Grassmannian signatures for CDMA systems

Codebooks constructed from Welch bound equality (WBE) sequences have been show to be optimal in terms of sum capacity in synchronous CDMA systems. Unfortunately, these codebooks are a function of the number of active signatures and need to be reassigned as the number of active users changes to maintain optimality. To mitigate the problems caused by the loss of the Welch bound equality property, in this paper we propose a special subclass of WBE sequences for which the interference power experienced by each user depends only on the number of active users and the dimensions of the code. In deference to the relationship with Grassmannian line packing, we refer to this as a Grassmannian signature set. We study the interference properties of this set, comment on the sequence design problem, and illustrate improvements over arbitrary WBE sequence sets via simulation.