LoRaWAN Airtime calculator, LoRa Packet duration calculation

This page mentions LoRaWAN Airtime calculator with formula used for LoRa Packet duration calculation. This calculator calculates LoRa Packet Time on Air.

Introduction: As mentioned below LoRaWAN packet consists of three main parts viz. preamble, header and payload. This is shown in the following figures. It is further categorized into implicit and explicit packet.

Implicit mode does not contain header part where as Explicit mode contains it. Following table mentions Spreading factor with time on air for Bandwidth of 125 KHz.

LoRaWAN Airtime calculator used for LoRa Packet duration calculation

EXAMPLE#1 (LoRaWAN Airtime calculator, SF= 7):
INPUTS :SF = 7, CR =1, BW =125 KHz, Preamble Symbols = 8, Payload size = 10 bytes, Header = present, Low data rate optimization = disabled
OUTPUTS: Preamble duration = 12.544 ms , Header + Payload duration = 28.672, LoRa packet duration = 41.216 ms

EXAMPLE#2 : (LoRa Packet duration calculator , SF =11)
INPUTS :SF = 11, CR =1, BW =125 KHz, Preamble Symbols = 8, Payload size = 10 bytes, Header = present (i.e. enabled with value = 0) , Low data rate optimization = enabled (i.e. value = 1)
OUTPUTS: Preamble duration = 200.704 ms , Header + Payload duration = 376.832 ms, LoRa packet duration = 577.536 ms

Formula or Equations used for LoRaWAN Airtime calculation

Following formula/equations are used for LoRa Packet duration calculation. It calculates LoRa packet time while transmission in the air for LoRaWAN system.

Following are the abbreviations of terms used in the formula.
Ts or T_Sym indicates symbol duration in msec
PL indicates Payload size in bytes
SF indicates spreading factor which ranges from 7 to 12
BW indicates bandwidth which can be 125 KHz, 250 KHz or 500 KHz
CRC indicates Cyclic Redundancy Check used for error detection of LoRaWAN packet, it can be either enabled (value =1) or disabled (value = 0), By default it is enabled.
Header ('H') can be implicit or explicit, i.e. H of value 0 indicates it is enabled and it is explicit mode where as H of value 1 indicates it is disabled and it is implicit mode.
Low Data Rate Optimize can be enabled (Value of DE = 1) or disabled (Value of DE = 0)
CR indicates Coding Rate (CR can be in the range from 1 to 4), By default it is 1
T_preamble = Preamble duration, n_preamble = Number of symbols in preamble
T_payload = Payload and header duration
payloadSymbNb = Number of symbols in payload period

Also refer LoRa tutorial and LoRa technology basics which mentions LoRa system features, protocol stack, physical layer, MAC layer, frequency bands, LoRa Classes, LoRa transceiver etc.

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