神经网络在移动信道卷积码译码中的应用

分析运用误差反向传播 (EBP)多层感知器神经网络 (NN)方法来进行卷积码译码的可能性 .仿真结果表明 :当涉及的码字位于译码窗口中间时 ,其性能最佳 ,而且即使考虑大的窗口性能也不会提高 .当神经网络规模较大时 ,神经网络体现出自适应、冗余容错性 .窗口宽度等于 3的系统最小 。

多径信号的Rake接收技术

对多路径传播条件下 QPSK扩频多径信号的统计特性进行了分析 ,给出了多径接收信号的包络和相位的概率分布特性 ;并在相干和非相干接收情况下 ,分析了多径信号的识别和获取方法 ;在此基础上 ,深入研究了导频辅助的相干 Rake接收和 M元正交调制的非相干 Rake接收技术。

A modified time domain interpolation method for LS channel estimation in OFDM systems

A modified time domain interpolation method is proposed for orthogonal frequency division multiplexing(OFDM)systems to address the problem that time domain interpolation in the least square(LS)channel estimation method based on comb-type pilots cannot choose the pilot spacing flexibly.Firstly,the estimated channel frequency response(CFR)at pilot positions in the frequency domain is obtained by LS channel estimation based on comb-type pilots,and the estimated channel impulse response(CIR)in the time domain is obtained by linear interpolation and inverse fast Fourier transform(IFFT).Secondly,the error of the estimated CIR obtained by linear interpolation is analyzed by theoretical deduction,and a method for correcting it is proposed.Finally,an estimated CFR at all subcarrier positions in the frequency domain is obtained by performing zero padding in the time domain and fast Fourier transform(FFT)on the modified CIR.The simulation results suggest that the proposed method gives similar performance to time domain interpolation,yet it does not need to meet the condition of time domain interpolation that the number of subcarriers must be an integral multiple of pilot spacing to use it.The proposed method allows for flexible pilot spacing,reducing the number of pilots and the consumption of subcarriers used for channel estimation.

用光驱改制CD/VCD实验

随着电脑多媒体技术的迅速发展,不少倍速光驱被淘汰下来。这些倍速光驱完全可以合理地加以改造,使物尽其用。笔者最近将一台光驱成功地改制成CD/VCD播放机,现将改制方法介绍给大家,希望给喜欢动手制作的爱好者一些有益的启发。在选材改制之前,我们先对光驱做一个大概的了解。光驱的全称是只读式光盘驱动器(即常说的CD-ROM)。