The construction of missile guidance codes resistant to random interference

Many types of missiles are guided by a finite set of distinct commands radioed from the ground in the form of a time-sequence of RF pulses. The command information is contained in the n − 1 time spacings between successive pulses in a group of size n, and is encoded and decoded by means of multitapped delay lines combined with AND gates. This paper discusses the problem of encoding command information (i.e., selecting the time spacings between pulses) so that m false pulses (m $$ n − 2) cannot combine with the n true pulses in any way to form a false command. Although it is very easy to state the restrictions that must be imposed on the time spacings between the pulses in the different commands, no general methods exist for finding, among codes satisfying these restrictions, those codes in which the longest command is as short as possible. This paper presents certain lower bounds, together with a few empirically derived codes approaching these lower bounds. The relationship between these codes and the well-known error-correcting binary codes of information theory is discussed in an appendix.