Optical QPSK/16QAM modulation based on serial-parallel MZM scheme in radio-over-fiber system

A novel scheme of optical modulation in 40 GHz radio-over fiber (RoF) system is proposed. It generates optical QPSK/16QAM signals in a serial-parallel structure of Mach-Zehnder modulators (MZMs). The millimeter-wave is obtained with optical frequency multiplication (OFM). Furthermore, modulation on optical-wave is transferred onto millimeter-wave. It can be used to increase transmission capacity of millimeter-wave RoF systems.     

Optimum weighting-coefficient-pair in inter-carrier interference self-cancellation scheme of OFDM system

As one of the most important components of the wideband wireless access technique, orthogonal frequency division multiplexing （OFDM） has a high usage rate of spectrum and combats inter-symbol interference （ISI） in multi-path fading channel. However, when there are frequency offsets during the signal transmission, the inter-carrier interference （ICI） is introduced, which significantly degrades the performance. The existing ICI self-cancellation schemes such as PCC-OFDM are not optimum to minimize the interference considering both noise and ICI. In this paper, a new metric named S1NR （signal-to-interference- and-noise ratio） is proposed. We discuss the optimization issue when a constant frequency offset exists and in time-varying channels. The optimum weighting-coefficient-pair （OWCP） is obtained, which maximizes SINR theoretically through the alternant iteration algorithm. Simulations show that the performance of OWCP-OFDM is better than that of PCC-OFDM, especially when the frequency offset is large. Although the ICI self-cancellation scheme suffers bandwidth inefficiency, from the simulation results we can also see that the performance of OWCP-OFDM is much better than that of the standard OFDM systems with the same bandwidth efficiency when a frequency offset exists. Moreover, since the redundant modulation provides the capability to suppress ICI as well as a receiving SNR gain, it can be considered as exchanging the bandwidth for SNR.     

使用混沌调制方法实现交流电机电磁干扰抑制

Instead of avoiding occurrence of chaos in motor drives,chaos is positively utilized in this paper.A new chaotic pulse width modulation (PWM) scheme is proposed and implemented for AC motors,which functions to significantly suppress harmonic peaks and hence acoustic noise.The key is to employ the Chua's circuit for generating a desired chaotic sequence.By using a practical induction motor,computer simulation and experimental results verify that the chaotic PWM has advantages of harmonic peak suppression and simple hardware implementation over the conventional PWM and random PWM.     

不同混沌源调制信号降低Boost型变换器电磁干扰水平研究

以Boost型DC／DC变换器为对象，研究在同一混沌调制模式下，不同混沌源对降低开关电源电磁干扰水平效果的影响。仿真结果表明：不同混沌源调制信号有不同的降低电磁干扰水平效果，Lorenz混沌源降低电磁干扰水平的效果较好。     

基于复小波包的多载波CDMA系统在Nakagami-m衰落信道下的性能

在分析多载波码分多址(MC-CDMA)的原理基础上, 提出了一种基于复小波包的MC-CDMA系统. 同时, 研究了该系统分别采用等增益合并和最大比合并时在Nakagami-m衰落信道下的性能; 并推导了相应的误码率表达式. 该系统能克服通常MC-CDMA系统由于插入循环前缀(CP)所带来的频谱效率的下降. 理论分析和仿真结果表明:该系统要优于通常MC-CDMA系统和基于实小波包的MC-CDMA系统, 有着优越的抗多径衰落和多址干扰能力,而且该系统也优于采用CP的通常MC-CDMA系统.