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Massive Machine-Type Communication (mMTC) is proposed by ITU to provide a large scale of connectivity services for billions of machine-type communications devices (MTCDs) via cellular networks. However, MTCDs are generally energy-constrained, security capability limited and short-packet transmission dominated. It has great challenges for massive MTCDs to perform short-packet transmission simultaneously while guaranteeing the confidentiality and energy efficiency of the information transmission. In this paper, we investigate the energy-efficient secure short-packet transmission of Non-Orthogonal Multiple Access (NOMA) assisted mMTC networks, in which MTCDs aim to transmit secrecy messages to the destination base station via trusted relays with a passive eavesdropper present. To realize secure, reliable and energy-efficient transmission, we maximize the secrecy energy efficiency (SEE) by implementing joint relay and power level selection. Furthermore, we formulate a decentralized stateless Q-learning-based multi-agent reinforcement learning (MARL) algorithm for the dynamic and complex mMTC systems. The simulation results show that adopting the proposed decentralized MARL algorithm and relaying with NOMA can improve the performance of SEE while reducing information exchange overhead. [ABSTRACT FROM AUTHOR]

Moving networks (MNs) with moving base stations (BSs) provide ubiquitous and constant services to cellular devices/user equipment (UEs) in 5-th generation systems. Moving BSs are mounted on top of vehicles. To describe the randomness of the BSs, a tractable stochastic geometry model for MNs is proposed. A definition of the conditional success probability and meta distribution (MD) of the signal-to-interference ratio (SIR) for MNs is proposed. The MD is used to assess the benefits of MNs. In single-tier MNs with high mobility, we determine the moments of the conditional success probability given the point process for the calculation of the MD and the mean local delay. The results show that the mean local delay is finite and the variance is reduced to 0. A closed-form approximation of the variance is proposed for general mobility levels. Using the approximated variance, we propose a beta approximation of the MD. The single-tier model is then extended to a two-tier heterogeneous MN model. Tractable expressions of the mean success probability and the variance for both the overall network and the typical UE in each tier are obtained. They reveal that moving BSs can reduce the variance among UEs while keeping the mean success probability constant. [ABSTRACT FROM AUTHOR]

The 5th-generation (5G) mobile networks and beyond need to support massive machine-type communications (MTC) devices with limited available radio resources. In this paper, we study the power-domain non-orthogonal multiple access (NOMA) technology to support energy-efficient massive MTC networks, where MTC devices exchange information using sporadic and low-rate short packets. We investigate the subchannel allocation and power control policy to maximize the achievable effective energy efficiency (EE) for uplink NOMA-based massive MTC networks, taking into account of short-packet communication characteristics. We model the subchannel allocation problem as a multi-agent Markov decision process and propose an efficient Q-learning algorithm to solve it. Furthermore, we obtain the optimal transmission power policy by approximating the achievable effective rate of uplink NOMA-based short packet communications. Compared with the existing OFDMA scheme, simulations validate that the proposed scheme can improve the achievable effective EE of massive MTC networks with 5.93%. [ABSTRACT FROM AUTHOR]

Given the optimal transmit beamforming vector, the user who has the worst signal-to-noise ratio (SNR) is referred to as a bottleneck user for a single-group multicasting system with multiple antennas at the transmit side. In this paper, we present some interesting insights into the bottleneck users, such as the maximum number as well as the optimal beamformer when the transmitter has an arbitrary number of antenna elements. The $\max$– $\min$ fair SNR problem is employed and the closed-form solutions are proposed from the weighted sum-SNR maximization perspective for different numbers of possible bottleneck users. A new heuristic beamforming algorithm based on the bottleneck users is also presented to improve the system performance in terms of the achievable rate for physical-layer multicasting. [ABSTRACT FROM PUBLISHER]

The objective of maximizing the minimum Euclidean distance between two received data vectors via real-valued linear precoding is considered for multiple-input multiple-output (MIMO) systems with arbitrary dimensions. Assuming that perfect channel state information (CSI) is available at both the transmitter side and the receiver side, a novel low-complexity precoding algorithm is proposed to recursively construct the full-rank, the rank-deficient and the rank-one precoders with respect to particular channel realization. From the lattice theoretical perspective, the full-rank precoder is generated by using well-known dense packing lattices, which can also be recursively involved into the construction of higher-dimensional rank-deficient precoders. Moreover, the optimal solution is clearly figured out for the specific case of rank-one precoder. The closed-form expression of the achievable minimum distance is obtained and the analytical results reveal the performance bounds for different rank-constraint precoders. Simulation results validate the efficiency of the proposed precoder as compared with the state of the art. [ABSTRACT FROM PUBLISHER]

In this paper, we study Shannon capacity of channels in the context of classical Ramsey numbers. We overview some of the results on capacity of noisy channels modeled by graphs, and how some constructions may contribute to our knowledge of this capacity. We present an improvement to the constructions by Abbott and Song and thus establish new lower bounds for a special type of multicolor Ramsey numbers. We prove that our construction implies that the supremum of the Shannon capacity over all graphs with independence number 2 cannot be achieved by any finite graph power. This can be generalized to graphs with bounded independence number. [ABSTRACT FROM AUTHOR]

Millimeter-wave (mmWave) and ultra-dense networks are two key technologies for the fifth-generation (5G) and beyond communication system. However, the ultra-dense deployment of small base stations (SBSs) might introduce severe interference to users that connect to SBSs. This paper analyzes the performance of 5G communication networks where the SBSs with coordinated beamforming, operating at mmWave frequency band and macro base stations (MBSs) operating at sub-6 GHz coexist. First, by utilizing a stochastic geometry approach, we obtain the cell association probability expressions in terms of different cell association biases, base station density ratios and probabilities of line of sight (LoS) link. Furthermore, we propose a clustering method to choose some SBSs to eliminate intra-cell interference. Then, we put forward an average distance from the Kth SBS to a user to obtain signal-to-interference-ratio (SINR) and rate coverage probability expressions. The simulation results validate the correctness of the expressions, and indicate that the optimal cardinality of coordinated SBSs increases with the density of SBSs. In addition, the relationship between the cluster size K and the average energy efficiency is obtained, which can be used to guide the coordination principle in 5G and beyond communication systems. [ABSTRACT FROM AUTHOR]

Confronted with the challenge of high performance for applications and the restriction of hardware resources for field-programmable gate arrays (FPGAs), partial dynamic reconfiguration technology is anticipated to accelerate the reconfiguration process and alleviate the device shortage. In this paper, we propose an integrated optimization framework for task partitioning, scheduling, and floorplanning on partially dynamically reconfigurable FPGAs. The partition, schedule, and floorplan of the tasks are represented by the partitioned sequence triple (P-ST) (PS, QS, RS), where (PS, QS) is a hybrid nested sequence pair for representing the spatial and temporal partitions, as well as the floorplan, and RS is the partitioned dynamic configuration order of the tasks. The floorplanning and scheduling of task modules can be computed from the P-ST in ${O}$ (${n}^{{2}}$) time. To integrate the exploration of the scheduling and floorplanning design space, we use a simulated annealing-based search engine and elaborate a perturbation method, where a randomly chosen task module is removed from the partition sequence triple and then reinserted into a proper position selected from all the ${O}$ (${n}^{ {3}}$) possible combinations of partition, schedule and floorplan. We also prove a sufficient and necessary condition for the feasibility of the partitioning of tasks and scheduling of task configurations, and derive conditions for the feasibility of the insertion points in a P-ST. The experimental results demonstrate the efficiency and effectiveness of the proposed framework. [ABSTRACT FROM AUTHOR]

In 3-D integrated circuits (3-D ICs), through silicon via (TSV) is a critical technique to provide vertical connections. However, the yield and reliability challenge of TSV in industry is one of key obstacles to adopt the 3-D ICs technology. Various fault-tolerance structures by using additional spare TSVs (s-TSVs) to repair faulty functional TSVs (f-TSVs) have been proposed in literature for yield and reliability enhancement. However, these structures are formed in standard cell placement stage where all the f-TSVs are already placed. In reality, since the s-TSVs can be only inserted into the whitespace, the quality of the generated repair solution is strongly dependent on the whitespace distribution. In this paper, we propose an efficient TSV planning and repair framework in floorplanning stage, which takes nonuniform TSV distribution and clustered TSV defect-distribution into account. The proposed framework mainly consists of four stages: 1) a whitespace redistribution algorithm that uses a probability-based strategy to make the whitespace distribution more reasonable for the f-TSV planning. Subsequently, a convex-cost flow-based model for f-TSV allocation considering the fault clustering; 2) a top-down globally partitioning combined with a bottom-up locally merging to partition f-TSVs into groups with minimum hardware cost; 3) the min-cost max-flow algorithm for s-TSV allocation with minimum wirelength overhead; and 4) an integer linear programming-based model to form a fault-tolerance structure with minimum multiplexer delay overhead. The experimental results demonstrate that the proposed repair framework can improve the yield with minimum hardware cost and multiplexer delay overhead. [ABSTRACT FROM AUTHOR]

Cooperative communications have recently been migrated to one of state-of-the-art features of 3GPP LTE-Advanced (LTE-A). Cooperative communications fundamentally change the abstraction of a wireless link and offer significant potential advantages for wireless communication networks. This article visits cooperative techniques, such as relay, distributed antennas systems (DAS), multicell coordination, Group Cell, Coordinated Multiple Point transmission and reception (CoMP), those turn the traditional cellular system into a cooperative system. In particular, we propose several joint processing policies to demonstrate the Group Cell (CoMP) concept. Results of a trial network implementation and a performance evaluation of the concept are also reported. [ABSTRACT FROM AUTHOR]

This article investigates the displacement damage on AlGaN/GaN high-electron-mobility transistors (HEMTs) using the 30-MeV fluorine ions. The electrical degradation and the defects in HEMTs were examined before and after irradiation. Three defect states are detected in a deep-level transient analysis system (DLTS), including a broad surface state peak ($N_{1}$) and two bulk defect peaks ($H_{1}$ and $H_{2}$). The energy levels of these two defects are $E_{\mathrm {C}} 0.63$ eV ($H_{2}$) and $E_{\mathrm {C}} 0.91$ eV ($H_{1}$), respectively. There is a linear relationship between the concentration of $H_{1}$ and the fluorine ion fluence. The radiation damage and electrical performance degradation of AlGaN/GaN HEMTs are simulated by combining with simulation software of different methods. The calculated results are in agreement with the experimental data. The performance degradation caused by heavy ion of the device is mainly caused by the $H_{1}$ defect. The effect of defects with shallow energy level is shielded by the Fermi-level pinning in deeper energy level. Moreover, the defect distribution of GaN in AlGaN/GaN heterojunction plays a major role. It is found that the method of combining experimental data with multiscale simulation is an effective way to predict the radiation damage of devices. [ABSTRACT FROM AUTHOR]

To explore the role of hydrogen in radiation degradation of AlGaN/GaN high-electron-mobility transistors (HEMTs), the performance degradation of the hydrogen untreated and pretreated devices is compared under the exposure of carbon ions. The energy of carbon ions is chosen as 7.6 MeV, and the maximum fluence reaches 4 × 1012 cm−2. By electrical character measuring, it is found that the positive shift of the threshold voltage and the decrease of the transconductance occur after to the irradiation. Hydrogen pretreatment accelerates the shift of threshold voltage and the decrease of the transconductance. The threshold voltage of the device is almost unchanged under 1-MeV electron irradiations. This means that the displacement damage leads to the shift of the threshold voltage. The height of Schottky barrier hardly changes in the hydrogen pretreated devices, showing that the ionization defects such as the formation of interface states under the gate are not the main cause of device degradation. Deep level transient spectrum (DLTS) results show that the irradiations cause the increase of gallium vacancies, and the hydrogen pretreatment inhibits its formation. According to the first principle calculation, the existence of hydrogen in GaN layer can reduce the formation energy of and the number of charges of the defects. It is speculated that hydrogen atoms participate in the evolution of radiation defects, which changes the types and number of defects in the devices. [ABSTRACT FROM AUTHOR]