1 Introduction

The twenty-firstcentury isexperiencing tremendous growth of data and Internet services[1]to meet the significant rise in socioeconomic developmental needs[2]and user demand.Smart devices demanding cellular wireless connectivity are increasing exponentially and have crossed the current world population[3].Wireless networks are also enhancing its capability to handle more devices,users and larger data traffic.

Advancement in high-speed railway(HSR)transportation has resulted in more passengers transiting through railway networks[4].HSR is currently becoming more and more popular,and this mode of public transportation is preferred in several countries due to its speed,safety,energy efficiency and larger passenger handling capacity[5–9].The demand for high-quality video,voice and data over broadband wireless communication in an HSR environment has thrown open various limitations of cellular wireless technology.

该团各个基层单位本着“加强文化交流融合，促进各民族文化发展繁荣”的精神，积极组织结亲干部和少数民族结亲户，共同学习了国家颁布的《宗教事务管理条例》，以及民族团结先进事迹，畅谈了维护祖国统一，加强民族团结，维护社会稳定的重要意义。向少数民族职工群众发放了民族团结教育书刊和新疆历史读本。还向少数民族职工群众赠送了民族团结主题书法作品。

The LTE-Advanced standardization was through 3GPP release 10 version of specification has introduced longterm evolution-advanced(LTE-Advanced)[10,11]which provides better bandwidth,higher efficiency and enhanced intercell interference coordination(eICIC).The data rates wereenhancedto1 Gbps(downlink,DL)/500 Mbps(uplink,UL)for low mobility application and 100 Mbps(DL)/50 Mbps(UL)for high mobility application[12]along with an increase in requirements of peak spectral efficiency to 30 bps/Hz (DL)/15 bps/Hz(UL). This enhancement has put forward significant implementation challenges to HSR system designers[13].

Figure 1 shows the architecture of LTE-Advanced with two distinct components:(1)evolved universal terrestrial radio access network(E-UTRAN)and(2)evolved packet core(EPC)[14].The EPC consists of mobility management entity(MME),serving gateways(S-GW)and packet data network gateway(P-GW)which provide services like signaling,handover,security,whereas the E-UTRAN incorporatesmultiple interconnected evolved NodeBs(eNBs)[15].These eNBs are interconnected using X2 interface,whereas they are connected to EPC through S1 interface.

A highly mobile HSR scenario involves long narrow strips,bridges,viaducts and directional antennas with reduced cell coverage.The deployment of wireless networks for such a scenario is challenging due to increased handover(HO)frequency resulting in significant performance degradation[16].To make the condition worse,the implementation of HO in LTE-Advanced is a hard HO which requires breaking the radio link with source before connecting with target eNB.Frequent HOs in such traditional networks would increase the network load and power consumption of user equipment(UE),thereby affecting the overall quality of services(QoS)[17].Group HO,frequent HO at short time intervals,Doppler frequency shift,penetration path loss and fading in propagation characteristics due to shielded carriage of trains,viaduct,hilly terrain and tunnel[18,19]are major concern for system designers in a high-speed scenario.

In order to improve communication in a long-distance HSR scenario,leaky coaxial cable(LCX)-based radio communication system[20]was introduced to provide better bandwidth and efficient frequency reuse.The need for repeaters to compensate for transmission losses,high maintenance cost and large deployment cost limits the acceptance of LCX system for high-speed train-ground information transmission.Radio-over-fiber(RoF)-based system [21,22]with remote antennal units(RAU)deployed along railway lines to transmit data wirelessly to the onboard unit is another promising technology for HSR communication.Support for higher bandwidth,cost-effectiveness,reduced power consumption due to linear radiated antenna,and reduced HO are the major features of RoF technology[23,24].

允许孩子犯每个年龄可以犯的错误，这是我在临床中慢慢总结出来的，犯这种错误的结果往往是好的。那些看起来很傻的错误是孩子成长的资源，而不是障碍。

Introduction of wireless local area networks(WLAN)to complement satellite communication in HSR scenario by M.Han et al.[25]was another significant work to overcome the limitation of HO and coverage.However,the bandwidth limitation,inherent delay in satellite-based system,blind spots,initial investment cost and requirement of line of sight have confined the scalability of this model in HSR.

A seamless HO scheme based on dual-link architecture was proposed by Lin Tian et al.[26].The system with two antennas in the front and rear takes advantage of bi-casting and dual antennas to implement soft HO with reduced overhead and latency.

3GPP TR-36.836 has introduced mobile relays as base station[27]to circumvent the connectivity issues in HSR.These multi-RAT relays would provide wireless connectivity and services to onboard UE.Such a shift in connectivity maintenance from portable mobile devices to relays has significantly reduced the UE power consumption[28],signal storming or group HO[29],Doppler frequency shift and penetration path loss[30].Though mobile relays have improved the performance between UE and eNB,the HO issues limiting the performance and reliability persist.Introducing relays as an intermediate node has only shifted the HO issues from UE to relay nodes.Increased load on these nodes has further deteriorated the packet latency,QoS,frequent HO and resilience capability of the overall system.

An effective two-link architecture based on distributed antenna system(DAS)and mobile relay was introduced by Liu et al.[31].Onboard devices in this system are connected to train relay nodes which are further interfaced to remote central station using multiple RAUs based on RoF technology.However,the proposed system has neglected the period of HO,which significantly affects the performance in real networks[32].An enhanced HO scheme[33]was proposed using special control mobile relays(cMRs)equipped in front of a train and several mobile relays were distributed across the train.This scheme also proposed an enhanced measurement procedure to reduce the duration of cMR signal measurement based on the direction of movement.The cMR-based scheme is effective in reducing the signaling overhead and HO interruption time,whereas failure of HO at cMR would inherently affect the overall connectivity of the system.

As soon as the DMR receives the RRC reconfiguration message,the device detaches from S-DeNB.Further,it uses the configuration details to synchronize with the T-DeNB by sending contention-free-based random access preamble message.At the same time,the S-DeNB forwards the buffered data and status transfer command to T-DeNB.Once successfully synchronized,the DMR sends a tracking area update to MME along with RRC connection configuration complete message.This will establish the uplink communication between DMR and T-DeNB.

In this paper,in order to overcome the limitations of existing systems,we introduce a novel HO scheme to enhance the QoS in an HSR communication environment by proposing the concept of torch nodes(TNs)and mobility-based adaptive measurement aggregation(AMA)to improve the existing HO mechanism.By introducing this approach through a distributed mobile relay(DMR)-based architecture,we also address the resilience capability in HSR systems.

The rest of the paper is organized as follows.In the next section,we present our proposed solution,describing the system architecture and operational procedures.Various stages of the proposed HO scheme are elaborated in Sect.3.Section 4 details the AMA mechanism.Implementation of simulation model and performance analysis will be carried out in Sect.5.Finally,in Sect.6 we summarize our results and present our conclusions.

2 Proposed system

Considering the rapid proliferation of smart devices among travelers and passenger accommodation capacity in highspeed trains,an onboard distributed relay mechanism is proposed for HSR as shown in Fig.2.The DMR nodes mounted on trains will act as relay nodes and equip the system to be resilient toward single-point failures.DMRs are further interfaced to the backhaul using WLAN Link(LTE-LAA)or LTE-Advanced.

Torch nodes(TNs)equipped in the front(TN-1)and rear(TN-2)of the train act as measurement nodes to provide prior information of donor eNBs(DeNBs)in a highly mobile environment.TNs report the measurement values to the onboard processing unit(OPU),which further uses this information for HO decision of respective DMRs.A global positioning system(GPS)integrated inertial measurement unit(IMU)is used to determine the speed of train.This unit is interfaced to OPU.

The OPU carries out two independent functionalities.The load balancer module of OPU effectively distributes the signaling load across multiple DMRs,whereas the measurement engine processes measurement details from TNs and DMRs based on speed of train and generates DMR-specific measurement report to be forwarded to respective DeNBs.OPU is connected with nodes using optical medium for faster data transfer and incorporates interface modules for TNs,DMRs,APs and IMU.Based on load sharing and network topology requirements,the OPU can be specific for each DMR node or a group of DMRs can share an OPU along with IMU.The block diagram of OPU is depicted in Fig.3.

Based on the load being handled by respective DMRs,the OPU will dynamically link UEs to respective DMRs,thereby curbing the issue of overload.The onboard UEs are interfaced to DMRs via OPU through WLAN access points(APs)deployed across carriages.

When the train is at a higher speed,the measurement details of TNs will provide prior information of upcoming DeNBs to which HO needs to be initiated.Leveraging this information will provide sufficient lead time for DMRs in initiating and executing HO in a highly mobile HSR environment.At lower speeds or when the train is stationary,the signal strength information from respective DMR will be given preference while estimating measurement reports.

Based on velocity readings from IMU,the OPU provides a mobility-based adaptive measurement aggregation mechanism of values collected by TNs and DMRs to generate periodic-or event-based measurement report.This adaptive reporting strategy based on speed of train will facilitate DMRs to effectively speculate the upcoming DeNBs and initiate the HO early.

3 Stages of proposed HO scheme

The handover scheme proposed has the following three stages:(1)HO preparation,(2)HO execution and(3)HO completion.

3.1 HO preparation stage

LTE-Advanced adopts a UE assistance-based networkcontrolled hard HO procedure.In the context of HSR,the relay nodes deployed in train will take over the connectivity aspect from UEs,by acting as enablers between UE and DeNB as shown in Fig.4.The DMRs will start its measurement procedure after receiving a measurement control command from the serving DeNB(S-DeNB).The DMRs will forward this measurement control command to OPU for configuring the TNs and IMU for initiating measurement in those nodes.

The measurement of DMRs,TNs and IMU will be forwarded as per pre-configured interval to the measurement engine module of OPU.This module implements an AMA mechanism based on the speed of train.Priority toward DMR measurement will be given at a time wherein the train is stationary or at lower speed.When the train attains moderate or higher speeds,AMA mechanism will give preference to readings from TNs,thereby facilitating an early reporting mechanism.This willprovide E-UTRAN and EPC with sufficient lead time in completing the HO procedures.

In contrast to the conventional approach of taking measurement parameters from a single MRN,it is essential to adapt to the varied mobility conditions and estimate the parameter values dynamically.Though various approaches can be applied to generate events as mentioned in Eq.(4),a weighted average mechanism to aggregate the S-DeNB and T-DeNB measurements across front TN(TN-1),rear TN(TN-2)and DMR is adopted here as shown in Eq.(6).The weights are determined on the basis of mobility conditions of HST.

Based on the LTE-Advanced radio resource control(RRC)specification,A3,A4 and A5 are the three event types defined to trigger the measurement reports.

在改革的思考中，宏观层面的人才培养目标设定是首要的，当下新闻传播教育的人才培养目标应该是“大传播”。所谓大传播指的是突破传统新闻传播人才培养是为传统媒体培养人才的既有设定，以更大格局、更广视野和更新技能，培养适应社会需求的具备扎实传统传媒素养，又具备互联网思维、了解智能传播技能、具备网络传播创新能力的人才，这个人才不仅仅是新闻传播人才，更是社会传播人才，是能够适应传统媒体和新兴媒体融合，适应各社会组织（包括传统媒体）各类传播所需要的广义的传播人才。

3.2 Handover execution stage

提起蒋海峰，紫云还真有些不舒服：“老伯，你再这样说，我就生气了。衣服我收下，今后就不要为我乱花钱了。”

3.3 Handover completion stage

Based on the tracking update message from DMR,the MME updates the DMR location and replies with a tracking area update accept command to the DMR.The T-DeNB will also send a path switch request message to inform the MME that the S-DeNB of the DMR has changed and the routing path needs to be modified.Then,the MME issues a user plane update request command to S-GW to switch the routing path.A successful update will result in S-GW replying with a user plane update response command to the MME and MME further notifying T-DeNB using a path switch request acknowledgement(ACK).This would enable the T-DeNB and S-GW to forward data to DMR along the new path.Further,T-DeNB sends a context release message to request S-DeNB in releasing the context of DMR.This will complete the HO process.HO execution and completion stages are depicted in Fig.5.

As observed,the proposed methodology will only modify the HO preparation stage of LTE-Advanced for reducing latency and improving the HO failure rates.Due to this strategy,the proposed mechanism can be easily adopted in the existing implementation with little or no modification in the mobile relay-based infrastructure setup.By adopting an AMA-based HO foreseeing approach,the system adapts itself to the dynamic nature of HSR environment.

4 AMA mechanism

The adaptive measurement aggregation is a mechanism with which the DMR decides the measurement parameters to be reported to the S-DeNB.The decision in this regard will give due consideration to the mobility aspects of train and implements a predictive approach at higher speeds by correlating the measurement values of TNs along with DMR measurements.

4.1 Measurement parameters

According to 3GPP,reference signal received power(RSRP)and reference signal received quality(RSRQ)are the major DMR-related values which need to be considered as measurement parameters in LTE-Advanced.

The RSRP measurement,RP,is the linear average of the power contributions by cell-specific resource elements that carry reference signals within the measurement frequency bandwidth as shown in Eq.(1).For absolute RSRP,the requirement would vary from±6 to±11 dB,whereas a relative measurement requirement varies from±2 to±3 dB for intra-frequency and widens to±6 dB for interfrequency measurement.The RSRP measurements are further mapped to integer numbers,whose value ranges from 0 to 97 before they are included in the RRC messages.

where PTXis the transmission power of DeNB,TLSis the path loss of the signal between DeNB and DMR and f(μ,σ)is the shadow fading which usually follows Gaussian distribution with mean μ being zero and variance σ2.For illustration,the path loss in dB[34]for a line of sight DeNB-DMR to model the propagation environment is as follows:

(1) Movement of HST at a lower speed(SLow)

采用SPSS 19.0统计学软件对数据进行处理，计量资料以“±s”表示，采用t检验，以P＜0.05为差异有统计学意义。

where(xt,yt)describes the position of DMR at time t and(xi,yi)defines the location of DeNBi.

目的基因Flagellin-3M2e由苏州金唯智生物科技有限公司合成，并构建于表达载体pET28a相应位置（EcoRI-XhoI），鼠伤寒沙门菌鞭毛蛋白基因为FljB（GenBank：JQ965932.1）。

ICP-OES工作条件：射频功率为1 300 W，等离子气体(氩气)流量为1.5 L/min，辅助气体流量为0.20 L/min，雾化气体流量为0.5 L/min，曝光时间为15 s。各元素光谱谱线的选择：镉228.800 nm、铅220.353 nm、汞194.168 nm、铬267.716 nm、砷188.979 nm，锑206.836 nm。

RSRQ is a cell-specific signal quality metric,expressed in dB,which is defined as NRBRP/RS,where NRBis the number of resource blocks over which the measurement is conducted,and RSis the RSSIE-UTRAparameter which represents the entire received power from all interference and thermal noise source.In LTE-Advanced,the RSRQ measurement is also mapped from dBm to an integer number ranging from 0 to 34.

Since RSRQ measurement combines signal strength and interference levels,this parameter is significant in assisting the mobility management in E-UTRAN.Mathematically,as the RSRQ measurement is proportional to the RSRP and signal strength,the current implementation considers RSRQ as the key measurement parameter along with mobility to implement the AMA mechanism.This optimizes and provides a fast,simplified and efficient aggregation and reporting mechanism.

In order to implement an effective HO mechanism for HSR,parameters with regard to mobility and service quality should also be considered while generating measurement reports.Such multi-criteria approach will provide an effective solution to enhance HO efficiency and increase resource utilization.In the current effort,the implementation consideration with regard to service quality is beyond the scope and will be addressed through a separate paper.

4.2 AMA based on HSR mobility

In order to exemplify the above,we denote by RQ1-FTN,RQ1-RTNand RQ1-DMRthe RSRQ measurements as observed by front TN,rear TN and DMR for S-DeNB,respectively,and by RQ2-FTN,RQ2-RTNand RQ2-DMRthe counterparts as reported for T-DeNB.A parameter pattern,RQ1-RTN≥RQ1-DMR≥RQ1-FTN,being reported for S-DeNB node observed for TTT duration,can be inferred to be a condition wherein the train is leaving the vicinity of a cell.Meanwhile,RQ2-FTN≥RQ2-DMRfor the T-DeNB node indicates that the train is entering the cell.

Measurement reporting in LTE-Advanced can be configured as periodic,event triggered or event-triggered periodic.Triggering events as de fined by 3GPP for monitoring the quality of serving cell and target cell are given in Table 1 and are calculated based on the entering conditions as elaborated in TS 36.331.

The triggering events as defined for LTE-Advanced are more suitable for low mobility scenarios,whereas their applicability in a highly mobility environment like HSR requires considerable modification.Along with the measurement parameters as observed from target and serving cells,it is indispensable that the system should also consider the velocity of high-speed train(HST)to dynamically adapt the triggering events in a highly mobile environment.Considering various mobility scenarios in HSR,the variation in event triggering based on HST speed,S,is identified as follows:

where FRis the frequency(Hz);dBPis the breakpoint distance;the distance d between DMR and DeNB is estimated as

没有回音。那个人动了，灯光飘移，一团人影渐渐清晰，是驼子。驼子拎着沉甸甸木桶，坠得半边身子歪歪趔趔，仿佛乌龟匐匍在地上，往前爬。

When stationary or at a lower speed than a threshold level(for example 200 km/h),the event triggering is considered based on the standard LTE-Advanced mechanism as detailed in Table 1.

采用木棉花80克、金樱花60克、麦冬60克、陈皮30克，混合均匀，采用中药粉碎机粉碎后过80目标准筛，每日1次，家禽每次2～4克，家畜每次5～6克，连续使用3～5日，用于治疗畜禽咽喉肿痛、咳嗽、失音、久咳不止、痈疽疮疖、呼吸道感染、高热死只等症状，有效率高达98.89%。也可采用木棉花木棉花80克、茵陈40克、黄连30克、甘草15克，粉碎过60目标准筛，混匀，每只鸡喂1克，拌料，用于畜禽咽喉肿痛、口腔溃烂、痈疖肿毒、不食无力、目呆，有效率高达97.34%。

In such a scenario,it is ideal to have the HO initiated at time THS-initiate,which is ΔT duration prior to the time THO-initiateas defined by the 3GPP specification.This would provide sufficient lead time in initiating the HO procedure in a high mobility HSR scenario.Moreover,the proposed method envisages significant reduction in the time for DMR to reenter(TReentry)and the time to re-establish the corresponding DMR connection during call drop

基于大数据方法可以了解市场上对六大战略性新兴产业人才紧缺岗位的真实情况。与此同时，可以使用该方法进行海淀区战略新兴产业紧缺人才需求目录的编制，作为海淀区战略新兴产业紧缺人才指导方案的基础。可以基于上述方法进行职业教育的供给侧改革研究。

At an increased mobility scenario wherein the value of SHighincreases beyond a threshold level(for example,200 km/h),it is essential for relay nodes to foresee the parameters of upcoming DeNB’s and correlate the data with the measurements of DeNB’s which are left behind to have an effective HO decision.Considering the assumption that the DeNBs deployed in an HSR is directional and continuous,the TNs deployed in the front and back of the train provide sufficient visibility to the futuristic and past parametric information.

In a realistic LTE-Advanced scenario,the network will combine multiple radio access technologies(RATs),frequencies and cell sizes for efficient deployment[35]and the UEs carry out parameter measurement for multi-RAT intra-/interfrequency mobility.For elaboration simplicity,we consider interfrequency E-UTRAN HO process in the current context,whereas the proposed system with minimal enhancement can also be employed for inter-RAT HO mechanism.

Considering this aspect,the HO event generated at HO initiate time for DMR-TN,THS-initiate,as shown in Eq.(4)provides a realistic and accurate HO decision-making scenario,in comparison with HO initiate time,THO-initiate,as recommended by 3GPP standard where event triggering occurs whenever the T-DeNB is better than the S-DeNB.

(2) Movement of HST at a higher speed(SHigh)

The OPU/DMR can be configured for periodic-or event-based reporting as per the measurement control command provided.Periodic configuration ensures that the OPU/DMR will report the measured signal strength values of target DeNB(T-DeNB)to S-DeNB in a fixed report interval(RI).S-DeNB performs HO when the signal quality of T-DeNB is above a threshold for continuous k reports,where the value of k is defined by cellular operator.During event-based reporting,the measurement control command will carry the appropriate event types and time-to-trigger(TTT)values.

where RQ-MNis the aggregate RSRQ measurement to be reported for event triggering,and Wi(i=1,2,3)is the significance parameter.

5 Simulation and performance analysis

5.1 Implementation of simulation model

The proposed model was designed and implemented on an object-oriented discrete event simulator[36]extended with an LTE-Advanced package[37].A representative illustration of the simulation environment on Omnet++involving a train traveling in an HSR environment between two stations is presented in Fig.6a.The simulated infrastructure consists of DeNBs,Routers,P-GW and Server.The DeNBs uses omnidirectional anisotropic antennas and are interconnected through X2 interface.

As shown in Fig.6b,the implementation of onboard train network involves front torch nodes(TN-1),rear torch nodes(TN-2),two distributed mobile relay nodes(DMR-1 and DMR-2),onboard processing units(OPU1 and OPU2)and train networks(TNET1 and TNET2).Figure 6c shows the implementation of TNET which establishes LAN connectivity across multiple coaches.TNETs are further interfaced to the UEs through wireless APs as shown in Fig.6d.IMU unit was implemented as a module in OPU,and implementation of load balancer was simplified to handle individual DMR.Table 2 summarizes the simulation parameters.The simulation uses ITU Urban Macro[38]for path loss and Jakes fading model[39].

自实行“科学高效的变化环节调度管理体系”以来，科队两级积极应对变化环节的熟练程度和响应速度均有明显提升，主要体现在全矿井变化环节处置时间和变化环节次数与去年同比分别下降21.83%和36.56%；而且没有出现因处置变化环节而引发的安全事故，保证了矿井的安全稳产，提升了矿井整体安全管理水平。

5.2 Simulation results

We validated the model and carried out simulations to assessthe performance ofthe proposed system in improving the HO latency and HO failure probability.Performance of the proposed model is compared with that of the single link mobile wireless relay node(MRN).The MRN uses only single wireless link to connect to DeNB,in comparison with the proposed DMR-TN system,which involves TNs for efficient estimation of measurements in a mobile environment,multiple antenna scheme to enhance the load distribution,enhanced monitoring using AMA and efficient message handling capabilities.

(1) HO latency

The HO latency is computed from the time when the SDeNB begins its HO to the time when the connection is established for data transmission to T-DeNB.The HO latency THO-latencyis estimated as follows:

where the THOis the time taken to handover;PSHOis the probability estimate value for calculating the average HO latency,and is considered based on[26,40].The probability estimate of successful handover for MRN scheme,PSHO-MRN,is derived as 0.97,and the probability estimate of successful handover for DMR-TN,PSHO-DMR-TN,is 0.999.The HO in the proposed approach significantly reduces the TReentryand TReconnectand increases the probability of success at each stage.The onboard measurement analyzer and multi-antenna with load balancer have reduced the HO latency in comparison with the existing systems.

制定体育与旅游产业融合发展规划，贯彻落实国家和陕西有关体育与旅游产业融合发展的纲领性文件精神。要深入调查陕西体育与旅游产业融合的资源状况、技术条件和市场发展特征。对如何整合陕西旅游与体育文化资源及打造资源共享、市场共用、优势互补、互利共赢的文化旅游项目等，要进行针对性和可操作性研究与设计。借助“一路一带”的历史机遇和经济转型发展的需求，打破原有的思想禁锢，厘清体育旅游发展思路，推动体育文化旅游企业产权改革，打造一批有影响力的体育文化旅游企业和品牌。同时，各级政府要提供宽松的外部环境和政策支持，吸引更多的投资主体加入体育文化旅游项目的开发，形成多元化的市场竞争者和经营者。

Figure 7 illustrates the HO latency of the simulation run wherein the proposed DMR-TN scheme outperforms the single-antenna-based MRN scheme.Although users with high mobility are expected to experience an increase in HO latency,the HO latency in the proposed solution is comparatively smaller and increases gradually as the speed increases.

总而言之，写作是一项综合技能，离不开遣词造句、谋篇布局，每个环节都很重要。英语写作能力的提高也不可能一蹴而就，是一个长期积累、逐步提高的过程，需要平时大量的练习。只要我们循序渐进、持之以恒，我们的英语写作水平就一定会不断提高。

(2) HO failure probability

Once HO is triggered,any subsequent degradation of T-DeNB signal strength below a threshold level will result in connection losses and an HO failure will occur if this interruption exceeds the predefined delay limit.In the proposed scheme,the measurement report from TNs provides a further assurance in estimating the T-DeNB,resulting in significant reduction in HO failures.Figure 8 shows that the HO failure probability of the simulated model is on an average of 0.01,whereas the value is near to 0.05 for MRN scheme.

(3) Communication interruption probability

The probability of communication interruption(CI)during an HO procedure provides a detailed overview of the efficacy of a model.For a system to provide improved QoS and seamless user experience,the communication interruption probability needs to be smaller.In the simulation model,we plotted the CI probability as a function of HO locations within a range of 1100–1500-m region in the overlap area.In comparison with the single-antenna MRN model,the interruption probability for the proposed DMRTN scheme is less than 0.1 for the majority of overlap area,as shown in the simulation results given in Fig.9.The involvement of torch nodes and adaptive measurement aggregation mechanism module has significantly contributed in decreasing the failure probability as the distance increases.

6 Conclusion and future work

This paper presents the details of a novel scheme to improve QoS in a high-speed railway communication system.The proposed scheme involves the following key features:(1)torch nodes to effectively forecast target DeNBs,(2)adaptive measurement aggregation based on mobility and(3)distributed mobile relays with load balancer for efficient resource utilization.The proposed scheme was simulated using Omnet++tool,and the performance is analyzed in terms of handover latency,handover failure probability and communication interruption probability.The preliminary analysis shows that the DMRTN scheme outperforms the single-antenna scheme and provides better performance with reduced handover failure and communication interruption probability.The proposed scheme can be easily implemented in high-speed railways with reduced implementation overhead.In the future work,we plan to carryout further optimization by considering service-based parameters(e.g.,voice,video,and data)to enhance handover efficiency and resource optimization.

Acknowledgements The authors would like to thank Centre for Development of Advanced Computing(C-DAC),Hyderabad,and Jawaharlal Nehru Technological University,Hyderabad,in facilitating this research work.

Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License(http://creativecommons.org/licenses/by/4.0/),which permits unrestricted use,distribution,and reproduction in any medium,provided you give appropriate credit to the original author(s)and the source,provide a link to the Creative Commons license,and indicate if changes were made.

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