Abstract: A cellular downlink system combining AMC and ARQ is considered. The BS obtains the channel state information through the feedback of the receiver, and then adaptively chooses the modulation and coding method at the physical layer to maximize the system spectrum efficiency. At the same time, ARQ at the data link layer is also adopted to improve the robustness performance. Based on this cross-layer system, the problem of spectral efficiency maximization for non-realtime services is studied, that is, how to maximize the spectral efficiency by optimally choosing the AMC parameters under the average delay constraint. First, the above cross-layer system is modeled under some reasonable assumptions. Then, the studied problem is formulated as a convex optimization one. Finally, this problem is solved with the classical Lagrangian method. Numerical simulations show that our proposed method is optimal.

Key words: AMC, ARQ, cross-layer design, Lagrangian method