Datasheet

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SX1272/73
WIRELESS, SENSING & TIMING DATASHEET
Rev. 2 - July 2014
©2014 Semtech Corporation
4.1.1.6. LoRa
TM
Packet Structure
The LoRa
TM
modem employs two types of packet format, explicit and implicit. The explicit packet includes a short header
that contains information about the number of bytes, coding rate and whether a CRC is used in the packet. The packet
format is shown in the following figure.
The LoRa
TM
packet comprises three elements:
 A preamble.
 An optional header.
 The data payload.
Figure 6. LoRa
TM
Packet Structure
Preamble
The preamble is used to synchronize receiver with the incoming data flow. By default the packet is configured with a 12
symbol long sequence. This is a programmable variable so the preamble length may be extended, for example in the
interest of reducing to receiver duty cycle in receive intensive applications. The transmitted preamble length may be
changed by setting the registers RegPreambleMsb and RegPreambleLsb from 6 to 65535, yielding total preamble lengths
of 6 + 4 to 65535 + 4 symbols, once the fixed overhead of the preamble data is considered. This permits the transmission
of near arbitrarily long preamble sequences.
The receiver undertakes a preamble detection process that periodically restarts. For this reason the preamble length
should be configured identical to the transmitter preamble length. Where the preamble length is not known, or can vary, the
maximum preamble length should be programmed on the receiver side.
Header
Depending upon the chosen mode of operation two types of header are available. The header type is selected by the
ImplictHeaderModeOn bit found within the
RegModemConfig1 register.
Explicit Header Mode
This is the default mode of operation. Here the header provides information on the payload, namely:
 The payload length in bytes.
 The forward error correction code rate
 The presence of an optional 16-bits CRC for the payload.