# Energy Efficiency of IoT Networks for Environmental Parameters of Bulgarian Cities
## 2 Related Works  
The parameters BW, SF, different loads and modulation methods in LoRa were used by [PERSON] et al. [13]. The authors study the influence of the data obtained from environmental parameters on the indicated characteristics of the wireless network. According to [PERSON] et al. [14], the communication setup parameters in LoRa have a significant impact on the performance of the wireless sensor network. Such is the power of the transmitter, BW, SF, and the number of measuring points. The choice of an appropriate method of communication depends on its application and requirements. The way data are transmitted is also an important factor in communication, as [PERSON] et al. [15] described. These authors offer a LoRa-based network with 3000 end devices. A real test for LoRa was performed and experiments were performed to find a simplified model that reduces data loss in LoRa. The authors found that the radio signal can reach distances above 1344 m with different values of SF in a combined indoor and outdoor communication environment. [PERSON] [16] points out that the European 868 MHz Industrial, Scientific and Medical (ISM) band is an appropriate frequency band due to the use of low frequencies for data transmission over LoRa wireless networks in European countries. The study in this article was carried out in Bulgaria and such a permitted frequency range was used. [PERSON] et al. [17] offer a system for monitoring the parameters of the environment. It is based on IoT and LoRa. The main purpose of this system is to determine the characteristics of water. When using wireless sensor networks, it is necessary to take into account exactly which environmental parameters will be measured. For example, the measurement of water characteristics differs, for example, from that of air or noise in an urban environment. Energy consumption is of great importance when using LoRa in IoT applications. According to [PERSON] et al. [2], the closer they are to the gateway, the less energy the wireless sensor devices consume. The sensor devices are designed to use a battery or solar panels. Reducing the energy consumed will increase the life of the device and the frequency of transmission of measurement data. The topology of the network also needs to be taken into account [18]. The \"star\" topology used in LoRa, in addition to its advantages, also has some limitations related to the high load on the central node, especially in networks with multiple wireless measuring stations. According to [PERSON] et al. [19], a complete wireless sensor data collection system covers the design of the network topology, the hardware and software of the sensor nodes, the protocols and the cloud web server platform. The authors propose a comprehensive project of the IoT network for the assessment of environmental parameters in urban conditions. The stages of network design and performance evaluation can be used in the present work. The design of a sensor network using LoRa technology is proposed by [PERSON] et al. [20]. The authors design the network on three levels and offer a sensor measurement system, as well as a methodology for designing wireless sensor networks in IoT. A disadvantage of this project is that the proposed methods and tools have not been tested in a real environment. From the review of the available literature, it can be concluded that the simulation studies of LoRa wireless sensor networks are carried out \"in principle\", without taking into account the influence of the environment in which they are used and the exact location of sensor devices. The evaluation of actually created networks is performed after their installation. This leads to inefficient use and detection of deficiencies once the network is installed. For this reason, the shortcomings of creating a wireless sensor network are difficult to overcome. Further research is needed on the simulation analysis of wireless sensor networks suitable for use in IoT.