“…, and after replacing E T BF , P ⋆ T BF , and γ by (10), (9) and (2), we can determine a sufficient distance d T BF,T BF (M ′ , M ′′ ) from which using M ′′ transmit antennas is more energy efficient than using M ′ antennas (M ′′ > M ′ ), as shown in (11). Thus, using more transmit antennas is not always a more energy efficient solution in TBF.…”