# Time Domain Analysis of NB-IoT Signals
## 1 Introduction  
Internet of things (IoT) embodies the concept of connecting devices from different environments with the aim to collect, process and exchange data via Internet protocols or other defined interfaces. Smart meters, automobile insurance black boxes, networked waste bins, smart bicycles are examples of IoT devices that can be both physical or virtual.  
The IoT represents a revolution in telecommunications by connecting different technologies and billions of objects in order to sustain smart decisions and the realization and the remote control of different objects. The IoT will help the development of many business sectors, such as manufacturing, transportation, agriculture, health, logistics (Figure 1). The total number of connected IoT devices was projected to reach 18 billion by 2022 [1; 2; 3].  
In recent years, many communication standards and protocols have been developed to support applications for machine-to-machine (M2M) communication, also termed Machine-Type Communication (MTC) [4; 5; 6; 7; 8; 9; 10; 11; 12; 13]. Standards and protocols such as NFC, RFID, Bluetooth Low-energy, ZigBee, Z-Wave, Wi-Fi are mostly dedicated to short-range applications while new Low-Power Wide-Area (LPWA) technologies such as LoRa, LoRaWAN, Weightless SIG, Sigfox and RPMA meet the need for wide-range communications between objects. These technologies operate in the unlicensed spectrum and provide massive connectivityfor devices but require the implementation of proper infrastructures. Cellular systems have also been considered in order to provide connectivity for MTC devices. For this, 3 GPP introduced in June 2016 a new cellular technology standard called NB-IoT (Narrow-Band IoT) to provide IoT services over cellular networks. NB-IoT is based on Long-Term Evolution (LTE) and therefore operates in the licensed spectrum. It is conceived to meet most of the IoT requirements, such as very good internal coverage, very low cost connectivity and low power consumption, as well as support for a huge number of connected devices. Unlike other IoT technologies on unlicensed bands, the use by NB-IoT of existing LTE infrastructures allows us to reduce costs for network implementation.  
In this work, after a brief description of the radio interface of the NB-IoT protocol, the results of a first set of time and code domain measurements on LTE/NB-IoT cells by means, respectively, of a spectrum and a vector analyzer will be described. The aim is to analyze the NB-IoT signal over time by showing how the analysis of individual sub-carriers enables the identification of control channels and signals of the NB-IoT standard including the Narrowband Reference Signal (NRS). Then, the results for the received power during transmission of the NRS obtained from measurements in the two different domains will be compared to verify their agreement. Power received during transmission of NRS is at the basis of the extrapolation methods set by the CEI 211-7/E technical standard [14] of the Italian Electrotechnical Commitee (Comitato Elettrotecnico Italiano). For this, the use of vector analyzers with measurements in the code domain is currently required. The agreement of results in the two domains demonstrates that time domain measurements by means of cheaper spectrum analyzers may be an alternative method.