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RF96/97/98

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

pay l o a--d







WIRELESS & SENSING

PRELIMINARY

DATASHEET

The header is transmitted with maximum error correction code (4/8). It also has its own CRC to allow the receiver to

discard invalid headers.

Implicit Header Mode

In certain scenarios, where the payload, coding rate and CRC presence are fixed or known in advance, it may be

advantageous to reduce transmission time by invoking implicit header mode. In this mode the header is removed from the

packet. In this case the payload length, error coding rate and presence of the payload CRC must be manually configured

on both sides of the radio link.

Note

With SF = 6 selected, implicit header mode is the only mode of operation possible.

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 = --

---

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

follows:

p r e a mble = (np r e a m b le + 4.25 )Ts y m

where npreamble is the programmed preamble length, PreambleLength.The payload duration depends upon the header

mode that is enabled. The following formulae give the payload duration in implicit (headerless) and explicit (with header)

modes.



8lpayload – 4SF + 24









-------------------------------------

(CR + 4)

where: l

pay l o a d > 0, implicit header

s ym 8

ceil -------------

4SF



pay l oad = 





– 4SF + 44

-----------------------------

(CR + 4)

where: l

> 0, explicit header

 Tsym 8 ceil-------------------4SF



Addition of these two durations gives the total packet on -air time.

Tpacket = Tpreamble + Tpayload

4.1.1.8. Frequency Hopping with LoRa

Frequency hopping spread spectrum (FHSS) is typically employed when the duration of a single packet could exceed

regulatory requirements relating to the maximum permittable channel dwell time. This is most notably the case in US

operation where the 902 to 928 MHz ISM band can be used ina frequency hopping mode. To ease implementation of

FHSS systems the frequency hopping mode of the LoRaTM modem can be enabled (see FhssMode of register RegTxCfg1).

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