Why do you need internet in your GNSS receiver?
Please note: Before reading this know we are trying to keep things simple so people can understand the very basics. As you can understand this is sometimes a challenge with complicated technology like this.
As you probably know it’s impossible for an RTK GNSS receiver to become centimeter accurate on its own. Whether it’s a €2000 or €20.000 RTK GNSS receiver, it will always need a correction source to optimize its performance (you can read in this article why this is necessary). There are two ways to get centimeter accurate RTK correction data. The first one is by setting up your own base station but that’s pretty time consuming and very sensitive for errors. This is the reason why most people choose a local RTK correction network (CORS network) like RTK FIX . This correction data, also known as RTCM, is sent over the internet. The protocol it’s using is called NTRIP. Because of this reason it’s necessary to have an active internet connection. Without internet you won’t be able to receive correction data from the RTK Network and no correction data means not being centimeter accurate.
The four components you need to get accurate RTK correction data are:
- RTK GNSS chip
- RTK netwerk (NTRIP caster)
- NTRIP client
In the RTK GNSS chip, the RTCM data is corrected. It takes the normal signals from the Global Navigation Satellite Systems along with a correction stream from an RTK correction network. An RTK network (NTRIP caster) is a CORS (Continuously Operating Reference Station) network which means it’s a network of multiple RTK GNSS base stations that broadcast corrections (like RTK FIX). The NTRIP client is the gateway for your correction data, it’s the place where the RTK correction data comes in. Without an NTRIP client it’s not possible to receive RTK correction data. The internet connects the NTRIP caster with the NTRIP client, so to receive all this data you’ll need to have an internet connection.
Why are there RTK GNSS receivers without an internet modem?
The reason there are RTK GPS receivers without an internet modem is because nowadays most land surveying software packages have NTRIP clients programmed in ( an NTRIP client is the gateway for your correction data). Because the software on your data collector or tablet now has the NTRIP client, your RTK GPS receiver doesn’t need it anymore. This does however mean that your data collector needs internet but most of them have this as a standard feature. Keep in mind there are still data collectors without an internet modem as well. You will notice that RTK GNSS receivers without internet are cheaper than RTK GNSS receivers with internet. You can see the connection diagram on how it works. (Keep in mind that this diagram is very simplified)
As you can see the NTRIP client on the data collector is making the connection to the RTK network via the internet (NTRIP). Your data collector (NTRIP Client) is sending its positioning data (GGA) to the RTK network (NTRIP caster/server). CORS networks like RTK FIX generate a virtual reference station to further optimize the accuracy but to do this it needs the users location. This is why GGA (positioning) data is important for VRS networks. After connecting the RTK network will send correction data (RTCM) to the NTRIP Client. This is the part that needs the internet.
The software on the data collector now has the correction data but can’t process it because the RTK GNSS chip is in the RTK GNSS receiver. The connection between the data collector (and thus software) to the RTK GPS receiver is made via bluetooth. This is a two-way connection. The data collector sends the correction data (RTCM) to the RTK GPS receiver so it can process it. On its turn it sends accurate positioning data (NMEA) back to the data collector so you can use it for surveying.
Here are some examples of RTK GNSS receivers without internet
Why are there GNSS receivers with an internet modem?
So why do manufacturers still produce RTK GNSS receivers with an internet modem installed? Well as you can probably understand, these RTK GPS receivers are not only used for land surveying. There are many applications where you need corrected positioning data (NMEA) straight out of the RTK GNSS antenna without any third party software. Think about a farmer that wants to ride a predetermined route over his land and only connects his RTK GPS receiver with an automatic steering system, the automatic steering system doesn’t have an NTRIP client and no internet so the NTRIP client must be in the RTK GNSS receiver and thus needs to have internet. There also still are data collectors with no internet in them which means the NTRIP client can’t be in the data collector. So the NTRIP client must be in the RTK GNSS receiver. You can see how that connection works on the diagram below.
As you can see, the GNSS receiver is the NTRIP client and is making the connection to the RTK network via internet. In this case is the GNSS receiver sending its positioning data (GGA) to the RTK network (NTRIP caster/server). And it gets the RTCM data from the RTK network which the chip in the receiver converts to NMEA data and sends it to a data collector (E.g. a tablet, drone or tractor).
Here are some examples of RTK GNSS receivers with internet
Which one do I need? 3G, 4G or 5G?
So now you know that having an internet modem in your GNSS receiver isn’t per se necessary. But if you came to the conclusion that you do need an internet modem in your GNSS receiver, what kind of internet modem do you need? Well this one is simple, everything above 3G is optimal, so 4G and 5G. Everything from 3G and below isn’t that great anymore. In some countries 3G doesn’t exist anymore and 2G will cease to exist in 2025. So if you want a GNSS receiver for the long term it’s better to choose one with 4G or 5G. 4G and 5G can also always downgrade, so if you’re somewhere where there is only 3G or 2G available, the 4G or 5G modem will downgrade to 3G or 2G so it will still be able to connect to the internet.
Here are some examples of RTK GNSS receivers with 4g or higher
Do I need internet in my RTK GNSS receiver?
It depends on where your NTRIP client is, is your NTRIP client in your data collector you don’t need internet in your RTK GNSS receiver. But is your NTRIP client in your RTK GNSS receiver you do need internet in you RTK GNSS receiver, otherwise it’s not possible to receive centimeter accurate RTK correction data.