LoRaWAN® Gateways: Radio Coexistence Issues and Solutions

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LoRa Alliance ® Whitepaper Page 38 of 49 LoRaWAN ® Gateways Radio Coexistence Issues and Solutions Copyright ©2021 LoRa Alliance, Inc. All rights reserved. www.lora-alliance.org The limit is then -121dBc in 3KHz RBW. Considering a 69dBm output power (conducted) transmitter, the limit of spurious emissions in 100KHz RBW is then: Spurious emissions = 69dBm - 10*Log(8MHz/3KHz) - 121 = -86dBm in 3KHz RBW or -71dBm in 100KHz BW This requirement is therefore more stringent regarding out-of-band performance. We are going to consider this one for the following calculation, although some spurious emissions may degrade performance by 15dB, according to the spurious emissions limit. The required isolation, considering out-of-band limits, is therefore: Isolation = -71dBm - (-124dBm) = 53dBm This isolation must be translated into distance separation. According to Figure 26, we can provide the following recommendations regarding antenna separation of LoRaWAN gateways with DVB-T/T2 transmitters: Min. Vertical Separation Min. Horizontal Separation 2m 150m 5.3 DVB-T/T2 OUTPUT POWER According to [6], DVB-T/T2 transmitters are considered high-power transmitters when the conducted output power is greater than 25W. The conducted power may reach up to 10KW (69dBm) and the radiated power can reach up to 200KW ERP (85dBm EIRP) in Germany, but it is limited to 50KW ERP (79dBm EIRP) in France. Considering 53dB isolation between antennas, as shown in §5.2, the maximum DVB- T/T2 power at the LoRaWAN RF port is 69dBm - 53dB = 16dBm. According to §3.4, the receiver must provide at least 60dB attenuation of the LTE emitters as out-of-band blocker rejection. The same rejection is expected for DVB-T/T2 emitters. Therefore, the maximum blocker input level at the LoRa RF port is +10dBm. Considering +16dBm DVB-T/T2 maximum input power at the LoRaWAN RF port, this means that 66dB to 70dB attenuation is required to avoid blocking due to DVB-T/T2. This is achievable using SAW filters in the LoRa receiver path, and no cavity filter is required for that purpose. However, due to the very high power in the proximity that could cause damage to the gateway, the usage of cavity filters is recommended to mitigate the risk. The cavity filter may have about 40dB to 50dB maximum attenuation in the UHF band, ensuring no damage of the gateway, even in case of poor installation.

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