非理想信道估计下的放大转发协同通信系统性能分析

针对两跳多中继放大转发协同通信系统,分析了信道估计误差对系统性能的影响。考虑机会中继和全参与中继两种中继策略,分别推导了系统误码率的闭式表达式,并分析了不同信道估计质量阶数下的系统分集增益。平均信噪比损失率分析表明机会中继较全参与中继对信道估计误差更为敏感。仿真结果验证了理论分析。     

估计误差下DF协作系统性能分析

信道估计误差是引起无线通信系统性能衰弱的重要因素之一。分析了瑞利信道条件下估计误差对译码前传协作系统性能的影响。推导并给出了估计误差条件下正交幅度调制信号译码前传协作系统码元错误概率的解析表达式和上界表达式,并分析了不同信道的方差对协作系统性能的影响。仿真结果显示,存在估计误差时,码元错误概率性能并未随着信噪比的增大而提高。同时发现,中继-目的链路的较大方差较源-中继链路显著改善码元错误概率性能。     

Nakagami信道的中断容量分析

本文讨论了Nakagami-m衰落信道系统的中断容量性能,在发射端未知信道信息,接收端的信道估计存在误差时,给出了计算中断容量上界和下界的表达式,它们是接收端的估计误差和信道参数的函数,仿真结果表明随着估计误差的增大中断容量的上界和下界同时降低,但是中断容量的下界随着信道参数的增大而增大,上界随着信道参数的增大而减小。     

非精确信道信息下的自适应MIMO-OFDM系统性能分析

由于自适应多入多出正交频分复用系统(MIMO-OFDM)可以大大提高系统的频谱效率,已经成为人们研究的热点,该文分析并讨论了自适应MIMO-OFDM系统中导致非精确信道信息的两个主要因素信道估计误差和信道信息时延对系统的频谱效率和误码率性能的影响。仿真结果表明,在22 MIMO-OFDM系统中,当信道估计误差小于-12dB时,系统频谱效率损失很小。此外信道预测可以大大降低系统对信道信息时延的敏感程度。     

双向多中继协同通信系统的性能分析

针对频率非选择性瑞利衰落信道,研究了双向多中继协同通信模型的系统性能。首先,基于模型的信号传输过程分析了系统的信道容量;然后,根据接收信噪比的累积分布函数推导了系统中断概率的闭合上界表达式;进一步在MPSK调制方式下,通过计算在高信噪比条件下的矩母函数,推导了平均误码率的闭合表达式。仿真结果验证了理论推导的正确性,并且表明双向多中继模型的中断概率和平均误码率两项性能指标都优于双向单中继模型。     

非理想信道信息下认知中继系统中断概率研究

本文针对存在信道估计误差的情况,分析了非理想信道状态信息下认知中继系统的性能.建立了非理想信道状态信息下认知中继系统的数学模型,推导出了非理想信道状态信息下认知中继系统中断概率的表达式.理论分析表明在非理想信道状态信息下认知中继系统的性能较理想状态有所下降,但更符合实际情况.同时数值仿真结果验证了理论分析的正确性.     

基于MMSE 信道估计的VRVP-MQAM 方法性能研究

信道估计对于VRVP-MQAM系统的整体性能至关重要,论述了VRVP-MQAM方法在实际应用中遇到的问题,针对假定CSI已知的传统研究方法,该文通过采用MMSE算法进行信道估计,研究了MMSE估计误差对VRVP-MQAM方法的ASE性能影响,并在Rayleigh衰落信道下进行了仿真,仿真结果表明:与信道状态已知(=1)相比,MMSE估计误差(=0.9时)会产生1~3 dB左右的ASE性能差距;当平均SNR为20 dB时,MMSE算法下信道状态的平均频谱效率为0.3 bps/Hz,比理想信道状态的平均频谱效率低。因此,VRVP-MQAM方法的应用将会越来越广泛。     

基于选择性分集技术的无线中继系统性能

采用中继传输能够抵抗无线信道的多径衰落,克服阴影效应,从而增强通信质量,提高频谱效率。该文首先给出了两跳中继系统模型,针对非再生及再生两类中继方式,简要介绍了采用非分集接收及最大比合并时的链路性能。考虑到接收机复杂度和系统实现的性能代价比,该文引入了处理相对简单但又具备分集优势的选择性合并方式,并根据中继节点不同的位置分布,分析了两类中继方式下系统的通信中断概率和误码率。数值结果表明,非再生中继传输具有较好的性能,同时中继系统若采用选择性分集接收,则既能降低收端复杂度,又能获得较大的性能增益。     

基于成对用户大规模MIMO中继系统的频谱效率性能分析

该文针对成对用户大规模MIMO中继系统,在中继采用最大比合并/最大比发射（MRC/MRT）预编码方案下,利用大数定律,推导出系统频谱效率的闭合表达式,显式的描述了频谱效率与中继天线数、该文针对成对用户大规模MIMO中继系统,在中继采用最大比合并/最大比发射（MRC/MRT）预编码方案下,利用大数定律,推导出系统频谱效率的闭合表达式,显式的描述了频谱效率与中继天线数、用户对个数以及信源用户和中继发射功率的关系。基于此,分析了当天线数增大时,在用户对个数固定不变和等比例增长两种情况下,频谱效率的渐进性能和所能获得的发射功率增益。结果表明,当用户数固定时,频谱效率将随天线数呈近似对数增长规律;当用户数随天线数等比例增长时,通过调整比例值,可满足平均每个用户的频谱效率达到任意指定值,且无需额外发射功率消耗。最后,通过数值仿真验证了所推导的频谱效率闭合表达式的精确性以及所有渐进性能的分析结果。      

MIMO中继系统中基于不完全信道信息的线性预编码算法

针对采用放大转发中继技术的多输入多输出系统,提出一种基于不完全信道状态信息的中继预编码设计方案.假设在中继端已知源-中继的全部信道状态信息,在中继-目的端的信道考虑信道估计误差及发射天线相关性,根据最小均方误差设计准则,推导获得目的端线性处理矩阵.在中继端最大发射功率约束条件下,通过理论推导求得中继端线性预编码矩阵的闭式解.数值仿真结果表明,在存在信道估计误差和天线相关性的条件下,所提方案能有效降低系统的误比特率和均方误差.     

Effect of Least Square Channel Estimation Errors on Achievable Rate in MIMO Fading Channels

The achievable rate of a multiple input multiple output (MIMO) fading channel is derived in the form of generalized mutual information (GMI) when least square (LS) channel estimation is employed to gain channel state information at receivers. The derived average GMI of a channel with LS channel estimation is compared with the known average GMI (equivalently, the lower bound on the ergodic capacity) of a channel with linear minimum mean square error channel estimation. An effective approximation method is also proposed to ease the numerical calculation of the average GMI of a MIMO channel with LS channel estimation.     

A union bound on the error probability of binary codes over block-fading channels

Block-fading is a popular channel model that approximates the behavior of different wireless communication systems. In this paper, a union bound on the error probability of binary-coded systems over block-fading channels is proposed. The bound is based on uniform interleaving of the coded sequence prior to transmission over the channel. The distribution of error bits over the fading blocks is computed. For a specific distribution pattern, the pairwise error probability is derived. Block-fading channels modeled as Rician and Nakagami distributions are studied. We consider coherent receivers with perfect and imperfect channel side information (SI) as well as noncoherent receivers employing square-law combining. Throughout the paper, imperfect SI is obtained using pilot-aided estimation. A lower bound on the performance of iterative receivers that perform joint decoding and channel estimation is obtained assuming the receiver knows the correct data and uses them as pilots. From this, the tradeoff between channel diversity and channel estimation is investigated and the optimal channel memory is approximated analytically. Furthermore, the optimal energy allocation for pilot signals is found for different channel memory lengths.     

On the Performance of the MIMO Zero-Forcing Receiver in the Presence of Channel Estimation Error

By employing spatial multiplexing, multiple-input multiple-output (MIMO) wireless antenna systems provide increases in capacity without the need for additional spectrum or power. Zero-forcing (ZF) detection is a simple and effective technique for retrieving multiple transmitted data streams at the receiver. However the detection requires knowledge of the channel state information (CSI) and in practice accurate CSI may not be available. In this letter, we investigate the effect of channel estimation error on the performance of MIMO ZF receivers in uncorrelated Rayleigh flat fading channels. By modeling the estimation error as independent complex Gaussian random variables, tight approximations for both the post-processing SNR distribution and bit error rate (BER) for MIMO ZF receivers with M-QAM and M-PSK modulated signals are derived in closed-form. Numerical results demonstrate the tightness of our analysis     

Time‐varying channel estimation for MIMO/OFDM systems using superimposed training and basis expansion models

An approach of superimposed training (ST)‐aided time‐varying (TV) channel estimation for multiple‐input multiple‐output orthogonal frequency division multiplexing systems is presented. By modeling the TV channel with the truncated discrete basis expansion model, a two‐step approach is adopted to estimate the TV channel. In addition, the mean square error (MSE) of the proposed channel estimation is analyzed, and its closed‐form expression is derived, which is a function of the data‐to‐ST power ratio. Using the developed channel MSE, we case the problem of ST power‐allocation by minimizing the lower bound on the average channel capacity. To enhance the performance of channel estimation, a low‐complexity decision feedback mechanism is introduced to iteratively mitigate the unknown data interference. Numerical results verify the performances of the proposed approach. Copyright © 2012 John Wiley & Sons, Ltd.     

Performance Bounds for MIMO-OFDM Channel Estimation

The performance of a mobile multiple-input multiple-output orthogonal-frequency-division multiplexing (MIMO-OFDM) system depends on the ability of the system to accurately account for the effects of the frequency-selective time-varying channel at every symbol time and at every frequency subcarrier. Typically, pilot symbols are strategically placed at various times over various subcarriers in order to calculate sample channel estimates, and then these estimates are interpolated or extrapolated forward to provide channel estimates where no pilot data was transmitted. Performance is highly dependent on the distribution of the pilots with respect to the coherence time and coherence bandwidth of the channel, and on the chosen channel parameterization. In this paper, a vector formulation of the Cramer-Rao bound (CRB) for biased estimators and for functions of parameters is used to derive a lower bound on the channel estimation and prediction error of such a system. Numerical calculations using the bound demonstrate the benefits of multiple antennas for channel estimation and prediction and illustrate the impact of modeling errors on estimation performance when using channel models based on calibrated arrays.     

Optimal diversity combining based on linear estimation of rician fading channels

Optimal receiver diversity combining employing linear channel estimation is examined. Based on the statistical properties of least-squares (LS) and minimum mean square error (MMSE) channel estimation, an optimal diversity receiver for wireless systems employing practical linear channel estimation on Rician fading channels is proposed. The new receiver structure includes the conventional maximal ratio combining receiver as a special case. Exact analytical expressions for the symbol error rates (SERs) of LS and MMSE channel estimation aided optimal diversity combining are derived. It is shown that, if an optimal detector is used, an MPSK wireless system with MMSE channel estimation has the same SER when the MMSE channel estimation is replaced by LS estimation. This is an interesting counterexample to the common perception that channel estimation with smaller mean square error leads to smaller SER. Extensive simulation results validate the theoretical results.     

Cramer–Rao bound based mean‐squared error and throughput analysis of superimposed pilots for semi‐blind multiple‐input multiple‐output wireless channel estimation

This work presents a study of the mean‐squared error (MSE) and throughput performance of superimposed pilots (SP) for the estimation of a multiple‐input multiple‐output (MIMO) wireless channel. The Cramer–Rao bound (CRB) is derived for SP based estimation of the MIMO channel matrix. Employing the CRB analysis, it is proved that the asymptotic MSE bound is potentially 3 dB lower than the MSE performance of the existing SP mean based estimation (SPME) schemes. Motivated by this observation, a novel SP semi‐blind scheme is presented for MIMO channel estimation. This scheme asymptotically achieves the CRB and hence has a lower MSE of estimation when compared with SPME schemes. We also derive closed form expressions for the optimal source‐pilot power allocation in SP by maximizing the post‐processing signal‐to‐noise power ratio at the receiver. In the final part, a new result is presented for the worst‐case capacity of a communication channel with correlated information symbols and noise. This framework is employed to quantify the throughput performance of SP and also to demonstrate the bandwidth efficiency of SP compared with that of a conventional pilot based system. Copyright © 2012 John Wiley & Sons, Ltd.     

信道估计误差对MIMO系统信道容量的影响研究

为了分析信道估计误差对信道容量的影响,结合MIMO系统接收端信道估计误差的特点,重新构建了MIMO信道的统计模型。利用Wishart分布的性质,推导了当MIMO信道矩阵满秩时,仅接收端已知信道CSI情况下系统信道容量的下限。仿真结果表明,MIMO系统信道容量对信道估计误差比较敏感。     

Location based spectrum sensing performance analysis over fading channels in cognitive radio networks

This paper analyzes the spectrum sensing performance over fading channel,in which a licensee and multiple unlicensed users coexist and operate in the licensed channel in a local area. The overall average probabilities of detection and false alarm by jointly taking the fading and the locations of all secondary users into account are derived,and a statistical model of cumulate interference is constructed. Based on the cumulate interference,a closed-form expression of outage probability at the primary user's receiver according to a specific distribution of the fading is obtained. Finally,the sensing parameters so as to minimize the total spectrum sensing error and maximize the average opportunistic throughput are obtained. It is noted that the overall average performance analysis and results here enable to benchmark the design of specific spectrum sensing algorithms.     

Effect of channel estimation error on M-QAM BER performance inRayleigh fading

We determine the bit-error rate (BER) of multilevel quadrature amplitude modulation (M-QAM) in flat Rayleigh fading with imperfect channel estimates, Despite its high spectral efficiency, M-QAM is not commonly used over fading channels because of the channel amplitude and phase variation. Since the decision regions of the demodulator depend on the channel fading, estimation error of the channel variation can severely degrade the demodulator performance. Among the various fading estimation techniques, pilot symbol assisted modulation (PSAM) proves to be an effective choice. We first characterize the distribution of the amplitude and phase estimates using PSAM. We then use this distribution to obtain the BER of M-QAM as a function of the PSAM and channel parameters. By using a change of variables, our exact BER expression has a particularly simple form that involves just a few finite-range integrals. This approach can be used to compute the BER for any value of M. We compute the BER for 16-QAM and 64-QAM numerically and verify our analytical results by computer simulation. We show that for these modulations, amplitude estimation error leads to a 1-dB degradation in average signal-to-noise ratio and combined amplitude-phase estimation error leads to 2.5-dB degradation for the parameters we consider