LoRaWAN® Gateways: Radio Coexistence Issues and Solutions

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LoRa Alliance ® Whitepaper Page 30 of 49 LoRaWAN ® Gateways Radio Coexistence Issues and Solutions Copyright ©2021 LoRa Alliance, Inc. All rights reserved. www.lora-alliance.org share the same mast or may be located very close to each other on neighboring rooftops: Figure 24: Example of multiple 3G/4G base stations located on the same site Fortunately, in dense urban areas, the LTE or HSPA base stations are rarely wide- area BS, but medium-range or local-area BS. Therefore, the radiated power of the BS is usually limited from 20W to 100W. However, the numerous BS surrounding the LoRaWAN gateway may generate a huge amount of radiated power. In the example of Figure 24, more than 12 three-sector BS are identified. Assuming a 100W radiated power for each, we have a total of 100 x 3 x 12 = 3600W or more radiated power in the vicinity of the LoRaWAN gateway. Although isolation between the LTE/HSPA BS and the LoRaWAN gateway antennas can be expected, a significant amount of power can be inserted into the gateway RF port, impacting both Tx and Rx paths. On the LoRaWAN receiver path, the LNA and the band-pass SAW filters have usually very low maximum input power, such as +13dBm, for example. There is obviously a high risk of damage to the LoRaWAN in the case of high radiated power in the vicinity. The LoRaWAN receiver could be protected using RF power limiters, for instance, but saturation or intermodulation of the receiver could occur then. On the LoRaWAN Tx path, the power amplifier may be also damaged due to high power in reverse mode. Therefore, considering the potential damage to the LoRaWAN gateway, cavity filters are recommended to mitigate the risk. A cavity filter having about 40dB attenuation in the LTE UL bands would ensure no damage to the gateway, even in case of poor installation.

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