Performance Analysis of WLAN Medium Access Control Protocols in Simulcast Radio-Over-Fiber-Based Distributed Antenna Systems

The performance of three wireless local-area network(WLAN) media access control(MAC) protocols is investigated and compared in the context of simulcast radioover-fiber-based distributed antenna systems(RoF-DASs) where multiple remote antenna units(RAUs) are connected to one access point(AP) with different-length fiber links.The three WLAN MAC protocols under investigation are distributed coordination function(DCF) in basic access mode,DCF in request/clear to send(RTS/CTS) exchange mode,and point coordination function(PCF).In the analysis,the inter-RAU hidden nodes problems and fiber-length difference effect are both taken into account.Results show that adaptive PCF mechanism has better throughput performances than the other two DCF modes,especially when the inserted fiber length is short.

Green Distributed Antenna Systems for Smart Communities: A Comprehensive Survey

Smart communities are an emerging communication means in which humans and smart devices will interact with each other and deliver ubiquitous services by exploiting social intelligence.Distributed antenna system(DAS),one of the key technologies to realize smart decisions in smart communities,can settle network smart coverage problem and improve system energy/spectrum efficiency significantly.Considering that energy consumption is an important element for community communications,in this paper,we survey the existing green DAS research for smart communities.In particular,our investigation covers antenna distribution,system capacity,spectrum efficiency,energy efficiency,and green access issues.Moreover,we analyze the existing application opportunities and challenges.This survey contributes to better understanding of the challenges and approaches for green DAS in existing smart community networks and further shed novel light on some future research directions.

Outage Analysis of Distributed Antenna Systems over Shadowed Nakagami-m Fading Channels

This paper presents an outage analysis of distributed antennas system(DAS) suffering from shadowed Nakagami-m fading environment where the desired signal also suffers from co-channel interference. The desired signal and interfering signal are subjected to path loss,multipath and shadowing fading. Based on Wilkinson's method,the signal to interference ratio(SIR) probability density function(PDF) of fixed DAS is obtained. Some numerical results of outage probability with different parameters are analyzed. The analysis results can provide sufficient precision for evaluating the outage performance of DAS.

Optimal antenna placement in distributed antenna systems

To minimize the outage probability of the cell （OPC） in downlink distributed antenna systems with selection transmission, a complex-encoding genetic algorithm （GA） is proposed to find the optimal locations of the antenna elements （AEs）. First, the outage probability at a fixed location in the cell is investigated. Next, an analytical expression of the OPC is derived, which is a function of the AE locations. Then the OPC is used as the objective function of the antenna placement optimization problem, and the complex- encoding GA is used to find the optimal AE locations in the cell. Numerical results show that the optimal AE locations are symmetric about the cell center, and the outage probability contours are also given with the optimal antenna placement. The algorithm has a good convergence and can also be used to determine the number of AEs which should be installed in order to satisfy the certain OPC value. Lastly, verification of the OPC＇s analytical expression is carried out by Monte Carlo simulations. The OPC with optimal AE locations is about 10% lower than the values with completely random located AEs.

Antenna selection based on large-scale fading for distributed MIMO systems

An antenna selection algorithm based on large-scale fading between the transmitter and receiver is proposed for the uplink receive antenna selection in distributed multiple-input multiple-output(D-MIMO) systems. By utilizing the radio access units(RAU) selection based on large-scale fading,the proposed algorithm decreases enormously the computational complexity. Based on the characteristics of distributed systems,an improved particle swarm optimization(PSO) has been proposed for the antenna selection after the RAU selection. In order to apply the improved PSO algorithm better in antenna selection,a general form of channel capacity was transformed into a binary expression by analyzing the formula of channel capacity. The proposed algorithm can make full use of the advantages of D-MIMO systems,and achieve near-optimal performance in terms of channel capacity with low computational complexity.

Asymptotic sum rate of MMSE receivers in multi-user distributed antenna systems

In this paper, the asymptotic sum rate of a multi-user distributed antenna system （DAS） is analyzed. To mitigate inter-user interference, minimum mean squared error （MMSE） receivers are utilized to cooperatively process received signals in the uplink. It shows that inter-user interference is efficiently mitigated and the uplink sum rate of a multi-user DAS is greatly improved by adopting MMSE receivers. For very large number of users and remote antennas, the asymptotic uplink sum rate of MMSE receivers is derived by using virtue of the random matrix theory, which can be The approximation is verified to be quite accurate by Monte Carlo simply calculated in an iterative way simulations.

Ergodic Capacity Analysis and Adaptive Transsmion Scheme in Multi-user Distributed Antenna Systems

This paper focuses on analyzing the ergodic capacity performance of limited feedback (LFB) beamforming in multi-user distributed antenna system (DAS). In such a system, multi-user interference (MUI) is inevitably due to the channel uncertainties caused by quantization error. Considering this, we propose a parameter named effective ergodic capacity rate (EECR), which denotes the capacity offset between finite rate feedback and perfect channel state information (CSI). The simulation results show that the derived approximated EECR is very tight to actual EECR. Based on the approximated EECR, an adaptive minimum bit feedback scheme is proposed, which can effectively reduce the overhead of feedback channel and the complexity of the system. The simulation results verify the effectiveness of the proposed scheme.

Distributed antenna wireless communication system coverage design and field trial over higher frequency band

This paper aims to examine the architecture design of a distributed antenna based Gbps wireless communication system using the high frequency band.In order to analyze the feasibility of the higher frequency band applications,the cumulative distribution of simulated user throughput in a cellular is investigated firstly.It shows that capacity improvement can be obtained using higher operating frequency band,especially in hotspot scenarios.Secondly,the architecture of the distributed antenna system(DAS) is introduced to overcome the disadvantages of weak coverage and rank deficient for the traditional multiple-input multiple-output(MIMO) systems using higher frequency bands in line-of-sight(LOS)environments.In addition,a software-defined-radio(SDR) based Gbps wireless transmission system with scalable hardware architecture is designed and implemented.Finally,a demo of outdoor DAS coverage for high data throughput application is given.Field trials show that 1 Gbps data rate and a large coverage in outdoor environments can be achieved over 6.05 GHz.It is proved that the Gbps DAS system at a higher frequency band can be a successful model for future wireless broadband coverage in hotspot scenarios.

Joint Antenna Selection and Robust Beamforming Design in Multi-cell Distributed Antenna System

Most of studies on Distributed Antenna System(DAS) focus on maximizing the sum capacity and perfect channel state information at transmitter(CSIT).However,CSI is inevitable imperfect in practical wireless networks.Based on the sources of error,there are two models.One assumes error lies in a bounded region,the other assumes random error.Accordingly,we propose two joint antenna selection(AS) and robustbeamforming schemes aiming to minimize the total transmit power at antenna nodes subject to quality of service(QoS) guarantee for all the mobile users(MUs) in multicell DAS.This problem is mathematically intractable.For the bounded error model,we cast it into a semidefinite program(SDP) using semidefinite relaxation(SDR) and S-procedure.For the second,we first design outage constrained robust beamforming and then formulate it as an SDP based on the Bernstein-type inequality,which we generalize it to the multi-cell DAS.Simulation results verify the effectiveness of the proposed methods.

Capacity Analysis on Distributed Antenna System with Imperfect CSI over Rayleigh Fading Channel

Considering that perfect channel state information(CSI)is hard to obtain in practice,the capacity of downlink distributed antennas system(DAS)with imperfect CSI is analyzed over Rayleigh fading channel.Based on the performance analysis,using the probability density function and numerical calculation,an accurate closedform expression of ergodic capacity of downlink DAS under imperfect CSI is derived.It includes the one under perfect CSI as a special case.This theoretical expression can provide good performance evaluation for downlink DAS for both perfect and imperfect CSI due to its accuracy.Simulation results indicate that the theoretical analysis agrees well with the corresponding simulation,and the capacity can be increased effectively by decreasing the estimation error and/or path loss.

Capacity and outage probability analysis of downlink MRT-SC in distributed antenna system

This paper investigates the downlink capacity distribution and the outage probability of the interested area of maximum ratio transmission-selection combining(MRT-SC) scheme in the distributed antenna system(DAS).Composite fading channels are assumed,which include path loss,lognormal shadowing and multi-path Rayleigh fading.Analytical approximations of the capacity's cumulative distribution function(CDF),the outage capacity,the mean capacity,and the outage probability of the interested area are derived by means of moment generation function(MGF) and Gauss-Hermite series expansion based approaches.The influence of antenna number,path loss exponent,and shadowing standard deviation on the capacity distribution are investigated.The simulation results agree with the analytical approximations well,and thus the analytical approximations are able to substitute the time-intensive Monte Carlo simulation for further investigation.

Dynamic Relay Selection Method for Distributed MIMO Relay System

The research on distributed MIMO relay system has been attracting much attention. In this paper, a decode-and-forward scheme distributed MIMO relay system is examined. For upper bound of channel capacity, the distance between transceivers is optimized when the propagation loss is brought close to actuality. Additionally, the number of relay is optimized whether total antenna element is fixed or not. When the number of relay is assumed to be infinite, the dynamic relay selection method based on the transmission rate is proposed. We represent that with the proposed method, the transmit power and the number of relays are saving.

Adaptive Energy Efficient Power Allocation Scheme for DAS with Multiple Receive Antennas

Energy efficiency(EE)of downlink distributed antenna system(DAS)with multiple receive antennas is investigated over composite Rayleigh fading channel that takes the path loss and lognormal shadow fading into account.Our aim is to maximize EE which is defined as the ratio of the transmission rate to the total consumed power under the constraints of the maximum transmit power of each remote antenna.According to the definition of EE,the optimized objective function is formulated with the help of Lagrangian method.By using the Karush-KuhnTucker(KKT)conditions and numerical calculation,considering both the static and dynamic circuit power consumptions,an adaptive energy efficient power allocation(PA)scheme is derived.This scheme is different from the conventional iterative PA schemes based on EE maximization since it can provide closed-form expression of PA coefficients.Moreover,it can obtain the EE performance close to the conventional iterative scheme and exhaustive search method while reducing the computation complexity greatly.Simulation results verify the effectiveness of the proposed scheme.

Transmit Antenna Selection with Power and Rate Allocation for Spatial Multiplexing in Distributed Antenna Systems

High spectral efficiency distributed antenna systems （DAS） require vertical Bell-Labs layered space-time （V-BLAST） like spatial multiplexing schemes. However, unlike normal point-to-point multiple input multiple output （MIMO） channels, DAS channels have different large-scale fadings from different transmit antennas, thus making equal power and rate transmission that is feasible in MIMO channels unrealistic in DAS channels. This paper proposes a novel transmit antenna selection scheme with power and rate allocation. The scheme is based on large-scale fading （shadow fading and path loss） and is suitable for VBLAST structures with zero-forcing and successive interference cancellation （ZF-SIC） receivers, ensuring balanced average symbol error rate （SER） performance in each layer. On the receiver side, a fixed detection order is used, which is obtained in the transmit antenna selection process. Simulation results show that the proposed scheme gives good performance gains over equal power and rate transmission systems without antenna selection.

室外广角漏缆对室内有源DAS系统覆盖效果的影响及优化策略研究

随着科技的不断发展,无线通信技术的应用越来越广泛,人们对通信服务的需求也越来越大。室内有源分布式天线系统(Distributed Antenna System,DAS)作为一种能够提高无线通信服务质量和覆盖范围的重要系统,受到越来越多的关注和应用。受室外广角漏缆等问题的影响,室内有源DAS系统的覆盖仍然存在一定的挑战。通过研究室外广角漏缆对室内有源DAS系统覆盖效果的影响,探索相应的优化策略,对于提高无线通信服务的质量和覆盖范围,推进无线通信技术的发展和创新具有重要意义和价值。

Forward Link Performance Analysis in CDMA Distributed Antenna Systems with Imperfect Channel Estimation

The impact of imperfect channel estimation on the forward-link performance inCDMA distributed antenna systems in multi-path fading environment is investigated. A detailedanalytical model based on a hybrid signal combining method is presented and exact outage probabilityexpression is derived. The investigation shows that the effect of imperfect channel estimatesvaries with system load. Furthermore, if simulcasting is employed, macro-diversity can decrease thesensitivity of forward-link to channel estimation errors and increase the forward-link outageperformance, which is contrary to the conclusion drawn based on the ideal channel estimationassumption.

5G室内分布系统规划建模及优化算法

由于5G移动通信技术中的多数新业务包括时代智慧家庭、智能工厂、虚拟现实等等都发生在室内场景,因此如何快速规划建设成本低且功率损耗少的5G网络室内分布系统,对电信运营商来说具有重要的意义。建立了更贴近实际场景下的5G室内分布系统规划数学模型,该模型以最小化部署成本和天线间最大输出信号功率偏差为目标,以满足每个天线的期望输出信号功率为约束,是一个带约束的混合变量多目标优化问题。基于哈夫曼编码思想,提出了适合室分系统结构的编码策略,利用该编码策略在MOEA/D-CM2M算法框架下设计出求解该模型的有效算法,并且能够通过一次运行提供多个规划方案。计算机仿真表明建立的模型与提出的算法十分有效,比两个真实案例的原设计分别节省了8.90%和20.09%的成本。

Energy Efficiency of Distributed Antenna Systems with D2D Communications Under Imperfect CSI

In this paper,we investigate the distributed antenna systems(DAS)based on device to device(DASD2D)communications under the imperfect channel state information(CSI).Our aim is to maximize the energy efficiency(EE)of the D2D users equipment(DUE)under the constraints of the maximum transmission power of D2D pairs and the quality of service(QoS)requirements of the cellular user equipment(CUE).The worst-case design is considered so that the QoS of the CUE can be guaranteed for every realization of the CSI error in the ellipsoid region.The EE objective function of the optimization problem is non-convex and non-linear,and thus this problem cannot be solved by the traditional optimization methods.To solve this problem,first we transform it to an EE maximization problem without uncertain parameters by exploiting the Markov and Cauchy-Schwartz inequality.Then using the fractional programming theory and difference of convex functions optimization method,the robust EE maximization algorithms based on the hard and soft protection method are developed to maximize the system’s EE performance,respectively.However,these two algorithms are designed at the cost of the reduced EE of the DUE.Therefore,in order to further improve the EE performance and make a trade-off between the EE performance and the robustness,the iterative update algorithms for the total power constraint and average interference constraint are developed to maximize the system’s EE performance,respectively.Simulation results demonstrate the effectiveness of the four proposed EE algorithms and illustrate the trade-off between the EE performance and robustness for the iterative update algorithms.

RoF-DAS架构下具有差错重传的预约式WLAN MAC协议研究

为减少控制帧消耗,降低系统接入时延,提出了预约式门限服务轮询接入(SGPA)策略,将站点接入时刻缓存区中的排队数据整合为数据集,对数据集进行统一发送和确认。针对RoF-DAS架构下WLAN差错重传机制与网络接入性能的定量关系进行分析,建立了具有内部数据的门限服务轮询(IAGP)排队模型,利用轮询系统中内部数据的到达和服务过程描述数据差错重传机制,然后基于马尔可夫链和概率母函数方法推导出站点数据时延性能与重传次数、重传概率等参数的定量关系表达式。仿真实验结果表明,SGPA与典型IEEE 802.11 PCF相比有效降低了接入时延;采用IAGP模型对系统时延性能分析的理论计算值与仿真结果一致。该分析模型为非理想信道环境和差错重传机制下的RoF-DAS WLAN网络接入性能分析提供了一种快速评估机制。

透镜天线在居民小区的应用探讨

如何实现优质的小区无线网络深度覆盖对于运营商而言,一直是个突出的挑战与困难。通过试点应用Luneburg透镜天线来解决此类问题。在多场景下进行对比试验,用以验证Luneburg透镜的覆盖性能,为运营商在当前网络环境下提供最新的现网实验数据,同时也为处理密集高层住宅小区的深度覆盖问题,提供了一个可能的解决方案。