基于MODIS红外通道的辐射传输计算

通过建立地气系统的红外辐射传输方程,基于MODIS红外通道进行辐射传输计算.利用快速精确的透过率模型PFAAST计算大气透过率,在红外辐射传输计算中考虑了地面反射大气辐射亮度的影响,指出地面反射大气辐射亮度在整个方程所占比重随着地表发射率变小而增加,其中MODIS第33通道对发射率的改变最为敏感,美国标准大气下,当发射率ε=0.65时,比重达到7.12%,因此,忽略地面反射大气辐射亮度,直接影响红外辐射传输计算的准确性.模拟了MODIS各红外通道辐射亮度,并与MODTRAN4.0模拟结果比较,相对误差不超过0.12%,模拟了大气倾斜路径对卫星红外通道观测亮温的影响.     

Outage probability of the free-space optical channel with doubly stochastic scintillation

We study the asymptotic outage probability of multiple-input multiple-output free-space optical communication with pulse-position modulation. In particular, we consider doubly stochastic scintillation models, lognormal-Rice and I-K distributions. First we consider the case when channel state information is available at the receiver only. Then we consider the case when it is also available at the transmitter.     

相干光通信中相位估计与信道均衡的联合使用

在使用高阶相位调制的100Gbit/s及以上速率的相干光通信系统中,激光器的相位噪声和光纤传输中的色散效应是影响系统性能的主要因素。为了补偿色散及相位噪声的影响,文章提出一种将电信道均衡与相位估计模块在电域联合使用的方法,相位估计在电信道均衡之后完成,其结果同时用于电信道均衡器的抽头系数更新。该方法可以有效降低对电信道均衡中迭代步长的要求,有助于系统获得更低的误码率和更稳定的误码性能,并且能够支持的传输距离也会增加。     

Outage analysis of the hybrid free-space optical and radio-frequency channel

We study the hybrid free-space optical (FSO) and radio-frequency (RF) channel from an information theoretic perspective. Since both links operate at vastly different carrier frequencies, we model the hybrid channel as a pair of parallel channels. Moreover, since the FSO channel signals at a higher rate than the RF channel, we incorporate this key feature in the parallel channel model. Both channels experience fading due to scintillation, which is slow compared to typical signalling rates. Under this framework, we study the fundamental limits of the hybrid channel. In particular, we analyse the outage probability in the large signal-to-noise ratio (SNR) regime, and obtain the outage diversity or SNR exponent of the hybrid system. First we consider the case when only the receiver has perfect channel state information (CSIR case), and obtain the exponents for general scintillation distributions. These exponents relate key system design parameters to the asymptotic outage performance and illustrate the benefits of using hybrid systems with respect to independent FSO or RF links. We next consider the case when perfect CSI is known at both the receiver and transmitter, and derive the optimal power allocation strategy that minimises the outage probability subject to peak and average power constraints. The optimal solution involves non-convex optimisation, which is intractable in practical systems. We therefore propose a suboptimal algorithm that achieves significant power savings (on the order of tens of dBs) over uniform power allocation. We show that the suboptimal algorithm has the same diversity as the optimal power allocation strategy.     

基于色散的ATM自由空间光交换结构

根据波导型光交换的一些弱点，提出了一类克服以上缺点的基于色散异步转移模式（ＡＴＭ）的自由空间光交换结构，并对该结构进行了一些讨论。     

Influence of channel estimation on the performance of a coherentDS-CDMA system

Direct-sequence code division multiple access (DS-CDMA) has become one of the favourite candidates for future mobile radio communication systems. The uplink of a coherent DS-CDMA system is investigated. The channel estimation is carried out via a control channel, which is transmitted simultaneously to the data channel. This concept is very closely related to the CODIT-CDMA concept. In the channel estimation, an averaging process is involved, which for long averaging periods, suppresses the noise influence efficiently. On the other hand, long averaging intervals lead to systematic errors in the estimated channel coefficients due to the time-variant behavior of the channel. Taking into account these effects, a closed-form analysis of the data-channel symbol-error rate (SER) is presented. This analysis allows the prediction of the system's performance and helps to optimize the parameter settings for channel estimation     

基于级联ISFA信道估计的光OFDM系统研究

采用训练序列与级联符号内频域平均(intra-symbol frequency-domain averaging,ISFA)的信道估计方法提高了直接检测光正交频分复用(OFDM)接收机中信道估计的准确性。通过Matlab编程建立了强度调制直接检测系统仿真平台,对不同调制格式的OFDM信号进行了数值仿真分析。结果表明,级联ISFA方法可以提供更为准确的信道估计,有效改善高阶QAM调制的OFDM信号误码性能,提高接收机的灵敏度。     

OFDM系统中信道估计方法的研究

LS算法是OFDM系统信道估计方法中计算复杂度最低性能最差的方法.根据有限长度h的能量分布,提出了一种改进算法.通过仿真,与LS算法和性能较好的LMMSE比较,验证了改进后的LS算法性能优于最初的LS算法,并可在实际中得到较好的应用.     

Improved bit-error-rate performance in frequency conversion of high-bit-rate data based on cross gain compression in semiconductor optical amplifiers

We describe a detailed calculation of the bit-error-rate performance of an optical frequency converter based on cross gain saturation in a semiconductor optical amplifier. Performance limits related to the slow-gain dynamics of the amplifier, as well as to noise, are presented and a modification to the detection system based on an adaptive decision threshold level that corrects for the performance deterioration due to dynamical effects is proposed.     

Maximal-ratio combining architectures and performance with channel estimation based on a training sequence

Maximum-ratio combining (MRC) is a simple and effective combining scheme for adaptive antenna arrays to combat noise, fading, and to a certain degree, cochannel interference. However, it requires estimation of the spatial signature (i.e., the channel gain and phase at each antenna element) of the desired signal across the array. Assuming that this estimate is obtained by correlation using a known training sequence of K symbols embedded in the useful signal, we proceed to develop a fully analytical assessment of the impact of estimation error on the output signal-to-noise ratio (SNR) of the array. The originality of the approach revolves around the derivation of the distribution of the normalized SNR, that is the real SNR normalized to the ideal (i.e., perfect estimation) SNR. The end result is a set of distributions which can potentially reduce or in certain cases eliminate the need for simulation to determine certain design parameters such as array size, training sequence length, etc. These are then applied to find closed-form expressions for the outage probability and the error probability in differential phase-shift keying and quarternary phase-shift keying after training in uncorrelated Rayleigh fading.     

双向中继系统中基于压缩感知信道估计算法

针对提高系统传输的频谱利用率问题,采用将压缩感知理论应用于双向中继系统进行信道估计。详细研究在双向中继系统中信道估计算法的设计方法、实现过程,并对广义正交匹配追踪算法(GOMP)与OMP算法及传统的LS信道估计算法进行分析与比较。结果表明GOMP信道估计算法在均方误差(MSE)和误比特率(BER)及需要运行的时间上均较小。在稀疏的信道中,GOMP算法相比于传统LS信道估计算法能有效地提高频谱利用率,相比于OMP算法提高了实时性,降低系统的复杂度。     

基于导频的OFDM系统信道估计方法研究

正交频分复用(OFDM)技术采用多载波传输方式,成为了第四代移动通信核心技术。OFDM系统可采用基于导频的信道估计方法,提高信道传输的准确性。文章在matlab环境下对块状导频进行仿真,对最小乘二算法和最小均方误差估计算法进行了比较,经过实验得出,块状导频更适合于慢衰落信道。     

Multilevel coding in free-space optical MIMO transmission with Q-ary PPM over the atmospheric turbulence channel

We propose an efficient coded modulation scheme for multiple input/multiple output free-space optical systems with Q-ary pulse-position modulation. It is based on multilevel coding and low-density parity-check codes as component codes. The proposed scheme provides excellent coding gain in the regime of strong atmospheric turbulence.     

基于FPGA的OFDM系统信道估计算法的设计

研究了OFDM系统信道估计算法的FPGA实现.首先探讨OFDM系统及其信道估计算法,然后采用VHDL硬件描述语言对OFDM系统中的发送端和接收端的各个模块进行实现,在接收端利用基于导频的信道估计算法得出发送端的数据,并且在Quartus II软件开发环境下对VHDL代码进行波形仿真与综合验证,最后选用以ALTERA公司生产的Cyclone II系列的EP2C35F672C6为核心的硬件平台上进行硬件设计.     

嵌入式模块接口性能测试系统的网络通信技术

为适应工程中各类嵌入式模块接口性能测试的网络化趋势,设计了稳定可靠的通信机制,实现客户机/服务器模式的测试系统.基于解决网络通信问题的套接字网络编程,利用MFC平台下的CAsyncSocket类特性,结合Windows平台的消息响应机制,设计了测试网络专用通信协议,分析了控制台和测试台的设计.嵌入式模块性能测试系统的运行结果表明,测试数据信息无差错传输,并且具有较好的可移植性及异常处理能力,满足自动化测试系统网络化的需求.     

基于相干光OFDM的WDM系统传输性能分析

首先对相干光OFDM WDM系统理论模型和基本原理进行了研究,然后基于Optisystem仿真软件,对相干光OFDM WDM传输系统进行了仿真分析,并研究了该系统的传输性能,发现基于相干检测的光OFDM技术和WDM技术结合,可以有效抑制光纤色散和非线性影响,提高系统的性能.将此系统与传统的NRZ WDM光传输系统进行比较,发现系统性能较NRZ系统有很大的提高.     

基于载波抑制双边带的光纤微波频率传递系统优化

针对采用分立器件实现载波抑制双边带(DSBCS)调制的被动补偿光纤环路微波频率传递方案的缺陷,对基于DSBCS调制的光纤环路微波频率传递系统进行稳定性优化设计和测试验证,设计了基于微波芯片的一体化接入节点电路,以腔体分隔的金属和高精度的温度控制模块屏蔽串扰、减小外界温度影响,实验测试了系统电路底噪、60 km光纤环路系...     

阵列天线时TD-SCDMA系统信道估计性能的新型改进

对阵列天线情况下广义Steiner估计器(GSE)得到的信道响应进行改进，充分利用信号的空间信息，提出了一种基于简化DOA估计方法的方向向量组合降噪方法，并将其与文献[I]和文献[2]中的改进方法进行性能比较。对于给定的车载环境，仿真实验表明，本文的新型改进方法与文献[2]中的改进方法获得几乎相同的性能，都明显好于文献[I]中的改进方法。然而，与文献[2]中方法相比，本文提出的方法具有更低的计算量。     

基于光外差理论的毫米波RoF系统研究

从理论上介绍了利用光外差法产生毫米波RoF系统的原理,并分析了制约其性能的因素.基于光外差理论,对传统的光外差系统结构进行了改进.实验证明,与传统的光外差系统相比,改进的光外差系统受相对强度噪声的影响更小,在相同的接收光功率的情况下,误码率平均降低了3～4dB;同时,在一定范围内,改进的光外差系统性能几乎不受激光器线宽...