## 1 Introduction
The usage of bandwidth is counted based on the Effective Radiated Power (ERP), while the spectrum access method for the 868 MHz ISM is based on Listen-Before-Talk (LBT) or duty cycling. The maximum ERP on LoRa basic frequencies (868.00-868.60), which are common with SigFox, is limited to 25 mW [4], although, EDs according to frequency regulation, support transmit power of up to 20 dBm (100 mW) [6]. Such power allocation is permitted for only one frequency channel (G3 band with a limit of 27 dBm), whilst 14 dBm can be used in any of six channels. The maximum transmit distance calculated with the Friis transmission equation for 14 dBm transmission power results in a theoretical range of more than 300 km [2]. For LoRa, the duty cycle calculation is based on channels with 1%, 0.1% and 10% access limit. Spreading factor is a customized parameter for each frame that is transmitted and is related to the chirp spread spectrum (CSS) modulation of the physical layer. The choice of SF between 7 to 12, provides a trade-off between range and throughput (data rate). By increasing the SF, the number of chips per symbol are getting increased, which reduces the signal to noise ratio (SNR) that is required for successful demodulation, but simultaneously also increases the time on air (slow transmission). Lower spreading factors increase the data transmission rate, allowing for more data to be transmitted within the ISM band's duty cycle limits [7]. Each SF corresponds to a different data rate, which ranges from 0.3 kbps to 27 kbps [8]. LoRaWAN GateWays (GW) are multichannel multi-modem transceivers [5], characterized by high sensitivity due to the usage of very low data rates and sub-GHz ISM radio bands [2], that are deployed such as base stations (cellular network model) that cover large areas. In most cases LoRaWAN network operators provide connectivity as a service [8], by offering the GWs infrastructure. Any GW forwards the received messages to the associated network server for processing [9]. Typically, each LoRa GW supports demodulation of signals from six quasi-orthogonal logical star networks in parallel (some chips support more [10]), that corresponds to the available spreading factors [11], while transmissions are also supported on different frequency channels [5]. Specifically, the sensitivity of the GWs ranges from \(-130.0\) dBm to \(-142.5\) dBm depending on the spreading factor [12], while the minimum required RSSI for successful decoding requires 5 to 7 dBm more than the sensitivity for each corresponding spreading factor [9]. Therefore, when the spreading factor increases, the possibility for successfully receiving a packet on a weak link also increases, which determines a longer communication range. Due to the message broadcast nature of the protocol, EDs could be clustered below more than one GWs. This happens because as long as a message transmission is heard by any GW within the network, that message is considered to be received [9]. Once a GW receives a message, encapsulates its data into a UDP packet [10] and forwards it to the network server of the LoRaWAN network. Next, a JSON string is produced from the network server for forwarding, including the payload, GW information, as well as additional information for physical communication parameters, such as RSSI and SNR [1]. LoRaWAN deployment efficiency is mostly controlled by an adaptive data rate (ADR) mechanism which is used to control the transmission of messages between EDs and GWs [13]. It is argued that LoRaWAN networks cannot truthfully scale without using a dynamic data rate allocation scheme [14]. The optimal choice of the data rate for transmissions is the one that can ensure energy-efficient operation and increase the capacity of a single GW [14]. So, in most cases, ADR schemes aim to maximize battery life and throughput by adjusting the data rate.