1. A method for processing communication signals, the method comprising: quantizing a channel estimate at a MIMO receiver onto a codebook based on a cost function, wherein said codebook comprises a plurality of unitary matrices; feeding back a codebook index from said MIMO receiver to a MIMO transmitter, wherein said codebook index is associated with one of said plurality of unitary matrices that minimizes said cost function; minimizing said cost function by choosing a smallest scalar cost from a plurality of scalar costs, wherein each one of said scalar costs is generated from one or more sums and one or more products of elements of a product matrix, wherein said product matrix is generated from one of said plurality of unitary matrices, a matrix comprising said channel estimate, and their respective Hermitian Transposes; and adjusting said codebook based on a plurality of said fed-back codebook indices.