RFM95 datasheet(25/121 Pages) HOPERF

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Page 25

RFM95/96/97/98(W)

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WIRELESS & SENSING

PRELIMINARY

DATASHEET

Forward error correction is particularly efficient in improving the reliability of the link in the presence of interference. So that

the coding rate (and so robustness to interference) can be changed in response to channel conditions - the coding rate can

optionally be included in the packet header for use by the receiver. Please consult Section 4.1.1.6 for more information on

the LoRaTM packet and header.

4.1.1.4. Signal Bandwidth

An increase in signal bandwidth permits the use of a higher effective data rate, thus reducing transmission time at the

expense of reduced sensitivity improvement. There are of course regulatory constraints in most countries on the

permissible occupied bandwidth. Contrary to the FSK modem which is described in terms of the single sideband

bandwidth, the LoRaTM modem bandwidth refers to the double sideband bandwidth (or total channel bandwidth). The range

of bandwidths relevant to most regulatory situations is given in the LoRaTM modem specifications table (see Section 2.4.5).

Bandwidth

(kHz)

Spreading Factor

Coding rate

Nominal Rb

(bps)

7.8

4/5

10.4

4/5

15.6

4/5

20.8

4/5

31.2

4/5

41.7

4/5

62.5

4/5

146

125

4/5

293

250

4/5

586

500

4/5

1172

Note

In the lower band (169 MHz), the 250 kHz and 500 kHz bandwidths are not supported.

4.1.1.5.

LoRaTM Transmission Parameter Relationship

With a knowledge of the key parameters that can be controlled by the user we define the LoRaTM symbol rate as:

Rs = -----

---

2SF

where BW is the programmed bandwidth and SF is the spreading factor. The transmitted signal is a constant envelope

signal. Equivalently, one chip is sent per second per Hz of bandwidth.

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