Control Frame Shaping in Power Controlled and Directional MAC Protocols?

This paper discusses the ideal shapes of control frames (i.e., RTS/CTS frames) in the IEEE 802.11 MAC layer for efficient power control and directional beam forming in mobile ad hoc networks (MANETs). Control frames are used to coordinate concurrent transmissions for collision avoidance. Most existing schemes are either overly conservative (i.e., using omnidirectional control frames without power control) or overly aggressive (i.e., using directional control frames with the minimal power). The former has low spatial reuse and the latter increases collisions. We propose two control frame shaping schemes that encourage spatial reuse while avoiding the collisions. The first scheme, called adaptive power control, uses a single RTS/CTS exchange to solve the hidden terminal problem caused by heterogeneous transmission powers. The second scheme, called control frame relay, uses multiple RTS/CTS frames to avoid both the hidden terminal and deafness problems. In designing these schemes, we assume an existing topology control protocol. By exploiting the benefits of regulated traffic and neighbor awareness that accompany a topology control process, the shapes of control frames can be reduced significantly. Extensive simulations were conducted and simulation results show that the proposed scheme outperforms several existing protocols in terms of spatial reuse and collision avoidance.