# Potential of Sub-GHz Wireless for Future IoT Wearables and Design of Compact 915 MHz Antenna
## 2 Comparison of Wireless Performance in the 915 MHz and 2.45 GHz ISM Bands
### DC Power Consumption
#### 2.2.1 Wireless Protocols  
In Table 2, a survey of potential Wireless Protocols for future IoT applications is reported. The overall protocols are characterized by different operating frequencies, maximum data rates, maximum communication ranges and network topologies and hence are optimized for specific applications. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Parameter** & **Name (Units)** & **915 MHz ISM Band** & **2.45**  GHz ISM Band** & **\(\Delta\) (dB)** \\ \hline \(P_{TX}\) & Transmit Power (dBm) & 0 & 0 & 0 \\ FSPL & Free-Space Path Loss (dB) & 41.22 & 49.78 & 8.6 \\ \(G_{TX}\) (1) & Calculated Tx Antenna Gain (dBi) & 0.09 & 5.48 & 5.4 \\ \(G_{RX}\)\({}^{1}\) & Rx Antenna Gain (dBi) & 0 & 0, +3 & 0, +3 \\ \(P_{RX}\) (2) & Calculated Total Received Power (dBm) & \(-41.13\) & \(-44.3\), \(-41.3\) & 3.16, 0.16 \\ \hline \hline \end{tabular} \({}^{1}\) Two values provided for \(G_{\text{RX}}\) (0 dBi, +3 dBi) at 2.45  GHz for comparison.  
\end{table} 
Table 1: Link budget comparison for 915 MHz and 2.45  GHz ISM Band. Bluetooth Basic Rate/Enhanced Data Rate (BR/EDR) protocol provides a maximum data rate of 3 Mbps, it can communicate only in peer-to-peer (P2P) mode and its target application is audio streaming [13]. Bluetooth Low Energy (BLE) also provides a high maximum data rate of 2 Mbps and is optimized to connect several devices such as fitness trackers, health monitors, PC peripherals and accessories. Moreover, it can enable several network topologies, e.g., P2P, Star and Mesh [41]. ZigBee is a protocol that provides a maximum data rate at 2.45 GHz of 250 kbps [14] and the possibility to implement P2P, Star and Mesh topologies. It is designed to provide interoperability for a range of applications such as home automation, health monitoring and telecommunication [14]. Z-Star is a proprietary protocol optimized for ultra-low power wireless sensor network applications; it provides a maximum data rate of 200 kbps, and the possibility to implement several kinds of network topologies including peer-to-peer (P2P), Star, Mesh and others. WiFi is a technology based on IEEE 802.11 standards that provides a maximum data rate of 54 Mbps at 2.45 GHz [34]. This protocol implements a Star network topology and is designed to allow connectivity for smart home products, localization applications, industrial sensor systems etc. [42]. HaLow is a low-power WiFi solution operating in the Sub-GHz frequency bands and provides a maximum data rate of 8.7 Mbps (under specific conditions, namely using a 2 MHz channel and 1 spatial stream) and a Star network topology. It is designed for building automation, healthcare, industrial, agricultural and other applications [35; 43]. ANT/ANT+ are low data rate (maximum 60 kbps) and Ultra-Low Power wireless protocols suited for Wireless Sensor Network applications. It allows the implementation of P2P, Star and Mesh network topology. LoRa is a protocol for Low Power Wide Area Network for the communication of wireless battery powered nodes at a maximum data rate of 300 kbps [37; 38]. UHF RFID is a protocol that allows deployment of wireless RFID tags to identify objects, with possibility to get further sensed information at a maximum data rate of 640 kbps [39; 40]. As for the operating frequency, it can be noticed that the majority of the protocols are designed to work in the 2.45 GHz ISM Bandwidth, namely Bluetooth BR/EDR and BLE, ZigBee, WiFi and ANT/ANT+, among them ZigBee is designed also for operation in Sub-GHz band and WiFi can operate also in the 5.8 GHz ISM Band. The protocols that are designed specifically to operate at Sub-GHz ISM Band are then Z-Star, HaLow, UHF RFID and LoRa. As for the maximum communication range, Bluetooth protocols ANT/ANT+ and UHF RFID are short range protocols, which ensure a communication respectively up to 10 m, 5 m and 15 m. WiFi communication can operate over a maximum range of 30 m. On the other hand, Z-Star, ZigBee and HaLow protocols can cover a distance up to 100 m, while LoRa can cover a distance of 2 to 5 km in an urban area.