Chip-interleaved block-spread code division multiple access. (Transactions Papers)

A novel multiuser-interference (MUI)-free code division multiple access (CDMA) transceiver for frequency-selective multipath channels is developed in this paper. Relying on chip-interleaving and zero padded transmissions, orthogonality among different users' spreading codes is maintained at the receiver even after frequency-selective propagation. As a result, deterministic multiuser separation with low-complexity code-matched filtering becomes possible without loss of maximum likelihood optimality. In addition to MUI-free reception, the proposed system guarantees channel-irrespective symbol detection and achieves high bandwidth efficiency by increasing the symbol block size. Filling the zero-gaps with known symbols allows for perfectly constant modulus transmissions. Important variants of the proposed transceivers are derived to include cyclic prefixed transmissions and various redundant or nonredundant precoding alternatives. (Semi-) blind channel estimation algorithms are also discussed. Simulation results demonstrate improved performance of the proposed system relative to competing alternatives. Index Terms--Block spreading, channel estimation, chip interleaving, code division multiple access (CDMA), multipath, multiuser interference.