... denoting the gradient of function Φ and i denot-ing the CG iteration.After D iterations of the conjugate gradient algorithm the set of search directions{d1, d2, , dD} and the set of gradi-ents ... also belong to the signal subspace. This is then the case for g cg,P. Therefore, the rank of span {g cg,0, g cg,1, , g cg,P−1, g cg,P} reduces to P yield-ing that in this case g cg,Pshould ... eigendecomposition of the covariance matrix of the received data. Indeed, the proposed algorithm involves the building of the signal subspace from the residual vectors of the conjugate gradient (CG) method.This...