# Evaluating the Impact of Pre-Configured Uplink Resources in Narrowband IoT
These strategies effectively balance network connectivity and energy consumption [7; 8]. In releases 15 and 16, 3 GPP introduced two critical mechanisms, Early Data Transmission (EDT) [9] and Preconfigured Uplink Resources (PURs) [10], to reduce energy consumption further. EDT involves timely data transmission during the Random Access Procedure (RAP) to minimize energy usage. PURs aim to streamline uplink (UL) transmissions by pre-allocating resources, reducing latency, and ensuring more efficient use of network resources. These strategies contribute to the continued success and sustainability of NB-IoT. This paper aims to explore the intricacies of NB-IoT energy efficiency. It provides a comprehensive study of EDT and PURs and their impact on energy consumption and latency, offering an in-depth look at the operational mechanisms of NB-IoT. We understand there has not been a detailed and realistic assessment of these optimizations. In a study by [PERSON] et al. [10], an analytical model was proposed to evaluate the effectiveness of PURs when sending packets and receiving acknowledgments at different layers. However, analytical modeling has limitations and lacks detail, while simulation offers more realistic and detailed scenarios at the cost of higher computational demands. To address the analytical limitations, we utilized the ns-3 network simulator to extend LENA-NB [11] and create a realistic environment for studying the behavior of EDT and PURs under various scenarios, including energy consumption, latency, impact of radio propagation models, PUR missed/failed slots, coverage levels, etc. The main contributions of this paper are summarized as follows:  
* An implementation of PURs inside LENA-NB. * A study on PURs on energy efficiency, latency, and scalability from a user and network perspective. * A comparative study on PURs with EDT and the default RAP, including energy-saving mechanisms. Since our study was conducted within a simulator environment, we argue that they are more accurate than the ones obtained by [PERSON] et al. [10]. Our study is motivated by the fact that a significant portion of energy consumption in NB-IoT occurs during radio connectivity. This is supported by various studies, including those by [PERSON] et al. [12], [PERSON] et al. [13], and [PERSON] et al. [14]. Figure 1 illustrates the energy consumption of an NB-IoT device during its various operational states for a single day, representing a scenario where only one packet is transmitted. It is important to note that a device, throughout its lifespan, circulates through only these operational states. As shown in Figure 1, the initial connection setup, also known as the Random Access Channel (RACH) procedure (orange); packet transmission (light blue); listening to a radio channel (purple); and receiving downlink traffic (red) account for almost all energy consumption. In contrast, the energy spent in PSM mode (dark blue) is negligible and not visible in the figure. Therefore, the opportunity to find energy savings is in the different active radio states and by introducing mechanisms such as EDT and PURs. The rest of this paper is organized as follows: Section 2 provides a detailed discussion of NB-IoT technology, operating states, and energy-saving mechanisms. Section 3 briefly describes our LENA-NB experimental setup in ns-3. Section 4 provides a detailed analysis of NB-IoT energy-saving mechanisms. Section 5 overviews previously published work on EDT and PURs, while Section 6 concludes the paper.