Issue link: https://read.uberflip.com/i/1428395
LoRaWAN ® L2 1.0.4 Specification © 2020 LoRa Alliance ® Page 13 of 90 The authors reserve the right to change specifications without notice. 3.3.2 First receive-window channel, data rate, and start 390 The first receive window RX1 uses a frequency that is a function of the uplink frequency and 391 a data rate that is a function of the uplink data rate. RX1 SHALL be open no longer than 392 RECEIVE_DELAY1 seconds after the end of the uplink modulation. 3 The relationship between 393 uplink and RX1 data rates is region-specific and detailed in the "LoRaWAN Regional 394 Parameters" [RP002] document. 395 3.3.3 Second receive window channel, data rate, and start 396 The second receive window RX2, if opened (see Section 3.3.1), uses a fixed configurable 397 frequency and data rate, and SHALL be open no longer than RECEIVE_DELAY2 seconds 398 after the end of the uplink modulation. 3 The frequency and data rate can be modified by MAC 399 commands (see Section 5). The default frequency and data rate are region-specific and 400 detailed in "LoRaWAN Regional Parameters" [RP002]. 401 3.3.4 Receive window duration 402 The duration of a receive window SHALL be at least the time required by the end-device's 403 radio transceiver to detect a downlink preamble starting at RECEIVE_DELAY1 or 404 RECEIVE_DELAY2 after the end of the uplink modulation. 405 406 Note: The end-device receive window duration has to accommodate the 407 maximum potential imprecision of the end-device's clock. The delay 408 between the end of the uplink and the start of the receive windows can 409 be changed from 1s to 15s for RX1 (and thereby from 2s to 16s for RX2) 410 using the OTAA (over-the-air activation) Join-Accept frame or the 411 RXTimingSetupReq MAC command. Therefore, this delay must be 412 accommodated when computing the maximum clock imprecision. 413 Example: A 30 ppm XTAL frequency error translates to ±30 µs after 1 s 414 and ±450 µs after 15 s. 415 3.3.5 Network transmitting to an end-device 416 If a Network Server intends to transmit a downlink to an end-device, it SHALL initiate the 417 transmission of the downlink frame precisely at the beginning of one of those two receive 418 windows. Such a downlink is referred to as a Class A downlink. The end-device SHALL open 419 a Class A RX1 receive window. If no frame intended for this end-device was received during 420 the RX1 receive window, the end-device SHALL open an RX2 receive window at the specified 421 timing, even if this interrupts the reception of a transmission using Class B or Class C downlink 422 timing and receive parameters. 423 3.3.6 Important notice regarding receive windows 424 An end-device SHALL NOT transmit another uplink packet before it has either received a 425 downlink packet in the first or second receive window related to the previous transmission or 426 if the second receive window related to the previous transmission has expired. 427 3 RECEIVE_DELAY1 and RECEIVE_DELAY2 are described in Section 6.