Network Deployment for Maximal Energy Efficiency in Uplink with Multislope Path Loss

This work aims to design the uplink (UL) of a cellular network for maximal energy efficiency (EE). Each base station (BS) is randomly deployed within a given area and is equipped with M antennas to serve K user equipments (UEs). A multislope (distance-dependent) path loss model is considered and linear processing is used, under the assumption that channel state information (CSI) is acquired by using pilot sequences (reused across the network). Within this setting, a lower bound on the UL spectral efficiency and a realistic circuit power consumption model are used to evaluate the network EE. Numerical results are first used to compute the optimal BS density and pilot reuse factor for a Massive multiple-input-multiple-output (MIMO) network (such that M ≫ K ≫ 1) with three different detection schemes, namely, maximum ratio combining (MRC), zero-forcing (ZF) and multicell minimum mean-squared error (M-MMSE). The numerical analysis shows that the EE is a unimodal function of BS density and achieves its maximum for a relatively small BS densification, irrespective of the employed detection scheme. Therefore, we concentrate on ZF and use stochastic geometry to compute a new lower bound on the spectral efficiency, which is then used to optimize, for a given BS density, the pilot reuse factor, number of BS antennas and UEs. Closedform expressions are computed from which valuable insights into the interplay between the optimization variables, hardware characteristics, and propagation environment can be obtained.