# Energy Efficiency of IoT Networks for Environmental Parameters of Bulgarian Cities
The simulation analyses presented in some of the available literature [9; 10] sources are related to \"hypothetical\" WSNs, which have a certain radius of availability and operating parameters. It is necessary to make studies which take into account the working conditions, geographical location, and number of nodes in the WSN. Table 1 provides a comparative analysis of the performance of four commonly used wireless communication technologies that are suitable for use in sensor networks. The difference in bandwidth between the compared wireless communication technologies is not large. [PERSON] [9] points out that the ZigBee over 802.15.4 protocol has more application capabilities than Bluetooth due to its long battery life, greater usable range, dimensional flexibility, and reliability of the network architecture. According to [PERSON] et al. [10], the effective use of network protocols depends to a large extent on specific practical applications,  
as well as network reliability, roaming capability, recovery mechanism, hardware cost and network installation and maintenance costs. LoRa technology shows more advantages in transmission distance and a lower power consumption than other technologies. Due to the potentially complex environment in which the sensor devices will operate, problems also arise when using LoRa technology. In an urban environment, these are the presence of buildings, trees, and features of the terrain that prevent the transmission of signals in wireless networks [11]. The LoRaWAN protocol ([[https://www.thethingsnetwork.org](https://www.thethingsnetwork.org)]([https://www.thethingsnetwork.org](https://www.thethingsnetwork.org)), accessed on 1 April 2022) is built on LoRa technology. LoRa provides the physical layer that allows for long-distance bonding. LoRaWAN defines the communication protocol and system architecture. Protocol and network architecture have the greatest impact on battery life at a node, network capacity, quality of service, security, and the variety of applications served by the network. If the sensors need to be used as portable devices, this requires a communication protocol for dynamic LoRa sensor networks. This protocol is \"multi-hop\". An advantage of this transmission method is that restrictions on the maximum distances at which WSN data are received/transmitted can be avoided. The limitations of multi-hop are that it has high latency and low reliability. When setting up communication in a LoRa network, the following key characteristics need to be taken into account [12]: Transmission Power (TP), which varies in the range [\(-\)4, 20 dBm], but due to some restrictions can be used in the range 2-20 dBm; Carrier Frequency (CF), which changes in steps of 61 Hz, in the range 137-1020 MHz, for which the scope depends on the scheme used and the region in which it is used; Spreading Factor (SF), which represents the ratio between the symbol rate and the chip rate and varies in the range of 6-12. High levels of this factor increase the signal-to-noise ratio (SNR), as well as increase the rate of transmission and time to transfer data packets; Bandwidth (BW), which represents the bandwidth of the transmission band. At higher BW values, more data are transmitted simultaneously, but at the expense of lower sensitivity and noise overlay in the signal. It is commonly used at frequencies of 125, 250 and 500 kHz; Code Rate (CR), which is a method of error correction. Higher CR levels allow for better noise reduction but reduce data rates. The default is 4/8, but it can have values of 4/5, 4/6, 4/7, or 4/8. The aim of this paper is to clarify the technical challenges related to the energy efficiency of using LoRa networks in six cities in Bulgaria.