# Evaluating the Impact of Pre-Configured Uplink Resources in Narrowband IoT
## 3 Simulation Environment  
The main reason for conducting a simulation study is that while it is clear from the standardization process that EDT and PURs can help reduce energy consumption and improve latency, there is currently no implementation of EDT or PURs by network operators, and no end devices support them. Based on our experience, network operators and end devices currently support release 13 and 14 features. LENA-NB [11] offers a simulation framework with a detailed implementation of radio access technology for NB-IoT, including control plane optimization [3] and EDT. Furthermore, LENA-NB includes  
Figure 5: The NB-IoT PUR process as defined in 3 GPP release 16, detailing a streamlined two-message protocol where Msg 3 (PUR data transmission) is used for data transmission and Msg 4 (PUR data response) for receiving the acknowledgment. several NB-IoT features to enhance network efficiency and reduce device costs. These features include the following:  
* A connection resume procedure: An important aspect of LENA-NB is implementing the connection resume procedure, which is part of the RRC connection setup procedure. This functionality lets devices quickly reconnect to the network without redoing the entire setup process. The implementation begins with the device receiving a unique resume ID during the RRC Connection Release phase, crucial for reinitiating a connection without a full setup. A data inactivity timer monitors transmission inactivity, triggering the Connection Release procedure when necessary. This process not only saves the specific entities of the device to the resume ID but also ensures efficient resource management by releasing the C-RNTI and cleaning up pending events. Upon attempting reconnection, the device uses the saved resume ID to restore its connection state, significantly reducing the time and resources required for network re-entry. * Cross-subframe scheduling In recognizing the absence of an NB-IoT-specific error model, LENA-NB employs a pragmatic approach using a lookup table derived from MATLAB NB-IoT Block Error Rate (BLER) simulations. This table assists in selecting optimal uplink and downlink configurations that meet BLER standards under various channel conditions, optimizing the simulator's performance across a wide range of scenarios. * A NB-IoT-specific energy state machine: To provide a detailed simulation of power efficiency, LENA-NB implements the eDRX and PSM techniques at the RRC level. The simulator incorporates an energy state machine that monitors the energy states of a device across different operations, including sending and receiving on various channels and modes, e.g., NPRACH, NPDCCH, NPDSCH, and NPUSCH. This state machine is critical in analyzing and optimizing energy use, drawing on a real-world power consumption data (Quectel BG95 NB-IoT/eMTC module [27]) to provide an accurate and comprehensive energy consumption analysis. These implementations and modifications are designed to provide a comprehensive understanding and evaluation of UE performance and efficiency in various operational scenarios. In our experiments, the simulator was extended with the implementation of PURs [28], as shown in Figure 6. This addition allows a UE to request specific radio resources, such as packet intervals, TBS, and offset. This request is sent by a UE RRC (ueRRC) to eNodeB RRC (enbRRC) before starting transmission, as shown in Figure 7. PURs were designed to handle a maximum packet size of 125 bytes. Packets larger than this limit must be segmented for transmission via PURs; otherwise, the system reverts to the default RAP for managing larger packets. Upon receiving a resource request, the enbRRC passes it to the eNodeB MAC layer (enbMAC), which then forwards it to the scheduler. The scheduler reserves all PUR-specific resources in the UL grid to ensure that these are not allocated to other transmissions. The scheduler then communicates the scheduling information and the assigned resources to ueRRC.