On-Off (Unipolar) Signaling

2 -On-Off (Unipolar) Signaling

In unipolar NRZ  a 1 is transmitted by a pulse p(t) for a duration of T_b seconds and a 0 is transmitted by no pulse for a duration of T_b seconds.           In unipolar RZ a 1 is transmitted by a pulse p(t) for a duration of T_b/2

seconds followed by zero voltage for a duration of T_b /2 seconds, and a 0 is transmitted by no pulse for a duration of T_b seconds

Note that the PSD  consists of both a discrete and a continuous part.

Properties of On-Off  Signaling

1.Transmission bandwidth : Is the same as in polar signaling. Thus,     On-Off signaling is not bandwidth efficient.

2. Error detection and correction capability : On-Off signaling has no error-detection or error-correction capability.

3. power spectral density : It has nonzero PSD at dc (w = 0)

4.Power efficiency : On-Off signaling requires twice as much power as polar signaling. for the same immunity, if on-off signaling uses pulses of amplitudes 2 and 0, polar signaling need only use pulses of amplitudes 1 and -1.  If a pulse of amplitude 1 or -1 has energy E, then the pulse of amplitude 2 has energy (2)²E = 4E, which is twice that required for the polar signal.

5. Transparency : on-off signaling is not transparent.

6. Adequate timing content : A long string of 0's  causes the absence of a      signal and can create an error in timing extraction.