Rtcm messages: which one and how often to send them

Q&A forumCategory: QuestionsRtcm messages: which one and how often to send them
amorosik asked 3 months ago

At the link

https://www.ardusimple.com/configuration-files/

 
You can see an example of rtcm messages sent from the base station to the rover and precisely the messages are indicated:
1005: Stationary RTK reference station ARP
1074: GPS MSM4
1084: GLONASS MSM4
1094: GALILEO MSM4
1230: GLONASS code-phase

The question is: which minimum sending period/frequency is good to maintain in order to maintain the fixed state of the rover?
1 sec, 5 sec, 10 sec?

Is the period/frequency of the different messages the same for everyone or are there some that must be sent more frequently than others?
I ask this because I see that in the above link appears “..or increase 1005 to only be sent once every 5 seconds ..”
So having a slow rtcm corrections transmission channel, which logic is good to follow to decide which messages to send and how often to send them?

 

2 Answers
Ardusimple Staff answered 3 months ago

Hi Amorosik,
If your base-rover link allows it, for simplicity a good starting point is all messages once per second. If you need to reduce the bandwidth you do many things:

  • 1005 content is valid for a lot of seconds, if you send it every 10 seconds is enough
  • You can send corrections every 2 seconds and you will still get good accuracy, but if you miss one message you are actually delaying potentially to 4 seconds the interval between messages
amorosik answered 3 months ago

Thank you very much for the reply
“..1005 content is valid for a lot of seconds ..”
Where do you find this information?
And for the other messages, how long are they ‘valid’?

Ardusimple Staff replied 3 months ago

Hi amorosik,
There’s not an exact number, it depends on your accuracy requirements. the older the correction, the worse the accuracy you will get. Usually after 30-60 seconds the corrections are not valid anymore and the system has the same accuracy as without corrections.

clive1 replied 3 months ago

Both 1005 and 1230 carry constant data
The survey location of your antenna is not dynamic, and the biases in the receiver are design related. They are non-critical, send them often enough that you’re not waiting on them.
The MSM messages are realtime, where their value diminishes with age. Sending them frequently also counters packet loss in transit. The radio subsystem should not attempt to retry transmission. They get stale quickly and the receiver is not holding a long history buffer to back fit into the distant past. Figure a couple of seconds at most.