## 1 Introduction
In the last category that includes Ingenu RPMA [13] and LoRa [14], the spread-spectrum (SS) technique replaced UNB at the physical layer for IoT applications, which uses wideband (noise-like signals) for data transmission and spreads the data stream across a considerably broader bandwidth than the actual data signal bandwidth. In SS-based systems, the data are delivered alternately by continually changing their carrier frequencies or their data patterns, which is different from narrowband, where a single RF band is used for data transmission. The transmitters of SS and narrowband operate at a similar level of transmit power. Thus, the SS-based technology's transmitters can transmit at a lower spectral power density (W/Hz) than narrowband transmitters. This is one of the key advantages of LPWAN technologies based on SS and explains its popularity for low-power IoT devices. It is also difficult to detect, intercept, demodulate, and jam SS transmissions. The SS technique can be classified into DSSS, FHSS, and CSS categories. Ingenu had developed the proprietary RPMA as one SS-based LPWAN technology that relies on DSSS modulation. RPMA does not utilize sub-bands like SigFox, but it uses a 2.4-GHz ISM band to realize a worldwide LPWAN technology. LoRa/LoRaWAN is open-source technology that can set up a private network autonomously and without a third-party infrastructure at a low cost. In contrast to SigFox and NB-IoT, LoRaWAN allows for the development of private networks and simple integration with a wide range of global network platforms (e.g., The Things Network). Because of its open access specs, LoRaWAN has piqued the curiosity of the research community almost from the moment it was introduced to the market. Despite different LPWAN family technologies, this paper mainly focuses on the recently proposed solutions to develop LoRa/LoRaWAN technology. Among all LPWAN technologies, LoRa has been chosen, depending on its market penetration and its enormous applications in industry, education, and communities. LoRa is a physical layer with low-energy and long-range communication technology operating in unlicensed radio bands at the sub-gigahertz level. LoRaWAN is the medium access control (MAC) protocol for the datalink layer and network layer on LoRa, backed and developed as a standard by the LoRa Alliance [15]. These features make LoRa networks a strong candidate for diverse IoT application deployments such as industrial sensor communications, smart cities, smart buildings, water quality measurement, remote environmental monitoring, smart meters, and intelligent agriculture. Hence, this paper describes the multiple and various features of LPWAN technologies and contrasts them concerning their implementation features as a guideline to analyze their performance and possible benefits. The main contributions of this paper can be summarized as follows:  
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2. Conduct a thorough review of the emerging LPWAN technologies, concentrating on their main features and limitations;
3. Perform an overview of LoRa/LoRaWAN technologies as a key player for IoT applications, especially in standalone network deployments;  
Figure 2: Types of cellular-based LPWAN technologies. 3. Examine and compare the commonly used LoRa/LoRaWAN simulation tools by highlighting their capabilities and features for enabling researchers to select the most suitable simulator based on their needs and programming skills;
4. Highlight the challenges, recent solutions, and future directions to provide guidelines toward precise deployment of LoRa/LoRaWAN technology as a global network. The rest of this article is structured as follows. In Section 2, we exhibit an overview of the considered LPWAN technologies and compare their main features. Section 3 focuses on LoRa/LoRaWAN technology and its technical features. In Section 4, we present the challenges and recent solutions to LoRaWAN. Section 5 surveys the available simulation tools to analyze LoRa/LoRaWAN performance. Then, we present the opportunity for enhancement and future works on LoRaWAN in Section 6.