Size optimization of a quad-cell alignment detector for short range free space optical interconnects

In this paper we consider geometry optimization of a quad-cell alignment detector for short range free space optical interconnects. The alignment technique uses alignment beams and quad detectors to detect different misalignment errors. We show that the size of the quad detector cells can be used as a design parameter to optimize the sensitivity of the alignment system. The sensitivity analysis and error signal generation are presented assuming standard Gaussian beam models. Results on optimum sensitivity for the case of transverse and angular misalignments are presented and discussed.     

Bidirectional colorless wired and wireless WDM-PON with improved dispersion tolerance for radio over fiber

We propose and demonstrate a bidirectional transmission, hybrid wired and wireless access network based on subcarrier modulation (SCM) techniques. The scheme simultaneously enables the dispersion-tolerant transmission of millimeter (mm)-wave signals for use in wireless access networks, downstream baseband signals for optical wired access networks, and optical continuous-wave (CW) carriers for use in upstream data remodulations. Error-free transmissions through a 25-km length of single mode fiber (SMF) for both the downstream baseband and the remodulated upstream signals are confirmed by bit-error-rate (BER) measurements. The dispersion tolerance of the radio-over-fiber (RoF) signal is assessed using numerical simulations.     

Characterization of Rayleigh backscattering performance of CS-SSB signal in carrier distributed passive optical network

Rayleigh backscattering (RB) is an intrinsic phenomenon when light propagating in fiber and its level is fixed by the fiber type and the network configuration used. Thus, RB noise would be one of the major impairments in a carrier distributed passive optical network (PON). Previously demonstrated carrier suppressed subcarrier-amplitude modulated phase shift keying (CSS-AMPSK) modulation may be useful to effectively mitigate the RB noise. However, this modulation is basically a carrier suppressed double sidebands modulation (CS-DSB) format, in which the same information is carried by the two sidebands with equal magnitude. This is not very power-efficient for PON. Here, we further extend our RB studies by using carrier suppressed single sideband non-return-to-zero (CS-SSB-NRZ) modulation. We experimentally characterize the CS-SSB-NRZ modulation when subjected to both contributions of RB: Carrier-RB and Signal-RB. Then, numerical simulations are performed, and the results are in good match with the experiment. Finally, upstream transmission experiment is performed showing the feasibility of using the CS-SSB-NRZ signal for the carrier distributed PON. The RB performance of the SSB-NRZ signals transmitted at different distances and driven at different radio-frequency (RF) f_s is also investigated.     

10 GHz passive harmonic mode-locking in Er-Yb double-clad fiber laser

In this paper we report passive harmonic mode-locking of an Erbium/Ytterbium-doped double-clad fiber laser with repetition rates up to 10 GHz. The modes synchronization was obtained using Nonlinear Polarization Rotation mechanism. The stable operation at 634th harmonic of the fundamental (15.8 MHz) repetition frequency was achieved. Soliton pulses with the duration of less than 900 fs and 300 mW average output power were obtained.     

一种用于金属表面的RFID天线设计

提出了一种用于金属物体表面的RFID天线。该天线包含一个耦合地板和翼型辐射贴片。天线尺寸为84 mm×25 mm×4.5 mm,当圆极化阅读器天线增益为7.5 dBi,辐射功率为30 dBm时,在902~928 MHz范围内阅读距离可达10 m。标签天线在金属物体表面的实测结果显示,该标签具有较好的远距离识别性能。     

载波频偏对正交频分复用波形外辐射源雷达性能影响的研究

利用正交频分复用(OFDM)波形外辐射源雷达进行目标跟踪和定位是国内外研究的热点之一。该文首先介绍了OFDM波形外辐射源雷达信号模型及其信号处理的关键技术。在此基础上重点从不同角度仿真研究了载波频偏估计误差对OFDM波形外辐射源雷达探测性能的影响,包括其对匹配滤波后目标参数估计精度的影响,对时域杂波抑制性能影响的定量分析,以及对参考信号重构误码率等方面的影响。仿真结果表明,不同时域杂波抑制算法对载波频偏估计误差要求不同;参考信号重构误码率对时域杂波抑制性能影响较大,对匹配滤波的影响较小。最后基于实测数据验证了分析结果的正确性。     

混合复用无源光网络中带有灰色预测的高效动态资源分配策略

针对混合复用无源光网络的用户接入距离增大,使得往返时延增加,造成网络中闲置时间增多,进而引起带宽浪费的问题,该文提出一种带有灰色预测的高效动态混合资源分配策略。通过对闲置时间内到达的数据进行灰色预测,动态确立光网络单元的带宽分配策略,以减小网络时延;利用波长结束时间的差异性,周期性地实时调整各波长的数据传输顺序,实现波长的高效利用和负载均衡。仿真结果表明,该动态资源分配策略有效地消除闲置时间的影响,且波长得到高效地利用,提高了带宽利用率的同时减少网络时延。     

基于最小二乘的短垂线阵匹配场处理

匹配场处理通常要求接收基阵能够覆盖整个水层,如此大尺度的布阵方式严重阻碍了该方法的广泛使用。为了缓解匹配场处理对阵形的苛刻要求,该文提出一种基于最小二乘的短垂线阵匹配场处理技术。该方法把接收阵的声场分解为模态函数矩阵和模态系数向量,并在最小范数意义下用最小二乘算法得到了各阶模态系数的估计值,在此基础上重新构造了短垂线阵的测量场向量,使得重构后的测量场包含更多的环境信息,从而提高了短垂线阵匹配场处理的性能。最后,在典型的Pekeris波导环境中进行仿真,以3种布放在水面附近的短垂线阵为例,分析了匹配场被动定位的性能,并用广义余弦量化分析了不同布阵方式对测量场的影响。结果表明：使用最小二乘算法对短阵的测量场进行声场重构后广义余弦变大,此时短垂线阵匹配场处理的定位性能得到改善,验证了该算法的有效性。     

基于压缩感知的外辐射源雷达分数阶杂波估计

参考信号信杂比(SCR)是评估外辐射源雷达积累增益损失的重要参数。利用数字电视地面广播(DTTB)辐射源中的PN序列进行信杂比估计时,将出现接收信号相对于本地帧头的分数阶时延问题,导致信杂比估计出现严重偏差。针对该问题,该文利用信号在时延维的稀疏性,提出基于压缩感知的信杂比估计算法。仿真结果表明,该算法对不同强弱的信号都能得到精确的时延和强度估计,从而保证了信杂比估计的准确性。实测数据处理结果表明,实测数据的参考信号信杂比较高,积累损失较小,约为0.5 dB;信杂比与基线距离有关,基线越长信杂比越低,积累损失越大。     

基于DOA和TDOI的主瓣扫描辐射源定位方法

针对具有已知扫描周期特性的辐射源无源定位问题,该文提出一种基于主瓣到达角(DOA)和扫描截获时间差(TDOI)的联合定位体制。通过对其定位误差的克拉美-罗下限(CRLB)推导,给出了联合定位体制的性能与DOA和信号截获时间(TOI)观测量的等效测角噪声功率比的关系。为了利用非线性联合观测量确定扫描辐射源的位置,通过将TDOI观测量转换成等效DOA观测量,给出一种加权伪线性最小二乘(WPLS)定位方法;为消除观测矩阵相关噪声导致的WPLS估计偏差,提出了一种加权辅助变量(WIV)定位方法,算法复杂度约为WPLS算法的2倍。仿真结果表明,WIV方法的定位误差在辐射源单个扫描周期内即可达到CRLB,定位性能与极大似然(ML)定位方法相当;随着观测次数的增多,WIV方法可以渐近达到无偏估计。