WO2016095748A1 - 一种用于可见光通信异构组网中的垂直切换方法 - Google Patents

一种用于可见光通信异构组网中的垂直切换方法 Download PDF

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WO2016095748A1
WO2016095748A1 PCT/CN2015/097020 CN2015097020W WO2016095748A1 WO 2016095748 A1 WO2016095748 A1 WO 2016095748A1 CN 2015097020 W CN2015097020 W CN 2015097020W WO 2016095748 A1 WO2016095748 A1 WO 2016095748A1
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vlc
algorithm
vertical
visible light
ivho
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PCT/CN2015/097020
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French (fr)
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田辉
张平
梁舒飞
范博
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北京邮电大学
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
    • H04B10/114—Indoor or close-range type systems
    • H04B10/116—Visible light communication

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  • the present application relates to the field of wireless communication technologies, and in particular, to a vertical handover method for heterogeneous networking in visible light communication.
  • visible light communication is an emerging wireless communication technology developed on the basis of white light emitting diode (LED) technology.
  • LED white light emitting diode
  • the visible light signal may be weakened in various cases to the extent that the MT (mobile terminal) cannot communicate normally.
  • the quality of communication avoids the interruption of data transmission, and the vertical switching between visible light and other wireless access technologies has become an indispensable measure in the convergence of heterogeneous networks for visible light communication.
  • the technical problem to be solved by the present application is how to detect different network link data during the operation of the visible light communication system, collect relevant system parameters, and process them, thereby using the vertical handover decision algorithm to improve visible light communication.
  • the present application proposes a vertical handover method for heterogeneous networking in visible light communication, which includes the following specific steps:
  • S1 the mobile terminal receives data on the VLC channel after the system starts running
  • S2 The system detects whether the received data is interrupted in real time
  • S4 The system predicts the relevant parameters of the current interrupt according to the pre-interruption condition, and performs the performance of the IVHO and DVHO algorithms based on the predicted value of the message transmission delay during the current interruption period calculated according to the parameters. Comparison;
  • the mobile terminal detects that the visible channel is in a congested state, and the channels of the remaining radio access networks are in an idle state, and executes a VHO algorithm.
  • the mobile terminal is configured to detect a plurality of different network link data, collect and process characteristic parameters of the related multiple different networks.
  • the characteristic parameters of the multiple different networks include: current received signal strength, bit rate, congestion level, and related information of data currently needed to be transmitted by different networks.
  • the mobile terminal is further configured to detect a current usage status of the network and quality levels of the multiple different network links and compare the quality.
  • step S3 includes:
  • S31 Collecting a current state of the network where the mobile terminal is located and a plurality of different accessible networks parameter;
  • step S5 further includes:
  • S52 The system detects whether the received data is interrupted in real time
  • step S54 If the VLC connection is restored before the end of the camping timer, the mobile terminal will continue the previously interrupted data transmission using the VLC channel, and jump to step S52; if the VLC connection is not restored before the resident timer expires The vertical switch is performed, the connection will be transferred to the cellular network, and after the current packet transmission is completed, it is detected whether the VLC connection is restored.
  • step S54 further includes: if the VLC connection is restored, the data transmission is switched back to the VLC network, and the process proceeds to step S52; if the VLC connection is not restored, the data continues to be transmitted in the cellular network.
  • the dwell time is set to 0 in the IVHO algorithm and is set to the maximum value of the short interrupt duration in the DVHO algorithm.
  • the present application proposes a vertical handover method for heterogeneous networking in visible light communication, which includes the following specific steps:
  • S02 The system detects whether the received data is interrupted in real time
  • S031 The system predicts the relevant parameters of the current interrupt according to the pre-interruption condition, and uses the predicted values of the IVHO and DVHO message transmission delays during the current interruption period calculated according to the parameters to be IVHO and DVHO.
  • the algorithm performs a performance comparison
  • S04 Perform vertical switching according to the determined vertical switching algorithm to be executed.
  • the mobile terminal detects that the visible channel is in a congested state, and the channels of the remaining radio access networks are in an idle state, and executes a VHO algorithm.
  • the mobile terminal is configured to detect a size of data not received when the data transmission is interrupted on the VLC channel, and a plurality of different network link data, collect and process characteristic parameters of the plurality of different networks.
  • the characteristic parameters of the multiple different networks include: current received signal strength, bit rate, congestion level, and related information of data currently needed to be transmitted by different networks.
  • the mobile terminal is further configured to detect a current usage status of the network and quality levels of the multiple different network links and compare the quality.
  • performing vertical switching according to the determined vertical switching algorithm to be executed includes:
  • the method further includes:
  • the mobile terminal will continue the previously interrupted data transmission using the VLC channel.
  • performing vertical switching according to the determined vertical switching algorithm to be executed includes:
  • connection will be transferred to the cellular network.
  • the method further includes: after the data connection is transferred to the cellular network, if the VLC connection is restored, the data transmission is switched back to the VLC network.
  • the dwell time is set to 0 in the IVHO algorithm and is set to the maximum value of the short interrupt duration in the DVHO algorithm.
  • the present application discloses a vertical handover method for a visible light communication heterogeneous networking.
  • the MT compares the quality of different links according to the current network usage status, and according to the actual needs of the current user. Select appropriate indicators to measure the performance of different networks, determine whether you need to switch according to the set VHO algorithm, and finally choose the appropriate target network.
  • the present application can ensure the continuity of the service, improve the QoS, and on the other hand, can make the service request in the entire system uniform. It is of great significance to improve the performance of visible light communication network systems by constructing the architecture of visible light communication heterogeneous networking and researching its mobility management while proposing appropriate vertical switching algorithms, and continuously improving the algorithm.
  • FIG. 1 is a flow chart showing the steps of a vertical switching method for a visible light communication heterogeneous networking in the embodiment of the present application;
  • FIG. 2 is a flowchart showing another step of a vertical switching method in a heterogeneous networking for visible light communication according to an embodiment of the present application
  • FIG. 3 is a flow chart showing the steps of combining two basic VHO algorithms for a vertical handover method in a heterogeneous communication network for visible light communication according to an embodiment of the present application;
  • FIGS. 4(a)-(e) are diagrams showing the comparison between the simulation performance of the vertical switching method for the visible light communication heterogeneous networking and the two basic VHO algorithms in the embodiment of the present application.
  • the present application proposes a vertical switching method for heterogeneous networking of visible light communication.
  • the interruption of visible light connection occurs when the MT moves out of the coverage of the visible light hotspot, and the occlusion of indoor obstacles caused by random motion or random motion of people
  • the main challenge of the vertical handoff algorithm is how to determine what type of interrupt is occurring and whether vertical handoff should be performed.
  • the two intuitive best practices are immediate vertical switching and waiting for VLC connection recovery, wherein the former is called IVHO (Immediate Vertical Handover).
  • IVHO immediate Vertical Handover
  • the algorithm which is called the DVHO (Dwell Vertical Handover) algorithm, does not achieve optimal performance in all cases.
  • the vertical handover method for the visible light communication heterogeneous networking uses the message transmission delay during the interruption as a measure of the performance of the algorithm.
  • the indicator and it is mainly determined by the duration of the interruption, the execution delay of the vertical handover, and the size of the unreceived message.
  • the MT calculates the ratio of the short interruption in the interrupt that has occurred in real time, and uses it as the estimated value of the probability that the next interruption is a short interruption, and at the same time, the estimated value of the probability that the next interruption is a long interruption can be obtained.
  • the transmission delay of the currently unreceived message is D IVHO when the IVHO is executed, and the transmission delay of the currently unreceived message is D DVHO when the DVHO is executed .
  • D IVHO when the IVHO is executed
  • D DVHO when the DVHO is executed .
  • the predicted value of D IVHO can be obtained according to the mean value of each parameter of the actual situation of the system before the occurrence of the interruption.
  • the predicted value of D DVHO takes the expected value of the message transmission delay when DVHO is executed next time. Then, the algorithm compares the predicted values of the two and then performs the better performance of the two basic vertical switching algorithms, so that the optimal delay performance can be achieved in all cases.
  • the present application can ensure continuity of services in a visible light communication heterogeneous network, improve QoS (quality of service), and can evenize service requests in the entire system, and improve the visible light communication network system. Performance is significant.
  • the present application proposes a vertical handover method for heterogeneous networking in visible light communication, which includes the following specific steps:
  • Step S1 After the system starts running, the mobile terminal receives data on the VLC channel.
  • the mobile terminal is configured to detect data of multiple different network links, collect and process characteristic parameters of multiple different networks, and use the same in a vertical handover decision algorithm, and the characteristics of multiple different networks.
  • the number includes: the current received signal strength, bit rate, congestion level, and related information of the data currently needed to be transmitted by different networks.
  • the mobile terminal is further configured to detect a current network usage status and a quality level of the multiple different network links, and compare, at a time when the vertical handover needs to be performed, determine whether the handover is required according to the set VHO algorithm, and Finally choose the right target network.
  • Step S2 The system detects in real time whether the received data is interrupted.
  • Step S3 When an interrupt occurs, the vertical switching decision process is triggered and determines the vertical switching that should be performed, ie, which type of vertical switching should be performed in the current situation.
  • step S3 includes:
  • Step S31 Collecting the state and parameters of the network where the current mobile terminal is located and a plurality of different accessible networks.
  • Step S32 analyzing and determining the searched state and parameters, and performing handover. That is, since the correlation parameter of the VLC network changes abruptly when the link between the optical signal and the MT is blocked, the intensity of the visible light signal received by the MT is generally used as a criterion for the handover trigger. Specifically, the following actual conditions can trigger the VHO between the VLC network and other radio access networks: the MT is temporarily away from the coverage of the VLC hotspot, or is located on the boundary of the VLC hotspot coverage, and the signal deteriorates to a certain extent, and needs to be The VHO is executed; the MT enters the visible light intensity gap due to occlusion, causing signal deterioration, and VHO needs to be performed.
  • Step S4 The system predicts related parameters of the current interrupt according to the pre-interruption condition, and performs performances of the IVHO and DVHO algorithms based on the predicted value of the message transmission delay during the current interruption period calculated according to the parameters. Comparison on.
  • Step S5 Performing the better performance of the IVHO and DVHO algorithms, and detecting whether the VLC connection is restored after the current packet transmission is completed.
  • step S5 of the present application further includes:
  • Step S51 After the system starts running, the mobile terminal receives data on the VLC channel.
  • Step S52 The system detects in real time whether the received data is interrupted.
  • Step S53 When an interrupt occurs, the vertical switching decision process is triggered, thereby determining the value of the dwell time before the vertical switching is performed.
  • the dwell time is set to 0 in the IVHO algorithm and is set to the maximum value of the short interrupt duration in the DVHO algorithm.
  • step S54 further includes: if the VLC connection is restored, the data transmission is switched back to the VLC network, and the process proceeds to step S52; if the VLC connection is not restored, the data continues to be transmitted in the cellular network, and the above operation is continuously repeated.
  • Step S54 If the VLC connection is restored before the timer of the camping timer expires, the mobile terminal will continue the previously interrupted data transmission using the VLC channel, and jump to step S52; if the VLC connection is not restored before the timer of the camping timer expires, Vertical switching is performed, the connection is transferred to the cellular network, and after the current packet transmission is completed, it is detected whether the VLC connection is restored.
  • Step S6 If the VLC connection is not restored, the received data continues to be transmitted in the cellular network, and the judgments of steps S5 and S6 are continuously repeated.
  • the method further includes: the mobile terminal detects that the visible channel is in a congested state, and the channels of the remaining radio access networks are in an idle state, and performs a VHO algorithm to dynamically adjust the load of each channel.
  • the present application proposes a vertical handover method for heterogeneous networking in visible light communication, which includes the following specific steps:
  • S02 The system detects whether the received data is interrupted in real time
  • S031 The system predicts the relevant parameters of the current interrupt according to the pre-interruption condition, and uses the predicted values of the IVHO and DVHO message transmission delays during the current interruption period calculated according to the parameters to be IVHO and DVHO.
  • the algorithm performs a performance comparison
  • S04 Perform vertical switching according to the determined vertical switching algorithm to be executed.
  • the mobile terminal detects that the visible channel is in a congested state, and the channels of the remaining radio access networks are in an idle state, and executes a VHO algorithm.
  • the mobile terminal is configured to detect a size of data not received when the data transmission is interrupted on the VLC channel, and a plurality of different network link data, collect and process characteristic parameters of the plurality of different networks.
  • the characteristic parameters of the multiple different networks include: current received signal strength, bit rate, congestion level, and related information of data currently needed to be transmitted by different networks.
  • the mobile terminal is further configured to detect a current usage status of the network and quality levels of the multiple different network links and compare the quality.
  • performing vertical switching according to the determined vertical switching algorithm to be executed includes:
  • the method further includes:
  • the mobile terminal will continue the previously interrupted data transmission using the VLC channel.
  • performing vertical switching according to the determined vertical switching algorithm to be executed includes:
  • connection will be transferred to the cellular network.
  • the method further includes: after the data connection is transferred to the cellular network, if the VLC connection is restored, the data transmission is switched back to the VLC network.
  • the dwell time is set to 0 in the IVHO algorithm and is set to the maximum value of the short interrupt duration in the DVHO algorithm.
  • the present application proposes a vertical handover method for heterogeneous networking in visible light communication.
  • the MT compares the quality of different links according to the current network usage status and the quality level of different links.
  • the appropriate indicators for measuring different network performances are selected according to the set VHO.
  • the algorithm determines if a switch is needed and ultimately selects the appropriate target network.
  • the triggering of the vertical handover is established on the state and parameter collection of the current MT and other accessible networks, and the execution of the handover is finally performed through analysis and judgment. Since the correlation parameter of the VLC network changes abruptly when the link between the optical signal and the MT is blocked, the present application will adopt the strength of the visible light signal received by the MT as a criterion for the handover trigger.
  • the target network when the vertical handover is triggered, the target network will establish a new channel, the current connection will be transferred to the new link, and at the same time, the original VLC channel will be cleared. However, the execution is not completed immediately after the vertical switch is triggered. First, due to the system's operation and decision process, the inherent time overhead will cause a certain handover delay. In addition, the present application will also decide whether to perform the handover after waiting for a period of time according to the designed vertical handover scheme.
  • a visible light signal source covers an indoor hotspot area for providing broadband wireless access.
  • the cell where the mobile terminal is located can cover a larger area and provide users with higher mobility. If the user uses a multi-mode mobile terminal, the two transmission media can be used to cooperatively transmit data and perform vertical switching between the two wireless networks when needed. If the link state of the visible channel becomes unavailable during transmission, it switches to the cellular connection. Once the visible light signal coverage is restored, since the wideband visible light channel is always preferred, the MT immediately switches back to the visible light channel.
  • the visible light connection is interrupted in both cases.
  • This type of interruption has a short duration and is temporary, and its duration is typically less than 2 seconds before the visible light connection is restored.
  • the shortest duration of the interruption caused by the MT temporarily leaving the service area is much longer than the maximum duration of the interruption when the light is blocked, which makes the two types of interruptions easily distinguishable. So we can use "long" interrupts and "short" Interrupts represent these two different interrupts, respectively.
  • the main challenge of the vertical handoff algorithm is how to determine what type of interrupt is occurring and whether vertical handoff should be performed. Therefore, in a hybrid network system of VLC and cellular, it is necessary to determine an appropriate handover indicator and handover method, thereby achieving excellent handover performance.
  • the MT receives data on the VLC channel when the system starts operating. Whenever an interrupt occurs, the vertical handoff decision process will be triggered to determine the value of the dwell time before the vertical switch is executed. If the VLC connection is restored before the end of the resident timer, the mobile terminal will continue the previously interrupted transmission using the VLC channel. Otherwise, a vertical switch will be performed and the connection will be transferred to the cellular channel.
  • the value of the dwell time is 0, so there is no unnecessary waiting delay for using the IVHO algorithm when a long interrupt occurs.
  • the DVHO algorithm sets the dwell time to the maximum value of the short interrupt duration to prevent excessive delays caused by sluggish data transmission after the communication switches to the narrowband wireless cellular channel in the event of a short outage.
  • any one can only perform better than the other under certain conditions, and no one can achieve the best performance under any circumstances.
  • the MT performs data transmission on the VLC channel, and the system detects whether the received data is interrupted in real time. If no interrupt is detected, the MT remains on the VLC channel for data transmission; When an interrupt is detected, the resident vertical switching process will be triggered, ie the dwell time is determined and the dwell timing begins. Before the end of the camping period, if the VLC channel recovery is detected, the MT continues to perform data transmission on the VLC channel; if no VLC channel recovery is detected, the vertical handover, that is, the VHO execution process, is performed after the camping timer ends, that is, Switch to cellular data transmission.
  • VLC channel recovery if VLC channel recovery is detected, it will immediately hang
  • the direct handover is the process performed by the VHO, and the data transmission continues on the VLC channel; if the VLC channel recovery is not detected, the data transmission continues on the cellular channel.
  • the present application considers designing a new vertical switching algorithm to perform reasonable operations on a plurality of different parameters, and using the output single variable as a unique parameter to determine which of the two basic algorithms described above is used. . Since this vertical handoff algorithm is based on prediction and estimation of certain unknown indicators, it is called a prediction-based vertical handoff algorithm (PVHO).
  • PVHO prediction-based vertical handoff algorithm
  • the MT calculates the ratio P short of the short interrupts that have occurred in the interrupt, and uses it as the estimated value of the probability that the next interrupt is a short interrupt:
  • N short and N long respectively represent the total number of short interruptions and long interruptions that have been recorded before the mobile terminal.
  • IVHO is often the best choice.
  • the best solution that can be used is mainly determined by three indicators: the size of the unreceived message, the duration of the short interruption, and the vertical switching execution delay. In the length of the message not received Longer, vertical switching execution delay is longer, and the interruption duration is relatively short, the DVHO scheme is preferred, it can avoid excessive delay caused by unnecessary switching, and its delay is smaller than IVHO Much more.
  • IVHO is the preferred scheme.
  • the transmission delay of the currently unreceived message is:
  • R CELL and R VLC represent the bit rate of the cellular network and VLC, respectively
  • S represents the size of the unreceived message
  • D Execution represents the execution delay of the vertical handover
  • D Short-Int represents the duration of the short interruption
  • D Dwell represents the resident. The maximum value of the time left.
  • D IVHO ⁇ D DVHO is actually, the delay performance of IVHO is better than DVHO.
  • D IVHO > D DVHO is actually, the delay performance of DVHO is better than IVHO.
  • the designed PVHO algorithm compares the predicted values of the two and then performs the better performance of the two basic vertical switching algorithms, so that the optimal delay performance can be achieved in all cases.
  • the same prediction value calculation method D IVHO and D IVHO the only difference is that in which the S and D Execution mean both the actual status of the system before the interrupt occurrence taken; and there are two different cases DVHO Then, the predicted value of D DVHO is the expected value of the message transmission delay when the DVHO was last executed, that is:
  • S, D Execution and D Short-Int also take the average of the actual situation before the interruption.
  • D IVHO when the predicted value of less than or equal to the predicted value D DVHO, PVHO determination algorithms executed IVHO, otherwise, the algorithm determines PVHO performed DVHO.
  • the MT performs data transmission on the VLC channel, and the system detects whether the received data is interrupted in real time. If no interrupt is detected, the MT remains in the VLC. Data transmission is performed on the channel; if an interruption is detected, the PVHO prediction process is entered. In the prediction process, the delay prediction value when the IVHO process is executed, and the delay prediction value when the DVHO process is executed are calculated. Comparing the two predicted values, if the delay prediction value of the IVHO process is smaller than the delay prediction value of the DVHO process, it indicates that the IVHO is superior, and in this case, the vertical handover, that is, the VHO execution process, is switched to the cellular data.
  • the delay prediction value of the IVHO process is not less than the delay prediction value of the DVHO process, it indicates that the IVHO is not optimal, in which case the resident vertical handover process will be triggered, that is, the dwell time is determined, and the station is started. Leave time.
  • the MT continues to perform data transmission on the VLC channel; if no VLC channel recovery is detected, the vertical handover, that is, the VHO execution process, is performed after the camping timer ends, that is, Switch to cellular data transmission.
  • the present application can adaptively select an appropriate switching mechanism when an interrupt occurs, and obtain excellent switching performance.
  • the simulation results show that the algorithm used in this application is optimal in almost all cases, or is very close to optimal.
  • the present application discloses a vertical handover method for a visible light communication heterogeneous networking.
  • the MT compares the quality of different links according to the current network usage status and the quality level of different links.
  • the appropriate indicators for measuring different network performances are selected according to the set VHO.
  • the algorithm determines if a switch is needed and ultimately selects the appropriate target network.
  • the present application can ensure the continuity of the service, improve the QoS, and on the other hand, can make the service request in the entire system uniform. It is of great significance to improve the performance of visible light communication network systems by constructing the architecture of visible light communication heterogeneous networking and researching its mobility management while proposing appropriate vertical switching algorithms, and continuously improving the algorithm.

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Abstract

本申请涉及一种用于可见光通信异构组网中的垂直切换方法，包括：系统运行后，移动终端在VLC信道上接收数据；系统实时检测接收数据是否发生中断；当中断发生，垂直切换决策进程被触发；系统根据预先多次的中断情况对当前中断的相关参数进行预测，根据这些参数计算出的当前中断期间的消息传输时延的预测值为标准将IVHO与DVHO两种算法进行性能上的比较；执行IVHO与DVHO两种算法中性能较优者，切换到蜂窝网络，并在当前包传输执行完毕后，检测VLC连接是否恢复；若VLC连接未恢复，接收数据继续在蜂窝网络中传输。本申请保证业务的连续性，提升QoS，同时使得整个系统中的业务请求均匀化，且不断对算法进行改进，对于改善可见光通信网络系统的性能具有重大意义。

Description

一种用于可见光通信异构组网中的垂直切换方法
本申请要求于2014年12月15日提交中国专利局、申请号为201410779054.2、发明名称为“一种用于可见光通信异构组网中的垂直切换方法”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及无线通信技术领域，尤其涉及一种用于可见光通信异构组网中的垂直切换方法。
背景技术
众所周知，可见光通信是一种在白光发光二极管(light emitting diode,LED)技术之上发展起来的新兴无线通信技术。照明作为一种人们日常生活中的重要需求，其网络早已覆盖了包括家庭、企业、公共场所、交通工具、矿井、加油站、医院在内的各种各样的人类活动空间，其中很多地方甚至尚未接入传统的无线通信网络。而可见光通信恰好可以将通信与照明有机结合起来，借助广泛覆盖的照明网络同时实现无线通信的功能，使得只要有照明设施的地方就可以连接无线网络，为解决通信“末端接入”和“深度覆盖”等问题提供了一种便捷而自然的方式。
虽然可见光通信具有诸多优势，但是可见光波长较短，在大气中被大量吸收，造成了通信距离短，障碍物阻挡不可穿透，存在大量单向信道等缺点，需要其他通信方式进行补充。而且，单一的通信接入技术的网络架构、信令流程及管理体系往往是针对特定的业务设计的，并且拥有其独立的资源管理模式，长此以往导致不同的通信网络之间相对独立，缺乏有效的协调，系统间存在干扰，覆盖区域有重复，而每一种网络的业务提供能力又是十分有限的。该现状促成了对不同种类的无线接入技术进行协调互通的需求，也使得异构组网体系和机理的确立成为了实现可见光通信异构网络高效可靠传输的关键。
然而，在实际应用中，可见光信号可能在多种情况下减弱到MT(mobile terminal，移动终端)无法进行正常通信的程度。为了保证终端与网络之间 的通信质量，避免数据传输中断，实现可见光与其他无线接入技术之间的垂直切换便成为了可见光通信异构网络融合中必不可少的措施。
发明内容
本申请所要解决的技术问题是如何通过在可见光通信系统的运行过程中，检测不同的网络链路数据，收集相关的系统参数，将其进行处理，从而用于垂直切换决策算法上，改善可见光通信网络系统的性能的关键问题。
为此目的，本申请提出了一种用于可见光通信异构组网中的垂直切换方法，包括以下具体步骤：
S1：在系统开始运行后，移动终端在VLC信道上接收数据；
S2：系统实时检测接收数据是否发生中断；
S3：当中断发生时，垂直切换决策进程被触发，并决定应执行的垂直切换；
S4：系统根据预先多次的中断情况对当前中断的相关参数进行预测，并以根据这些参数计算出的当前中断期间的消息传输时延的预测值为标准将IVHO与DVHO两种算法进行性能上的比较；
S5：执行所述IVHO与DVHO两种算法中性能较优者，并在当前包传输执行完毕后，检测VLC连接是否恢复；
S6：若所述VLC连接未恢复，接收数据继续在蜂窝网络中传输。
进一步地，所述移动终端检测到可见光信道处于拥挤状态，其余无线接入网络的信道处于空闲状态，执行VHO算法。
具体地，所述移动终端用于检测多个不同网络链路数据，收集相关的多个不同网络的特性参数并进行处理。
具体地，所述多个不同网络的特性参数包括：不同网络当前的接收信号强度，比特率，拥挤程度，以及当前需要传输的数据的相关信息。
具体地，所述移动终端还用于检测当前网络的使用状况以及所述多个不同网络链路的质量水平并进行比较。
进一步地，所述步骤S3包括：
S31：搜集当前所述移动终端所在网络以及多个不同可接入网络的状态与 参数；
S32：对搜索到的状态与参数进行分析以及判决，执行切换。
进一步地，所述步骤S5进一步包括：
S51：在系统开始运行后，移动终端在VLC信道上接收数据；
S52：系统实时检测接收数据是否发生中断；
S53：当发生中断时，所述垂直切换决策进程被触发，进而决定垂直切换执行前的驻留时间的值；
S54：若VLC连接在驻留计时器计时结束之前恢复，所述移动终端将使用VLC信道继续之前中断的数据传输，并跳转执行步骤S52；若VLC连接在驻留计时器计时结束之前没有恢复，垂直切换被执行，连接将被转移到蜂窝网络，并在当前包传输执行完毕后，检测VLC连接是否恢复。
进一步地，所述步骤S54进一步包括：若VLC连接恢复，数据传输切换回VLC网络，并跳转执行步骤S52；若VLC连接没有恢复，数据继续在蜂窝网络中传输。
具体地，所述驻留时间在IVHO算法中设置为0，在DVHO算法中设置为短中断持续时间的最大值。
为此目的，本申请提出了一种用于可见光通信异构组网中的垂直切换方法，包括以下具体步骤：
S01：在系统开始运行后，移动终端在可见光VLC信道上接收数据；
S02：系统实时检测接收数据是否发生中断；
S03：当中断发生时，按照如下步骤决定待执行的垂直切换算法：
S031：系统根据预先多次的中断情况对当前中断的相关参数进行预测，并以根据这些参数计算出的当前中断期间的IVHO和DVHO的消息传输时延的预测值为标准将IVHO与DVHO两种算法进行性能上的比较；
S032：当IVHO的消息传输时延的预测值小于DVHO的消息传输时延的预测值时，确定待执行的垂直切换算法为IVHO垂直切换算法；当IVHO的消息传输时延的预测值不小于DVHO的消息传输时延的预测值时，确定待执行的垂直切换算法为DVHO垂直切换算法；
S04：根据确定的待执行的垂直切换算法，进行垂直切换。
进一步地，所述移动终端检测到可见光信道处于拥挤状态，其余无线接入网络的信道处于空闲状态，执行VHO算法。
具体地，所述移动终端用于检测在VLC信道上数据传输中断时未接收数据的大小，以及多个不同网络链路数据，收集相关的多个不同网络的特性参数并进行处理。
具体地，所述多个不同网络的特性参数包括：不同网络当前的接收信号强度，比特率，拥挤程度，以及当前需要传输的数据的相关信息。
具体地，所述移动终端还用于检测当前网络的使用状况以及所述多个不同网络链路的质量水平并进行比较。
进一步地，当待执行的垂直切换算法为DVHO垂直切换算法时，所述根据确定的待执行的垂直切换算法，进行垂直切换包括：
S041：确定垂直切换执行前的驻留时间的值；
S042：若VLC连接在驻留计时器计时结束之前没有恢复，进行垂直切换，连接将被转移到蜂窝网络。
进一步地，当待执行的垂直切换算法为DVHO垂直切换算法时，所述方法还包括：
若VLC连接在驻留计时器计时结束之前恢复，所述移动终端将使用VLC信道继续之前中断的数据传输。
进一步地，当待执行的垂直切换算法为IVHO垂直切换算法时，所述根据确定的待执行的垂直切换算法，进行垂直切换包括：
直接进行垂直切换，连接将被转移到蜂窝网络。
进一步地，所述方法还包括：当数据连接被转移到蜂窝网络后，若VLC连接恢复，则数据传输切换回VLC网络。
具体地，所述驻留时间在IVHO算法中设置为0，在DVHO算法中设置为短中断持续时间的最大值。
本申请公开了一种用于可见光通信异构组网中的垂直切换方法，通过在可见光通信系统进行链路检测和参数收集的过程，根据检测到的不同网络的状态信息，在下一次需要执行垂直切换的时刻，MT根据当前网络的使用状况，不同链路的质量水平，将其进行多方面的比较，根据当前用户的实际需求， 选取合适的衡量不同网络性能的指标，按照设定好的VHO算法确定是否需要切换，并最终选择合适的目标网络。本申请一方面可以保证业务的连续性，提升QoS，另一方面也可以使得整个系统中的业务请求均匀化。在构建可见光通信异构组网的体系架构并研究其移动性管理的同时提出合适的垂直切换算法，并且不断对算法进行改进，对于改善可见光通信网络系统的性能具有重大意义。
附图说明
通过参考附图会更加清楚地理解本申请的特征和优点，附图是示意性的而不应理解为对本申请进行任何限制，在附图中：
图1示出了本申请实施例中的一种用于可见光通信异构组网中的垂直切换方法的步骤流程图；
图2示出了本申请实施例中的一种用于可见光通信异构组网中的垂直切换方法的另一步骤流程图；
图3示出了本申请实施例中的一种用于可见光通信异构组网中的垂直切换方法的结合两种基本VHO算法的步骤流程图；
图4(a)-(e)示出了本申请实施例中的一种用于可见光通信异构组网中的垂直切换方法的仿真性能与两种基本VHO算法的对比图。
具体实施方式
本申请提出了一种用于可见光通信异构组网中的垂直切换方法，可见光连接中断发生在MT移出可见光热点的覆盖范围时，以及人们的随机运动或者随机运动导致的室内障碍物的遮挡引起光线的阻塞时，我们可以使用“长”中断与“短”中断来分别代表这两种不同的中断。具体地，在可见光通信异构网络中，垂直切换算法的主要挑战便是如何确定发生的是哪种类型的中断，以及是否应当执行垂直切换。
进一步地，两种直观上的最佳方案分别为立即执行垂直切换和等待VLC连接恢复，其中，前者称为IVHO(Immediate Vertical Handover，立即垂直切 换)算法，后者称为DVHO(Dwell Vertical Handover，驻留垂直切换)算法，然而两者均不能在所有情况下达到最佳性能。
更进一步地，本申请提出的用于可见光通信异构组网中的垂直切换方法，即PVHO(Predictive Vertical Handover，基于预测的垂直切换)算法，采用中断期间的消息传输时延作为衡量算法性能的指标，且其主要由中断的持续时间、垂直切换的执行时延以及未接收消息的大小决定。其中，MT实时计算出已发生的中断中短中断的比率，并以其作为下一个中断为短中断的概率的估计值，同时可以得到下一个中断为长中断的概率的估计值。其中，执行IVHO时，当前未接收消息的传输时延为DIVHO，执行DVHO时，当前未接收消息的传输时延为DDVHO。在每一次切换中，若实际上DIVHO<DDVHO，则IVHO的时延性能优于DVHO，若实际上DIVHO>DDVHO，则DVHO优于IVHO。
更进一步地，在PVHO方案中，可根据发生此次中断之前系统实际情况的各参数各自的均值，得到DIVHO的预测值。而DDVHO的预测值则取下一次执行DVHO时的消息传输时延的期望值。继而，算法将两者的预测值进行比较，然后执行两种基本垂直切换算法中性能较好的那一种，从而在所有情况下均能达到最佳的时延性能。
综上所述，本申请可以保证可见光通信异构网络中业务的连续性，提升QoS(quality of service，服务质量)，也可以使得整个系统中的业务请求均匀化，对于改善可见光通信网络系统的性能具有重大意义。
下面将结合附图对本申请的实施例进行详细描述。
为了更好地理解与应用本申请提出的一种用于可见光通信异构组网中的垂直切换方法，以如下附图示例进行详细说明。
如图1所示，本申请提出了一种用于可见光通信异构组网中的垂直切换方法，包括以下具体步骤：
步骤S1：在系统开始运行后，移动终端在VLC信道上接收数据。其中，移动终端用于检测多个不同网络链路数据，收集相关的多个不同网络的特性参数并进行处理，从而用于垂直切换决策算法中，且多个不同网络的特性参 数包括：不同网络当前的接收信号强度，比特率，拥挤程度，以及当前需要传输的数据的相关信息。
进一步地，移动终端还用于检测当前网络的使用状况以及多个不同网络链路的质量水平并进行比较，在下一次需要执行垂直切换的时刻，按照设定好的VHO算法确定是否需要切换，并最终选择合适的目标网络。
步骤S2：系统实时检测接收数据是否发生中断。
步骤S3：当中断发生时，垂直切换决策进程被触发，并决定应执行的垂直切换，即决定当前情况下应执行哪一类垂直切换。
具体地，步骤S3包括：
步骤S31：搜集当前移动终端所在网络以及多个不同可接入网络的状态与参数。
步骤S32：对搜索到的状态与参数进行分析以及判决，执行切换。即由于在光信号与MT之间的链路受到阻断时，VLC网络的相关参数急剧变化，所以一般采用MT接收到的可见光信号的强度作为切换触发的标准。具体地，下面几种实际情况均可以触发VLC网络与其他无线接入网络之间的VHO：MT暂离VLC热点的覆盖范围，或者位于VLC热点覆盖范围的边界上，信号恶化到一定程度，需要执行VHO；MT由于遮挡而进入可见光强度缝隙中，造成信号恶化，需要执行VHO。
步骤S4：系统根据预先多次的中断情况对当前中断的相关参数进行预测，并以根据这些参数计算出的当前中断期间的消息传输时延的预测值为标准将IVHO与DVHO两种算法进行性能上的比较。
步骤S5：执行IVHO与DVHO两种算法中性能较优者，并在当前包传输执行完毕后，检测VLC连接是否恢复。
具体地，本申请步骤S5进一步包括：
步骤S51：在系统开始运行后，移动终端在VLC信道上接收数据。
步骤S52：系统实时检测接收数据是否发生中断。
步骤S53：当发生中断时，垂直切换决策进程被触发，进而决定垂直切换执行前的驻留时间的值。其中，驻留时间在IVHO算法中设置为0，在DVHO算法中设置为短中断持续时间的最大值。进一步地，步骤S54进一步包括：若VLC连接恢复，数据传输切换回VLC网络，并跳转执行步骤S52；若VLC连接没有恢复，数据继续在蜂窝网络中传输，并不断重复上述操作。
步骤S54：若VLC连接在驻留计时器计时结束之前恢复，移动终端将使用VLC信道继续之前中断的数据传输，并跳转执行步骤S52；若VLC连接在驻留计时器计时结束之前没有恢复，垂直切换被执行，连接将被转移到蜂窝网络，并在当前包传输执行完毕后，检测VLC连接是否恢复。
步骤S6：若VLC连接未恢复，接收数据继续在蜂窝网络中传输，并不断重复步骤S5和步骤S6的判断。
进一步地，还包括：移动终端检测到可见光信道处于拥挤状态，其余无线接入网络的信道处于空闲状态，执行VHO算法，动态调节各信道的负荷量。
本申请提出了一种用于可见光通信异构组网中的垂直切换方法，包括以下具体步骤：
S01：在系统开始运行后，移动终端在可见光VLC信道上接收数据；
S02：系统实时检测接收数据是否发生中断；
S03：当中断发生时，按照如下步骤决定待执行的垂直切换算法：
S031：系统根据预先多次的中断情况对当前中断的相关参数进行预测，并以根据这些参数计算出的当前中断期间的IVHO和DVHO的消息传输时延的预测值为标准将IVHO与DVHO两种算法进行性能上的比较；
S032：当IVHO的消息传输时延的预测值小于DVHO的消息传输时延的预测值时，确定待执行的垂直切换算法为IVHO垂直切换算法；当IVHO的消息传输时延的预测值不小于DVHO的消息传输时延的预测值时，确定待执行的垂直切换算法为DVHO垂直切换算法；
S04：根据确定的待执行的垂直切换算法，进行垂直切换。
进一步地，所述移动终端检测到可见光信道处于拥挤状态，其余无线接入网络的信道处于空闲状态，执行VHO算法。
具体地，所述移动终端用于检测在VLC信道上数据传输中断时未接收数据的大小，以及多个不同网络链路数据，收集相关的多个不同网络的特性参数并进行处理。
具体地，所述多个不同网络的特性参数包括：不同网络当前的接收信号强度，比特率，拥挤程度，以及当前需要传输的数据的相关信息。
具体地，所述移动终端还用于检测当前网络的使用状况以及所述多个不同网络链路的质量水平并进行比较。
进一步地，当待执行的垂直切换算法为DVHO垂直切换算法时，所述根据确定的待执行的垂直切换算法，进行垂直切换包括：
S041：确定垂直切换执行前的驻留时间的值；
S042：若VLC连接在驻留计时器计时结束之前没有恢复，进行垂直切换，连接将被转移到蜂窝网络。
进一步地，当待执行的垂直切换算法为DVHO垂直切换算法时，所述方法还包括：
若VLC连接在驻留计时器计时结束之前恢复，所述移动终端将使用VLC信道继续之前中断的数据传输。
进一步地，当待执行的垂直切换算法为IVHO垂直切换算法时，所述根据确定的待执行的垂直切换算法，进行垂直切换包括：
直接进行垂直切换，连接将被转移到蜂窝网络。
进一步地，所述方法还包括：当数据连接被转移到蜂窝网络后，若VLC连接恢复，则数据传输切换回VLC网络。
具体地，所述驻留时间在IVHO算法中设置为0，在DVHO算法中设置为短中断持续时间的最大值。
本申请提出了一种用于可见光通信异构组网中的垂直切换方法，通过在可见光通信系统进行链路检测和参数收集的过程，根据检测到的不同网络的状态信息，在下一次需要执行垂直切换的时刻，MT根据当前网络的使用状况，不同链路的质量水平，将其进行多方面的比较，根据当前用户的实际需求，选取合适的衡量不同网络性能的指标，按照设定好的VHO算法确定是否需要切换，并最终选择合适的目标网络。
进一步地，可见光通信异构网络中，垂直切换的触发建立在对当前MT所在网络和其他可接入网络的状态与参数搜集之上，通过分析和判决，最终进行切换的执行。由于在光信号与MT之间的链路受到阻断时，VLC网络的相关参数急剧变化，所以本申请将采用MT接收到的可见光信号的强度作为切换触发的标准。
更进一步地，当垂直切换被触发时，目标网络将建立新的信道，当前的连接将转移到新的链路，与此同时，原来的VLC信道将被清除。然而，在垂直切换被触发以后并不是立即就能够完成执行的。首先由于系统在运算和判决的过程中，固有的时间开销会造成一定的切换延迟。另外，本申请还会根据设计好的垂直切换方案，在等待一段时间之后再决定是否执行切换。
为了更好地理解与应用本申请提出的一种用于可见光通信异构组网中的垂直切换方法，结合图2-4进行以下示例，且本申请不局限以下示例。
具体地，在VLC与蜂窝网络组成的混合系统中，一个可见光信号源覆盖一个室内热点区域，用来提供宽带无线接入。而移动终端所在的蜂窝小区则可以覆盖更大的区域，为用户提供更高的移动性。如果用户使用多模移动终端，就可以采用两种传输媒质协同传输数据，并且在需要的时候在两种无线网络之间执行垂直切换。如果可见光信道的链路状态在传输过程中变为不可用，则切换到蜂窝连接。一旦可见光信号覆盖恢复，由于宽带可见光信道始终是首选，MT立即切换回可见光信道。
进一步地，通常情况下，可见光连接在两种情况下发生中断。一种发生在MT移出可见光热点的覆盖范围时，一旦发生，其通常持续至少几秒钟，甚至几分钟、几小时，直到移动终端返回可见光热点的覆盖范围内。另一种则发生在人们的随机运动或者随机运动导致的室内障碍物的遮挡引起光线阻塞时。这种类型的中断持续时间较短，而且是暂时性的，在可见光连接恢复前，它的持续时间通常小于2秒。在实际情况下，MT暂离服务区造成的中断的最短持续时间要比光线受到阻塞时发生的中断的最长持续时间要长得多，这使得两种类型的中断很容易被区分开来。因此，我们可以使用“长”中断与“短” 中断来分别代表这两种不同的中断。
更进一步地，每当中断出现时，MT接收到的可见光信号强度显著降低，这可以很容易地通过光接收器来检测到。因此，在这种混合系统中，垂直切换算法的主要挑战是如何确定发生的是哪种类型的中断，以及是否应当执行垂直切换。因此，在VLC与蜂窝的混合网络系统中，必须确定恰当的切换指标及切换方法，从而实现优异的切换性能。
综上所示，每当中断发生时，两种直观上可实现最小时延的方案分别为立即执行垂直切换和等待VLC连接恢复。于是，可以采用相应的两种基本的算法，用以提升VLC和蜂窝异构通信网络的数据传输性能。一种方案是立即垂直切换(IVHO)，另一种方案是驻留垂直切换(DVHO)算法。
如图3所示，在上述两种垂直切换算法中，在系统开始运行时，MT在VLC信道上接收数据。每当中断发生时，垂直切换决策进程将被触发，从而决定垂直切换执行前的驻留时间的值。如果VLC连接在驻留计时器计时结束之前恢复，则移动终端将使用VLC信道继续之前中断了的传输。否则，垂直切换将被执行，连接将被转移到蜂窝信道。在IVHO方案中，驻留时间的值为0，因此在发生长中断时使用IVHO算法不存在无谓的等待时延。与此相反，DVHO算法则将驻留时间设置为短中断持续时间的最大值，以防止发生短中断时，通信切换到窄带无线蜂窝信道后迟缓的数据传输造成的过度延迟。然而，这两种垂直切换方案中，任何一种都只能在一定条件下表现得优于另一种，没有哪一种能够在任何情况下均达到最佳性能。
也就是说在图3中，在系统开始运行后，MT在VLC信道上进行数据传输，系统实时检测接收数据是否发生中断，如果没有检测到中断，则MT保持在VLC信道上进行数据传输；如果检测到中断，则驻留垂直切换过程将被触发，即确定驻留时间，并开始驻留计时。在驻留计时结束之前，如果检测到VLC信道恢复，则MT继续在VLC信道上进行数据传输；如果没有检测到VLC信道恢复，则在驻留计时结束后进行垂直切换即VHO执行的过程，即切换至蜂窝数据传输。在蜂窝数据传输过程中，如果检测到VLC信道恢复，则立即进行垂 直切换即VHO执行的过程，继续在VLC信道上进行数据传输；如果没有检测到VLC信道恢复，则继续在蜂窝信道上进行数据传输。
对于立即垂直切换(IVHO)过程的流程示意图，则将图3中从“驻留计时”到“驻留结束”的过程删去即可。
进一步地，应当采用哪个量值作为衡量算法性能的指标，这是在VLC与蜂窝网络之间的垂直切换算法设计的过程中的一个关键问题。在这里，考虑到垂直切换最根本的目的在于尽量避免用户在通信过程中发生掉话或者尽量减小其影响，提升QoS，本申请采用中断期间的消息传输时延作为衡量算法性能的指标。中断期间的传输时延在很大程度上由这样几个参数决定：中断的持续时间、垂直切换的执行时延以及未接收消息的大小。这些参数均为变量，其值与网络的瞬时条件有关，根据这些具有不确定性和矛盾性的参数来决定采用何种切换算法将是十分困难的。
因此，本申请考虑设计一种新的垂直切换算法来将多个不同参数进行合理的运算，将输出的单一变量作为唯一的参数来决定究竟使用前文所述的两种基本算法中的哪一种。由于这种垂直切换算法是基于对某些未知指标的预测和估计的，所以称之为基于预测的垂直切换算法(PVHO)。
如图2所示，在该异构通信系统中，每次系统开始运行后，已发生的短中断和长中断的数目都会被MT记录下来。当下一个中断发生时，该MT计算出已经发生的中断中短中断的比率Pshort，并以其作为下一个中断为短中断的概率的估计值：
Figure PCTCN2015097020-appb-000001
同时也可得到下一个中断为长中断的概率的估计值。其中，Nshort和Nlong分别表示移动终端之前记录的已发生的短中断和长中断的总数。
每当中断发生时，一个消息可能只传输了一部分，而且更多的消息可能仍然在传输队列中等待。在长中断的情况下，IVHO往往是最好的选择。但是如果是在短中断的情况下，可使用的最佳方案主要由三个指标来决定：未接收消息的大小、短中断的持续时间和垂直切换执行时延。在未接收消息长度 比较长，垂直切换执行时延比较长，而且中断持续时间比较短的情况下，DVHO方案是首选的，它可以避免因不必要的切换带来的过度延迟，其时延相比于IVHO要小得多。与此相反，在未接收消息长度比较短，垂直切换执行时延比较短，而且中断持续时间比较长的情况下，则IVHO为首选方案。执行IVHO时，当前未接收消息的传输时延为：
Figure PCTCN2015097020-appb-000002
执行DVHO时，若实际发生的是短中断，则当前未接收消息的传输时延为：
Figure PCTCN2015097020-appb-000003
若实际发生的是长中断，则当前未接收消息的传输时延为：
Figure PCTCN2015097020-appb-000004
其中，RCELL和RVLC分别表示蜂窝网络和VLC的比特率，S表示未接收消息的大小，DExecution表示垂直切换的执行时延，DShort-Int表示短中断的持续时间，DDwell表示驻留时间的最大值。在每一次切换中，若实际上DIVHO<DDVHO，则IVHO的时延性能优于DVHO，若实际上DIVHO>DDVHO，则DVHO的时延性能优于IVHO。经过设计得出的PVHO算法就是将两者的预测值进行比较，然后执行两种基本垂直切换算法中性能较好的那一种，从而在所有情况下均能达到最佳的时延性能。
在PVHO方案中，DIVHO的预测值与DIVHO的计算方法相同，唯一的不同点在于其中的S和DExecution均取发生此次中断之前系统实际情况的均值；而DVHO中有两种不同情况，于是DDVHO的预测值为上一次执行DVHO时的消息传输时延的期望值，即为：
Figure PCTCN2015097020-appb-000005
其中，S、DExecution和DShort-Int也均取发生此次中断之前系统实际情况的均值。当DIVHO的预测值小于等于DDVHO的预测值时，PVHO算法判断执行IVHO，否则PVHO算法判断执行DVHO。
也就是说图2中，在系统开始运行后，MT在VLC信道上进行数据传输，系统实时检测接收数据是否发生中断，如果没有检测到中断，则MT保持在VLC 信道上进行数据传输；如果检测到中断，则进入PVHO预测过程。在该预测过程中，计算出当执行IVHO过程时的时延预测值，和当执行DVHO过程时的时延预测值。将这两个预测值进行比较，如果IVHO过程的时延预测值小于DVHO过程的时延预测值，则说明IVHO较优，此种情况中立即进行垂直切换即VHO执行的过程，切换至蜂窝数据传输；如果IVHO过程的时延预测值不小于DVHO过程的时延预测值，则说明IVHO不是较优的，此种情况中驻留垂直切换过程将被触发，即确定驻留时间，并开始驻留计时。在驻留计时结束之前，如果检测到VLC信道恢复，则MT继续在VLC信道上进行数据传输；如果没有检测到VLC信道恢复，则在驻留计时结束后进行垂直切换即VHO执行的过程，即切换至蜂窝数据传输。在上述两种情况下，在蜂窝数据传输过程中，如果检测到VLC信道恢复，则立即进行垂直切换即VHO执行的过程，继续在VLC信道上进行数据传输；如果没有检测到VLC信道恢复，则继续在蜂窝信道上进行数据传输。
如图4(a)-(e)所示，如果用
Figure PCTCN2015097020-appb-000006
和
Figure PCTCN2015097020-appb-000007
分别表示短中断和长中断的平均到达率，分别按照
Figure PCTCN2015097020-appb-000008
为5:1、2:1、1:1、1:2和1:5的比例构建室内仿真模型，在不同的
Figure PCTCN2015097020-appb-000009
情况下对三种垂直切换进行时延性能仿真。由仿真结果可以看出，当短中断占大多数时，在所有的平均消息长度下，IVHO几乎均表现出最差的时延性能，而其他两种算法的性能则十分近似。当两种中断比例相当时，IVHO的总体性能仍不及另外两种算法，但已比较接近，而PVHO算法的性能仍然在所有情况下优于或接近于DVHO，并在总体上优于DVHO。当长中断在所有中断中占大多数时，在几乎所有情况下，DVHO均表现出最差的时延性能，而PVHO和IVHO的性能相比之下则较为优越且十分接近。
综上所述，本申请能够实现在中断发生时自适应地选择合适的切换机制，并得到出色的切换性能。仿真结果表明，本申请所采用的算法几乎在所有的情况下均为最优，或者是十分接近最优的。
值得注意的是，虽然本申请提出的算法是针对蜂窝网络和VLC的，但是 它的应用可以拓展到任何将无线媒质与VLC属性集成在一起的系统。此外，虽然本申请给出的智能的垂直切换决策算法是由按照分布式的移动终端来实施的，但是它也可以在稍微做以修改后应用于集中式垂直切换控制系统。
本申请公开了一种用于可见光通信异构组网中的垂直切换方法，通过在可见光通信系统进行链路检测和参数收集的过程，根据检测到的不同网络的状态信息，在下一次需要执行垂直切换的时刻，MT根据当前网络的使用状况，不同链路的质量水平，将其进行多方面的比较，根据当前用户的实际需求，选取合适的衡量不同网络性能的指标，按照设定好的VHO算法确定是否需要切换，并最终选择合适的目标网络。本申请一方面可以保证业务的连续性，提升QoS，另一方面也可以使得整个系统中的业务请求均匀化。在构建可见光通信异构组网的体系架构并研究其移动性管理的同时提出合适的垂直切换算法，并且不断对算法进行改进，对于改善可见光通信网络系统的性能具有重大意义。
虽然结合附图描述了本申请的实施方式，但是本领域技术人员可以在不脱离本申请的精神和范围的情况下做出各种修改和变型，这样的修改和变型均落入由所附权利要求所限定的范围之内。

Claims (9)

  1. 一种用于可见光通信异构组网中的垂直切换方法，其特征在于，包括以下具体步骤：
    S1：在系统开始运行后，移动终端在VLC信道上接收数据；
    S2：系统实时检测接收数据是否发生中断；
    S3：当中断发生时，垂直切换决策进程被触发，并决定应执行的垂直切换；
    S4：系统根据预先多次的中断情况对当前中断的相关参数进行预测，并以根据这些参数计算出的当前中断期间的消息传输时延的预测值为标准将IVHO与DVHO两种算法进行性能上的比较；
    S5：执行所述IVHO与DVHO两种算法中性能较优者，并在当前包传输执行完毕后，检测VLC连接是否恢复；
    S6：若所述VLC连接未恢复，接收数据继续在蜂窝网络中传输。
  2. 如权利要求1所述的方法，其特征在于，还包括：所述移动终端检测到可见光信道处于拥挤状态，其余无线接入网络的信道处于空闲状态，执行VHO算法。
  3. 如权利要求1所述的方法，其特征在于，所述移动终端用于检测多个不同网络链路数据，收集相关的多个不同网络的特性参数并进行处理。
  4. 如权利要求3所述的方法，其特征在于，所述多个不同网络的特性参数包括：不同网络当前的接收信号强度，比特率，拥挤程度，以及当前需要传输的数据的相关信息。
  5. 如权利要求1所述的方法，其特征在于，所述移动终端还用于检测当前网络的使用状况以及所述多个不同网络链路的质量水平并进行比较。
  6. 如权利要求1所述的方法，其特征在于，所述步骤S3包括：
    S31：搜集当前所述移动终端所在网络以及多个不同可接入网络的状态与参数；
    S32：对搜索到的状态与参数进行分析以及判决，执行切换。
  7. 如权利要求1所述的方法，其特征在于，所述步骤S5进一步包括：
    S51：在系统开始运行后，移动终端在VLC信道上接收数据；
    S52：系统实时检测接收数据是否发生中断；
    S53：当发生中断时，所述垂直切换决策进程被触发，进而决定垂直切换执行前的驻留时间的值；
    S54：若VLC连接在驻留计时器计时结束之前恢复，所述移动终端将使用VLC信道继续之前中断的数据传输，并跳转执行步骤S52；若VLC连接在驻留计时器计时结束之前没有恢复，垂直切换被执行，连接将被转移到蜂窝网络，并在当前包传输执行完毕后，检测VLC连接是否恢复。
  8. 如权利要求7所述的方法，其特征在于，所述步骤S54进一步包括：若VLC连接恢复，数据传输切换回VLC网络，并跳转执行步骤S52；若VLC连接没有恢复，数据继续在蜂窝网络中传输。
  9. 如权利要求7或8所述的方法，其特征在于，所述驻留时间在IVHO算法中设置为0，在DVHO算法中设置为短中断持续时间的最大值。
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