Overloaded CDMA Systems with Displaced Binary Signatures

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.

[1]  Paul D. Alexander,et al.  Iterative multiuser detection for CDMA with FEC: near-single-user performance , 1998, IEEE Trans. Commun..

[2]  Shlomo Shamai,et al.  Spectral Efficiency of CDMA with Random Spreading , 1999, IEEE Trans. Inf. Theory.

[3]  Bernard Fino,et al.  Multiuser detection: , 1999, Ann. des Télécommunications.

[4]  Roy D. Yates,et al.  Iterative construction of optimum signature sequence sets in synchronous CDMA systems , 2001, IEEE Trans. Inf. Theory.

[5]  Bijan Jabbari,et al.  Spreading codes for direct sequence CDMA and wideband CDMA cellular networks , 1998, IEEE Commun. Mag..

[6]  H. Vincent Poor,et al.  Iterative (turbo) soft interference cancellation and decoding for coded CDMA , 1999, IEEE Trans. Commun..

[7]  Gerhard Fettweis,et al.  On the impact of soft decision functions on the performance of multistage parallel interference cancelers for CDMA systems , 2001, IEEE VTS 53rd Vehicular Technology Conference, Spring 2001. Proceedings (Cat. No.01CH37202).

[8]  Dimitris A. Pados,et al.  Minimum total-squared-correlation design of DS-CDMA binary signature sets , 2001, GLOBECOM'01. IEEE Global Telecommunications Conference (Cat. No.01CH37270).

[9]  Johannes B. Huber.  Iterated Soft-Decision Interfer-ence Cancellation for CDMA , 1998 .

[10]  Marc Moeneclaey,et al.  Increasing CDMA capacity using multiple orthogonal spreading sequence sets and successive interference cancellation , 2002, 2002 IEEE International Conference on Communications. Conference Proceedings. ICC 2002 (Cat. No.02CH37333).

[11]  P. Vijay Kumar,et al.  Quasi-orthogonal sequences for code-division multiple-access systems , 2000, IEEE Trans. Inf. Theory.

[12]  Lloyd R. Welch,et al.  Lower bounds on the maximum cross correlation of signals (Corresp.) , 1974, IEEE Trans. Inf. Theory.

[13]  Dimitris A. Pados,et al.  New bounds on the total squared correlation and optimum design of DS-CDMA binary signature sets , 2003, IEEE Trans. Commun..

[14]  Paul D. Alexander,et al.  Random Sequence Multisets for Synchronous Code-Division Multiple-Access Channels , 1998, IEEE Trans. Inf. Theory.

[15]  Marc Moeneclaey,et al.  Multiple access using two sets of orthogonal signal waveforms , 2000, IEEE Communications Letters.

[16]  Marc Moeneclaey,et al.  DS/CDMA with two sets of orthogonal spreading sequences and iterative detection , 2000, IEEE Communications Letters.

[17]  J.E. Mazo,et al.  Digital communications , 1985, Proceedings of the IEEE.

[18]  Venkat Anantharam,et al.  Optimal sequences and sum capacity of synchronous CDMA systems , 1999, IEEE Trans. Inf. Theory.

[19]  Giuseppe Caire,et al.  Successive interference cancellation with SISO decoding and EM channel estimation , 2001, IEEE Journal on Selected Areas in Communications.

[20]  Marc Moeneclaey,et al.  Extending the capacity of multiple access channels , 2000 .

[21]  James L. Massey,et al.  Optimum sequence multisets for synchronous code-division multiple-access channels , 1994, IEEE Trans. Inf. Theory.