  It is well-known that cross-layer scheduling which adapts power, rate and
user allocation can achieve significant gain on system capacity. However,
conventional cross-layer designs all require channel state information at the
base station (CSIT) which is difficult to obtain in practice. In this paper, we
focus on cross-layer resource optimization based on ACK/NAK feedback flows in
OFDM systems without explicit CSIT. While the problem can be modeled as Markov
Decision Process (MDP), brute force approach by policy iteration or value
iteration cannot lead to any viable solution. Thus, we derive a simple
closed-form solution for the MDP cross-layer problem, which is asymptotically
optimal for sufficiently small target packet error rate (PER). The proposed
solution also has low complexity and is suitable for realtime implementation.
It is also shown to achieve significant performance gain compared with systems
that do not utilize the ACK/NAK feedbacks for cross-layer designs or
cross-layer systems that utilize very unreliable CSIT for adaptation with
mismatch in CSIT error statistics. Asymptotic analysis is also provided to
obtain useful design insights.
