“…The following notations and lemmas are needful to prove the statistical property of Lemma Let n × n matrices M > 0, N > 0 (or N ≥ 0), then M > N if and only if λ 1 (NM ‐1 ) < 1, where λ 1 (NM ‐1 ) is the largest eigenvalue of the matrix NM ‐1 .Lemma Let M be an n × n positive definite matrix, that is M > 0, and α be some vector, then M − αα ′ ≥ 0 if and only if α ′ M −1 α ≤ 1.Lemma Let be two linear estimators of α . Suppose that , where denotes the covariance matrix of and .…”