Recently energy saving has become an important issue also for wired communication. In this paper we investigate the potential of using power back-off (PBO) as a means to achieve higher energy efficiency. Based on a global energy optimisation formulation we derive an energy efficient PBO (EEPBO) algorithm. Through simulation we compare EEPBO with continuous bit-loading to the near-optimal energy efficient spectrum balancing (EESB) algorithm and an integer bit-loading version of EEPBO with energy efficient iterative spectrum balancing (EEISB). By restricting the search to practical levels of PBO parameters instead of optimizing the bit-loading on each and every carrier separately we see a significant reduction in computational complexity. It also means that EEPBO is already supported by current VDSL2 systems. Still, even after restricting the spectrum to what the PBO in VDSL2 allows we can show, through simulations, that EEPBO achieves the same level of energy efficiency as the near-optimal methods. This high performance and low-complexity together with standard compliance makes EEPBO a very attractive choice for future energy efficient transmission in VDSL2.
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