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排序方式: 共有159条查询结果,搜索用时 15 毫秒
151.
This article studies downlink subcarrier assignment problem to maximize rate-sum capacity subject to total power and proportional rate constraints in orthogonal frequency division multiplexing (OFDM) systems. Previous algorithms assume that the initial power is equally distributed over all subcarriers. The presence of path loss makes the assumption not correct any more. This article proposes a novel subcarrier assignment algorithm which makes full use of path loss and rate proportionality information to improve rate-sum capacity. The proposed algorithm determines optimal initial power allocation according to path losses and rate proportionalities of different users, assigns subcarriers to users in a greedy fashion, and then exchanges subcarfiers between users to obtain fairer rate distribution. Simulation results show that the proposed algorithm approximately achieves double the capacity of static assignment schemes, such as fixed frequency band approach, and obtains better performance than previous subcarrier assignment algorithms in the presence of different path losses and proportional rate requirements.. 相似文献
152.
A40kmFiber-opticMicrowaveSubcarrierMultiplexingTransmissionSystemforMulti-channelFM-TVZHANGZhengxian;LINZhiyuan;LIZhitang;XuJ... 相似文献
153.
Bravi E. Moeyaert V. Betti S. Giaconi M. Froidure J.-C. Ghislain L. Blondel M. 《Photonic Network Communications》2000,2(4):393-401
In optical CATV systems based on subcarrier-multiplexing technique, the joint action of semiconductor laser chirp and fiber chromatic dispersion gives rise to intermodulation distortion phenomena affecting the transmission performance. This problem has been explained analytically, leading to a model valid for every kind of modulating signal and explored in the case of a Gaussian process. In this paper, the model is developed for the important specific case of an analogue SCM modulating signal. The results are assessed experimentally. 相似文献
154.
集成电路封装设计可靠性提高方法研究 总被引:1,自引:1,他引:0
集成电路封装是集成电路制造中的重要一环,集成电路封装的目的有:第一,对芯片进行保护,隔绝水汽灰尘以及防止氧化;第二,散热;第三,物理连接和电连接。在进行封装设计时,可以通过一些方法,增强产品的制造稳定性以及产品的可靠性。文章研究了引线框架、线弧、等离子清洗及塑封料对封装可靠性的影响以及一些获得高质量的方法。例如:引线框... 相似文献
155.
Free-space optics (FSO) is a safe, license-free, high speed and high-bandwidth cordless technique for broadcasting signals at the same speed as fiber optics. But the main drawback of FSO is the dissolution of the signals due to atmospheric turbulence and thus degrading the link performance. So, to enhance the bit error rate (BER) performance, spatial diversity is employed over the FSO links for single-input multiple-output FSO (SIMO-FSO) systems. In this paper, we analyze the BER performance of SIMO-FSO links with spatial diversity and multiple-input multiple-output FSO (MIMO-FSO) systems over gamma–gamma atmospheric turbulence fading channel with misalignment (pointing errors). The closed form expressions are derived for the same with various combining schemes in terms of the Meijer G function and also evaluate the results with 2D and 3D graphs. 相似文献
156.
针对多用户OFDM系统中的功率优化问题,提出了一种新的子载波、比特分配算法。利用匈牙利算法对子载波进行初始分配,然后根据信道的状态信息为每个子载波动态地分配比特,最后对分配的结果作进一步调整,直到发射总功率不再减小为止。仿真结果表明,调整后的结果比原有方法有所改善,在满足传输速率和误码率要求的条件下,有效地降低了系统发射总功率。 相似文献
157.
158.
基于啁啾相移光纤光栅的滤波器设计及应用 总被引:4,自引:1,他引:3
相移光纤光栅作为透射型带通滤波器件降低了使用成本和插入损耗.在光通信和传感领域有着较高的应用价值.啁啾相移光纤光栅的透射峰波长和数量由相移点的位置和数量来确定,透射峰特性受相移量的影响.采用分段切趾的方法获得满足光通信要求的滤波特性,利用传输矩阵法分析了切趾前后透射峰特性的变化,结果表明:切趾改善了滤波器的幅度和相位响应,依据滤波器的设计要求选取不同的切趾函数以及切趾比例;切趾还大大减弱了透射峰波长和深度对相移量的敏感度,适当切趾后相移量的影响可以忽略.并提出一种应用双通道啁啾相移光纤光栅滤波器产生脉冲毫米波副载波信号的方案. 相似文献
159.
Han‐Chieh Chao Reen‐Cheng Wang Jenn‐Yuh Hong 《Wireless Communications and Mobile Computing》2001,1(4):407-417
As the cover range for the radio cells becomes gradually smaller than before, the procedures for mobile terminals call setup and control become complicated due to the high handoff frequency. The broadcast nature of WDM star couplers makes the handoff scheme easier and reduces the number of reconnections. In this study, we proposed a channel allocation algorithm, called pre‐empted assigned offset (PAO) scheme, for the WDM‐ and SCM/WDM‐based PCN architectures. The main idea is to keep the offset conflict probability lower. The simulation results show that the proposed scheme outperforms those previously introduced schemes. Especially in offset conflict probability under a moderate roaming rate for WDM and even under heavy roaming situations for SCM/WDM. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献