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LoRaWAN® Gateways: Radio Coexistence Issues and Solutions

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LoRa Alliance ® Whitepaper Page 10 of 49 LoRaWAN ® Gateways Radio Coexistence Issues and Solutions Copyright ©2021 LoRa Alliance, Inc. All rights reserved. www.lora-alliance.org Colocalizing LoRaWAN gateways with LTE (or 3G, 2G) base stations may cause some issues if the RF filters and the installation are not carefully considered. The main issues to be faced are: • Out-of-band spurious emissions generated by a LTE transmitter falling in the LoRaWAN unlicensed band, causing desensitization of the LoRaWAN gateway • Out-of-band spurious emissions generated by a LoRaWAN transmitter falling in the LTE UL band, causing desensitization of the LTE base station • An LTE transmitter acting as an out-of-band blocker, causing desensitization of the LoRaWAN gateway • LTE transmitter intermodulation in the LoRaWAN receiver, causing desensitization of the LoRaWAN gateway • LTE transmitter intermodulation in the LoRaWAN transmitter, causing desensitization of the LTE base station or any other receiver • The total amount of radiated power by an LTE base station in the installation site may damage the LoRaWAN receiver To mitigate these potential issues, RF filters and antenna isolation must be carefully managed before and during the installation of the LoRaWAN gateway. The LTE DL is a major concern for radio coexistence with LoRaWAN. However, the LTE UL must be also considered. An outdoor LoRaWAN gateway embeds a LoRaWAN modem supporting one or more of the above unlicensed bands and a cellular 3G or 4G modem supporting several LTE bands. The global market trend is cellular modem to support a maximum of LTE bands to reach worldwide coverage. Each modem is connected to a dedicated antenna, one for the cellular modem and one for the LPWAN modem. These antennas could be designed based on different technologies and are separated by a defined distance, leading to a certain isolation or mutual coupling between both antennas. Distance between antennas is a key factor for antenna isolation. Obviously, this is less critical for outdoor LoRaWAN gateways, because the gateways are generally based in a large or medium-size enclosure. It is then naturally possible to optimize the antenna isolation when placing antennas at a sufficient distance, or even by deporting the antennas using coaxial cable and antenna brackets. However, even for outdoor LoRaWAN gateways, if no special care is taken during the design phase, isolation may be not enough. 3.2 LoRa ® /LTE ANTENNA ISOLATION The antenna isolation considered in this section is the isolation measured between the LoRaWAN gateway RF port and the LTE base station RF port. Isolation includes, therefore, the LoRa antenna gain, the LTE antenna gain, and the propagation losses.

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