# On the Benefits of Listen before Talk Scheme for NB-Fi Networks
## 1 Introduction  
Low-power wide-area networks (LPWANs) [1] are an important part of the Internet of Things, which, according to forecasts, will serve approximately 14% of all Internet connections [2] by 2023. NB-Fi (Narrow Band Fidelity) [3, 4] is a rather new and not so well studied LPWAN protocol widely deployed in several countries for environmental monitoring, data collection for smart homes and utilities, urban planning, and infrastructure management. NB-Fi networks operate in France [5], Serbia [6], Argentina [7], Moldova [8], Kazakhstan [9], and Russia [10]. Thus, the study of the benefits and the limits of this protocol is necessary to use this technology effectively and to satisfy the quality of service requirements in different scenarios. NB-Fi networks use license-exempt Industrial, Scientific, and Medical (ISM) bands; thus, for channel access, NB-Fi devices must abide by several restrictions imposed by the regulator. By default, NB-Fi devices do not sense the channel before transmission, i.e., they use the Aloha channel access method [11]. This channel access method can be easily implemented and is suitable for cheap Internet of Things (IoT) devices, but it forces devices to limit their duty cycle, i.e., the share of used channel time. Another possible channel access method is Listen Before Talk (LBT), also known as Carrier Sense Multiple Access (CSMA), when devices sense the channel before packet transmission. Implementation of the LBT mode is more complex, but, according to the classic research on CSMA [12], it provides a better packet delivery rate, and different implementations of LBT are often used in wireless networks [13, 14]. However, LBT introduces additional energy consumption, which is crucial for battery-supplied IoT devices. Thus, the motivation of our work is toinvestigate whether the properly configured LBT mode in NB-Fi networks can potentially improve the network performance and the quality of service of traffic in IoT scenarios. The LBT implementation described in the NB-Fi standard [3] corresponds to persistent CSMA, where the device listens to the channel and, if the channel is busy, should postpone transmission until it becomes idle. However, from the classic studies of CSMA, we know that persistent CSMA is not very efficient for wireless networks [12]. At the same time, although LBT or CSMA have been studied in theoretical works and recent technology-oriented papers, the existing results are not completely relevant to NB-Fi because these studies do not consider the peculiarities of this technology. Despite its importance, no studies have considered the LBT mode in NB-Fi, except for our previous work [15], where we compare the energy consumption of NB-Fi devices for LBT and non-LBT modes. Although energy consumption is an important indicator for IoT devices, which are often powered by batteries or low-power renewable sources of energy such as solar panels [16], the study [15] of LBT in NB-Fi networks does not consider other performance indicators such as PLR, delay and throughput, which are also important for IoT scenarios [17; 18]. Thus, the goal of our work is to close this gap and determine the most suitable implementation of LBT for NB-Fi networks to improve the PLR, delay, throughput, and energy consumption compared with the default non-LBT operation mode and with the straightforward implementation of LBT as it is described in the standard. In this paper, we extend the study of LBT in NB-Fi by accurately taking into account all the features of NB-Fi and comparing such important metrics as the PLR, delay, throughput, and energy consumption of NB-Fi devices when using channel access without LBT and when using different types of LBT. Moreover, we refine the sensors' energy consumption in different states based on the information provided by the vendor and thus obtain more accurate results than in [15].