THEOKKTU'AL FUXDAMKNTALS OF PULSE Tl< A NSM ISSK )N 



!)<).") 



maximum t(ilorable rms iiiters^niibol interference U referred to unit peak 

 amplitude of the rec'ei\'ed pulses heeomes for M = 0: 



Q = 1 

 U = 0.25 



4 

 0.112 



0.054 



In (13.14) and in the above table, U is the maximum tolerable rms 

 intersymbol interference from all sources, such as fine structure imper- 

 fections over the transmission band, band-edge phase distortion and a 

 low-frequency cut-off. Interference from these various sources may be 

 combined on a root-sum-square basis. 



In the above evaluation of rms intersymbol interference a balanced 

 pulse system was assumed. An unbalanced system can be obtained by 

 superposing on a balanced system an infinite sequence of pulses of equal 

 amplitude and polarity at uniform intervals as indicated in Fig. 44. This 

 superposed sj-stem will give rise to a fixed intersymbol interference or 

 displacement of the received pulse train, which does not alter the margin 

 for distinction between pulse amplitudes and Avhich can be corrected by 

 a fixed bias at the receiving end if necessary. For this reason, in the case 



n 



u 



n 



(a) 



BALANCED PULSE TRAIN WITH 

 EQUAL MAXIMUM AMPLITUDES OF 

 POSITIVE AND NEGATIVE PULSES 



Q 



Q 



(b) 



SUPERPOSED INFINITE PULSE TRAIN 



TJ 



n 



(c) 



UNBALANCED PULSE TRAIN 



(a) + (b) 



Fig. 44 Derivation of an unbalanced from a balanced pulse train by super- 

 position of an infinite train of pulses of equal amplitude. 



