基于DFT的非采样间隔信道OFDM系统信道估计

提出了一种改进的基于DFT的系统信道估计方法．该方法充分考虑了非采样间隔信道的冲激响应能量泄漏问题．通过计算能量增长率选择保留路径,实现了基于DFT的非采样间隔信道OFDM系统信道估计．仂真结果表明,改进算法的均方误差（MSE）及误码率（SER）介于传统的LS估计及MMSE估计之间．在信噪比为15dB时,改进算法的MSE相对LS估计有3．5dB的改善．     

用特殊训练符号的MIMO-OFDM信道估计算法

提出了一种使用特殊训练符号的MIMO-OFDM系统时域LS信道估计的改进算法.采用插零的恒包络指数序列作为训练符号,可以使系统获得较理想的峰平比(PAPR),并能减少码间干扰(ISI)的影响.仿真结果表明,恒包络训练符号比随机训练符号具有很大的优势,在信噪比为20 dB时,利用恒包络训练符号的信道估计算法比利用随机训练符号的算法均方误差(MSE)降低15 dB;在采用特殊训练符号的前提下,改进算法相对传统算法也表现出较大的优越性,信噪比为25 dB时,改进算法的MSE要比传统算法低10 dB.     

窄带干扰条件下水声OFDM系统LMMSE信道估计算法

因为正交频分复用（OFDM）系统中强窄带干扰引起水声信道估计性能退化,因此,提出了一种可实用的线性最小均方误差（LMMSE）信道估计方法.该方法结合最小二乘（LS）信道估计结果对受窄带干扰（NBJ）和加性高斯白噪声（AWGN）噪声干扰的导频子载波进行辨别,从而获得最有效信道抽头;根据导出的理论模型,给出了信道自相关、窄带干扰信号和噪声功率等参数的近似估计方法;并采用傅里叶变换以避免矩阵的求逆运算,减少了计算复杂度.仿真结果表明,在强干扰信号条件下,文中提出的方法接近理想状态的LMMSE方法.     

衰落信道下基于空时分集编码的解相关检测技术研究

多用户检测技术能够抑制小区干扰,增加系统容量,而多输入多输出(MIMO)系统可以增加系统空间分集度来抑制信道衰落,提高系统可靠性.作者在码分多址(CDMA)系统瑞利衰落信道环境下,采用MIMO多天线空间分集技术,探究解相关检测器的相关性能,并通过对不同情况下信噪比与误码率的仿真、分析和比较,实现了预期效果.     

一种有效的水声信道盲均衡算法

针对超指数迭代判决反馈盲均衡（SEIDFE）算法在水声通信系统中表现出的收敛性差的问题,提出了一种稳健性好、收敛快的双模式超指数迭代判决反馈盲均衡算法.该算法对均衡器输出的实部和虚部分别进行非线性变换以修正误差控制信号,从而纠正载波相位旋转;在此基础上,将一种新的自适应变步长算法应用到前馈滤波器前向权值的迭代步长中,提高算法收敛速度;并采取判决误差切换准则,将上述改进算法与判决导引算法有机结合起来,提高算法稳健性和收敛性能.仿真结果证明了该算法的有效性.     

多径Rayleigh衰落信道中二元正交码扩频多址通信系统的性能分析

研究了随机二元正交码直接序列扩频多址信号在多径Ｒａｙｌｅｉｇｈ衰落信道传输中，在非相干ＲＡＫＥ接收机中采用两种不同最大选择接收方案（最大输出信噪比选择及最大输出功率选择分集接收）时，系统的差错特性和差错概率表达式。数值计算结果示出了在多径衰落信道中，分集接收对扩频多址系统性能的影响，同时表明在多径Ｒａｙｌｅｉｇｈ衰落信道中，最大输出功率选择分集接收时扩频系统的差错性能优于最大输出信噪比选择时扩频系     

一种应用于OFDM通信系统的简化软判决算法

应用软判决算法可以对通信系统的性能进行改善.对解凋模块软信息的提取进行了理论分析,研究了一种含有信道状态信息(CSI)的软信息提取的简化表达,并通过在典型的OFDM通信系统,IEEE802.11a基带模型上,在无线多径信道下进行性能仿真.仿真结果表明应用了软判决的系统性能明显优于硬判决系统,并且软信息提取的简化算法在降低算法复杂度的同时几乎不影响系统性能.     

基于卡尔曼滤波的快时变稀疏信道估计新技术

针对高铁以及山区环境下正交频分复用（orthogonal frequency division multiplexing,OFDM）通信系统的信道估计问题,提出一种基于卡尔曼滤波的快时变稀疏信道估计方法.该方法基于快时变信道的基扩展模型（basic expansion model,BEM）,应用压缩感知（compressed sensing,CS）理论进行稀疏时延估计,并应用卡尔曼滤波（Kalman filter,KF）技术对BEM系数进行估计,进而获得信道增益.仿真结果表明,在相同信噪比（signal to noise ratio,SNR）条件下,随着归一化多普勒频移（frequency-normalized Doppler shift,FND）增大,新方法的信道估计均方差（mean square error,MSE）性能优于传统方法,如当SNR为20 dB,FND为0.1时,新方法较传统方法性能提升了4 dB,表明对信道时变性具有更优的鲁棒性;在相同的多普勒频移条件下,随着SNR增加,各方法的均方差均有所改善,新方法改善更明显,如当FND为0.2时,在信道估计均方差为0.06的条件下,新方法较传统方法获得了6 dB的信噪比增益,表明对抗信道噪声能力更强.      

蜂窝移动通信系统中信道借用指配策略的优化

分析了蜂窝移动通信系统信道指配策略中的一个重要策略－信用策略,包括最早出现的简单借用策略,到后来在此基础上发展而来的带信道序号的借用策略（ＢＣＯ）和带方向锁定的借用策略（ＢＤＣＬ）。在原指配策略的基础上,增加了共道信道中的被锁定信道在信道表中的位置和处理,澄清了原策略中在这一点上的模糊不清。同时,通过两个方面的措施优化了ＢＣＯ和ＢＤＣＬ算法,仿真结果表明优化的算法可以显著降低原算法的复杂性。     

典型水声信道盲均衡算法比较研究

水声通信系统因所处的环境复杂,水声信道均衡是一个非常重要的环节,在简介典型的4种盲均衡算法原理的基础上,即最小均方恒模算法(Least Mean Square Constant Modulus Alogorithm, LMS-CMA)、修正恒模算法(Modified Constant Modulus Alogorithm, MCMA)、判决引导(Decision Directed, DD)算法、双模式切换算法等,采用典型实数水声信道和混合相位的复数水声信道两种模型进行仿真测试,实验结果表明,相对于LMS-CMA和MCMA算法,双模式切换算法具有更快的收敛速度和更小的稳态剩余误差;相对于DD算法,双模式算法具有更佳的稳健性.     

A New Arithmetic Coding System Combining Source Channel Coding and MAP Decoding

A new arithmetic coding system combining source channel coding and maximum a posteriori decoding were proposed. It combines source coding and error correction tasks into one unified process by introducing an adaptive forbidden symbol. The proposed system achieves fixed length code words by adaptively adjusting the probability of the forbidden symbol and adding tail digits of variable length. The corresponding improved MAP decoding metric was derived. The proposed system can improve the performance. Simulations were performed on AWGN channels with various noise levels by using both hard and soft decision with BPSK modulation.The results show its performance is slightly better than that of our adaptive arithmetic error correcting coding system using a forbidden symbol.     

OFDM System Channel Estimation with Hidden Pilot

Channel estimation using pilot is common used in OFDM system.The pilot is usually time division multiplexed with the informative sequence.One of the main drawbacks is bandwidth losing.In this paper,a new method was proposed to perform channel estimation in OFDM system.The pilot is arithmetically added to the output of OFDM modulator.Receiver uses the hidden pilot to get an accurate estimation of the channel.Then pilot is removed after channel estimation.The Cramer-Rao lower bound for this method was deprived.The performance of the algorithm is then shown.Compared with traditional methods,the proposed algorithm increases the bandwidth efficiency dramatically.     

A Reduced Complexity Time-Delay Tracking and Channel Estimation for OFDM Systems

Introduction OFDM[1]is a special case of multicarrier trans-mission, where a single datastream is transmittedover a number of orthogonal subcarriers. Becausethe symbol duration increases for the lower rateparallel subcarriers, the relative amount of disper-sion in time caused by multipath delay spread is de-creased. Intersymbol interference is eliminated al-most completely by introducing a guard time in ev-ery OFDM symbol. Due to these advantages,OFDM is widely exploited for the communica…     

Impact of channel estimation error on channel capacity of multiple input multiple output system

In order to investigate the impact of channel estimation error on channel capacity of multiple input multiple output （MIMO） system, a novel method is proposed to explore the channel capacity in correlated Rayleigh fading environment. A system model is constructed based on the channel estimation error at receiver side. Using the properties of Wishart distribution, the lower bound of the channel capacity is derived when the MIMO channel is of full rank. Then a method is proposed to select the optimum set of transmit antennas based on the lower bound of the mean channel capacity. The novel method can be easily implemented with low computational complexity. The simulation results show that the channel capacity of MIMO system is sensitive to channel estimation error, and is maximized when the signal-to- noise ratio increases to a certain point. Proper selection of transmit antennas can increase the channel capacity of MIMO system by about 1 bit/s in a flat fading environment with deficient rank of channel matrix.     

An Adaptive Joint Source/Channel Coding Using Error Correcting Arithmetic Codes

An approximately optimal adaptive arithmetic coding (AC) system using a forbidden symbol (FS) over noisy channels was proposed which allows one to jointly and adaptively design the source decoding and channel correcting in a single process, with superior performance compared with traditional separated techniques. The concept of adaptiveness is applied not only to the source model but also to the amount of coding redundancy. In addition, an improved branch metric computing algorithm and a faster sequential searching algorithm compared with the system proposed by Grangetto were proposed. The proposed system is tested in the case of image transmission over the AWGN channel, and compared with traditional separated system in terms of packet error rate and complexity. Both hard and soft decoding were taken into account.     

Pragmatic physical layer abstraction method based on bit-LLR-wise exponential effective SNR mapping for bit interleaved coded orthogonal frequency division multiplexing system

In this paper, we analyze the physical layer abstraction for bit interleaved coded orthogonal frequency division multiplexing （BIC-OFDM） system from a parallel bit channel perspective. By combining the exponential effective SNR （signal-to-noise ratio） mapping （EESM） with the maximum a posteriori （MAP） algorithm, a bit LLR （log-likelihood ratio） wise EESM （BL-EESM） method is proposed. This method can abstract the link performance with high accuracy, especially for the case when channel estimation is imperfect. Afterward, the BL-EESM method is simplified by utilizing the non-linear quantization idea, which can reduce the times of exponential operation by two orders of magnitude at wide system bandwidth, yet shows little loss in accuracy. Our proposal can be applied to both system level simulations to save the time consumption and to practical terminals to facilitate the adaptive modulation and coding （AMC） procedure, bringing about throughput improvement at low hardware cost.     

Joint Distortion Model for Progressive Image Transmission Using Error Correcting Arithmetic Codes

A novel joint source channel distortion model was proposed, which can essentially estimate the average distortion in progressive image transmission. To improve the precision of the model, the redundancy generated by a forbidden symbol in the arithmetic codes is used to distinguish the quantization distortion and the channel distortion, all the coefficients from the first error one to the end of the sequence are set to be a value within the variance range of the coefficients instead of zero, then the error propagation coming from the entropy coding can be essentially estimated, which is disregarded in the most conventional joint source channel coding (JSCC) systems. The precision of the model in terms of average peak-signal-to-noise has been improved about 0.5 dB compared to classical works. An efficient unequal error protection system based on the model is developed, and can be used in the wireless communication systems.     

Joint distortion model for progressive image transmission using error correcting arithmetic codes

A novel joint source channel distortion model was proposed, which can essentially estimate the average distortion in progressive image transmission. To improve the precision of the model, the redundancy generated by a forbidden symbol in the arithmetic codes is used to distinguish the quantization distortion and the channel distortion, all the coefficients from the first error one to the end of the sequence are set to be a value within the variance range of the coefficients instead of zero, then the error propagation coming from the entropy coding can be essentially estimated, which is disregarded in the most conventional joint source channel coding （JSCC） systems. The precision of the model in terms of average peak-signal-to-noise has been improved about 0.5 dB compared to classical works. An efficient unequal error protection system based on the model is developed, and can be used in the wireless communication systems.     

多分量相移键控信号码速率盲估计

为解决单通道接收机同时截获到同一频带范围内的多分量相移键控信号的参数估计问题,提出了一种不经信号分离直接提取各独立信号分量码速率的盲估计算法.从理论上推导了多分量相移键控信号的二阶共轭循环自相关具有线性特性,因此可以不受干扰地提取各信号分量的码速率;进而提出了简单而有效的谱峰增强方法,与基于二阶共轭循环自相关获得的谱峰相比,用此法获得的谱峰更为清晰.仿真实验表明:用提出的算法,当双分量信号功率比为1:1且信噪比为-5 dB时,码速率估计的正确率可达98％;尤其是在单分量环境下,该算法比现有算法的性能提高4 dB以上.