Using beam forming antennas and ULB modulations in ad hoc networks have been recently focused on, as they allow to drastically improve ad-hoc network performances. This new technological context implies revisiting common network algorithms. When considering an multi-sector antenna uncommon with an uncommon high switch delay, packets have to be efficiently scheduled on beams at the MAC layer level, in order to improve the network capacity. We consider two optimization criteria: the network throughput and the maximum delay of packets. This paper proposes and studies a MAC scheduler, FIFO TBW, efficiently reducing the overhead due to beam switching delays. We give a first approach to to estimate the window duration parameter.