Due to the quantization of electromagnetic fields there is an upper frequency limit in the spectrum of any finite energy transmitted by an electromagnetic system.
由于电磁场的量子化效应，电磁系统发射有限能量的电磁场，其频谱必有一高频率上限。
2
Thus pulse shaping technique can be used not only shape the spectrum of the transmitted signal to increase the bandwidth efficiency but also to reduce its PAPR.