## 3 Architectures in the 5G and LPWAN-IoT and Smart Cities
### LPWAN Architecture  
LPWAN was developed to allow long-range communications at a low data rate and with low energy consumption. Hence, LPWAN devices are considered to be low complexity long-range devices. LPWAN works in the license-free frequency bands and the licensed frequency (cellular) bands. The LPWAN technology use case is not very common though it is gradually increasing and involves numerous different technologies due to different manufacturers/vendors. A typical LPWAN architecture is shown in Figure 4, which is common to many LPWAN technologies. The basic network topology for the LPWAN deployment is the star topology. Other topologies such as the tree topology are used with a greater number of nodes to increase the range. To increase the range further and with several nodes, a mesh topology is used. However, the mesh topology has higher complexity and energy consumption with minimal delay. Detailed discussions on the network topologies including their merits and demerits can be found in [40; 41; 42]. Technologies Concepts for LPWAN Market Players  
The conceptual technologies for the various LPWAN market players are discussed as follows:  
* LoRaWAN  
LoRaWAN is a low power wide area network built on LoRa which is envisioned for low-cost, low battery power-operated devices for wider coverage and ubiquity connectivity. LoRaWAN is owned by Semtech Corporation. It is in the family of the LoRa Alliance, an open, non-profit association of industrial vendors for IoT connectivity solutions. The LoRa is a proprietary PHY layer protocol, and the LoRaWAN was developed to define the upper layers protocols. It performs primarily as a network layer protocol for managing communications between LPWAN gateways and end-node devices as a routing protocol, maintained by the LoRa Alliance. It uses sub-1 GHz frequency bands with a proprietary modulation technique based on chirp spread spectrum (CSS) modulation. It covers a range of 10 km., and about 20 km in rural areas. The data rate is from 0.3 kbps to 37.5 kbps. Detailed upper layers specifications of the LoRaWAN are available in [43]. Simple ALOHA is used for channel access in the MAC layer. The use of different channels and orthogonal codes enables LoRa to establish a connection between multiple nodes [40]. LoRaWAN provides a reliable communication system during moderate traffic, though it encounters  
Figure 4: Typical LPWAN Architecture. the following problems such as duty cycle management, frequency hopping, and channel access mechanisms [23] once the traffic exceeds the maximum limits. * Sigfox  
Sigfox is a Global French network operator. Its PHY layer protocol is also proprietary and operates in a licensed-free band of sub-1 GHz radio bands. It is suited for low-energy devices and comprises base stations with cognitive-based software-defined radios (SDR) and IP-based network servers. It uses BPSK modulation techniques and ultra-narrow bands (UNB) of 100 Hz for carrier signals and spectral efficiency improvement. It has the following advantages such as improved receiver sensitivity, long-range, reduced power consumption, and high penetration rate through a sole object, which makes it suitable for deployment in underground or rough topography [44]. In rural or open space setting the connectivity, the range is over 40 km. However, only 140 uplink messages with a payload of 12 bytes and up to 4 downlink messages with each a payload of 8 bytes per day can be communicated through Sigfox [41]. Sigfox network reliability can be improved by using a time and frequency variation strategy with multiple transmissions [45]. * DASH7  
DASH7 is based on the DASH 7 Alliance Protocol (D7 AP) and was derived from the ISO 18000-7 standard. It is a low-power, long-range device that also operates in a licensed-free band of sub-1 GHz radio frequency. It uses narrowband two-level GFSK modulation with a channel bandwidth of 25 kHz or 200 kHz along with data whitening and forward error correction features [25].