Energy and Spectral Efficient Designs for a Multihop CC-HARQ Relay Network

Over block Rayleigh fading channels, three optimum designs to achieve energy efficiency (EE) and spectral efficiency (SE) in a multihop relay network with Chase-combining based hybrid automatic repeat request (CC-HARQ) are investigated in this paper. By adopting a new log-domain linear threshold approximation method, we first formulate our optimization problem with respect to EE and SE, in which the cross-layer parameters concerning frame length and transmit power are considered; Relative optimal schemes are then proposed to maximize EE and SE individually, joint optimization of frame length and transmit power is identified superior to single-parameter optimization and conventional scheme. Additionally, due to the conflicts between EE and SE, a fundamental EE-SE tradeoff metric to optimize both EE and SE is introduced, which can be applied to adjust EE and SE flexibly. Numerical simulation results verify the correctness of the analytical optimum schemes.