This paper proposes a direction for a White Space management scheme to enhance spectrum efficiency by considering unoccupied channel conditions according to the density of DTV transmitters and relays. Unoccupied channels are predicted to foresee White Space within three pilot areas, Uljin, Gangjin and Danyang, in Korea. We considered two DTV service coverage criteria based on two kinds of minimum field strength at Pt. 73 of 47 CFR which is determined according to the date of the TV license acquisition. No-talk regions depending on the DTV coverage criteria were derived by calculating the DTV propagation distances through empirical path loss models such as ITU-R P.1546. With these results, we derived the secondary service operation margins and calculated the enhanced spectrum efficiencies according to the distance and carrier frequency of terrestrial trunked radio (TETRA) - trunked mode operation (TMO) service as secondary users.