A new layered space-time detection algorithm for frequency selective fading multiple-input multiple-output channels based on particle filter

In this paper, a new observation equation of non-Gaussian frequency selective fading Bell Labs layered space time （BLAST） architecture system is proposed, which is used for frequency selective fading channels and non-Gaussian noise in an application environment of BLAST system. With othogonal matrix triangularization （QR decomposition） of the channel matrix, the static observation equation of frequency selective fading BLAST system is transformed into a dynamic state space model, and then the particle filter is used for space-time layered detection. Making the full use of the finite alphabet of the digital modulation communication signal, the optimal proposal distribution can be chosen to produce particle and update the weight. Incorporated with current method of reducing error propagation, a new space-time layered detection algorithm is proposed. Simulation result shows the validity of the proposed algorithm.

Factor-graph-based iterative channel estimation and signal detection algorithm over time-varying frequency-selective fading channels

The problem of soft-input so,output （ SISO ） detection for time-varying frequency-selec- tive fading channels is considered. Based on a suitably-designed factor graph and the sum-product al- gorithm, a low-complexity iterative message passing scheme is proposed for joint channel estima- tion, equalization and decoding. Two kinds of schedules （parallel and serial） are adopted in message updates to produce two algorithms with different latency. The computational complexity per iteration of the proposed algorithms grows only linearly with the channel length, which is a significantly de- crease compared to the optimal maximum a posteriori （MAP） detection with the exponential com- plexity. Computer simulations demonstrate the effectiveness of the proposed schemes in terms of bit error rate performance.

Linear and Nonlinear Time Domain Block Equalizers on MIMO Frequency Selective Channels

Single-Carrier (SC) transmission with the same bandwidth as Multi-Carrier (MC) transmission (such as OFDM) may have far shorter symbol duration and is considered to be more robust against time selective fading. In this paper, we proposed the novel equalization and signal separation schemes in time domain for short block length transmission, i.e., Block Linear Equalization (BLE) and Block Nonlinear Equalization (BNLE) on MIMO frequency selective fading channels. The proposed BLE uses the MMSE based inverse matrix in time domain and the BNLE utilizes the QRD-M (QR Decomposition with M algorithm) with appropriate receiver complexity. We compared the computational complexity among the conventional SC-FDE (Frequency Domain Equalization) scheme and the proposed equalizers. We also used the Low-Density Parity Check (LDPC) decoder concatenated to the proposed BLE and BNLE.

BLIND CHANNEL ESTIMATION IN DELAY DIVERSITY FOR FREQUENCY SELECTIVE CHANNELS

Delay diversity is an effective transmit diversity technique to combat adverse effects of fading. Thus far, previous work in delay diversity assumed that perfect estimates of current channel fading conditions are available at the receiver and training symbols are required to estimate the channel from the transmitter to the receiver. However, increasing the number of the antennas increases the required training interval and reduces the available time with in whichdata may be transmitted. Learning the channel coefficients becomes increasingly difficult for the frequency selective channels. In this paper, with the subspace method and the delay character of delay diversity, a channel estimation method is proposed, which does not use training symbols. It addresses the transmit diversity for a frequency selective channel from a single carrier perspective in the form of a simple equivalent flat fading model. Monte Carlo simulations give the performance of channel estimation and the performance comparison of our channel-estimation-based detector with decision feedback equalization, which uses the perfect channel information.

Controlling Ion Conductance and Channels to Achieve Synapticlike Frequency Selectivity

Enhancing ion conductance and controlling transport pathway in organic electrolyte could be used to modulate ionic kinetics to handle signals. In a Pt/Poly(3-hexylthiophene-2,5-diyl)/Polyethylene?Li CF3SO3/Pt hetero-junction, the electrolyte layer handled at high temperature showed nano-fiber microstructures accompanied with greatly improved salt solubility. Ions with high mobility were confined in the nano-fibrous channels leading to the semiconducting polymer layer,which is favorable for modulating dynamic doping at the semiconducting polymer/electrolyte interface by pulse frequency.Such a device realized synaptic-like frequency selectivity, i.e., depression at low frequency stimulation but potentiation at high-frequency stimulation.

Signal Detection for OFDM-IDMA Uplink over Doubly Selective Channels

Orthogonal frequency division multiplexing-interleave division multiple access (OFDM-IDMA) systems may suffer from serious inter-carrier interference (ICI) in time-and frequency-selective (doubly selective) channels. In such case, the conventional OFDM-IDMA detection algorithm for quasi-static channels will result in significantly performance degradation. In this paper, signal detection is investigated for OFDM-IDMA uplink over doubly selective channels. Firstly, the impact of time-varying channels for OFDM-IDMA uplink is analyzed, which leads to the failure of the conventional algorithm. Secondly, a novel iterative detection algorithm is developed based on an integrated interference canceller, which can iteratively estimate and mitigate the ICI as well as multiple access interference (MAI) simultaneously. In addition, an improved detection algorithm is derived for reducing the complexity using an approximation to the mean and variance of the interference. Simulation results indicate that the proposed algorithm can significantly enhance the system performance to the conventional case, and the improved algorithm can strike a balance between performance and complexity.

THE THEORETICAL BER PERFORMANCE ANALYSIS OF A COOPERATIVE DIVERSITY SCHEME IN FREQUENCY SELECTIVE FADING CHANNEL

A novel cooperative diversity scheme based on Distributed Space-Time Block Coding and Multi-Carrier Code Division Multiple Access (DSTBC-MC-CDMA) is proposed which works well in frequency selective fading channels with multiple single-antenna users. And an analytical error model is established to describe the symbol decoding errors between interusers, based on which a close form expression for theoretical Bit Error Rate (BER) performance of the scheme is derived to analyze the influence of the interuser decoding errors on the BER performance of the scheme. Then simulation is complimented to verify the analytic result above, which also shows that the BER performance of DSTBC-MC-CDMA outgoes that of non-cooperative MC-CDMA with considerable gains. Further- more, the simulations coincide with the theoretical results well.

Frequency Selectivity Analysis Based on Inductively Coupled Channel for Current Transmission Through Seawater

Inductively coupled channels are based on the electromagnetic induction principle and realize long-distance current signal transmission through seawater.Due to a few difficulties in performing actual experiments,it is unclear how the seawater medium affects the frequency selectivity of the current signal.In this paper,a dual dipole model of the inductively coupled seawater transmission channel is established for the traditional short-distance current field transmission mode.The transmission characteristics of electrical signals in seawater are theoretically derived.A platform is used to measure the amplitude-frequency and phase-frequency characteristics of the current signal transmission in seawater with transmission frequencies ranging from 30 kHz to 1 MHz,and transmission distances in the vertical range of 4 m.The COMSOL Multiphysics simulation and practical test analysis are carried out to analyze the frequency selectivity of seawater conductivity.It is proved that the seawater resistance increases as the frequency increases,which is the key problem that affects the current signal.This study provides an important theoretical support and experimental evidence for improving the transmission performance of long-distance underwater current signals.

车联网V2I场景下基于GNN的SC-FDMA智能信道估计

随着车联网的迅猛发展,车对路基础设施(Vehicle to Infrastructure,V2I)通信对车联网的可靠性和时延提出了更高的要求,而信道估计是接收机高可靠低时延通信的重要保障.为解决传统信道插值算法不能有效拟合V2I信道快时变特性、自适应多普勒频移能力弱和传统神经网络可解释性不强的问题,本文提出基于图神经网络(Graph Neural Network,GNN)的单载波频分多址(Single Carrier-Frequency Division Multiple Access,SC-FDMA)智能信道估计算法.该算法将信道频率响应中的数据点作为图的节点、符号间时域相关性作为边,将图化后的数据送入GraphSAGE信道插值器(GraphSAGE Channel Interpolator,GCI)中,通过边更新、聚合操作、节点更新三大模块进行网络训练,同时采用多普勒频移矢量作为节点特征控制网络拟合不同多普勒条件的信道,使得网络具备可解释性.最后,系统仿真验证了在不同速度环境下算法的有效性和鲁棒性,较线性插值、样条插值以及全连接网络,本文所提GCI在低、中和高速移动环境下具有最优的误码率(Bit Error Rate,BER)和归一化均方误差(Normalized Mean Square Error,NMSE)性能,特别地,在200 km/h高速移动条件下GCI的优势更为明显.

Response analyses on the drill-string channel for logging while drilling telemetry

Downhole acoustic telemetry(DAT),using a long drill string with periodical structures as the channel,is a prospective technology for improving the transmission rate of logging while drilling(LWD)data.Previous studies only focused on the acoustic property of a free drill string and neglected the coupling between pipes and fluid-filled boreholes.In addition to the drill-string waves,a series of fluid waves are recorded in the DAT channel,which has not been investigated yet.Unpredictable channel characteristics result in lower transmission rates and stability than expected.Therefore,a more realistic channel model is needed considering the fluid-filled borehole.In this paper,we propose a hybrid modeling method to investigate the response characteristics of the DAT channel.By combining the axial wavenumbers and excitation functions of mode waves in radially layered LWD structures,the channel model is approximated to the 1-D propagation,which considers transmission,reflection,and interconversion of the drillstring and fluid waves.The proposed 1-D approximation has been well validated by comparing the 2-D finite-difference modeling.It is revealed that the transmitted and converted fluid waves interfere with the drill-string wave,which characterizes the DAT channel as a particular coherent multi-path channel.When a fluid-filled borehole surrounds the drill string,the channel responses exhibit considerable delay as well as strong frequency selectivity in amplitude and phase.These new findings suggest that the complexity of the channel response has been underestimated in the past,and therefore channel measurements on the ground are unreliable.To address these channel characteristics,we apply a noncoherent demodulation strategy.The transmission rate for synthetic data reaches 15 bps in a 94.5 m long channel,indicating that the acoustic telemetry is promising to break the low-speed limitation of mud-pulse telemetry.

Polynomial rooting based frequency offset estimation for MIMO OFDM systems

Based on the frequency domain training sequences, the polynomial-based carrier frequency offset （CFO） estimation in multiple-input multiple-output （ MIMO ） orthogonal frequency division multiplexing （ OFDM ） systems is extensively investigated. By designing the training sequences to meet certain conditions and exploiting the Hermitian and real symmetric properties of the corresponding matrices, it is found that the roots of the polynomials corresponding to the cost functions are pairwise and that both meger CFO and fractional CFO can be estimated by the direct polynomial rooting approach. By analyzing the polynomials corresponding to the cost functions and their derivatives, it is shown that they have a common polynomial factor and the former can be expressed in a quadratic form of the common polynomial factor. Analytical results further reveal that the derivative polynomial rooting approach is equivalent to the direct one in estimation at the same signal-to-noise ratio（SNR） value and that the latter is superior to the former in complexity. Simulation results agree well with analytical results.

Sparse channel estimation for MIMO-OFDM systems using distributed compressed sensing

A sparse channel estimation method is proposed for doubly selective channels in multiple- input multiple-output （ MIMO ） orthogonal frequency division multiplexing （ OFDM ） systems. Based on the basis expansion model （BEM） of the channel, the joint-sparsity of MIMO-OFDM channels is described. The sparse characteristics enable us to cast the channel estimation as a distributed compressed sensing （DCS） problem. Then, a low complexity DCS-based estimation scheme is designed. Compared with the conventional compressed channel estimators based on the compressed sensing （CS） theory, the DCS-based method has an improved efficiency because it reconstructs the MIMO channels jointly rather than addresses them separately. Furthermore, the group-sparse structure of each single channel is also depicted. To effectively use this additional structure of the sparsity pattern, the DCS algorithm is modified. The modified algorithm can further enhance the estimation performance. Simulation results demonstrate the superiority of our method over fast fading channels in MIMO-OFDM systems.

SC-FDE系统的一种新型判决反馈均衡器

针对单载波频域均衡系统MMSE均衡器存在残留码间干扰的缺点,提出MMSE-RISIC判决反馈均衡器消除残留码间干扰。MMSE-RISIC均衡器采用传统MMSE均衡后的判决数据,对残留码间干扰进行估计并消除。残留码间干扰的估计主要采用FFT和IFFT运算,与其他方法相比计算量较小。对该均衡器在不同信道下进行了计算机仿真,结果表明,在频率选择性衰落信道条件下,系统性能有了较为明显的提高。

多发射天线STBC-SCFDE系统的性能研究

针对频率选择性衰落下2根以上发射天线的空时分组码—单载波频域均衡系统(STBC-SCFDE),提出了编码方案和检测方案的一般过程,并分别以3根及4根发射天线为例给出了具体的发射方案和接收方案。仿真结果表明,该方案下的多发射天线STBC SCFDE,在最大时延达到数10个符号周期的情况下仍然具有优良的性能,因而在高速无线通信中具有广阔的应用前景。

基于Matlab的MIMO-OFDM系统信道容量的研究

随着通信技术的发展,用户对更高的系统信道容量的需求日益提高。本文研究了一种频率选择性环境中MIMO-OFDM技术来实现高的频谱效率,从而提高系统容量。本文研究了系统信道容量的特性,并且运用Matlab仿真工具分析了MIMO-OFDM选择性衰落径数对信道容量的影响。研究结果表明,MIMO-OFDM技术可以极大的提高通信系统的容量。因此在宽带无线接入领域,MIMO与OFDM技术相结合的MIMO-OFDM技术已成为一种关键技术和发展趋势。

基于FABA-SISO的时变频率选择性衰落信道CPM信号盲均衡

该文针对时变频率选择性衰落信道下高阶连续相位调制(CPM)信号盲均衡中存在的均衡性能较差、复杂度较高以及收敛速度慢等问题,从双向自适应信道均衡的角度出发,将线性调制信号均衡中使用的前后向自适应软输入软输出(FABA-SISO)算法推广,建立一种新的基于FABA-SISO的信道盲均衡方法,并结合逐幸存处理(PSP)思想和Kalman滤波,提出一种适用于高阶CPM信号的自适应盲均衡算法。该算法通过使用FABA-SISO算法,同时利用过去、现在和将来的观察数据进行Kalman滤波信道估计,有效改善了信道估计的精度,同时使用PSP算法来降低系统的复杂度,使得算法具有较好的工程应用性。仿真结果表明所提算法具有良好的盲均衡性能以及收敛性。

基于DSTBC-MC-CDMA的无线网络协同发射分集系统

协同分集(cooperative diversity)技术通过使网络中各单天线用户共享彼此天线,形成虚拟的多天线阵列来实现发射或接收分集,可以有效地提高系统性能。该文提出无线网络中频率选择性衰落信道环境下的一种基于分布式空时分组码(Distributed Space Time Block Code,DSTBC)和MC-CDMA的协同发射分集方案,并给出了系统实现。建立了误码模型,探讨了协同用户间的信道状态信息(CSI)对系统误码性能的影响,分析了误码性能的上限,并给出了仿真结果。结果表明,DSTBC-MC-CDMA系统相对于未协同的MC-CDMA系统,获得了明显的性能增益。

MC V-BLAST系统的MIMO信道盲估计

本文研究多载波垂直分层空时(MCV-BLAST)系统的下行频率选择性衰落多输入多输出(MIMO)无线信道估计问题.本文首先为MCV-BLAST系统提出了一种新颖的移不变性编码方法.利用上述移不变性性质,本文进一步提出了相应的下行频率选择性衰落MIMO无线信道的盲估计方法.仿真结果表明了本文移不变性编码方法的有效性和信道盲估计方法的性能.

粒子滤波的MIMO-OFDM空频分层检测算法

针对BLAST系统应用环境中信道的频率选择性和测量噪声的非高斯性,建立了非高斯噪声环境下BLAST-OFDM系统的观测方程;通过对信道矩阵的QR分解将静态BLAST-OFDM系统的观测方程转化为空域的动态状态空间模型,并用粒子滤波进行空频分层检测;充分利用数字调制的有限字符特性,选择最优建议分布来产生粒子和更新权值,并与目前常用的抗误差传播算法相结合提出了一种新的空时分层检测算法。仿真结果表明了该算法的有效性。

宽带自适应MIMO-DFE空时接收机

设计了频率选择信道基于RLS算法的自适应判决反馈均衡MIMO-DFE空时接收机,由于这种接收机不需要信道识别,从而降低了接收机的复杂度。通过蒙特卡罗仿真评估了接收机在频率选择信道下的误符号率性能。仿真结果表明,在不加信道编码的情况下,该接收机在信噪比为 14dB时误符号率达到 10-3以下。