Sending big data packet by radio. What consequences ?


I'm developing a sketch that sends big data packets. The RF payload contains 8 long.

I'm wondering if it will increase a lot the power consumption ? (that sketch will run on EmonTH)

Or if it will cause more data lost ?



Robert Wall's picture

Re: Sending big data packet by radio. What consequences ?

It will increase power consumption somewhat. You can get a good estimate of that because JeeLabs does give you the message format, so you can calculate the length of your total message and compare that with the 'standard' message.

A standard JeeLib packet is your payload plus 9 bytes. Therefore the default sketch sending 3 integers is 15 bytes, yours would be 41 bytes. As the transmit power is many times the standby/sleep power, a rough working assumption is the power consumption would be 41/15 times larger. Depending on transmission conditions, it might be possible to reduce the transmitted power and economise on current consumption that way. Or you might be able to increase the interval between transmissions to the same effect.

Data will only be lost if there are collisions in the r.f. band. If there are other transmitters sharing the band, then the probability of a collision is of course increased.

pb66's picture

Re: Sending big data packet by radio. What consequences ?

As indicated by Robert the key concern would be collisions if multiple nodes are in play, however if THIS emonTH is transmitting less frequently and the others are short payloads and/or non-battery powered the issue can be reduced.

The issue is due to the receiver being tied up for ~4x as long to process this packet and while its tied up other packets could be missed, if you made the other nodes request an ack they could retry and if they were short they would be less likely to block THIS emonTH but the chances of being blocked increases with both packet size and number of nodes.

Another concern with 8 longs is content. if they are all counters and start at 1 then you will lose alot of packets due to the receiver crc checks failing as the reciever won't be able to sync with the data packet with long runs of 0's, see Data loss due to RF packets getting corrupted,


Eric_AMANN's picture

Re: Sending big data packet by radio. What consequences ?

Thank you both for giving me this very accurate information.

This is exactly what I was expecting !


Paul, these longs are meter index. They do not start at 1. So, I would not be concerned by the receiver crc checks failure.





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