Furthermore, spectrum sharing is not a viable option for 2G.
The 3G family (UMTS and HSPA) supports the data rate of 1–3 Mbps that exceeds the requirements of most M2M applications. For automotive M2M applications that need a broad range of data rates, 3G is an appropriate wireless network. Compared with 2G, devices, network equipment, and connectivity are more expensive and less power efficient.
4G technologies (LTE and LTE-A) have an “all IP” technology that makes network infrastructure deployments simpler and less expensive than older cellular networks. It offers improved spectral efficiency, greater longevity, bandwidth flexibility, and scalability, all of which meet the requirements for MTC applications. To cope with the increased complexity of the protocols in 4G, high-performance processors in the radios are required. This leads to higher cost in 4G and makes large-scale M2M deployments difficult.
5G technology supports the requirements of MTC design as the forefront of IoT by offering lower cost, better power efficiency, and increased data rate for both terminals and systems. It also offers minimum latency for delay sensitive applications, massive MTC access, and seamless integration of IoT devices, all without QoS deterioration [143]. A number of 5G features also fit well with the M2M path, namely, service creation, service provisioning, and dense deployments.
1.5.2 LTE Features Enhancement
LTE is introduced in 3GPP Release 8 [144]. The foundation of the LTE network is an IP network architecture used for mobile, fixed, and portable broadband access. The all-IP architecture of LTE enables new converging services based on the IP multimedia core subsystem. To achieve high data rates, LTE utilizes a combination of orthogonal frequency division multiple access (OFDMA), multiple-input, multiple-output (MIMO) antenna systems, scalable bandwidth, higher order modulation schemes, and spatial multiplexing in the downlink. LTE works in two modes: time division duplex (TDD) and frequency division duplex (FDD). In 3GPP Release 10, LTE Advanced was introduced as a more advanced version of LTE [145].
LTE enhancements have been included in subsequent releases of LTE standard for different LTE-based devices (i.e., Cat-M, Cat-0) to meet the requirements of M2M/IoT devices [146]. The new versions are called LTE-eMTC, or LTE-M by 3GPP, and promise new generation of devices with lower cost, ubiquitous coverage, and ultra-low battery life.
1.5.3 4G Features Enhancement
The emerging IoT environment is composed of various types of wireless access nodes that require seamless connectivity [147]. The 4G network exploits interoperability and integration between multiple radio access networks (RAN) and radio access technologies (RAT) to create a more solid heterogeneous networking paradigm. This section briefly summarizes the evolution of 4G and its features that accommodate connectivity in IoT.
Coverage extension: Relaying is a key radio access technology in 4G that extends base station range beyond its coverage area [148]. A relaying service is composed of chains of relaying nodes that adopt a suitable transmission scheme (and spectrum) based on the required latency and reliability [149]. With reference to IoT systems, the adoption of relaying services decreases network overload, leading to improved network scalability. It also alleviates the single point of failure issue and provides some mean of fault-tolerant communications in IoT systems.
Enhanced data rate and throughput: 4G networks utilize the concept of licensed and unlicensed carriers’ aggregation, where control-related traffic and non-critical transmissions are sent via licensed and unlicensed bands, respectively. Such techniques can be beneficial for scalable IoT systems that require high throughput.
Power saving: As elaborated in 3GPP Release 12, frequent link quality measurements at the device side are a main source of energy consumption in networks. To address this issue, the power-saving mode was introduced as a viable solution to manage data transmission. In power-saving mode, a device could transmit uplink data at any time. However, for downlink communication, the device is reachable only either when it is active in uplink or is at configurable time instances.
RAN as a service: RAN utilizes radio resource virtualization to create various virtual functions and to expose them via cloud platforms to distribute networks functionalities and management [150]. Also known as RAN as a service, it improves the flexibility of the communication infrastructure and allows IoT systems to self-heal and self-configure.
Device-to-device (D2D) communication: It entails the possibility of data exchange between two devices in the unlicensed band without involving base stations or with just its partial aid [151]. In this technology, devices serve as mobile relays to communicate in IoT environment.
1.5.4 5G Features Enhancement
The 5G cellular network provides advanced wireless connectivity for various use cases and vertical industries and paves the way for Industry 4.0. It exploits different technologies such as network slicing, network function virtualization (NFV), software defined network (SDN), and mobile edge computing (MEC) to pre-allocate resources for both communications and computing [152]. The broadband capability of 5G mobile network facilitates direct and seamless wireless communication from the field level to the cloud and enables new operating models without redesigning the production line for smart manufacturing [153]. In addition, private cellular connections could help in assigning spectrum bands and base stations such that data transmission is performed via secure and reserved channels [154, 155]. A main differentiator between 5G and previous generations of cellular networks lies in its significant emphasis on MTC and IoT. For instance, 5G air interface has enacted novel techniques in PHY and MAC layers that accommodate MTC [156]. It seems that 5G leads to convergence of the many different communication technologies as it becomes the standard wireless technology.
5G specifically focuses on supporting communication at very low latencies, unparalleled reliability, and massive IoT connectivity. Based on these distinct features in 5G networks, the emerging diversified telecommunication services are categorized into three main classes [157]: (1) ultra-reliable and low latency communications (URLLC); (2) enhanced mobile broadband (eMBB); and (3) massive machine-type communications (mMTC).
1.5.4.1 Ultra-Reliable and Low Latency Communications
Compared with 4G network, E2E radio network latency in 5G is reduced to 1 ms with peak data transfer rate of 20 Gbps; this offers an ultra-responsive connection with ultra-low latency [158].15 URLLC is expected to play a key role in a wide range of mission-critical and industrial automation applications such as remote medical assistant, autonomous vehicle control, and robot and drone control that rely on high data rates and low latency [159, 160]. One important aspect of URLLC scenarios is to communicate in real time or within a very short time. Consequently, applications that require highly reliable communication can be implemented in 5G, such as remote-controlled plants or smart factories. At the same time, 5G exploits lower frequency bands that propagate farther in the environment, providing a more robust means of communication between IoT devices in buildings. Such a feature also leads to prolonged devices battery life (about years).
In addition to highly reliable communications [161], 5G new radio introduces the concept of extra transmission redundancy to better support industrial applications in URLLC scenarios [162]. Design of URLLC services heavily relies on a number of factors including more reliable channel coding techniques, effective resource sharing (control-flow and data), and grant-free transmission for uplink data, all supported by 5G new radio standard [163].
1.5.4.2 Enhanced Mobile Broadband
5G is expected to support around 29 billion devices connected to IoT by 2022 [164, 165]. eMBB delivers high data rates across 5G coverage area, where downlink data rates of at least 100 Mbps per device is supported over a typical dense urban environment. With the increased bandwidth, the high-performance connectivity is also sustained for indoor spaces such as industrial campuses [166]. Therefore, bandwidth hungry