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Conventional silicon-based transistor downscaling is approaching its physical limits, and thus additional novel solutions are urgently desired to address this issue. Herein, we show that 2-D antimonene with heavy effective mass and high density of state (DOS) via strain engineering presents reliable transistor performance with the channel length (${L}_{\text {ch}}$) shrinking below 5 nm. As the biaxial tensile strain increases to 7%, the band switching gives rise to a heavy hole effective mass of $12.6{m}_{{0}}$ and a Van Hoff singularity-like DOS. This unique electronic structure can effectively suppress the tunneling current, resulting in steep subthreshold swings (SSs) and ideal ON-current (${I}_{ \mathrm{ON}}$). Especially, as ${L}_{\text {ch}}$ downscales to 2.2 nm, the OFF-current can be easily reduced to 0.1 $\mu \text{A}/\mu \text{m}$ with SS of 120 mV/dec (310 mV/dec for pristine antimonene) and ${I}_{ \mathrm{ON}}$ exceeds 900 $\mu \text{A}/\mu \text{m}$ , fulfilling the requirements for high-performance applications. Our results provide new insights on extending the scaling limit in energy-efficient gate-controlled devices. [ABSTRACT FROM AUTHOR]

This paper investigates a new analog beamforming architecture for massive multiple-input multiple-output (MIMO) systems, where each of the multiple transmit antennas is switched to be on or off to form a beam according to the channel state information at transmitters. This on–off analog beamforming (OABF) scheme has the advantages in terms of both hardware complexities and algorithmic complexities. OABF can completely remove the high-cost, power-consuming, and bulky analog phase shifters that are extensively employed by traditional analog beamforming schemes; it only requires the deployment of low-cost analog switches that are easy to implement. Moreover, we show that the beams formed by such simple antenna on–off switch operations can achieve rather good performances with low-complexity beamforming algorithms. Specifically, we first propose two optimal signal-to-noise ratio maximization algorithms to determine the on–off state of each switch under the per-antenna power constraint and the total power constraint, respectively. After that, we theoretically prove that OABF can achieve the full diversity gain and the full array gain with complexities up to a polynomial order. Numerical results are consistent with our theoretical analysis. We believe that the simple structure of OABF makes massive MIMO much easier to implement in real systems. [ABSTRACT FROM PUBLISHER]

This paper studies an untrusted relay channel, in which the destination sends artificial noise simultaneously with the source sending a message to the relay, in order to protect the source’s confidential message. The traditional amplify-and-forward (AF) scheme shows poor performance in this situation because of the interference power dilemma. Providing better security by using stronger artificial noise will consume more power of the relay, impairing the confidential message’s transmission. To solve this problem, this paper proposes a modulo-and-forward (MF) operation at the relay with nested lattice encoding at the source. For the proposed MF scheme with full channel state information at the transmitter (CSIT), theoretical analysis shows that the MF scheme approaches the secrecy capacity within 1/2 bit for all channel realizations, and, hence, achieves full generalized security degrees of freedom (G-SDoF). In contrast, the AF scheme can only achieve a small fraction of the G-SDoF. For the MF scheme without CSIT, the total outage event, defined as either connection outage or secrecy outage, is introduced. Based on this total outage definition, analysis shows that the proposed MF scheme achieves the full generalized secure diversity gain (G-SDG) of order one. On the other hand, the AF scheme can achieve a G-SDG of only 1/2 at most. [ABSTRACT FROM AUTHOR]

In this paper, we study a two-phase underlay cognitive relay network, where there exists an eavesdropper who can overhear the message. The secure data transmission from the secondary source to secondary destination is assisted by two decode-and-forward (DF) relays. Although the traditional opportunistic relaying technique can choose one relay to provide the best secure performance, it needs to continuously have the channel state information (CSI) of both relays, and may result in a high relay switching rate. To overcome these limitations, a secure switch-and-stay combining (SSSC) protocol is proposed where only one out of the two relays is activated to assist the secure data transmission, and the secure relay switching occurs when the relay cannot support the secure communication any longer. This security switching is assisted by either instantaneous or statistical eavesdropping CSI. For these two cases, we study the system secure performance of SSSC protocol, by deriving the analytical secrecy outage probability as well as an asymptotic expression for the high main-to-eavesdropper ratio (MER) region. We show that SSSC can substantially reduce the system complexity while achieving or approaching the full diversity order of opportunistic relaying in the presence of the instantaneous or statistical eavesdropping CSI. [ABSTRACT FROM AUTHOR]

The conventional two-way relaying (TWR) protocol requires that the transmitter (receiver) in one direction must be the receiver (transmitter) in the other direction, a limitation precluding the application of the TWR for sophisticated real-world wireless networks. In this paper, we study a more general multicell system consisting of a downlink (DL) traffic in one cell and an uplink (UL) traffic in an adjacent cell, with a multiantenna relay located in the cell edge and shared by both cells. For the coexistence of DL and UL transmissions, we propose exploiting the overheard signals from the adjacent cell (commonly known as the intercell interference) to improve the quality of signal reception in both cells. To reduce the power consumption to suit for green networks, we design the optimum relay precoder to minimize the total power at the relay yet satisfying the rate constraints for both the DL and UL traffic flows. The original precoder design is a nonconvex problem that is difficult to solve. To make the problem tractable, we transform the nonconvex problem to an equivalent quadratically constrained quadratic program (QCQP), which is then solved by the semidefinite relaxation (SDR) technique. Finally, simulations validate the effectiveness of our proposed protocol together with the optimized relay precoder. [ABSTRACT FROM PUBLISHER]

In spectrum underlay cognitive radio networks, secondary users (SUs) are allowed to reuse the spectrum allocated to a primary system. The interference between SUs actually carries information and can potentially be exploited to improve the network performance through information-theoretic interference processing. In this paper, we design an optimal joint power and rate control algorithm that maximizes the secondary system utility subject to the interference temperature constraints of primary users based on the capacity-approaching interference processing scheme called as the Han-Kobayashi scheme. The optimal solution is difficult to achieve because the optimization problem is in general non-convex. To make the optimization problem tractable, this paper first transforms the problem into a monotonic optimization problem through exploiting its hidden monotonicity. We then devise an effective algorithm to obtain the global optimal solution to the joint power and rate control problem in the Han-Kobayashi scheme. The key idea behind the proposed algorithm is to construct a sequence of shrinking polyblocks that approximate the upper boundary of the feasible region with increasing precision. Numerical results further show that the achieved utility of our scheme significantly outperforms the utility of conventional schemes which treat the interference between SUs as the noise. [ABSTRACT FROM PUBLISHER]

Accurate channel state information is of great importance in high-speed wireless communication. In this work, the problem of channel training for massive multiple-input multiple-output (MIMO) systems is investigated and a closed-loop channel training scheme is devised upon the maximum a posteriori (MAP) criterion. More specifically, at each channel use, the channel estimation is performed at the receiver according to the MAP criterion, and the expectation-maximization (EM) algorithm is employed to cope with the MAP estimation problem. Based on the parameter estimates, the predicted mean square error (PMSE) of the channel estimate is minimized to determine a preferred sounding beam for the next channel use, of which the index is fed back to the transmitter via a limited-rate channel. The performance superiority of the proposed approach is evidenced by comparing with various channel training schemes. [ABSTRACT FROM AUTHOR]

The proof-of-work (PoW) mining process requires a large amount of intensive computing, which leads to some plights such as heavy equipment and fixed access nodes in traditional blockchain networks. A novel mobile blockchain network with the help of a mobile edge computing (MEC) server is presented, where all mobile users participate in the PoW mining process. The traditional Bitcoin network adjusts the target difficulty value to ensure a stable block time. However, for MEC-assisted mobile blockchain networks, the adjusted difficulty value needs to be broadcast to all mobile users, which results in expensive communication costs. To maintain a stable block time of mobile blockchain networks, we formulate the delay-limited computation offloading strategy of the PoW-based mining task as a non-cooperative game that maximizes an individual revenue in the MEC-assisted mobile blockchain network. Specifically, the non-cooperative game problem can be divided into multiple sub-game optimization problems to obtain final solutions for all users. We analyze the sub-game optimization problem and prove the existence of Nash equilibrium (NE) of the non-cooperative game. Moreover, we design an alternating iterative algorithm based on the continuous relaxation and greedy rounding (CRGR) to achieve the NE of this game. Given the sub-optimal delay-limited computation offloading results, we also derive the optimal transmit power for an individual user within the maximum mining delay range. From the analytical results, we can see that the proposed CRGR-based alternating iterative algorithm can efficiently attain the sub-optimal delay-limited computation offloading strategies of all mobile users in the polynomial time. The individual transmit power increases accordingly with the delay-limited computation offloading strategies of all users. Numerical results demonstrate that the proposed CRGR-based alternating iterative algorithm has fast convergence and good stability. [ABSTRACT FROM AUTHOR]

This paper studies the performance of unmanned aerial vehicle (UAV)-enabled NOMA networks with selective incremental relaying and imperfect channel state information (CSI). In particular, an access point transmits a superposed signal based on NOMA principle to an UAV terminal (UT) which can act as a relay to assist the information transmission for a ground terminal (GT). Different from the conventional relaying protocol requiring UT to relay the message all the time no matter how the received signal quality of two terminals are, we propose a novel NOMA-based selective incremental relaying protocol that allows relay to forward messages on the condition of the received signal with satisfied quality at UT and the unsatisfied quality signal at GT. The closed-form solutions of outage probabilities for the two terminals are characterized with the elevation angle-based path loss exponent and small-scale fading. Moreover, the benchmark schemes are provided to exhibit the superiority of the proposed protocol. Finally, simulation and theoretical results validate the correctness of the outage analysis, demonstrate the advantage of the proposed relaying protocol over its counterparts, and show that the stronger impact of channel estimation error on GT than UT in terms of outage probability. [ABSTRACT FROM AUTHOR]

In this correspondence, we jointly optimize the caching decision and radio and computation resource allocation for video service in mobile edge computing (MEC) enabled network to maximize the system revenue. To tolerate the uncertainty in the network traffic and avoid “hard constraint” based on constant content request rate, we employ robust optimization to obtain optimal caching decisions, and then accordingly allocate the radio and computation resources for video transcoding. Simulation results demonstrate the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

Consensus is one of the key problems in blockchains. There are many articles analyzing the performance of threat models for blockchains. But the network stability seems lack of attention, which in fact affects the blockchain performance. This paper studies the performance of a well adopted consensus algorithm, Raft, in networks with non-negligible packet loss rate. In particular, we propose a simple but accurate analytical model to analyze the distributed network split probability. At a given time, we explicitly present the network split probability as a function of the network size, the packet loss rate, and the election timeout period. To validate our analysis, we implement a Raft simulator and the simulation results coincide with the analytical results. With the proposed model, one can predict the network split time and probability in theory and optimize the parameters in Raft consensus algorithm. [ABSTRACT FROM AUTHOR]

Vehicle-to-everything (V2X) communications, which provide wireless connectivity among vehicles, roadside drivers, passengers, and pedestrians, are attracting great interest. In this paper, we propose an energy-efficient relay assisted transmission scheme based on V2X communications in the uplink cellular networks for delay insensitive applications. We aim to maximize energy efficiency of the uplink while considering both the circuit power and transmit power consumption, as well as the delay constraint. The optimal resource allocation for direct transmission mode and V2X-enabled transmission mode are derived. For the V2X-enabled transmission mode, we first consider the transmission without the delay constraint and obtain the corresponding optimal power allocation. Based on the obtained result, we further propose the optimal resource allocation policy that satisfies the delay constraint and minimizes the energy consumption. Simulation results show that there exists an energy-delay tradeoff and the proposed V2X-enabled scheme can achieve significant energy saving with an acceptable delay compared with the traditional direct scheme, the decoding-and-forward based transmission scheme, and the opportunistic store-carry and forward based transmission scheme, especially when the cell radius is not small. [ABSTRACT FROM AUTHOR]

As a promising wireless access technique, sparse code multiple access (SCMA) directly maps the input bits to the transmitted multidimensional codewords according to the SCMA codebook. In general, SCMA codebook optimization and detector simplification are independent of each other. In this article, we propose a simplified SCMA codebook with a separable structure for implementing a low-complexity detector. For codebook design, a separable codebook structure is proposed to simplify the maximization of the minimum Euclidean distance (MED). With this structure, multiple one-dimensional complex codebooks corresponding to one resource element (RE) are determined by maximizing the MED of the superimposed codewords. Then, the entire codebook set is obtained based on a structure indicator matrix and the separable codebook structure. The proposed codebook has a larger MED than obtained by existing codebooks. Benefiting from the separable codebook structure, the signals transmitted over each RE can be independently used to recover the corresponding input bit information. Therefore, we propose a parallel maximum a posteriori (P-MAP) detector consisting of several low-complexity MAP detectors to reduce the complexity of the conventional multiuser message passing (MP) detector in SCMA. At the receiver, each RE is assigned a low-complexity MAP detector. Simulation results show that the proposed codebook outperforms the known optimal codebook over an AWGN channel. Moreover, the run time of the P-MAP detection algorithm is reduced by 99.8% compared to the Log-MPA algorithm. With the proposed codebook design scheme and the P-MAP detector, an SCMA unit can be separated into two independent non-SCMA units, which significantly increases system flexibility. [ABSTRACT FROM AUTHOR]

Conventional field-effect transistors (FETs) based on silicon downscaling are approaching physical limits, and thus, it is urgent to explore additional novel solutions to address this issue. The 2-D semiconductors have unique advantages as the channel material and provide a promising prospect for high-performance FETs in the post-Moore era. In this work, a new 2-D semiconductor, monolayer BeN2, is studied for the FET performance limits through first-principle quantum-transport simulations. Monolayer BeN2 exhibits a graphene-like planar structure with a direct bandgap of 1.3 eV. Transfer characteristics of sub-10-nm BeN2 FETs are thoroughly assessed through scaling gate length. In particular, 2-D BeN2 FETs with 10-nm gate present the ultrahigh ON-state current above $4500\,\, \mu \text{A}/\mu \text{m}$ for high-performance applications. Also, we realize the significant reduction of gate length (only 2.5 nm) against the International Technology Roadmap for Semiconductors (ITRS) requirements through introducing underlap structures. In addition, the performance of single devices based on monolayer BeN2 is evaluated and compared with some of the recently proposed 2-D devices. [ABSTRACT FROM AUTHOR]

Currently, video-on-demand (VoD) streaming over Internet is a popular application. Because of the rapidly growing video population and user population, how to maintain high user quality of experience (QoE) with low cost is a challenging problem for Internet video streaming providers. A promising technique to potentially benefit VoD streaming system is network coding. A number of recent works studied how to use network coding to simplify chunk scheduling strategy to enhance VoD streaming performance. Most of these works only covered extreme cases of pure coding or pure chunk scheduling, emphasizing implementation, and experimentation in peer-to-peer (P2P) scenario without analytically evaluating the realizable performance gains explicitly. In this paper we discuss the strength and weakness of a family of coding strategies for CDN-based VoD streaming systems. The coding schemes are characterized by block sizes while the chunk scheduling strategy is characterized by the order to download chunks. Both pure coding strategy and pure chunk scheduling strategy are special cases of this family of strategies. We then propose a model to evaluate the benefits brought by each strategy. Basically, the coding scheme with larger block size gives more streaming and scheduling benefits with the cost of heavier overheads (e.g., encoding and decoding). System designers can take advantage of our model to balance the tradeoff between coding gain and coding overheads. [ABSTRACT FROM PUBLISHER]

Robust spectral analysis of the sinusoidal signals corrupted by impulsive noise poses a big challenge in the signal processing community. In this paper, we address the issue of robust spectral analysis for multi-channel sinusoidal signals, including order detection and parameter estimation. The successive robust low-rank decomposition is firstly designed to extract the common signal subspace from the multi-channel data matrix. Subsequently, the number of sinusoidal poles is determined with a model order selection criterion, based on the so-obtained subspace. With the signal order information, the sinusoidal parameters and outliers are jointly estimated according to the maximum a posteriori criterion. To find a robust initial guess of the sinusoidal parameters, an estimator based on robust weighted linear prediction is developed. Additionally, the performance analysis is provided, which includes computational complexity, convergence verification of the sinusoidal parameter estimation, and asymptotic consistency of the signal order detection. Simulation results demonstrate the advantages of the proposed robust spectral analysis framework compared to state-of-the-art schemes. [ABSTRACT FROM AUTHOR]

Saccadic eye movement as a voluntary activity has become the basis of a promising approach for the implementation of human–computer interaction. Seeking blind source separation (BSS) model that can exactly describe eye movement generation and improve the quality of saccadic electrooculography (EOG) signals, we performed a comparative study between an instantaneous and a convolutional mixing model for multichannel EOG signals. Experiments involving seven subjects were carried out in a laboratory environment. The independent component analysis (ICA) method was adopted for BSS. The statistical indicators of the residual statistical dependence and the total square cross correlation for the convolutional model were 0.04 (second order)/0.08 (fourth order) and 1.25, respectively, which were lower than those of the instantaneous model by 0.3 (second order)/0.17 (fourth order) and 0.32, respectively. In addition, the average classification accuracies of the convolutional model were 95.76% (within subject) and 94.08% (between subject) in the case of upward, downward, left, and right saccade tasks, which were higher than those of the instantaneous model by 1.69% and 5.53%, respectively. Experiments revealed that the quality of the saccadic signals separated using the convolutional model was higher than that achieved using the instantaneous model. The outcomes of this research can serve as a valuable reference for multichannel EOG analysis and application. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the classical detection problem for vehicle networks with multiple antennas, by considering practical communication scenarios, where the interfering signals are correlated over time or frequency. In such cases, the conventional detector requires to estimate the joint distribution of the interfering signals, which imposes a huge computational complexity. To tackle this issue, we propose the joint use of a maximum likelihood detector (MLD) and a deep convolutional neural network (DCNN), where MLD is used to produce an initial detection result and DCNN improves the detection by exploiting the local correlation to suppress the interference. Furthermore, the improved DCNN is enhanced by devising the loss function through the cross-entropy of the detection, which can help to suppress the interfering signals and simultaneously force the residual interference to approach the Gaussian distribution. Simulation results are presented to verify the effectiveness of the proposed detector compared to the conventional one. The trained model and source code for this work are available at https://github.com/skypitcher/project_dcnnmld. [ABSTRACT FROM AUTHOR]

When research on the fifth generation mobile communications had just stepped into its startup period, a project called coordinated D2D-LAN was launched in China. The D2D-LAN project exemplifies information and optimization theory as the foundations for algorithms that provably enable seamless operation through combining cellular and mobile adhoc networks in license band. The core objective of the D2DLAN project is to bridge the gap between theory and practice, from wireless channel, physical, MAC, networking to application layers, for designing architectures and protocols to meet the data traffic surge problems. D2D-LAN leverages recent advances in wireless communications and signal processing, including the physical- layer network coding, utility optimization, and so on, which can exhibit vast potential for achieving high spectrum efficiency and full exploitation of communication resources. In this article, the application requirements, technological challenges, and some potential solutions are discussed. In particular, our recent results and key technologies employed in our demonstration system are detailed. [ABSTRACT FROM PUBLISHER]