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--- sensors:gnss:low_latency [2012/11/07 12:15]
karina
+++ sensors:gnss:low_latency [2021/08/14 04:21] (current)
@@ Line 6: / Line 6: @@
 [[http://www.scribd.com/doc/91055018/19/Fast-Update-Synchronized-RTK-5-or-10-Hz]]\\
-{{ :sensors:gnss:figure2_1.png?300 |Figure 2.1 Factors contributing to RTK latency}}
+The following description also applies to AgGPS542.
-A large part of the solution latency in Synchronized RTK processing is due to the data formatting and transmission of the base station data to the rover (see Figure2.1). The BD950 receiver includes a Low Latency positioning mode for applications that demand centimeter-level accuracy almost instantaneously. The Low Latency positioning mode delivers 20Hz position fixes with around 20msec latency with a precision that is only slightly less accurate than Synchronized RTK positioning.\\
+A large part of the solution latency in Synchronized RTK processing is due to the data formatting and transmission of the base station data to the rover (see Figure2.1). The BD950 receiver includes a Low Latency positioning mode for applications that demand centimeter-level accuracy almost instantaneously. The Low Latency positioning mode delivers 20Hz position fixes with around 20msec latency with a precision that is only slightly less accurate than Synchronized RTK positioning.
-The Low Latency positioning scheme relies on the predictability of the base station phase data. Phase measurements observed at a fixed base receiver generally exhibit a smooth trend. Variations in the carrier phase are caused by:
-  * Cycle slips
-  * Satellite motion
-  * Receiver and satellite clock variations
-  * Atmospheric delay
-Given a brief history of base station phase measurements, the BD950 receiver is able to accurately predict what they will be in the next few seconds. Instead of waiting for base station carrier phase measurements to arrive, the BD950 rover predicts or projects what the base carrier phase measurements will be for the current epoch. A baseline solution is then generated using the projected base stationcarrier phase measurements and the observed rover receiver carrierphase. The latency of the position solution derived from projected carrier phase is around 20 milliseconds for the BD950 receiver.\\
-With the Low Latency positioning scheme, accuracy is traded for timeliness. An increase in the data link delay relates to an increase in the projection time of the base station phase data. This leads to an increase in the uncertainty of the RTK solution. Figure2.3 presents an empirically derived model for the base receiver phase projection errorsas a function of data link delay.
-{{ :sensors:gnss:figure2_3.png?300 |Figure2.3 Phase projection for the low latency RTK solution}}
-The base phase prediction errors are governed by:
-  * Unmodeled Selective Availability errors
-  * Short term instabilities in the receiver and satellite clocks
-  * Unmodeled satellite orbit variations
-A data link latency of 1 second would result in phase projection errors approaching 0.02 cycles (0.004m). Multiplying the phase projection errors by a PDOP of 3.0 would yield an increase in noise for the Low Latency RTK solution of 3.0 × 0.004 = 0.012m over the Synchronized RTK solution. In many applications the slight noise increase in the Low Latency Solution is tolerable.
+{{ :sensors:gnss:figure2_1.png?300 |Figure 2.1 Factors contributing to RTK latency}}

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