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This work deals with the analysis of energy efficiency (EE) issues of hybrid automatic repeat request (HARQ) protocols such as Chase combining (CC) and incremental redundancy (IR), in a LTE baseband-based half-division duplex relay-assisted network. The EE performance is highly dependent on delay and circuitry power consumption, i.e., baseband and radio-frequency (RF) parts, and the effects of these components are investigated for amplify and forward (AF) and decode and forward (DF) protocols. Moreover, a realistic estimation of the baseband power consumption is provided. Our contributions in this paper can be summarized as follows: (1) an accurate estimation of power consumption of the main blocks of the LTE baseband is provided based on a real field-programmable gate array (FPGA) target and is integrated to a global energy consumption model (2) based on the previous power consumption evaluation; energy-efficiencies of DF protocol with HARQ-CC and HARQ-IR are investigated with various modulation orders; in addition, a quite insightful study of the energy efficiency-spectral efficiency trade-off is conducted, and (3) DF and AF protocols with HARQ are compared in terms of EE, and recommendations are suggested in order to jointly enhance the QoS and the energy efficiency of wireless systems.

This paper investigates a practical energy minimization problem for multiuser relay-assisted downlink cellular networks. The system adopts an hybrid-automatic-repeat-request of type I (HARQ-I) protocol and each user has an average delay constraint to be satisfied under a total power constraint for the system. The contribution of this paper lies in several folds: i) By introducing new constraints and new variables in the original problem, the solution is analytically obtained by the dual method. ii) An algorithm that jointly allocates for every user the optimal downlink power at base station (BS) and relay station (RS) and selects the RS (if cooperation is decided) is proposed. iii) Another binary integer programming algorithm that selects the optimal modulation and coding scheme (MCS) and optimizes the number of time-frequency resource blocks (RBs) between users is proposed. In order to corroborate our findings, simulation results in terms of energy-delay tradeoff, average starvation user rates and selected MCS statistics are presented. Our analyses show that relay-assisted strategy improves up to 30 % the energy consumption compared to non-relay-assisted one.

Introduction 2 Motivations and system model 3 Related works and contributions 4 Theoretical energy efficiency in relay assisted network 5 Simulation results 6 Conclusions and future works M. Maaz Cooperative communications 2 / 15

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