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BELL SYSTEM TECHNICAL JOURNAL 



The intersymbol interference will consist of currents resulting from 

 all of the preceding symbols. The contribution of any one symbol 

 will depend on its size, that is, on the number of added cells it represents, 

 and on how long it preceded the symbol in question. For a given 

 rate of selection the resultant of these contributions will be a maximum 

 for that particular sequence of symbols for which at every selection 

 preceding the one in question the operator had selected the largest 



possible symbol, that is, a voltage change of (5 — \)E. The form 

 of the received current is then as shown on Fig. 4, where A represents 

 the disturbed symbol. The curves are drawn for 5 equal to five. 

 The current resulting from one such change occurring at time zero is 



i= {s- 1)|^-"', 



where the damping constant, 



RC 



(13) 

 (14) 



If the interval between selections is r, then the time during which 

 any one interfering current is damped out before it makes its con- 

 tribution to the interference with the disturbed symbol is qr where q 

 is the number of selections by which it precedes the disturbed symbol. 

 The magnitude of its contribution is therefore from (13) 



