CSI Feedback-based CS for Underwater Acoustic Adaptive Modulation OFDM System with Channel Prediction

In this paper, we investigate the performance of adaptive modulation （AM） orthogonal frequency division multiplexing （OFDM） system in underwater acoustic （UWA） communications. The aim is to solve the problem of large feedback overhead for channel state information （CSI） in every subcarrier. A novel CSI feedback scheme is proposed based on the theory of compressed sensing （CS）. We propose a feedback from the receiver that only feedback the sparse channel parameters. Additionally, prediction of the channel state is proposed every several symbols to realize the AM in practice. We describe a linear channel prediction algorithm which is used in adaptive transmission. This system has been tested in the real underwater acoustic channel. The linear channel prediction makes the AM transmission techniques more feasible for acoustic channel communications. The simulation and experiment show that significant improvements can be obtained both in bit error rate （BER） and throughput in the AM scheme compared with the fixed Quadrature Phase Shift Keying （QPSK） modulation scheme. Moreover, the performance with standard CS outperforms the Discrete Cosine Transform （DCT） method.

Hardware Implementation and Simulations of Joint Coding and Modulation Diversity MIMO-OFDM Scheme

This paper presents an efficient Joint Coding and Modulation Diversity ( JCMD ) scheme. The proposed scheme applied modulation diversity technique to MIMO-OFDM system which can effectively use time, frequency and space diversity combined with channel coding. In fading channel,the proposed scheme not only achieves high spectral efficiency,but also greatly enhances the reliability of wireless transmission. The self- developed hardware prototype system proves that the proposed scheme can be realized and has high reliability. Compared with traditional MIMO-OFDM scheme based on bit-interleaved coded modulation ( BICM) ,software and hardware simulation results show that the proposed scheme with the optimal rotational angle can obtain a significant performance advantage both for precoded and non-precoded system in the condition of non-perfect channel knowledge and non-ideal synchronization.

基于深度学习的多用户MIMO-OFDM-IM系统符号检测技术

MIMO-OFDM-IM是将MIMO-OFDM(多输入多输出正交频分复用)和IM(索引调制)结合的一种新颖的多载波调制技术。为解决目前多用户MIMO-OFDM索引调制的符号检测技术仍存在的复杂度高和误码性能受用户数量影响严重的问题,提出一种基于深度学习的符号检测框架,在该框架中,编码器与解码器都由DNN(深度神经网络)构造,采用监督式学习训练数据。实验结果表明,该框架有效地解决了以上问题。

基于排序码本的水声自适应OFDM通信中信道状态信息反馈研究

水声(UWA)信道时延扩展大等特点导致信道频响(CFR)快衰落,水声通信(UWAC)技术发展受到挑战。发射端获取有效可靠的信道状态信息(CSI)是自适应通信的前提,针对水声自适应正交频分复用(OFDM)通信的需求,该文提出基于排序码本的信道状态信息分组排序拟合反馈算法(CSI-GSFF),包括分组、排序、数据拟合3个步骤。该算法首先将相邻导频子载波分组,以组为反馈单元;然后对各组内的导频子载波按照信道增益值进行排序,以减轻水声信道频响快衰落造成的反馈开销大等不利影响;最后进行多项式拟合,排序操作有效地降低了拟合阶数。通过实测海试时变信道数据仿真,结果表明,该文提出的信道状态信息反馈算法能够基本达到完美信道状态信息情形下的水声自适应OFDM通信系统误码率性能,同时可以有效地减少反馈开销。

A New High Rate Differential Space-Time-Frequency Modulation for MIMO-OFDM

In this paper, we propose a new differential space-time-frequency （DSTF） modulation for MIMOOFDM system with four transmit-antennas and arbitrary receive-antennas, which can improve the transmission rate since it can adopt high order quadrature amplitude modulation （QAM） modulation. Our proposed DSTF scheme embeds some full diversity full rate （FDFR） quasi-orthogonal space-time codes （QOSTBC） with QAM modulation into the frequency intervals and adopts the differential modulation in both time and frequency domains. The simulation results demonstrate that the proposed DSTF scheme can improve transmission rate greatly. Compared with the conventional differential unitary space-time modulation （DUSTM）, it can get better transmission performance in high transmission rate for MIMO-OFDM system.

Novel time-frequency differential space-time modulation for multi-antenna OFDM systems

Differential space-time （DST） modulation has been proposed recently for multiple-antenna systems over Rayleigh fading channels, where neither the transmitter nor the receiver knows the fading coefficients. Among existing schemes, differential modulation is always performed in the time domain and suffers performance degradations in frequency-selective fading channels. In order to combat the fast time and frequency-selective fading, a novel time-frequency differential space-time （TF-DST） modulation scheme, which adopts differential modulation in both time and frequency domains, is proposed for multi-antenna orthogonal frequency division multiplexing （OFDM） system. A corresponding suboptimal yet low-complexity non-coherent detection approach is also proposed. Simulation results demonstrate that the proposed system is robust for time and frequency-selective Rayleigh fading channels.

POWER ALLOCATION AND ADAPTIVE MODULATION STRATEGY FOR MIMO-OFDM SYSTEMS WITH IMPERFECT CSI

The presented scheme named M-CAP (Maximum CAPacity) uses the CSI (Channel State Information) and its statistics to deduce an equivalent channel according to which the transmit power is allocated to the subchannels. And then modulation scheme is determined adaptively according to the power allocated to each subchannel. The advantage of the M-CAP scheme is that it combines power allocation and adaptive modulation while maintaining a large capacity. We demonstrate by computer simulations that the proposed M-CAP scheme can significantly improve system performance compared with the traditional schemes.

基于OFDM的无线信号与电能反向同步传输方法

无线电能传输系统的稳定运行离不开信息传输技术的实现,该文针对无线信号与电能共享通道传输时存在耦合干扰及频谱利用率低的问题,提出一种基于正交频分复用技术(OFDM)的信号与电能反向同步传输新方法。该方法将电能载波等效为搭载全1信息的信号载波,采用OFDM技术实现信号的同步解耦与高速可靠传输时,即可减少电能传输过程对信号传输过程产生的串扰。电能通道采用串联谐振(S/LCC)补偿拓扑结构,使负载在一定范围内变化时输出电压稳定。松耦合变压器作为电能和信号传输的共同通道,可以同时、反向传输信号与电能两种不同频率的载波。首先介绍了系统的结构和OFDM基本原理;其次,对系统进行数学建模,分析研究信号与电能的传输特性;在此基础上,给出了信号调制与解调的设计方法。最后搭建电能传输功率为20 W、信号传输速率为85 kbit/s的实验平台,验证了所提方法的正确性。

Modulation Techniques for Li-Fi

Modulation techniques for light fidelity （Li-Fi） are reviewed in this paper. Li-Fi is the fully networked solution for nmltiple users that combines communication and illumination simultaneously. Light emitting diodes （LEDs） are used in Li-Fi as visible light transmitters, therefore, only intensity modulated direct detected modulation techniques can be achieved. Single carrier modulation techniques are straightforward to be used in Li-Fi, however, computationally complex equalization processes are required in fre- quency selective Li-Fi channels. On the other hand, multiearrier modulation techniques offer a viable solution for Li-Fi in terms of power, spectral and computational efficiency. In particular, orthogonal frequency division multiplexing （OFDM） based modulation techniques offer a practical solution for Li-Fi, especially when direct current （DC） wander, and adaptive bit and power loading techniques are considered. Li-Fi modulation techniques need to also satisfy illumination requirements. Flickering avoidance and dimming control are considered in the variant modulation techniques presented. This paper surveys the suitable modulation techniques for Li-Fi including those which explore time, frequency and colour domains.

Compressive Sensing Approach in Multicarrier Sparsely Indexing Modulation Systems

recently the indexed modulation(IM) technique in conjunction with the multi-carrier modulation gains an increasing attention. It conveys additional information on the subcarrier indices by activating specific subcarriers in the frequency domain besides the conventional amplitude-phase modulation of the activated subcarriers. Orthogonal frequency division multiplexing(OFDM) with IM(OFDM-IM) is deeply compared with the classical OFDM. It leads to an attractive trade-off between the spectral efficiency(SE) and the energy efficiency(EE). In this paper, the concept of the combinatorial modulation is introduced from a new point of view. The sparsity mapping is suggested intentionally to enable the compressive sensing(CS) concept in the data recovery process to provide further performance and EE enhancement without SE loss. Generating artificial data sparsity in the frequency domain along with naturally embedded channel sparsity in the time domain allows joint data recovery and channel estimation in a double sparsity framework. Based on simulation results, the performance of the proposed approach agrees with the predicted CS superiority even under low signal-to-noise ratio without channel coding. Moreover, the proposed sparsely indexed modulation system outperforms the conventional OFDM system and the OFDM-IM system in terms of error performance, peak-to-average power ratio(PAPR) and energy efficiency under the same spectral efficiency.

基于深度学习的OFDM-IM信号检测方法

正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)技术在无线通信领域中拥有着重要地位,但OFDM系统中存在子载波间干扰和较高的峰均比的缺点,使得OFDM系统在信号检测方面的表现不太理想。针对OFDM系统中信号检测性能较差的问题,提出一种基于自归一化网络的索引调制(Index Modulation for Self Normalizing Network,IM-SNN)算法,并采用4QAM、8QAM、16QAM的调制方式验证系统的信号检测性能。结果表明,所提出的算法提高了接收端解调信号的性能,有效增强了信号检测的能力,并表现出优于传统技术中最大似然检测(Maximum Likelihood Detection,MLD)算法及现有技术中基于深度神经网络的索引调制(Index Modulation in Deep Neural Network,IM-DNN)算法的系统误码率及网络损失。在3种调制方式下,性能改善0.6~8 dB。

基于联合特征参数和一维CNN的MIMO-OFDM系统调制识别算法

针对当前非协作通信中多输入多输出正交频分复用(multiple-input multiple-output orthogonal frequency division multiplexing,MIMO-OFDM)系统子载波的调制识别问题,提出了一种基于一维卷积神经网络(one-dimensional convolutional neural network,1D-CNN)的调制识别方法。首先,利用特征矩阵的联合近似对角化(joint approximate diagonalization of eigenvalue matrix,JADE)算法从接收端的混合信号中恢复发送信号;然后,提取恢复信号的循环谱切片和四次方谱作为浅层特征;最后,利用1D-CNN对特征进行训练,使用测试样本对所提出的调制识别方法进行仿真验证。仿真结果表明,所提方法对MIMO-OFDM系统中的5种信号可以进行有效识别,在信噪比为10 dB时的识别精度即可达到100%。

Performance Evaluation of Adaptive Modulation Based MC-CDMA System

In today’s scenario mobile phones are not used only for messaging and talking, now we use mobiles also to access internet. For that we need higher data rates. Mobiles use wireless communication channel, which is very fast varying channel. To increase the data rate we have to utilize the full channel based on the channel condition. For that we have to estimate the channel condition and based on that we have to vary the data rate so that our communication system performance parameters (bit error rate, throughput) do not change beyond the accepted level. To increase the data rate we are also using the multi-carrier CDMA system in conjunction with the above described adaptive modulation. Adaptive modulation, in conjunction with MC-CDMA transmission system is very assuring way to increase data rate. In current scenario demand of very high data rates up to 100 Mbits/s may be achieved with this scheme. In this paper, adaptive modulation based M-ary QAM, M-PSK and M-ary CPM systems applied to a MC-CDMA system in Rayleigh fading channel environment have been investigated and BER performances of all these digital modulation schemes have been compared.

Coded Orthogonal Time Frequency Space Modulation

Orthogonal time frequency space(OTFS)modulation is a novel two-dimensional modulation scheme for high-Doppler fading scenarios,which is implemented in the delay-Doppler(DD)domain.In time and frequency selective channels,OTFS modulation is more robust than the popular orthogonal frequency division multiplexing(OFDM)modulation technique.To further improve transmission reliability,some channel coding schemes are used in the OTFS modulation system.In this paper,the coded OTFS modulation system is considered and introduced in detail.Furthermore,the performance of the uncoded/coded OTFS system and OFDM system is analyzed with different relative speeds,modulation schemes,and iterations.Simulation results show that the OTFS system has the potential of full diversity gain and better robustness under high mobility scenarios.

Spectrally Efficient Multi-Carrier Modulation Using Gabor Transform

Non Orthogonal Frequency Division Multiplexing (NOFDM) systems make use of a transmission signal set which is not restricted to orthonormal bases unlike previous OFDM systems. The usage of non-orthogonal bases generally results in a trade-off between Bit Error Rate (BER) and receiver complexity. This paper studies the use of Gabor based on designing a Spectrally Efficient Multi-Carrier Modulation Scheme. Using Gabor Transform with a specific Gaussian envelope;we derive the expected BER-SNR performance. The spectral usage of such a NOFDM system when affected by a channel that imparts Additive White Gaussian Noise (AWGN) is estimated. We compare the obtained results with an OFDM system and observe that with comparable BER performance, this system gives a better spectral usage. The effect of window length on spectral usage is also analyzed.

OFDM with Generalized Cascade Index Modulation for Secure Communications

Cascade index modulation(CIM) is a recently proposed improvement of orthogonal frequency division multiplexing with index modulation(OFDM-IM) and achieves better error performance.In CIM, at least two different IM operations construct a super IM operation or achieve new functionality. First, we propose a OFDM with generalized CIM(OFDM-GCIM) scheme to achieve a joint IM of subcarrier selection and multiple-mode(MM)permutations by using a multilevel digital algorithm.Then, two schemes, called double CIM(D-CIM) and multiple-layer CIM(M-CIM), are proposed for secure communication, which combine new IM operation for disrupting the original order of bits and symbols with conventional OFDM-IM, to protect the legitimate users from eavesdropping in the wireless communications. A subcarrier-wise maximum likelihood(ML) detector and a low complexity log-likelihood ratio(LLR) detector are proposed for the legitimate users. A tight upper bound on the bit error rate(BER) of the proposed OFDM-GCIM, D-CIM and MCIM at the legitimate users are derived in closed form by employing the ML criteria detection. Computer simulations and numerical results show that the proposed OFDM-GCIM achieves superior error performance than OFDM-IM, and the error performance at the eavesdroppers demonstrates the security of D-CIM and M-CIM.

高速星间收发通信机OFDM调制解调研究

目前,国内外针对卫星组网的研究主要集中在卫星之间的星间链路研究方向。为实现卫星组网通信系统中大数据量的信息交互,首次提出了一种利用正交频分复用(orthogonal frequency division multiplexing,OFDM)技术的高速星间收发通信机的设计方案。相比传统单载波技术,OFDM技术凭借其较高的频谱利用率、良好的抗多径干扰能力以及能够灵活分配资源等特有的优势,可用于实现星间通信的高码速率传输。首先设计了星间收发通信机的总体架构,基于星间通信系统的特点以及16QAM调制解调方式的优点进行了相关的参数设计,然后根据设计参数,采用Verilog HDL硬件描述语言基于ISE开发平台和Modelsim软件完成了16QAM数字调制解调功能和时序的仿真,验证了设计的可行性。首次将OFDM技术应用到星间收发通信机,为其硬件实现奠定了基础,具有一定的参考价值。

Wireless Local Area Network Adaptive Modulation and Coding Technology Research

Expound the existing modulation mode of the present wireless local area network.Directing at the problem that when single modulation method conveys data with high speed in the frequency selective fading channel,the system throughput will be declined and the efficiency of the spectrum will be lowered.Put forward the scheme that the OFDM sub-carrier will use differ ent modulation modes after dynamic groups by amplitude frequency response.Simulation results show that the scheme will lower the complexity of the system achievement,and can get a higher spectrum efficiency.

基于高阶累积量的OFDM信号和单载波信号识别

本文提出了一种利用高阶累积量实现OFDM信号和单载波调制信号识别的方法。该方法利用接收信号的高阶累积量提取特征参数,并结合星座图聚类分析,采用一种决策树的多分类器实现信号的分类识别。使用的特征参数对信号的信道抖动和相位延时不敏感,且能抑制噪声的影响,易于工程实现。仿真和实验结果表明,该方法能有效识别出OFDM信号和单载波信号,具有一定的实际应用价值和发展前景。

基于空间调制的OFDM系统及其信号检测

针对当前通信领域的高速率传输要求,设计一种SM-OFDM系统传输方案。该方案在空间调制(Spatial Modulation,SM)技术的基础上加入正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)框架,同时为进一步提升此系统的信号检测能力,用深度神经网络检测框架代替传统的最大似然检测算法来进行信号检测。仿真结果表明,所提方案在低信噪比环境下优势明显,既可提高频谱效率,又可以保证较低的误码率。