LoRaWAN Specification v1.1 - Why can't multiple gateways be used for downlink messages?

On page 12, at the start of section 3.1 for Uplink messages it says they may be relayed via one or many gateways when sent from end-devices to the NS (network server), but at the start of section 3.2 for Downlink messages it says they are only relayed by a single gateway from the NS to an end-device.

Why does the specification only allow configuring multiple gateways as repeaters for uplink messages (to achieve a longer communication range), but not for downlink messages?

For example, given a LoRaWAN end-device that has a max range of 3km and is located 3km from the nearest gateway-1. If the end-device is able to transmit an uplink message to a NS via gateway-1 and gateway-2 (both configured as a repeater), where each gateway has a max possible LPWAN range of 20km, since the total distance from end-device to NS is 23km, then how can that end-device receive a downlink response from gateway-2 if it’s not permitted to send downlink messages via more than one gateway?

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In section 8 on Line 1880 it gives an example where one of the end-device’s uplinks may be used to send back a downlink message.

On Line 1893 it says for Class B end-devices specifically, “The gateway chosen to initiate this downlink communication is selected by the Network Server based on the signal quality indicators of the last uplink of the end-device”

Also, on Line 1924, it says for Class B end-devices specifically, "A mobile end-device must periodically inform the Network Server of its location to update the downlink route. This is done by transmitting a normal (possibly empty) “unconfirmed” or “confirmed” uplink

Because a node only has a single radio, it can only listen on a single frequency at a time for a possible downlink.

LoRaWAN networks don’t have remotely precise enough time synchronization to allow two gateways to transmit on the same frequency at the same time without making the signal substantially worse, rather than better.

The network server choses the best gateway to uniquely transmit the downlink; typically that which best heard the uplink, but possibly another based on availability, duty cycle limits, vs need to transmit other downlinks at overlapping time, etc


Hi @ltfschoen, any luck with sending a single downlink with multiple gateways?