Massive Access for Cellular Internet of Things Theory and Technique

With the increasing development of IoT, a massive number of IoT devices are desired to access various wireless networks, so as to provide a variety of advanced applications in industry, agriculture, medicine, and environment. In order to satisfy differential performance requirements of the IoT applications with limited wireless resources, one key point is the design of efficient multiple access schemes. In this chapter, we first discuss the advantages of cellular IoT over the other IoT networks and the development trend of cellular IoT in 5G and beyond. Then, we give an overview of massive access techniques of the cellular IoT, which will be frequently applied and redesigned for different scenarios of the cellular IoT in the sequent chapters. Finally, we introduce the objective and content of this book.

In this chapter, we consider a scenario where the wireless devices in the cellular IoT are fixed, such that CSI keeps unchanged during a relatively long time and the BS is capable of obtaining full CSI. In such a scenario, the benefits of spatial DoF offered by the multiple-antenna BS are exploited to support massive access. In particular, transmit beams and powers are jointly optimized to mitigate the intra-cluster and inter-cluster interference, so as to improve the overall performance. Specifically, we design the joint optimization algorithms from the perspectives of maximizing the weighted sum rate and minimizing the total power consumption, respectively. Moreover, in order to reduce the computational complexity, we design the massive access algorithms with ZF beamforming fixedly. Simulation results show that the proposed algorithms can achieve obvious performance gain over the baseline algorithms. Especially, the proposed algorithms are able to alleviate the impact of imperfect SIC on the performance of massive access.

In this chapter, we provide a comprehensive solution for the design, analysis, and optimization of a cellular IoT operated in FDD mode. First, we design a massive access framework based on channel quantization codebook. Then, we analyze the performance of the considered system, and derive exact closed-form expressions for average transmission rates in terms of transmit power, CSI accuracy, transmission 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 for massive access. Moreover, through asymptotic analysis, we reveal the impact of system parameters on average transmission rates, and hence present some guidelines on the design of massive access systems. Finally, simulation results validate our theoretical analysis, and show that a substantial performance gain can be obtained over traditional orthogonal multiple access (OMA) techniques in the scenario of massive access for the cellular IoT.

In this chapter, we propose a comprehensive fully non-orthogonal communication framework for cellular IoT in TDD mode. Firstly, we design a fully non-orthogonal communication scheme which consists of non-orthogonal channel estimation and non-orthogonal multiple access. Then, we analyze the performance of the proposed fully non-orthogonal communication, and derive a tight lower bound on the spectral efficiency in terms of key system parameters and channel conditions. Meanwhile, several novel insights are provided on spectral efficiency via asymptotic analysis in three important cases, i.e., a large number of base station (BS) antennas, a high BS transmit power, and perfect channel state information (CSI) at the BS. Finally, we optimize the performance of the proposed fully non-orthogonal communication and present two simple but efficient optimization algorithms for maximizing the weighted sum of spectral efficiency. Extensive simulation results validate the effectiveness of the proposed schemes.

In this chapter, we study the problem of massive access in the 5G cellular IoT, where the channels are fast-varying. To address the challenging issue of channel state information (CSI) acquisition and beam design for a massive number of IoT devices over fast time-varying fading channels, we design a non-orthogonal beamspace multiple access framework. In particular, the user equipments (UEs) are non-orthogonal not only in the temporal-frequency domain, but also in the beam domain. We analyze the performance of the proposed non-orthogonal beamspace multiple access scheme, and derive an upper bound on the weighted sum rate in terms of channel conditions and system parameters. For further improving the performance, we propose three non-orthogonal beam construction methods with different beamspace resolutions. Finally, extensively simulation results show the performance gain of the proposed non-orthogonal beamspace multiple access scheme over the baseline ones.

This chapter presents a summary about massive access for the cellular IoT in 5G and beyond. In particular, we discuss the theories and techniques of massive access and their applications in the cellular IoT according to the characteristics of available CSI at the BS in different scenarios. Firstly, a massive access scheme for a fixed cellular IoT where full CSI is available at the BS is designed. Especially, spatial beam and transmit power are jointly optimized according to instantaneous CSI from the perspectives of maximizing the weighted sum rate and minimizing the total power consumption, respectively. Then, a low-mobility cellular IoT operated in FDD mode that partial CSI is obtained through a quantization codebook is studied, and the corresponding massive access scheme is provided by optimizing the feedback resource. Furthermore, a TDD mode-based cellular IoT is considered, and a fully non-orthogonal massive access scheme is proposed. To exploit the benefits of fully non-orthogonal massive access, the transmit power at both the BS and IoT devices is optimized. Finally, to satisfy the requirement of high mobility, a non-orthogonal beamspace massive access scheme is given, which can achieve a better spectral efficiency over fast-varying fading channels. Moreover, we analyze the challenging issues in the existing massive access schemes, and point out the future research directions for further improving the overall performance of the cellular IoT.