共查询到18条相似文献,搜索用时 171 毫秒
1.
关于零相关窗互补码理论界的几点讨论 总被引:6,自引:0,他引:6
提出了一类新型的零相关窗互补码,这类新型零相关窗互补码可以表示为三个独立的元素:一对相互正交的互补码、一个正交矩阵和一个标号矩阵的组合。本文重点讨论了这类新型零相关窗互补码的副峰平方之和的理论界,证明了几个重要的定理。这些定理包括:副峰的平方之和只是相对偏移的函数、零相关窗互补码集的一致性、列旋转不变性及列排列不变性等。这些定理对零相关窗互补码的设计具有重要的指导意义。 相似文献
2.
LS码与、Walsh码的上行链路容量比较 总被引:1,自引:1,他引:0
该文首先分析了多径衰落信道下CDMA系统上行链路信道容量,文章对单用户接收机、多用户接收机两种情况下的信道容量分别作了讨论.对LS码和Walsh码的上行链路容量进行了比较.通过仿真可以看出在多用户检测条件下,两种扩频码提供的容量相差不大,而在单用户检测条件下,LS码则要大大优于Walsh码。 相似文献
3.
4.
对基于Hadamard矩阵的LA码和基于劳伦多项式(Laurent Polynomial)的LS码的生成及相关特性进行研究,从占空比、相关特性、零干扰窗长度、码字总数等方面仿真分析了LAS码的性能,并结合实际应用,理论分析了LAS-CDMA系统与传统CDMA系统的归一化容量,仿真比较了LAS码和Gold序列在准同步CDMA系统中的误码性能.仿真和理论分析表明:LAS码具有均匀的零干扰窗(Interference Free Window,IFW)特性;不同主码的互相关函数IFW附近存在较小的副峰,多址干扰较小;在准同步移动通信系统中,LAS-CDMA抗多址干扰性能明显优于传统CDMA系统,使用LAS码比使用Gold序列有更好的误码性能. 相似文献
5.
6.
7.
8.
9.
10.
在采用传统信号检验方式的CDMA无线通信网中,多址干扰限制了系统的容量和性能。多用户信号检测利用扩频码互相关信息在高斯信道中可以减小或消除多址干扰,缓解远近效应,增加系统容量。 相似文献
11.
Abdallah K. Farraj 《Wireless Personal Communications》2010,55(3):395-405
Inter symbol interference (ISI) and multiple access interference (MAI) appear in code division multiple access systems when the spreading codes are not orthogonal. ISI and MAI are function of the auto and cross correlation values of the spreading codes. In this paper we investigate the tradeoff between auto and cross correlation properties; we formulate the optimum solution for both cases, transform the problem from multi-criterion to single criterion optimization problem, then formulate the dual problem, and find the optimal tradeoff solution where minimum auto and cross correlation values are attained. Minimum Correlation codes show a great enhancement in performance compared to Hadamard codes. 相似文献
12.
13.
Minimum Cross Correlation Spreading Codes 总被引:1,自引:1,他引:0
Multiple access interference (MAI) appears in Code Division Multiple Access (CDMA) systems when the communication channel
is a multi-path channel and the spreading codes are not orthogonal. Orthogonality between spreading codes cannot be maintained
at the CDMA receiver because the codes may be asynchronous due to channel delay and multi-path spread. The receiver cannot
perfectly separate the different signals of the multiple access users, and the resultant MAI limits the capacity of CDMA systems.
MAI is a function of the cross correlation property between used spreading codes. In this paper we focus on the cross correlation
of the spreading codes, we propose a method to find spreading codes with minimum magnitude of cross correlation. Employing
these codes will reduce the resultant MAI in the CDMA system; hence it will increase the system capacity. A great enhancement
is shown by comparing found minimum cross correlation spreading codes (MCCSC) with Hadamard and Gold codes.
相似文献
Ahmad I. AmayrehEmail: |
14.
Christelle Garnier Yves Delignon Hassan El Ghazi Franois Septier 《Wireless Communications and Mobile Computing》2014,14(6):659-672
In this paper, we address the problem of multiple access interference (MAI) in a downlink multicarrier code division multiple access system. Because in the realistic case of correlated faded subcarriers, MAI greatly depends on the codes assigned to users, one way of improving performance without increasing receiver complexity consists in an appropriate code selection. We propose a code allocation strategy with the following properties: possible use with any code sequence and equalizer, low complexity, and efficient management of load variations. The allocation problem is formulated as a minimization problem of a cost function related to MAI. First, we provide analytical expressions for the channel frequency correlation function after maximum ratio combining, equal gain combining, and minimum mean square error equalization and for the MAI power. Then, by approximating these expressions, we define a simple cost function and build an iterative algorithm on the basis of the minimum maximum criterion to select the spreading codes. Finally, a complete analysis of the allocation efficiency is provided versus key parameters, in particular, the degree of correlation between the faded subcarriers, the system load, and the equalization techniques. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
15.
Zero correlation window (ZCW) or zero correlation zone (ZCZ) sequence can be used in quasi-synchronous code division multiple access (QS-CDMA) system to eliminate multiple access and multipath interferences. However, as the length of ZCW or ZCZ increases, fewer sequences are available. Recently, a new concept, sequence set with group-wise zero correlation window is introduced, which can increase the number of available sequences for a QS-CDMA system. In this article, a new method for generating sequence set with group-wise zero correlation window is presented. This method is based on a Hadamard matrix of size N×N and a pair of Hadamard matrices of size M×M. Compared with previous methods, the proposed sequence set has a group-wise zero correlation window for both periodic and aperiodic cross-correlation functions. 相似文献
16.
This paper presents blind channel estimation for downlink W-CDMA system that employs chaotic codes and Walsh codes for spreading information bits of the multiple users. In a W-CDMA system, while transmitting over multipath channels, both intersymbol interference (ISI) as a result of Inter Chip Interference and multiple access interference (MAI) cannot be easily eliminated. Although it is possible to design multiuser detectors that suppress MAI and ISI, these detectors often require explicit knowledge of at least the desired users’ signature waveform. Earlier work focused on a subspace based channel estimation algorithm for asynchronous CDMA systems to estimate the multiple users’ symbols, where only AWGN channel was considered. In our work, we study a similar subspace-based signature waveform estimation algorithm for downlink W-CDMA systems, which use chaotic codes instead of pseudo random codes, that provide estimates of the multiuser channel by exploiting structural information of the data output at the base station. In particular, we show that the subspace of the (data+noise) matrix contains sufficient information for unique determination of channels, and hence, the signature waveforms and signal constellation. We consider Rayleigh and Rician fading channel model to quantify the multipath channel effects. Performance measures like bit error rate and root mean square error are plotted for both chaotic codes and Walsh codes under Rayleigh and Rician fading channels. 相似文献
17.
《Communications, IEEE Transactions on》2006,54(8):1514-1514
In this paper, we present the construction of full-rate, fully diverse, and totally real space–time (ST) codes for ultra-wideband (UWB) transmissions. In particular, we construct two families of codes adapted to real carrierless UWB communications that employ pulse position modulation, pulse amplitude modulation, or a combination of the two. The first family encodes adjacent symbols and is constructed from totally real cyclic division algebras. The second family encodes the pulses used to convey one information symbol, and permits achieving high performance levels with reduced complexity. The first family of codes achieves only a fraction of the coding gain of the second one. Moreover, these coding gains are independent from the size of the transmitted constellation. For time-hopping multiple-access channels, the amplitude spreading code associated with the second family of codes is taken to be user-specific. In this case, a simple design criterion is proposed, and spreading matrices constructed according to this criterion permit reducing the level of multiple-access interference (MAI). Performance over realistic indoor UWB channels verify the theoretical claims, and show high performance levels and better immunity against MAI. 相似文献
18.
Abou-Rjeily C. Daniele N. Belfiore J.-C. 《Communications, IEEE Transactions on》2006,54(11):1960-1972
In this paper, we present the construction of full rate, fully diverse, and totally real space-time (ST) codes for ultra-wideband (UWB) transmissions. In particular, we construct two families of codes adapted to real carrierless UWB communications that employ pulse position modulation, pulse amplitude modulation, or a combination of the two. The first family encodes adjacent symbols and is constructed from totally real cyclic division algebras. The second family encodes the pulses used to convey one information symbol, and permits achieving high performance levels with reduced complexity. The first family of codes achieves only a fraction of the coding gain of the second one. Moreover, these coding gains are independent from the size of the transmitted constellation. For time-hopping multiple-access channels, the amplitude spreading code associated with the second family of codes is taken to be user-specific. In this case, a simple design criterion is proposed, and spreading matrices constructed according to this criterion permit reducing the level of multiple-access interference (MAI). Simulations performed over realistic indoor UWB channels verify the theoretical claims and show high performance levels and better immunity against MAI 相似文献