Multiuser Detection
Random sequence multisets for synchronous code-division multiple-access channels
IEEE Transactions on Information Theory
Spectral efficiency of CDMA with random spreading
IEEE Transactions on Information Theory
Optimal sequences and sum capacity of synchronous CDMA systems
IEEE Transactions on Information Theory
Quasi-orthogonal sequences for code-division multiple-access systems
IEEE Transactions on Information Theory
Iterative construction of optimum signature sequence sets in synchronous CDMA systems
IEEE Transactions on Information Theory
Spreading codes for direct sequence CDMA and wideband CDMA cellular networks
IEEE Communications Magazine
Extending the capacity of multiple access channels
IEEE Communications Magazine
Successive interference cancellation with SISO decoding and EM channel estimation
IEEE Journal on Selected Areas in Communications
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We extend three types of overloaded CDMA systems, by displacing in time the binary signature sequences of these systems: (1) random spreading (PN), (2) multiple-OCDMA (MO), and (3) PN/OCDMA (PN/O). For each of these systems, we determine the time shifts that minimize the overall multiuser interference power. The achievable channel load with coded and uncoded data is evaluated for the conventional (without displacement) and improved (with displacement) systems, as well as for systems based on quasi-Welch-bound-equality (QWBE) sequences, by means of several types of turbo detectors. For each system, the best performing turbo detector is selected in order to compare the performance of these systems. It is found that the improved systems substantially outperform their original counterparts. With uncoded data, (improved) PN/O yields the highest acceptable channel load. For coded data, MO allows for the highest acceptable channel load over all considered systems, both for the conventional and the improved systems. In the latter case, channel loads of about 280% are achievable with a low degradation as compared to a single user system.