768 



THE BELL SYSTEM TECHNICAL JOURNAL, AL\Y 1954 



Assume that pulses of unit peak amplitude but varying polarity are 

 transmitted at intervals t = n and consider the interference with a 

 given pulse from all pulses. As illustrated in Fig. 31, the first preceding 

 and following pulses will in accordance with (7.02) give rise to a pulse 

 echo dzai/2 and the second preceding and following pulses to a pulse 

 echo ±a2/2 etc., where the signs of the echoes depend on the polarity 

 of the pulses and on the signs of the coefficients Oi , 02 . The resultant 

 intersymbol interference Ua{t) will depend on the polarity of the various 



PULSE ECHOES FROM INDIVIDUAL PULSES 



a,/2 4 



82/2 ♦ 



PULSE 

 ECHOES 



1 



a,/2fIfai/2 



♦ a 1/2 



32 



T^T 



!t-a2/2 



n 



Ja3/2 



1-92/2 



ta3/2 



1-33/2 



-33 



xAJfa^A 



RESULTANT PULSE TRAIN AND INTERSYMBOL INTERFERENCE 



U;,= 



Fig. 31 — Combination of pulse echoes into intersymbol interference for a 

 particular case. 



