We investigate the electron transport in silicene with both staggered electric potential and magnetization; the latter comes from the magnetic proximity effect by depositing silicene on a magnetic insulator. It is shown that the silicene could be a spin and valley half metal under appropriate parameters when the spin–orbit interaction is considered; further, the filtered spin and valley could be controlled by modulating the staggered potential or magnetization. It is also found that in the spin-valve structure of silicene, not only can the antiparallel magnetization configuration significantly reduce the valve-structure conductance, but the reversing staggered electric potential can cause a high-performance magnetoresistance due to the spin and valley blocking effects. Our findings show that the silicene might be an ideal basis for the spin and valley filter analyzer devices.
针对水声正交频分多址(OFDMA)上行通信中用户导频数量少、分布不均匀,导致传统内插信道估计方法产生误码平层的问题,提出一种稀疏信道估计与导频优化方法.基于压缩感知(CS)理论估计稀疏信道冲激响应,并依据CS理论中测量矩阵互相关最小化原理,提出基于随机搜索的导频图案和导频功率联合优化算法.仿真结果表明,所提方法在不同多径扩展信道下的性能均优于基于线性内插的最小二乘估计、未经导频优化的CS信道估计以及单纯基于导频图案优化的CS信道估计.水池实验分别验证了交织式和广义式子载波分配的水声OFDMA上行通信性能,在接收信噪比高于10 d B时利用所提方法实现了两用户接入的可靠通信.
针对正交频分复用技术(Orthogonal Frequency Division Multiplexing,OFDM)在水声移动通信条件下存在对多普勒频偏敏感的缺陷,提出了一种基于频域变采样技术的多普勒补偿算法。利用移动通信条件下OFDM子载波正交性不变的特点,通过频域变采样实现对多普勒的快速补偿,并采用编码反馈校验技术跟踪系统多普勒变化,达到了OFDM移动通信条件下实时通信的目的。仿真和水池实验结果证实:频域变采样多普勒补偿算法不仅可以实时地跟踪通信载体运动变化,快速补偿多普勒,同时大幅降低了时域变采样多普勒补偿算法的计算量,降低了通信系统硬件平台复杂度。
