requiring a higher amount of battery are not permitted. The NB-IoT PHY layer is designed to conform to a subset of LTE standards; however, it exploits bandwidth of 180 KHz for narrowband transmission over uplink and downlink. FDMA and OFDMA are utilized for channel access in uplink and downlink, respectively [108]. An extensive review of NB-IoT PHY and MAC layers is discussed in [109].
The design objectives of NB-IoT encompass extended coverage, the multitude of devices with low data rate, and long battery life for delay-tolerant applications [110]. This technology is promising for indoor coverage and provides long-range and high sensitivity at the cost of adaptive throughput [111]. Three operation modes are provided for deployment of NB-IoT: stand-alone operation, guard-band operation, and in-band operation [103].
Connectivity of NB-IoT performs better than most of the competing technologies in terms of range, availability, and robustness. However, the latency of NB-IoT is unpredictable, and the procedure of random resource reservation increases the connection latency in dense networks [49]. Therefore, NB-IoT is not applicable to time-critical use cases such as safety systems. The main employments of NB-IoT for industrial applications are smart fleet management, smart logistic, and smart manufacturing [112, 113]. Recently, NB-IoT is exploited by telecom industry for smart lighting in the major cities [114].
The efficient utilization of existing cellular networks motivates different telecom manufacturers and vendors to promote NB-IoT standardization and commercialization. NB-IoT was initially proposed in 3GPP Release 13; further features and improvements such as localization methods, mobility, multicast services, and more technical details were specified in 3GPP Release 14 and beyond to satisfy the requirements of NB-IoT applications.
LTE-M. LTE machine type communication (MTC), termed as LTE-M, was proposed by 3GPP as a LPWAN standard to enable services and devices for M2M communication in IoT systems [91]. This standard adopts licensed frequency bands and relies on LTE-based protocols with the specifications of M2M communication in LTE advanced (LTE-A). Later, 3GPP defined a new profile for implementing MTC resources in LPWAN called Category 0 or CAT-0 [115]. In addition, two special categories were defined in the context of LTE that underpin IoT technology and the features of M2M communication: CAT-M for MTC and CAT-N for NB-IoT. CAT-M counts on mobile cellular network infrastructure to keep the coverage while reducing complexity. Different notions are used for each category; for instance, CAT-N standard is mainly referred to as NB-IoT, whereas CAT-M is known as CAT-M1, LTE eMTC, LTE-M2M, and LTE-M [116]. In this chapter, we will use LTE-M collectively for CAT-M.
The LTE-M standard supports both CAT-0 and CAT-M modes and takes advantage of existing LTE networks. It allows the LTE-installed infrastructure to be reused via a software upgrade to the existing LTE base stations [117]. LTE-M technology is highlighted by its efficient energy consumption that prolongs the battery lifetime of networks (more than 10 years). It also provides speeds of 300 Kbps and 375 Kbps for downlink and uplink, respectively [118]. LTE-M offers wireless network with low complexity and extended coverage for both indoors and underground. The performance of LTE-M for M2M communication is evaluated in [119] and discussed based on the network metrics. LTE-M supports a diverse range of vertical industries, applications, and deployment scenarios. For instance, Telstra and AT&T have used LTE-M in asset tracking and maintenance to provide wireless connection in IoT environments [120].
LTE-M has some advantages over NB-IoT, such as enhanced mobility, higher bandwidth and data rate, lower latency, and supporting voice over Internet (VoLTE) for simple use cases. In [121], LTE-M and NB-IoT are analyzed and compared for rural applications in terms of coverage and capacity. New network technologies such as NB-IoT and LTE-M, which are established by mobile technology and support LPWAN, are referred to as mobile IoT.
1.4.3 Comparative Study of Wireless Standards for Industrial IoT
As noted already, various wireless technologies and standards provide connectivity in industrial systems. To choose the appropriate wireless technology for an industrial IoT application, different factors should be considered. Tables 1.1 and 1.2 present the main technical differences among the aforementioned technologies. The comparison considers the PHY and MAC layer features along with various performance measures that each technology aims to fulfill. Such comparative study would assist in specifying potential wireless technologies for an industrial application.
Table 1.1 Comparison of Wireless Technologies: Short-Range Technologies.
| Zigbee | Wireless HART | ISAlOO.lla | WIA-PA | BLE | Wi-Fi HaLow | |
|---|---|---|---|---|---|---|
| Standard | IEEE 802.15.4 | PHY: IEEE 802.15.4 MAC: HART | IEEE 802.15.4 | IEEE 802.15.4 | IEEE 802.15.1 | IEEE 802.11.ah |
| Frequency band | 2.4 GHz | 2.4 GHz | 2.4 GHz | 2.4 GHz | 2.4 GHz | Sub-lGHz |
| Number of | 16 | 16 | 16 | 16 | 405 | 76 |
| Channels | ||||||
| Topology | Star, Tree, Mesh | Star, Mesh | Star, Mesh, Star-Mesh | Hybrid Star-Mesh | P2P, Star, Mesh7 | Star, Tree |
| Spreading | DSSS | DSSS, FHSS | DSSS, FHSS | DSSS | FHSS | MIMO-OFDM |
| MAC channel access | GTS, CSMA; Time slot is flexible | TSMP (TDMA, CSMA); Time slot of 10 ms | TDMA, CSMA; Time slot of 10–12 ms | TDMA, CSMA and FDMA; Time slot is configurable | TDMA | Hybrid EDCA/DCF |
| Channel bandwidth | 2 MHz | 2 MHz | 2 MHz | 20 MHz | 2 MHz8 | l/2/4/8/16 MHz |
| Range | 10–100 m | <600 m | <600 m (100 m9) | l–100 m | <100 m (<300 m7) | 90 m-l km |
| Data rate |
|