Data Sheet

Page 82
RFM95/96/97/98(W)
Tel: + 86-755-82973805 Fax: [phone] E-mail: [e-mail] http:/ / www.hoperf.com
WIRELESS & SENSING PRELIMINARY DATASHEET
Table 83 RssiSmoothing Options
RssiSmoothing Number of Samples Estimated Accuracy Response Time
‘000’ 2 ± 6 dB
‘001’ 4 ± 5 dB
‘010’ 8 ± 4 dB
‘011’ 16 ± 3 dB
‘100’ 32 ± 2 dB
‘101’ 64 ± 1.5 dB
‘110’ 128 ± 1.2 dB
‘111’ 256 ± 1.1 dB
2
( RssiSmoothing + 1 )
4 · RxBw [ kHz ]
[ ms ]
The RSSI is calibrated when the image and RSSI calibration process is launched.
5.5.5. RSSI in
LoRa
TM
Mode
The RSSI values reported by the LoRa
TM
modem differ from those expressed by the FSK/OOK modem. The following
formula shows the method used to interpret the LoRa
TM
RSSI values.
R S S I [ dB m ] = –137 + RSSI
5.5.6. Channel Filter
The role of the channel filter is to reject noise and interference outside of the wanted channel. The RFM95/96/97/98(W)
channel filtering is implemented with a 16-tap finite impulse response (FIR) filter. Rejection of the filter is high enough that
the filter stop-band performance is not the dominant influence on adjacent channel rejection performance. This is instead
limited by the RFM95/96/97/98(W) PLL phase noise.
Note To respect sampling criterion in the decimation chain of the receiver, the communication bit rate cannot be set at a
higher than twice the single side receiver bandwidth (BitRate < 2 x RxBw)
The programmed single side bandwidth RxBw of the channel filter is determined by the parameters RxBwMant and
RxBwExp in RegRxBw:
RxBw =
------------------------
F
----
X
----
O
----
S
----
C
-------------------------
RxB wMant
× 2
RxBwE x p + 2
The following channel filter bandwidths are hence accessible in the case of a 32 MHz reference oscillator.
Table 84 Available RxBw Settings
RxBw (kHz) RxBwMant
(binary/value)
RxBwExp
(decimal)
FSK / OOK
10b / 24 7 2.6
01b / 20 7 3.1
00b / 16 7 3.9
10b / 24 6 5.2