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DollarDollar (Semtech)  
From the definition of source code, the MAX_RX_WINDOW is 3000ms, it means that if detected a preamble during Rx1 window or Rx2 window, the max receiving duration is 3000ms? If the data packet exceed 3000ms, then the data can't be received? That's right? 
But, after tx completed, we set the Rx1 windower timer and Rx2 window timer simultaneously. So, if end-device detected the preamble during the Rx1 window and start to receive data, but the data packet duration over 1s. Then, after 1s from the beginning of RECEIVE_DELAY1, the receiving status will be abort and enter the Rx2 window timer event. So, even if end-device has been detected the preamble during Rx1 window, but as the data packet duration over 1s, and the RECEIVE_DELAY2 is 1s later after RECEIVE_DELAY1. Thus, end-device can't receive data packet correctly during the first receive window. 
So, if the end-device wants to receive data completely during Rx1 window, the time on air should not be exceed 1s? That's right?
But if time on air not exceed 3s, it's will be ok in the Rx2 window, that's right?
Best Answer chosen by Dollar (Semtech) 
GregoryGregory (Semtech Corporation) 
Your question is in two parts:

"it means that if detected a preamble during Rx1 window or Rx2 window, the max receiving duration is 3000ms"

Yes, this is correct. In the LoRaWAN stack, the packet time will never exceed 3 seconds in TX or Rx. 
On the node side, this is ensured by the function "ValidatePayloadLength (...)" which verify the amount of data to be transmitted compared to the data rate. 
If the frame is longer than the predefined length, the LORAMAC_STATUS_LENGTH_ERROR status will be returned.
On the GW side, the same kind of mechanism is used so that the time on air of any given packet over the network will never attain the 3 seconds.

"So, if the end-device wants to receive data completely during Rx1 window, the time on air should not be exceed 1s"

No, the limitation is at 3 seconds. 
After a Tx, the timer event "OnRxWindow1TimerEvent( )" will occur precisely after 1 second and the radio will go into Rx mode.
After 2 seconds, the timer event "OnRxWindow2TimerEvent( )" will occur and will lead to the configuration of the radio for the second reception window in the function "RxWindowSetup()".
However, before changing the radio, the code checks the radio status with the call to Radio.GetStatus( ) 
At this stage, or the radio is in "RF_IDLE" state and the code will configure the radio and go into Rx mode. 
Or the radio is in another state (meaning the radio is already busy) and the code will simply drop the command until the next irq from the radio.
Vyacheslav KhudyakovVyacheslav Khudyakov 
Hello, I have a question about using real-time data transmission in LoRaWAN. LORIOT company have shown data feed visualization in real-time (in their Youtube channel). Many experts prove that for LoRaWAN it is impossible. If it is possible, what is the maximum number of nodes can work in real-time per 1 gateway. I hope to get the answer. 
Best Answer chosen by Vyacheslav Khudyakov
GregoryGregory (Semtech Corporation) 
Hello Vyacheslav,
I would be glad to know who are these experts who "proved" LoRaWAN is impossible :-) There is no magic at play here, only technology and maths!

Lets go back to basics:
Each GW has at least one sx1301, the sx1301 is a huge digital baseband chip which emulates 49 LoRa demodulator and 1 FSK demodulator, all running in parallel.
The sx1301 has 8 channels and it is continuously scanning for the presence of preambles of any datarate on any of these 8 channels. Due to the orthogonalities of LoRa signals between them, the sx1301 can demodulate 8 LoRa packets at different datarate (DR0, DR1, ...DR7), at the same time, and on the same channel (providing you have a sufficient link margin between each packet). If you multiplex these parameters over time and the 8 channels, the number of nodes per GW can become staggering, even more as the network densify and the time on air of each packet decrease (due to ADR).

Everybody wants a definite answer as to how many nodes a GW can support but the answer is 4 dimensional:
- rssi/SNR of the received packets (simultaneous reception on the same channel)
- time on air of the packets (equivalent to datarate, the longer the packet, the longer one demodulator of the GW is used)
- frequency of the packets (two packets with the same datarate and the same RSSI/SNR will collide unless they are on 2 different frequencies).
- number of times per day a node will send a packet (taking resources another node could take)

The answer is thus incredibly complex to calculate because these 4 parameters all have an impact one on another. If you add the legislations which are different for each region (Duty Cycle, LBT,... ), the calcul becomes even more difficult to compute. So in the end you will be disappointed, there is no definite answer and even simulations can go from figures to figures depending on the input parameters. You can of course set your input parameters for your specific case and you will have a certain number but this number won't necessarily be representative of a real life deployment.

PS: to add some fun into the equation, LoRaWAN is all about country wide network deployment. At this level, the geographical distribution of the GWs over the territories also have an impact on the number of nodes the network can support :-)
jet sujet su 
     Why SX1278 switch from SLEEP mode to STANDBY mode need to be configured STANDBY  twice to succeed. 
         SX1278LoRaSetOpMode( RFLR_OPMODE_SLEEP );
         SX1278LoRaSetOpMode( RFLR_OPMODE_STANDBY );
         SX1278LoRaSetOpMode( RFLR_OPMODE_STANDBY );

If configured STANDBY Mode only once, and then read back the RegOpMode register value, still the SLEEP mode.

Is there a limit to the use of the RegOpMode register?

Best Answer chosen by jet su
GregoryGregory (Semtech Corporation) 
You don't need to configure Standby twice. The command is not immediate and the radio needs a few us to go from Sleep to Standby (please, refer to the datasheet for exact timing). If you add a small delay between the time you set the radio in Standby and the time you read the register, you will see the radio behave as expected.
Krzysztof ChojnowskiKrzysztof Chojnowski 
I observed that payload CRC error occures quite often when the two modems are very close to each other, especially with SF = 2048. What can be the reason of this behaviour? Please advise where to start debugging of this issue.
Best Answer chosen by Krzysztof Chojnowski
SebastienSebastien (Semtech Corporation) 
Dear Krzysztof,

Could you confirm that the CRC errors disappear when the modems are separated by a longer distance? This could be related to saturation of the receiver, although we have an internal AGC which takes care of saturation. It may fail for extremely large coupled powers, exceeding the max ratings of the chip. Also, do you see a difference when the "LowDataRateOptimize" is set?

There is 125kHz and 250kHz, 500kHz LoRa IQ Waveform library in "Tool and SW" ,but narrower than 62.5kHz is not.
Do you have  LoRa IQ Waveform library of narrower than 62.5kHz?
Best Answer chosen by HARA ARATA
SebastienSebastien (Semtech Corporation) 
Hi Hara,

Lower BW are made by simply playing the waveform files at a lower sampling rate. The OSR is set to 4, so play them at 500 kHz for LoRaBW=125 kHz, 250 kHz for LoRaBW=61.25 kHz, 125 kHz for LoRaBW=30.6 kHz, etc...

seunghak Leeseunghak Lee 
Dear all.

Hello. I have some questions about LoRaWAN ADR.

LoRaWAN 1.1 specification says: 
If an end-device's data rate is optimized by the network to use a data rate higher than its default data rate, it periodically needs to validate that the network still receives the uplink frames. 

Above paragaph,
1) Is it right that the end device sends "LinkCheckReq" to confirm the network still receives the uplink frames?

2) How often does the end device send the uplink frames to validate connectivity with network server?

Best regards.
Best Answer chosen by seunghak Lee
SunilSunil (Semtech) 
Answer for the questions:
1) Is it right that the end device sends "LinkCheckReq" to confirm the network still receives the uplink frames?
>>Yes, one can use the LinkCheckReq or try to send in a confirmed packet.
2) How often does the end device send the uplink frames to validate connectivity with network server?
>>This is left the the end device to decide. This depends on the power budget in the end device.

with regards
Umesh PatilUmesh Patil 
Trying to use same stm32l072 as end node and gatewa ...but its not working. what to do??
Best Answer chosen by Umesh Patil
SebastienSebastien (Semtech Corporation) 
Hi Umesh,

I suggest you describe tje debug steps you have been thru already, that will help understand what you are doing

Shashank KapoorShashank Kapoor 
Hello everybody, 
I am new to this topic so need help. I am trying to build my end node using STM32L151CBU6 and SX1272. When i disconnect the resistor which supplies power to sx1272 i am able to get 1.8uA of current consumption by putting the STM IC in standby mode. But if the resistor is connected i am unable to get the current consumption below 70uA. I even tried to write the RegOpMode register with 0x00 but still not able to get less current.
On the sx1272 side I did the following things
Disabled the RC oscillator
De-Initialized the IO's
Put sx1272 in sleep mode by writing the RegOpMode register as 0x00
Disabled SPI
on the stm side i did the following things
De-Initialized the UART
De-Initialized the ADC
De-Initialized the GPIO (Made all the GPIO as input and PULL-UP)
De-Initialized the HSE
De-Initialized the LSE
Put the STM32 in standby mode
I am trying to make the current consumption below 8uA.
Any help would be greatly appreciated
Best Answer chosen by Shashank Kapoor
GregoryGregory (Semtech Corporation) 
Hello Shashank,
The main issue with the Standby mode is that you do not keep the configuration of the MCU GPIO. This means that, unless connected to a known level through pull-ups or downs, you will have leakage pretty much everywhere. To fix this, we usually recommend the STOP mode where the GPIO configuration is kept. This way, you will not suffer from the leakage and you should get to a current consumption MCU+Radio down to 2 or 3uA
Krzysztof ChojnowskiKrzysztof Chojnowski 
According to the datasheet the PpmOffset is calculated as PpmOffset = 0.95 * measured Offset [PPM]. Which frequency should be taken into account to get the measured Offset [PPM]: the carrier, the bandwidth or the external crystal?
Best Answer chosen by Krzysztof Chojnowski
SebastienSebastien (Semtech Corporation) 
Dear Kryzsztof,

The offset in ppm can be computed from either the carrier frequency, or the reference (XTAL oscillator) frequency. This would give you the same results.

Silas ValeraSilas Valera 
I am working on providing LoRa connectivity option for our products. Our products are based on Silabs microcontrollers - EFM32PG. I am looking for LoRa library for SX1276 in C which I can port to use with EFM32PG. I understand that SX1276 is SPI driven so only certain low level SPI read/write functions would need to be re-written for use with EFM32G. Where can I find / download this library? Has anyone used EFM32 controllers with SX1276? Any pointer/direction would be very much appreciated :)
Thanks in advance!
Best Answer chosen by Silas Valera
Nestor AyusoNestor Ayuso
Hi, look at this is a working pot for EFM32