共查询到20条相似文献,搜索用时 15 毫秒
1.
In order to attain near-single user performance in uplink multicarrier code- division multiple-access (MC-CDMA) systems, multiuser
detection (MUD) methods may be employed which rely on simultaneous estimation of the channel frequency responses of multiple
users. Pilot symbol assisted (PSA) channel estimation is needed in fast fading channels and it can be performed either by
applying maximum likelihood (ML) criterion or minimum mean-squared error (MMSE) criterion. The performance of ML estimation
technique degrades significantly in the case of fractionally spaced (FS) multipath channels where dominant paths are closely
spaced with respect to the time resolution of the system. In such situation, the number of effective paths (which contribute
more towards signal power) becomes considerably less than the actual number of multipaths at low and moderate SNR values.
We propose an improved ML estimation method which considers only effective paths during the estimation process. The proposed
method performs nearly identical to the MMSE estimation method and it can also provide significant reduction in the computational
complexity when a large number of users are accommodated in the system. 相似文献
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快时变环境下OFDM系统中的信道估计 总被引:1,自引:0,他引:1
在OFDM系统中,怎样对快时变信道进行较为准确的估计是一个具有挑战性的课题。该文在利用信道基扩展模型的基础上,提出了一种适合于快时变环境下OFDM系统的信道估计方法,并且依据使估计的均方误差最小的准则,推导了相应最优的导频序列,包括最优的导频取值和最优的导频分布。可以证明,最优的导频序列是由一些相邻的等间隔等能量的子序列构成,每个子序列的导频之间满足一定的相位关系。仿真结果表明了所提估计算法在快时变环境下的有效性和采用所推导的最优导频序列进行估计的优越性。 相似文献
3.
Least-Squares Channel Estimation for Mobile OFDM Communication on Time-Varying Frequency-Selective Fading Channels 总被引:1,自引:0,他引:1
《Vehicular Technology, IEEE Transactions on》2008,57(6):3538-3550
4.
针对正交频分复用(OFDM)系统中的信道时变,基于时变信道的分段线性近似模型,提出一种改进的OFDM时变信道估计方案。该方案通过采用期望最大化(EM)迭代算法来提高符号平均信道脉冲响应的估计精度,从而提高时变信道估计的性能;此外,在迭代过程中进行带状子载波间干扰抑制,不仅进一步提高了时变信道估计的性能,而且降低了实现复杂度。理论分析和仿真结果表明,该算法以较低的复杂度代价有效提高了时变信道OFDM系统的性能。 相似文献
5.
The outdated channel state information (CSI) at the transmitter and receiver, which is resulted from time variation of channels, is considered in multiple-input multiple-output systems employing maximal ratio combining. Closed-form expressions for the cumulative distribution function of output signal-to-noise ratio and symbol error rate under time-varying channels are presented to evaluate the effect of outdated CSI. The analytical results are compared with Monte Carlo simulations and a good agreement is obtained. 相似文献
6.
This paper presents a decorrelating detector for DS-CDMAasynchronous systems over multipath fading channels. The decorrelatingreceiver applies the inverse correlation matrix of signature waveformsto detect the received signal. A procedure for finding such an inversematrix is developed. This procedure employs the reciprocal basis,derived from the basis of normalized user signatures, to cancelsimultaneously both the multiuser and the intersymbolinterference. The proposed multiuser detector operates over a finitedetection window, and the only restriction imposed on the set of signaturesis that the signatures must be independent at the receiver end. If the channelis slowly variant, the detectorcan be very efficient for high bit rate transmissions. Theoreticalbounds for the multiuser interference are obtained. Simulationresults, in which both binary and non-binary sequences are used,reveal that the behaviour of the detector approaches the single userbound when an adequate set of signatures is employed. The reducedcomplexity of this detector indicates that it could be a good candidatefor practical implementation. 相似文献
7.
Vidhyacharan Bhaskar 《Wireless Personal Communications》2011,61(1):201-207
In this letter, the analytical and simulated performance of punctured convolutional codes in an Asynchronous Code Division
Multiple Access (A-CDMA) system under imperfect phase tracking conditions are discussed. A time-varying Rician fading channel
is assumed. Analytical results show the variation of the Bit Error Rate (BER) with nominal loop Signal-to-Noise Ratio (SNR)
and the ratio of the loop bandwidth to the local oscillator bandwidth,
\dfracBoBLo{\dfrac{B_o}{B_{Lo}}}, in a phase locked loop. Simulated results are found to agree well with the analytical results. 相似文献
8.
Carlos Ribeiro M. Julia Fernández-Getino Garcia Víctor P. Gil Jiménez Atílio Gameiro Ana García Armada 《Wireless Personal Communications》2008,47(1):125-136
In this paper we propose a simple, yet flexible and efficient, channel estimator for the uplink in broadband orthogonal frequency
division multiplexing (OFDM) systems. The processing is performed in the time-domain, by extracting the Channel’s Impulse
Response (CIR) for each user from a joint training signal. In this OFDM system, the pilot sequence we advocate, where all
users share the same pilot sub-carriers, consists of one OFDM-symbol endowed with time-shifted properties per user, which
isolates each user’s CIR and is robust against multi-user interference. The feasibility of our approach is substantiated by
system simulation results obtained using BRAN-A broadband mobile wireless channel model.
相似文献
Ana García ArmadaEmail: |
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Hakan Doğan Niyazi Odabaşıoğlu Bahattin Karakaya 《Wireless Personal Communications》2017,96(1):163-181
The constant amplitude zero autocorrelation sequence based synchronization and its usage in the block-type channel estimation for the single carrier frequency division multiple access (SC-FDMA) systems are vulnerable to the time-varying channels. Therefore, the channel estimation errors limit the performance of SC-FDMA systems in fast fading environments and result an irreducible error floor. In this paper, cyclic prefix based maximum likelihood estimator of time/frequency synchronization with comb-type channel estimation for the SC-FDMA systems are proposed to track the channel variations. Moreover, the residual time/frequency offsets calculations are derived for SC-FDMA systems. Simulation results confirm and illustrate that the proposed receiver is capable of tracking fast fading channel parameters and improving the overall performance as compared with the conventional receiver. 相似文献
12.
We propose novel low-complexity iterative channel estimators based on B-splines. Local splines are adopted for computational simplicity. Minimum mean square error (MMSE) local splines with integral sampling are derived. The MSE of the proposed estimators depends on signal-to-noise ratio, fading rate, sampling interval, spline order and the number of weighting coefficients; these dependencies are investigated. The linear and cubic local splines with as few as seven weighting coefficients are capable of achieving MSE and BER performance comparable to those of the Wiener filter and the spheroidal basis expansion. However, a significantly lower complexity is achieved using B-splines 相似文献
13.
A novel fuzzy minimum output energy (MOE) detector is proposed for uplink multicarrier CDMA (MC-CDMA) systems with carrier frequency offset (CFO) over multipath fading channels. The proposed receiver involves the following stages. First, the fuzzy CFO constrained MOE detector after coarse CFO estimation is proposed to suppress multiple access interference and combat the degradation problem of the conventional MOE detector caused by the CFO effect. Next, using the signal subspace projection technique, the proposed detector can further reduce the enhanced noise due to the fuzzy CFO constrained detector. Finally, the output data obtained from these detectors are coherently combined to offer multipath diversity gain in accordance with the maximum ratio combining criterion. Furthermore, the proposed single input single output (SISO) robust detector can be easily extended for a multiple input multiple output (MIMO) MC-CDMA system with a high rate of performance. Simulation results show that the proposed SISO detector, which offers a similar performance as the optimal detector, can provide robustness against CFO and outperform the conventional detectors. The proposed MIMO detector with spatial multiplexing gain also exhibits excellent performance. 相似文献
14.
Mobility-induced Doppler spread and multipath propagation introduce the time- and frequency-selectivity (doubly selectivity) in fading channels. Based on the complex exponential basis expansion model (BEM) to approximate the doubly selective channel (DSC), a low-complexity channel estimation scheme for block transmission systems over DSC are developed in this paper. Using the developed scheme, the long data block is divided into a few short data subblocks in terms of the maximum normalized Doppler frequency and block length, and each subblock is performed to respective channel estimation. Thus the total calculation complexity is effectively decreased because the number of the BEM channel coefficients to estimate is greatly reduced for each sub-block. Moreover, by utilizing these channel estimation values to refit the true channel, we can obtain better channel estimation. Besides, the normalized mean square error (NMSE) expressions for the developed scheme and the existing scheme are derived in detail, respectively. Compared to the existing scheme, the proposed scheme has lower calculation complexity and superior performance. The simulation results verify the effectiveness of the developed scheme, and the theory values of the derived NMSE accord with corresponding simulation values. 相似文献
15.
《Broadcasting, IEEE Transactions on》2009,55(4):818-825
16.
Tsan-Ming Wu Tsung-Hua Tsai 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2009,55(5):2260-2282
Noncoherent and coherent multicode direct-sequence code-division multiple access (DS-CDMA) systems with successive interference cancellation (SIC) for multimedia reverse links over frequency-selective fading channels are studied. Followed by a RAKE receiver, the SIC scheme is applied for combating the multiple access interference. The bit error rate (BER) using the SIC technique over Nakagami-m fading channels is derived. Simulation results show that the multicode DS-CDMA system with SIC has demonstrated better performance than that without SIC under the multipath fading environment, while their corresponding numerical results from performance analyses are also provided for verifications. Furthermore, the coherent receiver could achieve a more satisfactory BER than the noncoherent counterpart at the expense of synchronization. 相似文献
17.
Performance Evaluation for Forward-Link Cellular DS-CDMA over Frequency-Selective Nakagami Multipath Fading Channels 总被引:1,自引:1,他引:0
The bit-error rate (BER) for a forward-link cellulardirect-sequence code-division multiple-access (DS-CDMA) systemis evaluated. This analysis takes into account the effects ofmulti-cell interference resulting from Nakagami multipath fading,frequency selectivity, path loss and mobile user spatialdistribution. Exponentially decaying multipath intensityprofile (MIP) is adopted in the model to investigate itssignificance on the overall performance. In order to evaluatethe BER performance efficiently, saddlepoint integration (SPI)is applied in the analysis. By fixing the number of resolvablemultipaths and varying the number of fingers for the RAKEreceiver, it can be shown that the capacity of a DS-CDMAcellular system increases almost linearly with the number ofRAKE fingers. 相似文献
18.
A characteristic function-based method is used to derive closed-form bit error probability (BEP) expressions for orthogonal frequency-division multiplexing (OFDM) systems in the presence of channel estimation error over frequency-selective Rayleigh fading channels and frequency-selective Ricean fading channels. Both single channel reception and diversity reception with maximal ratio combining (MRC) are examined. The BEP expressions are shown to be sums of several conditional probability functions which can be calculated by using proper complex Gaussian random variable theory and a characteristic function method. The closed-form BEP expressions can be used to accurately investigate the bit error rate performance degradation caused by channel estimation error under different wireless channel environment models. The performances of two interpolation methods, a sine interpolator with Hamming windowing and a Wiener interpolator, are compared. 相似文献
19.
该文对OFDM系统中基于导频的时变信道估计进行了研究,采用分组导频对一个OFDM符号间隔内某些时刻的信道冲击响应值进行估计,提出一种利用低通插值估计一个符号间隔内其他时刻的信道值的方法。仿真结果表明该文采用的低通插值方法所得到的估计均方误差要小于用线性插值或直接用信道模型产生的系数进行插值所得到的估计均方误差。 相似文献
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