关键词: 周期拟完美序列, 循环Hadamard(Ⅱ)型差集, 乘子群, CDMA移动通信, 流密码

Abstract: Periodic quasi-perfect sequences are very important in CDMA mobile communication and in stream ciphers. The relation between periodic quasi-perfect sequences and cyclic Hadamard difference sets of type (Ⅱ) is studied, the enumerating formula for periodic quasi-perfect sequences is given,the multiplier groups of some cyclic Hadamard difference sets of type (Ⅱ) are determined, and the numbers of some periodic quasiperfect sequences corresponding to cyclic Hadamard difference sets of type (Ⅱ) are obtained.

Key words: periodic quasi-perfect sequences, cyclic Hadamard difference sets of type(Ⅱ), multiplier groups, CDMA mobile communications, stream cryptography