MIMO channel orthogonalisations applying universal eigenbasis

Some mathematical fundamentals of the multiple input multiple output (MIMO) channel orthogonalisations using prolate spheroidal wave functions (PSWFs) as a universal basis are presented. In contrast to the Karhunen-Loeve expansion or singular value decomposition, the PSWF basis is -invariant- to the properties of the MIMO channel covariance matrix and provides an almost minimum set of eigenfunctions that allow the channel to be represented with a predefined accuracy.