Issue link: https://read.uberflip.com/i/1428395
LoRaWAN ® L2 1.0.4 Specification © 2020 LoRa Alliance ® Page 18 of 90 The authors reserve the right to change specifications without notice. For uplink frames, the FCtrl content of the frame header is 513 514 Bits 7 6 5 4 [3..0] FCtrl ADR ADRACKReq ACK ClassB FOptsLen Table 8: FCtrl uplink frame format 515 516 4.3.1.1 Adaptive data-rate control in frame header (ADR, ADRACKReq in FCtrl) 517 LoRaWAN allows end-devices to use any of the possible data rates and transmit (TX) power 518 individually. This feature is used by Network Servers to adapt and optimize the number of 519 retransmissions, the data rate, and the TX power of end-devices. This is referred to as the 520 adaptive data rate (ADR) and, when it is enabled, end-devices will be optimized to use the 521 fastest data rate and minimum TX power possible. 522 ADR control may not be possible when radio channel attenuation changes rapidly and/or 523 continuously. When the Network is unable to control the data rate of an end-device, the end- 524 device's application layer SHOULD control it. It is RECOMMENDED that a variety of different 525 data rates be used in this case. The application layer SHOULD always try to minimize the 526 aggregated airtime, given the network conditions. 527 If the uplink ADR bit is set, the Network may control the number of retransmissions, the data 528 rate, and the TX power of the end-device through the appropriate MAC commands. If the ADR 529 bit is unset, the Network Server SHALL accept that the end-device MAY not comply with any 530 attempt to control the number of retransmissions, the data rate, or the TX power of the end- 531 device regardless of the received signal quality. The Network MAY still send commands to 532 inform the end-device of the recommended configuration using the LinkADRReq command. 533 An end-device SHOULD accept the channel mask controls present in LinkADRReq, even 534 when the ADR bit is not set. The end-device SHALL respond to all LinkADRReq commands 535 with a LinkADRAns indicating which command elements were accepted and which were 536 rejected. This behavior differs from when the uplink ADR bit is set, in which case the end- 537 device accepts or rejects the entire command. 538 539 Note: A Network Server may not infer any actual end-device state in the 540 case where the uplink ADR bit is not set, regardless of the state of the 541 individual Status bits of LinkADRAns. These are provided for offline 542 debugging. 543 544 When the downlink ADR bit is set, it informs the end-device that the Network Server is able to 545 send ADR commands. The end-device MAY set/unset the uplink ADR bit independently. 546 When the downlink ADR bit is unset, it signals the end-device that, owing to rapid changes of 547 the radio channel, the Network temporarily cannot estimate the best data rate. In that case, 548 the end-device has the choice to 549 Unset the ADR uplink bit and control its uplink data rate, TX power and channel plan 550 following its own strategy. This SHOULD be the typical strategy for a mobile end-device, or 551 Ignore it (keep the uplink ADR bit set) and apply the normal ADR backoff algorithm in the 552 absence of downlinks. This SHOULD be the typical strategy for a stationary end-device. 553