基于正交信道的双M-ary扩频通信方案

针对传统系统中伪码资源缺乏以及同步实现较困难等方面的问题,提出一种新的双M-ary扩频通信系统方案,该系统采用两条正交支路传输信息,其中在同相支路上采用M-ary双正交扩频调制,在正交支路上采用CPSK扩频调制。该方案能够利用信息自身扩频调制准确实现同步,不需要额外提供同步资源。仿真结果表明,它与传统M-ary扩频方案性能相一致,但在传输比特信息时,它只需约四分之一的传统M-ary扩频的条数,有效地节省了扩频码资源。

一种基于非正交信道的分布式中继选择及功率分配方法

针对非正交两跳多中继协作通信系统中的分布式中继选择问题,提出了一种基于非正交信道的中继选择准则,简化了系统的设计。分析了其误码率性能,给出了其解析表达式和以总功率为约束条件下的最优功率分配方案。仿真结果表明,最佳中继选择准则明显优于传统的中继选择准则,且在最优功率分配方案下,可以获得明显的分集增益,系统的误码率显著下降。

一类高斯脏纸正交中继信道的容量

研究了一类依赖信道状态的高斯脏纸正交中继信道,其中,源节点到中继节点间的信道以及源节点和中继节点到目的节点间的信道相互正交,且分别受到服从高斯分布的加性干扰Sr和Sd的影响。假设Sr和Sd相互独立,且源节点和中继节点均非因果已知Sr和Sd,基于协作的脏纸编码(dirty-paper coding,DPC)和部分译码前传(partial-decode-and-forward,PDF)中继策略,得到了该信道容量的确切表达式。该信道容量的表达式与不受干扰的正交中继信道的容量表达式相同,此结果表明:即使目的节点未知加性干扰Sr和Sd,但通过协作的脏纸编码,可以完全消除加性干扰对信道容量的影响。

一类有信道状态的半确定性正交中继信道的容量

该文研究了一类有信道状态的正交中继信道的容量。在该信道中,源节点到中继节点间的信道与源节点和中继节点到目的节点间的信道是正交的,且这两个正交信道的传输受到同一信道状态的控制,而信道状态在源节点和中继节点处是非因果已知的。基于叠加码,协作的GP(Gel’fand-Pinsker)编码以及部分译码前传(PartialDecode-and-Forward,PDF)中继策略,该文首先得到了该信道的容量的下界。其次,针对半确定的正交中继信道,其目的节点的信道输出是中继节点信道输入、源节点信道输入以及信道状态的确定性函数,得到了该信道的容量的确切表达式。

一种改进的正交频分复用信道同步估计算法

针对当前正交频分复用系统的同步算法检测正确率低、计算复杂度高的难题,提出一种改进正交频分复用信道同步估计算法。首先对正交频分复用的工作原理进行分析,并构建加权的横幅零自相关特性序列,然后分别对OFDM系统定时和频偏同步进行估计,最后采用具体实例对算法的性能进行测试。测试结果表明,相对于当前经典同步算法,本文算法降低了定时同步估计误差,提高了检测正确率,提高了系统的通信性能。

基于Macro-Femto的正交信道配置异构网络覆盖性能与能效性能分析

针对由Macro和Femto组成的异构网络,推导出当采用正交信道配置时系统的覆盖性能和能效性能.根据信道配置方式,首先分别得到了Macro和Femto系统的中断概率精确表达式,然后根据系统覆盖性能,推导出采用正交信道配置时异构网络的能效表达式.仿真结果表明,采用正交信道配置时,单位带宽下的能效将随Femto占用带宽增加而增加.

稀疏水声OFDM系统迭代LS自适应信道估计

为了消除水声OFDM系统中噪声对稀疏多径信道估计的影响,提出了基于阈值探测的迭代最小二乘自适应信道估计方法。该方法根据最小方差准则引入加权因子对误差平方进行加权求和,由此导出一个迭代方程进行自适应信道估计。该迭代方程具有计算复杂度低的优点,不会带来大的矩阵运算。在该方法基础上,提出基于阈值探测的稀疏信道估计方法,探测最有效信道抽头,消除噪声干扰的影响。最后讨论了不同训练符号长度对MSE性能的影响,给出了在一定训练符号长度、阈值等参数条件下改进算法的性能仿真,并对仿真结果进行了分析。

一种基于DFT时域插值的OFDM水声信道估计改进方法

信道估计作为OFDM通信系统中的重要部分,其性能关系到整个系统的误比特率。本文提出了一种基于DFT时域插值的信道估计改进方法,用于OFDM水声通信系统。该方法利用噪声门限抑制多径之间的信道估计噪声,计算简单,达到较好的信道估计效果。对该方法进行了理论分析,仿真实验以及海试。在海试中得到传输距离2km,有效数据率2.8kbit/s,证明该方法可以用于中短程浅海水声通信。

一种正交码时分多子信道扩谱方案及其在卫星通信中的应用

文中从提高卫星通信的抗干扰能力出发,基于M-ary扩频、直接序列扩频、跳频及正交频分复用等技术思想,提出了一种正交码时分多子信道扩谱调制(OC-TDMSCSSM)新技术,建立了数学模型,推导了信号格式,给出了实验系统的输出信号频谱,分析了其在加性白高斯噪声信道下误码率性能。理论分析与仿真表明,该方案与DS/FH系统相比,具有良好的误码性能及较强的抗干扰能力。

基于流量延时调度机制的大数据传输控制算法研究

为解决无线传感网数据传输过程中存在的流量控制困难、拥塞发生次数高、网络传输带宽难以提升等不足,提出了一种基于流量延时调度机制的大数据传输控制算法.首先,考虑到无线传感网存在的信道正交现象,设计了时间片正交方式优化传输带宽,采用流量匹配方式构建了基于大数据稳定机制的流量匹配方法,针对信道碰撞现象进行优化,显著稳定了数据传输带宽.然后,基于分片缓存方案,通过延时阈值设计流量延时控制方法,节点当仅当传输过程中出现低于延时阈值的情况时,启动数据重传输,有效改善了节点在发生链路抖动时频繁重传数据的现象,优化了网络传输控制性能.仿真实验表明:与当前大数据流量控制领域里常用的基于线性超混沌评估机制的云网络大数据稳定评测算法、基于TDMA起伏追踪机制的LTE网络数据传输优化算法相比,本文算法网络传输带宽较高、拥塞控制能力较强的特点,具有较高的实际部署价值.

远距医护高速智能通信之建构(英文)

亚洲地区65岁以上高龄人口将于2020年突破总人口20%,健康老化问题日趋严重,老人紧急状况预警系统之建构势在必然,远距医护高速智能通信可供作通信平台。该平台包含低剖面、高速传输、传感网络及信号处理等理论,能通过高速芯片及智能型指挥控制等技术来完成。该文透过人体动态等现象,集结预警临界点设定,研究驱动无线收发机达到预警效果,并作实验型建构叙述。未来结合人体智能及有线网络将更能发挥远距医护功效。

Adaptive channel estimation based on pilot signals and transform-domain processing in SISO/MIMO OFDM systems

Based on the transform-domain characteristics of pilot signals,a band suppression filter is used as a transform-domain filter to restrain the interference of noise in channel estimation.The performance effect on channel estimation for an orthogonal frequency division multiplex （OFDM） system by different energy coefficients in the transform domain and the energy coefficient under the different signal-to-noise ratios （SNR） are also analyzed.A new energy coefficient expression is deduced.It is theoretically proven that dynamically selecting an energy coefficient can significantly improve the performance of channel estimation.Simulation results show that the proposed algorithm can achieve better performance close to the theoretic bounds of perfect channel estimation. The algorithm is adapted to single-input single-output （SISO） OFDM and multi-input multi-output （MIMO） OFDM systems.

Improved Kalman filter channel estimation method for OFDM systems in fast time-varying environment

Under analyzing several characteristics of frequency-selective fast fading channels, such as large Doppler spread and multi-path interference, a low-dimensional Kalman filter method based on pilot signals is presented for the channel estimation of orthogonal frequency division multiplexing （OFDM） systems. For simplicity, a one-dimensional autoregressive （AR） process is used to model the time-varying channel, and the least square （LS） algorithm based on pilot signals is adopted to track the time-varying channel fading factor a. The low-dimensional Kalman filter estimator greatly reduces the complexity of the high-dimensional Kalman filter. To utilize the relationship of fading channel in frequency domain, a minimum mean-square-error （MMSE） combiner is used to refine the estimation results. The simulation results in the frequency band of 5.5 GHz show that the proposed method achieves a good symbol error rate （SER） performance close to the theoretical bound of ideal channel estimation.

Digital broadcast channel estimation with compressive sensing

In order to reduce the pilot number and improve spectral efficiency, recently emerged compressive sensing （CS） is applied to the digital broadcast channel estimation. According to the six channel profiles of the European Telecommunication Standards Institute（ETSI） digital radio mondiale （DRM） standard, the subspace pursuit （SP） algorithm is employed for delay spread and attenuation estimation of each path in the case where the channel profile is identified and the multipath number is known. The stop condition for SP is that the sparsity of the estimation equals the multipath number. For the case where the multipath number is unknown, the orthogonal matching pursuit （OMP） algorithm is employed for channel estimation, while the stop condition is that the estimation achieves the noise variance. Simulation results show that with the same number of pilots, CS algorithms outperform the traditional cubic-spline-interpolation-based least squares （LS） channel estimation. SP is also demonstrated to be better than OMP when the multipath number is known as a priori.

New subspace algorithm for blind channel estimation in OFDM systems

In order to increase the transmission efficiency,a subspace-based algorithm for blind channel estimation using second-order statistics is proposed in orthogonal frequency division multiplexing (OFDM) systems.Because the transmission equation of OFDM systems does not exactly have the desired structure to directly derive a subspace algorithm,the algorithm first divides the OFDM signals into three parts,then,by exploiting the redundancy introduced by the cyclic prefix (CP) in OFDM signals,a new equation with Toeplitz channel matrix is derived.Based on the equation,a new blind subspace algorithm is developed.Toeplitz structure eases the derivation of the subspace algorithm and practical computation.Moreover the algorithm does not change the existing OFDM system,is robust to channel order overdetermination,and the channel zero locations.The performances are demonstrated by simulation results.

A simple channel estimator for space-time coded OFDM systems in rapid fading channels

A simple channel estimator for space-time coded orthogonal frequency division multiplexing (OFDM) systems in rapid fading channels is proposed. The channels at the training bauds are estimated using the EM (expectation-maximization) algorithm, while the channels at the data bauds are estimated based on the method for modelling the time-varying channel as the linear combination of several time-invariant " Doppler channels". Computer simulations showed that this estimator outperforms the decision-directed tracking in rapid fading channels and that the performance of this method can be improved by iteration.

Frequency Diversity for OFDM Mobile Communication via Underwater Acoustic Channels

The major constraint on the performance of orthogonal frequency division multiplexing （OFDM） based underwater acoustic （UWA） communication is to keep subcarriers orthogonal. In this paper, Doppler estimation and the respective compensation technique along with various diversity techniques were deliberated for OFDM-based systems best suited for underwater wireless information exchange. In practice, for mobile communication, adjustment and tuning of transducers in order to get spatial diversity is extremely difficult. Considering the relatively low coherence bandwidth in UWA, the frequency diversity design with the Doppler compensation function was elaborated here. The outfield experiments of mobile underwater acoustic communication （UWAC） based on OFDM were carried out with 0.17 bit/（s-Hz） spectral efficiency. The validity and the dependability of the scheme were also analyzed.

A modified time domain interpolation method for LS channel estimation in OFDM systems

A modified time domain interpolation method is proposed for orthogonal frequency division multiplexing(OFDM)systems to address the problem that time domain interpolation in the least square(LS)channel estimation method based on comb-type pilots cannot choose the pilot spacing flexibly.Firstly,the estimated channel frequency response(CFR)at pilot positions in the frequency domain is obtained by LS channel estimation based on comb-type pilots,and the estimated channel impulse response(CIR)in the time domain is obtained by linear interpolation and inverse fast Fourier transform(IFFT).Secondly,the error of the estimated CIR obtained by linear interpolation is analyzed by theoretical deduction,and a method for correcting it is proposed.Finally,an estimated CFR at all subcarrier positions in the frequency domain is obtained by performing zero padding in the time domain and fast Fourier transform(FFT)on the modified CIR.The simulation results suggest that the proposed method gives similar performance to time domain interpolation,yet it does not need to meet the condition of time domain interpolation that the number of subcarriers must be an integral multiple of pilot spacing to use it.The proposed method allows for flexible pilot spacing,reducing the number of pilots and the consumption of subcarriers used for channel estimation.

Joint Energy-Efficient Power Allocation and Beamforming Design for mm Wave-NOMA System with Imperfect CSI

The joint power allocation(PA)and beamforming(BF)design problem is studied to maximize the energy efficiency of a two-user downlink millimeter-wave system with non-orthogonal multiple access under imperfect channel state information(CSI).By means of block coordinate descent,convex-concave procedure,and successive convex approximate,we propose a suboptimal joint PA and BF design scheme to address this non-convex problem.Simulation results verify that the proposed joint PA and BF design scheme is more effective when compared to some existing schemes.

基于BATMAN-adv的多跳无线网络

无线自组网具有去中心化、多信道、多跳等特点,适用于专网和临时应急网络的快速搭建。为了使网络具有更宽的覆盖、更强的绕射能力和更高的吞吐量,系统选择一种支持IEEE802.11 ac的三射频接口物理层节点,在此基础上,结合BATMAN-adv路由协议进行研究,实现了一种基于多接口多信道的自组网系统。仿真实验数据表明,该系统在5G频谱中能够全双工使用正交信道降低干扰,将网络链路拓展至5跳以上,网络损耗衰减低于30%,网络吞吐量高于300 Mbps。