In this chapter, fundamental concepts are introduced for the waveform design. Generalized definition of the waveform is given to provide a basis for the discussions in the first two parts. Several relationships for the waveform design are investigated, and then application requirements of different wireless communications standards are discussed. Impacts of the waveform design on radio access technologies (RATs) are examined. At the end, standardization perspective of the waveform design is presented through the example of fifth generation (5G) new radio (NR) frame.

This chapter aims to provide an in-depth understanding of orthogonal frequency division multiplexing (OFDM) as well as its performance in the presence of a multipath channel and various impairments. Also, major alternative waveforms, which provide better time -frequency localization compared to OFDM using various filtering/windowing approaches with certain trade-offs, are overviewed to present a complete picture of the waveform design discussions of next -generation wireless technologies.

The upcoming generations of wireless communications are characterized by a wide variety of applications. This necessitates a provision of flexible radio access technologies (RATs) capable of adapting to changing user (and network) requirements. One of the most significant development in this regard is the introduction of mixed or multiple numerology concept for the fifth generation (5G) of wireless communication. However, flexibility offered by the mixed numerology concept comes with its own set of challenges, including the novel type of interference referred to as inter-numerology interference (INI). This chapter looks at the various implementation-related issues for 5G's mixed numerology systems such INI in particular. In addition to discussing the analytical models of INI, mechanisms for its mitigation are also described. Moreover, the generalization of numerology concept to other domains is briefly explored for future communication networks.

In search of a flexible waveform, this chapter starts by manipulating orthogonal frequency division multiplexing (OFDM) into being more flexible to further optimize time and frequency localization to facilitate a better coexistence of different, more advanced numerologies. Dissatisfied with the performance of using manipulated OFDM waveforms solely, the hybrid waveform concept in which a plurality of currently available waveforms are used within a uniting frame structure to better satisfy various needs simultaneously is introduced. Waveform multiplexing approaches for hybrid waveforms are presented. Emerging solutions regarding determining a number of active numerologies, selection of active numerologies and scheduling of users to and within numerologies as part of the system conditions are discussed.

In this chapter, the relation between the modulation and waveform is discussed. The flexibility perspectives in the modulation design are also illustrated. Prevalent modulation options for OFDM waveform are classified, studied, analyzed, categorized, and compared in terms of their reliability, SE, PAPR, PE, 00B leakage, and their computational complexity performances. Furthermore, the connection between these transmission schemes and the requirements of future wireless networks is provided. Besides the presented modulation schemes for the basic OFDM waveform, some other fl exible modulation options for OFDM variants are given. Finally, envision for futuristic modulation options for beyond 5G is presented.

The service limitations of conventional orthogonal frequency division multiplexing (OFDM)-based technologies have motivated academia and industry to seek for new solutions in order to support the emerging services and use cases of future wireless networks. In this chapter, promising frequency-domain index modulation (IM) options, i.e., OFDM with IM (OFDM-IM), generalized OFDM with index modulation (OFDM-GIM), dual-mode OFDM (DM-OFDM), OFDM with interleaved subcarrier IM (OFDM-ISIM), are considered as complementary waveforms of classical OFDM. In frequency-domain IM, data information is sent not only via modulated subcarriers but also via proper activation of the subcarriers resulting in higher spectral efficiency (SE) and better error performance compared with OFDM-based schemes. Furthermore, features of OFDM, including intelligent subcarrier selection and adaptive activation ratio, are assessed. Lastly, the flexible utilization of these features is discussed to control channel effects, hardware impairments, asynchronicity, and to serve wide range requirements of fifth generation (5G) and beyond networks.

Massive multiple -input multiple -output (MIMO) is one of the key technologies for fifth generation (5G) and beyond [1]. By utilizing a large number of antennas, it can significantly improve the spectrum efficiency and is promising to achieve 5G key performance indicators. However, the application of large-scale antenna arrays leads to new challenges for physical layer signal processing. In this chapter, we will focus on massive MIMO systems and give a comprehensive introduction on massive MIMO technology for 5G and beyond.

As the wireless communication world regarded fifth generation (5G) technology to overcome the rapid rise of wireless data traffic demand, millimeter -wave (mmWave) frequency bands have been considered as an outstanding solution to satisfy the requirement of 5G networks. In this chapter, beamforming structures in mmWave systems are extensively explained after a brief introduction of these techniques in earlier systems. This practical chapter helps one to examine the beam management concept that is introduced exclusively in mmWave frequencies, where the processes and performance for this concept are studied. New challenges and some future directions for beamforming and beam management have been debated at the end of this chapter.

Relying on the activation states of transmit antennas to convey additional information, SM can achieve an attractive compromise between spectral efficiency and energy efficiency with a simple design philosophy, which has been verified by extensive studies. This chapter first discussed the basic principles, variants, and enhancements of SM and then showed the broad prospects of the SM concept in various implementations, including integration with other promising techniques and applications to emerging communication systems.

In this chapter, we have provided a brief overview of the concept of RISs, illustrated their potential for future wireless networks over simple propagation scenarios, covered the recent contributions in this frontier, and outlined potential use -cases of RISs in future wireless networks. As discussed earlier, the radical concept of communications through RISs may be a potential remedy for saturated wireless networks under the existing plethora of modern PHY and medium access control layer solutions. The fundamental idea behind the concept of RIS-assisted wireless networks is moving the functions that are usually implemented at the transmitter or receiver ends of communication systems to the environment. Within this perspective, the integration of RISs with emerging technologies, such as massive MIMO, mmWave communications, VLC, THz communication, IoT, and UAV networks, appears as a promising and unexplored research direction. The development of empirical RIS architectures as well as RIS-assisted channel models also stands out as an interesting future research direction.

The wide variety in enabling technologies, operating scenarios, environments, and use cases required for the fifth generation (5G) communication system and beyond 5G (B5G) entails the availability of descriptive channel models. In this chapter, we revise the key requirements of efficient channel modeling for 5G and beyond, highlight the outstanding and expected challenges, and present the main efforts made in this domain by leading industrial and research entities. We review channel modeling through machine learning (ML) as a promising channel modeling approach and revise the compressed sensing (CS) -based channel modeling and estimation framework.

Digital revolution and recent advances in telecommunications technology enable one to design communication systems that operate within the regions close to the theoretical capacity limits. Ever-increasing demand for wireless communications and emerging numerous high -capacity services and applications mandate providers to employ more bandwidth (BW)-oriented solutions to meet the requirements. Trend and predictions point out that marketplace targets data rates around 10 Gbps or even more within the upcoming decade. It is clear that such rates could only be achieved by employing more BW with the state-of-the-art technology. Considering the fact that bands in the range of 0.1-10 terahertz (THz), which are known as THz bands, are not allocated yet for specific active services around the globe, there is an enormous potential to achieve the desired data rates. Although THz bands look promising to achieve data rates on the order of several tens of Gbps, realization of fully operational THz communications systems obliges to carry out a multidisciplinary effort, including statistical propagation and channel characterizations, adaptive transceiver designs, reconfigurable platforms, advanced signal -processing algorithms and techniques along with upper layer protocols equipped with various security and privacy levels. Thus, this chapter provides an overview on the open issues, and the state-of-t

In this chapter, visible light communication (VLC) is introduced as a promising candidate to complement radio access technologies in fifth generation (5G) and beyond wireless networks. Starting with the brief history of VLC and standardization activities, it provides an overview of VLC system design, which includes the transmitter and receiver design, channel modeling, and medium access control (MAC). Besides, the integration of VLC with other communication technologies such as infrared (IR), power line communication (PLC), and radio frequency (RF) is also discussed to show how these technologies can work together and complement each other. Furthermore, the integration of VLC in 5G networks is also discussed from the implementation perspective. Finally, this chapter is concluded with the applications and future directions of VLC in 5G and beyond.

Wireless communication, like any other technology, is driven by the ever-increasing user requirements. Evolving from basic text and voice services, the current communication networks are capable of providing extremely high data rates with low latency and strict reliability. The diversity in user and application requirements is reflected in the various technologies being considered for enabling future networks. Some of these well-established enablers include small cells, millimeter-wave (mmWave) communications, full-duplex systems, massive multiple-input multiple-output (mMIMO) antenna systems, beamforming and more adaptive physical layer (PHY) and medium access control layer designs [1]. Simultaneous incorporation of such diverse technologies necessitates flexible and coordinated network architecture. This chapter attempts to look at the evolution of coordination mechanisms through the different cellular generations. Starting from the initial proposition for intercell or co-channel interference (CCI)* mitigation in Long Term Evolution (LTE), their applicability for various fifth generation (5G) service requirements is discussed. Later, the focus is turned toward future wireless networks, where the potential advantages of coordination are highlighted for different network architectures, applications and requirements.

The radio resource scarcity of classical orthogonal radio access -based technologies has encouraged academia and industry to search for a way out in order to support the exponential growth of data rate, system capacity, and communication latency in beyond 5G wireless communications. Recently, the concept of non orthogonal radio accessing, where user equipment (UEs) with different services intentionally share the same radio resources, is proposed to compensate the radio resource scarcity. The focus of this chapter is to emphasize the potential of non orthogonal access technologies in next generation networks. The fundamentals of power -domain non -orthogonal multiple accessing (PD-NOMA) are revised considering system sum -rate and user fairness and compared with conventional orthogonal frequency division multiple access (OFDMA). Furthermore, state-of-the-art NOMAbased schemes, including low -density spreading (LDS) and index modulation (IM), grant -free (GF) random access, and relatively novel concept of waveform coexistence for multiple accessing, are discussed. Finally, future directions and potential non -orthogonal radio access technologies are analyzed considering practical scenarios.

This chapter is organised as follows: Section 16.2 will briefly summarise CR and its integral phases, while Section 16.3 will elaborate the traditional spectrum sensing techniques by introducing their key features and main limitations. The predictive spectrum sensing idea and the corresponding state-of-the-art will be presented in Section 16.4, and finally Section 16.6 will conclude the chapter.

In this section, we first brief ML techniques useful in wireless communications and networking, and more details can be found in Generally speaking, it is well known that ML techniques can be viewed as the following three categories: supervised learning where a "teacher" is available (i.e. typically through training data set), unsupervised learning, and reinforcement learning (RL). However, to apply ML to wireless communications and networking, another concept to categorize ML techniques is more important, model-based or model-free.

Physical layer security (PLS) has emerged as a promising and powerful concept for securing future wireless technologies, including fifth generation (5G) and beyond networks, as it has the potential to solve many of the problems associated with conventional cryptography -based approaches. In this chapter, the principles of PLS as a complementary solution to cryptography for future networks are presented. The concepts, merits, and demerits for different types of PLS techniques are discussed and explained. Moreover, the recent applications of PLS to different emerging wireless technologies are also presented. Furthermore, the details about physical layer authentication methods against spoofing attacks and details about jamming attacks and related solutions are also included.

Non-orthogonal multiple access (NOMA) has been envisioned as a promising candidate for the next generation of wireless communication systems. By multiplexing users over the same time-frequency resource block, NOMA can increase the number of served users and enhance the system spectral efficiency (SE), compared with conventional orthogonal multiple access (OMA). Nonetheless, from the security perspective, sharing the same time-frequency resource among users imposes secrecy challenges. In this regard, physical layer security (PLS) has been introduced as an additional protecting layer to traditional encryption methods for securing communication confidentiality, via exploiting the randomness nature of wireless transmission media. The application of PLS to NOMA networks has drawn great attention recently. Existing works on this cover various scenarios, including single-input single-output (SISO), multiple-input multiple-output (MIMO), and massive MIMO systems. Moreover, PLS has also been considered when NOMA is combined with other advanced transmission technologies, such as simultaneous wireless information and power transfer (SWIPT), relay, full-duplex (FD), and millimeter wave (mmWave). This chapter aims to provide a comprehensive survey on the research progress of PLS-assisted NOMA systems. Toward this, we first introduce the fundamentals of NOMA and PLS, respectively. Then, we classify the existing PLS-assisted NOMA frameworks into three categories based on the number of antennas at the base station (BS), namely, SISO-, MIMO-, and massive MIMO-based systems. A detailed presentation of the state-of-the-art on PLS-assisted NOMA systems is further provided.