Multi-sequences with d-perfect property

Sequences with almost perfect linear complexity profile are defined by Niederreiter (Proceedings of the Salzburg Conference 1986, Vol. 5, Teubner, Stuttgart, 1987, pp. 221-233). Xing and Lam (IEEE Trans. Inform. Theory 45 (1999) 1267; J. Complexity 16 (2000) 661) extended this concept from the case of single sequences to the case of multi-sequences and further proposed the concept of d-perfect multi-sequences. In this paper, based on the technique of m-continued fractions due to Dai et al. we investigate the property of d-perfect multi-sequences and obtain a sufficient and necessary condition of d-perfect multi-sequences. We show that d-perfect multi-sequences are not always strongly d-perfect. In particular, we give an example to disprove the conjecture proposed by Xing (2000) on d-perfect multi-sequences.