## 3 Deployment Overview
### Network Operation  
Figure 5 depicts the network setup, with the nodes on the left and the gateway with Internet access on the right. Nodes operate on a 60 second period with an active sub-period of 1750 ms and a sleep sub-period of 58,250 ms, as depicted in Figure 6. During the active sub-period, the nodes sample the environmental sensors (100 ms) and then perform three transmit cycles. At each transmit cycle, the node transmits three different packets, one with each of the IEEE 802.15.4g SUN modulations (i.e., SUN-FSK, SUN-OQPSK, and SUN-OFDM). Between two consecutive packets in a transmit cycle, there is a 50 ms inter-packet delay. Furthermore, between the first and second cycle, there is a 100 ms delay, whereas between the second and third cycle there is a 200 ms delay. Figure 4: Gateway setup with 3\(\times\) OpenMote-B boards acting as IEEE 802.15.4g SUN receivers, 1 xRaspberry Pi 3B+ (not displayed), and a Huawei E3531 HSPA+ modem for Internet access. Figure 5: Hardware setup. Before each packet transmission, nodes execute a CSMA/CA (Carrier Sense Multiple Access/ Collision Avoidance) protocol with CCA (Clear Channel Assessment) to determine if the channel is busy. That is, prior to transmitting, the radio samples the channel to determine the energy present. If the energy is below the CCA threshold for the current modulation, the CSMA/CA succeeds, and the packet is loaded to the radio transceiver and transmitted subsequently. Otherwise, if the energy is above the CCA threshold for the current modulation, the node draws a random number between zero and 100 (representing the number of slots with each slot being 100 \(\upmu\)s) and the transmission is delayed. The CCA threshold values for SUN-FSK, SUN-OQPSK, and SUN-OFDM have been determined experimentally and set to \(-\)94 dBm, \(-\)93 dBm, and \(-\)91 dBm, respectively. The configuration parameters for the different IEEE 802.15-4 SUN modulations that are used to transmit the data packets are summarized in Table 2. As can be observed, all modulations provide an effective data rate of 50 kbps, but they trade off the link budget and occupied bandwidth. For example, SUN-FSK provides a good link budget (i.e., 129 dB) and the largest number of channels available (i.e., 34) thanks to its narrow bandwidth occupation (i.e., 200 kHz). In contrast, SUN-OQPSK provides the highest link budget (i.e, 131 dB) at the expense of bandwidth occupation (i.e., 1300 kHz). Finally, SUN-OFDM provides a trade-off between channel occupation (i.e., 800 kHz) and link budget (i.e., 120 dB). Notice that for all the SUN modulations, the transmit power of the AT86 RF215 radio transceiver was set to its maximum value. However, there is a 6 dB offset between the value of the transmit power and the actual transmit power of the radio transceiver depending on the selected modulation. Hence, for SUN-FSK and SUN-OQPSK, the packets are transmitted with 15 dBm, whereas for SUN-OFDM, they are transmitted with 9 dBm. In terms of payload, each packet contains the fields depicted in Figure 7, as summarized next:  
* The PAN_ID field is 2 bytes and is set to 0 xCAFE for all packets being transmitted. The gateway filters all packets that are not received with such a value to avoid received packets from other networks;
* The EUI_16 field is 2 bytes and contains the last 2 bytes of the EUI-64 address of the nodes transmitting the packet;
* The TX_MODE field is 1 byte and refers to the modulation being used to transmit the packet; SUN-FSK (0), SUN-OQPSK (1), and SUN-OFDM (2);
* The TX_COUNTER field is 1 byte and indicates the packet repetition within the current period (i.e., 1, 2, or 3);
* The PACKET_COUNTER field is 4 bytes and is an absolute sequence number to allow for packet identification and eventual node resets;
* The TEMPERATURE, HUMIDITY, PRESSURE, and LIGHT fields are 2 bytes each and are devoted to storing the sensor measurements.