Title :
On quasi-orthogonal signatures for CDMA systems
Author :
Heath, Robert W. ; Strohmer, T. ; Paulraj, A.J.
Author_Institution :
Dept. of Math., Univ. of California, Davis, CA
fDate :
3/1/2006 12:00:00 AM
Abstract :
Sum capacity optimal signatures in synchronous code-division multiple-access (CDMA) systems are functions of the codebook length as well as the number of active users. A new signature set must be assigned every time the number of active users changes. This correspondence considers signature sets that are less sensitive to changes in the number of active users. Equiangular signature sequences are proven to solve a certain max-min signal-to-interference-plus-noise problem, which results from their interference invariance. Unions of orthonormal bases have subsets that come close to satisfying the Welch bound. Bounds on the maximum number of bases with minimum maximum correlation are derived and a new construction algorithm is provided. Connections are made between these signature design problems, Grassmannian line packing, frame theory, and algebraic geometry
Keywords :
code division multiple access; encoding; interference (signal); minimax techniques; number theory; sequences; Grassmannian line packing; Welch bound; algebraic geometry; code-division multiple-access; codebook length; equiangular signature sequence; frame theory; minimum maximum correlation; quasiorthogonal signature; signal-to-interference-plus-noise problem; sum capacity; synchronous CDMA system; Circuits; Code division multiplexing; Colored noise; Fading; Gaussian channels; Geometry; Interference; Iterative algorithms; Multiaccess communication; White noise; Code-division multiple-access (CDMA) systems; Walsh sequences;
Journal_Title :
Information Theory, IEEE Transactions on
DOI :
10.1109/TIT.2005.864469
