSS, Inertial, and Multisensor Integrated Navigation Systems Paul D. Groves ISBN: 978-1-58053-255-6 Offers a solid understanding of satellite navigation, inertial navigation, terrestrial radio navigation, dead reckoning, feature matching, and integrated navigation. Covers all short-range wireless positioning methods, surveying each technique’s theory of operation, advantages and disadvantages, applicability in different domains, implementation procedures, and accuracy. Wireless Positioning Technologies and Applications Alan Bensky ISBN: 978-1-59693-130-5 Order now at ArtechHouse.com. Enter promotion code GPS08 in the online shopping cart to receive your savings. Offer expires 2/29/08. 685 Canton Street Norwood, MA 02062. Phone: 781-769-9750, Toll-Free 1-800-225-9977 32 GPS World | January 2008 www.gpsworld.com http://www.ArtechHouse.com http://www.ArtechHouse.com http://www.ArtechHouse.com http://www.gpsworld.com

Table of Contents Feed for the Digital Edition of GPS World - January 2008

GPS - January 2008 Contents Out in Front Expert Advice The Money-Go-Round u-Nav Latest Acquisition Apples to Apples Global SBAS 2008 GPS Receiver Survey Advertisers Index & Company Directory The Manufacturer's Road Year of the Who Working Indoor Up and Down Good, Better, Best Marketplace Classifieds Seen + Heard

GPS World - January 2008

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