LoRaWAN® Gateways: Radio Coexistence Issues and Solutions

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LoRa Alliance ® Whitepaper Page 24 of 49 LoRaWAN ® Gateways Radio Coexistence Issues and Solutions Copyright ©2021 LoRa Alliance, Inc. All rights reserved. www.lora-alliance.org Frequency Offset from LoRaWAN Channel Blocker Rejection (typical) Required Attenuation in RF Filters to Achieve 150dB Total Attenuation 0.2MHz 75dB 75dB 2MHz 93dB 57dB 5MHz 100dB 50dB 10MHz 105dB 45dB Obviously, it is not possible to achieve 75dB attenuation at 0.2MHz offset from the LoRaWAN band. No filtering technology can achieve such performance. The separation distance may be increased in this case, but it would be hardly possible to reach 75dB isolation, according to Figure 11. This means that guard band less than 2MHz must be strongly avoided. Therefore, 57dB (60dB) is the minimum requirement for RF filter rejection of LTE DL bands. Achieving 57dB attenuation at 2MHz offset is only possible when using cavity filters. Surface acoustic wave (SAW), bulk acoustic wave (BAW), and ceramic filter technologies would not be able to meet such sharp slopes. SAW filters could be only used when the guard band is greater than 5MHz. When using SAW filters (or BAW or ceramic filters), the 60dB attenuation can be divided, for example, in 20dB in the first band-pass filter and 40dB in the second band- pass filter. Reducing the attenuation in the first band-pass filter minimizes insertion losses of the filter and therefore improves the sensitivity of the LoRaWAN receiver. As opposite, when using a cavity filter as first band-pass filter, the maximum attenuation must be completed by the cavity filter (50dB or more), relaxing the required attenuation for the second band-pass filter (10dB or less). 3.5 OUT-OF-BAND SPURIOUS EMISSIONS GENERATED BY THE LoRaWAN EMITTER Considering 45dB isolation between the LoRa antenna and LTE antenna, the transmitter of the LoRaWAN gateways should be designed to reduce the spurious emissions and the noise generated in the LTE BS UL bands below -124dBm + 45dB = -79dBm in a 100KHz-resolution bandwidth. This is typical noise performance, depending on the gateway and LTE UL band. All LoRaWAN gateways do not meet the -79dBm out-of-band noise in LTE bands due to the architecture of the gateway or due to the guard band between LoRaWAN band and LTE band.

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