Issue link: https://read.uberflip.com/i/1423190
LoRa Alliance ® Whitepaper Page 8 of 49 LoRaWAN ® Gateways Radio Coexistence Issues and Solutions Copyright ©2021 LoRa Alliance, Inc. All rights reserved. www.lora-alliance.org Figure 7: Transmit intermodulation principle. LPF, low pass filter; PA, power amplifier; SPDT, single pole double throw. The principle of IMD on the transmitter is basically the same as the one described for the receiver in §2.4. The IMD level can be determined using the following mathematical formulas: • IM3 right = P f1 -2x(OIP3-P f2 ) • IM3 left = P f2 -2x(OIP3-P f1 ) Intermodulation product levels can be estimated based on PA (or SPDT) OIP3, interferer level at PA (or SPDT) output (Pf2), and useful signal level at PA (or SPDT) output (Pf1). Intermodulation product frequencies depend on the f1 and f2 frequencies. Considering a LPWAN gateway, the consequences of transmit intermodulation could be: IM3 product falling in the LoRaWAN receive band, causing desensitization of the LoRaWAN gateway. (Note that this is only possible in full-duplex configuration, because in the half-duplex configuration, transmitter and receiver are not active simultaneously.) • IM3 product falling in the cellular uplink (UL) band, causing desensitization of the colocated cellular base station. • IM3 product falling in the cellular downlink (DL) band, causing desensitization of the LoRaWAN gateway cellular backhaul. • IM3 product falling in any receive (Rx) band, causing desensitization of a colocated radio system. 3 COLOCATION WITH GSM/UMTS/LTE TRANSMITTERS 3.1 LoRaWAN COEXISTENCE ISSUES DUE TO CELLULAR NETWORKS LoRaWAN end-devices and gateways communicate in the unlicensed frequency bands. This is a benefit for the operator or customer, who does not need to apply and pay for a license from the government to transmit on these frequencies.