Multiple Access Techniques for 5G Wireless Networks and Beyond

This chapter discusses the evolution of cellular communication systems, leading to the definition of 5G. For each cellular generation, we provide an overview of the multiple access techniques and network architectures, as well as their relevant shortcomings. The 3GPP standards group release time line is summarized to highlight the demand for increased data rates, increased system capacity, and lower latency capabilities as well as the exponential increase in system features. The IMT-2020 requirements for 5G have targeted wide-ranging system requirements from its inception, as indicated by the definition of three use case pillars: enhanced mobile broadband, massive machine to machine communications and ultra-reliable and low-latency communications. To address the widely varying requirements for these use cases, a dynamic system is required that supports: flexible orthogonal frequency division multiple access systems parameters, a network architecture utilizing software-defined networking principles, spectral agility utilizing different deployments (licensed, unlicensed, and shared spectrum) over wider frequency ranges such as millimeter wave bands. The essential technologies such as massive multi-antenna systems, carrier aggregation, higher-order modulation, and orthogonal and non-orthogonal multiple access techniques are also discussed.

In this chapter, different variants envisioned for the 5G new radio (NR) waveform implementation are discussed, satisfying the 5G NR requirements for release 15 and beyond. We outline the limitations of conventional CP-OFDM in serving the potential use cases for NR. Two main classes of waveform preprocessing are considered to increase the spectral decay rate of CP-OFDM, namely windowing and filtering. Three waveforms are selected for the comparison, namely windowed overlap-add (WOLA) as a windowing technique, universal filtered orthogonal frequency division multiplex (UF-OFDM) and filtered orthogonal frequency division multiplex (f-OFDM) as subband filtering techniques. We outline the design principles of all three waveforms and discuss the overall performance and implementation aspects.

In this chapter, we discuss Filter Bank Multicarrier Modulation (FBMC), a transmission scheme with superior spectral properties when compared with orthogonal frequency-division multiplexing. We first provide a general motivation, followed by a detailed description of the underlying idea behind FBMC. We then present a matrix-based system model and explain how to efficiently generate FBMC signals. Afterward, we assess the performance of one-tap equalizers in doubly selective channels. We also describe how to restore complex orthogonality in FBMC by a simple spreading technique and how such method improves certain aspects of FBMC.

The next generation of wireless networks will face different challenges arising from new application scenarios. A multicarrier waveform, being superior to the 4G waveform orthogonal frequency division multiplexing (OFDM), therefore, has been an important research item on the physical layer. In the 5G standardization process, improving the spectral efficiency of OFDM is one primary goal of waveform engineering. To this end, simple signal processing techniques such as time domain windowing and subband-based filtering are favorable solutions because of their low complexity and straightforward backward comparability. In this chapter, we introduce an advanced multicarrier waveform termed generalized frequency division multiplexing (GFDM). It serves as a multicarrier waveform framework that nicely encapsulates the above-mentioned signal processing techniques with additional design space reserved for forward comparability beyond 5G. While providing the flexibility, it has a hardware-friendly structure that permits energy efficiency implementation. This feature makes it a strong candidate solution for mixed-service mixed-numerology networks.

Non-orthogonal multiple access (NOMA) is a potential enabler for the development of 5G and beyond wireless networks. By allowing multiple users to share the same resource (time/frequency/code/space), NOMA can scale up the number of served users, increase the spectral efficiency, and improve user-fairness compared to existing orthogonal multiple access (OMA) techniques. The basic premise behind NOMA in a single-cell network is to reap the benefits promised by information theory for the downlink and uplink transmission of wireless systems, modeled respectively by the broadcast channel (BC) and multiple access channel (MAC). The capacity regions of the BC and MAC have been established several decades ago, and concurrent non-orthogonal transmission is the optimal transmission strategy in both cases. Unlike the single-cell setting, the capacity region of multi-cell wireless networks, commonly modeled by the interference channel (IC), is in general unknown. However, it is known that OMA is suboptimal. This chapter reviews what information theory promises and proposes for NOMA in single- and multi-cell networks with both single- and multi-antenna nodes. Furthermore, relevant physical layer security channel models are proposed and discussed.

Non-orthogonal multiple access (NOMA) has been recognized as a promising multi-user access technique for the next generation cellular communication networks. In this chapter, we first review the basic concepts of downlink NOMA transmission and introduce the two-user, multi-user, and multi-channel NOMA schemes. Then, we investigate the optimal power allocation for these downlink NOMA schemes under different performance criteria, including the maximin fairness, sum rate, and energy efficiency. User weights and quality-of-service (QoS) constraints are taken into account. We show that in most cases the optimal NOMA power allocation can be analytically characterized, while in other cases the NOMA power allocation problems can be numerically solved via convex optimization methods.

This chapter aims to provide a comprehensive solution for the design, analysis, and optimization of a multiple-antenna non-orthogonal multiple access (NOMA) system for multiuser downlink communication with both time duplex division (TDD) and frequency duplex division (FDD) modes. First, we design a new framework for multiple-antenna NOMA, including user clustering, channel state information (CSI) acquisition, superposition coding, transmit beamforming, and successive interference cancellation (SIC). Then, we analyze the performance of the designed system and derive exact closed-form expressions for average transmission rates in terms of transmit power, CSI accuracy, transmit mode, and channel conditions. For further enhancing the system performance, we optimize three key parameters, i.e., transmit power, feedback bits, and transmission mode. Especially, we propose a low-complexity joint optimization scheme, so as to fully exploit the potential of multiple-antenna techniques in NOMA. Moreover, through asymptotic analysis, we reveal the impact of system parameters on average transmission rates, and hence present some guidelines on the design of multiple-antenna NOMA. Finally, simulation results validate our theoretical analysis and show that a substantial performance gain can be obtained over traditional orthogonal multiple access (OMA) technology under practical conditions.

Non-orthogonal multiple access (NOMA) enables the messages of multiple users to be multiplexed in the power domain by superposition coding at the transmitter side and to be decoded by successive interference cancelation (SIC) at the receiver side. This non-orthogonality enables each user to occupy the whole time–frequency resources such that it overcomes the loss of degree-of-freedom (DoF) caused by orthogonal multiple access (OMA). Therefore, NOMA can achieve higher spectrum efficiency, support massive connectivity, and reduce latency. In this chapter, NOMA is introduced to millimeter wave (mmWave) networks to further improve the spectrum efficiency and support massive connectivity. The unicast, multicast, and cooperative multicast transmissions for mmWave-NOMA networks are studied. Their performance in terms of coverage probability, outage probability, and sum rate is also provided.

Full-duplex (FD) has the potential to double the resource utilization of cellular networks by enabling simultaneous transmissions in the uplink (UL) and downlink (DL) directions using the same time and frequency resource. Several challenges arise from integrating FD with non-orthogonal multiple access (NOMA) networks. This chapter focuses on the resource optimization challenges in full-duplex NOMA networks, as well as the practical challenges of incorporating in-band full-duplex (IBFD) base stations within NOMA networks. In particular, the problems of UL and DL dynamic resource optimization, mode selection, and power allocation are discussed. Moreover, the objectives and tools of FD-NOMA network optimization are presented. Subsequently, the chapter surveys the state of the art on FD-NOMA, and highlights the existing works’ modelling, objectives, and methodologies. Finally, the chapter provides numerical results and discusses the open problems of FD-NOMA cellular networks.

In this chapter, the problem of resource allocation in heterogeneous non-orthogonal multiple access (NOMA) with energy cooperation is discussed. In particular, the focus is on maximizing the energy efficiency and deriving its optimal user association and power control solution subject to users’ rate and energy constraints. The results confirm the proposed joint user association and power control scheme is capable of achieving higher energy efficiency compared with the conventional resource allocation schemes. This chapter is structured as follows. Section 10.1 presents a review of the related literature about NOMA heterogeneous networks and energy cooperation, respectively. Section 10.2 presents the system model and the formulation problem. After that, Sects. 10.3 and 10.4 describe the proposed resource allocation scheme and provide simulation results, respectively. Finally, Sect. 10.5 summarizes the chapter and presents the future works.

At the time of writing, vehicular communications are enjoying substantial research attention as a benefit of its compelling applications. However, the ever-increasing tele-traffic is expected to result in overcrowding of the available band. As a potent resort, non-orthogonal multiple access (NOMA) can be exploited to improve the bandwidth efficiency and support massive connectivity. Whilst traditional, multiple-input multiple-output (MIMO) can be utilized to enhance the attainable bandwidth efficiency or link reliability. However, in hostile vehicle-to-vehicle (V2V) wireless propagation environments, the achievable multiple-antenna gain is eroded by the channel correlation. As a promising MIMO technique, spatial modulation (SM) only activates a single transmit antenna (Tx) in any symbol-interval and hence completely avoids the inter-antenna interference (IAI), hence showing robustness against channel correlation. Inspired by the benefits of NOMA and the robustness of SM against channel correlation, we intrinsically amalgamate them into NOMA-SM in order to deal with the deleterious effects of wireless V2V environments as well as to support improved bandwidth efficiency. Moreover, the bandwidth efficiency of NOMA-SM is further boosted with the aid of a massive Tx configuration. Specifically, a spatio-temporally correlated Rician channel is considered for a V2V scenario. We investigate the bit error rate (BER) performance of NOMA-SM via Monte Carlo simulations, where the impact of the Rician K-factor, spatial correlation of the antenna array, time-varying effect of the V2V channel, and the power allocation factor is discussed. Furthermore, we also analyse the capacity of NOMA-SM. By analysing the capacity and deriving closed-form upper bounds on the capacity, a pair of power allocation optimization schemes is formulated. The optimal solutions are demonstrated to be achievable with the aid of our proposed algorithm. Instead of simply invoking a pair of popular techniques, we intrinsically amalgamate SM and NOMA to conceive a new system component exhibiting distinct benefits in the V2V scenarios considered.

Sparse Code Multiple Access (SCMA) enables non-orthogonal transmissions of multiple users’ signals among code and power domain, which could greatly improve the spectral efficiency. Due to the sparsity of the multi-dimensional codewords, the low-complexity message-passing algorithm (MPA) can be adopted and near maximum likelihood (ML) performance for multi-user detection can be achieved. In this chapter, a general description of SCMA including the system model, codebook mapping, and multi-user detection schemes are provided. The performance analysis for SCMA, such as the codeword error probability and cutoff rate, are introduced. A general introduction on the codebooks design is given, and approaches of some efficient construction for the multi-dimensional constellations/codebooks are discussed.

In this chapter, we start with a comparison on non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA). We show that the performance difference between NOMA and OMA is marginal assuming perfect channel state information (CSI), capacity-achieving coding, and centralized control. The real challenges arise from channels without such idealistic assumptions. We will then discuss an interleave division multiple access (IDMA) scheme that provides an efficient NOMA solution in non-idealistic channel considerations. We will outline the following attractive features of IDMA:

Finally, we will briefly compare several proposals for LTE fifth-generation (5G) cellular systems. We will show that they share with IDMA the principle of reducing short cycles in their graphic representations so as to facilitate iterative detection. Some of the software used in this chapter are available in the following site: http://​www.​ee.​cityu.​edu.​hk/​7Eliping/​Research/​Simulationpackag​e/​.

Pattern division multiple access (PDMA) is a kind of non-orthogonal multiple access technology based on the principle of the introduced reasonable diversity between multi-user and joint design between transmitter and receiver to promote the capacity. PDMA can be used in 5G typical scenarios like eMBB, URLLC and mMTC, enhancing spectrum efficiency, increasing connections and decreasing latency. Followed by research work on key technologies of PDMA, PDMA was formerly included in the new technology trend report of ITU-R and now is being hotly discussed in 5G new radio standardization in 3GPP, also PDMA has passed the MIIT of China 5G trial. Further, more and more PDMA based extension technologies are being proposed by academics, pushing forward PDMA development.

The need for ubiquitous coverage and the increasing demand for high data rate services, keeps constant pressure on the cellular network infrastructure. There has been intense research to improve the system spectral efficiency and coverage, and a significant part of this effort focused on developing and optimizing the multiple access techniques. One such technique that has been recently proposed is the low density spreading (LDS), which manages the multiple access interference to offer efficient and low complexity multiuser detection. The LDS technique has shown a promising performance as a multiple access technique for cellular systems. This chapter will give an overview on the LDS multiple access technique. The motivations for the LDS design will be highlighted by comparing it to conventional spreading techniques, including brief history of the early work on LDS. Furthermore, a background on the design of LDS in multicarrier communications, such as signatures design, a belief propagation multiuser detection, etc., will be presented along with the challenges and opportunities associated with the multicarrier LDS multiple access.

In this chapter, the grant-free multiple access scheme is introduced for a transmission without dynamic scheduling. A few key technical components have been addressed, including the grant-free resource configuration, user equipment activity identification with contention transmission, HARQ procedure and soft-combining, contention resolutions. Numerical and simulation evaluation results have also been provided to demonstrate the performance of the grant-free scheme operating with OFDMA and NOMA. The grant-free multiple access scheme is able to achieve transmission latency and control signaling reduction, and the device energy saving; thus, it provides a promising solution to small data transmissions, massive connectivity, and low-latency applications such as mMTC and URLLC services.

The support of Internet of Things (IoT) calls for physical and media access control (MAC) solutions capable to support a very large number of wireless devices transmitting short packets with low duty cycle. This chapter provides a survey of random access (RA) schemes devised for terrestrial and satellite applications which are suited to support IoT. The RA schemes presented are typically based on multiple access techniques described in the previous chapters. In particular, RA is exploiting time-, frequency-, and code-division multiple access techniques or combinations thereof. Various flavors of non-orthogonal multiple access (NOMA) are also adopted to increase the RA scheme spectral and power efficiency. The chapter is organized as follows: Sect. 17.1 summarizes the main terrestrial RA techniques and their suitability for 5G IoT applications; Sect. 17.2 provides a survey of 5G NOMA-based RA proposals for IoT; finally, Sect. 17.3 illustrates the most promising NOMA-based RA schemes proposed or adopted for satellite networks which are also of interest to the more general terrestrial wireless applications.

Non-orthogonal multiple access (NOMA) is a novel multi-user multiplexing scheme, which overlaps the radio resources of multiple users in an non-orthogonal manner in order to improve spectral efficiency. NOMA is able to contribute to the improvement of the trade-off between system capacity and user fairness by assigning different power ratios to the multiplexed users depending on their relative channel quality. In this chapter, we focus on downlink NOMA and its combination with open-loop SU-MIMO and assess its performance under realistic conditions. In particular, we introduce the results of the experimental trials we conducted in both indoor and outdoor environments using two users served by 2 \(\times \) 2 open-loop single-user (SU)-MIMO.

Non-orthogonal multiple access (NOMA) was originally proposed as a multiuser access technique for radio frequency (RF) cellular networks. In this chapter, we discuss the application of NOMA to visible light communication (VLC) networks, also referred to as light fidelity (LiFi), as part of the more general field of optical wireless communications (OWC). LiFi differs from RF-based cellular communication in that it generally uses intensity modulation (IM), where information is modulated onto the intensities of the emitted light, and hence, the signals have to be real and nonnegative. By studying the performance of NOMA and characterizing its gain over orthogonal multiple access (OMA) techniques, this chapter demonstrates that NOMA is a promising multiuser technology for the deployment of future LiFi networks.

In this chapter, we investigate the downlink transmission of a non-orthogonal multiple access (NOMA)-based integrated terrestrial-satellite network, in which the NOMA-based terrestrial networks and the satellite cooperatively provide coverage for ground users while reusing the entire bandwidth. A channel quality-based scheme is proposed to select users for the satellite, and we then formulate the terrestrial user pairing as a max–min problem to maximize the minimum channel correlation between users in one NOMA group. We first investigate the capacity performance of the terrestrial networks and the satellite networks separately. Then, a joint iteration algorithm is proposed to maximize the total system capacity, where we introduce the interference temperature limit for the satellite since the satellite can cause interference to all BS users. Finally, numerical results are provided to evaluate the user paring scheme as well as the total system performance.

This chapter is to conclude the book and also provide discussions for promising future research directions. Particularly, in this book, various important topics about multiple access techniques, including the fundamental limits of these multiple access techniques and their applications to practical communication systems, have been discussed. Since multiple access techniques for 5G wireless networks and beyond are still emerging research topics, there are still plenty of open problems. In particular, it is not clear how these multiple access techniques can be efficiently used together with conventional multiple access techniques, advanced physical layer technologies, as well as other communication systems other than cellular networks, and these challenges will be discussed in detail in this chapter.