说明：  模拟连续独立信号。产生一段在[-1,+1]上均匀分布的独立随机信号，长度为0.5s。(1)绘制该段信号的波形；(2)求自相关函数；(3)计算其功率谱
(Continuous independent analog signals. Produce a in [-1,+1] on the uniform distribution of independent random signals, a length of 0.5s. (1) Draw the waveform of the paragraph (2) Find the autocorrelation function (3) to calculate the power spectrum)