On Quasi-Orthogonal Signatures for CDMA Systems
Robert W. Heath Jr, Thomas
Strohmer, and Arogyaswami J.
IEEE Trans. on Info Theory, vol. 52, no. 3, pp. 1217- 1226, March 2006.
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-intererference-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
newconstruction algorithm is provided. Connections are made between
these signature design problems, Grassmannian line packing, frame theory,
and algebraic geometry.
Welch bound equality sequences, Grassmannian packing, sequence design
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