JPL's Wireless Communication Reference Website Chapter: Digital Transmission. Section: Digital Modulation.

Nyquist Pulse Shaping

Pulse Shapes

In digital transmission, signal pulse shapes usually are chosen to satisfy the following requirements

• Bandwidth limitations (e.g. sinc shaped pulses)
• Zero crossings of one pulse coinside with sample moments of other pulses (e.g. sinc pulses or raised cosines)
• Rapid decreases of pulse energy outside the main bit interval (e.g. raised cosine)
• Appropriate for use with matched filters (e.q. Square Root Nyquist pulses)

Example signal

Contributed by Joop Talstra, Philips Research
Raised-cosine modulation of the bitstream:

101010101010101011100100100110011

raised_cosine = sinc(t/T) cos(a t/T)/(1- (2 a t/T)2)

blank  = bitstream with rectangular pulses
blue:  a = 0 (sinc)
red:  a = 0.5 
green: a = 1.0
cyan: a = 1.2

sample_time = T = 22

JPL's Wireless Communication Reference Website © 1997.