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Int. J. Electron. Commun. (AEÜ) 69 (2015) 1514–1524

Contents lists available at ScienceDirect

International Journal of Electronics andCommunications (AEÜ)

j ourna l h omepage: www.elsev ier .com/ locate /aeue

EGULAR PAPER

cross-layer mobility handover scheme for IPv6-based vehicularetworks

ang Xiaonan ∗, Le Deguang, Yao Yufenghangshu Institute of Technology, Jiangsu, Changshu 215500, China

r t i c l e i n f o

rticle history:eceived 17 December 2013ccepted 7 July 2015

eywords:ehicular network

Pv6

a b s t r a c t

This paper proposes a cross-layer mobility handover scheme for IPv6-based vehicular networks. In thisscheme, the architecture for vehicular networks is proposed and it is made up of three hierarchies includ-ing road domains, road segments and clusters. A vehicular network is made up of multiple road domains,a road domain consists of multiple road segments, and a road segment includes multiple clusters. Basedon this architecture, the cluster generation algorithm based on the link duration time is proposed, andthe cross-layer mobility handover algorithm is presented. In the handover algorithm, the handover in

oad domainoad segmentluster

the network layer (L3) is launched before the one in the link layer (L2). Through the L3 handover processthe information on the L2 handover can be acquired in order to achieve the fast L2 handover. Moreover,during the L3 handover process, a vehicle does not need to be configured with a care-of address, so theL3 handover delay and packet loss are reduced. The performance of the proposed scheme is evaluated,and the data results show that this scheme shortens the handover delay and lowers the packet loss rate.

© 2015 Elsevier GmbH. All rights reserved.

. Introduction

With the technology development of vehicular networks andhe emergence of new applications, it is necessary to connect vehic-lar networks to the Internet in order to meet users’ demands forew applications [1,2]. These applications require vehicular net-orks to support seamless wireless Internet services in vehiclesith high speed [3].

In wireless networks, the total handover is made up of the L2andover and L3 handover. In the L2 handover, the channel scan-ing is time-consuming, and it is a main factor influencing theandover delay [4]. In the L3 handover, the care-of address config-ration occupies a large proportion of the L3 handover delay. The3 handover standards such as mobile Internet protocol version 6MIPv6) [5] are typically applied in the wired networks. When theserotocols are applied in wireless networks, they cannot work effi-iently due to high packet loss and long delay [6]. Moreover, these3 handover protocols are totally separated from the L2 handovernes, and they do not help improve the L2 handover performance.

In order to shorten the total handover delay and lower theacket loss, this paper proposes a cross-layer mobility handovercheme for vehicular networks. The main goal of this scheme is to

∗ Corresponding author. Tel.: +86 15851550692.E-mail address: ninawang9@163.com (X. Wang).

ttp://dx.doi.org/10.1016/j.aeue.2015.07.003434-8411/© 2015 Elsevier GmbH. All rights reserved.

combine the L3 handover with the L2 handover to improve the totalhandover performance. This paper has the following contributions:

1) The architecture for vehicular networks is proposed, and it ismade up of three hierarchies including road domains, road seg-ments and clusters. A vehicular network is made up of multipleroad domains, a road domain consists of multiple road segments,and a road segment is composed of multiple clusters.

2) Based on this architecture, the cluster generation algorithmbased on the link duration time is proposed.

3) Based on this architecture, the cross-layer mobility handoveralgorithm is presented. In this algorithm, the L3 handover islaunched before the L2 one. Through the L3 handover process, avehicle can acquire the channel information in order to achievethe fast L2 handover without scanning all channels. Moreover,in the L3 handover process, a vehicle does not need to be config-ured with a care-of address. As a result, the total handover delayis reduced and the packet loss rate is lowered.

The remainder of this paper is organized as follows. In Section

2, the related work on the handover schemes is discussed. Theproposed handover scheme is presented in Section 3, and the per-formance is evaluated in Sections 4 and 5. This paper concludeswith a summary in Section 6.

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. Related work

In wireless networks, two kinds of handovers are included,amely the L2 handover and L3 handover.

.1. L2 handover

In the L2 handover, the channel scanning is time-consuming,nd it is a main factor influencing the handover delay [4]. Therefore,he L2 handover schemes focus on reducing the scanning delay.

Chiu et al. [7] propose a fast handover scheme where the infor-ation on the physical layer is shared with the link layer in order to

educe the handover delay. This scheme operates based on mobileulti-hop relay technique that allows inter-vehicle communica-

ions to access the Internet via a relay vehicle. In Ref. [8], thehannels usually used by access points are selected in order to avoidhe full scanning process and reduce the scanning delay.

In Refs. [9,10], a mobile node first performs the full pre-scanningrocess in order to get the information on all neighbor access points.ased on the information, the mobile node selects the best accessoint to perform the L2 handover. The data results show that the2 handover delay is reduced to some extent.

.2. L3 handover

The L3 handover standards such as MIPv6 [5] are typicallypplied in wired networks. When these protocols are applied inireless networks, they cannot work efficiently due to high packet

oss and long delay [6].Islam and Huh [11] propose the sensor PMIPv6 (SPMIPv6).

PMIPv6 presents the network architecture and message formatsor the mobility handover process, and it also evaluates the mobilityandover cost. The results show that SPMIPv6 reduces the mobil-

ty handover cost significantly. In Ref. [12], the mobility handoverrocess is achieved in the link layer, so the mobility handover delaynd cost are reduced.

Bag et al. [13] propose a scheme which reduces both the mobilityandover cost and tunnel establishment cost. This scheme dependsn dispatch types to determine source or destination of a packet. As

result, intermediate nodes forwarding a packet have to identifyll dispatch types in order to determine the next hop, so the delays increased and the network scalability is also limited. Moreover,

header structure is added between the adaptation layer and theetwork layer, so the transmission delay is increased.

Denko and Wei [14] propose a mobility management scheme forntegrating MANETs into the Internet using multiple mobile gate-

ay (MGs) and foreign agents (FAs). This scheme extends the ad hocn demand distance vector (AODV) and MIP to achieve the integra-ion. The simulation results show that the use of both multiple MGsnd the hybrid gate discovery mechanism enhances the networkerformance. Fan et al. [15] provide the localized mobility manage-ent scheme in mesh networks which uses the multi-path routing

o achieve the mobility handover. However, this scheme requiresome special signaling costs to deal with mobile terminals, so theelay is prolonged to some extent.

Lee et al. [16] use an intermediate-mobile access gatewayiMAG) to perform the mobility handover for vehicular networks.MAG must be geographically located between the home domainnd foreign domain, so this scheme cannot support the globalobility management. In addition, iMAG must store the infor-ation on all road-side units, and maintaining the information

onsumes a lot of network resources.

In Ref. [17], clusters are employed to improve the mobility han-

over performance. In this scheme, cluster heads are in charge of IPobility for other vehicles. Wang and Qian [18] propose a mobil-

ty handover scheme for IPv6-based vehicular networks, and this

n. (AEÜ) 69 (2015) 1514–1524 1515

scheme improves the handover performance to some extent. How-ever, this scheme does not use the information in the link layer toshorten the handover delay.

Kim et al. [19] propose an enhanced PFMIPv6 (ePFMIPv6) forvehicular networks. In ePFMIPv6, the serving MAG pre-establishesa tunnel with multiple candidate MAGs. When the serving MAGperforms the mobility handover, it can forward the packets to thenext MAG. ePFMIPv6 shortens the mobility handover delay andlowers the packet loss, but it increases the mobility handover cost.

In the above L3 handover schemes, a mobile node needs to beconfigured with a care-of address. These schemes do not addresshow to reduce the care-of address configuration delay although thecare-of address configuration delay occupies a large proportion ofthe L3 handover delay.

2.3. Our solution

From the above discussion, it can be seen that the followingfactors influence the handover performance:

1) The L3 handover is totally separated from the L2 handover, andit does not help improve the L2 handover performance.

2) The channel scanning is time-consuming and occupies a largeproportion of the L2 handover.

3) The care-of address configuration is time-consuming and occu-pies a large proportion of the L3 handover.

In order to shorten the handover delay and lower the packetloss, this paper proposes a cross-layer mobility handover schemefor IPv6-based vehicular networks. The main goal of this scheme isto combine the L3 handover with the L2 handover to improve thetotal handover performance. This scheme proposes the followingstrategies to improve the handover performance:

1) The L3 handover provides the channel information in order tohelp achieve the fast L2 handover without scanning all channels.

2) In the L2 handover, a vehicle does not need to scan all channels,so the L2 handover delay is reduced.

3) In the L3 handover, a vehicle does not need to be configured witha care-of address, so the L3 handover delay is reduced.

3. Cross-layer mobility handover

3.1. Architecture

A vehicular network is made up of access routers (ARs), basestations and vehicles. An AR is connected to the IPv6 Internet, anda base station is connected to an AR. The area covered by all basestations connected to one AR is called a road domain (RD), andthe area covered by a base station is called a road segment (RS).Vehicles are divided into three categories: a cluster head (CH) withrouting and forwarding function, a cluster member (CM) withoutrouting or forwarding function, and an isolated vehicle (IV). A CHcommunicates directly with a base station, and a CM achieves thecommunication with the Internet through its CH. An IV is a nodewhich does not join a cluster.

In this way, the architecture is made up of three hierarchies: anRD which is identified by an AR, an RS which is identified by a basestation, and a cluster which is identified by a CH.

An RD is made up of multiple RS, and an RS consists of a num-ber of clusters. A CH is usually acted by large automobiles, such asbuses. A vehicle is uniquely identified by its home address duringthe mobility process, as shown in Fig. 1.

1516 X. Wang et al. / Int. J. Electron. Commu

Fig. 1. Architecture.

Table 1IPv6 address structure.

(128-i-j) bits i bits j bits

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RD ID RS ID Vehicle ID

.2. Address structure

Based on the proposed architecture, the hierarchical IPv6ddress structure for vehicular networks is proposed, as shown inable 1.

In Table 1, an address consists of three parts. The first part isD ID which is the global routing prefix and uniquely identifies anD. In an RD, the RD IDs of the base stations and the RD IDs ofhe addresses acquired from this RD are the same, and the value isqual to the one of the AR in the same RD. The second part is RS IDhich uniquely identifies an RS. The RS IDs of the IPv6 addresses

cquired from one RS are the same, and the value is equal to thene of the base station in the same RS. The third part is vehicle IDhich uniquely identifies a vehicle. The address of an AR or a base

tation is preconfigured, the RD ID and vehicle ID of an AR’s addressre zero, and the vehicle ID of a base station is zero.

The values of i and j are determined by the size of a vehicularetwork and the density of vehicles. Taking generality into account,his scheme sets i to 16 and j to 32, as shown in Fig. 1. The IPv6ddress configuration for vehicular networks is achieved throughur previous work [20]. After a CH acquires an address in an RS, theR in the same RD records the associate relationship between theH and the base station in the same RS.

.3. Establishment of clusters

In this scheme, a CH is acted by a large automobile.fter a large bus starts, it marks itself as a CH and periodi-ally broadcasts a dedicated short range communication (DSRC)essage-BasicSafetyMessage [21] whose payload includes the

ode type, the speed, the mobile angle, the geographic coordinate,he working channel and the address of the base station in the RShere it is located.

If a vehicle is not a large automobile, then it marks itself as an IVnd scans all channels to receive the DSRC messages from neigh-or CHs. Then, the IV selects the CH with the longest link durationime, joins the cluster identified by the CH, marks itself as a CM andegins to periodically broadcast BasicSafetyMessage whose pay-

oad includes the node type, the speed, the mobile angle, and theeographic coordinate.

A vehicle can acquire its geographic coordinate through someystems, for example, the global positioning system (GPS). It is

n. (AEÜ) 69 (2015) 1514–1524

assumed that the coordinate of the vehicle Vi/Vj is (xi, yi)/(xj, yj),the speed of Vi/Vj is vi/vj, the moving angle of Vi/Vj is �i/�j (0 ≤ �i,�j < 2�), and the communication range of a vehicle is r. Then, thelink duration time Tij between Vi and Vj can be estimated accordingto Eq. (1) [22].

Tij =√

(a2 + c2)r2 − (ad − bc)2 − (ab + cd)a2 + c2

(1)

where

a = vi cos �i − vj cos �j

b = xi − xj

c = vi sin �i − vj sin �j

d = yi − yj

3.4. Mobility handover for CH

In this scheme, a base station stores the geographical coordi-nates and working channels of its neighbor base stations, and a CHperiodically broadcasts a DSRC message whose payload includesthe mobile angle, speed and geographic coordinate. The work inRef. [23] has shown that a node can determine the neighbor nodewith the best communication performance via listening to a DSRCmessage from its neighbors. This scheme adopts the method in Ref.[23] to determine the next RS where a CH is entering. It is assumedthat the CH C1 is located in the RS S1 which is identified by thebase station B1. Then, B1 can acquire C1’s mobile angle, speed andgeographic coordinate through receiving a DSRC message from C1.If B1 detects that C1 is leaving its communication range, then itcalculates the link duration time between C1 and its neighbor basestations according to formula (1) and selects as C1’s next base sta-tion the base station B2 with the largest link duration time. That is,the RS identified by B2 is C1’s next RS.

3.4.1. CH inter-RS handoverIf B1 and B2 belong to one RD where the AR is R1, then B1

launches the following operations:

1) B1 sends R1 a Handover message whose payload is the addressesof C1 and B2.

2) After R1 receives the Handover message, it updates C1’s asso-ciate base station with B2 and returns a Handover-Ack messageto B1.

3) After B1 receives the Handover-Ack message, it sends C1 a Han-dover message whose payload is B2’s working channel.

4) After C1 receives the Handover message, it uses B2’s workingchannel to directly switch to B2 and begins to receive the datamessages from B2, as shown in Fig. 2(a) and (b).

In Fig. 2(a) and (b), at the time T1, C1 is leaving B1’s communica-tion range and entering the next RS identified by B2, R1 stores theassociate relationship between C1 and B1, and B1 launches the CHinter-RS handover by sending a Handover message. At the time T2,C1 switches to B2 and R1 stores the associate relationship betweenC1 and B2. At this stage, the CH inter-RS handover process ends.

3.4.2. CH inter-RD handoverIf B1 belongs to the RD where the AR is R1 and B2 belongs to the

RD where the AR is R2, then B1 launches the following operations:

1) B1 sends R2 a Handover message whose payload is the addressesof C1 and B2.

2) After R2 receives the Handover message, it can determinethat B1 belongs to the different RD by checking B1’s address.

X. Wang et al. / Int. J. Electron. Commu

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Fig. 2. CH inter-RS handover.

Therefore, R2 records the associate relationship between C1and B2, and sends a Handover message to the AR HR of theRD where C1 acquires the home address. The payload of theHandover message is C1’s address.

) After HR receives the Handover message, it updates C1’sassociate AR with R2 and returns a Handover-Ack message to R2.

) After R2 receives the Handover-Ack message, it sends B1 aHandover-Ack message. After B1 receives the Handover-Ackmessage, it sends C1 a Handover message whose payload is B2’sworking channel.

) After C1 receives the Handover message, it uses B2’s workingchannel to directly switch to B2 and begins to receive the datamessages from B2, as shown in Fig. 3(a) and (b).

In Fig. 3(a) and (b), at the time T1, C1 is leaving B1’s communica-ion range and entering the next RS identified by B2, HR stores thessociate relationship between C1 and R1, R1 stores the associateelationship between C1 and B1, and B1 launches the CH inter-D handover by sending a Handover message. At the time T2, C1witches to B2, HR stores the associate relationship between C1 and2, and R2 stores the associate relationship between C1 and B2. At

his stage, the CH inter-RD handover process ends.

In the CH inter-RS/inter-RD handover process, the L3 handovers performed before the L2 one. If B2 receives the data messagesestined for C1 but it does not receive a DSRC message from C1, then

n. (AEÜ) 69 (2015) 1514–1524 1517

it stores these data messages. After C1 switches to B2, B2 forwardsthese data messages to C1.

3.5. Mobility handover for CM

It is assumed that the CH C1 of the CM M1 is located in the RSS1 which is identified by the base station B1, S1 belongs to the RDwhere the AR is R1, and the IPv6 node N1 is located in the subnetwhere the AR is R2. Then, the communication process between M1and N1 is as follows:

1) M1 sends C1 a data message whose destination address is N1.C1 forwards this data message to B1. B1 records the associaterelationship between M1 and C1, and then forwards the datamessage to R1.

2) After R1 receives the data message, it records the associate rela-tionship between M1 and C1, and then builds a tunnel reachingR2. Through this tunnel, the data message reaches R2 whichforwards the data message to N1.

3) The data message returned by N1 first reaches R2 which routesthe message to R1 through the tunnel. Based on the associaterelationship between M1 and C1 and the one between C1 andB1, R1 forwards the data message to B1. Similarly, accordingto the relationship between M1 and C1, B1 forwards the datamessage to C1 which then forwards the data message to M1, asshown in Fig. 4.

In Fig. 4, after the life time of the associate relationship betweenM1 and C1 expires, it is deleted from B1 and R1.

In this scheme, a CH or CM periodically broadcasts a DSRCmessage whose payload includes the mobile angle, speed and geo-graphic coordinate. This scheme adopts the method in Ref. [23] todetermine the next cluster where a CM is entering. It is assumedthat the CH C1 of the CM M1 is located in the RS S1 which is iden-tified by the base station B1, and S1 belongs to the RD where theAR is R1. Through listening to a DSRC message from M1, C1 canacquire M1’s mobile angle, speed and geographic coordinate. If C1detects that M1 is leaving its communication range, then it cal-culates the link duration time between M1 and its neighbor CHsaccording to Eq. (1) and selects as M1’s next CH the CH C2 withthe largest link duration time. That is, the cluster identified by C2is M1’s next cluster.

This scheme employs a DSRC message to determine the nextcluster head. Since a CM periodically broadcasts a DSRC message,it does not need to support the additional operations to determinethe next cluster head. Moreover, it is the CH that determines thenext CH for its CM, so the CM does not need to report its neighborsto its CH.

In this scheme, only if a CM is communicating with an IPv6 nodeduring its mobility process, the handover process for a CM is per-formed. The handover process for a CM is discussed according tothe following three situations.

3.5.1. CM intra-RS handoverIf C1 and C2 belong to one RS and M1 is communicating with an

IPv6 node, then C1 launches the following operations:

1) C1 sends B1 a Handover message whose payload is the addressesof M1 and C2.

2) After B1 receives the Handover message, it updates M1’s CH withC2 and then returns a Handover-Ack message to C1.

3) After C1 receives the Handover-Ack message, it sends M1 a Han-dover message whose payload is C2’s working channel.

1518 X. Wang et al. / Int. J. Electron. Commun. (AEÜ) 69 (2015) 1514–1524

Fig. 3. CH inter-RD handover.

Fig. 4. Communication process.

X. Wang et al. / Int. J. Electron. Commun. (AEÜ) 69 (2015) 1514–1524 1519

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) After M1 receives the Handover message, it uses C2’s workingchannel to directly switch to C2 and starts receiving the datamessages from C2.

.5.2. CM inter-RS handoverIf C1 and C2 belong to different RS in the same RD, C2 is located

n the RS which is identified by the base station B2, and M1 isommunicating with an IPv6 node, then C1 launches the followingperations:

) C1 sends B2 a Handover message whose payload is the addressesof M1 and C2.

) After B2 receives the Handover message, it stores the associaterelationship between M1 and C2 and sends a Handover messageto R1.

) After R1 receives the Handover message, it updates M1’s CHwith C2, and returns a Handover-Ack message to B2. After B2receives the Handover-Ack message, it sends C1 a Handover-Ackmessage.

) After C1 receives the Handover-Ack message, it sends M1 a Han-dover message whose payload is C2’s working channel.

) After M1 receives the Handover message, it uses C2’s workingchannel to directly switch to C2 and starts receiving the datamessages from C2, as shown in Fig. 5(a) and (b).

In Fig. 5(a) and (b), at the time T1, M1 is leaving C1’s commu-

ication range and entering the next cluster identified by C2, R1nd B1 store the associate relationship between M1 and C1, and C1aunches the CM inter-RS handover by sending a Handover mes-age. At the time T2, M1 switches to C2 and marks C2 as its CH, and

S handover.

R1 and B2 store the associate relationship between M1 and C2. Atthis stage, the CM inter-RS handover process ends.

3.5.3. CM inter-RD handoverIf C1 and C2 belong to different RD, C2 is located in the RS which

is identified by the base station B2, C2 is located in the RD where theAR is R2, and M1 is communicating with an IPv6 node in the subnetwhere the AR is R3, then C1 launches the following operations:

1) C1 sends B2 a Handover message whose payload is the addressesof M1, C2 and R3.

2) After B2 receives the Handover message, it stores the relation-ship between M1 and C2, and forwards the Handover message toR2. R2 stores the relationship between M1 and C2, and forwardsthe Handover message to R3.

3) After R3 receives the Handover message, it establishes the tunnelreaching R2 and returns a Handover-Ack message to R2. After R2receives the Handover-Ack message, it sends a Handover-Ackmessage to B2 which then sends a Handover-Ack message toC1.

4) After C1 receives the Handover-Ack message, it sends M1 a Han-dover message whose payload is C2’s working channel.

5) After M1 receives the Handover messages, it uses C2’s workingchannel to directly switch to C2 and starts receiving the datamessages from C2, as shown in Fig. 6(a) and (b).

In Fig. 6(a) and (b), at the time T1, M1 is leaving C1’s commu-

nication range and entering the next cluster identified by C2, R1and B1 store the associate relationship between M1 and C1, and C1launches the CM inter-RD handover by sending a Handover mes-sage. At the time T2, M1 switches to C2 and marks C2 as its CH, and

1520 X. Wang et al. / Int. J. Electron. Commun. (AEÜ) 69 (2015) 1514–1524

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2 and B2 store the associate relationship between M1 and C2. Athis stage, the CM inter-RD handover process ends.

In the CM intra-RS/inter-RS/inter-RD handover process, the L3andover is launched before the L2 one. If C2 receives the data mes-ages destined for M1 but it does not receive a DSRC message from1, then it stores these data messages. After M1 switches to C2, C2

orwards these data messages to M1.

. Analysis

.1. Handover delay

.1.1. CH handover delayBased on Fig. 2(b), the CH inter-RS mobility handover delay

CH-RS is made up of the L3 handover delay TL3-CH-RS and the L2andover delay TL2, as shown in Eq. (2) where tHandover/tHandover-Ack

s the delay of transmitting a Handover/Handover-Ack messageetween two neighbor nodes, DAR-BS is the distance between anR and a base station in the same RD, and DBS-CH is the distanceetween a base station and a CH in the same RS.

TCH-RS = TL3-CH-RS + TL2

where

TL3-CH-RS = tHandover · DAR-BS + tHandover-Ack · DAR-BS

+ tHandover · DBS-CH

(2)

Based on Fig. 3(b), the CH inter-RD mobility handover delayCH-RD is made up of the L3 handover delay TL3-CH-RD and the2 handover delay TL2, as shown in Eq. (3) where DAR-HR is the

D handover.

distance between the AR of the RD where a vehicle is located andthe AR where the vehicle acquires an address.

TCH-RD = TL3-CH-RD + TL2

where

TL3-CH-RD = (tHandover + tHandover-Ack) · DAR-BS

+ (tHandover + tHandover-Ack) · DAR-HR + tHandover · DBS-CH

(3)

4.1.2. CM handover delayThe CM intra-RS mobility handover delay TCM-CH includes the L3

handover delay TL3-CM-CH and the L2 handover delay TL2, as shownin Eq. (4) where DCH-CM is the distance between a cluster memberand a cluster head in the same cluster.

TCM-CH = TL3-CM-CH + TL2

where

TL3-CM-CH = (tHandover + tHandover-Ack) · DBS-CH

+ tHandover · DCH-CM

(4)

Based on Fig. 5(b), the CM inter-RS mobility handover delayTCM-RS consists of the L3 handover delay TL3-CM-RS and the L2 han-dover delay TL2, as shown in Eq. (5).

TCM-RS = TL3-CM-RS + TL2

where

TL3-CM-RS = (tHandover + tHandover-Ack) · DAR-BS

(5)

+ (tHandover + tHandover-Ack) · DBS-CH + tHandover · DCH-CM

Based on Fig. 6(b), the CM inter-RD mobility handover delayTCM-RD is made up of the L3 handover delay TL3-CM-RD and the L2handover delay TL2, as shown Eq. (6) where DAR-DR is the distance

ommun. (AEÜ) 69 (2015) 1514–1524 1521

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Table 2Simulation parameters.

Parameters Values

v 10–30 m/sTL2 25 msR 1–2 kmr 200–300 mtHandover/tHandover-Ack 5 msDAR-BS/DBS-CH/DCH-CM 1DAR-HR/DAR-DR 4Rounds 10

X. Wang et al. / Int. J. Electron. C

etween the AR of the RD where a vehicle is located and the AR ofhe subnet where a destination IPv6 node is located.

TCM-RD = TL3-CM-RD + TL2

where

TL3-CM-RD = (tHandover + tHandover-Ack) · DAR-BS

+ (tHandover + tHandover-Ack) · DBS-CH

+ (tHandover + tHandover-Ack) · DAR-DR + tHandover · DCH-CM

(6)

.2. Packet loss

The real-world traffic traces and synthetic mobility modelsemonstrate that it is a reasonable assumption that the vehiclerrival follows Poisson distribution [24,25]. In this scheme, theehicle arrival follows Poisson distribution. It is assumed that theosition of a base station is 0, the transmission range of a base sta-ion is R, � is the vehicle density measured in vehicles per metervpm), and the transmission range of a CH or CM is r which is lesshan R. For a vehicle located at x in [0,R], p1(x) is the probabilityf a CH being directly connected to a base station, and p2(x) is therobability of a CM being connected to a base station through aH which is directed connected to a base station. Then, p1(x) and2(x) are shown in Eqs. (7) and (8) [26] where gBS(x) is the prob-bility that a CH and a base station separated by a distance x areirectly connected, and gCH(x) is the probability that a CM and a CHeparated by a distance x are directly connected.

1(x) = gBS(x) (7)

2(x) = 1 − e−∫ 2r

0gCH(‖x−y‖)�p1(y)dy

(8)

.2.1. CH packet lossDuring the CH inter-RS and inter-RD mobility handover pro-

esses, the L3 handover is performed before the L2 one, so duringhe L3 handover a CH can still receive the data messages from theriginal serving base station. As a result, the inter-RS packet lossate PCH-RS and inter-RD packet loss rate PCH-RD are shown in Eqs.9) and (10) where v is the average speed.

CH-RS = tHandover-Ack · DAR-BS + tHandover · DBS-CH + TL2

R/v· p1(x) (9)

CH-RD = tHandover-Ack · (DAR-BS + DAR-HR) + tHandover · DBS-CH + TL2

R/v

·p1(x) (10)

.2.2. CM packet lossDuring the CM intra-RS, inter-RS and inter-RD mobility han-

over processes, the L3 handover is performed before the L2 one,o during the L3 handover a CM can receive the data messages fromhe original CH. As a result, the intra-RS packet loss rate PCM-CH, thenter-RS packet loss rate PCM-RS and the inter-RD packet loss rateCM-RD are shown in Eqs. (11)–(13).

CM-CH = tHandover-Ack · DBS-CH + tHandover · DCH-CM + TL2

r/v· p2(x)

(11)

tHandover-Ack · (DAR-BS + DBS-CH) + tHandover · DCH-CM + TL2

CM-RS =

r/v

·p2(x) (12)

Confidence level 0.95Simulation time 500 s

PCM-RD

= tHandover-Ack · (DAR-DR + DAR-BS + DBS-CH) + tHandover · DCH-CM + TL2

r/v

·p2(x) (13)

Based on Eqs. (14) and (15) [26], PCH-RS, PCH-RD, PCM-CH, PCM-RSand PCM-RD can be evaluated.

gBS(x) ={

1; x ≤ R

0; otherwise(14)

gCH(x) ={

1; x ≤ r

0; otherwise(15)

5. Simulation

NS-2 is used to evaluate the performance of the proposedscheme. In this scheme, the link protocol adopts the IEEE 802.11pstandard which is defined by Ref. [27], so the simulation parametersare set based on Ref. [27], as shown in Table 2. In the simulation,after a node starts it periodically broadcasts a BasicSafetyMessageat a rate of every 100 ms. The average speed of a vehicle rangesfrom 10 m/s to 30 m/s, and the L2 handover delay is set to 25 ms.The average data of 10 simulation rounds are used to evaluate thehandover delay and packet loss rate, and the simulation time forone round is 500 s. The traffic model follows Poisson distribution.In Poisson process, the number of events in a given interval followsPoisson distribution [28,29]. In the traffic model, Poisson process isused to describe the arrivals of vehicles in a given interval. That is,in a given period the number of vehicles arriving follows Poissondistribution.

5.1. The effect of speed

5.1.1. The effect of speed on CHWhen R is 1 km, the CH handover delay and packet loss rate

based on speed are shown in Figs. 7 and 8.With the increase in speed, the frequency of a CH performing the

inter-RS/inter-RD mobility handover increases and the link stabil-ity weakens, so both the network traffic and the packet loss rategrow, as shown in Fig. 8. Since the retransmission of the lost pack-ets causes the extra delay, there is a slight increment in the delay,as shown in Fig. 7. From Figs. 7 and 8, it can be seen that both theinter-RS handover delay and packet loss rate are lower than theinter-RD ones.

5.1.2. The effect of speed on CMWhen r is 250 m, the CM handover delay and packet loss rate

based on speed are shown in Figs. 9 and 10.

1522 X. Wang et al. / Int. J. Electron. Commun. (AEÜ) 69 (2015) 1514–1524

0

20

40

60

80

100

120

10 15 20 25 30

Speed( m/s)

Del

ay(m

s)Inter- RS-Ana Inter- RS-SimInter- RD-Ana Inter- RD-Sim

Fig. 7. CH handover delay based on speed.

0

1

2

3

4

5

10 15 20 25 30

Speed(m/s)

Loss

rate

(‰)

Inter-RS-Ana In ter-RS-SimInter-RD-Ana In ter-RD-Sim

Fig. 8. CH packet loss rate based on speed.

0

20

40

60

80

100

10 15 20 25 30

Speed(m/s)

Del

ay(m

s)

Intra-RS-Ana Intra-RS-SimInter- RS-Ana Inter- RS-SimInter- RD-Ana Inter- RD-Sim

Fig. 9. CM handover delay based on speed.

0

2

4

6

8

10

10 15 20 25 30

Speed(m/s)

Loss

rate

(‰)

Intra-RS-Ana In tra-R S-SimInter-RS-Ana Inter-RS-SimInter- RD-Ana In ter-RD-Sim

Fig. 10. CM packet loss rate based on speed.

0

20

40

60

80

100

1000 12 00 1400 160 0 1800 2000R

Del

ay(m

s)

Inter-RS-Ana Inter-RS-SimInter-RD-Ana Inter-RD-Sim

Fig. 11. CH handover delay based on R.

0

0.5

1

1.5

2

1000 120 0 14 00 1600 1800 200 0

Loss

rate

(‰)

Inter-RS-Ana Inter-RS-SimInter-R D-Ana In ter-RD-Sim

R

Fig. 12. CH loss rate based on R.

With the increase in speed, the frequency of a CM performingthe intra-RS/inter-RS/inter-RD mobility handover increases and thelink stability weakens, so both the network traffic and the packetloss rate grow, as shown in Fig. 10. Since the retransmission of thelost packets causes the extra delay, there is a slight increment inthe delay, as shown in Fig. 9. From Figs. 9 and 10, it can be seen thatthe intra-RS handover delay and packet loss rate are minimum, andthe inter-RD handover delay and packet loss rate are maximum.

5.2. The effect of communication range

5.2.1. The effect of communication range on CHWhen the average speed is 20 m/s, the CH handover delay and

packet loss rate based on R are shown in Figs. 11 and 12.When R increases, the frequency of a CH performing the

inter-RS/inter-RD handover reduces. Therefore, the network trafficcaused by the CH handover decreases and the network performanceenhances. As a result, the packet loss rate and the additional delaycaused by the retransmission of the lost packets are reduced. Hence,the packet loss rate and the handover delay are reduced, as shownin Figs. 11 and 12.

5.2.2. The effect of communication range on CMWhen the speed is 20 m/s, the CM handover delay and packet

loss rate based on r are shown in Figs. 13 and 14.With the increased in r, the frequency of a CM performing

the intra-RS/inter-RS/inter-RD handover decreases, so the network

traffic caused by the CM handover reduces and the network perfor-mance enhances. Also, the packet loss rate and the additional delaycaused by the retransmission of the lost packets are reduced, so thehandover delay is decreased, as shown in Figs. 13 and 14.

X. Wang et al. / Int. J. Electron. Commun. (AEÜ) 69 (2015) 1514–1524 1523

0

20

40

60

80

100

120

200 22 5 25 0 27 5 30 0

r

Del

ay(m

s)Intra-RS-Ana Intra-RS-SimInter-RS-Ana Inter-RS-SimInter-RD-Ana In ter-RD-Sim

Fig. 13. CM handover delay based on r.

0

2

4

6

8

10

200 22 5 25 0 27 5 30 0

r

Loss

rate

(‰)

Intra-RS-Ana Intra-RS-SimInter-RS-Ana Inter-RS-SimInter-R D-Ana Inter-RD-Sim

Fig. 14. CM loss rate based on r.

ra

1

2

50

60

70

80

90

20 22 24 26 28 30

Speed( m/s)

Del

ay(m

s)

Pro posed Stand ard ePFMIPv6

Fig. 15. Delay comparison based on speed.

0

2

4

6

8

20 22 24 26 28 30

Loss

rate

(%)

Pro posed Stand ard ePFMIPv6

reduces and the network performance enhances. As a result, thepacket loss rate and the additional delay caused by the retransmis-sion of the lost packets are reduced, so the handover delay is also

From Fig. 7 to Fig. 14, it can be seen that the delay and packet lossate in the simulation do not totally match the ones in the analysis,nd the main reasons are analyzed as follows:

) The analysis only focuses on the delay caused by the handoverprocess itself. That is, the handover delay in the analysis is theinterval from the time when the handover process is launchedto the time when the handover process is complete, and it doesnot include the extra delay caused by the retransmission of thelost packets. In the simulation, the handover delay is made upof the delay caused by the handover process itself and the extradelay caused by the retransmission of the lost packets. Therefore,compared with the handover delay in the analysis, the handoverdelay in the simulation has a slight increment which tends to beequal to the extra delay caused by the retransmission of the lostpackets.

) The analysis only focuses on the packet loss caused by the han-dover process itself, so the packet loss does not include the extrapacket loss caused by the link instability. In the simulation, thepacket loss is made up of the packet loss caused by the han-dover process itself and the extra packet loss caused by the linkinstability. Therefore, compared with the packet loss rate in theanalysis, the packet loss rate in the simulation has a slight incre-ment which tends to be equal to the extra packet loss rate caused

by the link instability.

Speed( m/s)

Fig. 16. Loss rate comparison based on speed.

5.3. Comparison

In order to evaluate the performance of this scheme, we compareour scheme with the standard [1] and the new handover scheme– ePFMIPv6 [19]. When R is 1 km and r is 250 m, the handoverdelay and packet loss rate comparison based on speed are shownin Figs. 15 and 16.

With the increase in speed, the link stability weakens and thefrequency of a vehicle performing the mobility handover increases.Therefore, the network traffic caused by the handover grows andthe network performance degrades. As a result, the handover delaysand the packet loss rates in these three solutions all grow, as shownin Figs. 15 and 16. In this scheme, the number of CMs is much morethan the number of CHs, so the overall performance tends to presentthe performance of the CM handover. When the speed increases,the frequency of a CM performing the Inter-RD handover grows.Because the packet loss rate and the delay in the inter-RD handoverare more than the ones in both the intra-RS handover and inter-RShandover, the packet loss rate and the delay grow with the increasein speed.

Since the number of CMs is much more than the number of CHs,the overall performance tends to present the performance of theCM handover. Therefore, the handover delay and packet loss ratebased on r are evaluated. When the speed is 10 m/s and R is 1 km,the handover delay and packet loss rate based on r are shown inFigs. 17 and 18.

With the increase in r, the frequency of a vehicle performing thehandover decreases, so the network traffic caused by the handover

decreased, as shown in Figs. 17 and 18.

1524 X. Wang et al. / Int. J. Electron. Commu

50

60

70

80

90

100

200 22 5 25 0 27 5 300

r

Del

ay(m

s)Proposed Standard ePFMIPv6

Fig. 17. Delay comparison based on communication range.

0

1

2

3

4

200 22 5 25 0 27 5 300r

Loss

rate

(%)

Pro posed Stand ard ePFMIPv6

hsniaaivslnd

6

Ipahc

dm

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

Fig. 18. Loss rate comparison based on communication range.

From Fig. 15 to Fig. 18, it can be seen that the proposed schemeas better performance than the standard and ePFMIPv6. In thetandard and ePMIPv6, a vehicle needs to be configured with aew care-of address, so the frequent change of a vehicle’s address

ncreases the packet loss rate. In addition, a vehicle needs to scanll channels to achieve the L2 handover, so the total handover delaynd packet loss rate grow. In the proposed scheme, the L3 handovers performed before the L2 one. Through the L3 handover process, aehicle can achieve the L2 handover without scanning all channels,o the L2 handover delay is shortened and the packet loss rate isowered. Moreover, during the L3 handover process, a vehicle doesot need to be configured with a care-of address, so the handoverelay in L3 is reduced and the packet loss is decreased.

. Conclusion

This paper proposes a cross-layer mobility handover scheme forPv6-based vehicular networks. In this scheme, the L3 handover iserformed before the L2 one, and through the L3 handover process

vehicle can achieve the fast L2 handover. Moreover, during the L3andover process, a vehicle does not need to be configured with a

are-of address.

The performance of the proposed scheme is evaluated and theata results show that this scheme improves the handover perfor-ance.

[

[

n. (AEÜ) 69 (2015) 1514–1524

Acknowledgements

This work is supported by Jiangsu Nature Science Foundation(BK20141230) and National Natural Science Foundation of China(61202440).

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