共查询到20条相似文献,搜索用时 15 毫秒
1.
提出了MC DS-CDMA(多载波直扩码分多址)系统中的SDCMA(最陡下降常模算法)和LSCMA(最小二乘常模算法)的盲检测方法,并把这2种CMA(常模算法)盲检测和基于子空间的MMSE(最小均方误差)检测方法相比较。仿真结果表明这2种CMA盲检测方法性能明显优于基于子空间的MMSE检测方法,而且运算复杂度也低于后者。在收敛速度上,LSCMA检测方法远快于SDCMA检测方法。 相似文献
2.
Hui Liu Guanghan Xu 《Communications, IEEE Transactions on》1996,44(10):1346-1354
Synchronous code-division multiple-access (CDMA) techniques possess intrinsic protection against co-channel interference due to orthogonal codes employed and thus, offers higher capacity than existing frequency-division multiple-access (FDMA) or time-division multiple-access (TDMA) systems. In the presence of multipath, however, each signal is subject to frequency-selective fading and the orthogonality condition does not necessarily hold leading to increased cross correlation. In these scenarios, multiuser detection need to be performed to suppress interference and recover the message symbols. To implement such a technique, explicit knowledge of the (nonorthogonal) signature waveforms of all users is required. We propose a blind estimation scheme that provides closed-form estimates of the signature waveforms by exploiting the structure information of the data output. In particular, we show that the subspace of the data matrix contains sufficient information for unique determination of the signature waveforms. Based on this observation, a multiple signal classification (MUSIC)-like algorithm is derived. Performance analysis of the new approach is also presented 相似文献
3.
4.
本文针对异步DS-CDMA系统,在理论上分析了信道阶、信道头和尾对子空间盲特征波形估计算法性能的影响,并进行了计算机仿真.首先提出了一个特征波形分解模型,将特征波形分解为m阶主要部分和次要部分,得到了相应的m阶子空间算法;然后运用矩阵扰动理论,证明了特征波形分解的可行性,即m阶子空间算法的特征波形估计逼近于m阶主要部分;最后从矩阵特征值分解的稳定程度出发,推导了特征波形分解准则,该准则指出应该避免考虑次要部分,采用尽可能小的信道阶.仿真结果验证了理论分析的正确性. 相似文献
5.
We propose a subspace based blind channel estimation method for orthogonal frequency-division multiplexing (OFDM) systems over a time-dispersive channel. Our approach is motivated by the resemblance of the multichannel signal model resulting from oversampling (or use of multiple receive sensors) of the received OFDM signal to that in conventional single carrier system. The proposed algorithm distinguishes itself from many previously reported channel estimation methods by the elimination of the cyclic prefix, thereby leading to higher channel utilization. Comparison of the proposed method with other two reported subspace channel estimation methods is presented by computer simulations to support its effectiveness. 相似文献
6.
利用循环前缀(CP)引入的信息冗余,在利用接受信号的二阶统计特性实现正交频分复用(OFDM)系统信道盲估计的子空间算法基础上,采用矩阵变换的方法,改善信息序列的非周期相关函数,推导出信道估计的新算法。 相似文献
7.
8.
The conventional frequency domain square-root raised cosine (Nyquist) chip waveform has much poorer anti-multiple-access-interference
(anti-MAI) capability than the optimal band- limited waveform in direct sequence code division multiple access (DS-CDMA) systems.
However, the digital implementation of the optimal chip pulse is very costly due to the slow decaying rate of the time waveform.
In addition, its eye diagram and envelope uniformity are worse than the Nyquist pulse for a wide range of roll-off factor,
which will incur performance degradation due to timing jitters and post non-linear processing. In this paper, based on an
elementary density function of a second-order polynomial, a class of second-order continuity pulses is proposed. From this
class of pulses, we can find some members having faster decaying rate, bigger eye opening, more uniform envelope and stronger
anti-MAI capability than the Nyquist waveform. The normalized-band-width-pulse-shape-factor product, the decaying rate of
the tail of the time waveform, the opening of the eye diagram, and the envelope uniformity of the second-order continuity
pulses are addressed in the paper that provide the basic information for the selection of the chip pulse for CDMA systems. 相似文献
9.
SunLiping HuGuangrui 《电子科学学刊(英文版)》2004,21(1):10-15
Blind Adaptive Step-size Constant Modulus Algorithm (AS-CMA) for multiuser detection in DS-CDMA systems is presented.It combines the CMA and the concept of variable step-size,uses a second LMS algorithm for the step size.It adjusts the step-size according to the minimum output-energy principle within a specified range,thus overcomes the problems of bad effect of fixed step-size LMS algorithm.Compared with Adaptive Step-size LMS (AS-LMS) algorithm,through simulations,this algorithm can adapt the changes of the environment,suppress multiple access interference in the dynamic environment and the stability of Signal to Interference Ratio (SIR) is superior to that of AS-LMS. 相似文献
10.
Li Zi Cai Yueming 《电子科学学刊(英文版)》2006,23(2):197-199
Compared with the traditional channel estimation methods, blind channel estimation methods can increase the bandwidth efficiency of the systems, but their precision is low and they converge slowly. In this paper, the Cramer-Rao Bound (CRB) for blind channel estimation in complex-valued Single-Input Multiple-Output (SIMO) channel is derived. In the simulations, the correctness of the CRB is validated and some channel estimation methods are evaluated by using the CRB. 相似文献
11.
The least-squares and the subspace methods are two well-known approaches for blind channel identification/equalization. When the order of the channel is known, the algorithms are able to identify the channel, under the so-called length and zero conditions. Furthermore, in the noiseless case, the channel can be perfectly equalized. Less is known about the performance of these algorithms in the practically inevitable cases in which the channel possesses long tails of “small” impulse response terms. We study the performance of the mth-order least-squares and subspace methods using a perturbation analysis approach. We partition the true impulse response into the mth-order significant part and the tails. We show that the mth-order least-squares or subspace methods estimate an impulse response that is “close” to the mth-order significant part. The closeness depends on the diversity of the mth-order significant part and the size of the tails. Furthermore, we show that if we try to model not only the “large” terms but also some “small” ones, then the quality of our estimate may degrade dramatically; thus, we should avoid modeling “small” terms. Finally, we present simulations using measured microwave radio channels, highlighting potential advantages and shortcomings of the least-squares and subspace methods 相似文献
12.
13.
14.
针对一种全盲的判决反馈均衡器(DFE)进行研究,它对快速时变信道的均衡非常有效。利用基于二阶统计量(SOS)的子空间法来得到关于信道系数的确定性估计,然后利用这个估计值求出DFE抽头系数在MMSE意义上的最优解,以此进行DFE的初始化。相比传统的利用周期性训练序列初始化DFE的方法,文章提出的方法不仅节省了带宽资源,而且对于信道的突发性时变能够自适应地重新初始化,从而避免了DFE均衡器的病态收敛。 相似文献
15.
This paper deals with a blind channel estimation method for space-time coded block transmission system. By concatenating the
real part and imaginary part of the received signal to form an elongated vector, we derive an equivalent input–output system
model. Then channel state information (CSI) is blindly estimated using subspace method, utilizing only the redundancy inherent
in space-time block coding (STBC) and cyclic prefix (CP). The estimation ambiguity, which is common to all blind methods,
is analyzed in detail and we prove that there only exist four scalar indeterminacies. Three effective methods to eliminate
the ambiguities are also proposed. Compared with other blind channel estimation methods for space time systems, this method
needs neither redundant precoding nor oversampling, and thus has higher data rate. Besides, this method is robust to channel
order overestimation, which is effectively demonstrated by numerical simulations.
This work was supported by NSFC (60496310, 60672093), NSFJS(BK2005061) and BK2005061. 相似文献
16.
在相关检测的OFDM系统中,信道估计具有十分重要的意义。研究了一种在单音干扰环境下的OFDM系统中基于预编码的盲信道估计方案。利用接收的干扰信号的频域信息对单音干扰信号进行准确估计与重构,有效地消除了干扰信号的影响,提高了单音干扰下盲信道估计的准确性。与其他盲信道估计算法相比,基于预编码的盲信道估计算法具有较低的运算复杂度以及较快的收敛速度。仿真结果表明了该算法在干扰估计以及信道估计两方面都取得了较好的性能。 相似文献
17.
18.
MIMO-OFDM系统信道估计技术的分析 总被引:3,自引:0,他引:3
介绍了MIMO—OFDM系统的信道估计技术,根据是否使用训练序列信息,信道估计可以分为导频辅助信道估计和盲信道估计,本文首先较全面地介绍了导频辅助信道估计技术,然后介绍了一种运用较多的基于子空间的盲信道估计技术,最后计算机仿真分析比较它们的性能。 相似文献
19.
Cramer-Rao bounds for the estimation of multipath parameters and mobiles' positions in asynchronous DS-CDMA systems 总被引:2,自引:0,他引:2
Commercial applications for the location of subscribers of wireless services continue to expand. Consequently, finding the Cramer-Rao lower bound (CRLB), which serves as an optimality criterion for the location estimation problem, is of interest. In this paper, we derive the deterministic CRLBs for the estimation of the specular multipath parameters and the positions of the mobiles in an asynchronous direct sequence code division multiple access (DS-CDMA) system operating over specular multipath fading channels. We assume a multilateral radio location system where the location estimates are obtained from some or all of the estimated signal parameters at different clusters of antennas of arbitrary geometry. Extension for unilateral and composite radio location techniques is also discussed. As an application example, we use numerical simulations to investigate the effects of specular multipath and multiple access interference (MAI) on the positioning accuracy for different radio location techniques. 相似文献