共查询到19条相似文献,搜索用时 265 毫秒
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相关衰落信道Turbo乘积编码MDPSK的分集接收 总被引:1,自引:1,他引:0
由于无线衰落信道中差分检测Turbo乘积编码调制具有良好的性能,文中研究了相关平坦Rayleigh衰落信道中差分检测Turbo乘积编码MDPSK信号的等增益分集,这种等增益分集接收无需任何信道状态信息.研究结果表明,等增益合并可以改善快衰落信道中TPC-MDPSK的错误平底效应,等增益分集合并的Turbo乘积编码的MDPSK信号在相关系数为0.5的平坦Rayleigh衰落信道中的性能和独立衰落信道中的系统性能相差仅1 dB. 相似文献
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Turbo编码V-BLAST MIMO-OFDM系统中的联合迭代判决反馈信道估计与检测 总被引:1,自引:0,他引:1
针对Turbo编码V-BLAST MIMO—OFDM系统,提出了一种联合迭代判决反馈信道估计与检测方案,该方案将Turbo迭代译码与最小二乘(LS,least square)信道估计相结合,充分利用Turbo迭代译码后的信息位和校验位软值信息来改善信道估计性能。仿真结果表明,该方案不仅纠正了低信噪比时的差错传播问题,还使得整个系统的信道估计性能得到进一步提高,且适合于非常恶劣的信道环境。 相似文献
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在研究传统的空时编码 OFDM 系统模型及误码率性能的基础上,提出了 Turbo 码级联空时格码的 OFDM 系统方案;并给出了该系统在无线瑞利衰落信道中的性能上界和误码率仿真结果,仿真结果表明:该系统能最大限度地利用所有的分集资源,获得相当大的分集增益和编码增益。 相似文献
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本文研究了OFDM空时发射分集系统的子空间信道盲估计方法。该方法仅利用空时编码及OFDM调制引入的冗余,在接收天线小于发射天线时,也可以对信道进行盲估计。对盲估计方法所共有的估计模糊性问题进行了详细的论述,证明估计仅存在两个标量不确定因子。这种方法不需要对信号进行冗余预编码,系统将有更高的速率;同时也不需要对系统输出进行过采样或采用多天线接收。由于不需要确切知道信道的阶数,算法对信道阶数过估计有较好的鲁棒性。 相似文献
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Qu Daiming Zhu Guangxi 《电子科学学刊(英文版)》2006,23(1):1-6
The turbo equalization approach is studied for Orthogonal Frequency Division Multiplexing (OFDM) system with combined error control coding and linear precoding. While previous literatures employed linear precodcr of small size for complexity reasons, this paper proposes to use a linear precoder of size larger than or equal to the maximum length of the equivalent discrete-time channel in order to achieve full frequency diversity and reduce complexities of the error control coder/decoder. Also a low complexity Linear Minimum Mean Square Error (LMMSE) turbo equalizer is derived for the receiver. Through simulation and performance analysis, it is shown that the performance of the proposed scheme over frequency selective fading channel reaches the matched filter bound; compared with the same coded OFDM without linear precoding, the proposed scheme shows an Signal-to-Noise Ratio (SNR) improvement of at least 6dB at a bit error rate of 10 6 over a multipath channel with exponential power delay profile. Convergence behavior of the proposed scheme with turbo equalization using various type of linear precoder/transformer, various interleaver size and error control coder of various constraint length is also investigated. 相似文献
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We consider a space-time coded (STC) orthogonal frequency-division multiplexing (OFDM) system with multiple transmitter and receiver antennas over correlated frequency- and time-selective fading channels. It is shown that the product of the time-selectivity order and the frequency-selectivity order is a key parameter to characterize the outage capacity of the correlated fading channel. It is also observed that STCs with large effective lengths and ideal built-in interleavers are more effective in exploiting the natural diversity in multiple-antenna correlated fading channels. We then propose a low-density parity-check (LDPC)-code-based STC-OFDM system. Compared with the conventional space-time trellis code (STTC), the LDPC-based STC can significantly improve the system performance by exploiting both the spatial diversity and the selective-fading diversity in wireless channels. Compared with the previously proposed turbo-code-based STC scheme, LDPC-based STC exhibits lower receiver complexity and more flexible scalability. We also consider receiver design for LDPC-based STC-OFDM systems in unknown fast fading channels and propose a novel turbo receiver employing a maximum a posteriori expectation-maximization (MAP-EM) demodulator and a soft LDPC decoder, which can significantly reduce the error floor in fast fading channels with a modest computational complexity. With such a turbo receiver, the proposed LDPC-based STC-OFDM system is a promising solution to highly efficient data transmission over selective-fading mobile wireless channels 相似文献
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Performance Analysis of Tikhonov Regularized LS Channel Estimation for MIMO OFDM Systems with Virtual Carriers 总被引:1,自引:0,他引:1
In this paper the effect of virtual carriers (VCs) on channel estimation performance is considered for multiple input multiple
output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. The link between the number of VCs and the inverse
problem in a conventional LS channel estimation is identified. It is observed that a linear increase in VCs contributes to
an exponential increase of the system inverse problem as the condition number of the inverse matrix is exponentially increased.
A solution is proposed using a low complexity modified LS channel estimation. The performance analysis of the modified LS
channel estimation, regarding the effect of VCs, show gains in both the mean square error (MSE) performance of channel estimation
as well as bit error rate (BER) system performance compared to conventional LS. The performance is improved irrespective of
the increasing number of VCs as the estimator is shown to be insensitive to the increase of VCs in the OFDM system. The complexity
reduction is also considered and an approach is proposed showing a similar complexity as LS. 相似文献
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Ye Li 《Wireless Communications, IEEE Transactions on》2002,1(1):67-75
Multiple transmit-and-receive antennas can be used in orthogonal frequency division multiplexing (OFDM) systems to improve communication quality and capacity. In this paper, we present two techniques to improve the performance and reduce the complexity of channel parameter estimation: optimum training-sequence design and simplified channel estimation. The optimal training sequences not only simplify the initial channel estimation, but also attain the best estimation performance. The simplified channel estimation significantly reduces the complexity of the channel estimation at the expense of a negligible performance degradation. The effectiveness of the new techniques is demonstrated through the simulation of an OFDM system with two-transmit and two-receive antennas. The space-time coding with 240 information bits per codeword is used for transmit diversity. From the simulation, the required signal-to-noise ratio is only about 9 dB for a 10% word error rate for a channel with the typical urban- or hilly-terrain delay profile and a 40-Hz Doppler frequency 相似文献
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《Vehicular Technology, IEEE Transactions on》2005,54(4):1361-1371
In this paper, deliberate level clipping and turbo coding are combined to achieve an orthogonal frequency division multiplexing (OFDM) transmission system with a low peak-to-average power ratio (PAR) and a good performance. Using the linear approximation technique based on the minimum mean square error (MMSE) criterion, we first modify the metric computation for the turbo decoding in order to consider the distortion effects of the nonlinearity, caused by the Cartesian clipper. Also, this paper introduces a modified turbo decoder which simultaneously performs the data estimation and signal reconstruction. In other words, the turbo decoder iteratively recovers the clipped signal by using the estimated data, and then improves the data estimation by using the newly recovered signal. Numerical results are presented showing an improvement in the performance of the OFDM transmission system over the nonlinear channel, an increase in the efficiency of the high power amplifier (HPA), and/or an expansion of the transmitter coverage area. 相似文献
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文章研究了OFDM-MIMO系统中的循环延迟分集(CDD),以及基于Alamouti的空时分组编码(STBC)与空频分组编码(SFBC),针对发射分集方案所必须知道的信道信息,对两种信道估计方法,即最小二乘(LS)+线性插值与最小均方误差(MMSE)插值进行了研究。通过链路仿真还给出了以上分集方案在不同信道条件下的性能曲线,此外,对两种信道估计方法的误帧率做了统计。结果表明,CDD结合信道编译码可获得分集增益,有效对抗无线信道的衰落性。STBC,SFBC在不需要外码的情况下便可获得较大分集增益,且分别适用于频率选择性衰落与时间选择性衰落信道。而MMSE估计可以获得较为理想的误帧率,为分集方案提供较准确的信道参数以提高系统的可靠性。 相似文献