对码元序列进行基带成型滤波，来减少码间串扰，采用的是升余弦滚降滤波器，可以通过更改参数的方式来更改成根升余弦滚降滤波器-Symbol sequence baseband shaping filter to reduce inter-symbol interference, raised cosine roll-off filter, you can change the parameters to change into a root raised cosine roll-off filter