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Almost perfect autocorrelation sequences are defined as complex periodic sequences such that all the out-of-phase autocorrelation coefficients are zero except one. The study is restricted to (-1,+1)-sequences. In this case, such sequences exist only if the period n is a multiple of 4. After setting up theoretical results, several sequences are constructed for every period n multiple of 4 in the range 8>
J. Wolfmann (Wed,) studied this question.