GPS World, January 2014

Algorithms Methods INNOVATION 80 70 60 50 40 30 20 10 0 500 1000 1500 2000 Epoch number PRN 9 PRN 12 PRN 14 PRN 15 PRN 18 PRN 19 PRN 21 PRN 22 PRN 25 PRN 27 FIGURE 6 Satellite elevation angles MEMS IMU Tactical Grade IMU 0 Degrees Size 762 953 813 cm 16 16 10 cm Mass 059 kg 0725 kg Max data rate 200 Hz 100 Hz Gyroscope Range 100 s 1000 s Bias 20 s 1 hr Scale factor 1 150 ppm Random walk 225 0125 Accelerometer Range 2 g 50 g Bias 30 mg 10 mg Scale factor 1 300 ppm Random walk 015 m s 0198 m s TABLE 1 Characteristics of the MEMS and tactical grade IMUs and a MEMS grade IMU were used This IMU is a six degree of freedom inertial system but data from only the vertical gyroscope the forward accelerometer and the transversal accelerometer was used TABLE 1 gives the main characteristics of both IMUs The odometer data was collected using a commercial data logger through an On Board Diagnostics version II OBDII interface Another GPS receiver of the same type was used for the base station measurements The GPS data was logged at 1 Hz Several road trajectories were driven using the above GHVFULEHG FRQ JXUDWLRQ H KDYH VHOHFWHG RQH RI WKH WUDMHFWRULHV which covers several real life scenarios encountered in a typical road journey to show the performance of the proposed algorithm The test was carried out in the city of Kingston Ontario Canada The starting and end point of the trajectory was near a wellsurveyed point at Fort Henry National Historic Site where the base station receiver was located The length of the trajectory was about 30 minutes and the total distance traveled was about 33 kilometers with a maximum baseline length of about 15 kilometers The trajectory incorporated a portion of Highway 401 with a maximum speed limit of 100 kilometers per hour and 0 100 200 300 400 500 600 3 2 1 0 ï ï ï ï Cycles Epochs FIGURE 7 DD carrier phase estimation error reference satellite with PRN 22 Measured Estimated 0 100 200 300 400 500 600 ï ï ï ï Cycles ï ï ï ï 2000 0 Epochs FIGURE 8 Measured versus estimated DD carrier phase reference satellite with PRN 22 suburban areas with a maximum speed limit of 80 kilometers per hour It also included different scenarios including sharp turns high speeds and slopes FIGURE 5 shows measured carrier phases at the rover for the different satellites Some satellites show very poor presence whereas some others are consistently available Satellites elevation angles can be seen in FIGURE 6 Results H VWDUW E VKRZLQJ VRPH UHVXOWV RI FDUULHU SKDVH HVWLPDWLRQ errors Processing is done on what is considered to be a cycle slipfree portion of the data set for some persistent satellites usually with moderate to high elevation angles Then we show results for WKH F FOH VOLS GHWHFWLRQ SURFHVV E DUWL FLDOO LQWURGXFLQJ F FOH slips in different scenarios In the ensuing discussion including WDEOHV DQG JXUHV ZH VKRZ UHVXOWV LQGLFDWLQJ VDWHOOLWH QXPEHUV without any mention of reference satellites which should be implicit as we are dealing with DD data FIGURE 7 shows DD carrier phase estimation errors whereas FIGURE 8 shows DD measured carrier phases versus DD estimated carrier phases for sample satellite PRN 22 As can be seen in TABLE 2 the root mean square RMS error varies from 093 to 358 cycles with standard deviations from 085 to 247 cycles Estimated phases are approximately identical to the measured ones Nevertheless most of the DD carrier phase estimates have www gpsworld com January 2014 GPS World 67