## 7 Discussion  
The fast-evolving concept of the Internet of Things, comprising millions of computing machines and software programs; billions of devices such as sensors, actuators, and robots; and trillions of digitized sentient objects represents a definitive future direction to adopt the most advanced information communication technology infrastructure with futuristic architectures. Services and smart solutions brought about by IoT can be utilized in pretty much every industry, from energy and automation to financial management and health. However, the selection of the IoT solution and its successful deployment are challenging tasks, since the most appropriate choice for IoT networks involves battery-life-limited wireless sensors. Reliable power maintenance for a prolonged period, specifically in remote and distant areas, inside buildings, or underground, is important. Some solutions involve conserving energy by reducing the energy costs related to data sampling and processing and finding feasible environmental energy harvesting method. The choice of radio communication technology also has a huge impact on a sensor's power consumption rate. Hence, in this paper we first gave a broad and yet comprehensive overview of the requirements and challenges of developing a smart IoT application, outlining essentials for the proposed smart parking solution. LPWAN and similar technologies used with wireless sensors are increasing the IoT development pace rapidly and are becoming the leading choices in this field for both licensed and unlicensed bands. LPWANs allow for very low power consumption, brief messaging, decreased device costs, outdoor and indoor coverage, easy network installation, and scalability. With these benefits in rural regions, the coverage of the cell network is usually high, and the installation costs, unlike with technologies such as WiFi or similar systems, are more affordable. The metropolitan use cases of LPWAN vary from smart parking, flood monitoring, and weather tracking in weather stations to monitoring infrastructure and buildings, smart metering and lightning, and even waste management. The three widely used cellular LPWAN networks, Sigfox, LoRaWAN (in the unlicensed spectrum), and NB-IoT (in the licensed spectra for 2G, 3G, and 4G), provide high scalability for thousands of end devices. NB-IoT is currently ahead of the others and allows more than 100k devices per base station, while for Sigfox and LoRaWAN the number is 5k. NB-IoT offers the maximum payload length and data transmission of up to 1600 bytes, while LoRaWAN allows 243 bytes at the maximum and Sigfox only 12 bytes. NB-IoT's design includes 20 dB coverage, working on a single battery charge for over 15 years. It is also compatible with the LTE cellular network infrastructure that currently exists, providing the same level of security. Regarding the data rate, Sigfox has a fixed data rate of up to 100 bps, with the limitation of 140 messages per day maximally. LoRaWAN's data rate range is from 0.3 up to 27 kbps, while for NB-IoT the peak data rates are 26 kbps in the downlink and 66 kbps in the uplink. LPWANs generally do not perform well in terms of latency due to the network characteristics. The experimental measurements indicate a need for latency reduction techniques, showing an average latency of 5 s for LoRaWAN and 0.072 s for NB-IoT. The spread spectrum and the narrowband techniques are the two main classes of modulation techniques used with LPWAN technologies to increase the range of the radio network. NB-IoT uses narrowband modulation techniques to provide a high linking capacity by encoding the signal at a low bandwidth. Using FDMA in the uplink and orthogonal FDMA (OFDMA) in the downlink, the data rate for NB-IoT is limited to 200 kbps in the downlink and 20 kbps in the uplink.