Quantum analysis on the four-photon interference

We present a theory for quantum interference of four photons generated by spontaneous parametric downconversion. Detailed investigation of the dependence of fourfold coincidence count rate on time delay between the incident and the reflective pump laser pulses is carried out. Gaussian type dependence is found, and good agreement between our theoretical results and experimental data reported in the literature is achieved.     

Laser frequency stabilization based on Sagnac interferometric spectroscopy

A simple method based on Sagnac interferometric spectroscopy (SIS) is applied for frequency stabilization of diode lasers. Sagnac interferometric spectra of rubidium vapor are investigated both theoretically and experimentally. The interference signal at the output of the Sagnac interferometer displays a sharp dispersion feature near the atomic resonance. This dispersion curve is used as the feedback error signal to stabilize the laser frequency. Linewidth of a diode laser is stabilized down to 1 MHz by this modulation-free method.     

A New Class of Efficient Block-Iterative Interference Cancellation Techniques for Digital Communication Receivers

A new and efficient class of nonlinear receivers is introduced for digital communication systems. These iterated-decision receivers use optimized multipass algorithms to successively cancel interference from a block of received data and generate symbol decisions whose reliability increases monotonically with each iteration. Two variants of such receivers are discussed: the iterated-decision equalizer and the iterated-decision multiuser detector. Iterated-decision equalizers, designed to equalize intersymbol interference (ISI) channels, asymptotically achieve the performance of maximum-likelihood sequence detection (MLSD), but only have a computational complexity on the order of a linear equalizer (LE). Even more importantly, unlike the decision-feedback equalizer (DFE), iterated-decision equalizers can be readily used in conjunction with error-control coding. Similarly, iterated-decision multiuser detectors, designed to cancel multiple-access interference (MAI) in typical wireless environments, approach the performance of the optimum multiuser detector in uncoded systems with a computational complexity comparable to a decorrelating detector or a linear minimum mean-square error (MMSE) multiuser detector.     

一种空时盲自适应RAKE接收机

多址干扰是直扩码分多址系统中的一个主要问题.多用户检测技术和阵列天线已成为解决这一问题的两种主要方法,将这两种方法结合起来的空时处理能大大提高系统的容量和性能.本文提出了一种空时盲自适应RAKE接收机.研究结果表明,该接收机具有较强的抑制多址干扰和克服"远-近"效应的能力,且能快速收敛.     

测控系统中的软件抗干扰技术

测控系统在使用中存在着大量的干扰源,严重影响了系统运行的可靠性。通常使用硬件抗干扰措施与软件抗干扰措施来抑制系统中出现的各种干扰。软件抗干扰措施是硬件抗干扰措施的一个补充和延伸,具有简单、灵活、方便、耗费硬件资源少及容易实现等特点。软件抗干扰技术的使用会显著提高系统的可靠性。本文着重讨论了测控系统中的软件抗干扰技术。     

一种针对双衰落信道OFDM的新均衡算法

在OFDM系统中，子载波间的正交性是保证OFDM性能的重要保障。针对双选择性衰落信道下的OFDM系统，该文在分析载波间干扰（ICI）的基础上，提出了一种采用频域迭代消除ICI的均衡算法。分析和仿真结果表明此方法能有效地保证载波间的正交性和改善了OFDM系统的误码率（BER）性能。     

数字调制系统码间干扰分析

通信系统中引起误码的主要因素是噪声和码间干扰。主要针对频带传输系统包括多进制调制系统如何能消除码间干扰问题进行了分析，提出了无码间干扰传输系统的传输函数应满足的条件、最高码元传输速率与系统带宽之间的关系以及不同调制系统的频带利用率。     

旋转矩阵法抗多用户间干扰

研究了一种新的MIMO系统下多用户间干扰抑制技术(旋转矩阵法),此方法增加了码字间的欧氏距离,降低成对差错率,与传统方法(TDMA/CDMA)系统相比:保证了频带利用率;并对接收机进行设计,为降低算法复杂度采用了MMSEML分组接收机。仿真证明,在没有编码、不用正交信号、在高信噪比下,系统可明显降低用户间干扰,而MMSEML接收机降低算法复杂度的同时在信噪比22dB时,误码率可达到3·3E3。     

卫星导航接收机抗干扰性能评估方法研究

卫星导航接收机的抗干扰是导航战研究的一项重要内容。合理的抗干扰性能评估方法是对接收机的抗干扰性能进行正确评估的基础,目前卫星导航接收机还没有建立统一的抗干扰性能评价方法。在吸取GPS系统抗干扰性能评估方法的合理性的基础上,提出一种在接收机输入端对抗干扰性能进行评估的方法,与传统的抗干扰性能评估方法相比,该方法更具有工程实际意义。     

一种消除TD-SCDMA系统小区间干扰的方法

时分-同步码分多址(TD-SCDMA)系统采用的扩频码码长最大为16,当邻小区用户处于2小区边缘时会对本小区造成较大的干扰。针对上行链路提出了一种新的干扰消除方法:串行干扰消除-联合检测(SIC-JD)。该方法采用复杂低的SIC对上行链路中的小区间干扰进行消除,对于小区内干扰和残留的小区间干扰采用联合检测进行消除。3GPP case1信道下的仿真结果显示了此方法能够有效消除小区间和小区内干扰,提高接收机性能。