RF98 datasheet(28/121 Pages) HOPE

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RF96/97/98

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WIRELESS & SENSING

PRELIMINARY

DATASHEET

Principle of Operation

The principle behind the FHSS scheme is that a portion of each LoRaTM packet is transmitted on each hopping channel

from a look up table of frequencies managed by the host microcontroller.

After a predetermined hopping period the

transmitter and receiver change to the next channel in a predefined list of hopping frequencies to continue transmission

and reception of the next portion of the packet. The time which the transmission will dwell in any given channel is

determined by HoppingPeriod which is an integer multiple of symbol periods:

HoppingPeriod = Ts × FreqHoppingPeriod

The frequency hopping transmission and reception process starts at channel 0. The preamble and header are transmitted

first on channel 0. At the beginning of each transmission the interrupt the channel counter FhssPresentChannel is

incremented and the interrupt signal FhssChangeChannel is generated. The new frequency must then be programmed

within the hopping period to ensure it is taken into account for the next hop, the interrupt FhssChangeChannel is then to be

cleared by writing a logical

„1‟.

FHSS Reception always starts on channel 0. The receiver waits for a valid preamble detection before starting the

frequency hopping process as described above. Note that in the eventuality of header CRC corruption, the receiver will

automatically request channel 0 and recommence the valid preamble detection process.

Timing of Channel Updates

The interrupt requesting the channel change, FhssChannelChange, is generated upon transition to the new frequency. The

frequency hopping process is recapitulated in the diagram below:

Figure 6. Interrupts generated in the case of successful frequency hopping communication.

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