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LoRaWAN® Specification v1.0.3

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LoRaWAN 1.0.3 Specification ©2018 LoRa™ Alliance Page 53 of 72 The authors reserve the right to change specifications without notice. 15 Beaconing (Class B option) 1390 15.1 Beacon physical layer 1391 Besides relaying messages between end-devices and Network Servers, gateways MAY 1392 participate in providing a time-synchronization mechanisms by sending beacons at regular 1393 fixed intervals. All beacons are transmitted in radio packet implicit mode, that is, without a 1394 LoRa physical header and with no CRC being appended by the radio. 1395 1396 PHY Preamble BCNPayload Figure 20 : beacon physical format 1397 The beacon Preamble SHALL begin with (a longer than default) 10 unmodulated symbols. 1398 This allows end-devices to implement a low power duty-cycled beacon search. 1399 The beacon frame length is tightly coupled to the operation of the radio Physical layer. 1400 Therefore the actual frame length and content might change from one region implementation 1401 to another. The beacon content, modulation parameters and frequencies to use are specified 1402 in [PHY] for each region. 1403 15.2 Beacon frame content 1404 The beacon payload BCNPayload consists of a network common part and an OPTIONAL 1405 gateway-specific part. 1406 1407 Size (bytes) 2 to 5 4 2 7 0 to 3 2 BCNPayload RFU Time CRC GwSpecific RFU CRC Compulsory common part Optional part Figure 21 : beacon frame content 1408 The common part contains an RFU field equal to 0, a timestamp Time in seconds since 1409 January 6, 1980 00:00:00 UTC (start of the GPS epoch) modulo 2^32. The integrity of the 1410 beacon's network common part is protected by a 16 bits CRC. The CRC-16 is computed on 1411 the RFU+Time fields as defined in the IEEE 802.15.4-2003 section 7.2.1.8. This CRC uses 1412 the following polynomial P(x) = x 16 + x 12 + x 5 + x 0 . The CRC is calculated on the bytes in the 1413 order they are sent over-the-air 1414 For example: This is a valid EU868 beacon frame: 1415 00 00 | 00 00 02 CC | A2 7E | 00 | 01 20 00 | 00 81 03 | DE 55 1416 Bytes are transmitted left to right. The first CRC is calculated on [00 00 00 00 02 CC]. The 1417 corresponding field values are: 1418 1419 Field RFU Time CRC InfoDesc lat long CRC Value Hex 0000 CC020000 7EA2 0 002001 038100 55DE Figure 22 : example of beacon CRC calculation (1) 1420 1421 The optional gateway specific part provides additional information regarding the gateway 1422 sending a beacon and therefore may differ for each gateway. The RFU field when applicable 1423

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