If the period of an

-sequence is

with

relative prime to

, then the vector

, a period of the

-sequence, can be decomposed in a special way into two subsequences of lengths

and

. The properties and structures of the

-sequence and its subsequences are studied under such decomposition. The following applications are direct consequences. The correlation technique for the detection of

- sequences can be improved. The weight distributions of a class of cyclic codes can be easily obtained. A scheme for improving the feedback communication is developed. And a method for designing cyclic codes with desirable weights is suggested.