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Dual-hop communication systems are known to extend coverage and reduce transmit power in scenarios where one-hop communication is not possible. The $\alpha -\eta -\mu$ fading distribution is a general fading distribution that can be reduced to other fading distributions like Rayleigh, Nakagami- $m$ , $\alpha$ - $\mu$ , and $\eta$ - $\mu$. In this paper, we study the statistics of the end-to-end signal to noise ratio (SNR) of a dual-hop amplify and forward system with semi-blind relay over independent but not necessarily identical $\alpha -\eta -\mu$ fading channels. Specifically, we derive an expression for the $n$ th moment of the end-to-end SNR. The derived expression is then utilized to find the average value, the amount of fading, and the ergodic capacity of the end-to-end SNR. Numerical results are provided and compared to simulations to validate the derived expressions. [ABSTRACT FROM AUTHOR]

In this paper, we exploit the concept of array pattern synthesis to design cluster beamformers with partial channel state information for non-orthogonal multiple access downlink multiuser transmission in millimeter wave channels. Using the information on angle-of-departure region for each user, we formulate an array pattern nulling problem to design each cluster beamformer for minimizing inter-cluster interferences, which is solved by using semidefinite programing. Further, we exploit linear programing to solve a power allocation problem for each user in the cluster to achieve a target signal-to-interference-and-noise ratio. Numerical results are presented to verify the validity of the proposed schemes. [ABSTRACT FROM AUTHOR]

A major challenge in designing a spectral co-existence between radar and communication systems is how to simultaneously provide efficient utilization of the shared spectrum while maintaining a reliable performance for both systems. Due to its flexibility in using linear independent waveforms and superiority in terms of target detection and estimation, the collocated multiple-input-multiple-output (MIMO) radars provide a paramount capability in realizing spectrum sharing with communication systems. In this paper, we consider the use of joint transmit and receive beamformers for both the MIMO radar and MIMO communication systems. Specifically, we design a two-tier alternating optimization spectrum sharing framework that is based on interference alignment (IA) approach. The effectiveness of spectrum sharing between radar and communication systems is guaranteed by mitigating the mutual interference signals in the shared spectral band. Subsequently, motivated by the excellent performance provided by IA in different wireless network scenarios, we propose a spectrum sharing framework that consists of a main iterative algorithm with two subalgorithms included within its operation. The first subalgorithm is used to maximize the signal-to-interference-plus-noise ratio of the radar system, whereas the second one is utilized to maximize the average sum-rate of the communication system. The main iterative algorithm is proposed to jointly optimize the transmit and receive beamforming filters of both systems by performing alternating optimization between the two subalgorithms. The convergences of the proposed algorithm and its subalgorithms are numerically verified. Simulation results are provided to confirm the superiority of the proposed framework for both systems. [ABSTRACT FROM AUTHOR]

Prior works on performance analysis for cognitive radio networks often assume perfect channel state information (CSI), which may not be readily available. This paper investigates the effects of the outdated CSI on the performance of a dual-hop multi-antenna multi-relay spectrum sharing system. To exploit the benefits of available multiple antennas, collaborative zero-forcing beamforming is considered at the secondary user (SU) source node with the outdated CSI and maximum ratio combining diversity reception at the destination node. The $N$ th best relay selection strategy is adopted at the relays. Analytical outage probability and bit-error rate expressions are derived for the SU. Moreover, we examine the high signal-to-noise ratio regime and present closed-form expressions for the asymptotic outage probability and asymptotic bit-error rate with and without feedback delay. In addition, we derive the closed-form ergodic capacity expression for the special case of our considered system, and analyze the effects of delay on the capacity. Furthermore, the closed-form outage probability expression for the primary user is obtained and the impact of delay on the interference on the primary user is investigated. Monte Carlo simulations are carried out to verify our analysis. [ABSTRACT FROM AUTHOR]

Ambient backscatter (AmBack) communication, also called “modulation in the air,” has drawn growing interest by both academia and industry recently. In this paper, we investigate and analyze an AmBack system, where the user is equipped with an AmBack circuit at the transmitter and maximum ratio combing at the receiver. By harvesting power from the surrounding radio frequency source, the circuit operation and the signal backscattering can be supported. However, if there is not enough harvested power for the circuit operation, the signal backscattering will be suspended. Different from previous works on AmBack, an adaptive scheme is proposed to opportunistically exploit the residual or full user battery power for insufficient harvested power so that the signal backscattering is always available. However, there is no exact closed-form expression for the outage probability, and its approximation is obtained to facilitate our analysis. For comparison, the traditional non-adaptive scheme is also analyzed, and a closed-form expression for the outage probability is derived. In order to get more insight into both schemes, asymptotic outage performance is also derived when the number of receiver antennas/the noise power is sufficiently large/low. Simulation results demonstrate the tightness and the correctness of the derived outage probabilities, and show that the proposed adaptive scheme can significantly outperform the traditional non-adaptive scheme. [ABSTRACT FROM AUTHOR]

To improve the secrecy performance of the untrusted relay system with a multiple-antenna destination, a novel full-duplex destination jamming scheme with optimal antenna selection (FDJ-OAS) is proposed in this paper. The approximate closed-form expressions of the average achievable secrecy rate are derived for the proposed scheme. To attain more insightful results, the approximated closed-form expressions for the average achievable secrecy rate and the optimal power allocation factor for FDJ-OAS are derived in the case with a large-scale antenna array, and simple power allocation solutions are also provided in the high and low SNR regimes, respectively. Furthermore, we derive the asymptotic expressions for the secrecy outage probability under different asymptotic conditions for the proposed scheme, and the analysis results indicate that the secrecy diversity order of FDJ-OAS is significantly superior to that of the comparable schemes. Simulation results show that the analytical curves match well with the simulation results, and the advantage of FDJ-OAS is also clearly demonstrated through performance comparison. [ABSTRACT FROM AUTHOR]

In this paper, we first propose a joint user and relay selection (JURS) scheme to enhance physical layer security in a multi-user multi-relay network, where the best pair of the user and relay that maximizes the user-to-destination signal-to-interference-to-noise ratio (SINR) is jointly selected. We analytically examine the secrecy outage probability (SOP) of this scheme, based on which the optimal power allocation between the useful signal and artificial noise at the users is determined in order to minimize the corresponding SOP. To avoid the high complexity of the joint selection, we also propose a separate user and relay selection (SURS) scheme, where one relay is firstly selected to maximize the relay-to-destination SINR and a user is then selected to maximize the SINR from the user to the selected relay. We also derive the SOP of the SURS scheme and determine the corresponding optimal power allocation. As expected, the JURS scheme can outperform the SURS scheme. However, our examination also indicates that the low-complex SURS scheme can achieve similar secrecy performance as the high-complex JURS scheme under some specific conditions, e.g., when the number of users is much larger than that of the relays or when the average signal-to-noise ratio of user-to-relay channel is much higher than that of the relay-to-destination channel. [ABSTRACT FROM AUTHOR]

In this correspondence paper, we investigate the problem of user scheduling in a cooperative non-orthogonal multiple access (NOMA) system consisting of a base station, a weak user, and $K$ intermediate users. During each transmission, an intermediate user is scheduled to receive its own message and forward the message destined for the weak user. For this type of cooperative NOMA system, a novel scheduling scheme is proposed to achieve full diversity and scheduling fairness simultaneously. With the consideration that all channels experience independent but non-identically distributed Rayleigh fading, outage probabilities of the weak user and the scheduled intermediate user are derived in closed-form expressions. It is theoretically shown that the proposed scheme provides full diversity for both the weak user and the scheduled intermediate user. Furthermore, theoretical results also demonstrate that the proposed scheme schedules each intermediate user with the same probability 1/ $K$ , demonstrating that scheduling fairness is also guaranteed. [ABSTRACT FROM AUTHOR]

In this paper, we focus on a comprehensive dynamic adaptive streaming over HTTP (DASH) framework, which consists of video content analysis at the HTTP adaptive streaming server, joint optimization of segment switch and resource allocation at eNodeB, and playback information extraction at the client, to improve the quality of experience (QoE) of the DASH clients over long-term evolution networks. We explore the unique characteristics of each segment by establishing the size-time and size-distortion models based on the video packet information extracted from the encoder rather than modeling the entire video sequence by a fixed function. Video quality, stability, and playback continuity can be predicted and reflected by these constructed models. Considering the above three factors, we develop an accumulative QoE model by calculating and predicting the QoE factors of each segment. Then, the entire framework is formulated as a mixed-integer non-linear programming mathematical model to maximize the total QoE of the DASH clients, where decisions on resource allocation and video segment switch are jointly optimized in a semi-synchronous centralized mode. Resource allocation consists of resource block assignment and modulation and coding scheme selection rather than only determining the resource utilization percentage. To perform the optimization, we develop a low-complexity heuristic algorithm that decomposes the original problem into multiple subproblems. The simulation results show that our proposed algorithms can efficiently improve the QoE level compared with other existing algorithms. [ABSTRACT FROM AUTHOR]

In this paper, we consider the joint power and modulation optimization in two-user non-orthogonal multiple access (NOMA) channels based on error-rate performance criterion and finite-alphabet inputs. Specifically, with joint maximum-likelihood detection being employed at each user's receiver, the users’ transmission power levels are jointly determined with the 4-QAM constellation of one of the users being rotated such that the probability of dominant pairwise error event in the NOMA channel is minimized. Toward solving the joint power and modulation problem, our results are twofold. First, with $M$ antennas at the receiver, closed-form expressions for the optimal angles as a function of $M$ , the channel coefficients, and the users’ power levels are derived. Second, closed-form expressions are derived for the joint power allocation with optimal rotation by casting the joint optimization as a piecewise convex optimization problem over its sub-domains. Using the proposed joint optimization, the error-rate performance of NOMA improves significantly and it outperforms traditional NOMA power allocation methods for the selected transmission rates. The proposed approach thus represents a rather distinct approach in NOMA optimization, and it is applicable in the uplink NOMA where users share the same time/frequency channel or in the downlink NOMA where users are multiplexed in the power domain. [ABSTRACT FROM AUTHOR]

In the development of analog signal compressive sensing (CS), the degradation of reconstruction performance under noise is the main bottleneck because the CS framework is very sensitive to noise. This paper proposes an adaptive channelization-based orthogonal matching pursuit algorithm (C-OMP) combining the channelization and the adaptive iteration methods. The proposed C-OMP has two steps: channel screening and global iteration. Based on the proposed method, the original signal can be recovered adaptively in high probability of success with fewer observations under the noise background. Simultaneously, the noise can be reduced as much as possible to enhance the output signal-to-noise ratio (SNR) by excluding the noise channel during the channel screening and separating noise atoms during the global iteration. The relationship between the probability of successful reconstruction and the number of observations is mathematically analyzed. Furthermore, the parameter settings, computational complexity, and output SNR are analytically evaluated. The simulation results confirm the analytical results and further demonstrate the effectiveness and advantages of the C-OMP in the noise environment. Overall, the proposed algorithm considerably improves the performance of the analog signal CS in the practical noisy environment. [ABSTRACT FROM AUTHOR]

In this correspondence paper, we design a massive nonorthogonal multiple access (NOMA) scheme with delay provisioning for cellular internet-of-things. In the context of massive access, the severe interuser interference decreases the quality of the received signal, such that it is a nontrivial task to provide a delay provisioning for heterogeneous wireless services. To solve this challenge, we propose a massive NOMA scheme to meet the delay requirements of a large number of users by exploiting the properties of rateless codes. Especially, we present a power allocation algorithm to minimize the power consumption while achieving delay-constrained massive access. Finally, simulation results validate the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the secrecy performance of a dual-hop cooperative relaying network, where a source node communicates with a destination node via an amplify-and-forward relay node and via direct link in the presence of a passive eavesdropper. In this network, the eavesdropper exploits the advantages of both direct and relay links. We assume that the source, relay, and eavesdropper nodes are mobile, and the destination node is stationary. Moreover, we consider that the source-relay, relay-destination, and source-destination links experience Rayleigh fading, whereas source-eavesdropper and relay-eavesdropper links undergo double-Rayleigh fading. Examples of such scenario are encountered in vehicle-to-vehicle communication and/or vehicle-to-infrastructure communication under cooperative vehicular networks. In particular, we derive new tight closed-form expressions for the secrecy outage probability and ergodic secrecy capacity of the considered system under mixed fading environments. In addition, we present an effective secrecy diversity order within the main-to-eavesdropper ratio ranges of practical interest, and demonstrate that the secrecy diversity order of 2 can be achieved. Finally, the numerical and simulation results corroborate our analytical findings, and show the occurrence conditions for secrecy outage probability and ergodic secrecy capacity floors, and impacts of channel conditions and relay and eavesdropper positions on the system secrecy performance. [ABSTRACT FROM AUTHOR]

In this paper, we study the connectivity between two fixed terminal nodes within a geometrically bounded network of relay nodes and fixed infrastructure nodes. We assume that a communication path, between the terminal nodes, can be established by direct connection (1-hop), via a relay node (2-hop) or via the infrastructure network; the choice is based on link viability in a Rayleigh fading environment. We adopt a probabilistic approach to our analysis considering a homogeneous spatial distribution of relay nodes and an inhomogeneous spatial distribution of infrastructure nodes. Our analysis of the relationship between relay and infrastructure densities for a prescribed outage probability shows that reliance on infrastructure connectivity can be appreciably reduced by employing direct and 2-hop connectivity. We further show that, as the relay density increases, optimum connectivity is achieved by employing a non uniform spatial thinning of the infrastructure, which is dependent upon the geometric extent of the network. Our analysis provides an insight into multi-mode connectivity in bounded network domains and has application in many fields including cellular and vehicle-to-infrastructure (V2X), which are often modelled as having finite extent and where reducing the reliance on fixed infrastructure can effectively reduce operating expenditure costs. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new adaptive link layer protocol that consists in adapting packet length and Modulation and Coding Scheme (MCS) to Average Signal to Noise Ratio or instantaneous SNR (ISNR). Adaptive MCS and adaptive packet length offer higher throughput than adaptive MCS and fixed packet length as considered in previous studies. The best strategy is to adapt the MCS and packet length to ISNR. Adaptive MCS and adaptive packet length offer 1–2 dB gains with respect to adaptive MCS and fixed packet length. The proposed adaptive link layer protocol has been implemented by quantizing the SNR on the feedback channel over four bits and yielding close results to unquantized SNR. [ABSTRACT FROM AUTHOR]

In this paper, we study a secure cooperative transmission system in which a transmitter (Alice) intends to send a secret message to an authorized receiver (Bob), with the aid of a friendly private cooperative jammer (Oscar), in the presence of a malicious eavesdropper (Eve). Specifically, artificial noise (AN) assisted secrecy beamforming is utilized for secure transmission. Under the imperfect channel state information (CSI) of legitimate channels and the statistic CSI of illegitimate channels, the optimal power allocation ratio between the information-bearing signal and the AN signal for maximizing secrecy rate is derived. Through mathematical analysis, we notice that the high channel estimation error is greatly detrimental to the realization of the positive secrecy rate in secure system. For overcoming this drawback, back propagation neural network (BPNN) is employed for a high accuracy channel estimation to simulate a realistic security communication scenario. The numerical results show that the channel estimation errors result in a decrease in secrecy rate, but the BPNN channel estimator still can guarantee secure transmission that verifies the feasibility of the application of physical layer security. Analytical derivations and numerical simulations are presented to validate the correctness of obtained expressions and our analysis. [ABSTRACT FROM AUTHOR]

For an uplink sparse code multiple access (SCMA) system, a codebook-domain superposition transmission can be applied to increase the multiplexing gain by efficient utilization of the codebooks as multiple access resources. However, the destructive collision of superposed codewords can restrict the performance improvement of the system because of the increasing interlayer interferences. In this paper, we analyze the effects of the interlayer interferences on the bit error rates, and optimize the SCMA codebooks that can mitigate the interlayer interferences. Simulation results show that the optimized codebooks can provide a noticeable gain to improve the performance of uplink SCMA systems applied with superposition transmission. [ABSTRACT FROM AUTHOR]

This paper analyzes statistical properties of the Poisson line Cox point process useful in the modeling of vehicular networks. The point process is created by a two-stage construction: a Poisson line process to model road infrastructure and independent Poisson point processes, conditionally on the Poisson lines, to model vehicles on the roads. We derive basic properties of the point process, including the general quadratic position of the points, the nearest distance distribution, the Laplace functional, the densities of facets of the Cox–Voronoi tessellation, and the asymptotic behavior of the typical Voronoi cell under vehicular densification. These properties are closely linked to features that are important in vehicular networks. [ABSTRACT FROM AUTHOR]

In hybrid digital-analog (HDA) systems, resource allocation has been utilized to achieve the desired distortion performance. However, existing studies on this issue assume error-free digital transmission, which is not valid for fading channels. With time-varying channel fading, the exact channel state information is not available at the transmitter. Thus, random outage and resulting digital distortion cannot be ignored. Moreover, rate allocation should be considered in resource allocation, since it not only determines the amount of information for digital transmission and that for analog transmission but also affects the outage probability. Based on above-mentioned observations, in this paper, we attempt to perform joint rate and resource allocation strategies to optimize system distortion in HDA systems over fading channels. Consider a bandwidth expansion scenario where a memoryless Gaussian source is transmitted in an HDA system with the entropy-constrained scalar quantizer. First, we formulate the joint allocation problem as an expected system distortion minimization problem where both analog and digital distortions are considered. Then, in the limit of low outage probability, we decompose the problem into two coupled subproblems based on the block coordinate descent method and propose an iterative gradient algorithm to approach the optimal solution. Furthermore, we extend our work to the multivariate Gaussian source scenario where a two-stage fast algorithm integrating rounding and greedy strategies is proposed to optimize the joint rate and resource allocation problem. Finally, simulation results demonstrate that the proposed algorithms can achieve up to 2.3 dB gains in terms of the signal-to-distortion ratio over existing schemes under the single Gaussian source scenario, and up to 3.5 dB gains under the multivariate Gaussian source scenario. [ABSTRACT FROM AUTHOR]

In this paper, we study an unmanned aerial vehicle (UAV)-enabled wireless sensor network, where a UAV is dispatched to collect the sensed data from distributed sensor nodes (SNs) for estimating an unknown parameter. It is revealed that in order to minimize the mean square error for the estimation, the UAV should collect the data from as many SNs as possible, based on which an optimization problem is formulated to design the UAV's trajectory subject to its practical mobility constraints. Although the problem is nonconvex and NP-hard, we show that the optimal UAV trajectory consists of connected line segments only. With this simplification, an efficient suboptimal solution is proposed by leveraging the classic traveling salesman problem and applying convex optimization techniques. Simulation results show that the proposed trajectory design achieves a significant performance gain in terms of the number of SNs whose data are successfully collected, as compared with other benchmark schemes. [ABSTRACT FROM AUTHOR]

Array beamforming (BF) has received considerable attention as a means of anti-jamming by combining desired signals constructively and jamming signals destructively. However, even with BF, the state-of-the-art reactive jammer (RJ) can easily detect the target channels from the leakage of the transmit power and concentrate its own power to the detected band to degrade communication performance. In this paper, we attempt to mitigate this problem by exploiting fake information, the so-called decoy signal, and proper BF at the transmitter and the receiver, and show that it is possible to deceive the RJ into allocating a large portion of its own power to the decoy signal. In this regard, we attempt to maximize the signal-to-jamming-plus-noise power ratio (SJNR) at the receiver and the signal-to-leakage power ratio at the transmitter by optimizing the BF strategy. Through numerical simulations measuring the SJNR and the channel capacity, we demonstrate the effectiveness of the proposed BF scheme, especially in high-power RJ environments. [ABSTRACT FROM AUTHOR]

In this paper, we compare the performance of time-switching relaying (TSR) and power-splitting relaying (PSR) protocols in two-hop networks with a battery-assisted energy-harvesting (EH) amplify-and-forward relay. In this battery-assisted relay framework, the EH relay augments the harvested energy with energy drawn from a battery. Using expressions derived for throughput and average battery energy consumption, we investigate maximization of throughput for given battery energy availability per time slot and minimization of battery energy consumption for target throughput requirement. When only statistical channel knowledge is available, PSR results in better throughput performance at practical signal-to-noise ratios. However, in the typical low battery energy and low target throughput regime, it is TSR that is more battery energy efficient. When second-hop instantaneous channel knowledge is available, we observe dramatical energy savings that increases lifetime of nodes. Simulation results are presented to demonstrate accuracy of the derived expressions. [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]

In this correspondence paper, we present novel results related to the error performance of coherent systems in the presence of the imperfect carrier phase estimation over Gamma shadowed Nakagami- $m$ fading environment. Taking the Tikhonov-distributed phase error process into account, binary and quaternary phase-shift keying signal detection is analyzed. Based on the Maclaurin series expansion of the complementary error function, approximated closed-form expressions for the bit error rate (BER) are derived. These expressions are simplified to those already reported in literature, which are valid in the case without shadowing. The asymptotic closed-form expressions for noisy reference loss are also presented. We examine the effect of phase-locked loop parameters on both BER and noisy reference loss. Analytical results are validated by independent Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

One of the main challenges in orthogonal frequency division multiplexing (OFDM)–subcarrier index modulation (SIM) systems is the huge amount of resources required to obtain channel state information at the receiver side. In this paper, a differential subcarrier index modulation (DSIM) scheme is proposed, which entirely avoids the need for any channel knowledge at the receiver side. As such, time and energy resources spent in the channel estimation process are perceived. In DSIM, part of the transmitted block is modulated through ordinary signal modulation, whereas the second part is transmitted by selecting a specific permutation of the active subcarriers. The transmitted signals are designed to facilitate differential demodulation at the receiver side. A derivation is conducted for the average bit error probability of DSIM and an upper bound expression is obtained. Derived theoretical expression is substantiated through Monte Carlo simulation results. Reported results reveal that differential demodulation degrades the error performance of coherent SIM by nearly 4 dB in signal-to-noise-ratio. [ABSTRACT FROM AUTHOR]

Coding-based slotted ALOHA is one effective way to guarantee communication reliability for multislot messages when the acknowledgment mechanism is difficult to use. Prior to the transmission of an $m$ -slot message, $n$ single-slot coded packets are constructed using erasure-correcting codes, such that any $m$ successfully received coded packets can yield a correct reception of the message. This paper considers the coding-based slotted ALOHA for one-hop broadcasting with delivery deadline $D$ (in unit of slot), which requires every message to be sent out within the deadline since its arrival on the head of the queue. We derive exact closed-form expressions for important performance metrics for any $1\leq m \leq n \leq D$. In particular, a simple closed-form suboptimal transmission probability for the reliability maximization is then heuristically proposed, and moreover, the minimum value of $n$ under reliability constraint is investigated. [ABSTRACT FROM AUTHOR]

An onboard mobile communication system can be operated when the height of an aircraft is above 3000 m and the maximum equivalent isotropic radiated power outside an aircraft is below $-$ 13 dBm for 200 kHz bandwidth in a 1800 MHz system based on the Electronic Communications Committee reports. However, in order to provide seamless connectivity for aircraft passengers, the onboard communication system should be in operation in every phase of the flight. Therefore, in this paper, the compatibility of an in-cabin long term evolution (LTE) 1800 MHz femto cellular system with the current terrestrial LTE 1800 systems are investigated when an aircraft is stationary on the ground. Edinburgh Airport in Scotland and the existing LTE cells that provide network coverage at the airport are modeled through a simulation platform. Three Airbus A321 aircraft are modeled, while stationary, in the parked position on the apron and an in-cabin LTE femto cellular system is deployed within each aircraft. Signal-to-noise-plus-interference ratio and power leakage from the in-cabin evolved NodeBs in the downlink direction are considered as performance metrics to investigate the coexistence of the terrestrial and in-cabin systems. The simulation results show that the in-cabin LTE 1800 MHz femto cellular system can be operated without causing any significant interference to the existing terrestrial LTE 1800 MHz system while the aircraft is parked on the apron. However, it may be advisable to only operate the system when the aircraft doors are closed, in order to mitigate any possible interference effect on the users who are boarding the aircraft through the passenger boarding bridge. According to the results shown for a linear apron concept, the legislation governing the onboard mobile communication systems should be revised, in order to pave the way to the goal of seamless mobile connectivity in the next generation of communication systems. [ABSTRACT FROM AUTHOR]

Accommodating the fast-growing multimedia traffic demands at low cost is critical to ensure the future competitiveness of cellular networks. Cognitive radio (CR) emerges as a key technology to enhance radio spectrum utilization and provides an effective solution to meet critical spectrum demands for future mobile multimedia traffics. In this paper, we investigate reliable downlink video transmission in underlay cellular CR networks by means of cooperative diversity. We use RaptorQ code as the Application Layer Forward Error Correction scheme to combat packet loss arising from the primary user interference and other channel conditions such as channel fading. For implementing cooperative diversity, we select the best relay based on the ability of successful decoding using RaptorQ and the value of signal-to-interference-plus-noise ratio at the destination node. Moreover, for efficient primary user channel utilization, the selected relay performs merging of the encoding coefficients before forwarding to the destination. We evaluate the performance of the proposed framework under various time sharing scenarios between the direct and best indirect transmission links in terms of decoding overhead, probability of decoding failure, and peak signal-to-noise ratio of the received videos. Numerical results show that the proposed scheme outperforms the baseline transmission scheme and conventional relaying schemes using Amplify-and-Forward and Decode-and-Forward transmission techniques. [ABSTRACT FROM AUTHOR]

This paper studies the statistical channel state information (S-CSI) acquisition problem in the nonstationary massive multiple-input multiple-output (MIMO) environment, where both the instantaneous and statistical channel states are time varying. First, we set up a hidden statistical channel state Markov model (HSCSM model). Then, the parameter of the HSCSM model is estimated through the observed sequence of received signals. Next, based on the HSCSM model and its estimated parameter, the S-CSI is obtained through a maximum a-posteriori decision process. Simulation results show that an accurate S-CSI acquisition can be achieved by the proposed approach in the nonstationary massive MIMO environment. In addition, the estimation accuracy rate of the proposed approach increases with the length of observation sequence as well as the number of antennas, where a tradeoff between them exists given a limited computing ability/storage space. [ABSTRACT FROM AUTHOR]

In this paper, we consider secure transmission of a private file, which comprises multiple packets. A network-coding assisted automatic-repeat-request (ARQ) scheme is proposed to improve the security at both file level and packet level. Specially, the ARQ protocol degrades the intercept probability of the whole file at the eavesdropper, while the network coding guarantees the per-packet security. The closed-form intercept probability and outage probability of the whole file and each packet are analytically presented, and we then investigate the tradeoff between the security performance and the outage probability. The proposed scheme is further extended to the cooperative ARQ scenario, and simulation results are provided to corroborate our theoretical findings. [ABSTRACT FROM AUTHOR]

Spectrum sensing in next-generation wireless radio networks is considered a key technology to overcome the problem of spectrum scarcity. Unfortunately, many approaches to spectrum sensing do not work well in low signal-to-noise ratio (SNR) environments. This paper proposes and analyzes a new algorithm named kernelized generalized likelihood ratio test (KGLRT) for spectrum sensing in cognitive radio systems to overcome this problem. Effectively, KGLRT uses a nonlinear kernel to map input data onto a high-dimensional feature space; then, the widely accepted (linear) generalized likelihood ratio test is used for hypothesis testing. This new algorithm gives a gain of 4 dB in SNR over its linear counterpart. A theoretical analysis for this algorithm is given for the first time and is shown analogous to algorithms used in image signal processing. The detection metrics are found to be concentrated random variables; furthermore, the probability distributions of the detection metrics are proved to follow the F -distributions, which agree with the results obtained using the concentration inequality. The analytical thresholds are derived for target false-alarm probabilities. The thresholds are independent of noise power; thus, the proposed algorithm can overcome noise uncertainty issues at very low SNR levels. Simulations validate the theoretical results. [ABSTRACT FROM AUTHOR]

This paper considers a secure nonorthogonal multiple access system, where confidential messages are transmitted from a base station to multiple legitimate destinations and wiretapped by multiple illegitimate receivers. It is assumed that all the channels experience a Nakagami- $m$ fading model and all the nodes are equipped with multiple antennas, respectively. Both noncolluding and colluding eavesdroppers are considered, respectively. A max–min (MM) transmit antenna selection (TAS) strategy is adopted to improve the secrecy performance of the target system, in which both users in user paring are considered simultaneously. In particular, closed-form expressions for the cumulative distribution function of the signal-to-interference-noise ratio at the legitimate user are derived first. Then, we obtain the exact and asymptotic analytical results in a closed form for the secrecy outage probability of an MM TAS scheme. Monte Carlo simulation results are presented to corroborate the correctness of the analysis. The results show that the secrecy diversity order is zero and nonzero for fixed and dynamic power allocations, respectively. [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]

This paper investigates the scenario in which a weak desired signal reaches a poorly selective receiver along with a high-powered pulsed radar occupying a neighboring channel. Traditionally, an automatic gain control (AGC) is used to fit the high-powered radar into the dynamic range of the receiver. However, this approach desensitizes the receiver because it also sacrifices the signal-to-noise ratio (SNR) of the desired signal. We propose the use of an auxiliary receive path to address this problem of strong neighboring channel signals. In this method, receiver gain is not lowered to avoid clipping. Instead, the strong signal is allowed to clip and distort the desired signal. This paper shows that only a subset of the symbols contained in the desired signal will be distorted; hence, redundancy within the desired signal (due to forward error correction) can be exploited to “fill the gaps” created by the distortion. The auxiliary path samples the envelope of the strong neighboring-channel signal and informs the decoder about which symbols are distorted (or “bad”) and which symbols are not distorted (or “good”). This additional information is shown to improve the estimation performance of the decoder in the presence of high-powered neighboring-channel radar. Using simulation and hardware-based experiments, it is shown that auxiliary-path-based receivers can obtain a significantly better throughput performance than AGC-based receivers. [ABSTRACT FROM AUTHOR]

Multipath fading can degrade the performance of a wireless communication system significantly when the data rate is as high as those systems beyond Long-Term Evolution Advanced (LTE-A). To combat the multipath-fading effects, orthogonal frequency-division multiplexing (OFDM) techniques have been extensively studied and used in existing systems. However, another effective method to combat multipath fading is a code-division multiple access (CDMA) scheme, which has not been extensively investigated for relay network communication systems. This paper considers uplink CDMA relay networks (consisting of multiple sources, multiple relays, and a single destination) and downlinks (consisting of a combined source, multiple relays, and multiple destinations) under multipath fading. The objective of this paper is to propose a unique, simple, and effective method of finding optimum nonbinary pseudo noise (PN) spreading and despreading sequences employing a maximum signal-to-interference-plus-noise ratio (SINR) criterion and channel state information (CSI). This paper also examines the sensitivity of the proposed schemes to 1-bit quantization, mistiming alignment, wideband jamming, and imperfect CSI. Simulation results verify that the proposed method shows much faster convergence in finding optimum PN sequences and better performance than existing schemes under the same environment. [ABSTRACT FROM AUTHOR]

Recently, there has been strong interest in exploiting advanced physical-layer techniques to increase the capacity of multihop wireless networks. Several recent studies have emerged with a particular focus on successive interference cancelation (SIC) as an effective approach to allow multiple adjacent concurrent transmissions to coexist, enabling multipacket reception. This paper is in line with those efforts in that we attempt to understand the benefits of SIC on the throughput performance of wireless networks. We consider a cross-layer design for the joint congestion control, routing, and scheduling problem in wireless networks where nodes are endowed with SIC capabilities and under the general physical signal-to-interference-plus-noise ratio (SINR) interference model. We use duality theory to decompose the joint design problem into congestion control and routing/scheduling subproblems, which interact through congestion prices. This decomposition enables us to solve the joint cross-layer design problem in a completely distributed manner. Given that the problem of scheduling with SIC and under the SINR interference regime is NP-hard, this paper develops a decentralized approach that allows links to coordinate their transmissions and, therefore, efficiently solve the link scheduling problem. Numerically, we show that our decentralized algorithm achieves similar results to those obtained by other centralized methods (e.g., greedy maximal scheduling). We also study the performance gains SIC brings to wireless networks, and we show that flows in the network achieve up to twice their rates in most instances, in comparison with networks without interference cancelation capabilities. These gains are attributed to the capabilities of SIC to better manage the interference and promote higher spatial reuse in the network. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a new architecture and performance analysis for beam index modulation (BIM) wireless communication implemented with the aid of analog beamforming. The BIM concept is presented in order to extend and adapt the spatial modulation concept to sparse wireless communication channel environments. It is shown that when compared with the conventional beamforming and SM strategies, the BIM system can achieve higher spectrum efficiency in high signal-to-noise ratio and non-line-of-sight (nLoS) sparse channel scenarios. Furthermore, different to the previous spatial scattering modulation (SSM) work the proposed BIM architectures have reduced hardware complexity, and, importantly, in some nLoS sparse channel conditions the BIM can also outperform the SSM. The above findings were further validated by some demonstrative experiments that were conducted at 10 GHz. [ABSTRACT FROM AUTHOR]

As an emerging paradigm, device-to-device (D2D) communication has the capability to complement and enhance the conventional cellular network by offering high spectral and energy efficiency. However, the problem of cochannel interference makes the resource allocation very complex and challenging in underlay D2D communication networks. This paper proposes a novel joint power control and resource scheduling scheme to enhance both the network throughput and the users’ fairness of the underlay D2D communication networks. Unlike other previous work in this area, our scheme aims at maximizing the sum of all users’ proportional fairness functions, while simultaneously taking into account factors such as fairness, signal-to-interference-plus-noise ratio requirements, and severe interference. The proposed scheme offers a practical solution because it works for lengthy time slots, a realistic scenario for the underlay D2D communication system. We also take into consideration the time-varying feature of user's channel condition in our proposed solution. Numerical results confirm that our proposed scheme not only dramatically improves the system throughput, but also boosts the system fairness while guaranteeing the Quality-of-Service levels of all D2D users and cellular users. [ABSTRACT FROM AUTHOR]

This paper investigates outage performance analysis and beamforming designs of a dual-hop multiple-input multiple-output (MIMO) amplify-and-forward (AF) relay channel with hardware impairments. We derive analytical closed-form expressions of the exact outage probability with fixed-gain and variable-gain relaying beamforming schemes. Moreover, asymptotic outage probability expressions are analyzed at high signal-to-noise ratio (SNR), which show that how hardware impairments and the number of relay antennas affect the system performance. We find that the outage probability in both relaying beamforming schemes has lower bounds with the increase of the SNR. Especially in the fixed-gain relaying beamforming scheme, we obtain a simple floor of the outage probability that is a monotone increasing function of hardware impairments’ level. To further compensate the performance loss brought by hardware impairments, we optimize the beamforming matrix for the dual-hop MIMO AF relay network by maximizing the end-to-end signal-to-noise-and-distortion ratio with the relay's power constraint. We derive optimal beamforming designs for sum-power constraint and for per-antenna power constraints. Our results show that the performance of the variable-gain relaying is superior to the fixed-gain relaying, especially for the case with varying scaling factor of the relay beamforming matrix. It is also shown that more performance gains can be attained with the proposed optimal beamforming designs. [ABSTRACT FROM AUTHOR]

The extensive study of transmit antenna (TA) subset selection (TAS) in the context of spatial modulation (SM) has recently revealed that significant performance gains are attainable compared to SM systems operating without TAS. However, the existing TAS techniques conceived for SM were studied by considering a frequency-flat channel, which does not represent practical frequency-selective channels. In this paper, we address this open problem by designing TAS schemes for zero-padded single-carrier SM systems. Specifically, we employ a partial successive interference cancellation (SIC) receiver and invoke Euclidean distance based TA subset selection (ED-TAS) for each of the subchannels. Furthermore, we show using a theoretical analysis that the parallel subchannels obtained are nearly identical, which enables us to employ majority logic decision to obtain a single TA subset to be used in all the subchannels. The computational burden is additionally reduced by restricting the number of subchannels over which the ED-TAS technique is invoked. Furthermore, the proposed TAS schemes are extended to the multiuser scenario. The theoretical insights developed are validated using simulation results. Specifically, a signal-to-noise ratio gain as high as 3 dB is observed in the single user scenario and about 1 dB in case of a two-user scenario upon employing our TAS. [ABSTRACT FROM AUTHOR]

Multihop relaying is used for increasing the communication range of cognitive radio networks. To circumvent the implied loss in throughput due to multihop relaying, in this paper, we propose incremental relaying (IR) for cooperative multihop cognitive radio networks (CMHCRNs). Two IR protocols that select a relay from the qualified relays (the relays whose received signal-to-noise-ratio (SNR) values are greater than a predefined threshold) in each hop are proposed to study the performance of the considered CMHCRN. The first protocol is named IR-based highest SNR (IR-HSNR) protocol that selects a relay with best SNR to the destination. Another one, termed IR-based highest transmit power (IR-HTP) protocol, selects a relay with the highest available transmit power. Expressions for the exact outage probability and throughput are derived for both routing protocols by considering both peak–power and peak–interference constraints. Moreover, closed-form expressions for floor values of outage probability and throughput are derived for both the protocols. It is shown through numerical results that throughput of the considered system shows a concave behavior with respect to number of relaying hops for both the proposed protocols. It is further observed that the performance of the IR-HSNR is superior to that of the IR-HTP, whereas the latter has lower implementation complexity. [ABSTRACT FROM AUTHOR]

This paper investigates the robust transmission design (RTD) of a multicell device-to-device (D2D) underlaid cellular network with imperfect channel state information (CSI). The bounded model is adopted to characterize the CSI impairment and the aim is to maximize the worst-case sum rate of the system. To protect cellular communications, it is assumed that the interference from all D2D transmitters to each base station (BS) is power-limited. It is first shown that the worst-case signal-to-interference-plus-noise ratio (SINR) of each D2D link can be obtained directly, while that of cellular links cannot be similarly found since the channel estimation error vectors of cellular links are coupled in the SINR expressions. To solve the nonconvex problem, the objective function of the original problem is replaced with its lower bound, and the resulted problem is decomposed into multiple semidefinite programming (SDP) subproblems, which are convex and have computationally efficient solutions. An iterative RTD algorithm is then proposed to obtain a suboptimal solution. Simulation results show that D2D communication can significantly increase the performance of the conventional cellular systems while causing tolerable interference to cellular users. In addition, the proposed RTD algorithm outperforms the conventional nonrobust transmission design greatly in terms of network spectral efficiency. [ABSTRACT FROM AUTHOR]

Antenna selection (AS) is a promising technology to substantially reduce the complexity of massive multiple-input multiple-output (MIMO) systems. However, spatial correlation and imperfect estimation of channel state information (CSI) are well known to have a direct impact on the capacity of feasible MIMO schemes. In this paper, a tight closed-form approximation of the ergodic capacity for correlated Rayleigh fading multiuser MIMO channels with receive AS and imperfect CSI is presented. The derived expression takes into account the spatial correlation at both link sides and channel estimation error at the receiver. It can be used for arbitrary numbers of users, antennas, and receive RF chains. Furthermore, a concise analytical capacity formula is derived in the high signal-to-noise ratio (SNR) region. Numerical results validate the accuracy of our closed-form expressions over different channel conditions and SNRs. The new capacity approximation extends the state-of-the-art and enables efficient performance evaluation of varied multiantenna applications including massive MIMO for 5G systems. [ABSTRACT FROM AUTHOR]

Recently, there has been an increasing interest in offloading the 3GPP LTE data by using device-to-device (D2D) communications between devices. However, the peer discovering is challenging, especially in the indoor environment, since traditional users use a cellular signal to find peers, leading to incurring interference to other cellular users. In this paper, we propose ROOMMATEs, a novel approach for indoor peer discovery process, which is the enabler for indoor D2D communications in long term evolution (LTE) networks. It is a centralized approach utilizing, but not limited to, the ubiquitous WiFi network/femtocell network, combining with eNodeB in order to deliver the best results. ROOMMATEs is an unsupervised, yet energy efficient algorithm that can find surrounding user equipments (UEs) while minimizing interference and consuming much less energy. Based on the results, ROOMMATEs proves to be highly energy efficient, saving on average 24% per UE and improving signal-to-interference-plus-noise ratio in order of tens of decibels compared to other approaches. Moreover, ROOMMATEs provides indoor place identification for UEs with high accuracy using a small number of observations. ROOMMATEs is robust to missing and noisy data, works with various UEs’ brands/models, and requires no user interactions. [ABSTRACT FROM AUTHOR]

Two-stage beamforming is a transmit strategy that uses two types of beamformers to reduce the feedback overhead of frequency-division-duplexing massive multiple-input multiple-output systems that are spatially correlated. In this paper, we present large system analysis of two-stage beamforming when a transmitter has limited channel information from feedback and when regularized-zero-forcing (RZF) is used as a second-stage beamformer. We consider two random-vector-quantization-based feedback schemes that can be respectively applied when users have perfect channel information or perfect effective channel information. For each feedback method, we analyze both expected signal-to-interference-plus-noise ratio (SINR) and expected rate loss and then characterize their bounds as a function of the number of feedback bits. From the characterization, we reveal that the sum rate of two-stage beamforming is very sensitive to the regularization parameter of RZF, especially when the number of feedback bits is limited. Motivated by this, we derive the optimal regularization parameter that maximizes the SINR of two-stage beamforming with limited feedback. Using simulations, we verify the tightness of the characterized bounds and quantify how the use of the optimal regularization parameter improves the sum rate of two-stage beamforming. [ABSTRACT FROM AUTHOR]

Communications systems operating in the millimeter-wave (mmWave) and terahertz (THz) band have been recently suggested to enable high data-rate vehicle-to-vehicle (V2V) communications in 5G and beyond wireless networks. However, massive deployment of such systems may lead to significant interference, affecting the performance of information transmission. While the multipath interference caused by the signal reflections from the road has been extensively discussed in the literature, the interference caused by the vehicles on the side lanes has been insufficiently studied so far. In this paper, using a combination of measurement, simulation, and analytical methods, we comprehensively characterize the interference from the side lanes in two typical deployments including highway and urban road environments for millimeter-wave and low terahertz bands. Both the multipath interference and direct interference from the transmitting vehicles on the side lanes are taken into account. As a result of our study, we reveal that: the interference from the side lanes can be well approximated using two-dimensional stochastic models without any significant loss of accuracy; and even when highly directional antennas are used there are special spatial configurations, where the interference may greatly affect the performance of the communication systems. We lately apply the developed models to estimate the signal-to-interference ratio and link capacity of mmWave/THz band V2V communications. [ABSTRACT FROM AUTHOR]

This paper analyzes the achievable rate of the single-carrier system with a frequency-domain equalizer (SC-FDE) under the receiver in-phase/quadrature phase (I/Q) imbalance in the radio frequency front-end. We consider linear schemes based on the minimum mean square error (MMSE), zero-forcing equalization, and a matched filter. We derive the achievable rate of the SC-FDE system hit by the I/Q imbalance for the mentioned scenarios. We show that depending on the value of I/Q imbalance parameters, the achievable rate of the system approaches a saturation level. To examine the validity of our analysis, we compare it with the simulation results and exhibit their consistency. We also consider nonlinear schemes such as an iterative block decision feedback equalizer (IB-DFE), which is an iterative scheme. We obtain the mutual information achieved by the IB-DFE in the high-signal-to-noise-ratio regime and after enough number of iterations. [ABSTRACT FROM AUTHOR]

The optimum designs of multihop networks operating in an interference-limited environment are studied in this paper. The objective is to identify the optimum operation parameters that can maximize the end-to-end throughput of a multihop link in the network. The optimum designs are performed with respect to two parameters, the number of hops, and the signal-to-interference ratio (SIR) threshold for successful transmission. Under a fixed total transmission power, more hops means shorter distance for each hop, but also less power per hop and longer delays. A higher SIR threshold can achieve a higher throughput by employing high-order modulations, but at the cost of a higher outage probability. We capture these tradeoff relationships by deriving the throughput, which is expressed as an explicit function of a number of system parameters. It is shown through theoretical analysis that the throughput is quasi-concave in the number of hops or the SIR threshold, and the optimum design parameters that can maximize the throughput are obtained analytically and verified through simulations. [ABSTRACT FROM AUTHOR]

In heterogeneous cellular networks (HetNets) with macro base station (BS) and multiple small BSs (SBSs), cell association of user equipment (UE) affects UE transmission rate and network throughput. Conventional cell association rules are usually based on UE received signal-to-interference-and-noise-ratio (SINR) without being aware of other UE statistical characteristics, such as user movement and distribution. User behaviors can indeed be exploited for improving long-term network performance. In this paper, we investigate UE cell association in HetNets by exploiting both individual and clustering user behaviors with the aim to maximize long-term system throughput. We model the problem as a stochastic optimization problem, and prove that it is PSPACE-hard. For mathematical tractability, we solve the problem in two steps. In the first step, we investigate UE association for a specific SBS. We use a restless multiarmed bandit model to derive an association priority index for the SBS. In the second step, we develop an index enabled association (IDEA) policy for making the cell association decisions in general HetNets based on the indices derived in the first step. IDEA determines a set of admissible BSs for a UE based on SINR, and then associates the UE with the BS that has the smallest index in the set. We conduct simulation experiments to compare IDEA with other three cell association policies. Numerical results demonstrate the significant advantages of IDEA in typical scenarios. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a scheme referred to as integer-forcing message recovering (IFMR) to enable receivers to recover their desirable messages in interference channels. Compared to the state-of-the-art integer-forcing linear receiver (IFLR), our proposed IFMR approach needs to decode considerably less number of messages. In our method, each receiver recovers independent linear integer combinations of the desirable messages each from two independent equations. We propose an efficient polynomial-time algorithm to sequentially find the equations and integer combinations with maximum rates and analyze its complexity. We evaluate the performance of our scheme and compare the results with the minimum mean-square error linear receiver (MMSELR) and lattice-reduction-aided successive interference cancellation with signal-to-interference-plus-noise ratio maximizing preprocessing (LaR-aided SIC with SINR-Max), as well as the IFLR schemes. The results indicate that our IFMR scheme outperforms the MMSELR and LaR-aided SIC with SINR-Max schemes, in terms of achievable rate, considerably. Also, compared to the IFLR, the IFMR scheme achieves slightly less rates in moderate signal-to-noise ratios, with significantly less overall implementation complexity. [ABSTRACT FROM PUBLISHER]