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

摘要： 揭示了周期拟完美序列与循环Hadamard(Ⅱ)型差集的深刻对应关系，进而建立了周期拟完美序列的计数公式；并且通过决定循环Hadamard(Ⅱ)型差集的乘子群，分别求出了各族循环Hadamard(Ⅱ)型差集对应的本质不同的拟完美序列的个数。

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