A joint optimization method considering both Partial-Spectrum-Reuse (PSR) scheme and base-station-sleep (BSS) is proposed for improving the energy efficiency in heterogeneous networks (HetNets). We derive the coverage probabilities for both the macro-tier and micro-tier networks, followed by maximizing the HetNet's coverage probability through optimizing both the PSR factor and macro-micro base station's active probability ratio (APR). Furthermore, the problem of energy-consumption-minimization in the whole HetNet can be addressed by analyzing the relationship between the optimal PSR factor and APR. Numerical results show that the proposed joint optimization method is capable of saving network energy consumption of up to 50% when the signal-to-interference-and-noise ratio (SINR) target is set to be 20 dB.

The main constraint to the performance improvement of two-tier heterogeneous network (HetNet) comes from the cross-tier interference (CTI) due to the frequency reuse among cells. A user-pairing aided uplink power control algorithm based on the non- cooperative game theory can be employed in consideration of user diversity gain for alleviating the CTI. In order to maximize the overall performance, the macro-tier users with higher channel gains and the femto-tier users with lower channel gains are scheduled alternately to be "active" in one time slot but to be "opposite" in the next time slot in the proposed scheme. Numerical results show that the proposed scheme is capable of outperforming the traditional stochastic schedule based strategy by more than 30% improvement in terms of average macrocell capacity. Furthermore, an obvious performance gain in terms of the percentage of femtocells that beyond their signal- to-interference-and-noise ratio (SINR) target can also be achieved by executing the macro-tier link- qualityprotection strategy.