Tradeoff Analysis and Joint Optimization of Link-Layer Energy Efficiency and Effective Capacity Toward Green Communications

A joint optimization problem of link-layer energy efficiency (EE) and effective capacity (EC) in a Nakagami-m fading channel under a delay-outage probability constraint and an average transmit power constraint is considered and investigated in this paper. First, a normalized multi-objective optimization problem (MOP) is formulated and transformed into a single-objective optimization problem (SOP), by applying the weighted sum method. The formulated SOP is then proved to be continuously differentiable and strictly quasiconvex in the optimum average input power, which turns out to be a cup shape curve. Furthermore, the weighted quasiconvex tradeoff problem is solved by first using Charnes-Cooper transformation and then applying Karush-Kuhn-Tucker (KKT) conditions. The proposed optimal power allocation, which includes the optimal strategy for the link-layer EE-maximization problem and the EC-maximization problem as extreme cases, is proved to be sufficient for the Pareto optimal set of the original EE-EC MOP. Moreover, we prove that the optimum average power level monotonically decreases with the importance weight, but strictly increases with the normalization factor, the circuit power and the power amplifier efficiency. Simulation results confirm the analytical derivations and further show the effects of fading severeness and transmission power limit on the tradeoff performance

Multi-carrier link-layer energy efficiency and effective capacity tradeoff

A joint energy and spectral efficient power allocation strategy for a point-to-point multi-carrier link, subject to a delay-outage probability constraint, is proposed in this paper. Since the two objectives, namely, link-layer energy efficiency (EE) and effective capacity (EC), conflict with each other, the tradeoff problem falls into the scope of multi-objective optimization problems (MOP). With the ε-constraint approach, the MOP is converted into a single-objective optimization problem (SOP) by maximizing the multi-carrier EC, subject to an EE constraint. Then, by introducing an adjustable performance indicator, EE-loss-rate (αEE), into the EE constraint limit, the tradeoff level is flexibly controlled. Finally, we prove that the proposed tradeoff formulation is a concave maximization problem and the optimum power allocation strategy can be derived using Lagrangian method. Analytical results indicate that the proposed power allocation has a similar structure to the one for EE-maximization problem over a frequency-selective fading channel, but with a different cut-off threshold