Browsing by Author "Tayyab, Muhammad"

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  • Energy-Efficient Mobility for Small-Cell Overlaid Cellular Networks
    (2021) Tayyab, Muhammad
     School of Electrical Engineering | Doctoral dissertation (article-based)
    To satisfy the ever-growing demand for enhanced data rate in future cellular networks, an ultra-densification approach is introduced to shrink the coverage of base stations (BSs) and improve frequency reuse. A gain in system capacity is anticipated by increasing the density of BSs; however this gain is expected to come at the expense of a high number of handovers (HOs), increased HO delays, increased HO failures (HOFs), and a high ping pong (PP) rate, which for moderate-to-high-speed users implies significant signaling overhead traffic resulting in an unsatisfactory user experience.In this thesis, we provide a simulation analysis to study the performance of current 3GPP cellular networks (e.g. Long Term Evolution (LTE)/ New Radio (NR)) with a legacy downlink handover (DL-HO) procedure by taking into account the cell sizes and user mobility. In particular, the potential problems of HOFs are highlighted especially in the case of ultra-densification. Moreover, this work derives a power consumption model and addresses the signaling overhead and power consumption that results from the transmission and reception of HO signaling both at the BS and at the User Equipment (UE) during DL-HO. The DL-HO analysis exhibits that the measurement report (MeasReport) transmission is the largest contributor to air-interface signaling and its power consumption is higher than random access channel (RACH) signaling and the signaling confirming the HO. In order to cope with the problem of high MeasReport signaling and effectively reduce the associated power consumption, a handover that is based on the uplink (UL) reference signal, referred to here as UL-HO, is proposed that exploits uplink (UL) reference signals (RSs), namely the sounding reference signal (SRS), transmitted by UEs. The performance of UL-HO is compared with DL-HO to quantify the potential benefits in terms of reduction in HO rates, HOFs, PPs, UE, and BS power consumption. After this, we then highlight another major challenge of today's cellular networks which is the increasing demand for voice and data services in fast-moving public transportation (i.e. bus, tram, train, subway, etc.), especially in urban areas. To this end, we investigate the utilization of mobile relay nodes (MRNs) in vehicles to facilitate efficient group HO and reduce the energy consumption for all on-board UEs. In this thesis, we also address the DL-HO performance of an MRN to identify the causes of MRN HOFs towards the donor BS (DBS) that are more critical for the on-board UEs.To sort out the problem of MRN HOF to the DBS, we extend the applicability of the UL-HO scheme for the MRN to eliminate the MeasReprot signaling during MRN HO to the DBS. Therefore the HO delay can be reduced, decreasing the chances of single point of failure (SPoF) and thus, uninterrupted services can be provided to on-board UEs. Moreover, we analyze the impact of on-board UE cluster size on HO performance and the associated power consumption.
  • Handover Performance and Power Consumption Analysis of LTE Mobile Relays
    (2020-11) Tayyab, Muhammad; Koudouridis, G. P.; Gelabert, X.; Jantti, R.
     A4 Artikkeli konferenssijulkaisussa
    Mobile relay node (MRN) is one of the cheaper options for reliable communication when users are moving by public transport (i.e. bus, tram, train, subway, etc.), especially in urban areas. Critically, MRNs need to maintain a backhaul connection with the fixed infrastructure via a donor eNB, (DeNB). If the MRN fails to successfully handover (HO) from one DeNB to another, it will create a single point of failure, i.e. the connection of all UEs connected to MRN will be dropped. In this paper, we address the HO performance of a MRN including a power consumption analysis thereof. We investigate the potential gains in terms of HO rate, HO failure ratio (HOFR), ping-pong (PP) rate and power consumption (both at UE and eNB) when a MRN is deployed on a bus traveling along the cell edges of surrounding macro BSs. We also look over the MRN HO failure cases to identify the causes of HO failures that are more critical for the UEs onboard. Numerical results indicate that deploying a MRN on the roof-top of a bus improves the HO rates 15%, HOFR 8%, PP rate 17%, UE power consumption 21%, and eNB power consumption 14% on average for all simulated cases. We have also established that UL transmission errors are the most dominant causes of turning MRN to a single point of failure during a HO.
  • Receiver Power Consumption during Handover in LTE
    (2019) Tayyab, Muhammad; Koudouridis, G. P.; Gelaberr, X.; Jäntti, Riku
     A4 Artikkeli konferenssijulkaisussa
    Recently, handover (HO) has gathered huge interest as the cellular mobile users desire for better quality of service (QoS) and continuous connection has increased. The power consumption is increasing day by day due to growing data rate demands of the users that directly impacts operators' operational expenditures (OPEX) and, not least, the environment by increased CO2 emissions. In this paper, we address the power consumption caused by the air-interface signaling messages received at both the eNB and User Equipment (UE) during HO in a Long Term Evolution (LTE) cellular network. A receiver power consumption model is presented with a detailed quantitative analysis using system level simulations. Numerical results indicate that the largest contributor to received air-interface HO signaling overhead is the reception of the measurement report by the eNB.
  • A Simulation Study on Handover in LTE Ultra-Small Cell Deployment: A 5G Challenge
    (2019) Tayyab, Muhammad; Gelabert, Xavier; Jäntti, Riku
     A4 Artikkeli konferenssijulkaisussa
    Future cellular networks need to support data hungry applications with enhanced data rates possibly via cell densification (ultra-small cells). The key objective of this work is to study the performance of a cellular network by taking into account the user mobility when LTE ultra-small cell network is deployed. Handover (HO) issues are analyzed considering various cell sizes, user speeds, and HO optimization related parameters. This study is very helpful to realize the problem of HO in 5G standalone network deployment as it shows the impact of LTE ultra-small cell deployment on the HO performance. A system level simulator is used to perform simulation and the results show that, as expected, the ultra-densification results in an increased number of HOs. Also, increasing the offset values have a significant impact on the HO reliability while changing the Time to Trigger (TTT) values has a less-significant impact.
  • A Survey on Handover Management: From LTE to NR
    (2019) Tayyab, Muhammad; Gelabert, Xavier; Jäntti, Riku
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    To satisfy the high data demands in future cellular networks, an ultra-densification approach is introduced to shrink the coverage of base station (BS) and improve the frequency reuse. The gain in capacity is expected but at the expense of increased interference, frequent handovers (HOs), increased HO failure (HOF) rates, increased HO delays, increase in ping pong rate, high energy consumption, increased overheads due to frequent HO, high packet losses and bad user experience mostly in high-speed user equipment (UE) scenarios. This paper presents the general concepts of radio access mobility in cellular networks with possible challenges and current research focus. In this article, we provide an overview of HO management in long-term evolution (LTE) and 5G new radio (NR) to highlight the main differences in basic HO scenarios. A detailed literature survey on radio access mobility in LTE, heterogeneous networks (HetNets) and NR is provided. In addition, this paper suggests HO management challenges and enhancing techniques with a discussion on the key points that need to be considered in formulating an efficient HO scheme.
  • Uplink Reference Signal Based Handover with Mobile Relay Node Assisted User Clustering
    (2020-12) Tayyab, Muhammad; Koudouridis, G. P.; Gelabert, X.; Jantti, R.
     A4 Artikkeli konferenssijulkaisussa
    In today's cellular networks, an increasing number of connected devices on-board in fast-moving vehicles would require more efficient handover (HO) procedures. To this end, we investigate the utilization of mobile relay nodes (MRNs) in vehicles to facilitate efficient HO and HO-related power consumption reductions for all on-board user equipments (UEs). In particular, the potential gains in terms of HO rate, HO failure ratio (HOFR), ping-pong (PP) rate, and total power consumption are studied for different UE cluster sizes. To eliminate the measurement power-consuming procedure, uplink (UL) reference signals (RS) transmitted by UEs are exploited. Four different case scenarios are simulated utilizing both the DL and UL RS based HO procedure, with and without deploying MRNs on the buses traveling along the cell edges of surrounding macro BSs. Simulation results indicate that the UL RS based HO procedure can improve HO performance significantly because it reduces the air-interface signaling messages, namely the measurement report (MeasReport) transmission and reception. Also, in terms of power consumption, deploying MRNs is a more attractive solution with substantial power reduction for onboard UEs of higher cluster size.
  • Uplink Reference Signals for Energy-Efficient Handover
    (2020) Tayyab, Muhammad; Koudouridis, George P.; Gelabert, Xavier; Jäntti, Riku
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    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%.
  • Uplink Reference Signals for Power-Efficient Handover in Cellular Networks with Mobile Relays
    (2021) Tayyab, Muhammad; Koudouridis, George P.; Gelabert, Xavier; Jantti, Riku
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    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.