User-Number Threshold-Based Small-Cell On/Off Control Scheme: Performance Evaluation and Optimization

In this paper, we study the energy efficiency of small-cell on/off control schemes in which small-cells turn on when the number of active users reaches a certain threshold value called on-threshold. In particular, we derive analytical formulas for various performance metrics such as expected small-cell power consumption, average consumed energy per transmitted bit, expected energy saving, and energy saving probability. Moreover, we show that the expected small-cell power consumption strictly decreases with increased on-threshold value and derive a mathematical expression for the optimal on-threshold value that minimizes the average consumed energy per transmitted bit. With simulation results, we not only verify the validity of the analytical results but also discuss how the theoretical results can be used in system performance evaluation and optimization. We believe that many of the results in this paper can be used in practical small-cell network design and operation.