SX1276IMLTRT View Datasheet(PDF) - Semtech Corporation

Part Name

Description

Manufacturer

SX1276IMLTRT

137 MHz to 1020 MHz Low Power Long Range Transceiver

Semtech Corporation 

WIRELESS, SENSING & TIMING

SX1276/77/78/79

DATASHEET

Low Data Rate Optimization

Given the potentially long duration of the packet at high spreading factors the option is given to improve the robustness of

the transmission to variations in frequency over the duration of the packet transmission and reception. The bit

LowDataRateOptimize increases the robustness of the LoRa link at these low effective data rates. Its use is mandated

when the symbol duration exceeds 16ms. Note that both the transmitter and the receiver must have the same setting for

LowDataRateOptimize.

Payload

The packet payload is a variable-length field that contains the actual data coded at the error rate either as specified in the

header in explicit mode or in the register settings in implicit mode. An optional CRC may be appended. For more

information on the payload and how it is loaded from the data buffer FIFO please see Section 4.1.2.3.

4.1.1.7. Time on air

For a given combination of spreading factor (SF), coding rate (CR) and signal bandwidth (BW) the total on-the-air

transmission time of a LoRaTM packet can be calculated as follows. From the definition of the symbol rate it is convenient

to define the symbol rate:

Ts = R--1---s

The LoRa packet duration is the sum of the duration of the preamble and the transmitted packet. The preamble length is calculated as

follows:

Tpreamble = (npreamble + 4.25)Tsym

where npreamble is the programmed preamble length, taken from the registers RegPreambleMsb and RegPreambleLsb.The

payload duration depends upon the header mode that is enabled. The following formula gives the number of payload

symbols.

npayload = 8 + maxceil (---8---P----L-----–-----4---S---F--4----+(--S--2-F--8----–-+---2--1-D--6---EC----)-R----C-----–-----2---0---I--H-----) (CR + 4), 0

With the following dependencies:

 PL is the number of Payload bytes (1 to 255)

 SF is the spreading factor (6 to 12)

 IH=0 when the header is enabled, IH=1 when no header is present

 DE=1 when LowDataRateOptimize=1, DE=0 otherwise

 CR is the coding rate (1 corresponding to 4/5, 4 to 4/8)

The Payload duration is then the symbol period multiplied by the number of Payload symbols

Tpayload = npayload × Ts

The time on air, or packet duration, in simply then the sum of the preamble and payload duration.

Tpacket = Tpreamble + Tpayload

Rev. 4 - March 2015

©2015 Semtech Corporation

Page 31

www.semtech.com

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