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Enabling CSMA for LoRaWAN TR013-1.0.0 ©2023 LoRa Alliance ® Page 6 of 18 The authors reserve the right to change specifications without notice. 3 Enabling Carrier Sense in LoRa Radios 126 127 Accurate detection of the presence of a LoRa frame through the radio is key to enabling 128 CSMA for LoRaWAN. This section introduces technical solutions to enable accurate 129 detection of LoRa frames. 130 131 Because LoRa modulation is unique, its unique features need to be considered in order to 132 accurately detect when a channel is in use. LoRa modulation allows the concurrent reception 133 of frames with different Spreading Factors (SFs) within the same channel (SF orthogonality). 134 At the same time, LoRa frames can be received under the noise floor. Therefore, considering 135 such attributes is key to enabling reliable and efficient CSMA for LoRaWAN networks. 136 137 A commonly used metric for estimating an occupied channel is the Received Signal Strength 138 Indicator (RSSI). RSSI, however, is not a suitable predictor to detect the presence of a LoRa 139 frame for two reasons. First, relying on RSSI for carrier sense loses potential transmission 140 opportunities offered by LoRa's orthogonality. For example, withholding an SF7 transmission 141 due to high RSSI caused by an SF12 frame is an inefficient use of spectrum resources. 142 Second, LoRa frames traversing underneath or near the noise floor would be missed by RSSI 143 measurements. For example, the RSSI threshold of -80dBm translates to an outdoor detection 144 range of approximately 100m at 14dBm transmission power [TOSN'22]. The range is further 145 reduced indoors and is significantly smaller compared to the potential collision range of 146 LoRaWAN. Therefore, relying on RSSI to detect the presence of a LoRa frame may lead to 147 inaccurate channel sensing with numerous missing detections of LoRa transmissions. 148 149 Alternatively, all LoRa radios are equipped with a Channel Activity Detection (CAD) module 150 that is specially designed for LoRa. It has the following important features as demonstrated in 151 [TOSN'22]: 152 • CAD is SF-selective, i.e., it can detect transmissions in a specified SF while remaining 153 insensitive to other transmissions of different SFs. 154 • CAD is an energy-efficient operation compared with the energy consumption of data 155 transmissions. 156 • CAD works indoors and outdoors with a high detection accuracy. Therefore, instead 157 of RSSI, the CAD module is better suited to be utilized as an effective and a reliable 158 tool to estimate channel occupancy. 159 160 A request to the CAD module reports back either a busy or a free channel for the selected 161 channel and SF combination for the duration of a set number of LoRa symbols [AN1200.48]. 162 To this end, a CAD request that results in a busy channel is referred to as a failed CAD. 163 Otherwise, a clear channel is assumed. 164 165 The CAD module requires configuration prior to use. The configuration is subject to the version 166 of LoRa modem implementation integrated into the radio module. Therefore, for radio-specific 167 details about CAD configuration, the reader is expected to refer to the radio's datasheets. 168