Direct sequence (DS) code-division multiple-access (CDMA) is a modulation and multiple access technique currently being implemented in digital cellular mobile radio communication systems. The conventional quasisynchronous (QS) DS-CDMA communication system is generalized, and the problem of optimal spreading pseudonoise (PN) sequence design for new QS DS-CDMA communication systems is formulated. The classes of optimal PN sequences which have good pseudo-randomness and very small cross-correlation values for some range of offsets are designed by using a matrix-based approach. In contrast to the case of the other sequences, the optimal PN sequences produce small multiple-access interference (MAI) which is not affected by the number of users if there are sufficiently large number of users in the link. The new results are compared with the commonly used PN sequences to prove the superiority of our designed sequences, and the system performance of the QS-CDMA systems using different PN sequences are also evaluated.

Based on the properties of wavelet orthogonal basis, three novel wavelet-based multi-carrier CDMA (MC-CDMA) systems are proposed, and their advantages and performances are investigated by the comparison with the conventional MC-CDMA systems. For the additive white Gaussian noise (AWGN) channel, all three wavelet-based MC-CDMA systems possess the same bit error rates as the corresponding MC/BPSK-CDMA and MC/QPSK-CDMA systems, but have significant higher bandwidth efficiency than the conventional MC-CDMA systems by the suitable choice of wavelet functions. Their potential applications in the broadband wireless communications to improve bandwidth efficiency and combat the fading and narrowband interference are also discussed.

The improved minimum-order augmented pipelining (IMAP) algorithm, which belongs to the class of the clustered look-ahead (CLA) technique, is proposed in this paper. IMAP algorithm is optimized in the aspects of the minimization of augmented pipelining order and undesirable quantization effects simultaneously. The proposed 1-D IMAP digital filter can be easily transformed to the 2-D structure for fast video signal processing. This IMAP digital filter is especially suitable for highly computing oriented video signal processing algorithms such as spatio-temporal filtering, motion estimation or bandwidth reduction algorithm.

In this paper, the problem of optimal PN sequence design for quasi-synchronous (QS) DS-CDMA communication systems is formulated, and classes of optimal PN sequences which have good pseudorandomness and small cross-correlation values for some range of offsets are designed. The new results are compared with the commonly used PN sequences, and the system performances of the QS CDMA systems using different PN sequences are also evaluated.