What is PPP or Precise Point Positioning?

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- everything RF

Oct 14, 2020

Precise Point Positioning (PPP) is a navigation technique that is used to provide high-level position accuracy using GNSS Satellites. PPP makes use of a network of global reference stations to compute precise estimates of GNSS satellite orbits and clock errors. These calculations are then delivered to the end-user via satellite or over the internet. The PPP technique is more robust and accurate than Real Time Kinematics (RTK) and the Differential Global Navigation Satellite System (DGNSS) techniques. This technique can deliver an accuracy of up to 3 centimeters. This positioning technique is widely used in robotics, autonomous navigation, agriculture, construction, mining and where centimeter-scale precision is generally needed.

Like most GNSS techniques that rely on satellite signals, PPP is affected by satellite line-of-sight obstructions. The accuracy of the satellite clocks and orbits is one of the most important factors affecting the quality of the PPP algorithm. However since it gets the reference signal from the Satellite, it can require a line-of-sight view.

Another point to note is that PPP takes significantly more time than RTK and SBAS systems to get an accurate location fix. It can take up to 40 min (usually 10-15 min) to receive and compute satellite orbit / receiver clock information. However, if precise reference satellite orbit and receiver clock information is readily available in PPP can provide real-time location. There has been no standard defined for Real-Time PPP, but a standardization effort is being carried by the Radio Technical Commission for Maritime Services (RTCM).

Other factors that can affect PPP is the number of satellites available, satellite geometry, receiver multipath environment and atmospheric conditions. For example, when a GNSS signal passes through the charged particles of the ionosphere and then through the water vapor in the troposphere, it slows down and creates a receiver clock error. This process is called ionospheric delay. However, this delay can be mitigated by using a Dual-Frequency GNSS solution. In this case, two separate signals at different frequencies (L1 and L5) can be used. Since both signals operate at different frequencies they will have different wavelengths both signals will not get affected by the ionosphere at the same time.

RTK vs PPP for Positioning

  • The PPP technique does not require any local reference stations in the vicinity of the GNSS Receiver
  • PPP is more accurate than RTK i.e PPP can provide an accuracy of up to 3 cm and RTK up to 10 cm
  • PPP takes significantly longer to acquire a precise location than RTK
  • PPP is impacted more by tropospheric and environmental effects than RTK