mDot data transmission constraints

[FARRUKH]

Hello again!
I’m using AT commands for transmitting some data from one mDot and receiving at other in serial mode.

When I transmit one data packet each second, I receive two packets all together after exactly two seconds,
When I transmit one data packet every two seconds or with more delay in between, reception is alright.
Doing reception of data with interrupt, don’t think there is any issue with receive side.

Where I can find limitations/constraints to be considered while transmitting data?

mDot buffer size is 512 bytes, if data is written to this buffer, will it start transmitting packet instantly ? or will take some time before transmission starts?

Update: I’ve just tied receiver mDot directly to uart-usb converter, and found it actually receives two packets together.

• This topic was modified 7 years, 3 months ago by FARRUKH.

[Mark Makarychev]

Are you using the EU868 or US915 band? Sounds like this might be due to duty-cycle restrictions. US915 has a 400ms TX time restriction, whereas EU868 generally has a 1% TX duty-cycle (spread across about 8 channels, so almost 10%). If the mDot tries to send a message, but doesn’t find an available channel (where its duty-cycle timeout hasn’t ended yet), it will try to transmit this package together with the next one, when it gets an available channel. I’m not 100% sure, but I believe this is the procedure that goes on when there are no more available channels at a given time.

[FARRUKH]

I’m using mDot 868, Serial Data mode, 0.25kbps data rate.
Channel selection is automatic while using serial mode, right?
I’m still unable to locate issue, one mDot sends packet to other, and other one replies back, whole process taking four seconds, packet is always sent after about two seconds of writing it from COM port at 9600 baud. There may be some timeout parameter that isn’t mentioned in AT command manual.

[Jason Reiss]

P2P uses a single channel.

869.525 can use 10% duty-cycle
869.7-870 can use 100% if erp < 7dBm Setting for 100% duty-cycle At+txf=869850000 At+txp=4 At+ant=3 http://www.erodocdb.dk/docs/doc98/official/pdf/rec7003e.pdf

[Jason Reiss]

Also, at DR0, 50 bytes payload will take 2.5 seconds to transmit.

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