RPMA is a proprietary LPWAN technology provided by the company Ingenu.
In contrast to Sigfox and LoRa it operates in the unlicensed 2.4 GHz band, which is globally available.
No technical specification of the technology is publicly available !
RPMA uses DSSS modulation and applies a pseudo- random time of arrival that helps separating users that are multiplexed on the same radio resource [50].
Transmission consists of two slots, a downlink slot and an uplink slot.
Variable packet sizes can be transmitted within a slot.
RPMA uses closed loop power control and a large range of spreading factors can be selected. The transmission is adapted to the estimated link performance.
It is claimed that RPMA supports an extreme maximum path loss of around 170 dB.
TPA81 is a thermopile array detecting infra-red in the 2um-22um range.
Ah, RAK811 Rev 2.0?!, does that explain fact that the 811 Sensor & 811 tracker bds have been AWOL from RAK Ali shop in recent weeks/months? I have been using several of each since earlier in the year and now want to step up with more of each but couldnt find on Ali site to buy…reached out to both @kenyu & @rakwireless to ask where to buy but not even the courtesy of msg ack let alone response to key q of where to buy 
After (if i recall correctly) you flagging the 811N had ‘disappeared’ without warning of LTB opp earlier in the year I was/am concerned that the 811 Sensor & tracker bds also now obsolete, wasting my efforts wrt prod dev… 
Any clue wrt differences from earlier version?
sorry Jeff no I don’t… I’m just the messenger 