Cooperation and Directionality: Friends or Foes?

As the two key technologies that have the potential to reshape the landscape of next-generation wireless network, cooperative communications and directional antenna system so far have been developed in parallel, if not in isolation from each other. In order to establish a thorough comparison between the relative system performance of cooperative diversity and directional transmission in an adhoc environment, we design and quantitatively evaluate three medium access control protocols, namely O-CoopMAC, D-NoopMAC and D-CoopMAC. The study yields the unexpected yet crucial observation that cooperative forwarding significantly limits the spatial reuse created by transmission directionality, and therefore can appreciably degrade the performance of a directional system with a sufficiently narrow antenna beam. To the best knowledge of the authors, this is the first paper to systematically compare the performance of these two technologies in an adhoc environment and reveal the key fact that cooperation and directionality can be rather foes than friends!