RF96 datasheet(26/121 Pages) HOPE

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RF96/97/98

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WIRELESS & SENSING

PRELIMINARY

DATASHEET

4.1.1.6. LoRa

TM Packet Structure

The LoRaTM 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 LoRaTM packet comprises three elements:

 A preamble.

 An optional header.

 The data payload.

Preamble

Figure 5. LoRa

TM Packet Structure

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. However, the minimum length suffices for all

communication. The transmitted preamble length may be changed by setting the register PreambleLength 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 a near arbitrarily long preamble sequence.

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

ImplictHeaderMode

bit found within the RegSymbTimeoutMsb 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.

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