RE: What is the maximum duty cycle with extended packed?

FormerMember — Wed, 23 Nov 2016 08:33:58 GMT

In FCC, the duty cycle is based on the maximum time on air on one channel over a period of 100 ms. So in a worst case scenario, we will have to consider that the transmit channel over 100 ms will remain the same.

The duty cycle will depend on the maximum amount of data that will be sent, the size of the packets on air, and the connection interval.

This is the sequence for one DLE packet:

Radio TX ramp-up is 150 us (TIFS), where 40 us of these will modulate a carrier on-air.

Radio RX ramp-up is 150 us, no modulation on-air in RX mode.

The worse-case scenario, which is 265 bytes packets (Preamble 1 byte + Access address 4 bytes + 2 bytes Header + 251 bytes user data payload + 4 bytes MIC + 3 bytes CRC) and with the shortest ACK possiblr (no user data back from the central), it will look like this:

(265 [bytes] / (1/1Mbit) [us]) * 8 = 2120 us of time transmitting the packet.

The ACK payload will consist of:

1 byte preamble + 4 byte address + 2 byte header + 3 byte CRC = 10 bytes = 80 us transmit time. In addition, there is a 150 us TIFS here, so the total time for receiving an ACK is 80 + 150 = 230 us.

The total time for one sequence in the worst-case scenario is (150 + 2120) + (150 + 80) = 2500 us.

The total time of modulated TX output is (40 us + 2120 us) = 2160 us.

The worst-case duty cycle is then: 2160 us/2500 us = 0.864 --> duty cycle: 86.4 %