Cooperation within the Small Cell: The indoor,correlated shadowing case

The deployment of Small Cells in fourth generation (4G) communication systems is aimed at providing significant capacity improvements and higher availabilities. However, the design of Small Cell systems in indoor environments is especially challenging due to high shadowing attenuation induced by clutter and human blockage. This paper studies node cooperation and multiple relaying and proposes novel analytical formulas for the outage probability of cooperative Small Cells suffering from shadowing. The channel fading gains are modeled as correlated lognormal random variables, in order to reflect the properties of indoor propagation environments. Various cooperative strategies are considered, taking into account the use of one or two relays and different receiver combining techniques. In addition, the relative performance of each cooperative configuration and the benefit of cooperation over non-cooperation are investigated. Finally, interesting and useful insights are produced regarding the impact of the correlated lognormal environment parameters on the configuration of cooperative Small Cells.     

Cooperative diversity performance of selection relaying over correlated shadowing

The study of relaying systems has found renewed interest in the context of cooperative diversity for communication channels suffering from fading. In particular, dual-hop relaying with diversity combining of the relayed and direct path at the receiver has practical importance and can be considered as a building block for forming larger communication systems. This paper presents novel analytical expressions and numerical results on cooperative diversity performance using selection relaying over correlated lognormal channels for both SC and MRC techniques at the receiver. In addition, an exact framework for comparing the performance and efficiency of the medium access protocol and relay capabilities (TDMA/half-duplex, SDMA/full-duplex) is proposed. Finally, based on the analysis and novel mathematical expressions for the outage probability, we investigate the impact of the lognormal parameters (including correlation) on the cooperative system performance and its efficiency.     

On the secure performance of Internet of Vehicles in Nakagami-m fading scenarios

With the vigorous development of today’s wireless communication industry, the Internet of Vehicles (IoV), as one of its application scenarios, has received extensive attention from researchers. Ensuring the security of information transmission is one of the many problems to be solved in the IoV system. To fit the actual scene, this paper considers the impacts of both the channel characteristics of Nakagami-m fading and the distribution of the vehicles’ positions in the real road scenario of the IoV. According to the random distribution characteristics of vehicle terminal position, a system model with a transmitter base station, a legitimate vehicle terminal, and an eavesdropper is established. The approximate and asymptotic analytical expressions of the secrecy outage probability over the Nakagami-m fading channels are derived. Finally, the correctness of the proposed analysis models established in this paper is verified by Monte Carlo simulation and numerical analysis. The secrecy outage performance and the influencing factors of the considered model in the Nakagami-m fading environment are discussed and analyzed.     

Outage performance analysis for relay-assisted UWOC systems over GGD weak turbulence with nonzero boresight pointing errors

In this paper, we mainly investigate the outage performance of serial and parallel relay-assisted underwater wireless optical communication (UWOC) systems based on a newly proposed aggregated underwater fading model. In order to overcome the deficiency of the traditional underwater weak turbulence models, that is, they could not accurately fit the measured data in the laboratory, the generalized gamma distribution (GGD) which has been verified by a series of experiments is chosen for the first time to characterize the weak oceanic turbulence. Then, we establish a new receiving signal model which has integrated the implicit path loss plus multipath propagation effect shown by fading free impulse response (FFIR), GGD weak oceanic turbulence, and nonzero boresight pointing errors. Next, we deduce the closed-form expression of the probability density function (PDF) of the hybrid fading considering GGD weak turbulence and nonzero boresight errors based on the new receiving signal model above through double-exponential Taylor expansion and higher transcendental Whittaker function. Finally, the analytical expressions of the outage probabilities for point-to-point (P2P) link, serial and parallel relay-assisted UWOC systems are further derived respectively under the proposed aggregated channel. Numerical simulations are also provided to validate the accuracy of the theoretical formulae derived above, and to show the effects of the key system parameters on the outage performance of relaying UWOC systems.     

Performance estimation of free space optical links over negative exponential atmospheric turbulence channels

In this work, we study the performance of free space optical links with fading statistics modelled by the negative exponential distribution which describes channels under strong atmospheric turbulence conditions. We investigate the availability and the practical channel capacity's bounds, for links with fast and slow fading statistics, with line of sight architecture and intensity modulation with direct detection, through the evaluation of the outage probability and the outage and average capacity. Moreover, the average error probability, for on-off keying cases, is estimated. For these, very significant, magnitudes we extract closed form mathematical expressions for, practically valuation of link's performance.     

On the dimensioning of cellular OFDMA networks

In this paper, we address the issue of cellular OFDMA network dimensioning. Network design consists of evaluating cell coverage and capacity and may involve many parameters related to environment, system configuration, and quality of service (QoS) requirements. In order to quickly study the impact of each of these parameters, analytical formulas are needed. The key function for network dimensioning is the Signal to Interference Ratio (SIR) distribution. We thus analyze in an original way the traditional issue of deriving outage probabilities in OFDMA cellular networks. Our study takes into account the joint effect of path-loss, shadowing, and fast fading effects. Starting from the Mean Instantaneous Capacity (MIC), we derive the effective SIR distribution as a function of the number of sub-carriers per sub-channel. Our formula, based on a fluid model approach, is easily computable and can be obtained for a mobile station (MS) located at any distance from its serving base station (BS). We validate our approach by comparing all results to Monte Carlo simulations performed in a hexagonal network, and we show how our analytical study can be used to analyze outage capacity, coverage holes, and network densification. The proposed framework is a powerful tool to study performances of cellular OFDMA networks (e.g. WiMAX, LTE).     

Performance analysis of wireless powered sensor network with opportunistic scheduling over generalized κ−μ shadowed fading channels

This paper investigates the performance of a multi-node wireless powered sensor network (WPSN) with an opportunistic scheduling scheme over $\kappa -\mu$ shadowed fading channels. The system assumes that all the sensor nodes (SNs) are energy constrained and harvest energy from a hybrid access point (HAP) in the downlink. In contrast, the node with the best end-to-end instantaneous signal-to-noise ratio (SNR) is scheduled for information transmission to HAP in the uplink. For the underlying system model, approximate closed-form analytical expressions is developed with the help of the moment matching method, which is then used to evaluate the system performances such as outage probability, effective throughput, and average bit error rate (BER). In addition, we also perform an asymptotic analysis by assuming that the system operates at a high SNR region, which gives us valuable insights about the diversity order and coding gain. The accuracy of the analysis is further confirmed with Monte-Carlo simulations, which validate the correctness of the theoretical analysis.     

Performance characterization of two-way multi-hop underwater networks in turbulent channels [Invited]

This Letter investigates the performance of the two-way multi-hop system for underwater optical wireless communications. With the decode-and-forward(DF) relaying, the two-way multi-hop system is modeled, where the effects of absorption, scattering, and oceanic turbulence are all taken into account. An exact closed-form expression for outage probability is derived under the assumption that the oceanic turbulence obeys a log-normal distribution. Numerical results demonstrate the impacts of various parameters on the outage performance and indicate that the two-way multi-hop system significantly improves the performance in comparison to both the one-way multi-hop system and the two-way two-hop system.     

单模光纤中偏振模色散的仿真模型

利用琼斯矩阵法研究了长单模光纤中偏振模色散的仿真模型.考虑到偏振模色散的随机性,该模型中单模光纤被看作是一系列短双折射光纤段的级联,相邻两段之间耦合角是随机的.研究结果表明,当短双折射光纤段等长时,偏振模色散呈现随波长周期性变化的特点;不符合实际情况.当短双折射光纤段不等长且服从高斯分布时,周期性逐渐消失;当其长度均方差为均值的20%,周期性完全消失.最后比较了偏振模色散的时域统计特性.取短双折射光纤段的长度服从高斯分布且均方差为均值的20%,偏振模色散的统计特性接近于实际分布.因此得出结论:为了正确估计偏振模色散的影响,在单模光纤的级联模型中,短双折射光纤段的长度应服从高斯分布,均方差为其均值的20%.     

Outage performance of CoMP-CNOMA networks with duplex mode selection

This paper investigates the outage performance of a downlink coordinated multipoint cooperative non-orthogonal multiple access (CoMP-CNOMA) network, where two near users cooperatively relay the information to a far user. It is assumed that the near users support both the half-duplex relaying mode and the full-duplex relaying mode. Since the full-duplex mode may be inferior to the half-duplex mode due to the residual self-interference under the full-duplex mode, we propose a duplex mode selection strategy for the near users to dynamically choose the duplex mode for relaying. Under the proposed duplex mode selection strategy, the closed form expressions for the outage probabilities of all the users are derived. The theoretical results match well with the Monte Carlo simulations. It is shown that the proposed duplex mode selection strategy can provide low outage probabilities of all the users simultaneously, while the existing duplex mode selection strategies either achieve higher outage probabilities of all the users or achieve slightly better outage performance of the far user at the sacrifice of much worse outage performance of the near users.     

Improvement of Nonlinear Modulation by Cascaded Mach-Zehnder Configuration

A two-stage cascaded Mach-Zehnder modulator is employed for the linear external modulation of a laser. The modulation electric fields are applied on the first and second stages in the Z and Y directions, respectively. Because of the inherent versatility of the adjustable modulation parameters, improved modulation perfor mances with a high modulation depth and a high linear response are demonstrated. When a modulation depth of 21 % is required, the ratios of the second and third harmonic terms to the fundamental term can be simultaneously achieved as low as 104 and 86.7 dB, respectively.     

Relay selection scheme based on deep reinforcement learning in wireless sensor networks

Cooperative communication technology has realized the enhancement in the wireless communication system’s spectrum utilization rate without resorting to any additional equipment; additionally, it ensures system reliability in transmission, increasingly becoming a research focus within the sphere of wireless sensor networks (WSNs). Since the selection of relay is crucial to cooperative communication technology, this paper proposes two different relay selection schemes subject to deep reinforcement learning (DRL), in response to the issues in WSNs with relay selection in cooperative communications, which can be summarized as the Deep-Q-Network Based Relay Selection Scheme (DQN-RSS), as well as the Proximal Policy Optimization Based Relay Selection Scheme (PPO-RSS); it further compared the commonly used Q-learning relay selection scheme (Q-RSS) with random relay selection scheme. First, the cooperative communication process in WSNs is modeled as a Markov decision process, and DRL algorithm is trained in accordance with the outage probability, as well as mutual information (MI). Under the condition of unknown instantaneous channel state information (CSI), the best relay is adaptively selected from multiple candidate relays. Thereafter, in view of the slow convergence speed of Q-RSS in high-dimensional state space, the DRL algorithm is used to accelerate the convergence. In particular, we employ DRL algorithm to deal with high-dimensional state space while speeding up learning. The experimental results reveal that under the same conditions, the random relay selection scheme always has the worst performance. And compared to Q-RSS, the two relay selection schemes designed in this paper greatly reduce the number of iterations and speed up the convergence speed, thereby reducing the computational complexity and overhead of the source node selecting the best relay strategy. In addition, the two relay selection schemes designed and raised in this paper are featured by lower-level outage probability with lower-level energy consumption and larger system capacity. In particular, PPO-RSS has higher reliability and practicability.     

Operation of low driving voltage cascaded modulator over non-cascaded modulator for 4 dB extinction ratio at 100 giga bit per second (Gbps)

This paper describes improved results when comparing cascaded traveling wave electro absorption modulator (TWEAM) to non-cascaded TWEAM by simulation. Large signal modeling is used for both types of modulators to achieve 4 and 10 dB extinction ratios (ERs) with flat frequency response for applications in short distance as well as long distance optical fiber communication. To obtain 4 and 10 dB ERs with 110 GHz 3 dB bandwidth, a cascaded TWEAM requires 0.4 V peak to peak (V_P-P) and 1 V_P-P input driving voltages respectively. A non-cascaded TWEAM requires about two times the input driving voltage compared to the cascaded modulator to achieve the same values of ER and 3 dB bandwidth. Both modulators have been simulated with the same bias and also use the same circuit parameters except for the total active segment lengths (1 and 0.5 mm for cascaded and non-cascaded modulator respectively) and microstrip lengths to obtain the same ERs and 3 dB bandwidths.     

含遮蔽抛射沉积模型的有限尺寸效应

含遮蔽抛射沉积模型是在抛射沉积(BD)模型的基础上考虑了粒子以一定的角度分布倾斜入射的情况.本文应用外推方法确定了大尺寸极限下含遮蔽抛射沉积模型的各标度指数,讨论了该模型的有限尺寸效应及其标度性质.从模拟结果可以看出含遮蔽BD模型的有限尺寸效应与BD模型有所不同,遮蔽这种非局域作用可以显著地改变BD模型的标度性质. 关键词： 遮蔽效应 抛射沉积模型 有限尺寸效应 动力学标度     

Outage Performance of Wireless Powered Decode-and-Forward Relaying Networks in Rician Fading

This paper investigates the outage performance of simultaneous wireless information and power transfer (SWIPT)-enabled relay networks with the decode-and-forward relaying protocol, where the effect of the energy triggering threshold at the relay on the system performance is considered. The closed-form expressions of the system outage probability and throughput are derived in Rician channel fading. Monte Carlo Simulation method is used to verify the accuracy of the derived closed-form expressions. The effects of some system parameters on the system performances are discussed via simulations, which show that the system outage probability increases with the increase of the minimum transmission rate required by the users and also decreases with the increase of the energy conversion efficiency. Besides, the system throughput increaseswith the increment of the transmit power of the source node, as well as the energy conversion efficiency. Additionally, the outage performance of the system with the equal two-hop distance is better than that of the system with unequal two-hop distance.     

Creation of multi-frequency terahertz waves by optimized cascaded difference frequency generation

A new scheme which generates multi-frequency terahertz (THz) waves from planar waveguide by the optimized cascaded difference frequency generation (OCDFG) is proposed. A THz wave with frequency ω_T1 is generated by the OCDFG with two infrared pump waves, and simultaneously a series of cascaded optical waves with a frequency interval ω_T1 is generated. The THz wave with a frequency of M-times ω_T1 is generated by mixing the m-th-order and the (m+M)-th-order cascaded optical wave. The phase mismatch distributions of cascaded difference frequency generation (CDFG) are modulated by changing the thickness of planar waveguide step by step, thereby satisfying the phase-matching condition from first-order to high-order cascaded Stokes process step by step. As a result, the intensity of THz wave can be enhanced and modulated by controlling the cascading order of OCDFG.     

p-A Drell-Yan过程中的核效应

利用色偶极模型,在靶静止系中计算了800GeV质子与原子核碰撞的Drell-Yan过程的微分截面,并与E772实验结果进行了比较.结果发现:不考虑能量损失,只计及p-A碰撞中的核遮蔽效应,理论计算就与实验数据甚好符合.     

Monostatic and bistatic statistical shadowing functions from a one-dimensional stationary randomly rough surface according to the observation length: I. Single scattering

When solving electromagnetic rough-surface scattering problems, the effect of shadowing by the surface roughness often needs to be considered, especially as the illumination angle approaches grazing incidence. This paper presents the Ricciardi-Sato, as well as the Wagner and the Smith formulations for calculating the monostatic and bistatic statistical shadowing functions from a one-dimensional rough stationary surface, which are valid for an uncorrelated Gaussian process with an infinite surface length. In this paper, these formulations are extended to include a finite surface length and any uncorrelated process. The inclusion of a finite surface length is needed to extend the single-reflection shadowing function to the more general multiple-reflection case, presented in the following companion paper. Comparisons of these shadowing functions with the exact numerical solution for the shadowing (using surfaces with Gaussian and Lorentzian autocorrelation functions for a Gaussian process) shows that the Smith formulation without correlation is a good approximation, and that including correlation only weakly improves the model. This paper also presents a method to include the shadowing effect in the electromagnetic scattering problem.