Problem description

The oracle validation calculates the expected tx_power of a beacon based on the max_eirp for the region and the asserted gain of the gateway. This validation can fail because the gateway-rs code will report the beacon with the actual tx_power that it received from the packet forwarder in the tx_ack packet.

If the gateway-rs code requests a transmission with a power level the packet forwarder does not support the packet forwarder will attempt to find a lower power level that it does support. Due to a bug in the packet forwarder code it will pick a higher power level if no lower power level exists.

This change tries to solve several problems that are dependent on each other and require changes over several subsystems. The oracles should allow tx_power levels lower or equal to validate. The gateway-rs code should stop using MIN_CONDUCTED_POWER. The packet forwarder code should stop sending at a higher power level than requested. If the packet forwarder stops transmitting packets with too much power the low power regions such as EU868 and AS923 will not be able to transmit if their asserted gain is larger than 4dBi. To solve this the packet forwarder code must be changed to allow more than 16 power lookup table entries so that they can support the lower power levels while still supporting the higher power levels. Finally the packet forwarder configurations must be changed to include a baseline for the lower power levels.

oracles

[X] make beacon validation accept beacons with a lower or equal tx_power (https://github.com/helium/oracles/pull/381)

gateway-rs

[X] update beacon crate to allow checking for lower or equal tx power (https://github.com/helium/gateway-rs/pull/372)
[X] remove MIN_CONDUCTED_POWER (https://github.com/helium/gateway-rs/pull/373)

sx1301 packet forwarder

[x] allow packet forwarder to have more 32 LUT entries (https://github.com/helium/lora_gateway/pull/4)
[ ] fix lut entry selection to only select power levels lower or equal to the requested power level
[ ] add configuration for the remaining power levels 0dBm - 12dBm

sx1302/sx1302 packet forwarder

[x] allow packet forwarder to have more 32 LUT entries (https://github.com/helium/sx1302_hal/pull/34)
[x] fix lut entry selection to only select power levels lower or equal to the requested power level (https://github.com/helium/sx1302_hal/pull/35)
[ ] add configuration for the remaining power levels 0dBm - 12dBm

comms

[ ] contact makers to update their packet forwarders to match the new behavior

helium / oracles

Beacon verification with non deterministic `tx_power` #384