US902 and AU915 change from 64+8 channels to 8+1 channels defined at TTN

nestorayuso · April 26, 2018, 10:36am

Specifications US902 and AU915 use 64+8 channels but as simple gateways only have 8+1 channels, the network server must disable a lot of channels on the device after a join using one (or two) MAC command LinkADRReq

In my tests with TTN I see it is done in the US902 region but not in the AU915 region.
I also see if LinkADRReq packet is lost, the TTN server does not resend the LinkADRReq until a LinkADRAns response is received.

The use of AU915 as specified in LoRaWAN 1.0.2 and TTN in Australia is tricky because “ACMA regulation requires hopping over at least 20 channels”. Using the TTN Frequency plan and simple gateways with 8+1 channels, all ends up reciving only 8 of every 20 packets sent, it is a 60% packet loss.

AU915 region is now using all over South America and LoRaWAN 1.0.3 and 1.1 removed the ACMA limitation of 20 channels. The Network Server must manage devices to comply with this regulation so I think TTN needs two differents Frequency plans AU915_Australia and AU915_Rest_of_the_world

Joey · April 26, 2018, 11:48am

I disagree AU915 is already operation in Australia and will meet the Australian requirements.

Already in Australia AU915 has been used by TTN operation for a year or more

The fundamental thing is to operate the LoRa module on as many channels as the gateway has available (ie 8, 16, 64 etc) AND transmit limit of 400mS…which meets the hopping requirement (for both US and Australia)
(ie number of hops = 0, just transmit once).

AU915 is 98% derived from US902-928MHz LoRa… operational with the differences being uplinks start at 915.2MHz (Number of hops = 0 , just transmit once)

I have confirmed this with network operators and module manufacturers.

There are two RF requirements

The country RF regulatory standard
LoRaWAN specification (The LoRaWAN standard has to fit in to the country RF regulation)

The Australia RF regulations calls upon Australian Standard AS/NZS 4268: Latest addition Feb 2017.
This standard ($168 AUD!!!) heavily references the FCC 15.247 test method and similar procedures.
(If you follow the history of Australian RF regulations for the 915MHz band… you will see that initially ACA (now ACMA) accepted FCC 15.247 test reports provided the lower band started at 915MHz.

****AS/NZS 4268 is derived from 15.247 test procedures, just read it *****

There are two methods of achieving transmit compliance in the 915-928MHz in Australia

Hopping every 400mS
(same as FCC 15.247) up to 1 watt (limited 20 Hopping channels instead of 50)
BUT ! you don’t need 20 or 50 channels if you limit the Tx time to 400mS and then wait a period between transmissions. This is the reason for max spreading factor SF10 (SF12 > 400mS Tx payload)
New AS/NZS 4268:Feb2017 - Any modulation scheme provide it meets the power spectral density (PSD) of 25mW/3kHz [previously min Tx bandwidth >500KHz, but this has been removed]

AU915 LoRaWAN1.01 was written prior to Feb 2017 and 1.1 was written after,

LoRa

125KHz channels can transmit in either mode 1 and 2 above
for 1 : One transmission <400mS but allows up to 1 watt
for 2 : There is NO max Tx on time but the power must be limited to PSD 25mW/3kHz (my guess is PSD max 125mW )

250KHz
for 1: for 1 : One transmission <400mS but allows up to 1 watt
for 2 : There is NO max Tx on time but the power must be limited to PSD 25mW/3kHz (my guess is PSD max 1watt)

500KHz channels
For 2 There is NO max Tx on time but the power must be limited to PSD 25mW/3kHz (my guess is PSD max 1watt)

If the transmitter meets the PSD requirement of 25mW/3kHz then you can transmit as long as you like… ie SF12 etc

Regs Joe
Ex RF product engineer - putting products through Australian RF regulations

nestorayuso · April 26, 2018, 1:13pm

Thanks for your response about regulations in Australia. My particular case is to use AU915 in South America.

Using TTN limits the usage to just 8+1 channels as specified here. https://www.thethingsnetwork.org/docs/lorawan/frequency-plans.html#au915-928

I am using devices with stack LoRaMac-node with OTAA and ADR. I am not manually dissabling any channel, I prefer the Network Server to do it for me. In TTN server in US902 I see it is done but not in AU915. Can someone confirm LinkADRReq ChMask commands are not sent on AU915? maybe because ADR is not implemented in AU915 server?

Also in US902 can someone confirm if LinkADRAns is not received, a LinkADRReq is re-sent?

With the following code it is impossible to urge a device to use just 8+1 channels as needed for TTN.

github.com

Lora-net/LoRaMac-node/blob/v4.4.1/src/mac/region/RegionAU915.c#L395


bool RegionAU915ChanMaskSet( ChanMaskSetParams_t* chanMaskSet )

{

uint8_t nbChannels = RegionCommonCountChannels( chanMaskSet->ChannelsMaskIn, 0, 4 );



// Check the number of active channels

// According to ACMA regulation, we require at least 20 125KHz channels, if

// the node shall utilize 125KHz channels.

if( ( nbChannels < 20 ) &&

    ( nbChannels > 0 ) )

{

    return false;

}



switch( chanMaskSet->ChannelsMaskType )

{

    case CHANNELS_MASK:

    {

        RegionCommonChanMaskCopy( ChannelsMask, chanMaskSet->ChannelsMaskIn, 6 );



        for( uint8_t i = 0; i < 6; i++ )

        { // Copy-And the channels mask

I think the Australian regulation resume you expose is fine, maybe the LoRaWAN 1.0.2 is wrong and they fixed on 1.1

TTN uses 1.0.2

Joey · April 26, 2018, 7:11pm

AU915 code “should be” almost identical to US except for the UPLINK channel offset of 12.9MHz (ie starting at 915.2MHz)

LoRaWAN 1.01 and 1.02 are the same for specification AU915.

Try manually fix 8 or 16 channels first.

I think this is a code issue in both US and AU915 because of how close the code base is.
Is there a way on github to compare the two code bases?

Regs
Joseph