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.

为了在不显著提升计算复杂度的情况下,有效提升通信系统的误码率(BER)性能,利用深度学习在数据处理方面的强大能力,提出一种面向基于蜂窝网络的车联网(C-V2X)通信的基于深度学习的联合信道估计与均衡算法——V-EstEqNet.与传统算法分两个阶段分别进行信道估计与均衡不同,V-EstEqNet将通信系统接收机中的信道估计与信道均衡进行联合考虑,并利用深度学习网络直接对接收数据进行校正和恢复,无须进行显式的信道估计环节即可完成信道均衡.具体而言,首先利用大量的接收数据对网络进行离线训练,使网络学习到叠加在接收数据中的信道特性;然后利用该特性恢复原始的发送数据.仿真实验结果表明,在不同的速度场景下,所提算法可以更加有效地追踪信道特性;同时,相较于传统信道估计算法(最小二乘法(LS)和线性最小均方误差法(LMMSE))配合传统信道均衡算法(迫零(ZF)均衡算法和最小均方误差(MMSE)均衡算法),所提算法在低速环境下有最高有6 dB的BER增益,在高速环境下最高有9 dB的BER增益.

基于长期演进(LTE)的车辆到一切(LTE-V2X)标准沿用LTE标准的帧格式,并采用块状导频辅助的单载波频分多址(SC-FDMA)系统完成信道估计.然而,由于V2X信道的时变特性,接收机信道估计面对巨大的技术挑战.因此,设计了一种基于滑窗滤波和多项式拟合的时变信道估计方法.针对导频符号处的噪声问题,在最小二乘(LS)方法基础上,采用了自适应长度的滑动窗口滤波进行降噪处理,从而保证导频符号处的信道估计精度.另外,根据多普勒频移大小,设计了自适应阶次的多项式拟合方法来跟踪数据符号处的信道变化.仿真结果表明,所提方法在LS方法的基础上有良好的去噪效果,在低速移动情况下的估计精度介于LS方法和线性最小均方误差(LMMSE)方法之间,而该方法在高速移动条件下能更好地拟合信道的时变特性,且性能上超过了LMMSE方法结合线性插值的信道估计方法.以上结果说明,所提方法相对于对比方法具有更好的自适应性,适用于不同的信道噪声和终端移动速度下的LTE-V2X通信场景.

实践教学体系对于培养应用型人才的应用能力具有基础的支撑作用.本文基于OBE理念,提出应用型人才培养目标的制定流程以及人才培养方案设计实施路线图;对通信工程专业人才的能力进行科学分解,构建支撑能力培养的实践教学体系;对各实践教环节进行详细设计,实践证明,实施该实践教学体系显著提高了人才的应用能力.

大规模多输入多输出(Multiple-Input Multiple-Output,MIMO)技术凭借其高能量效率和高频谱效率的优势成为下一代移动通信的核心技术之一,其系统增益的基础在于基站能够精确获知信道状态信息(Channel State Information,CSI).由于大规模MIMO系统中基站天线数量巨大,基站获取下行信道状态信息将造成巨大的系统开销,传统基于码本或矢量量化的反馈方法受到挑战,频分双工(Frequency Division Duplex,FDD)模式下5G通信的实际应用也受到制约,而人工智能技术尤其是深度学习(Deep Learning,DL)为解决大规模MIMO系统中的CSI反馈问题提供了新的思路.围绕大规模MIMO系统CSI反馈存在的问题,阐述了CSI反馈的背景,构建了FDD大规模MIMO系统模型,详细描述了代表性的国内外基于DL的CSI反馈方案,最后对基于人工智能的大规模MIMO信道状态信息反馈进行了展望和总结.

基于深度学习的信道估计方法中,训练网络模型需要大量的数据运算,且所有用户数据都需要集中上传至服务器上,存在隐私泄漏的隐患.针对上述问题,提出了一种基于联邦学习的LTE-V2X(Long Term Evolution-Vehicle to Everything)信道估计算法,采用CNN-LSTM-DNN(Convolutional Neural Network-Long Short Term Memory-Deep Neural Network)模型对时变的信道进行估计,并将学习网络模型所需要的计算分配到车载用户中,在降低道旁基站负载的同时也保护了车载用户数据的隐私.仿真结果表明,基于联邦学习的信道估计算法在车载用户高速移动的场景下,较传统的信道估计算法平均有10 dB以上的归一化均方误差(Normalized Mean Square Error,NMSE)增益以及3 dB以上的误码率(Bit Error Rate,BER)增益,且较集中式学习算法相比,NMSE性能差距在3 dB以内;BER性能差距在1 dB以内,所提算法能够有效追踪时变的信道,且与集中式学习算法相比仅损失了极少的性能.

6G vehicle-to-everything (V2X) communication will be combined with vehicle automatic driving technology and play an important role in automatic driving. However, in 6G V2X systems, vehicle users have the characteristics of high-speed movement. Therefore, how to provide stable and reliable wireless link quality and improve channel gain has become a problem that must be solved. To solve this problem, a new multi-user scheduling algorithm based on block diagonalization (BD) precoding for 6G ultra-massive multiple-input multiple-output (MIMO) systems is proposed in this paper. The algorithm takes advantage of the sensitive nature of BD precoding to channel correlation, uses the Pearson coefficient after matrix vectorization to measure the channel correlation between users, defines the scheduling factor to measure the channel quality according to the user noise enhancement factor, and jointly considers the influence of the correlation between user channels and channel quality, ensuring the selection of high-quality channels while minimizing channel correlation. Simulation results show that compared with the multi-user scheduling algorithm based on subspace correlation, condition number, and geometric angle, the proposed algorithm can obtain higher user channel gain, effectively reduce the system bit error rate, and can be applied to 6G V2X communication.

Cyber-physical systems (CPSs) are characterized by integrating computation and physical processes. To cope with the challenges of the application of the CPSs in all kinds of environments, especially the cellular vehicle-to-everything (C-V2X) which needs high quality end-to-end communication, the robustness and reliability for CPSs are very crucial. Aiming at the technical challenges of information transmission caused by the fading effect and the fast time-varying characteristics of the channel for C-V2X communication, an improved Tomlinson–Harashima precoding (THP) algorithm for multiple input multiple output (MIMO) systems is proposed. Channel state information (CSI) and correlation are exploited to compensate instantaneous CSI, which could reflect current real-time channel status exactly. Further, the iterative water filling power allocation algorithm and the multiuser scheduling algorithm based on the greedy algorithm are jointly optimized and applied to the THP, which could improve the system performance. Simulation results show that the proposed algorithm can be efficiently applied to high-speed mobility scenarios and improve bit error ratio (BER) performance as well as spectrum utilization.

A complementary M-ary orthogonal spreading (CMOS) architecture with orthogonal frequency division multiplexing (OFDM) is proposed to improve performance of bit-error rate (BER) and spectrum efficiency for high frequency (HF) communications. The CMOS-OFDM architecture is based on orthogonal complementary pairs with their central elements being zero. It is well known that complementary pairs theoretically reduce peak-to-mean envelope power ratio (PMEPR) of OFDM due to their ideal aperiodic auto-correlation properties. However, many practical OFDM applications, such as HF OFDM and IEEE 802.11, require that no data should be modulated to direct current (DC) subcarrier, which will destroy ideal properties of traditional complementary pairs and hence increase their PMEPRs. Compared with traditional complementary pairs, the proposed zero-centre complementary pairs (ZCCPs) in CMOS-OFDM architecture may maintain ideal properties and hence be more suitable for OFDM systems as long as zero element in the centre is modulated to DC subcarrier. The corresponding simulation results and numerical analyses over the HF fading channel modelled by ITU-R F.1487 are provided. Different from the previous researches on HF OFDM systems, the proposed HF CMOS-OFDM architecture using the constructed ZCCPs not only possesses excellent BER performance, but also may firmly resist PMEPR to 3 dB or near to 3 dB.

针对目前扇区天线邻居发现方法面临节点冲突概率大和发现时间长的问题,提出一种用于自组织网络的多天线扇区切换的邻居信息发现维护方法.将邻居发现子帧划分成多个微时隙,通过三次握手,在降低节点冲突的同时减少邻居发现时间,提高邻居发现效率.仿真结果表明,文章提出的方法在邻居发现时间和邻居发现节点对数等方面优于现有DTRA协议.

天线的性能参数通常是在理想条件下分析得出的,然而在工程实践中,天线架设在不同的地形环境中,其性能会受到不同程度的影响.针对这一问题,文章利用电磁仿真软件HFSS建立基础仿真模型,分析了不同地形环境对短波三线天线性能的影响情况,得出了对短波发信天线场设计与天线架设有实际指导意义的结果.

高宽带网络电台为当前信息化战场提供及时精确的战场信息.文章基于高宽带电台设计的DTRA协议,提出一种基于多天线扇区切换的动态时隙分配算法,该算法根据网络节点业务需求调整当前时隙并进行动态分配.仿真结果表明,文章提出的方法能够有效提高时隙利用率,优于DTRA协议的时隙分配算法.

The basis function sequence is estimated by using the eigenvalue decomposition method for the Transform Domain Communication System(TDCS) signal under the asynchronous conditions. Because the feature vectors obtained by eigen decomposition covariance matrix are not unique, the segmented feature vectors have defects of scalar fuzzy. An improved algorithm is proposed by theoretical analysis of eigenvalue decomposition algorithm. The segmentation period of received signal is expanded to two times of the basis function cycle. The maximum eigenvector of covariance matrix is obtained by using eigenvalue decomposition algorithm. Sliding the window with a length as the basis function period in the maximum eigenvector,the basis function sequence can be estimated when the two-norm of the window reaches the maximum value. Through the experimental simulation, the improved algorithm can effectively overcome the defects of the partial positive and negative number of the segment vector. The bit error performance of the system is basically the same as that of the system under the condition of synchronization.

Based on spread spectrum technique, two wireless video transmission schemes are designed and implemented in this paper, namely direct sequence spread spectrum (DSSS) scheme and multi-code spread spectrum (MCSS) scheme. We use software defined radio (SDR) method for hardware implementation of two schemes, where a XILINX Virtex-4 field programmable gate array (FPGA) for the transmitter and another Virtex-5 FPGA for the receiver. In order to evaluate their performance, we compared the two designed schemes with our previous work on orthogonal frequency division multiplexing (OFDM) scheme. The experimental results show that two schemes of DSSS and MCSS have better anti-jamming performance than OFDM scheme at the cost of spectrum efficiency. Also, DSSS scheme possesses higher power efficiency than MCSS scheme and OFDM scheme due to its lower peak-to-average power ratio.

In order to solve the problem of local basis function sequence synchronization estimation blindly when spectrum environment of sending and receiving ends is inconsistent in transform domain communication system (TDCS). In this paper, an improved algorithm for blind synchronization of TDCS signals is proposed. Compared with the traditional F_ norm based blind synchronization method, the performance of the system is signiifcantly improved. The received TDCS signals were divided into continuous multiple observation vectors based on the cycle of basis local function, segmented vectors by cross-correlation method to estimate the sampling time delay. The received TDCS signals were divided into vectors according to the cycle of basis local function after the synchronization, and then the covariance matrix of the signal vectors was analyzed using the eigenvalue decomposition method to get the largest eigenvector which was the estimated basis function sequence. The simulation results show that estimated basis function correlation demodulation receiving signals to get the bit error rate is consistent with bit error rate of the sending and receiving ends basis function under the same condition.

The efficient allocation of multi-interface multi-channel Wireless Mesh Network channel resources is a hot topic recently. Effective channel management mechanisms need to be designed to ensure the full and efficient use of channel resources. In this paper, combined with the channel load that network buyers perceived, the channel reassignment problem of multi-interface multi-channel Wireless Mesh Network is modeled as a simple auction model, and the LBAM mechanism based on load balance is proposed and designed. LBAM not only meets the strategy-proofness, but also achieves high channel utilization and buyer satisfaction ratio showed by the simulation experiments. At the same time, due to the consideration of channel load condition in the design of LBAM, simulation experiments also analyzed that it has a significant effect on the improvement of network throughput when the network load is heavy.

The High Band Radio network has extensive value in the military application. A Dynamic Slot Allocation Algorithm (DSA) based on the High Band Radio network TDMA protocol is proposed in this paper, DSA algorithm allocates slots dynamically according to the difference of network traffics. The simulation results show that DSA algorithm can sustain TDMA protocol improving the network characters according to the difference of the network traffics.

Based on the sampling-concatenating operation with any integer interval, a large number of orthogonal subsets are designed for M-ary spread spectrum (MSS) communications with orthogonal frequency division multiplexing (OFDM) modulation. Any two sequences in the designed subset are orthogonal to each other, that is, the in-phase cross-correlation (IPCC) between them is equal to zero. Compared with the previous researches, the designed multiple subsets may possess more sequences at the cost of the peak-to-mean envelope power ratio (PMEPR) and inter-subset IPCC, which will be suitable for MSS-OFDM communications where the larger number of sequences means higher data rate. We provide a simple example to show how the designed algorithm works, and the corresponding performance of PMEPR and IPCC is analyzed.

In this letter, we present a generalized orthogonal Golay complementary sequence (OGCS) set that consists of multiple subsets, therein, each subset is a conventional OGCS set, and any two sequences from different subsets have three-valued low in-phase cross-correlation (IPCC). At the cost of slight reduction of IPCC performance, the number of sequences in our set is enormously enlarged. When our set is applied to high frequency M-ary spread spectrum communication link with orthogonal frequency division multiplexing modulation, the peak-to-mean envelope power ratio of the transmitted signal can be controlled not to exceed 3 dB, and the data rate can be higher than the one from the existing sequence sets. Finally, the simulation results show a desirable tradeoff between bit error rate and spectral efficiency.

For M-ary spread spectrum (MSS) communication systems with orthogonal frequency division multiplexing (OFDM) technique, a simple scheme to generate lots of MSS sequences is presented on the basis of circular shift and selection operation. The number of the generated sequences is far larger than sequence length at the cost of the decreased correlation property, which is significantly important to improve spectrum efficiency of MSS-OFDM systems since more sequences may support higher data rate. We provide the related simulations and analyses of the decreased correlation property. Also, the peak-to-average power ratio (PAPR) of the generated sequences is calculated and discussed due to OFDM modulation. The evaluation results show that the proposed scheme may obtain a good trade-off between spectrum efficiency and bit error rate performance.