  In the paper, we investigate the delay-aware data transmission in renewable
energy aided multi-carrier system. Besides utilizing the local renewables, the
transmitter can also purchase grid power. By scheduling the amount of
transmitted data (The data are stored in a buffer before transmission), the
sub-carrier allocation, and the renewable allocation in each transmission
period, the transmitter aims to minimize the purchasing cost under a buffer
delay constraint. By theoretical analysis of the formulated stochastic
optimization problem, we find that transmit the scheduled data through the
subcarrier with best condition is optimal and greedy renewable energy is
approximately optimal. Furthermore, based on the theoretical derives and
Lyapunov optimization, an on-line algorithm, which does NOT require future
information, is proposed. Numerical results illustrate the delay and cost
performance of the proposed algorithm. In addition, the comparisons with the
delay-optimal policy and cost-optimal policy are carried out.
