Gateway Capacity Question

While looking at the new SX1302 baseband receiver chip it raised some questions about the operation and capacity of gateways using the existing SX1301 chip.

Gateways are typically constructed in modules which consist of a SX1301 baseband receiver and two SX1257 radio receivers. This configuration can provide up to 8 separate radio channels.

With this arrangement a gateway can receive 8 nodes simultaneously. Its typically thought that this means the 8 nodes are on 8 different radio channels.

However, can someone confirm, this is not necessary. We could receive two nodes on the same radio channel provided their transmissions are orthogonal. In fact we could receive three nodes on the same channel provided all three transmissions are orthogonal to each other. The 8 node limit comes from the number of decoders in the SX1301 baseband receiver.

By orthogonal I mean different Chip Rate, which is the rate of change of frequency vs time. For example SF 7 BW=125kHz is orthogonal to SF9 BW=125kHz. Whereas SF 7 BW=125kHz is not orthogonal to SF 9 BW=250kHz.

Dear Tony_Smith

It is not necessary that the 8 nodes are on 8 different radio channels.

SX1301 emulates 49x LoRa demodulators and 1x(G)FSK demodulator.

IF0 to IF7 LoRa channels
Those channels can be connected individually to Radio A or B. The channel bandwidth is 125 kHz
and cannot be modified or configured. Each channel IF frequency can be individually configured. On each of those channels any data rate can be received without prior configuration. Several packet using different data rates may be demodulated simultaneously even on the same channel. Those
channels are intended to be used for a massive asynchronous star network of 10000’s of sensor
nodes. Each sensor may use a random channel (amongst IF0 to 7) and a different data rate for any
The SX1301 digital baseband chip scans the 8 channels (IF0 to IF7) for preambles of all data rates at
all times. The chip is able to demodulate simultaneously up to 8 packets. Any combination of up to 8
packets is possible (e.g. one SF7 packet on IF0, one SF12 packet on IF7 and one SF9 packet on IF1
The SX1301 can detect simultaneously preambles corresponding to all data rates on all IF0 to IF7
channels. However it cannot demodulate more than 8 packets simultaneously. This is because the
SX1301 architecture separates the preamble detection and acquisition task from the demodulation
process. The number of simultaneous demodulation (in this case 8) is an arbitrary system parameter
and may be set to any value for a customer specific circuit.

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