  We consider the problem of transmission energy op- timization via range
assignment for Low Power Nodes (LPNs) in Long Term Evolution (LTE) Heterogenous
Networks (HetNets). The optimization is subject to the load coupling model,
where the cells interfere with one another. Each cell provides data service for
its users so as to maintain a target Quality-of-Service (QoS). We prove that,
irrespective the presence of maximum power limit or its value, operating at
full load is optimal. We perform energy minimization by optimizing the
association between User Equipments (UEs) and cells via selecting cell-
specific offsets on LPNs. Moreover, the optimization problem is proved to be
NP-hard. We propose a tabu search algorithm for offset optimization (TSO). For
each offset, TSO computes the optimal power solution such that all cells
operate at full load. Numerical results demonstrate the significant performance
improvement of TSO on optimizing the sum transmission energy, compared to the
conventional solution where uniform offset is used for all LPNs.
