Search

Deep learning (DL) based autoencoder is a potential architecture to implement end-to-end communication systems. In this paper, we first give a brief introduction to the autoencoder-represented communication system. Then, we propose a novel generalized data representation (GDR) to improve the data rate of DL-based communication systems. Finally, simulation results show that the proposed GDR scheme has lower training complexity, comparable block error rate performance and higher channel capacity than the conventional one-hot vector scheme. Furthermore, we investigate the effect of signal-to-noise ratio (SNR) in DL-based communication systems and show that training at high SNR can produce a good training convergence performance for the autoencoder.

Free space optical (FSO) communication is an upcoming attractive alternative technology for transporting high-bandwidth data when the existing RF/fiber-optic communication is neither realistic nor viable. However, the presence of FSO channel turbulences such as fog, smoke, rain, dust, snow, and/or sand can critically degrade the quality of the FSO communication system. There is a great technical development in today's optical components such as LED, laser, optical detector, detector's sensitivity at high bandwidth, modulation techniques, power requirements, total weight, and total size. In spite of all these technological developments, the major limitation of FSO communication quality is the atmosphere. Optical absorption and scattering due to the FSO channel's components in the atmosphere drastically reduce the transmitted optical power. Further, the arbitrary atmospheric formation due to random fluctuation of optical turbulence can alter the wavefront quality of the traveling optical signal, develop the intensity fading and thus result in random signal losses and inter symbol interference (ISI) at the receiver plane. Weather conditions thus ultimately determine the FSO communication system quality not only in ground-to-ground FSO applications but also for deep space laser satellite optical communications because a portion of the optical beam always in the atmospheric turbulence medium that causes time-varying scattering effects.

Multiple-input multiple-output (MIMO) spatial multiplexing technique can improve the transmission rate of free-space optical (FSO) links in the next generation of wireless networks. However, there are several practical limitations that should be carefully considered for implementing such links. In this paper, we study the performance of an FSO MIMO multiplexing link under beam wander and nonzero boresight pointing error effects where there are transmission interruption and interference between sub-channels. We also investigate the impact of different parameters, e.g., receiver field of view, the separation distance among transmitters as well as the separation distance among receivers, and the receiver aperture size in designing a reliable link in order to minimize bit-error rate. Our results can be used for the practical design of FSO MIMO multiplexing links.

This paper improves the Monte-Carlo integration model for multiple scattering channel of ultraviolet communication. An importance sampling method is introduced to improve the convergence speed of the original Monte-Carlo integration model. We compare the convergence speed and calculation speed of the proposed Monte-Carlo integration model based on importance sampling, the original Monte-Carlo integration model based on uniform sampling and a widely used Monte-Carlo simulation model. Simulation results show that the computation efficiency of the proposed model is about 9.6 times of the original Monte-Carlo integration model and is about 4.35 times of the Monte-Carlo simulation model.

In the small-cell networks (SCNs) with multiple small-cell base stations (ScBSs), the joint design of beamforming vectors, user scheduling and ScBS sleeping is investigated with the constraints on proportional rate. A long-term grid-energy expenditure minimization problem is formulated for the considered SCNs, which are powered by the smart grid and natural renewable energy. Since the scheduled user indicators are coupled with the beamforming vectors, the formulated problem is challenging to handle. In order to decouple the beamforming vectors from the scheduled user indicators, the Lyapunov optimization technique is used. As a result, a practical two-scale algorithm is proposed to allocate the user scheduling indicators and ScBS sleeping variables at the coarse-grained granularity (frame) as well as obtain the beamforming vectors at the fine-grained granularity (slot). Numerical results are used to verify the performance of the proposed two-scale algorithm., Comment: This work was accepted by IEEE ICC 2019

The privacy concern exists when the central server has the copies of datasets. Hence, there is a paradigm shift for the learning networks to change from centralized in-cloud learning to distributed \mbox{on-device} learning. Benefit from the parallel computing, the on-device learning networks have a lower bandwidth requirement than the in-cloud learning networks. Moreover, the on-device learning networks also have several desirable characteristics such as privacy preserving and flexibility. However, the \mbox{on-device} learning networks are vulnerable to the malfunctioning terminals across the networks. The worst-case malfunctioning terminals are the Byzantine adversaries, that can perform arbitrary harmful operations to compromise the learned model based on the full knowledge of the networks. Hence, the design of secure learning algorithms becomes an emerging topic in the on-device learning networks with Byzantine adversaries. In this article, we present a comprehensive overview of the prevalent secure learning algorithms for the two promising on-device learning networks: Federated-Learning networks and decentralized-learning networks. We also review several future research directions in the \mbox{Federated-Learning} and decentralized-learning networks., Comment: This work was in part accepted by IEEE Network

The performance of free-space optical quantum communications deteriorates due to the presence of atmosphere turbulence. In this paper, the $P$-function of a coherent state passing through a turbulent atmosphere channel in the presence of thermal noise is derived using the additive property of the thermal noise channel. The analytical form of the density operator for this turbulent coherent state and its corresponding matrix representation in Fock basis is deducted. Using this matrix representation of density operator for turbulent coherent state, the error probability of optical quantum communication system for binary phase shift keying is analyzed.

Due to copyright restrictions, the access to the full text of this article is only available via subscription. N/A

Vertical cavity surface emitting laser (VCSEL) array is increasingly integrated in consumer electronic devices as light sources for biometrics and interaction between terminals. In this study, we proposed a high-speed multi-user optical wireless communication (OWC) method based on a near-infrared VCSEL array, and then experimentally demonstrated a two-user quadrature amplitude modulation (QAM) orthogonal frequency division multiple access (OFDMA) system in a typical indoor environment over a 2-m link. The measured 3-dB bandwidth is around 1.02 GHz for both links, then the maximum sum rate reaches up to 2.7 Gbps for two users with bit-error-rate (BER) of 0 and 3.2 × 10−3 respectively. The designed VCSEL-based QAM–OFDMA OWC system depicts the feasibility of potential scenarios for the interactive information transfer between terminals.

A camera assisted received signal strength (CA-RSS) algorithm is proposed for visible light positioning (VLP) systems. The basic idea of CA-RSS is to use simultaneously visual and strength information of visible lights to achieve accurate positioning at low computational cost. With rectangular LED layout, the irradiance angles of the visible lights can be estimated by visual information. Based on the estimated irradiance angles, the distances between the LEDs and the receiver can be obtained. Then, the two-dimensional (2D) position of the receiver can be calculated using a linear least square method. In addition, based on the solid geometry theory, we propose an independent solution method for three-dimensional (3D) positioning, which can avoid error propagation issue when compared with dependent solution method. To extend further CA-RSS for scenarios having different LED orientations and heights, we then propose a generalized CA-RSS algorithm for broader applications. Moreover, considering the imperfect channel model in practice, we propose a calibration method of Lambertian model for practical uses. Simulation results show that the proposed algorithm can achieve 90th percentile accuracies of less than 12.5 cm for 3D positioning regardless of the orientation of the receiver and the orientation and the height of the LEDs. In addition, experimental results show that using the calibration method, the proposed algorithm achieves an average 3D positioning error of 6.31 cm with different receiver orientations.

Effective capacity is defined as the maximum constant traffic arrival rate that a communication channel can support in order to guarantee a certain statistical delay constraint. We investigate the effective capacity performance of the optical wireless communications employing the coherent detection and polarization multiplexing over the Gamma–Gamma turbulence fading channels with pointing errors. We consider two different power adaptation techniques, namely, independent power adaptation and joint power adaptation. Closed-form effective capacity expressions are developed for both power adaptation schemes. Asymptotic analyses provide the increments of the effective capacities in the high signal-to-noise ratio regimes, in both nonstringent and stringent statistical delay constraints, for every 1 dB increase of the average transmit optical power. Our analysis reveals the superiority of the joint power-adaptation technique in order to support the stringent statistical delay constraint services over the optical wireless communication channels impaired by the strong turbulence fading and/or large pointing errors. However, the numerical results demonstrate that the performance gap between the joint and independent power adaptations becomes significantly reduced as the statistical delay constraints become loose and/or the channel impairments (i.e., turbulence fading and/or pointing error) become weak.

Due to environmental concerns of rising energy consumption caused by explosive growth in the demands of wireless multimedia services, energy efficiency has become an important consideration in the design of future wireless communication systems. In this paper, we investigate and propose an energy-efficient scheme of joint antenna-subcarrier-power allocation for min-rate guaranteed services in the downlink multiuser orthogonal frequency division multiplexing distributed antenna systems (OFDM-DASs) with limited backhaul capacity. Our aim is to maximize the energy efficiency in an OFDM-DAS based on the constraints of users’ Quality of Service, subcarrier reuse, backhaul capacity, and remote antenna units’ transmit power. By exploring the properties of the complex nonconvex energy efficiency optimization problem, we transform the problem into an equivalent problem based on fractional programming, and then, use the alternating direction multiplier method to decompose the problem into a series of simpler subproblems, where their optimal or suboptimal solutions can be easily achieved. We propose the corresponding low-complexity methods to solve the subproblems and, then, the whole problem. The numerical results demonstrate the effectiveness of the proposed low-complexity energy-efficient scheme and illustrate the fundamental tradeoff among energy consumption, spectral efficiency, and energy efficiency.

Non-orthogonal multiple access (NOMA) is a promising technique for the fifth generation mobile communication due to its high spectral efficiency. By applying superposition coding and successive interference cancellation techniques at the receiver, multiple users can be multiplexed on the same subchannel in NOMA systems. Previous works focus on subchannel assignment and power allocation to achieve the maximization of sum rate; however, the energy-efficient resource allocation problem has not been well studied for NOMA systems. In this paper, we aim to optimize subchannel assignment and power allocation to maximize the energy efficiency for the downlink NOMA network. Assuming perfect knowledge of the channel state information at base station, we propose a low-complexity suboptimal algorithm, which includes energy-efficient subchannel assignment and power proportional factors determination for subchannel multiplexed users. We also propose a novel power allocation across subchannels to further maximize energy efficiency. Since both optimization problems are non-convex, difference of convex programming is used to transform and approximate the original non-convex problems to convex optimization problems. Solutions to the resulting optimization problems can be obtained by solving the convex sub-problems iteratively. Simulation results show that the NOMA system equipped with the proposed algorithms yields much better sum rate and energy efficiency performance than the conventional orthogonal frequency division multiple access scheme.

An opportunistic scheduling scheme is proposed for the downlink of a coordinated multi-point (CoMP) system, which exploits both spatial multiplexing and multiuser diversity gains while maintaining fair resource sharing among users. The proposed scheduling scheme consists of two steps in each time slot: selecting a base station (BS) at each user, and then selecting a user at each BS. Although the proposed scheme selects users in a distributed manner, the channels among the selected users are proved to be orthogonal when the number of users approaches infinity. Simulation results demonstrate that the proposed scheme yields a better throughput than the existing scheduling schemes designed for fair resource sharing in CoMP systems.

Free-space optical communication using on–off keying (OOK) and source information transformation is proposed. It is shown that the source information transformation allows the proposed system to detect the OOK signal without requiring the knowledge of instantaneous channel state information and the probability density function (pdf) of the turbulence model. Analytical expressions are derived for the pdf of the detection threshold, and an upper bound is obtained on the average bit error rate (BER). Numerical studies show that the proposed system can achieve comparable performance to the idealized adaptive detection system, with a greatly reduced level of implementation complexity and a signal-to-noise ratio performance loss of only $1.8$ dB at a BER of $1\times 10^{-9}$ for a lognormal turbulence channel with $\sigma =0.25$ .

In visible light communication (VLC) systems, optical orthogonal frequency-division multiplexing (O-OFDM) is an appealing modulation scheme. Recently, a number of O-OFDM schemes have been proposed. Among them, direct-current O-OFDM (DCO-OFDM) is a widely used scheme for its high spectral efficiency and low complexity. Since VLC involves a combination of illumination and communication, different optical power is often required to achieve a certain illumination level. However, clipping noise will dominate a severe performance degradation of DCO-OFDM when a relatively high or low illumination level is imposed, and it restricts applications of DCO-OFDM in future VLC systems. To address this problem, an enhanced DCO-OFDM (eDCO-OFDM) scheme is proposed. By introducing a piecewise function with adaptive slopes according to the required optical power, the proposed eDCO-OFDM scheme has the potential to effectively eliminate the clipping noise. Furthermore, two parameter selection mechanisms with different complexities and performance gains are designed for the piecewise function in the eDCO-OFDM scheme. Simulation results verify the energy and spectral efficiency of the proposed scheme under the constraints of optical power.

A pilot-symbol assisted subcarrier phase-shift keying (PSK) free-space optical communication system is studied with maximum likelihood (ML) phase estimation. Using the phase error probability density function of ML estimation phase error, we study the error rate performance of the subcarrier PSK system with carrier phase error in lognormal and Gamma–Gamma turbulence channels. The closed-form expressions are derived for the asymptotic signal-to-noise ratio (SNR) performance loss for the imperfectly synchronized systems over turbulence channels, and the analytical expressions are verified with numerical results. These expressions reveal how the subcarrier PSK systems with ML estimated phase error are influenced by the pilot length and the modulation order in large SNR regimes.

Prior results on exact error rates and outage probabilities of diversity receptions over arbitrarily correlated fading channels involve intractable nested integrals, which makes the performance analyses challenging to carry out. In this paper, we derive asymptotic expressions and asymptotically tight bounds for error rates and outage probabilities of diversity receptions (including maximal-ratio combining, selection combining, and equal-gain combining) over arbitrarily correlated Beckmann fading channels. These new asymptotic performance expressions reveal insights into the diversity systems over arbitrarily correlated Beckmann fading channels, and the accuracy of the asymptotic performance expressions is explicitly quantified by the performance bounds. Using these analytical tools, one can assess the performance of the diversity reception systems over arbitrarily correlated Beckmann fading channels without resorting to time-consuming Monte Carlo simulation or numerical multifold integration.

Hybrid-selection maximal-ratio combining (HS/MRC) is a useful diversity reception technique to reduce the number of radio frequency chains, and this diversity scheme has been well studied. However, past studies on HS/MRC have often ignored the significant insertion loss associated with hardware implementation of HS/MRC. Therefore, we consider a special class of two-stage diversity receptions known as hierarchical diversity with low insertion loss. The asymptotic error rate performances of hierarchical selection-combining MRC (SC-MRC) and hierarchical selection-combining equal-gain combining are studied for Rician fading channels with arbitrary correlation. Based on our asymptotic analysis, it is shown that, for a practical number of antenna branches, SC-MRC will suffer, at most, 0.6-dB performance losses with respect to HS/MRC; however, SC-MRC will incur significantly less insertion loss. Based on closed-form asymptotic error expressions, we also study unique transmission properties of two-stage diversity receptions over Rician channels with arbitrary branch correlation.

Performance of wireless powered relay with amplify-and-forward protocol is studied for Nakagami- $m$ fading channels. Different from the existing literature, we consider the nonlinearity of the energy harvester. An analytical expression is derived for the complementary cumulative distribution function (CCDF) of the end-to-end signal-to-noise ratio. Using the CCDF, outage capacity is calculated.

The problem of joint power control and time switching is studied for a simultaneous wireless information and power transferring system that supports wireless nodes (WNs) with heterogeneous traffic. Using the stochastic optimization theory, a dynamic algorithm, which can trade average power consumption for WNs' delay, is proposed to allocate the transmission power and time switching factor jointly. A control parameter is defined in the dynamic algorithm to facilitate the tradeoff.

Prior performance analyses of diversity receptions over arbitrarily correlated Nakagami- $m$ fading channels use power correlation matrix to define correlation among branches. However, the power correlation matrix cannot uniquely determine the joint probability density function of the branch amplitudes as well as the system performance. In this paper, we derive asymptotically tight and closed-form upper and lower bounds for the error rates and the outage probabilities of maximum-ratio combining, equal-gain combining, and selection combining over arbitrarily correlated Nakagami- $m$ fading channels. The correlation between the Nakagami- $m$ random variables is defined through the correlation matrix of the accompanying Gaussian random variables, which can uniquely determine the joint probability density function of the Nakagami- $m$ variables. Using the analytical results and Monte Carlo simulation, we show that the performance of diversity reception systems over Nakagami- $m$ fading channels cannot be uniquely determined by the power correlation matrix of the branches. Furthermore, we also study the factors that determine the asymptotic performance of the diversity receptions.

Free-space optical communication links operating over lognormal turbulence channels using on-off keying (OOK) are studied in this paper. Such systems can suffer from irreducible error floors that result from the use of demodulation with fixed and unoptimized detection thresholds. The resulting error floors are analyzed for the general case of low- and high-state offsets (i.e., finite extinction ratios). An electrical signal-to-noise ratio (SNR) optimized detection system is applied. The system uses the electrical SNRs to implement adaptive detection thresholds and eliminate the error floors. The system can accommodate operation with finite extinction ratios, as it uses the method of moments and maximum likelihhod estimation techniques to estimate the low- and high-state offsets and electrical SNR. Numerical results show that the SNR gap between the electrical-SNR-optimized detection system and the adaptive detection system is 2.3 dB at a bit-error rate of $10^{-5}$ without a state offset. The SNR gap increases to 4.5 dB with a state offset of $\xi =0.2$ .

The joint design of beamforming vector and artificial noise covariance matrix is investigated for the multiple-input-single-output-multiple-eavesdropper simultaneous wireless information and power transferring \mbox{(MISOME-SWIPT)} systems. In the MISOME-SWIPT system, the base station delivers information signals to the legitimate user equipments and broadcasts jamming signals to the eavesdroppers. A secrecy energy efficiency (SEE) maximization problem is formulated for the considered \mbox{MISOME-SWIPT} system with imperfect channel state information, where the SEE is defined as the ratio of sum secrecy rate over total power consumption. Since the formulated SEE maximization problem is non-convex, it is first recast into a series of convex problems in order to obtain the optimal solution with a reasonable computational complexity. Two suboptimal solutions are also proposed based on the heuristic beamforming techniques that trade performance for computational complexity. In addition, the analysis of computational complexity is performed for the optimal and suboptimal solutions. Numerical results are used to verify the performance of proposed algorithms and to reveal practical insights., This work was accepted by IEEE JSAC. arXiv admin note: text overlap with arXiv:1808.02004

The joint design of beamforming vector and artificial noise covariance matrix is investigated for multiple-input-single-output-multiple-eavesdropper simultaneous wireless information and power transferring (MISOME-SWIPT) systems. A secrecy energy efficiency (SEE) maximization problem is formulated in the MISOME-SWIPT system with imperfect channel state information and proportional secrecy rate constraints. Since the formulated SEE maximization problem is non-convex, it is first recast into a series of convex problems in order to obtain the optimal solution with a reasonable computational complexity. Numerical results are used to verify the performance of the proposed algorithm and to reveal practical insights., This work was accepted in IEEE Globecom 2018

Non-orthogonal multiple access (NOMA) is considered to be a key technology for fifth-generation mobile communication networks due to its superior spectral efficiency. In this paper, the problem of energy efficient subchannel and power allocation is investigated for a downlink NOMA heterogeneous network. The energy efficient resource allocation problem is first formulated as a mixed integer nonconvex optimization problem. By exploiting convex relaxation and dual decomposition techniques, a closed-form expression is derived via a Lagrangian approach. Simulation results show that the proposed algorithm can converge within ten iterations and obtain high system energy efficiency.

In traditional cognitive radio networks, the spectrum sharing schemes are spectrum-efficient in specific circumstances. In order to improve the robustness of spectrum sharing schemes in a dynamic environment from the perspective of energy efficiency, an adaptive spectrum sharing scheme is proposed for full duplex cognitive radios in this work. The proposed schemes allow secondary users (SUs) to adapt their way of accessing the licensed spectrum according to the behaviors of primary users (PUs). The SUs adaptively decide to access the licensed spectrum in the transmit phase, provided that PUs' traffic arrives at a low rate and energy efficiency gains exist. Based on the intermittent nature of the arrival and departure processes of PUs' traffic, the closed-form expressions of energy efficiency for the traditional and the proposed schemes are investigated. By defining energy efficiency gain and energy efficiency loss, the impacts of the spectrum sensing error and channel estimation error are analyzed to evaluate the energy efficiency of the proposed scheme. It shows that the proposed adaptive spectrum sharing scheme improves the overall energy efficiency. The numerical results validate the energy efficiency improvements and the robustness of the proposed scheme.

Exact outage probability analysis for equal-gain combining (EGC) over lognormal fading channels results in multi-fold integrals, and traditional asymptotic analysis techniques cannot work for lognormal fading channels due to the channels' infinite diversity order. In this work, we derive a closed-form asymptotic outage probability expression for dual-branch EGC over correlated lognormal fading channels with different statistics. The new result reveals insights into the long-standing problem of asymptotic analysis for correlated lognormal fading channels, paving the way for analysis on more general channel models. The result also provides an efficient way to evaluate the performance of dual-branch EGC over correlated and nonidentically distributed lognormal channels at high signal-to-noise ratio.

The problem of full-duplex primary users (PUs) signal extraction is studied for cognitive radio networks, and the polarization Jones vector distance (PJVD) is used as the extraction metric. Based on the orientation and magnitude difference of the signal samples from different PUs, the PJVD based signal extraction (PJVD-SE) can efficiently detect each PU's signal polarization by calculating the PJVD between any two samples. Due to the Gaussian distributed noise, the resultant PJVD for primary samples is noncentral chi-squared distributed. Based on the distribution, the extraction error probability is investigated. Theoretical analysis shows that the proposed PJVD-SE technique outperforms the polarization similarity based technique in terms of both error probability and computation complexity. It is found that the performance gain is proportional to the SU's antenna number, PUs' polarization angle and PUs' signal amplitude difference. In addition, the presented analytical studies are verified through extensive simulation results and the performance of PJVD-SE is validated.

Absorption, scattering and turbulence are the three main characteristics for underwater optical wireless communications (UOWC). Among these three factors, absorption and scattering, respectively, characterize the energy loss and direction change when photons propagate through underwater wireless channels interacting with water molecules or suspended particles. In recent years, several analytical methods originated from free space optical communications are used to model various underwater channels, while only statistical models are employed to consider the effects of absorption and scattering containing all the scattering components. To facilitate in-depth theoretical analysis, we propose an expression to model the spatial probability density function of optical intensity for all scattering components in UOWC links in this paper. After that, we model the photodiode receiving process and give a clear explanation on the related parameters. Numerical results indicate that the bit-error rate performance deteriorates as the turbulence gets stronger, and larger multiple-input multiple-output array can alleviate the negative effect caused by fading. Besides, the effect of turbulence on BER is more important than that of the link geometry, and the increase in transmitted power will weaken the diversity gain from MIMO configuration.

Absorption and scattering are traditionally considered as the most important factors to affect the performance of underwater optical wireless communications (UOWC). Recently, the theoretical models from free space optical (FSO) communications are applied to model the underwater turbulence, and the turbulence-induced fading may introduce fluctuations to the light intensity. However, the effect of turbulence on UOWC channels might be different from FSO channels due to the interference from absorption and scattering. In this work, we first introduce the log-normal distribution to represent the weak turbulence. After that, we deduce the average capacity of turbulent buoy- based multiple-input multiple-output (MIMO) systems. Numerical results demonstrate that turbulence will boost the average capacity under low transmitted signal-to-noise ratio (SNR) and reduce the average capacity when the transmitted SNR which is defined as the transmitted power divided by the noise at the receiver is sufficiently high enough. Besides, stronger turbulence exerts more influence on the capacity, and the increasing attenuation length will eliminate the effect of turbulence. Moreover, MIMO could offset the impact of turbulence-induced fading, which indicates that it cannot improve the capacity performance under low SNR but could bring positive effects when SNR becomes high.

One promising approach to address the supply-demand mismatch between the terrestrial infrastructure and the temporary and/or unexpected traffic demands is to leverage the unmanned aerial vehicle (UAV) technologies. Motivated by the recent advancement of UAV technologies and retromodulator based free space optical communication, we propose a novel edge-computing empowered radio access network architecture where the fronthaul and backhaul links are mounted on the UAVs for rapid event response and flexible deployment. The implementation of hardware and networking technologies for the proposed architecture are investigated. Due to the limited payload and endurance as well as the high mobility of UAVs, research challenges related to the communication resource management and recent research progress are reported., This work is accepted by IEEE Wireless Communications Magazine

The double-scattering channel model is known to constitute an accurate representation of rank-deficiency (i.e. keyhole) in multiple-input multiple-output (MIMO) channels. The double-Nakagami channel is a general case of the double-scattering model. In this paper, a simple and accurate approximate probability density function (PDF) is proposed for double-Nakagami fading based on Hankel’s expression, which is found to be accurate for a wide range of the Nakagami parameters through the Kolmogorov-Smirnov test. Moreover, a new approximate PDF is deduced for the generalized-K distribution, as a sum of weighted generalized Gamma functions. The proposed approximation allows a tractable performance analysis for MIMO systems. Closed-form symbol error rate approximation expressions are also derived for multi-branch maximal ratio combining reception.

A new (Beaulieu-Xie) fading model was recently proposed to describe line-of-sight and non-line-of-sight components in wireless channels. In this work, we consider both outage probability and error rate performance of selective combining over this new fading channel model with arbitrary channel correlation. Closed-form expressions are obtained for asymptotically tight upper and lower bounds. The analytical results are verified by Monte Carlo simulations.

With the maturity of unmanned aerial vehicle (UAV) technology, this work investigates the integration of UAV into wireless communication systems. Since the UAV is powered by a capacity-limited battery, this work proposes to use the radio energy harvesting technology at the UAV in order to extend the lifetime of UAV empowered base station. To extract the most weighted throughput of UAV empowered wireless systems, the dirty paper coding scheme and information-theoretic uplink-downlink channel duality are exploited to propose an extracting the most weighted throughput algorithm. Numerical results are used to verify the proposed algorithm., Comment: This work was accepted by BSC 2018, Toronto, Canada

This paper investigates the physical-layer security for an indoor visible light communication (VLC) network consisting of a transmitter, a legitimate receiver and an eavesdropper. Both the main channel and the wiretapping channel have nonnegative inputs, which are corrupted by additive white Gaussian noises. Considering the illumination requirement and the physical characteristics of lighting source, the input is also constrained in both its average and peak optical intensities. Two scenarios are investigated: one is only with an average optical intensity constraint, and the other is with both average and peak optical intensity constraints. Based on information theory, closed-form expressions of the upper and lower bounds on secrecy capacity for the two scenarios are derived. Numerical results show that the upper and lower bounds on secrecy capacity are tight, which validates the derived closed-form expressions. Moreover, the asymptotic behaviors in the high signal-to-noise ratio (SNR) regime are analyzed from the theoretical aspects. At high SNR, when only considering the average optical intensity constraint, a small performance gap exists between the asymptotic upper and lower bounds on secrecy capacity. When considering both average and peak optical intensity constraints, the asymptotic upper and lower bounds on secrecy capacity coincide with each other. These conclusions are also confirmed by numerical results., Comment: Accepted by IEEE Transactions on Communications, 2018

Level crossing rate (LCR) and average fade duration (AFD) of a new (Beaulieu-Xie) fading model are analyzed. The characteristic function method is used to derive the LCR for a diversity scheme using maximal ratio combining. The LCR and AFD of the Beaulieu-Xie fading model show improvement beyond the performance levels of the Ricean and Nakagami-m fading models.

In this paper, we consider the secure transmission design for a multiple-input single-output Femtocell overlaid with a Macrocell in co-channel deployment. The Femtocell base station sends confidential messages to information receiving Femtocell users (FUs) and energy signals to energy receiving (ER) FUs while limiting the interference to Macrocell users (MUs). The ER FUs have the potential to wiretap the confidential messages. By taking fairness into account, we propose a sum logarithmic secrecy rate maximization beamforming design problem under the interference constraints for MUs and energy harvesting (EH) constraints for ER FUs. The formulated design problem is nontrivial to solve due to the nonconvexity which lies in the objective and the constraints. To tackle the design problem, a semidefinite relaxation and successive convex approximation based algorithm is proposed. Simulation results demonstrate the effectiveness of the proposed beamforming design., Comment: 5 pages, 2 figures, Conference paper, Presented in BSC 2018

Non-orthogonal multiple access (NOMA) has attracted much recent attention owing to its capability for improving the system spectral efficiency in wireless communications. Deploying NOMA in heterogeneous network can satisfy users' explosive data traffic requirements, and NOMA will likely play an important role in the fifth-generation (5G) mobile communication networks. However, NOMA brings new technical challenges on resource allocation due to the mutual cross-tier interference in heterogeneous networks. In this article, to study the tradeoff between data rate performance and energy consumption in NOMA, we examine the problem of energy-efficient user scheduling and power optimization in 5G NOMA heterogeneous networks. The energy-efficient user scheduling and power allocation schemes are introduced for the downlink 5G NOMA heterogeneous network for perfect and imperfect channel state information (CSI) respectively. Simulation results show that the resource allocation schemes can significantly increase the energy efficiency of 5G NOMA heterogeneous network for both cases of perfect CSI and imperfect CSI.

A recently proposed fading model which can be used to describe both line-of-sight and non-line-of-sight components of a fading channel is analyzed. The outage probability and error rate performance of equal-gain combining over arbitrary correlated Beaulieu-Xie fading channels is considered. Asymptoticallytight closed-form lower and upper bounds are derived and these analytical results are verified via Monte Carlo simulations.

Security is a critical issue in full duplex (FD) communication systems due to the broadcast nature of wireless channels. In this paper, joint design of information and artificial noise beamforming vectors is proposed for the FD simultaneous wireless information and power transferring (FD-SWIPT) systems with loopback self-interference cancellation. To guarantee high security and energy harvesting performance of the FD-SWIPT system, the proposed design is formulated as a secrecy rate maximization problem under energy transfer rate constraints. Although the secrecy rate maximization problem is non-convex, we solve it via semidefinite relaxation and a two-dimensional search. We prove the optimality of our proposed algorithm and demonstrate its performance via simulations., Comment: Accepted in ICC 2018

Uplink transmission design for visible light communication (VLC) is challenging due to the high optical power requirement for reliable links, which may result in unpleasant irradiance to humans. Current studies have proposed to use radio frequency (RF) communication for uplink while treating VLC as a downlink transmission technique. However, in typical scenarios such as hospitals or aircraft cabins, non-RF communications are preferred. Thus, it is beneficial to design a system which can utilize VLC for uplink transmission while minimizing its optical power. In this paper, we propose a amplify and forward based VLC uplink system which can significantly mitigate the optical power of the source light. The multi- carrier modulation scheme termed DC biased optical orthogonal frequency division multiplexing is employed, and the theoretical model of the proposed uplink system is studied. Based on this analytical model, the key system parameters are optimized. Numerical and simulation results verify that, when compared to an equal power allocation based relay system and a reference system without a relay, the proposed system can simultaneously achieve higher spectral efficiency and lower the source optical power.

We investigate the precoding, remote radio head (RRH) selection and signal splitting in the simultaneous wireless information and power transferring (SWIPT) cloud radio access networks \mbox{(C-RANs)}. The objective is to minimize the power consumption of the SWIPT C-RAN. Different from the existing literature, we consider the nonlinear fronthaul power consumption and the multiple antenna RRHs. By switching off the unnecessary RRHs, the group sparsity of the precoding coefficients is introduced, which indicates that the precoding process and the RRH selection are coupled. In order to overcome these issues, a group sparse precoding and signal splitting algorithm is proposed based on the majorization-minimization framework, and the convergence behavior is established. Numerical results are used to verify our proposed studies., Comment: Accepted by IEEE Globecom 2017

Prior visible-light communication (VLC) positioning systems require the receiver to be placed towards a certain angle, or extra sensors like gyroscopes must be equipped to estimate the angle of the receiver. In this work, we propose a positioning scheme using cameras based on angle difference of arrival (ADOA). ADOA-based positioning does not need the receiver to know its tilting angle, and the position estimation is modeled as a three-variate optimization problem in a finite search region, which is tractable in most smart devices. Our experimental and numerical results show that the ADOA-based VLC positioning scheme achieves accuracy of centimeters and the average cost time is as low as 0.2 seconds.

Statistical delay quality-of-service (QoS) aware adaptive resource allocation scheme is proposed for a multi-carrier coherent free space optical (FSO) communications based fronthaul network. The proposed resource allocation assigns remote radio heads (RRHs) to the suitable aggregation nodes (ANs) and allocates the transmit power to the orthogonal optical carriers. Specifically, the proposed resource allocation provides delay-QoS at the link layer by maximizing the effective sum capacity of the all the RRHs subject to transmit power budgets at the RRHs and capacity constraint of the wired fronthaul links connecting the ANs with the baseband unit (BBU) pool. The considered resource allocation is formulated as a mixed-integer non-linear programing (MINLP) problem. We use two transmission link optimization techniques, namely, independent link optimization (ILO) and joint link optimization (JLO), in order to solve the proposed MINLP problem. Under both optimization techniques, the proposed MINLP problem is decomposed into two subproblems which are iteratively solved in order to obtain the optical transmit power allocation and assignments of RRHs to the ANs. Our analysis reveals that the optical transmit power allocation and RRH-AN assignments depend on both the atmospheric turbulence fading and delay-QoS requirements. Numerical results demonstrate that the JLO technique achieves significant higher effective capacity (EC) compared to the ILO technique in the strict statistical delay-QoS constraints. However, the EC performance gap between the JLO and ILO techniques is reduced in the loose statistical delay-QoS constraints.

Traditionally, primary users (PUs) in cognitive radio networks typically work in frequency division duplex or time division duplex mode, and secondary users (SUs) can protect PUs by blindly learning every PU's signal space and transmitting in the orthogonal space. However, the fifth-generation communication promotes the full-duplex technique and PUs are likely to work in FD mode in the future, i.e., two PUs transmit simultaneously at the same frequency. The emerged problem is that the sample of signal may be a compound signal from multiple PUs, and each PU's signal space cannot be directly derived, thus the available degree of freedom (DoF) for SUs' transmission may be limited and strong interference will be incurred to PUs. In this work, cognitive radio communications with full-duplex PUs is studied. Based on the distinctive polarization features of samples from different PUs, we propose a novel blind polarization adaption technique, which allows SUs to extract the signal space of each PU from the hybrid samples by studying polarization similarity of the sampled vectors. In order to reduce the polarization similarity inaccuracy induced by noise depolarization effect, a subspace based noise suppression method is also proposed. Numerical results show that the noise can be largely suppressed even in the low signal-to-noise-ratio region, which allows the proposed polarization similarity based polarization adaption technique to guarantee satisfactory interference level on PUs.

A robust quality-of-service (QoS) based secure transmission design is investigated for a cooperative jamming aided multiple-input single- output system with unknown eavesdroppers. By assuming legitimate receiver's channel state information (CSI) is imperfect and eavesdroppers' CSI is unavailable, our system design goal is to maximize the power of artificial jamming signals, and to guarantee a minimum QoS at the legitimate receiver. The transmit beamforming vector and covariance matrix of jamming signals are jointly optimized under individual power constraints. As this optimization problem is non-convex, we propose a solution method by using the semidefinite relaxation approach. Numerical results show that, our design, in which the precoding scheme of information transmission is transmit beamforming, outperforms its transmit covariance based counterpart.