A heuristic approach to mobility robustness in 4G LTE public safety networks

In this paper we study 3GPP mobility robustness in the context of Public Safety (PS) communications. In specific, we investigate the scenario in which 4G LTE connectivity is provisioned by means of Aerial evolved Node Bs (AeNBs) mounted on Low Altitude Platforms (LAPs) raised in the sky at an altitude ranging from few hundreds meters to one kilometer. Given the peculiarities of PS communications, the event of handover (HO) is particularly crucial for PS users. It is well understood that a trade-off exists between events of radio link failure (RLF) and HO completion, which is usually achieved by proper tuning of handover parameters. We propose a policy-based HO parameters adjustment in the form of a heuristic, which exploits the information provided by the Mobility Robustness Optimisation (MRO), in order to to achieve such a trade-off. Using simulations, we show that our heuristic solution can achieve the above mentioned trade-off, taking into account the different HO phases and incorporating a suitable Air-to-Ground (ATG) signal propagation model.