It is now well known that employing channel adaptive signaling in wireless communication systems can yield large improvements in almost any performance metric. Unfortunately, many kinds of channel adaptive techniques have been deemed impractical in the past because of the problem of obtaining channel knowledge at the transmitter. The transmitter in many systems (such as those using frequency division duplexing) can not leverage techniques such as training to obtain channel state information. Over the last few years, research has repeatedly shown that allowing the receiver to send a small number of information bits about the channel conditions to the transmitter can allow near optimal channel adaptation. These practical systems, which are commonly referred to as limited or finite-rate feedback systems, supply benefits nearly identical to unrealizable perfect transmitter channel knowledge systems when they are judiciously designed. In this tutorial, we provide a broad look at the field of limited feedback wireless communications. We review work in systems using various combinations of single antenna, multiple antenna, narrowband, broadband, single-user, and multiuser technology. We also provide a synopsis of the role of limited feedback in the standardization of next generation wireless systems.

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An overview of limited feedback in wireless communication systems

Cognitive radios have been proposed as a means to implement efficient reuse of the licensed spectrum. The key feature of a cognitive radio is its ability to recognize the primary (licensed) user and adapt its communication strategy to minimize the interference that it generates. We consider a communication scenario in which the primary and the cognitive user wish to communicate to different receivers, subject to mutual interference. Modeling the cognitive radio as a transmitter with side-information about the primary transmission, we characterize the largest rate at which the cognitive radio can reliably communicate under the constraint that (i) no interference is created for the primary user, and (ii) the primary encoder-decoder pair is oblivious to the presence of the cognitive radio.

Cognitive Radio: An Information-Theoretic Perspective

The sixth generation (6G) wireless communication networks are envisioned to revolutionize customer services and applications via the Internet of Things (IoT) towards a future of fully intelligent and autonomous systems. In this article, we explore the emerging opportunities brought by 6G technologies in IoT networks and applications, by conducting a holistic survey on the convergence of 6G and IoT. We first shed light on some of the most fundamental 6G technologies that are expected to empower future IoT networks, including edge intelligence, reconfigurable intelligent surfaces, space-air-ground-underwater communications, Terahertz communications, massive ultra-reliable and low-latency communications, and blockchain. Particularly, compared to the other related survey papers, we provide an in-depth discussion of the roles of 6G in a wide range of prospective IoT applications via five key domains, namely Healthcare Internet of Things, Vehicular Internet of Things and Autonomous Driving, Unmanned Aerial Vehicles, Satellite Internet of Things, and Industrial Internet of Things. Finally, we highlight interesting research challenges and point out potential directions to spur further research in this promising area.

6G Internet of Things: A Comprehensive Survey

The sixth-generation (6G) wireless communication networks are envisioned to revolutionize customer services and applications via the Internet of Things (IoT) toward a future of fully intelligent and autonomous systems. In this article, we explore the emerging opportunities brought by 6G technologies in IoT networks and applications, by conducting a holistic survey on the convergence of 6G and IoT. We first shed light on some of the most fundamental 6G technologies that are expected to empower future IoT networks, including edge intelligence, reconfigurable intelligent surfaces, space–air–ground–underwater communications, Terahertz communications, massive ultrareliable and low-latency communications, and blockchain. Particularly, compared to the other related survey papers, we provide an in-depth discussion of the roles of 6G in a wide range of prospective IoT applications via five key domains, namely, healthcare IoTs, Vehicular IoTs and Autonomous Driving, Unmanned Aerial Vehicles, Satellite IoTs, and Industrial IoTs. Finally, we highlight interesting research challenges and point out potential directions to spur further research in this promising area. 

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The combination of simultaneous wireless information and power transfer (SWIPT) and non-orthogonal multiple access (NOMA) is a potential solution to improve spectral efficiency and energy efficiency (EE) of the upcoming fifth generation (5G) networks, especially in order to support the functionality of the Internet of things (IoT) and the massive machine-type communications (mMTC) scenarios. In this paper, we investigate joint power allocation and time switching (TS) control for EE optimization in a TS-based SWIPT NOMA system. Our aim is to optimize the EE of the system whilst satisfying the constraints on maximum transmit power budget, minimum data rate, and minimum harvested energy per terminal. The considered EE optimization problem is neither linear nor convex involving joint optimization of power allocation and time switching factors and, thus, is extremely difficult to solve directly. In order to tackle this problem, we develop a dual-layer algorithm where Dinkelbach method is employed both in the inner layer to optimize the power allocation and in the outer layer to control the time switching assignment. Furthermore, a simplified but practical special case with equal time switching factors in all terminals is considered. Numerical results validate the theoretical findings and demonstrate that significant performance gain over orthogonal multiple access scheme in terms of EE can be achieved by the proposed algorithms in a SWIPT-enabled NOMA system.

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Energy Efficiency Optimization for NOMA With SWIPT

Energy harvesting (EH) is a prominent method to extend the operation time of energy-limited wireless networks. By integrating EH into wireless communications, the same spectrum is able to be used by simultaneous wireless information and power transfer (SWIPT) without affecting the quality of service. In this paper, we propose a joint subcarrier and power allocation-based SWIPT scheme in orthogonal frequency division multiplexing (OFDM) systems. Specifically, the received OFDM subcarriers are partitioned into two groups. A fraction of the received subcarriers are allocated to form one group, which is used for information decoding (ID), and the remaining subcarriers form the other group, which is used for energy harvesting. Thus, no splitter is needed at the receiver. A joint subcarrier and power allocation problem is formulated to maximize the harvested energy, subject to the ID constraint. By using the dual decomposition method, an efficient algorithm is proposed to solve this joint resource allocation problem.

Simultaneous Wireless Information and Power Transfer Based on Joint Subcarrier and Power Allocation in OFDM Systems

The universal filtered multi-carrier (UFMC) has been taken as a promising candidate for future wireless communication, where a finite impulse response filter is employed to shape the waveform and enhance its resistance to inter-carrier interference. In previous studies, the Dolph–Chebyshev filter had been used due to its low-sidelobe levels, but at the cost of low flexibility to filter the performance control. Hence, this paper puts forward an effective scheme to design an anti-interference filter for UFMC system, where the Nyquist condition (or sampling inter-symbol interference equivalently), the in-band distortion, and the out-of-band emission are taken into consideration. First, this paper models the filter design as a constrained minimax optimization concerning above-mentioned filter performance indexes. Then, the original nonconvex constraints on Nyquist condition are approximately transformed to a linear matrix inequation and two linear inequations. Finally, the optimization problem is solved by semi-definite programming. The numerical examples explicitly demonstrate the flexible performance tradeoff of the proposed method, in which the included filter performance indexes can be effectively controlled. Moreover, the bit-error-rate (BER) tests of the UFMC system confirms the effectiveness of our study, where the designed filters show BER advantages over filters of the previous literature. Therefore, the proposed waveform shaping filters can benefit variant applications of UFMC for its flexible performance tradeoffs as well as the improved anti-interference performance.

Design of Waveform Shaping Filter in the UFMC System

A Novel Ad hoc Routing Protocol Based on Mobility Prediction

By supporting asynchronous transmission and flexible subband (SB) setting, filtered orthogonal frequency division multiplexing (f-OFDM) has been identified as one of the most promising waveforms for future wireless communications, which makes the deep investigation on the f-OFDM an urgent mission. Therefore, this paper investigates the downlink interference of asynchronous f-OFDM systems under different SB configurations. We initially classify the overall interference into two categories, termed as the inner-SB and inter-SB interferences. Subsequently, the closed-form expressions for interference and its variances are derived on the basis of interference structures and are then verified via simulations. Some important influencing factors, such as the timing offset between the user of interest and the interfering user, the width of guard band, as well as the choice of SB filter, are simulated and analyzed. Our simulations and comparisons explicitly reveal the interference characteristic of the f-OFDM systems, which will benefit the design of the f-OFDM systems in the future.

Interference Analysis in the Asynchronous f-OFDM Systems

As receiver performance will be degraded by carrier frequency offset (CFO), Doppler shift, and low signal-to-noise ratio (SNR), a novel estimator that jointly considers CFO, Doppler shift, and SNR is proposed in this paper. The proposed algorithm uses the Fourier transform (FT) to calculate the power spectral density of time-varying channels through channel estimates. Then, a new periodogram technique is utilized to estimate CFO, Doppler shift, and SNR together. Unlike conventional methods in sinusoid estimation, which rely on the peak-value search of a periodogram, this paper exploits the hypothesis test to address the random frequency modulation of time-varying channels. Furthermore, to optimize estimation performance, a theoretical analysis is also provided on the influences of some key parameters, e.g., the length of the signal processed with fast FT , the amplitude threshold value, the SNR dynamic range, and the velocity dynamic range. Correspondingly, the appropriate key parameters are chosen according to this analysis and are validated by simulations. The results are consistent with our analysis and present high accuracy over a wide range of velocities and SNRs.

Jingyu Hua

Papers

Simultaneous Wireless Information and Power Transfer Based on Joint Subcarrier and Power Allocation in OFDM Systems

Design of Waveform Shaping Filter in the UFMC System

A Novel Ad hoc Routing Protocol Based on Mobility Prediction

Interference Analysis in the Asynchronous f-OFDM Systems

Novel Scheme for Joint Estimation of SNR, Doppler, and Carrier Frequency Offset in Double-Selective Wireless Channels