Recently, several directional MAC protocols using smart antennas or directional antennas have been proposed for wireless ad hoc networks including our proposed MAC protocol called SWAMP (Smart antennas based Wider-range Access MAC Protocol). This paper first outlines issues of directional MAC protocols and investigates different factors which reduce the probability of successful transmissions, such as location information staleness, deafness and hidden- and exposed-terminal problems arisen due to directional transmissions. In addition, this paper proposes solutions of location information staleness and exposed-terminal problems. The experimental results show that the optimization of parameters associated with location information staleness, such as the beamwidth, retry limit and lifetime of the table information improves the reliability of the transmission and the overall network performance.