喷泉码多路并行转发中继系统传输时间分析

为了降低传输协议的复杂度,避免引入大量的反馈链路,将喷泉码应用于多级多路并行中继网络中进行开环差错控制.给出了采用喷泉码编码时的网络传输方案和帧格式,分析并比较了基于喷泉码方案和基于自动重传请求方案的传输时间.研究表明,应用喷泉码时系统的传输时间远小于应用ARQ时的传输时间,并且随着中继数的增加,喷泉码方案的优势越来越明显.     

LTE TDD系统中下行HARQ机制的研究

在对长期演进(long term evolution,LTE)下行数据发送机制详细分析的基础上,针对下行数据发送过程的实现,提出一种混合自动重传请求(hybrid automatic repeat request,HARQ)选择方案,遵照协议给出的反馈时延的时隙关系,在设计中采用反馈判断和优先重传的方案,实现了HARQ反馈和重传时刻的正确映射,并研究了同步HARQ和异步HARQ的往返时间(round trip time,RTT),仿真分析了不同上下行配置对HARQRTT的影响,提出了一种最小化RTT的方法,从而为网络侧提供业务不同时的配置选择提供了参考.     

3G长期演进系统中的混合自动重传请求技术

3G长期演进系统(LTE)的标准化工作已经全面展开,并得到了大家的广泛关注。各种先进的无线传输技术即将在该系统中得到应用,包括混合自动重传请求(HARQ)技术。根据重传发生时刻的不同,HARQ可以分为同步和异步两类。同步HARQ由于接收端预先已知传输的发生时刻,HARQ进程的序号可以从子帧号获得;异步HARQ进程的传输可以发生在任何时刻,HARQ进程的处理序号需要连同数据一起发送。由于HARQ技术能够很好地补偿无线移动信道时变和多径衰落对信号传输的影响,已成为LTE中的关键技术之一。该技术将会随着3G长期演进系统的发展不断完善。     

AdaCode:IEEE 802.11n长距离无线链路自适应编码算法

通过在实验床上的大量真实测量,分析了长距离无线链路中导致吞吐率低下的原因,总结了数据帧出错模式和丢包特点.在此基础上,提出了MAC（Media Access Control）层自适应编码算法AdaCode.该算法将帧间编码和帧内编码有机结合起来,帧间编码使用喷泉码LT（Luby Transform）码,帧内编码使用RS（Reed Solomon）码,根据链路中数据帧误比特率和丢包率的实时变化,动态选择最佳编码率,使接收端能够解码出所有数据帧,从而避免重传,极大提升了链路吞吐率.在MATLAB平台上实现了AdaCode,并使用实验床测得的真实数据进行仿真.仿真结果表明在固定物理层发送速率和可变发送速率两种情况下,AdaCode都能有效提升链路吞吐率.     

面向6G高铁移动场景的R10编码传输方案

6G时代越来越多的智能应用将在高铁中部署,需要高铁移动网络提供可靠和高效的传输服务。然而,受高速移动影响,车-地通信链路呈现快时变特性,采用传统的信道估计、反馈机制难以有效跟踪链路的快速时变,因此高铁移动网络亟需高效的前向纠错无反馈传输方案。由于R10编码兼顾了喷泉码和系统码的优点,将其引入高铁移动场景,提出了一种基于R10编码的高速移动车-地编码传输方案。采用该方案,发送端编码过程加入结构化冗余信息结合特定编码规则生成并发送任意数量编码符号,而接收端只需要收集一定数量编码符号结合结构化冗余信息即可更精准地恢复原数据,因此可实现更低的误码率。仿真实验表明,所提方案与传统无需反馈编码传输方案相比误比特率大大降低。以Turbo码为例,误比特率降低了约13%。     

有限反馈MIMO下行系统中基于黄金码的传输方案与解码方法

针对有限反馈多输入多输出下行系统,结合黄金码与预编码技术,提出一种新的预编码设计准则、码字选择方案及新的传输方案和相应的低复杂度解码方法。事实上,在充分利用黄金码能够克服信道深度衰落这一特性的基础上,对所选预编码码字进行重新构造,得到一个二重预编码矩阵,将其作为发送信号,从而能够实现线性解码。与此同时,针对传统的MIMO下行系统传输方案提出了ML和MMSE的联合解码方法,使其能通过一个门限值动态地调节解码复杂度。数值仿真结果证明了本文所提方案性能的优越性。     

中继协作无线网络中不完美反馈下基于网络编码的重传方案

无线广播网络传输过程中,目的节点反馈信息丢失或部分丢失导致发送节点不能了解目的节点的真实接收状态.为提高不完美反馈下无线网络的重传效率,本文提出中继协作无线网络中不完美反馈下基于网络编码的重传方案.本方案基于部分可观察马尔科夫决策过程对不完美反馈下的重传过程进行建模.发送节点根据系统观测状态和最大置信度更新系统估计状态,根据数据包发送顺序,优先选择最早丢失且能够恢复最多丢包的编码包重传.目的节点缓存不可解编码包以提升编解码机会.重传过程中源节点关注目的节点请求包需求,相同情况优先选择传输可靠性较高的中继节点,以提升传输有效性.仿真结果表明,在不完美反馈下相对于传统方案,本方案可有效提高重传效率.     

一种基于网络编码的重传算法研究

无线网络中,节点发送的数据分组传输失败后,执行重传机制。传统的重传机制ARQ由于在一次重传中只能发送一个丢失的数据分组,因此传输效率比较低。利用网络编码技术和AQR重传机制,我们可以在重传中使用网络编码,广播发送由多个丢失数据分组编码得到的编码分组,从而提高重传效率。本文中我们提出一种将网络编码应用于多个发送方多个接收方(MSMR)无线网络中的算法RMBNC。理论推导和仿真分析验证了我们提出的算法的有效性。     

D2D网络中基于牺牲节点的网络编码协作重传策略

针对D2D无线网络中多终端并发协作重传过程中平均解码时延较高的问题,提出了一种牺牲节点的协作重传策略.在重传阶段,发送终端在立即可解网络编码(Instantly Decodable Network Coding,IDNC)图上根据接收终端与发送终端的链路质量、终端数据包权重和接收终端的连通度选择出发送终端的最优编码包,...     

协作中继中联合乘积码的网络编码应用

在协作中继系统中应用网络编码可以提高网络的吞吐量,基于异或的网络编码并没有很好的纠错能力.提出了一种基于乘积码的网络编码方式,中继联合各个接收端的信息块,转发一次冗余块编码以提高各个接收端解码能力.理论和仿真曲线都证明了相对于简单的异或型网络编码,基于乘积码的网络编码可以提供更好的性能.     

Improving Wireless TCP Throughput by a Novel TCM-Based Hybrid ARQ

A novel hybrid ARQ (HARQ) scheme using a concatenated two-state trellis-coded modulation (CT-TCM) code is proposed for improving wireless TCP throughput. A distinguished feature of the proposed scheme is that the heavily punctured TCM codes are used for retransmissions of the corrupted data block, which are combined at the receiver with the previously received sequences of the same data block for decoding. By this method, significantly improved coding gain and efficient spectrum utilization can be achieved with very low complexity. A Markov model is developed to evaluate TCP throughput over the proposed HARQ in wireless link. By both analysis and simulation, we demonstrate that compared with other existing TCM-based ARQ schemes, significant improvement of TCP throughput over wireless links is achieved by the proposed CT-TCM HARQ while smaller buffer size is required at the access point.     

B3G时代LTE技术崭露头角

介绍长期演进项目（LTE）的技术特征,对比传统的宽频通信技术,突出了LTE技术优势,对LTE核心技术OFDM（正交频分复用）、MIMO（多输入多输出）、HARQ（混合自动重传）、AMC（自适应编码调制）等进行了介绍,同时对上下行编码方案,接入网结构变化进行了解释,最后对WiMAX以及WiFi技术进行对比分析,着重分析了LTE的技术优势,说明LTE技术在B3G时代势不可当的发展趋势。     

一种CQI辅助的HARQ改进方案

下一代移动通信系统在高速移动的条件下,需要更高的吞吐量和更大的带宽。这就需要采用更好的信道编码（turbo码等）、HARQ策略和信道均衡技术。但是,turbo译码是一个复杂的过程,在进行信号处理时会耗费用户大量的时间和功率。因此与turbo译码相关的HARQ策略会对系统性能产生很大影响。提出了一种CQI辅助的HARQ策略。这种策略主要利用了已经测量得到的CQI来跳过HARQ在首次传输和重传过程中不必要的解调和译码过程。通过采用HARQ策略,当误帧率高于门限时可以节省UE端大约55%的功率。     

Downlink scheduling optimization in CDMA networks

The problem of allocating radio resources in the downlink of a code-division multiple access (CDMA) network is studied. The modulation and coding schemes, numbers of multicodes, and transmit powers used for all mobile stations (MS) are jointly chosen so as to maximize the total transmission bit rate, subject to certain constraints. Based on the discrete and nonlinear nature of the proposed model, a mixed-integer nonlinear programming optimization problem is formulated. It is shown that the optimal allocation generally involves simultaneous transmissions to several MS. A scheduler which uses knowledge of MS traffic loads is also proposed and shown to yield a significant improvement in throughput.     

Optimizing the ARQ performance in downlink packet data systems with scheduling

Third generation wireless systems typically employ adaptive coding and modulation, scheduling, and Hybrid Automatic Repeat reQuest (HARQ) techniques to provide high-speed packet data service on the downlink. Two main considerations in designing such a system are algorithms for the selection of coding and modulation schemes based on the channel quality of the link and algorithms for the selection of the user to whom a particular slot is assigned. We propose a systematic approach to optimize the mapping between signal-to-interference-and-noise ratio (SINR) and modulation and coding scheme (MCS) to maximize the throughput by taking into account the type of HARQ scheme employed. We also propose to incorporate frame error rate (FER) and retransmission information as a part of the scheduling decision. The proposed scheduler ranking methods based on using an effective rate rather than the instantaneous rate provide natural priority to retransmissions over new transmissions, and priority to users with better channel quality. Extensive simulation results comparing performance of the proposed methods to conventional methods are presented.     

On Broadcast Stability of Queue-Based Dynamic Network Coding Over Erasure Channels

The transmission of packets is considered from one source to multiple receivers over single-hop erasure channels. The objective is to evaluate the stability properties of different transmission schemes with and without network coding. First, the throughput limitation of retransmission schemes is discussed and the stability benefits are shown for randomly coded transmissions, which, however, need not optimize the stable throughput for finite coding field size and finite packet block size. Next, a dynamic scheme is introduced for distributing packets among virtual queues depending on the channel feedback and performing linear network coding based on the instantaneous queue contents. The difference of the maximum stable throughput from the min-cut rate is bounded as function of the order of erasure probabilities depending on the complexity allowed for network coding and queue management. This queue-based network coding scheme can asymptotically optimize the stable throughput to the max-flow min-cut bound, as the erasure probabilities go to zero. This is realized for a finite coding field size without accumulating packet blocks at the source to start network coding. The comparison of random and queue-based dynamic network coding with plain retransmissions opens up new questions regarding the tradeoffs of stable throughput, packet delay, overhead, and complexity.      

适合TCP的网络编码重传机制

通过理论分析,看出基于反馈的重传方法比定量重传的方法有更低的解码延迟。提出了一种新型的基于反馈的网络编码(FNC)重传机制,利用seen机制中的隐含信息来获取接收方解码所需的重传分组个数,并改变了编码规则使部分分组可以提前解码。该机制不仅可以处理有固定误码率的随机分组丢失,还可以有效地应对大量突发性分组丢失。仿真结果显示,该机制在高误码率下也能保持较高的吞吐量,且极大地减少了解码延迟,传输过程基本不受分组丢失的影响,有效地对拥塞控制协议隐藏了链路错误。算法简单有效,更适于在实际系统中应用。     

Multiuser receiver scheme for full‐rate space–time coded CDMA system with imperfect estimation

By introducing a full‐rate space–time coding (STC) scheme, a synchronous CDMA (code division multiple access) system with full‐rate STC is given, and the corresponding uplink performance is investigated in Rayleigh fading channel with imperfect estimation. Considering that existing STC‐CDMA system has high decoding complexity, low‐complexity multiuser receiver schemes are developed for perfect and imperfect estimations, respectively. The schemes can make full use of the complex orthogonality of STC to reduce the high decoding complexity of the existing scheme, and have linear decoding complexity compared with the existing scheme with exponential decoding complexity. Moreover, the proposed schemes can achieve almost the same performance as the existing scheme. Compared with full‐diversity STC‐CDMA, the given full‐rate STC‐CDMA can achieve full data rate, low complexity, and partial diversity, and form efficient spatial interleaving. Thus, the concatenation of channel coding can effectively compensate for the performance loss due to partial diversity. Simulation results show that the full‐rate STC‐CDMA has lower bit error rate (BER) than full‐diversity STC‐CDMA systems under the same system throughput and concatenation of channel code. Moreover, the system BER with imperfect estimation are worse than that with perfect estimation due to the estimation error, which implies that the developed multiuser receiver schemes are valid and reasonable. Copyright © 2010 John Wiley & Sons, Ltd.     

Resource allocation algorithm for LTE networks using fuzzy based adaptive priority and effective bandwidth estimation

In this paper, we propose a scheme to allocate resource blocks for the Long Term Evolution (LTE) downlink based on the estimation of the effective bandwidths of traffic flows, where users’ priorities are adaptively computed using fuzzy logic. The effective bandwidth of each user traffic flow that is estimated through the parameters of the adaptive β-Multifractal Wavelet Mode modeling, is used to attain their quality of service (QoS) parameters. The proposed allocation scheme aims to guarantee the QoS parameters of users respecting the constraints of modulation and code schemes (modulation and coding scheme) of the LTE downlink transmission. The proposed algorithm considers the average channel quality and the adaptive estimation of effective bandwidth to decide about the scheduling of available radio resources. The efficiency of the proposed scheme is verified through simulations and compared to other algorithms in the literature in terms of parameters such as: system throughput, required data rate not provided, fairness index, data loss rate and network delay.     

A multi-CRC selective HARQ scheme for MIMO systems

A multi-Cyclic Redundancy Check （CRC） selective Hybrid Automatic-Repeat-reQuest （HARQ） scheme for improving the throughput efficiency of Multiple Input Multiple Output （MIMO） systems is proposed in this paper. According to different feedback information from the receiver, the proposed HARQ scheme employs two strategies, referred to as retransmission frame selection and space diversity. These two strategies decrease the successive frame errors upon retransmission. Theoretic analysis and computer simulation results show that this HARQ scheme achieves higher throughput than the existing HARQ schemes even in poor conditions of low Signal-to-Noise Ratio （SNR）.