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181.
定时跟踪是DS-CDMA系统中Rake接收的关键技术,性能的好坏直接影响着扩频系统能否正常接收.文中首先对扩频系统中定时跟踪原理做出分析,然后重点介绍了PN码的"基于能量窗重心的定时跟踪"新算法,并选择了这个算法来实现CDMA2000-1x上行链路的PN码定时跟踪.最后,经过在典型城市环境下的现场实测,误帧率达到CDMA2000-1x的标准要求. 相似文献
182.
Generalized Steiner systems GS(2, 4, v, g) were first introduced by Etzion and were used to construct optimal constant weight codes over an alphabet of size g + 1 with minimum Hamming distance 5, in which each codeword has length v and weight 4. Etzion conjectured that the necessary conditions v 1 (mod 3) and v ; 7 are also sufficient for the existence of a GS(2,4,v,2). Except for the example of a GS(2,4,10,2) and some recursive constructions given by Etzion, nothing else is known about this conjecture. In this paper, Weil's theorem on character sum estimates is used to show that the conjecture is true for any prime power v 7 (mod 12) except v = 7, for which there does not exist a GS(2,4,7,2). 相似文献
183.
The results of FEM investigation of the triaxial stress state in multilayer structural elements subjected to axial and bending loads are presented. The distribution regularities of the stiffness and stresses or strains depending on the geometric and mechanical characteristics of layers and their position in the cross section of beams and bars are examined. The optimization of these elements is carried out using the dependences of the Bareisis—Paulauskas method and the Optim-98 computer program created by the present authors. As the optimization criteria, the strength, stiffness, mass, and cost of the structural elements are considered. 相似文献
184.
Todd D. Vance 《Designs, Codes and Cryptography》2000,19(1):27-43
The weight distribution of GRM (generalized Reed-Muller) codes is unknown in general. This article describes and applies some new techniques to the codes over F3. Specifically, we decompose GRM codewords into words from smaller codes and use this decomposition, along with a projective geometry technique, to relate weights occurring in one code with weights occurring in simpler codes. In doing so, we discover a new gap in the weight distribution of many codes. In particular, we show there is no word of weight 3m–2 in GRM3(4,m) for m>6, and for even-order codes over the ternary field, we show that under certain conditions, there is no word of weight d+, where d is the minimum distance and is the largest integer dividing all weights occurring in the code. 相似文献
185.
Let V and W be n-dimensional vector spaces over GF(2). A function Q : V W is called crooked (a notion introduced by Bending and Fon-Der-Flaass) if it satisfies the following three properties:
We show that crooked functions can be used to construct distance regular graphs with parameters of a Kasami distance regular graph, symmetric 5-class association schemes similar to those recently constructed by de Caen and van Dam from Kasami graphs, and uniformly packed codes with the same parameters as the double error-correcting BCH codes and Preparata codes. 相似文献
186.
A new interference cancellation technique for direct-detection optical code- division multiple-access (OCDMA) network employing
pulse-position modulation (PPM) is proposed in this paper. The multiple access interference (MAI) estimation is achieved by
pre-reserving one of optical spreading code sequences at the receiver based on the correlation property of padded modified
prime codes (PMPC). The estimated interference is then cancelled out after photo-detection process. Additionally, the transmitted
signal is Manchester-coded to further improve the system performance. Based on this proposed interference canceller in a shot-noise
limited regime, we have obtained an expression for the upper bound of the bit-error probability (BEP) taking into account
effects of both MAI and shot-noise. This BEP is compared with that of a PPM-OCDMA without cancellation. Finally, the receiver
structure of the proposed optical network unit (ONU) is fairly simple to compare with the conventional cancellation schemes. 相似文献
187.
在3GPP标准中规定,扩频加扰模块为信道编码的后续模块。文中对此模块中数据调制,数据扩绕,Midamble码调制等进行了介绍,并一一列举出其实现的算法和简单的实现步骤。 相似文献
188.
对直接序列扩频通信的信号检测方法进行了综述,重点讨论了自相关域检测方法、四阶累积量方法、谱分析与信号子空间分解法,其中四阶统积量方法和谱分析与信号子空间分解法的最低检测门限远低于相关算法,谱分析与信号子空间分解法在直接序列扩频(DS/SS)信号的伪码周期估计以及伪码序列盲估计中,利用功率谱二次处理结合信号子空间分解的方法可以实现对低信噪比DS/SS信号的估计。 相似文献
189.
基于无线传感器网络中监测数据具有较高时空相关性的应用场景。提出了一种基于数据融合的局部能量高效汇聚分簇协议LEEAC,该协议通过反映局部空间相关性的数据相异度对节点剩余能量进行约束,并使用约束后的预测能量作为竞选簇头的主要依据,被选举的簇头在传感器网络中具有良好的分布性。同时通过引入数据鉴定码,减少了簇内数据传输阶段的通信量以及簇头数据融合的工作量,从而大大节约了能量消耗。实验结果表明,LEEAC协议能够有效均衡网络能量消耗。延长网络生存时间。 相似文献
190.