Capacity of LoRa gateway


(Quy-Lam Hoang) #1

LoRa is the technology help devices can send messages at different data rate depend on the Spread Factor.
I have a question about the Lora gateway. According to the question number 2 of this document LoRa-FAQs from Semtech, they said that:

They are multi-channel, multi-modem transceivers and can demodulate on multiple channels simultaneously and even demodulate multiple signals on the same channel simultaneously due to the properties of LoRa.

It can "demodulate multiple signals on the same channel simultaneously" means when 2 nodes transmit 2 packets on the same channel with different Spread Factor at the same time, the gateway can demodulate and receive successfully both of them. Is this true??? Can anyone explain that

Thank you


How many user support by Gateway?
#2

Hi and welcome to the TTN forum.

maybe this helps in understanding > http://sakshamaghoslya.blogspot.dk/p/lora_6.html
and did you see the webinair by Thomas Telkamp ?


(Quy-Lam Hoang) #3

Hi BoRRoZ,

Thanks for your reply. I've read that blogspot, and I understand the capacity of LoRa gateway.
But when I watched this video https://www.youtube.com/watch?v=hMOwbNUpDQA
From 15:30 second, the author explains the covering ability of the gateway and he said that it can cover 800 devices in parallel (8 channel, duty cycle 1%). Is it correct???
I think It should be 8_channels*6_SFs*100 = 4800 devices the gateway can cover (of course just in the theory)
That why I posted this question. Can you make it correct. Thanks


#4

if we talk about a gateway with a semtech chipset (SX1301) then this chip is able to to scan 8 channels for preambles at all data rates simultaneously up to 8 packets.
(one SF7 on IF0 / one SF12 on IF7 ect up to 8)
however it cannot demodulate more then 8 packets simultaneouly, so in fact the you tube video is right.
but he, I'm not a gateway specialist :sunglasses:


How many gateways are needed to support 1,000 nodes sending 10 bytes per 5 minutes?
(Zhijin) #5

According to the LoRa modulation, one example is given to show the benefit of LoRa on capacity as following. According to the calculation, LoRa should allow different users using different SFs to transmit over same frequency at the same time. But it is conflict with the LoRaWAN gateway which only can receive concurrently two different SFs on the same frequency. So confusing!


(Arjan) #6

Where did that "concurrently two different SFs" come from?


(Zhijin) #7


page 40


(Thomas Telkamp) #8

Indeed, that's not clear in the slides.

It says the concentrator can receive two different SFs on the same frequency (you changed that to 'only two'), meaning to say that you're not limited to only one.

But it should better read 'you can receive more than one SF concurrently on the same frequency'.


(Zhijin) #9

Thanks for the clarification. I agree with that the gateway can receive more than one SF concurrently on the same frequency. But then the question comes to the original one: can the SFs from 7-12 be used at the same time on the same frequency to support 6 nodes transmission concurrently or only 2 different SFs can be supported in LoRa?


#10

yes that should be possible imho

(off course NOT with a 'single channel' gateway based on a RFM 95 !)


(Quy-Lam Hoang) #11

I got it now. Thanks for your explanation ^^


(Zhijin) #12

Thanks for your info. In addition to the example in the last paragraph, within one single channel (i,e. IF0), is that possible for the chip to demodulate all the signals if the 8 packets are all transmitted over one channel (IF0) with different SFs? What do you mean for your last sentence of course not with a single channel gateway"?


#13
  • yes
  • this info is about the semtech 1301 chip, a 'real' LoRaWAN chip, some users confuse this with the single channel projects made with an RFM95W+ESP/ARDUINO ( these should only be used and connected to TTN for test purposes)