Issue link: https://read.uberflip.com/i/1423190
LoRa Alliance ® Whitepaper Page 6 of 49 LoRaWAN ® Gateways Radio Coexistence Issues and Solutions Copyright ©2021 LoRa Alliance, Inc. All rights reserved. www.lora-alliance.org 2.4 RECEIVER LINEARITY Intermodulation distortion (IMD) occurs when several sources of out-of-band or in-band interference generate additional interference within the band due to nonlinearities of the receiver. The IMD can be mitigated by using high-linearity receiver (LNA, switch) and high out-of-band rejection filters. Figure 5: Receiver desensitization due to IMD The nonlinear elements of the receiver are characterized by their third-order output intercept point (OIP3) (or third-order input intercept point [IIP3]) performance to determine the overall IMD performance of the whole receiver. 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 ) Online calculators are also available as detailed in [3]. Note that amplitude-modulated wideband signals such as wideband code division multiple access (WCDMA) and long-term evolution (LTE) would generate intermodulation products when injected into a nonlinear receiver. Constant amplitude- modulated signals such as Gaussian minimum-shift keying (GMSK) do not generate intermodulation products when injected into a nonlinear receiver. 2.5 OUT-OF-BAND SPURIOUS EMISSIONS Spurious emissions are unexpected radiations in the receive band generated by other transmitters. These transmitters may be other radio systems operating in the same band or in different bands. In this case, there is no way to avoid the desensitization except by moving the receiver far away from the transmitter causing the interference. The receiver also may be desensitized by spurious emissions generated by other transmitters from the same equipment. This may occur when a device embeds multiple radio systems. In this case, the manufacturer must reduce the level of the spurious emissions to ensure radio coexistence within the device.