多源分布式协作空时网络编码系统的设计

为改善传统空时编码协作方案中节点功率消耗过高和传输效率较低的问题,在多信源、单中继协作网络中提出一种新的空时网络编码方案。该方案利用中继节点的多天线优势实现接收分集,并在中继节点设计空时网络编码,再按照编码矩阵特点转发信号到目的节点。仿真验证了信源数、中继天线数不同时的系统性能,并分析了传统空时编码协作方案与提出方案的性能差距和传输效率,得出该方案是一种易于实现,性能良好的高效无线数据传输方式的结论。     

采用压缩感知的协作多点信道反馈算法研究

协作多点技术（ Coordinated Multiple Points,CoMP）作为LTE-A的最重要候选技术之一,已经得到广泛的关注。在协作多点中,有很多种传输方案,其中一种基于联合传输下的全局预编码方案能够获得极佳的系统性能,而实现该方案的前提是基站可以得到较为完整的信道状态信息。因此在信道反馈时选择显式反馈,因为相比较其他反馈方式,它可以反馈更为完整的信道状态信息,而显式反馈的缺点为需要的反馈量过大。文中利用一种采用压缩感知的信道反馈新方法对联合传输下的全局预编码方案信道显式反馈信息进行压缩,仿真结果显示在不影响系统性能的前提下,能够有效地减少反馈量,使得系统发挥最佳性能。     

空时分组编码的多用户CDMA系统在MIMO Rayleigh衰落信道中的性能

通过引入正交空时编码方案,文中给出了基于各种空时编码的多用户CDMA系统,研究了该系统在多天线Rayleigh衰落信道下的性能.针对空时编码CDMA系统,提出了一种低复杂度多用户接收机方案,该方案可利用空时编码的复正交性简化已有方案的高译码复杂度.与已有方案指数性译码复杂度相比,所提方案具有线性复杂度.在此基础上,给出了系统性能分析,并利用相关数学计算,详细推导了系统平均误比特率(BER),得到了比较紧的平均BER闭式表达式.仿真结果表明所获得的平均BER理论值与相应的仿真值是一致的,而且所提的接收机方案可实现与原有方案相近的性能.在相同系统吞吐量和级联码情况下,所给出的满速率空时编码要好于相应的满分集空时编码CDMA系统,有较低的误比特率.     

空时分组码在TD-SCDMA系统中的应用技术研究

提出了一种空时分组码与TD-SCDMA系统联合检测算法相结合的新方法,提出在发送端两根天线采用基于数据域的域空时分组码编码方案,即以一个突发中的数据域为单位进行空时分组码的编码。接收端采用一根天线接收,算法可应用于多根天线,并对系统矩阵进行了扩充,对一个突发中的两个数据域同时进行译码。与传统的联合检测算法比较,由于采用了发送分集技术,性能有所提高。     

空时分组码在TD-SCDMA系统中的应用技术研究

提出了一种空时分组码与TD-SCDMA系统联合检测算法相结合的新方法,提出在发送端两根天线采用基于数据域的域空时分组码编码方案,即以一个突发中的数据域为单位进行空时分组码的编码.接收端采用一根天线接收,算法可应用于多根天线,并对系统矩阵进行了扩充,对一个突发中的两个数据域同时进行译码.与传统的联合检测算法比较,由于采用了发送分集技术,性能有所提高.     

分布式MIMO 系统的迭代空时检测算法

针对未来无线通信系统中广义分布式天线阵的架构,提出了一种适用于分布式多输入多输出（MIMO） 系统的LST-STBC 空时编码方案．该方案通过具有差错控制编码的分层空时（LST）结构与基于正交设计的分组空 时码（STBC）的有效结合,同时获得了分集和复用增益．针对提出的空时编码结构,接收端采用基于软干扰抵消和 最小均方误差（MMSE）的迭代检测算法,通过检测和译码软信息的迭代,有效降低了系统的误码率．仿真结果表 明,文中提出的基于接收端迭代检测的空时编码方案能有效提高分布式MIMO 系统的传输速率和传输质量．     

空间分集技术在CFBM-MC-CDMA系统中的应用研究

给出了一种简单的空时编码方案，提出了应用该方案的基于复数滤波器组调制的多载波码分多址(CF-BM-MC-CDMA)通信系统的模型。理论分析可知，采用空时编码天线发射分集技术的CFBM-MC-CDMA系统与未采用天线分集的系统相比，其多址干扰功率降低了一半。仿真结果表明，系统采用天线分集技术能显著提高其误比特率性能，在低信噪比区域，系统采用两天线分集接收的性能要比采用两天线分集发射的性能好得多。     

分布式CoMP系统中联合预处理方法研究

在分布式多点协同传输系统中,为进一步提升小区边缘用户接收性能和提高频谱利用率,提出一种联合预处理方法。该方法采用预编码和空时编码相结合的联合编码模型。在分布式天线系统的各远端天线单元(RAU)根据信道状态好坏,形成针对用户传输的协作集合。协作集合中各RAU采用相应的预编码规则对同一用户数据进行预处理,并通过空时分组码的方式发送数据。协同的各RAU进行联合传输,用户端使用最大比合并的方式接收。仿真实验结果表明,该方法能有效地改善系统误码率性能,提高边缘用户接收可靠性。     

提高MIMO信道BER性能的干扰对齐方案

为提高多输入多输出(MIMO)X信道的比特误码率(BER)性能,提出一种干扰对齐方案。在发送端将数据按照Alamouti编码方案重复发送,在接收端通过重新配置天线工作模式改变信道系数,构成具有正交结构的等效信道矩阵,通过矩阵运算消除干扰,并采用低复杂度的PIC群译码算法进行译码。仿真结果验证了该方案的有效性。     

基于多链拓展编码方案的量子遗传算法

为了提高量子遗传算法的性能,提出了一种基于多链拓展编码方案的量子遗传算法。根据编码方案,将每个量子位分解为多个并列的基因,有效地拓展了搜索空间;结合编码方案提出量子更新策略,并引入了动态调整旋转角机制对个体进行更新,使用量子非门变异策略实现量子变异。仿真实验中,分析了使用不同变异概率[0,0.1,…,0.9,1]时对算法性能的影响,对比了分别使用普通量子遗传算法、双链编码方案、三链编码方案以及四链编码方案的量子遗传算法在优化函数极值问题时算法的性能。实验结果证明,通过增加基因链可以显著提高算法的性能,多链拓展编码方案可以提高量子遗传算法的性能,是有效的。     

基于空时块编码的飞行器全向无线通信分析

将空时块编码引入飞行器全向无线传输中,用于抑制传统飞行器全向通信中不同天线发送信号在空间中发生干涉的问题.从等效合成天线增益和适合的应用场景两方面对基于空时块编码的传输方案的性能进行分析和讨论.针对不同的传输场景进行了仿真评估.仿真结果表明:使用空时块编码的方案性能与天线数量和天线方向图有关;相比传统方案,采用空时块编码能够有效抑制信号在空间中的深衰减,降低通信链路中断概率,从而大幅改善飞行器全向通信能力.     

基于多级反馈式喷泉码的深空传输协议研究

针对深空环境中高误码率、长传输时延的通信特点,在传统喷泉码的基础上提出了一种基于多级反馈式喷泉码的深空通信传输协议。给出了基于多级反馈式喷泉码传输协议具体的编码结构和传输方案,从理论上分析了该传输协议与非反馈喷泉码传输协议的编码有效性和传输时间,并通过实验比较了上述两种传输协议以及基于喷泉码的译码转发传输协议在不同误码率和传输距离的深空通信环境下的传输性能。实验结果表明,基于多级反馈式喷泉码的传输协议提高了编码有效性,减少了文件传输时延。     

Parallel implementation of back-propagation algorithm in networks of workstations

This work presents an efficient mapping scheme for the multilayer perceptron (MLP) network trained using back-propagation (BP) algorithm on network of workstations (NOWs). Hybrid partitioning (HP) scheme is used to partition the network and each partition is mapped on to processors in NOWs. We derive the processing time and memory space required to implement the parallel BP algorithm in NOWs. The performance parameters like speed-up and space reduction factor are evaluated for the HP scheme and it is compared with earlier work involving vertical partitioning (VP) scheme for mapping the MLP on NOWs. The performance of the HP scheme is evaluated by solving optical character recognition (OCR) problem in a network of ALPHA machines. The analytical and experimental performance shows that the proposed parallel algorithm has better speed-up, less communication time, and better space reduction factor than the earlier algorithm. This work also presents a simple and efficient static mapping scheme on heterogeneous system. Using divisible load scheduling theory, a closed-form expression for number of neurons assigned to each processor in the NOW is obtained. Analytical and experimental results for static mapping problem on NOWs are also presented.     

基于布隆过滤器所有权证明的高效安全可去重云存储方案

可去重云存储系统中一般采用收敛加密算法,通过计算数据的哈希值作为其加密密钥,使得重复的数据加密后得到相同的密文,可实现对重复数据的删除;然后通过所有权证明（PoW）,验证用户数据的真实性来保障数据安全。针对可去重云存储系统中所有权证明时间开销过高导致整个系统性能下降问题,提出了一种基于布隆过滤器进行所有权证明的高效安全方法,实现用户计算哈希值与初始化值的快速验证。最后,提出一种支持细粒度重复数据删除的BF方案,当文件级数据存在重复时进行所有权证明,否则只需要进行局部的文件块级数据重复检测。通过仿真对比实验,结果表明所提BF方案空间开销低于经典Baseline方案,同时时间开销低于经典Baseline方案,在数据文件越大的情况下性能优势更加明显。     

Performance of multiuser CDMA system with space-time block coding in MIMO Rayleigh fading channels

In this paper, by introducing orthogonal space-time coding scheme, the multiuser CDMA systems with different space time codes are given, and corresponding system performance is investigated over Rayleigh fading channel. A low-complexity multiuser receiver scheme is developed for space-time coded CDMA systems. The scheme can make full use of the complex orthogonality of space-time coding to simplify the high decoding complexity of the existing scheme. Compared to the existing scheme with exponential decoding complexity, it has linear decoding complexity. Based on the performance analysis and mathematical calculation, average bit error rate (BER) of the system is derived in detail, and tight closed-form approximation expressions of BER are attained. Simulation results on average BER are in agreement with the theory analysis. The results show that the proposed scheme can achieve almost the same performance as the existing scheme. Moreover, on the condition of same system throughput and concatenation of channel code, the given full-rate space-time coded CDMA system has lower BER than the full-diversity space-time coded CDMA systems.     

Cross layer multicarrier MIMO cognitive cooperation scheme for wireless hybrid ad hoc networks

The special multi-scenario of the topology in the wireless hybrid ad hoc networks is studied in this paper. A new performance evaluation link cognitive cooperation air time metric (LCCATM) and a novel cross layer multicarrier MIMO cognitive cooperation scheme are proposed. The proposed scheme integrated the attributes both of the new performance evaluation of the cooperative diversity and the attributes of the topology space. With the help of the proposed scheme, the cooperative ability of the networks is not only cognitive, but also topology aware. The average achievable sum rates and the outage probability of the networks are all examined with the cross layer constraints. The simulation results show that the proposed scheme can enhance the average rate performance and make the outage probability stable.     

并行密文倒排索引研究

加密数据是保护用户隐私的一个方法,特别在开放系统中的数据处理需求更为迫切,但要解决如何在密文上进行检索的问题。针对SSE-1密文检索方案的一些性能缺陷,采用不同的加密策略,在lucene倒排索引的基础上,设计了密文倒排索引Crypt-Lucene,同时结合云计算特点,设计了并行构建Crypt-Lucene方案,理论分析了方案的性能,并通过实验证明了方法的有效性。实验结果表明,Crypt-Lucene与SSE-1相比,索引构建时间减少了约为60%,同时具有较好的空间性能,对于大文档集合,利用MapReduce在4结点构成的Hadoop集群上并行构建8个Crypt-Lucene索引能减少83.4%的时间。     

Moment preserving schemes for Euler equations

A high order accurate finite difference scheme is proposed for one-dimensional Euler equations. In the scheme a set of first three moments of each signal are preserved during the updating. The scheme is one of 5th order in space and 4th order in time. This feature is different from that in typical existing methods in which the use of the first three polynomials results in only 3rd order accuracy in space. The scheme has different features from the existing high order schemes, and the most noticeable are the simultaneous discretization both in space and time, and the use of moments of Riemann invariants instead of primitive physical variables. Numerical examples are given to show the accuracy of the scheme and its robustness for the flows involving shocks.     

Job scheduling in mesh multicomputers

A new approach for dynamic job scheduling in mesh-connected multiprocessor systems, which supports a multiuser environment, is proposed in this paper. Our approach combines a submesh reservation policy with a priority-based scheduling policy to obtain high performance in terms of high throughput, high utilization, and low turn-around times for jobs. This high performance is achieved at the expense of scheduling jobs in a strictly fair, FCFS fashion; in fact, the algorithm is parameterized to allow trade-offs between performance and (short-term) POPS fairness. The proposed scheduler can be used with any submesh allocation policy. A fast and efficient implementation of the proposed scheduler has also been presented. The performance of the proposed scheme has been compared with the FCFS policy, the only existing scheduling strategy for meshes, to demonstrate the effectiveness of the proposed approach. Simulation results indicate that our scheduling strategy outperforms the FCFS policy significantly. Specifically, our strategy significantly reduces the average waiting delay of jobs over the FCFS policy. The fast implementation of the proposed scheduler results in low allocation and deallocation time overhead, as well as low space overhead