# River Water Quality Monitoring Using LoRa-Based IoT
## 3 IoT Technologies
### LPWAN  
Narrow Band-IoT (NB-IoT) is a technology developed by the 3 rd Generation Partnership Project (3 GPP) and is implemented over existing Long-Term Evolution (LTE) cellular networks [9]. It occupies a 200 kHz block of an LTE carrier and can be implemented on the mobile network in three different modes; see Figure 1.  
In any of the operating modes, there is a 10 kHz guard band between the blocks, leaving 180 kHz of usable bandwidth for data. The great advantage of this technology, as it is integrated into mobile networks, is its great coverage in both external and internal environments. The disadvantage is that there are costs associated with mobile operators. Sigfox technology, also called \"Sigfox OG Technology\", was the first LPWAN to be developed in 2010 by the French company with the same name, but it was acquired in 2022 by UnaBiz [11]. Communications use Binary Phase Shift Keying (BPSK) modulation, with a bandwidth of just 100 Hz, allowing low energy consumption and high receiver sensitivity at the expense of a maximum throughput of just 100 b/s. The devices (sensors) communicate with the base stations, using the free Industrial Scientific and Medical (ISM) frequency band, 868 MHz in Europe. Devices send messages over the air to the base stations, then these messages go through a backhaul (Internet connection) to Sigfox Cloud, where they are stored and can be accessed by the customer's end platform, as shown in the Sigfox network architecture in Figure 2. It is also possible to send messages in the opposite direction. The Sigfox network has good coverage, especially in Europe, but with operator costs as the main disadvantage. LoRa is a protocol developed by the French company Cycleo (Grenoble, French), which was acquired by Semtech (Semtech Corporation, Camarillo, CA, USA) in 2012. Like Sigfox, LoRa uses the ISM band for communications, but using a proprietary modulation technique derived from existing Chirp Spread Spectrum (CSS) technology [12]. LoRaWAN is an LPWAN standard managed by LoRa Alliance [13], based on LoRa, designed to connect wireless devices to the Internet, and meets the main IoT requirements, such as bidirectional communications, security, mobility and location services. There are some LoRaWAN operators, and they have good coverage. Figure 1: LTE carrier operation modes for NB-IoT: (**a**) in-band; (**b**) guard band; (**c**) stand-alone (adapted from [10]). The LoRaWAN network architecture (Figure 3) uses a star-of-stars topology, where gateways relay messages between end-devices and a central network server [13]. Connected via standard Internet connections (backhaul), gateways convert RF packets to IP packets and vice versa [13]. The specification defines three classes of operation for the devices [13]. Class A supports (going in both directions) communication, requires the most energy (producing a lot with very little waste) and is required in all devices. The downlink is available only after a device TX (uplink). Class B tools (going in both directions) communicate with scheduled downlink slots. Class C has the same uplink schedule as Class A but always keeps the receiving window open, providing less latency but more energy use. A summary of the characteristics of the LPWAN networks covered here is presented in Table 1.  
Figure 3: LoRaWAN network architecture: Gateway receives messages from any end node, forwards these data messages to the network server, and they are finally accessed by the application server (adapted from [14]). Figure 2: Sigfox network architecture: A device broadcasts a message using its radio antenna; multiple base stations in the area will receive the message, and the base stations then send the message to the Sigfox Cloud, which eventually sends the message to the customer’s end platform. (adapted from [11]). These LPWAN networks present a compromise between some parameters [15] in terms of some IoT factors, which are shown in Figure 4.  
In summary, each technology has a place in IoT networks.