3.3 Receive Windows

  1. Following each uplink transmission the end-device opens two short receive windows. The
  2. receive window start times are defined using the end of the transmission as a reference.

22

  1. See the LoRa radio transceiver datasheet for a description of LoRa radio packet implicit/explicit modes.
  2. This specification does not describe the transmission of multicast messages from a network server to many end-devices.
  3. No payload integrity check is done at this level to keep messages as short as possible with minimum impact on any duty-cycle limitations of the ISM bands used.

©2016 LoRa™ Alliance Page 11 of 70

The authors reserve the right to change specifications without notice.

LoRaWAN Specification

1
2 Figure 4: End-device receive slot timing.

3.3.1 First receive window channel, data rate, and start

  1. The first receive window RX1 uses a frequency that is a function of the uplink frequency and

5 a data rate that is a function of the data rate used for the uplink. RX1 opens

  1. RECEIVE_DELAY11 seconds (+/- 20 microseconds) after the end of the uplink modulation.
  2. The relationship between uplink and RX1 slot downlink data rate is region specific and
  3. detailed in the LoRaWAN Regional Parameters document [PARAMS]. By default the first
  4. receive window datarate is identical to the datarate of the last uplink.

3.3.2 Second receive window channel, data rate, and start

  1. The second receive window RX2 uses a fixed configurable frequency and data rate and
  2. opens RECEIVE_DELAY21 seconds (+/- 20 microseconds) after the end of the uplink
  3. modulation. The frequency and data rate used can be modified through MAC commands
  4. (see Section 5).The default frequency and data rate to use are region specific and detailed
  5. in the LoRaWAN Regional Parameters document [PARAMS].

3.3.3 Receive window duration

  1. The length of a receive window must be at least the time required by the end-device‘s radio
  2. transceiver to effectively detect a downlink preamble.

3.3.4 Receiver activity during the receive windows

  1. If a preamble is detected during one of the receive windows, the radio receiver stays active

21 until the downlink frame is demodulated. If a frame was detected and subsequently

  1. demodulated during the first receive window and the frame was intended for this end-device
  2. after address and MIC (message integrity code) checks, the end-device does not open the
  3. second receive window.

3.3.5 Network sending a message to an end-device

  1. If the network intends to transmit a downlink to an end-device, it will always initiate the
  2. transmission precisely at the beginning of one of those two receive windows.

1 RECEIVE_DELAY1 and RECEIVE_DELAY2 are described in Chapter 6.

©2016 LoRa™ Alliance Page 12 of 70

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LoRaWAN Specification

3.3.6 Important notice on receive windows

  1. An end-device shall not transmit another uplink message before it either has received a
  2. downlink message in the first or second receive window of the previous transmission, or the
  3. second receive window of the previous transmission is expired.

3.3.7 Receiving or transmitting other protocols

  1. The node may listen or transmit other protocols or do any transactions between the
  2. LoRaWAN transmission and reception windows, as long as the end-device remains
  3. compatible with the local regulation and compliant with the LoRaWAN specification.

©2016 LoRa™ Alliance Page 13 of 70

The authors reserve the right to change specifications without notice.

LoRaWAN Specification

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