Electronic – Low latency, high channel period wireless protocols

5 bytes (8 bits) at 1kbaud (1000 Hz) means that the payload is 40 bits and this with my simple maths implies a minimum latency of 40 milli seconds. Given that the payload will need to be packaged like this....

• Preamble to lock-in the receiver possibly as low as 24 bits)
• Header (address of the receiver possibly 8 bits)
• Payload ( 40 bits)
• Error check (16 bits)

Total number of bits is 88 bits and at 1kbaud this is a latency of 88 milli seconds just to receive and check the data is valid.

Going at 10kbaud means a latency of obviously 8.8 milli seconds.

This device can transmit at 115.2kbps and has an output power of +8dBm so is a more likely contender and here is the matching receiver module: -

I've not gone into looking at these in any technical detail but they do seem the sort of module to use. They are FM too so there's a couple of dB more resilience for the same transmit power/ distance compared to AM.

My question is what is the lowest latency one way rf link?

You have to consider what an AM or FM receiver has to do to lock-in to a transmission and then consider how this might affect latency. See the picture below. The left (red) is random demodulated noise due to no transmission being present and, in the centre of the picture the transmission starts. Towards the right, the filtered receiver data slicer (blue) gains lock to the transmitted signal: -

You can't expect instantly to start receiving data unless you are transmitting some form of preamble all the time. This may not be allowed in some countries (at some frequencies) so do your homework and look for RF circuits that "get in lock" in the quickest possible time.

In my experience, locking into a freshly started preamble may take up to 10ms but there may be newer circuits out there that are much better. Clearly you also want to send data as fast as you can.