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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

基于FRFT与盲分离的扩频通信网络跳频信号时差估计

针对扩频通信网络跳频信号时差估计结果误差过高,导致信号定位追踪能力下降,多领域内信号传播停滞的问题,为增强扩频通信网络跳频信号的传播效率,提高辐射源跟踪和定位系统的信号探测能力,提出基于分数阶傅立叶变换(FRFT:Fractional Fourier Transform)与盲分离的扩频通信网络跳频信号时差估计算法的方法。采用盲分离方法获取满足跳频信号时差估计条件的两条信道,即平坦衰落信道和频率选择性衰落信道,利用FRFT估计两条信道特征,分别将平坦衰落信道特征和频率选择性衰落信道特征与最大似然块检测算法结合,实现扩频通信网络跳频信号的时差估计。实验结果表明,该方法无论是在正常环境中,还是在噪声干扰环境中,其均方根误差均处于较低水平、估计成功率均处于较高水平。

面向高速移动场景的OFDM系统信道估计综述

近年来,高速移动通信受到业界的广泛关注,其中接收机侧的信道估计直接决定了系统的通信质量。正交频分复用(orthogonal frequency division multiplexing,OFDM)以其高带宽效率和抗多径衰落的特性,在目前的无线通信中被广泛采用。综述了高速移动场景下OFDM系统信道估计方法;描述了OFDM的系统模型;分析了高速移动场景下信道的时间/频率选择性衰落特性(双选特性)和稀疏特性。基于深度学习和压缩感知的信道估计方法,其高精度和低复杂度被用于高速移动场景,该文分别对基于深度学习和压缩感知的信道估计算法进行了归纳、对比、分析,探讨了高速移动场景下信道估计的发展趋势。

下一代铁路移动通信中公专网系统间干扰协调的研究

针对下一代铁路移动通信技术中公专网系统间存在频率干扰的情况,研究干扰产生的原因、发生干扰的场景并分析抑制干扰采用的方法,研究3GPP中基站隔离度的要求并给出公转网无线系统部署要求,以及驻波比(VSWR)、带外信号抑制比和滤波器插入损耗等参数相互制约的关系,通过仿真得出三者间的关系以及铁路专网无线通信系统滤波器指标要求。

网络参数对低压宽带电力线信道的影响

在电力线载波信道的研究中，目前有关电网结构对电力线载波性能的影响研究较少，多径效应和频率选择性衰落现象难以从现有模型得到合理解释，也对电力线节点间的通信性能和路径拓扑中继理论支持不足，制约了宽带电力线载波通信性能的提升。针对此，通过使用基于传输线理论的方法对低压电力线通信信道仿真建模，分析了不同网络拓扑结构对频率为2～30MHz的低压宽带电力线信道特性的影响。仿真得到不同电力线长度、分支长度、单节点分支数、分布式分支数和负载阻抗的低压宽带电力线信道频率响应，并通过反傅里叶变换得到对应的信道时域冲激响应。结果表明，电力线信道频率响应中的峰值点和陷波频点的位置和衰减会受到上述网络参数的影响，时域冲激响应也会因此而衰减和失真。本文的研究对于宽带电力线通信技术在能源互联网中的有效应用具有重要意义。

频率选择性衰落MIMO信道容量分析

随着传输速率越来越高,信号所占用的带宽越来越宽,实际信道呈现出频率选择性衰落特性。根据频率选择性衰落信道特性,建立了频率选择性衰落MIMO信道模型,采用频域和时域的方法研究了在频率选择性衰落下,发射端已知和未知信道状态信息的MIMO信道容量,并给出了相关的仿真结果。研究结果表明:在相同发射功率和传输带宽下,MIMO系统可以不牺牲信号带宽而显著提高信道的容量,并且天线数量和输入信噪比的大小对信道容量具有不同的影响。研究结果为如何提高频率选择性衰落环境下MIMO信道容量提供了依据。

航空信道仿真研究

在对航空信道物理特性分析的基础上,提出了一个适用于空-空、地-空无线链路的宽带频率选择性衰落频域信道仿真器。选择合适的仿真参数,该仿真器可以模拟航空器在停场、滑行、飞行等状态的无线衰落信道。宽带频率选择性信道仿真器由多个并行子信道仿真器在频域构成,每个子信道为一个简单结构的平坦衰落模型,执行独立的瑞利衰落,这样的多个并行子信道构成了一个宽带频率选择性信道的仿真结构,非常适合正交频分复用或者多载波码分多址系统信道的计算机仿真。

短波电离层反射信道模型的建立与仿真

工作在短波波段的电子战设备进行天波通信时 ,会受到电离层高度变化和多径传播的影响 ,使信号产生多普勒展宽和多径时延 ,表现为时间选择性衰落和频率选择性衰落 ,严重影响信号质量。本文介绍了短波电离层反射信道对信号的影响 ,推导出信道的理论模型 ,提出了实现方案 ,并利用systemview进行了信道仿真 ,结果表明 。

OFDM系统的迭代联合信道估计与符号检测算法

提出了通过降低导频功率来提高OFDM传输效率,同时采用迭代的联合信道估计和符号检测算法来保证较好误码性能的接收方案。理论分析与仿真结果表明,当数据信息与导频信息的功率比不高于10dB时,本文提出的算法能够有效地降低系统误码率,同时该方法还具有算法简单,收敛速度快的特点。