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Trimble R12i: Latest GNSS Receiver Has Breakthrough Enhancements

True North | Winter 2021

Trimble R12i: Latest GNSS Receiver Has Breakthrough Enhancements

Introduction

Real Time Kinematic (RTK) is a well-established concept in the surveying community. Base-Rover and Network based RTK configurations are used in a wide range of projects and applications. Surveyors are accustomed to looking at a job site and coming to quick conclusions as to where they can use their GPS equipment and where they can’t. Read on to see how this is changing.

It is understood that in a Base-Rover setup, radio range and its performance are limiting factors, and in a network solution, cellular signal strength or distance to correction sources are determining factors for accuracy and dependability. Receiving the critical corrections is at stake here. “Corrections” are literally the differential values that Base receiver finds by comparing its known coordinates and the real-time coordinates it measures. We can then make the presumption that the Rover is experiencing the same error vector at the same time. This enables us to calculate the accurate coordinates for the rover in real time.

Fig 1 - RTK Concept

Fig 1 - RTK Concept

But before corrections are utilized to achieve a “fixed” status/solution, the receiver first works out its initial “rough” position based on signals received from satellites. To that end, one needs an open sky and absence of three signal-starving conditions: blocking structures (lack of signal), reflecting objects (multipath signal) and partial passage (noisy signal). The use of GNSS (Global Navigation Satellite System) receivers is hindered by these factors in urban and forested areas. Trimble has introduced a new receiver that can mitigate these possible error sources better than any on the market today. (Drum roll, please)

Fig 2 - Signal-starving situations

Fig 2 - Signal-starving situations

Trimble R12i

Early in 2020 Trimble announced the R12 and R12i receivers. Was your reaction, “Well, another receiver and lots more channels nobody needs? After all, it looks the same as the R10 or R10-2, right? Over 600 channels, the same reported accuracy of 0.8/1.5 cm Horizontal / Vertical accuracy and pretty much a carbon copy of specification as before.”

There is a big difference though.

For the record, once the analog signals received through the antenna are converted to digital signals, they are fed into different channels, possibly 2-5 channels for each satellite. That is why the number of channels needed are so much more than numbers of satellites a receiver can possibly lock on to at any time.

To better understand how the Trimble R12 and R12i (R12i has Trimble “Tip” technology so you can measure with the pole out of plumb) read Ryan Zinck’s article in this newsletter. To get a fixed solution under canopy, we need to dive into the technical details.

The R12 and R12i series is a new breed of receiver that can process the received signals in a much different and more efficient way. The new processing system, called Trimble ProPoint, has two novel features: first, it uses the newly introduced L5 frequency and second, it has become frequency and constellation agnostic, both of which will be explained in the following paragraphs.

L5: The Real Game Changer

Historically, survey grade receivers were equipped to receive satellite signals in two frequencies (L1 and L2), transmitted from US NAVSTAR satellites (aka: GPS). These are carrier signals that are modulated with “message components”, i.e signals from different frequencies. L1 is used for main distance (pseudo-range) measurements and L2 is used for determination of the ionospheric and tropospheric effects on a measurement to improve the accuracy.

The game changer is the addition of a third frequency. L5 band as it is officially named, is the third civilian GPS signal. It is broadcasted in a radio band reserved exclusively for aviation safety services. It features higher power, greater bandwidth, and an advanced signal design. When combined with L1 and L2, L5 provides a highly robust service.

In 2009, the Air Force successfully broadcasted an experimental L5 signal on the GPS IIR-20(M) satellite, followed by the first GPS IIF satellite with a full L5 transmitter which was launched in May 2010. On February 5, 2016, the final satellite in the IIF-block was successfully launched, completing the block.

Briefly, L5 signals are more powerful, more accurate and more reliable. The higher power makes it possible to penetrate tree canopy and its wider bandwidth helps to mitigate multipath. Unlike the early, secretive days in Global Positioning, all countries have accepted a common baseline that facilitates use of L5 across the different constellations, such as Russian GLONASS, Chinese Beidou and European Galileo constellations.

Another important feature of L5 is that it is protected far better than L1 and L2 against external interferences. This, thanks to higher protection standards that aeronautical navigation radio services demand. At the time of this writing, 66 satellites are transmitting operational signals in L5.

It is expected that L5 will play a more central role, even in pseudo range measurements, eventually surpassing L1. L5 is also being considered to use alongside L1 in new cellphones for better positioning accuracy.

Frequency Agnostic Receivers

An open sky is vital to obtain a “fixed” status/solution. In North America, up to the early 2000s, only US GPS satellites were available. Later, GLONASS, Galileo and Beidou became available which eliminated the need for surveyors to perform mission planning to ensure they’d have six satellites at all times while they were surveying.

Nevertheless, getting a “fix” was still a challenge. Almost all receivers of the time needed to first get their “fixed” status on at least 5 to 6 US NAVSTAR satellites before adding other non-GPS satellites to augment the results. This dependency on the initial GPS “fix” was an obstacle that was mitigated by the introduction of constellation and frequency agnostic receivers. These receivers impartially mix all the received signals and process them with newly developed algorithms to create a faster and more dependable positional solution.

Trimble is among the first to implement all these features into the new ProPoint RTK engine that resides in the R12 and R12i receivers. It is limiting to suggest that ProPoint is only about L5 implementation or becoming constellation agnostic. Here is the official shortlist of the new ProPoint features:

  • Better RTK and Trimble RTX performance near canopy: Increased accuracy, reliability and productivity near tree canopy
  • Robust performance in urban environments: Advanced signal filtering and error modelling providing better protection against jamming and multipath
  • Flexible signal management: Survey-grade positioning using the most combinations of GNSS constellations and signals

Another improvement on data integrity is achieved by the updated HD-GNSS feature that has existed in Trimble R10 receivers for some time. HD-GNSS is a way to ensure the data quality over a whole range of position “fixes” covering from “float” solution to “fixed”. In many receivers you are either get a fixed or float message. Thanks to HD-GNSS you will get a realistic accuracy estimation that will allow you to measure a point even if the accuracy is not at its best e.g. 5 cm instead of standard 2 cm. ie, no float solution.

Finally, it is good to know that despite the name difference, R12 and R12i receivers have essentially the same hardware as the tried and true R10. R12(i) and R10 are both equipped with the new Maxwell 7 chip (rather than Maxwell 6 in R10) and again both have the same powerful processors and RF modules.

Make sure you book a demo of the R12 or R12i with your local Cansel representative. It will change the way you look at every job from this point forward.

Peter Afshar
3D Systems and Services Specialist
Cansel