GPS World - January 2008 - (Page 28)

SYSTEM DESIGN & TEST | Receiver Design 12 11 10 9 8 7 6 5 4 3 GSA 2 GSV 1 0 1500 1800 2100 2400 2700 3000 3300 3600 3900 4200 4500 4800 5100 5400 5700 6000 6300 6600 6900 -148 -148.5 -149 -149.5 -150 -150.5 -151 -151.5 -152 -152.5 -153 -153.5 -154 -154.5 -155 -155.5 -156 -156.5 Simulation time (sec) / Power level (dBm) 100 90 80 2D position error (meters) 70 60 50 40 30 20 10 0 -125 -130 -135 -140 -145 -150 Signal power on all satellites (dBm) -155 -160 Mean (ACQ) Mean (TRK) 50th %ile (ACQ) 50th %ile (TRK) 95th %ile (ACQ) 95th %ile (TRK) Number of satellites reported p FIGURE 3 Number of satellites tracked (GSV) and used in navigation fix (GSA) versus signal power 100 90 80 Percent of measurements 70 60 50 40 30 20 10 0 -148.5 -149 -149.5 -150 -150.5 -151 -151.5 -152 -152.5 -153 -153.5 -154 -154.5 -155 -155.5 -156 -156.5 -157 GPS signal power on all satellites (dBm) 3D Fix 2D Fix No Fix p FIGURE 5 2D error versus signal power for cold start first fix (dashed) and tracking (solid) in a static scenario p FIGURE 4 Position availability versus signal power NavtechGPS GNSS Education Since 1984 UPCOMING COURSES Have you registered?* February 25-29, 2008 New Orleans, Louisiana USA Course 356 - GPS Operations for Engineers and Technical Professionals (5 Days) 1, 2 and 3 day courses also available June 2-6, 2008 Annapolis, Maryland USA Course 356 - GPS Operations for Engineers and Technical Professionals Course 447 - Applied Kalman Filtering (4.5 Days) Course 448 - Advanced Receiver Processing of GNSS Signals (4 Days) $25.00 Off * Mention this ad when you call to register or of our on-line registration and receive $25.00 off your total course fee. www.NavtechGPS.com 800.628.0885 or 703.256.8900 courses@navtechgps.com makes it possible to assess whether or not a given receiver’s navigation output is still practically usable as the receiver approaches its tracking sensitivity limit, and to quantify the degradation in accuracy. e deﬁnitions of position tracking sensitivity, signal tracking sensitivity, and availability described earlier can be used to extract the desired ﬁgures of merit from the plots. Acquisition. The determination of the acquisition threshold is somewhat more challenging to automate in a single run than the tracking test. Instead, the test must be carried out in batches of independent trials at each power level. The range of power levels and the number of trials at each level are determined by user requirements on statistical conﬁdence, as follows. For this test, we follow the methodology outlined in Annex F.6 of 3GPP Technical Standard 34.171, which contains a derivation relating a desired conﬁdence bound to a minimum number of successful independent trials. is method requires the user to ﬁrst choose a desired conﬁdence bound and two criteria — maximum acceptable TTFF and position error — for declaring a given acquisition attempt successful. (Absent other speciﬁc requirements, reasonable values are 95 percent conﬁdence bound, 300 seconds, and 100 meter 2D error, respectively.) Given a desired conﬁdence bound, the derivation speciﬁes the required number of good starts (as deﬁned by the success criteria) necessary to consider the measurement statistically valid. Once the above-mentioned values are determined, the simulator is set to an initial power level of –130 dBm, and a set of independent starts is performed. (When possible, it is extremely helpful to automate this step by means of a batch script or similar functionality in the receiver’s control interface.) For each start, the receiver is allowed to run until it either produces at least one valid position ﬁx or reaches the chosen TTFF time-out. If the receiver fails to produce a valid ﬁx within the allowed time, or fails to produce a ﬁx whose error is within the allowed limit, the attempt is recorded as a failure; otherwise it is recorded as a success. e process continues until the number of successes corresponding to the desired conﬁdence bound www.gpsworld.com 28 GPS World | January 2008 http://www.NavtechGPS.com http://www.NavtechGPS.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

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.