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In this paper, we present the delay-constrained performance analysis of a multi-antenna-assisted multiuser non-orthogonal multiple access (NOMA) based spectrum sharing system over Rayleigh fading channels. We derive analytical expressions for the sum effective rate (ER) for the downlink NOMA system under a peak interference constraint. In particular, we show the effect of the availability of different levels of channel state information (instantaneous and statistical) on the system performance. We also show the effect of different parameters of interest, including the peak tolerable interference power, the delay exponent, the number of antennas and the number of users, on the sum ER of the system under consideration. An excellent agreement between simulation and theoretical results confirms the accuracy of the analysis. [ABSTRACT FROM AUTHOR]

In cognitive radio networks (CRNs), secondary users (SUs) can opportunistically access the licensed bands through spectrum sensing while primary users (PUs) are inactive. While collaborative spectrum sensing (CSS) exploits the benefits of cooperation, the spectrum sensing data falsification (SSDF) attackers are subsequently introduced, which aim at undermining the performance of CRNs. We thus are motivated to maximize the throughput of the CRNs under SSDF attacks. First, to better discern SSDF attackers, we designate a double reputation based algorithm to differentiate the SSDF attackers and honest secondary users (HSUs). Then the trade off problem is formulated to find the optimal network parameters including, sensing duration, global decision threshold, energy detection threshold, reputation thresholds for maximizing the throughput of the secondary users network (SUN) subject to limited interference with the PUs. To address the non-convexity of the optimization problem, dummy variables are introduced and the alternative optimization method is adopted. Numerical results show that the proposed algorithm is effective in increasing throughput of the SUN with sufficient protection to the PUs. [ABSTRACT FROM AUTHOR]

This paper studies the application of network non-orthogonal multiple access (N-NOMA) to vehicular communication networks, modeled by a Poisson line Cox point process (PLC). Particularly, the road infrastructure is modeled by a Poisson line point process (PLP), whereas base stations (BSs) and users are located according to 1D homogeneous Poisson point processes (HPPPs) on each road. In the considered N-NOMA scheme, there are two types of users, i.e., coordinated multi-point (CoMP) users which are far from their BSs and NOMA users which are close to their BSs, where the CoMP users and the NOMA users are served simultaneously by applying the principle of NOMA. Specifically, the BSs collaborate with each other to provide reliable transmission for the CoMP user by applying Almouti coding, while each BS employs superposition coding to opportunistically serve an additional NOMA user. Compared to a conventional OMA based scheme, where only a CoMP user is served, the proposed N-NOMA scheme significantly improves the performance in terms of outage sum rates and user connectivity, since more users are served in the same resource block. A comprehensive analytical framework is developed to characterize the system level performance of the proposed N-NOMA scheme by applying PLC. Closed form expressions for the outage probabilities achieved by the CoMP and NOMA users are obtained. Computer simulation results are provided to show the superior performance of the proposed scheme and also validate the accuracy of the developed analytical results. [ABSTRACT FROM AUTHOR]

In this paper we investigate downlink performance in a non-orthogonal multiple access (NOMA) based vehicular communication network. In contrast to the previous works wherein the vehicles are simply assumed to be located anywhere in the coverage area, we consider practical cases where vehicles are located on a system of roads. We then adopt a system model based on Poisson Line Cox Point (PLC) processes, where the road system is represented through a Poisson Line (PL) Process. Vehicles ordered according to their distances to their corresponding roadside units (RSUs) are then served by using power domain NOMA. Adopting analytical tools from the stochastic geometry, we then analyse the outage performance of the system. Numerical results corroborate our analysis and demonstrate how the system settings influence the considered NOMA based V2X network. [ABSTRACT FROM AUTHOR]

Precise estimation of transmission input&output shaft torque and wheel speed is significant to the development of torque distribution and coordinated control method for the power split hybrid powertrain system. This paper studies an estimation method of transmission input and output torque as well as drive wheel speed using an unknown input observer in different operating modes for a compound power split hybrid powertrain system. Firstly, the configuration and dynamic characteristic of power split transmission is analyzed. Then, state equations in different operating modes are established, and a Takagi-Sugeno (T-S) fuzzy model is utilized to deal with the nonlinearities of load resistance torque. Furthermore, an unknown input reduced-order observer is designed to estimate the transmission input&output shaft torque and wheel speed. The asymptotical stability of the developed observer is verified based on Lyapunov theory. Finally, the performance of the unknown input observer is assessed by comparing with the Luenberger observer based on Matlab/Simulink simulation platform and test bench. Simulation and experiment results show that, the proposed observer can estimate the transmission input&output shaft torque and wheel speed more effectively in different operating modes. [ABSTRACT FROM AUTHOR]

Due to cost reduction and device miniaturization, amateur drones are now widely used in numerous civilian and commercial applications. However, the abuse of amateur drones has resulted in emerging threats to personal privacy and public security. To alleviate these threats, we design an acoustic-based surveillance system, which can achieve the capacity of amateur drones detection and localization with 24/7 (24 hours per day and 7 days per week under normal circumstances) availability. In the designed system, a detection fusion algorithm and a TDOA estimation algorithm based on the Bayesian filter are applied to improve the performance of drone detection and localization. Field experiments are carried out, and the results demonstrate that the designed system can detect and locate an amateur drone in real time with high accuracy and 24/7 availability. [ABSTRACT FROM AUTHOR]

Crowdsensing has been recognized as a promising data collection paradigm, in which a platform outsources sensing tasks to a large number of users. However, requesting users to report raw data may give rise to many practical concerns, such as a significant overhead of communication and central processing, besides users’ privacy concerns. In many scenarios (e.g, advertising and recommendation), the data collector directly benefits from statistical aggregation of raw data. Thus motivated, we consider the data collection problem based on user's local histograms, which is intimately related to the fundamental trade-off between the platform's accuracy and users’ privacy. Because of users’ social relationship, their data are often correlated, indicating that users’ privacy may be leaked from others’ data. To tackle this challenge, we first utilize Gaussian Markov random fields to model the correlation structure embedded in users’ data. The data collection is modeled as a Stackelberg game where the platform decides its reward policy and users decide their noise levels while taking into account the social coupling among users. For the reward policy design, we first establish the relationship between users’ Nash equilibrium and the payment mechanism, and then optimize the platform's accuracy under a budget constraint. Further, since the noise levels are users’ private information, they may use falsified noise levels to achieve higher payoffs, which in turn impairs the crowdsensing performance. It turns out that with the insight into the correlation structure among users’ data, the information asymmetry can be overcome based on peer prediction. We revisit the payment mechanism to guarantee dominant truthfulness of each user's strategy. Theoretical analysis and numerical results demonstrate the effectiveness of the proposed mechanism. [ABSTRACT FROM AUTHOR]

This correspondence considers non-orthogonal multiple access (NOMA) assisted mobile edge computing (MEC), where the power and time allocation is jointly optimized to reduce the energy consumption of computation offloading. Closed-form expressions for the optimal power and time allocation solutions are obtained and used to establish the conditions for determining whether the conventional orthogonal multiple access (OMA), pure NOMA or hybrid NOMA should be used for MEC offloading. [ABSTRACT FROM AUTHOR]

In this paper, some new results on the distribution of the squared generalized singular values are presented, and the outage performance of a generalized singular value decomposition based precoding scheme in the two-user multiple-input multiple-output security broadcast scenario is characterized. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the outage performance of hybrid automatic repeat request with chase combining (HARQ-CC) assisted downlink non-orthogonal multiple access (NOMA) systems. A closed-form expression of the individual outage probability and the diversity gain are obtained firstly. Based on the developed analytical outage probability, a tradeoff between the minimum number of retransmissions and the transmit power allocation coefficient is then provided for a given target rate. The provided simulation results demonstrate the accuracy of the developed analytical results. Moreover, it is shown that NOMA combined with the HARQ-CC can achieve a significant advantage when only average channel state information is known at the transmitter. Particularly, the performance of the user with less transmit power in NOMA systems can be efficiently improved by utilizing HARQ-CC. [ABSTRACT FROM AUTHOR]

It is a promising solution for real-time multitarget tracking to implement particle cardinality balanced multitarget multi-Bernoulli (CBMeMBer) filters in hardware platforms. However, this solution is difficult to materialize since there is a contradiction between the time-varying number of Bernoulli intensity components in CBMeMBer filters and the limited number of particles in hardware platforms. Moreover, real-time hardware implementation requires a resampling procedure that is suitable for parallel processing, while the existing parallel resampling algorithms oversimplify this procedure, resulting in estimation performance degradation. In this paper, we propose an optimization algorithm of particle allocation to overcome the above-mentioned contradiction, and a parallel resampling algorithm to improve the estimation performance. Numerical experiments demonstrate the effectiveness of the proposed algorithms in multitarget tracking. [ABSTRACT FROM AUTHOR]

This correspondence studies a new secrecy beamforming (SBF) scheme for multiple-input single-output non-orthogonal multiple access (MISO-NOMA) systems. In particular, the proposed SBF scheme efficiently exploits artificial noise to protect the confidential information of two NOMA assisted legitimate users, such that only the eavesdropper's channel is degraded. Considering a practical assumption of the imperfect worst-case successive interference cancellation which is a unique character in employing NOMA transmission, we derive a closed-form expression for the secrecy outage probability to characterize the secrecy performance. After that, we carry out an analysis of secrecy diversity order to provide further insights about secure MISO-NOMA transmission. Numerical results are provided to demonstrate the accuracy of the developed analytical results and the effectiveness of the proposed SBF scheme. [ABSTRACT FROM AUTHOR]

This paper investigates an outage-constrained secrecy rate maximization (OC-SRM) problem based on the statistical channel uncertainty assumption in an underlay multiple-input multiple-output (MIMO) cognitive radio network, where the secondary transmitter provides simultaneous wireless information and power transfer to receivers. Our objective is to design the transmit covariance matrix and artificial noise aided covariance matrix through maximizing the secrecy rate of the secondary user while satisfying the given outage probability requirements. The designed problem is nonconvex and challenging. We employ the existing theory to reformulate the original problem into two equivalent subproblems by introducing auxiliary variables in order to overcome the difficulty arising from the Shannon capacity expression. The Bernstein-type inequality approach is resorted to conservatively approximate the probabilistic constraints. The merit of the transformation and conversion is that the tractable solutions of the original OC-SRM problem can be easily obtained through solving two convex conic subproblems alternately. Furthermore, we extend the proposed algorithm to solve full uncertainty model design. Numerical results demonstrate the efficacy of the proposed designs. [ABSTRACT FROM AUTHOR]

In this paper, we consider non-orthogonal multiple access (NOMA) relaying networks, where one base station communicates with two mobile users with the aid of multiple relays. We propose a two-stage relay selection strategy for NOMA networks with decode-and-forward (DF) and amplify-and-forward (AF) relaying protocols with different quality of service requirements at the users, respectively. Then, the outage probabilities of the NOMA two-stage DF and AF schemes are obtained in closed-form expressions, and the diversity order is determined based on their asymptotic expressions at high signal-to-noise ratio. Both of the developed analytical results and carried out computer simulations show that NOMA two-stage DF (AF) relaying is superior to existing relay selection strategies developed for cooperative NOMA and orthogonal multiple access networks. [ABSTRACT FROM PUBLISHER]

The key to the launching control of a dual-clutch transmission (DCT) lies in the coordination control of the engine and dual clutches, along with the accurate closed-loop control of the torque transmitted by each clutch and the output torque of the engine. The implementation feasibility and precision of the clutch torque closed-loop control are completely dependent on the effective real-time estimation of the clutch torque, which cannot be directly measured. Therefore, the high-order sliding-mode observer and unknown input observer are used to estimate the transmitted torque of the twin clutches on the basis of the self-designed control strategy and estimation of the vehicle drag torque. First, for the launching clutch slipping phase, an improved engine constant speed control is proposed based on the dynamic equations of a dry DCT with dual intermediate shafts, and the minimum value principle is applied to achieve the optimum launching control of the clutches. Meanwhile, the separating conditions of the separated clutch and the torque distribution are determined to ensure approximate friction work and avoid power cycle, and the target curve of the clutch-transmitted torque is obtained according to different conditions. Then, the vehicle drag torque is estimated using the recursive least-square method with a double forgetting factor, the angular acceleration of the engine and output shaft is refactored utilizing a high-order sliding-mode observer algorithm, and the transmitted torque of the twin clutches are estimated using the unknown input observer. Then, the DCT launching process is simulated under different driving conditions on the MATLAB/Simulink software platform. Finally, the bench test is conducted to verify the effectiveness of the self-designed clutch torque estimation method. The simulation and hardware-in-the-loop (HIL) test results show that the proposed methods of high-order sliding-mode observer and unknown input observer can effectively estimate the clutch-transmitted torque and lay a solid foundation for the subsequent development of the launching control strategy for a real vehicle with a DCT. [ABSTRACT FROM AUTHOR]

Nonorthogonal multiple access (NOMA) represents a paradigm shift from conventional orthogonal multiple-access (MA) concepts and has been recognized as one of the key enabling technologies for fifth-generation mobile networks. In this paper, the impact of user pairing on the performance of two NOMA systems, i.e., NOMA with fixed power allocation (F-NOMA) and cognitive-radio-inspired NOMA (CR-NOMA), is characterized. For F-NOMA, both analytical and numerical results are provided to demonstrate that F-NOMA can offer a larger sum rate than orthogonal MA, and the performance gain of F-NOMA over conventional MA can be further enlarged by selecting users whose channel conditions are more distinctive. For CR-NOMA, the quality of service (QoS) for users with poorer channel conditions can be guaranteed since the transmit power allocated to other users is constrained following the concept of cognitive radio networks. Because of this constraint, CR-NOMA exhibits a different behavior compared with F-NOMA. For example, for the user with the best channel condition, CR-NOMA prefers to pair it with the user with the second best channel condition, whereas the user with the worst channel condition is preferred by F-NOMA. [ABSTRACT FROM AUTHOR]

In this paper, we investigate physical-layer security in a random wireless network where both legitimate and eavesdropping nodes are randomly deployed. In the first scenario, we study the basic random network without a protected zone around the source node. The probability density functions (pdfs) for the composite channel gain with both fading and path loss is derived and used to calculate the probability of secure connection and ergodic secrecy capacity. In the second scenario, we consider the use of secrecy protected zone around the source node to enhance the security in a noise-limited network. Here, we study the following two cases: 1) The eavesdroppers are aware of the secrecy protected zone, and 2) the eavesdroppers are unaware of the secrecy protected zone. Moreover, the distribution of the distances between the origin and random nodes outside the secrecy protected zone is derived. In the final scenario, the interferer protected zones around the legitimate receivers are used to improve the physical-layer security by restructuring the interference. The derived analytical results are verified by the Monte Carlo simulations. It is shown that the application of secrecy and interferer protected zones lead to significant improvement in security, depending on different system parameters. [ABSTRACT FROM AUTHOR]

In this paper, we consider underlay cognitive radio (CR) networks with one primary receiver, one cognitive transmitter–receiver pair, and one energy harvesting relay. The transmission power of the secondary source is opportunistically determined by its interference to the primary receiver, and the relay transmission is powered by the energy harvested from the radio-frequency observations at the relay. For the considered CR networks with simultaneous wireless information and power transfer (SWIPT), we derive analytical expressions for the outage probability, as well as their high signal-to-noise ratio (SNR) approximations in closed form. The developed analytical results demonstrate that the use of SWIPT will not cause any loss in diversity gain, but the outage probability achieved by the SWIPT-CR scheme asymptotically decays as \log \mboxSNR/\mboxSNR, whereas a decaying rate of \mbox1/\mboxSNR is achieved by a conventional CR network. Computer simulation results are also provided to demonstrate the accuracy of the presented analysis. [ABSTRACT FROM AUTHOR]

In this paper, we consider a cloud radio access networks (C-RANs) in which base stations (BSs) are uniformly distributed inside a disk. The outage probability and the ergodic rate achieved by these C-RANs are analyzed, where stochastic geometry is used to capture the randomness of BS locations. Compared with existing studies to C-RANs, more accurate analytical results are developed by applying the Gauss–Chebyshev integration, as confirmed by our simulation results. [ABSTRACT FROM PUBLISHER]

In this paper, a cognitive-radio-inspired asymmetric network coding (CR-AsNC) scheme is proposed for multiple-input–multiple-output (MIMO) cellular transmissions, where information exchange among users and base-station (BS) broadcasting can be accomplished simultaneously. The key idea is to apply the concept of cognitive radio (CR) in network coding transmissions, where the BS tries sending new information while helping users' transmissions as a relay. In particular, we design an asymmetric network coding method for information exchange between the BS and the users, although many existing works consider the design of network coding in symmetric scenarios. To approach the optimal performance, an iterative precoding design for CR-AsNC is first developed. Then, a channel-diagonalization-based precoding design with low complexity is proposed, to which power allocation can be optimized with a closed-form solution. The simulation results show that the proposed CR-AsNC scheme with precoding optimization can significantly improve system transmission performance. [ABSTRACT FROM PUBLISHER]

In delay-tolerant networks (DTNs), stable end-to-end connections do not always exist. Messages are forwarded, assisted by the mobility of nodes, in a store–carry–forward paradigm. The mobility of nodes in most DTNs has a certain statistical regularity; thus, using historical information in DTNs to compute the delivery quality of nodes can help to select good forwarding nodes. This paper aims to establish a routing scheme based on multihop delivery quality, which is designed to reduce the energy consumption of message forwarding while maintaining a high delivery rate. We characterized the multihop delivery quality of each node with an expected delay and an expected probability, parameterized by the remaining hop count. Based on these two quality metrics, we developed two algorithms, namely, the delay-inferred forwarding (DIF) algorithm and the probability-inferred forwarding (PIF) algorithm. The basic idea of DIF and PIF is to find the optimal forwarding path by minimizing the expected delay and by maximizing the expected probability, respectively, in the hop graph that is defined in this paper. We performed extensive trace-driven simulations to compare our algorithm to other representative routing algorithms using several real traces. We observed the following: 1) Compared with the delegation algorithm, which uses one-hop delivery quality, both DIF and PIF significantly improve the message delivery rate, and they yield more improvements as the mobility of nodes becomes more regular; and 2) compared with the state-of-the-art optimal opportunistic forwarding (OOF) algorithm, which also uses a multihop delivery quality, DIF and PIF have significantly smaller forwarding overhead (with the maximum reduction in the number of forwarding being over 40%), whereas they are quite close to OOF in terms of both delivery rate and average delay. [ABSTRACT FROM PUBLISHER]

This paper studies different secrecy rate optimization problems for a multiple-input–multiple-output (MIMO) secrecy channel. In particular, we consider a scenario where a communication through a MIMO channel is overheard by a multiple-antenna eavesdropper. In this secrecy network, we first investigate two secrecy rate optimization problems: 1) power minimization and 2) secrecy rate maximization. These optimization problems are not convex due to the nonconvex secrecy rate constraint. However, by approximating this secrecy rate constraint based on Taylor series expansion, we propose iterative algorithms to solve these secrecy rate optimization problems. In addition, we provide the convergence analysis for the proposed algorithms. These iterative optimization approaches are developed under the assumption that the transmitter has perfect channel state information. However, there are practical difficulties in having perfect channel state information at the transmitter. Hence, robust secrecy rate optimization techniques based on the worst-case secrecy rate are considered by incorporating channel uncertainties. By exploiting the S-Procedure, we show that these robust optimization problems can be formulated into semidefinite programming at low signal-to-noise ratios (SNRs). Simulation results have been provided to validate the convergence of the proposed algorithms. In addition, numerical results show that the proposed robust optimization techniques outperform the nonrobust schemes in terms of the worst-case secrecy rates and the achieved secrecy rates. [ABSTRACT FROM PUBLISHER]

In this paper, we first propose a new cooperative multiple-access transmission protocol by utilizing the cooperation among the sources and external relays. The impact of linear detection methods on the reception reliability is then investigated, whereas many existing works rely on the ideal theoretic criterion, i.e., the capacity region of the multiple-access channel. Analytical results are developed to show that, for a scenario with K users and K relays, the proposed scheme can ensure a minimal diversity gain of (K + \1) achievable for all users, whereas conventional approaches can only achieve a diversity gain of 1. Numerical results are also provided to demonstrate the performance of the proposed protocol. [ABSTRACT FROM PUBLISHER]

In this paper, we study how to improve wireless security for bidirectional communications. For the scenario with single-antenna nodes, effective criteria for relay and jamming node selection are developed to ensure that the probability to have nonzero secrecy rates is approaching one, given sufficient relays. For the scenario with multiple-antenna nodes, effective precoding is proposed to ensure that the mutual information obtained at the eavesdropper decreases to zero when there is a sufficient number of relays. [ABSTRACT FROM PUBLISHER]

In this correspondence, we investigate a two-phase two-way relay protocol for a scenario without channel coding or channel estimation. The considered configuration represents practical sensor networks, where the nodes wish to exchange some low-rate messages (e.g., 1 bit) via a shared relay under strict complexity or latency constraint (corresponding to our assumptions of no-coding and no-channel estimation). A new scheme that incorporates single-threshold noncoherent energy detection and a digital network coding process at the relay node is proposed. Energy detection is optimized for both phases of the protocol, and a threshold that exhibits no error floors is derived in closed form. Numerical results validate the efficiency of the proposed scheme and introduce the two-way relay channel as an efficient structure for noncoherent and uncoded systems as well. [ABSTRACT FROM PUBLISHER]

We consider multiple-input–multiple-output (MIMO) two-way relaying channels where a pair of multiantenna users wishes to exchange information with the help of a nonregenerative multiantenna relay. A low-complexity joint beamforming and power management scheme is proposed. The proposed beamformers first align the channel matrices of the user pair and then decompose the aligned channel into parallel subchannels. Two power management issues, i.e., power allocation and power control, are addressed in this paper. First, sum-rate optimizing power allocation is proposed to allocate power between all subchannels and nodes. Second, quality of service (QoS) satisfying power control is proposed to minimize the total transmission power in the network. Simulation results justify that the proposed joint beamforming and power management scheme delivers better sum-rate performance or consumes lower transmission power when compared with existing schemes. [ABSTRACT FROM PUBLISHER]

In this paper, we first study the design of network coding for the generalized multiple-input–multiple-output (MIMO) Y channels, where K users wish to exchange information with each other within two time slots. Precoding at each user and the relay is carefully constructed to ensure that the signals from the same user pair are grouped together and that cross-pair interference can be canceled. In addition, a simple mapping function is proposed to ensure low-complexity detection at the relay. Exact expressions of symbol error rate (SER) are then developed to establish the explicit relationship between the diversity gain and the number of node antennas. Monte Carlo simulation is also provided to demonstrate the performance of the proposed scheme. [ABSTRACT FROM PUBLISHER]

In multiple-input–single-output (MISO) broadcast channels, the achievable diversity gain is limited by the number of source transmitter antennas. Cooperative transmission is able to provide another dimension of diversity gain improvement. In this paper, we introduce a spectrally efficient cooperative transmission protocol in MISO broadcast channels using linear precoding and nonorthogonal relaying. The proposed protocol can achieve maximum diversity gain expressed as the sum of the number of source transmitter antennas and the number of available relays. The diversity and multiplexing tradeoff of the proposed protocol outperforms the noncooperative scheme, even when only a single relay is used. For a large number of relay candidates, the diversity and multiplexing tradeoff of the proposed protocol completely surpasses the existing noncooperative scheme. [ABSTRACT FROM PUBLISHER]

Cooperative diversity has been recognized as an effective and low-cost technique to combat multipath fading and enhance transmission reliability. Motivated by the fact that many existing cooperative protocols suffer some loss of ergodic capacity, network coding, which is a technique that is well known for its capability to increase system throughput, is proposed in this paper to be combined with cooperative diversity for uplink transmissions. Two kinds of information-theoretic metrics, i.e., outage and ergodic capacities, are developed for the proposed transmission scheme to assist with performance evaluation. The developed analytic results, which are shown to fit well with Monte Carlo simulation, demonstrate that the proposed protocol can achieve better system robustness and larger system throughput simultaneously than comparable schemes. The application of the proposed transmission protocol to scheduling is also studied to achieve better fairness–throughput tradeoff. [ABSTRACT FROM PUBLISHER]

Existing work has shown that random coding across multicast sessions can significantly reduce system delay. However, such a scheme requires the strong assumption that each source has priori information of other sources' messages. The broadcasting nature of radio propagation can provide an opportunity to realize collaboration across sessions without causing much system overhead. In this paper, we propose the application of network coding to multisource-multidestination (MSMD) scenarios and provide formal analysis for the improvement of system delay. In particular, two types of analytical results have been developed, with one based on the outage probability and the other based on the use of practical convolutional codes. Monte Carlo simulation results have also been provided to demonstrate the delay performance of the proposed network-coded protocol. [ABSTRACT FROM AUTHOR]

As a combination of ad hoc networks and wireless local area network (WLAN), the wireless mesh network (WMN) provides a low-cost convenient solution to the last-mile networkconnectivity problem. As such, existing route protocols designed to provide security and privacy protection for ad hoc networks are no longer applicable in WMNs. On the other hand, little research has focused on privacy-preserving routing for WMNs. In this paper, we propose two solutions for security and privacy protection in WMNs. The first scheme relies on group signatures, together with user credentials, to deliver security and privacy protection. By enforcing access control using user credentials, the user's identity has to be disclosed to mesh routers. To avoid this, our second scheme employs pairwise secrets between any two users to achieve stronger privacy protection. In the second scheme, the user is kept anonymous to mesh routers. Finally, we analyze these two schemes in terms of security, privacy, and performance. [ABSTRACT FROM AUTHOR]

Orthogonal space-time block coding (OSTBC) in multiple-antenna wireless systems has recently emerged as one of the most promising reliability-enhancing technologies for high-speed, high-quality data services. In this paper, we propose a technique to achieve joint channel estimation and symbol detection for OSTBC in frequency-selective fading channels. The key observation is that a multiple-input-single-output system, which is using OSTBC, can be transformed into an equivalent single-input-multiple-output system using the implicit redundancy in OSTBC. This allows a probabilistic method, known as the Baum-Welch algorithm, to be applied at each output branch. As each output branch is a function of the same input, redundant information may be exchanged between the multiple branches to improve detection performance. The proposed technique does not require multiple antennas at the receiver and only has moderate computational complexity. Furthermore, the Cramer-Rao lower bound (CRB) is also developed to facilitate performance analysis. Simulation results are provided to demonstrate the performance of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Reconfigurable intelligent surface (RIS) assisted non-orthogonal multiple access (NOMA) transmission can effectively improve the energy/spectrum efficiency in wireless networks. This paper designs a low-complexity scheme to achieve the balanced tradeoff between the sum-rate and power consumption in a RIS-assisted NOMA system, which can be measured by energy efficiency. To solve the formulated problem effectively, the original non-convex problem is first decomposed into two subproblems, i.e., beamforming optimization and phase shift optimization. Alternating optimization is proposed to solve these two subproblems iteratively. In particular, successive convex approximation (SCA) is utilized to convert the non-convex constraints to convex ones. The provided simulation results demonstrate that the proposed scheme can achieve superior performance on energy efficiency compared to the random phase shifts and orthogonal multiple access (OMA) schemes. [ABSTRACT FROM AUTHOR]

Due to the scarcity of channel availability in IEEE 802.11p standard, applications related to infotainment and multimedia services are vulnerable to suffer from delays and connectivity. Cognitive radio (CR) has the potential to overcome the issue of spectrum scarcity. By making use of the CR technology, secondary users (SU) can access a radio frequency spectrum other than 802.11p through spectrum sensing. Majority of low complex existing algorithms are based on energy detection that are considering the static environment of SUs. In practice, the algorithms, which considers mobility are mainly focused on low vehicle speed. However, the combined effect of primary user (PU) activity statistics and SU mobility has not been tackled while evaluating the performance of opportunistic spectrum access. In particular, this work considers the joint impact of PU activity and vehicle mobility on spectrum sensing performance by considering single lane and double lane vehicular scenarios. We also evaluate the impact of traffic densities on sensing performance. The main contribution of this work is to show the impact of PU activity statistics on sensing performance by deriving analytical expressions for miss-detection probability. These expressions are used for analysis and simulation of cognitive radio enabled vehicular communications. From our observations, it is noted that the probability of vehicle connectivity is improved approximately by 50 $\%$ for initial distance of SU when spectrum sensing is employed under PU activity. [ABSTRACT FROM AUTHOR]

The combination of non-orthogonal multiple access (NOMA) and intelligent reflecting surface (IRS) is an efficient solution to significantly enhance the energy efficiency of the wireless communication system. In this paper, a downlink multi-cluster NOMA network is considered, where each cluster is supported by one IRS. This paper aims to minimize the transmit power by jointly optimizing the beamforming, the power allocation and the phase shift of each IRS. The formulated problem is non-convex and challenging to be solved due to the coupled variables, i.e., the beamforming vector, the power allocation coefficient and the phase shift matrix. To address this non-convex problem, an alternating optimization based algorithm is proposed. Specifically, the primal problem is divided into two subproblems for beamforming optimization and phase shifting feasiblity, where the two subproblems are solved iteratively. Moreover, to guarantee the feasibility of the beamforming optimization problem, an iterative algorithm is proposed to search the feasible initial points. To reduce the complexity, a simplified algorithm based on partial exhaustive search for this system model is also proposed. Simulation results demonstrate that the proposed alternating algorithm can yield a better performance gain than the partial exhaustive search algorithm, NOMA with random IRS phase shift scheme and OMA-IRS scheme. [ABSTRACT FROM AUTHOR]

This paper proposes a novel probabilistic buffer-aided (BA) relay selection (RS) scheme for cooperative relay networks. Different from most existing BA RS schemes that are determined by the wireless channel condition and the buffer state, the proposed scheme also utilizes additional randomness to decide the link selection outcome. In particular, we first select the strongest available source-to-relay and relay-to-destination links, respectively, and then probabilistically select one from these two links. Some previously proposed BA RS schemes can be viewed as special cases of the proposed scheme, such as the max-link scheme and the scheme with reduced packet delay. Then, the outage probability and average packet delay are analyzed. Both the analytical and simulation results show that different tradeoffs between the outage probability and average packet delay can be easily achieved by adjusting a single corresponding parameter. [ABSTRACT FROM AUTHOR]

Non-orthogonal multiple access (NOMA) has been considered as a key technology in the fifth-generation mobile communication networks due to its superior spectrum efficiency. Since the heterogeneous network has been emerged to satisfy users’ explosive data rate requirements and large connectivity of mobile Internet, implementing NOMA policy in heterogeneous networks (HetNets) has become an inevitable trend to enhance the 5G system throughput and spectrum efficiency. In this paper, we aim to maximize the entire system energy efficiency, including the macrocell and small cells, in a NOMA HetNet via subchannel allocation and power allocation. By considering the co-channel interference and cross-tier interference, the energy efficient resource allocation problem is formulated as a mixed integer nonconvex optimization problem. It is challenging to obtain the optimal solution; therefore, a suboptimal algorithm is proposed to alternatively optimize the macrocell and the small cells resource allocation. Specifically, convex relaxation and dual-decomposition techniques are exploited to optimize the subchannel allocation and power allocation. Moreover, optimal closed-form power allocation expressions are derived for small cell and macrocell user equipments by the Lagrangian approach. Simulations results show that the proposed algorithms can converge within ten iterations and can also attain higher system energy efficiency than the reference schemes. [ABSTRACT FROM AUTHOR]

Cellular networks are increasingly densified to deal with the fast growing wireless traffic. Interference mitigation plays a key role for the dense cellular networks. Successive interference cancellation (SIC) and fractional frequency reuse (FFR) are two representative inter-cell interference (ICI) mitigation techniques. In this paper, we study the application of both SIC and FFR for LTE uplink networks, and develop an analytical model to investigate their interactions and impact on network performance. The performance gains with FFR and SIC are related to key system functionalities and variables, such as SIC parameters, FFR bandwidth partition, uplink power control and sector antennas. The ICIs from individual cell sectors are approximated by log-normal random variables, which enables low complexity computation of the aggregate ICI with FFR and SIC. Then, network performance of site throughput and outage probability is computed. The model is fast and has small modeling deviation, which is validated by simulations. Numerical results show that both SIC and FFR can largely improve network performance, but SIC has a stronger impact than FFR. In addition, most of the network performance gains with SIC could be obtained with a small number of SIC stages applied to a few sectors. [ABSTRACT FROM AUTHOR]

In this paper, we develop various beamforming techniques for downlink transmission for multiple-input single-output nonorthogonal multiple access (NOMA) systems. First, a beamforming approach with perfect channel state information is investigated to provide the required quality of service for all users. Taylor series approximation and semidefinite relaxation (SDR) techniques are employed to reformulate the original nonconvex power minimization problem to a tractable one. Furthermore, a fairness-based beamforming approach is proposed through a max–min formulation to maintain fairness between users. Next, we consider a robust scheme by incorporating channel uncertainties, where the transmit power is minimized while satisfying the outage probability requirement at each user. Through exploiting the SDR approach, the original nonconvex problem is reformulated in a linear matrix inequality form to obtain the optimal solution. Numerical results demonstrate that the robust scheme can achieve better performance compared to the nonrobust scheme in terms of the rate satisfaction ratio. Furthermore, simulation results confirm that NOMA consumes a little over half transmit power needed by orthogonal multiple access for the same data rate requirements. Hence, NOMA has the potential to significantly improve the system performance in terms of transmit power consumption in future 5G networks and beyond. [ABSTRACT FROM AUTHOR]

This correspondence paper investigates relay selection (RS) schemes for cooperative downlink nonorthogonal multiple access (NOMA) networks with multiple relays. Two optimal RS schemes, termed as the two-stage weighted-max-min (WMM) and max-weighted-harmonic-mean (MWHM) schemes, are proposed for cooperative NOMA with fixed and adaptive power allocations (PAs) at the relays, respectively. Then, the outage probabilities of the two proposed RS schemes are analyzed, and their diversity gains are also determined. The provided simulation results show that the proposed optimal two-stage WMM and MWHM schemes outperform the existing suboptimal RS schemes for cooperative NOMA networks with fixed and adaptive PAs at the relays, respectively. [ABSTRACT FROM AUTHOR]

Interrelay interference (IRI) is known to degrade the performance of virtual full-duplex (FD) relaying schemes. Although interference avoidance and cancelation strategies have been proposed in the existing literature, most studies reflect the traditional information theoretical viewpoint of interference as a degrading factor on information decoding (ID). However, from energy harvesting (EH) perspective, the IRI could be beneficial. This motivates the study of simultaneous wireless information and power transfer in decode-and-forward multiple input multiple output virtual FD relaying system, where the IRI serves as an additional source of energy to the relay. To manage the degrading effect of the IRI on the ID receiver, transmit antenna selection is proposed at the relay. In addition, precoding matrices that optimize the ID and EH receivers are jointly designed. The simulated results show that although IRI could be a degrading factor from the information viewpoint, it can be properly managed and exploited for EH at the relay while maintaining the end-to-end data rate. In addition, the results show that the end-to-end information rate and harvested energy can be simultaneously achieved using the proposed precoders. [ABSTRACT FROM AUTHOR]

This paper studies the secrecy rate maximization problem of a secure wireless communication system in the presence of multiple eavesdroppers. The security of the communication link is enhanced through cooperative jamming with the help of multiple jammers. First, a feasibility condition is derived to achieve a positive secrecy rate at the destination. Then, we solve the original secrecy rate maximization problem, which is not convex in terms of power allocation at the jammers. To circumvent this nonconvexity, the achievable secrecy rate is approximated for a given power allocation at the jammers, and the approximated problem is formulated into a geometric programming one. Based on this approximation, an iterative algorithm has been developed to obtain the optimal power allocation at the jammers. Next, we provide a bisection approach, based on 1-D search, to validate the optimality of the proposed algorithm. In addition, by assuming Rayleigh fading, the secrecy outage probability (SOP) of the proposed cooperative jamming scheme is analyzed. More specifically, a single-integral form expression for the SOP is derived for the most general case, as well as a closed-form expression for the special case of two cooperative jammers and one eavesdropper. Simulation results have been provided to validate the convergence and the optimality of the proposed algorithm, as well as the theoretical derivations of the presented SOP analysis. [ABSTRACT FROM AUTHOR]

This paper proposes a novel non-orthogonal multiple access (NOMA)-based cooperative transmission scheme for a spectrum-sharing cognitive radio network (CRN), whereby a secondary transmitter (ST) serves as a relay and helps transmit the primary and secondary messages simultaneously by employing NOMA signaling. This cooperation is particularly useful when the ST has good channel conditions to a primary receiver but lacks the radio spectrum. To evaluate the performance of the proposed scheme, the outage probability and system throughput for the primary and secondary networks are derived in closed forms. Simulation results demonstrate the superior performance gains for both networks thanks to the use of the proposed NOMA-based cooperative transmission scheme. It is also revealed that NOMA outperforms conventional orthogonal multiple access (OMA) and achieves better spectrum utilization. [ABSTRACT FROM AUTHOR]

In this paper, nonorthogonal multiple access (NOMA) is applied to large-scale underlay cognitive radio (CR) networks with randomly deployed users. To characterize the performance of the considered network, new closed-form expressions of the outage probability are derived using stochastic geometry. More importantly, by carrying out the diversity analysis, new insights are obtained under the two scenarios with different power constraints: 1) fixed transmit power of the primary transmitters (PTs); and 2) transmit power of the PTs being proportional to that of the secondary base station. For the first scenario, a diversity order of $m$ is experienced at the $m$th-ordered NOMA user. For the second scenario, there is an asymptotic error floor for the outage probability. Simulation results are provided to verify the accuracy of the derived results. A pivotal conclusion is reached that by carefully designing target data rates and power allocation coefficients of users, NOMA can outperform conventional orthogonal multiple access in underlay CR networks. [ABSTRACT FROM PUBLISHER]

This paper investigates the buffer-aided relay selection problem for a decode-and-forward cooperative wireless network with K relays. We propose a new relay selection scheme that incorporates the status of the relay buffers and the instantaneous strength of the wireless links. Specifically, each link is assigned with a weight related to the buffer status; then, the best relay is selected with the largest weight among all the qualified source–relay and relay–destination links. We derive the closed-form expression for the outage probability and the diversity gain by introducing several Markov chains (MCs) to model the evolution of the buffer status. The analysis shows that the proposed scheme can achieve the optimal diversity gain \mbox{2}K for a small L (i.e., L\ge \mbox3), an improvement in comparison with the existing max-link scheme that achieves the optimal diversity gain only when L is sufficiently large, where $L$ denotes the buffer size of each relay. The provided theoretical and numerical results confirm the performance gain of the proposed relay selection scheme over the existing max-link scheme. [ABSTRACT FROM PUBLISHER]

The application of non-orthogonal multiple access (NOMA) to multi-layer multicast video streaming is envisioned to address the explosively growing demand for capacity which is dominated mostly by multimedia content. In this paper, a joint power allocation and subgrouping scheme is developed to enhance the performance of NOMA-based multi-layer multicast systems. An optimization problem is formulated to maximize the overall sum multicast rate whilst satisfying the maximum transmission power and proportional rate constraints. Due to the complexity of the optimization problem, we first derive two power allocation techniques for the 2-layer case considering arbitrary subgrouping which are based on the iterative implementation and closed-form analysis, respectively. We then generalize the low-complexity closed-form solution for the general multi-layer case. This scheme successively allocates power to each layer stream while assuring that the minimum target rate and proportionality are guaranteed, particularly for the transmission rate of the high-priority base layer stream. A sub-optimal joint power allocation and subgrouping scheme is also designed by incorporating the power allocation scheme into the proposed iterative subgrouping techniques. Simulation results show the effectiveness of the power allocation and subgrouping schemes in enhancing the sum multicast rate performance. In addition, the proposed power allocation scheme ensures substantially higher rates for the base layer stream, which is crucial in robust delivery of standard quality video to all users. [ABSTRACT FROM AUTHOR]

With low-cost energy consumption, the reconfigurable intelligent surface (RIS) technique is a potential solution to the real-time data processing for intelligent transportation systems (ITSs). In this paper, an intelligent transmissive surface is introduced into the vehicular communications, enabling vehicle-to-infrastructure (V2I) signals to penetrate the intelligent RIS to access the base station (BS) on the opposite side of the vehicle. Considering that the vehicle-to-vehicle (V2V) communication reuses the spectrum spanned for V2I link, we investigate the ergodic capacity optimization problem for the vehicle performing V2I communications with the assistance of RIS, while meeting the low-latency and high-reliability requirements of the V2V link. The RIS transmission coefficients and power allocation of vehicles are jointly optimized, for the management of the desired and undesired vehicular communication links. Moreover, the expression of optimal phase shifts is derived in a closed-form, which reveals that the performance gain brought by RIS is proportional to the number of intelligent elements, while inversely proportional to the distance from vehicle-to-BS, in a quadratic form. Moreover, in the case of discrete phase shifts, an intelligent algorithm is proposed for the beamforming design at RIS. Afterwards, with the objective to maximize the ergodic capacity of the V2I link, the optimal power allocation is also proposed. Simulation results confirm the accuracy of the proposed resource allocation strategy, and that the system performance in terms of the ergodic V2I capacity can be significantly improved by the RIS. [ABSTRACT FROM AUTHOR]

Conventional direction-of-arrival (DOA) estimation algorithms are sensitive to array imperfections and outliers, making it challenging to realize accurate estimates in real applications. Facing the challenge, we propose a robust variational Bayesian inference based DOA estimation algorithm using the linear sparse array in this paper, where accurate DOA estimation with increased number of degrees of freedom (DOFs) is realized. With the mixture of von Mises model, a prior-grid scheme is further proposed to alleviate the computational burden introduced by the Bayesian variational inference framework. Since there is no restriction on the prior knowledge of the number of sources, the proposed algorithm is friendly to actual scenarios. Simulation results demonstrate the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

In this paper, we consider an energy efficient resource allocation technique for a hybrid time division multiple access (TDMA) - non-orthogonal multiple access (NOMA) system. In such a hybrid system, the available time for transmission is divided into several sub-time slots, and a sub-time slot is allocated to serve a group of users (i.e., cluster). Furthermore, signals for the users in each cluster are transmitted based on the NOMA approach. With NOMA, multiple users can be served simultaneously through utilizing power domain multiplexing at transmitter and successive interference cancellation (SIC) at receiver. In this paper, to maximize the energy efficiency (EE), we jointly allocate both the available time slots and the available transmit power in the hybrid TDMA-NOMA system. In particular, we formulate an EE maximization (EE-Max) problem aiming to maximize the overall EE of the system with a per-user minimum rate and transmit power constraints. However, this joint optimization problem is non-convex in nature, and thus, cannot be solved directly. Therefore, we develop an iterative algorithm by approximating the original problem into a convex one with sequential convex approximation (SCA) and a novel second-order cone (SOC) approach. Simulation results demonstrate that the performance of the proposed hybrid TDMA-NOMA system with joint resource allocation outperforms the system with equal time allocation in terms of the overall EE. Simulation results further confirm that the proposed iterative approaches with SCA and SOC techniques converge within a few number of iterations while yielding the solution to the original non-convex problem. [ABSTRACT FROM AUTHOR]

Efficient connectivity in cellular-connected unmanned aerial vehicles (UAV)s is limited by scarcity of the radio spectrum and strong inter-cell interference (ICI). To address these issues, we propose an aerial-terrestrial network non-orthogonal multiple access (ATN-NOMA) scheme. In this proposed scheme, we pair the aerial user (AU) and terrestrial user (TU) in a NOMA setting to leverage their asymmetric channel gains and rate demands in downlink communications. In ATN-NOMA, the strong ICI issue at the AU receiver is further managed by an elevation-angle based user association, equipping the AU with an adjustable beamwidth directional antenna, and forming a beamforming among the coordinated terrestrial base stations (BS)s. We then obtain the optimal beamwidth and suboptimal power allocation so that the TUs’ sum-rate is maximized subject to the AU’s Quality-of-Service (QoS) requirement. The corresponding optimization problem is non-convex in which we exploit the structure of the problem and apply successive convex approximation (SCA) to obtain a suboptimal solution. We then derive the statistical properties, which consequently enable us to estimate the aggregated ICI. In cases where no interfering BSs have the same elevation angle as the coordinated BSs, we further approximate the AU’s outage probability. We then compare the TUs’ sum-rate and the outage probability of the ATN-NOMA with multiple existing schemes. Extensive simulation results show that our proposed ATN-NOMA scheme outperforms existing schemes by 52-91% in terms of the sum-rate, and its analytical outage probability can be as low as the order of $10^{-17}$. Furthermore, we show that the pairing of AU and TU in multi-cell networks remains beneficial, subject to effective mitigation of ICI. [ABSTRACT FROM AUTHOR]