Performance of Physical-Layer Network Coding in Asymmetric Two-Way Relay Channels

In this paper, we study the performance of physical-layer network coding in asymmetric two-way relay channels using four different cases having different poor channels:phase asymmetry, downlink asymmetry, uplink asymmetry and node asymmetry. The decision and mapping rule for symmetric and asymmetric cases are studied. The performance in terms of bit error rate for each case will be studied and analysed by computer simulation. Analytical and simulation results show that uplink asymmetry is the worst case;intra-phase asymmetry and unreliable uplink channels will more severely affect the performance degradation, which is caused by channel asymmetry.

MSMSE-based optimal beamforming design and simplification on AF MIMO two-way relay channels

An optimal cooperative beamforming for the amplify-and-forward (AF) MIMO two-way relay channels was designed. Supposing the channel state information (CSI) was perfectly known by the receiver and transmitter as well as the relay, optimal beamforming vectors (matrices) of all nodes were jointly designed based on the criterion of minimizing the sum mean square errors (MSMSE). The analysis result shows that the performance effect of transmitting and receiving beamforming pairs is to maximize the receive signal-to-noise ratio (SNR) at two communication nodes, and the rank of the optimal relay beamforming matrix is no larger than two when there is only one data stream at each source node. A simplified algorithm was put forward to accomplish the design based on the analysis conclusions. Simulation results provide that the system performance, which is characterized in terms of bit error rates (BER), is significantly improved by cooperative beamforming, and the performance of the simplified method is not only very close to the optimal one but also with faster iteration speed and much lower computational complexity.

Energy efficiency enhancement of two-way amplifier forward relaying with channel estimation error

In order to save energy consumption of two-way amplifier forward(AF) relaying with channel estimation error, an energy efficiency enhancement scheme is proposed in this work. Firstly, through the analysis of two-way AF relaying mode with channel estimation error, the resultant instantaneous SNRs at end nodes is obtained. Then, by using a high SNR approximation, outage possibility is acquired and its simple closed-form expression is represented. Specially, for using the energy resource more efficiently, a low-complexity power allocation and transmission mode selection policy is proposed to enhance the energy efficiency of two-way AF relay system. Finally, relay priority region is identified in which cooperative diversity energy gain can be achieved. The computer simulations are presented to verify our analytical results, indicating that the proposed policy outperforms direct transmission by an energy gain of 3 dB at the relative channel estimation error less than 0.001. The results also show that the two-way AF relaying transmission loses the two-way AF relaying transmission loses its superiority to direct transmission in terms of energy efficiency when channel estimation error reaches 0.03.

Numerical Prediction of Wall Effect on Propeller in Restricted Channel

In restricted channel, the hydrodynamic performance of propeller is affected by the wall. In the present work, two cylindrical channels with different diameters being 1.8D and 5.0D are adopted to study the influence of wall on the hydrodynamic performance and wake field of the propeller model DTMB4119. The numerical simulations are carried out by the single-phase solver pimpleDyMFoam in open source platform OpenFOAM. The Reynolds Averaged Navier-Stokes equations (RANS) are adopted to solve the flow field. The arbitrary mesh interface (AMI) method is used to simulate the rotation of propeller. The designed advance ratio, J = 0.833, is applied in all the computations. For the 5.0 D case, the predicted results of open water performance are in good agreement with experiment data. In restricted channel, the predicted results of thrust and torque coefficients are larger than the open water case. The pressure on the wall of restricted channel downstream increases and approaches the results in open water gradually. Due to the flux conservation, higher negative induced velocity is investigated in the flow field of the propeller in restricted channel.

Diversity-multiplexing tradeoff of half-duplex multi-input multi-output two-way relay channel with decode-and-forward protocol

A multi-input multi-output(MIMO) separated two-way relay channel(STWRC) is considered,where two users exchange their messages via a relay node.When each link is quasi-static Rayleigh fading,the achievable diversity-multiplexing tradeoff(DMT) of the half-duplex STWRC is analyzed.Firstly,the achievable DMT of the STWRC with static decode-and-forward(DF) protocol is obtained.Then,a dynamic decode-and-forward(DDF) protocol for the STWRC is proposed,where the relay listening time varies dynamically with the channel qualities of the links between two users and the relay.Finally,the achievable DMT of the proposed DDF protocol is derived in a case-bycase manner.Numerical examples are also provided to verify the theoretical analysis of both protocols.

Optimal cooperative beamforming design schemes for AF MOMO two-way relay channels

In this paper,beamforming parameters in multiple input multiple output(MIMO) two-way relay channels(TWRCs) are designed.We investigate three communicating scenarios,in which,the source nodes are all equipped with multiple antennas.In the first scenario,one pair of source nodes are communicating with each other under the help of a single multi-antenna equipped relay.A centralized scheme is correspondingly developed where the optimal relay beamforming(RaB) is jointly designed with the transmit beamformings(TBs) and the receive beamformings(RcBs) at both source nodes to minimize the sum of mean square errors(SMSE).In the second scenario,one pair of users in the first scenario is extended to multi-pair of source nodes.We derive a general expression of the optimal RaB matrix of this scenario in the second scheme,and based on which,a RaB matrix is designed to cancel the inter-pair interference(IPI) and to minimize the intra-pair SMSE.At last,we consider a distributed scenario where multiple single-antenna equipped relays are helping the communication between one pair of source nodes.In the scheme associated with this scenario,beamformings are developed under relay total power constraint and relay individual power constraint,respectively.The simulation results reveal that beamformings at source and relay nodes significantly improve the performance in the sense of average bit error rate(BER).The proposed multi-pair scheme has made superior progress in BER performance because it not only can cancel the IPIs but also can balance the useful signal and the noise at each user.Moreover,in one-pair scenarios,the performance of the centralized scheme is better than the distributed one,but the latter is nevertheless much more practical.

Integrated Scheduling Optimization of Two-Way Channel Ships Entering and Leaving Ports and Tugboat Distribution

According to the passage rules of ships in the bidirectional channel,the realistic conditions of the limited number of tugboats in the port are taken into account.This paper studies the problems faced in the integrated scheduling optimization in terms of ship arrival and departure and tugboat allocation in two-way channel.A mixed integer programming model with minimum waiting time was established,and a heuristic algorithm was designed to solve the problem.Experimental results show that the model and algorithm in this paper can effectively solve such problems and provide support for port management.

基于水动力空化的微通道设备研究进展

针对微通道设备中的水动力空化现象,从限流元件的几何形状及尺寸、工作流体和通道粗糙度3个方面分析了其影响规律.限流元件的常见形状主要有微孔、微文丘里、微隔膜和微柱,不同几何形状的限流元件具有不同的空化流动特性;限流元件自身的尺寸参数以及尺寸缩小引起的尺度效应都对空化流型起着重要作用.常用的工作流体包含去离子水、乙醇、磷酸盐缓冲盐水(PBS)、制冷剂(R-123)、聚乙烯醇(PVA)微泡(MBs)悬浮液、全氟戊烷(PFC5)悬浮液、二氧化钛(TiO_(2))纳米颗粒悬浮液、多元液体混合物等;与水相比,其余工作流体均不同程度地提高了空化强度.粗糙度的引入主要体现于通道的表面粗糙元件和侧壁粗糙元件,其空化强度相较于光滑表面得到明显提高.微通道水动力空化设备主要应用于能量收集、液相剥离和生物医学领域.基于近年来国内外对微尺度水动力空化的研究现状,设想了微通道设备中的水动力空化现象的潜在研究方向及应用趋势.

极浅水域船舶航行阻力及下沉量数值计算方法

针对舰船在极浅水域中的航行阻力及航行安全预报问题,提出了静力平衡方程与叠模定常流计算相结合的数值计算方法。经分析比较可知,该方法只需进行一次姿态调整,姿态收敛偏差即可小于5%。水动力计算结果与水池模型试验结果对比表明:当深度/吃水比(h/T_(m))为1.18时,阻力预报相对偏差为3%左右、下沉量绝对偏差小于2 mm,触底航速预报相对偏差小于5%。该方法可有效避免计算过程中姿态波动导致解算失败的问题,具有良好的计算稳定性和收敛性,且计算精度较高,可为浅水航行船舶航行性能数值计算提供借鉴和参考。

乌江限制性航道船舶快速性预报研究

文中以乌江航道为例,针对当前推广应用的千吨级绿色高能效标准船型,基于乌江标准船型的船模阻力与自航试验,测试了不同水深状态下阻力及自航性能参数.采用傅汝德换算法估算实船阻力及有效功率,分析各工况下有效功率与航速的对应规律,为标准船型选定合适的主机功率.结合船舶能源应用现状制定不同动力方案,计算并比较各方案对应的碳排放与必要运费率,最终推荐柴油-天然气双燃料动力模式.

考虑引航员拖轮调配的船舶交通组织优化

为解决限制性双向航道的船舶交通组织问题,提高港口通航效率,从应用需求出发,综合考虑了引航员、拖轮、潮汐、安全距离以及单双向航道中的交通冲突因素,以船舶总等待时间最小为优化目标,建立了混合整数规划模型。考虑到模型的特征,提出了改进差分进化算法(improved differential evolution,IDE)来解决该问题。经过不同规模算例的试验,将所得到的船舶调度结果与先到先服务和其他算法结果进行比较验证,模型和算法可以有效地为限制性双向航道提供船舶交通组织方案。

基于万吨级船舶阻力变化的大型人工水道断面尺度研究

针对国内现行规范在可通行3000 t级以上船舶的大型人工水道断面尺度设计方面的规定不足,从限制性航道航速经济性角度出发,定义大型人工水道的经济航速断面,基于数学模型研究满足万吨级船舶(总长130 m×型宽22 m×设计吃水5.5 m)通航要求的经济航速断面尺度推荐参数区间。具体包括:基于完全非线性Boussinesq方程的开源程序包FUNWAVE-TVD建立了限制性航道中船行波传播变形及阻力变化数学模型,模拟研究了不同边坡比、航道底宽条件下船舶阻力变化规律,重点分析了航道底宽、边坡比对航行阻力的影响。研究结果表明:在大型人工水道设计时,对于梯形断面,经济航速断面设计时,坡比采用1:3较优,水深8 m时底宽取90 m,断面系数为7.54较优;水深9 m时,底宽取70 m,断面系数为7.21较优。

基于海事调度规则的长距离受限航道通航效率影响研究

根据特定时段混合船舶流特征,优化海事调度规则是提升航道通航效率的低成本、高效率方法。文章以长距离受限航道通航效率提升为研究对象,以平均等待时间(AWT)、港口服务水平(AWT/AST)、泊位利用率(ρ)、航道通过能力(T)为指标,基于靠港船舶AIS数据建立Arena港口生产作业仿真系统,分析先到先得(FCFS)、港口效益优先(PEP)和综合效益优先(CBP)等海事调度规则对通航效率的影响。以RSOT长距离受限航道为案例,基于2021—2022年靠港船舶AIS数据的研究结果表明:FCFS和PEP规则的效果基本一致,CBP规则可以有效降低大部分船型平均等待时间的同时提升了港口服务水平。其中:10万t级原油船AWT降幅最大达到62%,货船泊位利用率ρ增长达到64%;在当前船舶到港密度流增加20%时依然保持高效率,成品油船AWT和AWT/AST降幅最大达到62%,货船泊位、原油泊位和成品油泊位利用率ρ值分别提升67%、28%和26%,航道通过能力T值的提升可达到14%。研究结论可以为该类长距离受限航道的海事调度规则优化和通航效率提升提供借鉴。

海底管道穿越受限制海域铺管施工工艺创新应用

针对海底管道路由穿越已有航道等限制性区域给铺设作业带来的困难,结合香港海域某海底管道铺设项目,制定施工准备、预铺设、实施底拖作业等过程的具体方案。通过制定施工方案和优化辅助措施,如非均匀浮筒绑扎和浮筒快速回收技术,提高底拖作业成功率和效率,保障航道畅通。该施工方案的应用对于此类限制性区域内的海底管道铺设具有一定参考价值。

Opportunistic Relaying Schemes for Amplify and Forward Bidirectional Relay Channels with Multi antenna Sources

We consider a two-way relay network where the Amplify-and-Forward (AF) protocol is adopted by all relays in this paper.The network consists of two multi-antenna source nodes and multiple distributed single-antenna relays.Two opportunistic relaying schemes are proposed to efficiently utilize the antennas of the source nodes and the relay nodes.In the first scheme,the best relay is selected out by a max-min-max criterion before transmitting.After that,at each source,only the antenna with the largest channel gain between itself and the best relay is activated to transmit and receive signals with full power.In the second scheme,assisted by the best relay which is selected by the typical max-min criterion,both source nodes use all their antennas to exchange data,and match filter beamforming techniques are employed at both source nodes.Further analyses show that all schemes can achieve the full diversity order,and the conclusions are not only mathematically demonstrated but numerically illustrated.System performance comparisons are carried out by numerical methods in terms of rate sum and outage probability,respectively.The beamforming assisted scheme can be found to be superior to the antenna selection scheme when accurate Channel State Information (CSI) is available at the transmitters.Otherwise,the latter is very suitable.

Fast Sparse Multipath Channel Estimation with Smooth L0 Algorithm for Broadband Wireless Communication Systems

Broadband wireless channels are often time dispersive and become strongly frequency selective in delay spread domain. Commonly, these channels are composed of a few dominant coefficients and a large part of coefficients are approximately zero or under noise floor. To exploit sparsity of multi-path channels (MPCs), there are various methods have been proposed. They are, namely, greedy algorithms, iterative algorithms, and convex program. The former two algorithms are easy to be implemented but not stable;on the other hand, the last method is stable but difficult to be implemented as practical channel estimation problems be-cause of computational complexity. In this paper, we introduce a novel channel estimation strategy using smooth L0 (SL0) algorithm which combines stable and low complexity. Computer simulations confirm the effectiveness of the introduced algorithm. We also give various simulations to verify the sensing training signal method.

Automatic Classification of Superimposed Modulations for 5G MIMO Two-Way Cognitive Relay Networks

To promote reliable and secure communications in the cognitive radio network,the automatic modulation classification algorithms have been mainly proposed to estimate a single modulation.In this paper,we address the classification of superimposed modulations dedicated to 5G multipleinput multiple-output(MIMO)two-way cognitive relay network in realistic channels modeled with Nakagami-m distribution.Our purpose consists of classifying pairs of users modulations from superimposed signals.To achieve this goal,we apply the higher-order statistics in conjunction with the Multi-BoostAB classifier.We use several efficiency metrics including the true positive(TP)rate,false positive(FP)rate,precision,recall,F-Measure and receiver operating characteristic(ROC)area in order to evaluate the performance of the proposed algorithm in terms of correct superimposed modulations classification.Computer simulations prove that our proposal allows obtaining a good probability of classification for ten superimposed modulations at a low signal-to-noise ratio,including the worst case(i.e.,m=0.5),where the fading distribution follows a one-sided Gaussian distribution.We also carry out a comparative study between our proposal usingMultiBoostAB classifier with the decision tree(J48)classifier.Simulation results show that the performance of MultiBoostAB on the superimposed modulations classifications outperforms the one of J48 classifier.In addition,we study the impact of the symbols number,path loss exponent and relay position on the performance of the proposed automatic classification superimposed modulations in terms of probability of correct classification.

PERFORMANCE ANALYSIS OF TWO-WAY AMPLIFY-AND-FORWARD RELAYING SYSTEM WITH MULTIPLE INTERFERERS AT THE RELAY

In this paper,we investigate the performance of the two-way Amplify-and-Forward(AF) relaying systems in an interference-limited Rayleigh fading environment.More specifically,assuming the presence of Rayleigh faded multiple interferers at the AF relay and noisy sources,an approximate closed-form expression for the Overall Outage Probability(OOP) and an integral expression for the average Symbol Error Probability(SEP) are derived.The analysis results are verified through com-parison with the Monte Carlo simulation results.

基于改进DBSCAN算法的受限航道船舶会遇规律挖掘研究

受限航道船舶会遇态势复杂多变,为了识别潜在航行风险,提出一种基于SO-DBSCAN(self-optimal DBSCAN)算法的受限航道船舶会遇规律挖掘方法。首先,构建了基于船速比修正的受限航道动态船舶领域模型,考虑受限航道船舶安全间距以及航速对交通流的影响,引入船速比修正因子改进藤井模型;其次,提出一种基于动态舷角的会遇态势划分方法,结合国际海上避碰规则相关条款要求,采用船舶间动态舷角关系及航行速度作为引导划分出14种会遇态势;最后,引入Silhouette Coefficient和Calinski-Harabasz评估指标,并以加权和最大为目标函数自主求解最优的聚类策略,通过采集天津港受限航道的AIS数据进行实例验证,挖掘会遇时空规律并识别会遇热点。研究表明:该水域内船舶在15:00—17:00时间段内会遇较为频繁,会遇关键区域主要集中在42#~48#灯浮和22#~32#灯浮附近,结果符合航海实际;基于SO-DBSCAN算法的受限航道船舶会遇规律挖掘方法不仅能够解决传统基于密度聚类算法调参复杂的问题,还能够有效识别会遇高风险区域。

A CFD Study of the Resistance Behavior of a Planing Hull in Restricted Waterways

The demand for high-speed boats that operating near to shoreline is increasing nowadays.Understanding the behavior and attitude of high-speed boats when moving in different waterways is very important for boat designer.This research uses a CFD(Computational Fluid Dynamics)analysis to investigate the shallow water effects on prismatic planing hull.The turbulence fl ow around the hull was described by Reynolds Navier Stokes equations RANSE using the k-ɛturbulence model.The free surface was modelled by the volume of fl uid(VOF)method.The analysis is steady for all the ranges of speeds except those close to the critical speed range Fh=0.84 to 1.27 due to the propagation of the planing hull solitary waves at this range.In this study,the planing hull lift force,total resistance,and wave pattern for the range of subcritical speeds,critical speeds,and supercritical speeds have been calculated using CFD.The numerical results have been compared with experimental results.The dynamic pressure distribution on the planing hull and its wave pattern at critical speed in shallow water were compared with those in deep water.The numerical results give a good agreement with the experimental results whereas total average error equals 7%for numerical lift force,and 8%for numerical total resistance.The worst effect on the planing hull in shallow channels occurs at the critical speed range,where solitary wave formulates.