Cross-layer directional antenna MAC protocol for wireless ad hoc networks

In this paper we propose a Directional Antenna Medium Access (DAMA) protocol and its enhanced version called EDAMA (enhanced DAMA), which takes advantage of the benefits offered by directional antennas. Both of these schemes have been inspired by the IEEE 802.11 MAC, with major enhancements including a new neighbor discovery scheme, an optimized circular directional transmission of RTS and CTS to prevent the hidden node problem, reduce collisions and decrease node deafness, and also a multi-buffer management scheme. A pair of communicating nodes using these schemes simultaneously transmits the circular directional RTS and CTS only to those sectors with neighbors, hence reducing overall communication delay and enhancing throughput. The main difference between DAMA and EDAMA lies in the way buffering is provided in the MAC layer. Unlike DAMA which uses a single MAC buffer for all antenna beams as in IEEE 802.11, EDAMA employs separate buffers for each of the antenna sectors and introduces an integrated network and MAC cross-layer design. This helps in eliminating the “self induced blocking” problem prominent in existing directional MAC protocols. We have compared DAMA, EDAMA, IEEE 802.11 and two recently proposed directional MAC protocols, and results show that DAMA and EDAMA perform better than existing MAC protocols in the majority of the scenarios investigated, while EDAMA is observed to perform best. We also point out that the performance usually depends on the network topology and traffic pattern.