OFDM闭环发射分集结合自适应功率分配

将自适应功率分配技术应用于多发送多接收天线正交频分复用(MIMO-OFDM)系统,如何在载波和天线间分配能量是个关键问题。该文提出：对不同发射天线的各个子载波采用闭环发射分集方案;接着再进行载波间的功率分配,该算法的目标是使误码率最小。文中用数学方法证明了此方案是使总误码率最小的最佳方案。仿真结果显示：在误码率取0.1%时,对于两根发射天线一根接收天线4个子载波的OFDM系统,与传统的将开环发射分集与OFDM相结合的算法相比,此算法能带来6.5dB的增益。     

接近最优的编码MIMO系统的发送天线子集选择算法

多天线无线系统可提供更大的信道容量和更好的抗衰落能力,发送端利用反馈的部分信道状态信息进行发送天线子集选择能够进一步提高信道容量。该文提出了一种MIMO系统的快速的、动态的天线子集选择算法,其提供的信道容量高于已有的静态算法,且接近于最优天线选择算法,而无需计算所有可能的天线子集组合的信道容量,因而具有更低的复杂度。将本文算法与比特交织编码调制(BICM)技术相结合,对各天线速率进行适配,提出了空时自适应比特交织编码调制(ST-ABICM)方案。仿真结果证实了该方案性能的优越性。     

Analog antenna combining in transmit correlated channels: Transceiver design and performance evaluation

In this paper we study space-time coding schemes for a novel OFDM-based MIMO system which performs adaptive signal combining in radio-frequency (RF). Assuming perfect channel knowledge at the receiver and statistical channel state information at the transmitter, we consider the problem of selecting the transmit and receive RF weights (beamformers), as well as the time and frequency linear precoders, under the assumption of Rayleigh channels. The transmission scheme is based on orthogonal beam division multiplexing (OBDM) and minimum mean-square error (MMSE) receive beamforming, i.e., the data is transmitted by means of several transmit beamformers matched to the spatial correlation matrix, whereas the receive beamformers are selected to minimize the MSE of the linear MMSE receiver. Finally, the performance of the proposed scheme is evaluated by means of Monte Carlo simulations.     

多径信道下OFDM系统中的两种线性载波间干扰抑制技术

载波间干扰(ICI)是影响正交频分复用(OFDM)系统性能的重要因素。该文研究了不同延迟线长度L下的频域RAKE(F-RAKE)和频域均衡(F-FIR)两种线性ICI抑制技术。假设接收端已知信道信息,F-FIR采用最小均方误差(MMSE)准则。结果表明L=3时,F-RAKE比标准接收机的载干比(CIR)高2～5dB,而F-FIR则高出2～7dB;随着L的增加,两种接收机所能获得的CIR增益逐渐降低。从计算复杂度来看,F-FIR的计算量是F-PAKE的L倍,工程中可以通过选取不同延迟线长度和接收机结构来达到计算复杂度和性能的折衷。     

无线多媒体通信的码分多址技术

本文介绍了多载波直扩码分多址技术,它的提出使大容量及高速率数据传输的移动、个人和多媒体通信系统更易实现。     

Frequency estimators for MIMO-OFDM systems

Orthogonal frequency division multiplexing (OFDM) systems are known to be sensitive to carrier frequency offset (CFO). This paper is concerned with the CFO estimation for multiple input multiple output (MIMO) systems employing OFDM waveforms. We present two approaches to derive maximum likelihood (ML) pilot-assisted frequency estimators that use either two or multiple identical training symbols. It is shown that the resulting ML frequency estimators are similar to maximum ratio combining versions of Moose estimator and Yu–Su solution, respectively. Numerical examples demonstrate that the proposed frequency estimators are robust against spatial Signal-to-noise ratio (SNR) variation and they yield performance superior to that of the corresponding single-antenna system.     

A Phase Adjustment Based Partial Transmit Sequence Scheme for PAPR Reduction

The peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing signal is normally very large and is crucial for the analog amplifier in the transmitter. It is therefore necessary to reduce the PAPR before the signal is transmitted. In this paper, a PAPR reduction scheme is presented based on the partial transmit sequence (PTS) method. By allowing each subblock of data to be rotated by an arbitrary angle, a simple yet efficient phase search algorithm is proposed. With a prespecified number of iterations, the proposed method gives the best phase vector for a combination of data blocks to achieve the smallest PAPR value. Our simulation results show that the proposed scheme provides significant computational savings while yielding a performance similar to that of the conventional PTS method.     

一种新的基于判决反馈的OFDM系统信道估计方法

提出了一种基于判决反馈机制的信道估计方法,采用少量导频估计出初始信道信息,再从接收端检测出的符号中选取一组包含了少量错误的符号作为准导频,反馈到信道估计器,与初始的导频一起构成数量更多的导频序列,经过几次迭代,达到提高信道估计精度的目的。为提高初始估计的精度。信道估计采用了一种频域分集的方法。计算机仿真表明,在多径瑞利衰落信道下,本文的方法可以在较低的复杂度下有效地提高信道估计的精度,在MMSE接收条件下,系统具有良好的误比特率（BER）性能。     

简明的联合收发端天线选择算法

For reducing the computational complexity of the problem of joint transmit and receive antenna selection in Multiple-Input- Multiple-Output (MIMO) systems, we present a concise joint transmit/receive antenna selec-tion algorithm. Using a novel partition of the channel matrix, we drive a concise formula. This formula enables us to augment the chan-nel matrix in such a way that the computational complexity of the greedy Joint Transmit/Receive Antenna Selection (JTRAS) algorithm is reduced by a factor of 4nL, where nL is the number of selected antennas. A de-coupled version of the proposed algorithm is also proposed to further improve the efficien-cy of the JTRAS algorithm, with some capacity degradation as a tradeoff. The computational complexity and the perform-ance of the proposed approaches are evalu-ated mathematically and verified by computer simulations. The results have shown that the proposed joint antenna selection algorithm maintains the capacity perormance of the JTRAS algorithm while its computational complexity is only 1/4nL of that of the JTRAS algorithm. The decoupled version of the proposed algorithm further reduces the computational complexity of the joint antenna selection and has better performance than other decoupling-based algorithms when the selected antenna subset is small as compared to the total number of antennas.     

一种基于串行干扰抵消的OFDM UWB多址方案

研究了高峰值传输速率时UWB系统的多址性能,对一种干扰抑制的OFDM传输方案进行了调整,提出了一种基于串行干扰抵消的两用户OFDM UWB多址方案.仿真结果显示所提出的方案可适度改善无纠错编码的OFDM UWB系统的误符号性能.     

应用PTS降低MIMO-OFDM信号峰均比技术研究

多输入多输出正交频分复用（MIMO—OFDM）系统已成为新一代高速通信系统研究中的热点。而系统所产生的高峰均比（PAPR）信号是限制MIMO—OFDM技术实用化的主要障碍。在对部分传输序列（PTS）技术进行研究的基础上。本文提出了一种应用PTS降低MIMO—OFDM信号峰均比（PAPR）的方案一并行PTS。仿真结果表明。该方法能有效降低MIMO—OFDM信号峰均比。     

一种新的基于判决反馈的OFDM频率跟踪算法

该文提出了一种新的用于多径信道的基于判决反馈的OFDM载波频率跟踪算法。该算法具有精度高,计算量小,实现简单的优点。基于该算法的特点同时提出了根据信道特性加权的改进方法,加强了对抗频率选择性衰落信道的能力,进一步提高了在低信噪比下的跟踪性能。     

集中式MIMO雷达研究进展：正交波形设计与信号处理

集中式多输入多输出（Multiple Input Multiple Output,MIMO）雷达通常利用正交波形增加发射波形自由度,采用数字阵列拓展空间收发自由度,使得雷达接收机的天线孔径获得明显扩展,最终带来空间分辨率、测角精确度、杂波抑制能力等大幅度提升。但是,这些性能提升的前提是发射波形具有正交特性。事实上,在实际应用中,在不牺牲时域/频域资源情况下,受限于时宽带宽积,无法获得完全正交的波形集合,从而限制了MIMO雷达系统性能。本文对集中式MIMO雷达正交波形复用的技术原理进行了系统回顾,分别归纳了三种快时间发射波形设计方法：时分复用（Time Division Multiplexing, TDM）、码分复用（Code Division Multiplexing,CDM）和频分复用 （Frequency Division Multiplexing, FDM）,以及两种慢时间发射波形设计方法：多普勒分复用（Doppler Division Multiplexing,DDM）和随机相位编码波形,并对其优缺点进行对比。同时,对快时间MIMO和慢时间MIMO的信号处理流程进行归纳综合,给出基于匹配滤波的集中式MIMO雷达统一信号处理框架。为了展示不同波形对成像性能的影响,本文给出了基于三维匹配滤波的MIMO雷达成像结果。最后,结合实际应用问题,指出当前MIMO雷达面临的技术难点和发展趋势。     

重叠正交变换在正交频分复用中的应用

本文将重叠正交变换(Lapped orthogonal transform)用于正交频分复用(OFDM)系统的调制和解调,提出了新的OFDM实现方案;并以一个多径信道为例,把它与传统的采用DFT的OFDM系统做了比较,指出新方案在无线通信中能有效地降低误码率。     

采用时域联合稀疏恢复的多输入多输出水声信道压缩感知估计

多输入多输出(MIMO)水声通信技术可以在极其有限的水声信道频带资源内提高信道容量,但多径和同道干扰的同时存在,使传统信道估计算法如最小二乘算法、压缩感知估计算法的性能急剧下降。考虑到通信数据块间水声信道多径结构存在一定的相关性,该文利用这种数据块间多径结构的时间域相关性建立水声MIMO信道的时域联合稀疏模型,并利用同步正交匹配追踪算法进行多个数据块联合稀疏恢复信道估计,提高MIMO信道多径稀疏位置的检测增益并抑制同道干扰,提高水声MIMO信道的估计性能。仿真和MIMO水声通信海试实验表明了所提方法的有效性。     

阵列天线在OFDM系统下行链路中的应用

正交频分多址(OFDM:orthogonal frequency division multiplexing)技术由于其在多径环境下克服码间干扰的固有特点,在移动通信中已得到广泛地应用。利用阵列天线上行链路信号到达角估计实时信息,计算OFDM系统下行链路阵列天线权重,将阵列天线应用于下行链路中,最后给出系统误码率性能的计算机仿真结果。