Sum capacity of equal-power users in overloaded channels

We consider the sum capacity of code-division multiple-access (CDMA) signature-sequence sets in overloaded channels that contain an orthogonal subset of dimension N. We introduce a family of signature-sequence sets that consists of a hierarchy of orthogonal subsets (HOS), and show that various signature-sequence sets designed for channel overloading belong to this family. Assuming an equal average energy (EAE) constraint on the user signals, an expression for the sum capacity of the HOS family is derived. We point out that the maximum sum capacity over the HOS family is achieved by the multiple-orthogonal (m-O) CDMA sequence sets. The sum capacity of m-O is only slightly less than the upper bound imposed by the Gaussian multiple-access channel. Moreover, m-O is superior to a system with N orthogonal sequences and (K-N) pseudonoise (PN) sequences (PN/O), which, in turn, outperforms a system with K PN sequences. Both for PN/O and sequence sets over HOS, there is no additional loss in sum capacity if we require the sequences to consist of chips that are binary or quaternary valued.

[1]  Alan S. Willsky,et al.  Low complexity optimal joint detection for oversaturated multiple access communications , 1997, IEEE Trans. Signal Process..

[2]  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).

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

[4]  A. Soshnikov.  A Note on Universality of the Distribution of the Largest Eigenvalues in Certain Sample Covariance Matrices , 2001, math/0104113.

[5]  D. P. Taylor,et al.  Vector assignment scheme for M+N users in N-dimensional global additive channel , 1992 .

[6]  Marc Moeneclaey,et al.  Sum capacity of the OCDMA/OCDMA signature sequence set , 2002, IEEE Communications Letters.

[7]  D. P. Taylor,et al.  Multiuser signaling in the symbol-synchronous AWGN channel , 1995, IEEE Trans. Inf. Theory.

[8]  Marc Moeneclaey,et al.  An excess signaling concept with Walsh-Hadamard spreading and joint detection , 2000, Globecom '00 - IEEE. Global Telecommunications Conference. Conference Record (Cat. No.00CH37137).

[9]  J. Massey,et al.  Welch’s Bound and Sequence Sets for Code-Division Multiple-Access Systems , 1993 .

[10]  Robert W. Heath,et al.  Grassmannian signatures for CDMA systems , 2003, GLOBECOM '03. IEEE Global Telecommunications Conference (IEEE Cat. No.03CH37489).

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

[12]  Thomas M. Cover,et al.  Elements of Information Theory , 2005 .

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

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

[15]  H. Hadinejad-Mahram,et al.  Analysis of a CDMA downlink with non-orthogonal spreading sequences for fading channels , 2000, VTC2000-Spring. 2000 IEEE 51st Vehicular Technology Conference Proceedings (Cat. No.00CH37026).

[16]  Dilip V. Sarwate.  Meeting the Welch Bound with Equality , 1998, SETA.

[17]  Marc Moeneclaey,et al.  Sum capacity of binary signatures that minimize the total squared correlation , 2004, International Symposium onInformation Theory, 2004. ISIT 2004. Proceedings..

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

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

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

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

[22]  Z. Bai.  METHODOLOGIES IN SPECTRAL ANALYSIS OF LARGE DIMENSIONAL RANDOM MATRICES , A REVIEW , 1999 .

[23]  T. Strohmer,et al.  On the design of optimal spreading sequences for CDMA systems , 2002, Conference Record of the Thirty-Sixth Asilomar Conference on Signals, Systems and Computers, 2002..

[24]  Ramjee Prasad,et al.  Overview of multicarrier CDMA , 1997, IEEE Commun. Mag..

[25]  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..

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