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--- sensors:gnss:synchronized [2012/11/07 13:27]
karina
+++ sensors:gnss:synchronized [2021/08/14 04:21] (current)
@@ Line 1: / Line 1: @@
 ==== Synchronized RTK mode ====
-Precise time reference — Many systems that must be accurately synchronized use GNSS as a source of accurate time. GNSS can be used as a reference clock for time code generators or Network Time Protocol (NTP) time servers. Sensors (for seismology or other monitoring application), can use GNSS as a precise time source, so events may be timed accurately. Time division multiple access (TDMA) communications networks often rely on this precise timing to synchronize RF generating equipment, network equipment, and multiplexers. (from [[http://en.wikipedia.org/wiki/GNSS_applications]])
+Very precise position reference, but only 1 hz output.
 == From: "BD950™ - Reference Manual": ==
 [[http://www.scribd.com/doc/91055018/19/Fast-Update-Synchronized-RTK-5-or-10-Hz]]\\
-Synchronized RTK is the most widely used technique to achieve centimeter-level position estimates between a fixed base station and a roving receiver. Typically, the update rate for Synchronized RTK is once per second (1Hz). With Synchronized RTK, the rover receiver must wait until the base station measurements are received before computing a baseline vector. The latency of the synchronized position fixes is dominated by the data link delay (seeFigure2.1). Given a 4800 baud data link, the latency of the Synchronized RTK fixes will approach 0.5 seconds. The solution latency could be reduced by using a 9600 baud or higher bandwidth data link.\\
+Synchronized RTK is the most widely used technique to achieve centimeter-level position estimates between a fixed base station and a roving receiver. Typically, the update rate for Synchronized RTK is once per second (1Hz). With Synchronized RTK, the rover receiver must wait until the base station measurements are received before computing a baseline vector. The latency of the synchronized position fixes is dominated by the data link delay (see Figure2.1). Given a 4800 baud data link, the latency of the Synchronized RTK fixes will approach 0.5 seconds. The solution latency could be reduced by using a 9600 baud or higher bandwidth data link.\\
-The Synchronized RTK solution yields the highest precision possible and suits low dynamic applications such as human-mounted guidance. Airborne applications such as photogrammetry, or aircraft landing system calibration, demand update rates in excess of 1 Hz, to sample the platform trajectory. Data postprocessing can generate the results of the mission back in the office. However, this would require raw GPS data to be stored and postprocessed. Postprocessing presents datamanagement problems, particularly for large data sets collected at 5 or 10Hz. The BD950 receiver includes a positioning mode—termed
+The Synchronized RTK solution yields the highest precision possible and suits low dynamic applications such as human-mounted guidance. Airborne applications such as photogrammetry, or aircraft landing system calibration, demand update rates in excess of 1 Hz, to sample the platform trajectory.
-//Fast Update Synchronized RTK// —which addresses high speedpositioning applications.
+{{ :sensors:gnss:figure2_1.png?300 |Figure 2.1 Factors contributing to RTK latency}}
-== Fast Update Synchronized RTK (5 or 10 Hz) ==
-The Fast Update Synchronized RTK scheme has the same latency andprecision as the 1 Hz synchronized approach. However, positionsolutions are generated 5 or 10 times per second (5 or 10 Hz), see Figure 2.2.
-{{ :sensors:gnss:fast_synchronized.jpg?300 |Figure2.2 Fast update rate synchronized RTK (5 Hz)}}
-The BD950 base station must be configured to output CMR data ineither the 5 Hz or 10 Hz CMR Mode. In the Fast Output Mode, theBD950 base receiver interleaves the 1Hz CMR measurement datawith highly compressed information at the x.2, x.4, x.6 and x.8 secondepochs for 5Hz output. At the 10Hz CMR output rate, packets aresent at x.1, x.2, x.3,..., x.9 seconds between the x.0 epochs. The totaldata throughput requirement for the Fast Mode is less than 9600 bpsfor 9 satellites.
-The BD950 rover synchronizes its own 5 or 10Hz measurements withthose received from the base. Results are then generated and can beoutput at 5 or 10 Hz. The data link throughput is critical to theoperation of the Fast Update Synchronized RTK scheme. Use at least a9600 baud data link to achieve satisfactory results.
-//Note – The Fast Update Synchronized RTK mode is only supported through the CMR format. The RTCM messages cannot be output at 5or 10 Hz.//

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