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91.
92.
Nico M. Van Dijk 《商业与工业应用随机模型》1990,6(2):85-100
This paper studies a system of parallel service facilities or processors with mixed exponential and non-exponential queues, a non-exponential finite source input and interdependent arrival as well as departure blocking such as due to a common pool or shared resource. A concrete invariance condition upon the blocking protocol is provided. Under this condition the stationary busy source distribution is shown to be of an insensitive product form. The result unifies and extends known product form results as will be illustrated by several examples. 相似文献
93.
In this paper, we propose and give the performance of a novel uplink system based on the combination of multi-carrier (MC),
code division multiple access (CDMA) and multiple input multiple output (MIMO) techniques. First, we describe the interests
of spread-spectrum multi-carrier multiple access (SS-MC-MA) scheme for uplink, especially compared to MC-CDMA. Classically,
with SS-MC-MA, each user spreads its data symbols on a specific subset of adjacent or multiplexed subcarriers, to facilitate
the channel estimation and reduce complexity at the reception. In order to compensate for the lack of frequency diversity
of SS-MC-MA with adjacent subcarriers, we first combine it with an orthogonal space-time block code (STBC) and demonstrate
the resulting spatial diversity gain. Then, we propose to allocate the subsets to the different users by applying a frequency
hopping pattern (FH). In that case, each user benefits from the frequency diversity linked to the total bandwidth as with
the multiplexed subcarriers solution, while keeping the advantages of the adjacent subcarriers solution. The gain provided
by the use of the frequency hopping is stressed on. Finally, the performance of this scheme is evaluated over realistic MIMO
channel with channel turbo coding for systems offering asymptotic spectrum efficiency of 1, 2, 3 and 4.5 bit/s/Hz. Thus, the
efficiency of the novel proposed STBC FH SS-MC-MA system as a very promising multiple access and modulation scheme for the
uplink of the future wideband wireless networks is successfully demonstrated. 相似文献
94.
利用天线空间相关函数和方向特性将完全不相关的信道衰落矩阵映射为更符合实际的部分相关MIMO(multiple input multiple output)信道衰落矩阵,结合STTC(space-time trellis code)空时编码方式建立部分相关的STTC-MIMO系统,并将基于SAGE(space-alternating generalized expectation-maximization)的信道估计算法应用在这一系统中.结果显示,和ML(most-likelihood)估计相比,部分相关信道中使用SAGE估计算法可以使系统信噪比提高约1 dB.此外,空时编码(space-time codes)的纠错性能对MIMO系统的信噪比也有极大的影响. 相似文献
95.
As a hot‐spot of 5G, the research on detection algorithms for massive multiple input multiple output (MIMO) system is significant but difficult. The traditional MIMO detection algorithms or their improvements are not appropriate for large scaled antennas. In this paper, we propose artificial bee colony (ABC) detection algorithm for massive MIMO system. As one advanced technology of swarm intelligence, ABC algorithm is most efficient for large scaled constrained numerical combinatorial optimization problem. Therefore, we employ it to search the optimum solution vector in the modulation alphabet with linear detection result as initial. Simulation and data analysis prove the correctness and efficiency. Versus the scale of massive MIMO systems from 64 × 64 to 1024 × 1024 with uncoded four‐quadrature‐amplitude‐modulation signals, the proposed ABC detection algorithm obtains bit error rate of 10 − 5 at low average received signal‐to‐noise‐ratio of 12 dB with rapid convergence rate, which approximates the optimum bit error rate performance of the maximum likelihood and achieves the theoretical optimum spectral efficiency with low required average received signal‐to‐noise‐ratio of 10 dB in similar increasing regularity, over finite time of low polynomial computational complexity of per symbol, where NT denotes the transmitting antennas' number. The proposed ABC detection algorithm is efficient for massive MIMO system. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
96.
97.
多功能SHPB装置及水泥石材料的动态性能研究 总被引:1,自引:0,他引:1
为了研究在一定温度和压力下的水泥石的动态力学性能,研制了多功能SHPB材料动态性能测试装置,该装置可分别进行材料的拉伸,压缩,扭转性能测试,拉,压试验可以在带围压和温度的三向应力状态下进行,文中还对水泥石改性材料的动态力学性能进行了实验研究。 相似文献
98.
分析了WinDriver开发驱动程序的原理,介绍了在WindowsXP下利用WinDriver驱动程序开发软件来开发PC104(ISA)总线硬件设备驱动程序的流程和在VC++编译环境下使用WinDriver产生API函数编程的方法,为硬件设备驱动程序的开发提供了一种简捷高效的途径。 相似文献
99.
介绍了应用于CPU的板载DC/DC BUCK降压型连续电感电流模式开关电源电路(VRD)输入端输入电容的一种快速选取方法。文中阐明了输入端电容的重要作用,详细分析了其参数,工作原理等,并进一步推导出了具体的输入电容选择的工程计算应用公式,可以帮助工程技术人员根据不同的设计要求快速选取满足要求的输入电容设计方案,大大简化了整个设计过程。 相似文献
100.
Sajid Bashir Muhammad Naeem Adnan Ahmed Khan Syed Ismail Shah 《International Journal of Communication Systems》2010,23(1):109-124
The paper discusses a sequence detector based on univariate marginal distribution algorithm (UMDA) that jointly estimates the symbols transmitted in a multiple input multiple output (MIMO) communication system. While an optimal maximum likelihood detection using an exhaustive search method is prohibitively complex, it has been shown that sphere decoder (SD) achieves the optimal bit error rate (BER) performance with polynomial time complexity for smaller array sizes. However, the worst‐case complexity of SD is exponential in the problem dimensions, this brings in question its practical implementation for larger number of spatial layers and for higher‐order signal constellation. The proposed detector shows promising results for this overly difficult and complicated operating environment, confirmed through simulation results. A performance comparison of the UMDA detector with SD is presented for higher‐order complex MIMO architectures with limited average transmit power. The proposed detector achieves substantial performance gain for higher‐order systems attaining a near optimal BER performance with reduced computational complexity as compared with SD. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献