  This work is the second of a two-part series of papers on the effectiveness
of cooperative techniques in non-centralized carrier sense-based ad hoc
wireless networks. While Part I extensively discussed reactive cooperation,
characterized by relayed transmissions triggered by failure events at the
intended receiver, Part II investigates in depth proactive solutions, in which
the source of a packet exploits channel state information to preemptively
coordinate with relays in order to achieve the optimal overall rate to the
destination. In particular, this work shows by means of both analysis and
simulation that the performance of reactive cooperation is reduced by the
intrinsic nature of the considered medium access policy, which biases the
distribution of the available relays, locating them in unfavorable positions
for rate optimization. Moreover, the highly dynamic nature of interference that
characterizes non-infrastructured ad hoc networks is proved to hamper the
efficacy and the reliability of preemptively allocated cooperative links, as
unpredicted births and deaths of surrounding transmissions may force relays to
abort their support and/or change the maximum achievable rate at the intended
receiver. As a general conclusion, our work extensively suggests that
CSMA-based link layers are not apt to effectively support cooperative
strategies in large-scale non-centralized ad hoc networks.
