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When a vehicle moves from one base station (BS) to another, a large number of on-board user equipments (UE) may simultaneously and individually perform a handover (HO) procedure, resulting in increased HO overheads. A mobile relay node (MRN), connected via a wireless backhaul to a donor base station (DBS), is deployed on the rooftop of a bus to improve the link quality and reduce the associated HO overhead via group mobility. However, at moderate to high speeds, the on-board UEs can still suffer from frequent HOs due to the MRN failing to HO to a new DBS using the legacy downlink measurement-based HO (DL-HO) method. As a consequence, the connection towards all associated mobile users will be lost which poses tight reliability requirements on the backhaul link to avoid becoming a single point of failure (SPoF). In order to improve the reliability during group handover, in this work, we propose an uplink reference signal (UL RS) based HO procedure (coined as UL-HO) for the MRN which relies on the existing sounding reference signal in long term evolution (LTE) /new radio (NR). In the proposed scheme, and unlike the legacy DL-HO procedure in LTE/NR, the measurement report (MeasReport) transmission is not required between MRN and the DBS, therefore the HO delay can be reduced, decreasing the SPoF chances and thus, uninterrupted services can be provided to on-board UEs. We investigate the gain in terms of HO rate, HO failure rate, ping-pong rate and power consumption (both at the UE and the BS). Performance evaluations demonstrate that the proposed UL-HO scheme outperforms the legacy DL-HO scheme in current cellular networks.

The ever-growing data rate demand from cellular users increases the associated power consumption that directly contributes to the global warming of the environment. Also, achieving high system capacity by increasing the density of the base stations (BSs) increases the number of handovers (HOs) which for moderate-to-high-speed users implies significant signaling traffic overhead. One of the key research objectives of this paper is to identify the different signaling overheads occurring during the HO procedure in current 3GPP cellular networks (e.g. Long Term Evolution (LTE)/ New Radio (NR)) and, among those, which are the main contributors to power consumption. Specifically, we analyze the impact of signaling messages transmitted and received during HO on the power consumption for both the BS and the User Equipment (UE). System-level simulations are performed for a detailed quantitative analysis. Our analysis shows that the transmission of the measurement reports is the largest contributor to air-interface signaling and that its contributed total power consumption is higher than the random access channel (RACH) signaling and the signaling confirming the HO. To eliminate measurement reports and effectively reduce the power consumption associated with the HO in future networks, we propose a HO procedure that exploits uplink (UL) reference signals (RSs), namely the sounding reference signal (SRS), transmitted by UEs. The numerical results show that the proposed SRS-based method reduces the total power consumption during the HO procedure by 30% in comparison to the legacy downlink RS based measurement method in current cellular networks. Also, this method improves the UE battery lifetime by reducing the RS transmissions and measurements significantly, UE transmitted power consumption by 48% and received power consumption by 27%.