HetNets With Random DTX Scheme: Local Delay and Energy Efficiency

Heterogeneous cellular networks (HetNets) are to be deployed for future wireless communications to meet the ever-increasing mobile traffic demand. However, the dense and random deployment of small cells and their uncoordinated operation raise important concerns about energy efficiency. On the other hand, discontinuous transmission (DTX) mode at the base station (BS) serves as an effective technology to improve energy efficiency of the overall system. In this paper, we investigate energy efficiency under a finite local delay constraint in the downlink HetNets with the random DTX scheme. Using a stochastic-geometry-based model, we derive the local delay and energy efficiency in a general case and obtain closed-form expressions in some special cases. These results give insights into the effect of key system parameters, such as path-loss exponents, BS densities, signal-to-interference-ratio (SIR) threshold, and mute probability on system performance. We also provide the low-rate and high-rate asymptotic behavior of the maximum energy efficiency. It is analytically shown that it is less energy efficient to apply the random DTX scheme in the low-rate regime. In the high-rate regime, however, a random DTX scheme is essential to achieve the finite local delay and higher energy efficiency. Finally, we extend the analysis to the load-aware DTX scheme, where the mute probability depends on the user activity level.