The standardization activities of wireless mobile telecommunications have begun with analog standards that were introduced in the 1980s, and a new generation develops almost every 10 years to meet the exponentially growing market demand. The leap from analog to digital started in second-generation (2G) systems, along with the use of mobile data services. The 3G digital evolution enabled video calls and global positioning system (GPS) services on mobile devices. The 4G systems pushed the limits of data services further by better exploiting the time-frequency resources using orthogonal frequency-division multiple access (OFDMA) as an air interface [1]. Recently, the International Telecommunications Union (ITU) has defined the expectations for 5G [2], and the study of the nextgeneration wireless system is in progress with a harmony between academia, industry, and standardization entities to accomplish its first deployment in 2020.5G is envisioned to improve major key performance indicators (KPIs), such as peak data rate, spectral efficiency, power consumption, complexity, connection density, latency, and mobility, significantly. Furthermore, the new standard should support a diverse range of services all under the same network [3]. The IMT-2020 vision defines the use cases into three main categories as enhanced mobile broadband (eMBB), massive machine-type communications (mMTC), and ultra-reliable low-latency communications (URLLC) featuring 20 Gb/s peak data rate, 10 6 /km 2 device density, and less than 1 ms latency, respectively [4]. A flexible air interface is required to meet these different requirements. As a result, the waveform, which is the main component of any air interface, has to be designed precisely to facilitate such flexibility [5].This chapter aims to provide a complete picture of the ongoing 5G waveform discussions and overviews the major candidates. The chapter is organized as follows: Section II provides a brief description of the waveform and reveals the 5G use cases and waveform design requirements. Also, this section presents the main features of CP-OFDM that is currently deployed in 4G LTE systems. CP-OFDM is the baseline of the 5G waveform discussions since the performance of a new waveform is usually compared with it. Section III examines the essential characteristics of the major waveform candidates along with the related advantages and disadvantages. Section IV summarizes and compares the key features of the waveforms. Finally, Section V concludes the chapter. This is the pre-peer reviewed version of the article which has been published in final form at [https://onlinelibrary.wiley.com/doi/abs/10.1002/9781119333142.ch2]. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.

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The Internet of things (IoT), which is the network of physical devices embedded with sensors, actuators, and connectivity, is being accelerated into the mainstream by the emergence of 5G wireless networking. This paper presents an uncoordinated non-orthogonal random access protocol, an enhancement to the recently introduced Aloha-NOMA protocol, which provides high throughput, while being matched to the low complexity requirements and the sporadic traffic pattern of IoT devices. Under ideal conditions it has been shown that Aloha-NOMA, using power-domain orthogonality, can significantly increase the throughput using SIC (Successive Interference Cancellation) to enable correct reception of multiple simultaneous transmitted signals. For this ideal performance, the enhanced Aloha-NOMA receiver adaptively learns the number of active devices (which is not known a priori) using a form of multi-hypothesis testing. For small numbers of simultaneous transmissions, it is shown that there can be substantial throughput gain of 6.9 dB relative to pure Aloha for 0.25 probability of transmission and up to 3 active transmitters.

Millimeter wave (mmWave) is a key technology to support high data rate demands for 5G applications. Highly directional transmissions are crucial at these frequencies to compensate for high isotropic pathloss. This reliance on directional beamforming, however, makes the cell discovery (cell search) challenging since both base station (gNB) and user equipment (UE) jointly perform a search over angular space to locate potential beams to initiate communication. In the cell discovery phase, sequential beam sweeping is performed through the angular coverage region in order to transmit synchronization signals. The sweeping pattern can either be a linear rotation or a hopping pattern that makes use of additional information. This paper proposes beam sweeping pattern prediction, based on the dynamic distribution of user traffic, using a form of recurrent neural networks (RNNs) called Gated Recurrent Unit (GRU). The spatial distribution of users is inferred from data in call detail records (CDRs) of the cellular network. Results show that the users spatial distribution and their approximate location (direction) can be accurately predicted based on CDRs data using GRU, which is then used to calculate the sweeping pattern in the angular domain during cell search.

Various emerging applications in future wireless networks require rethinking the access techniques not only from the capacity perspective but also satisfying a wide variety of requirements under the same framework. Traditional Orthogonal Frequency Division Multiplexing (OFDM)-based schemes still suffer from some limitations that stand in front of their existence in future technologies. The main goal of this study is to pave the way towards rethinking the waveform design by providing the main components of a wireless communication system. The concept of the multidimensional lattice is introduced, exploiting the angular dimension that opens a new horizon in research for 5G technology and beyond. The study proposes a new way of waveform design procedure that considers the multidimensional grid, which is essential for exploiting the opportunities in spatial domain effectively. In addition, the waveform design criteria for various applications and frequency bands are presented.