A Cross-Layer Scheme for Handover in 802.16e Network with F-HMIPv6 Mobility

doi:10.4236/cn.2009.11005

Paper Menu >>

Journal Menu >>

Communications and Network, 2009, 35-41

doi:10.4236/cn.2009.11005 Published Online August 2009 (http://www.scirp.org/journal/cn)

A Cross-Layer Scheme for Handover in 802.16e

Network with F-HMIPv6 Mobility

Yi ZHENG, Yong ZHANG, Yinglei TENG, Mei SONG

Beijing University of Posts and Telecommunications, Beijing, China

Email: {zhengyibupt, bjzhangyong, lilytengtt}@gmail.com; [email protected]

Abstract: IEEE802.16e is the major global cellular wireless standard that enables low-cost mobile Internet

application. However, existing handover process system still has latency affects time-sensitive applications. In

this paper, the handover procedures of 802.16e and Fast Handover for Hierarchical MIPv6 (F-HMIPv6) are

reconstructed to achieve a better transmission performance. The concept of cross layer design is adopted to

refine the existing handover procedure specified in 802.16e MAC layer and F-HMIPv6. More specifically,

layer2 and layer3 signaling messages for handover are analyzed and combined/interleaved to optimize the

handover performance. Extensive simulations show that the proposed scheme in this paper is superior to the

other scheme proposed by IETF.

Keywords: handover, cross layer, 802.16e, F-HMIPv6

1. Introduction

Recently, wireless access technologies have been evolv-

ing for diverse capabilities and services. The Third Gen-

eration Partnership Project (3GPP) has been defining

Universal Terrestrial Radio Access (UTRA) for 3G radio

access，as well as the optimization of the network archi-

tecture with HSxPA [1]. The CDMA2000 mobile com-

munication system also has been evolved into 1xEV-Dx

for high speed data services. As one of wireless access

technologies, Mobile WiMAX was successfully adopted

by ITU as one of the IMT-2000 technologies in Novem-

ber 2007. Since then mobile WiMAX (IP-OFDMA) has

officially become a major global cellular wireless stan-

dard along with 3GPP UMTS/HSPA and 3GPP2 CDMA/

EVDO [2].

Mobile WiMAX is a fast growing broadband access

technology that enables low-cost mobile Internet applica-

tions, and realizes the convergence of mobile and fixed

broadband access in a single air interface and network

architecture. The IEEE802.16e provides high bandwidth,

low-cost, scalable solutions that extend services from

backbone networks to wireless users. Because of a larger

coverage area, portability and mobility have become sig-

nificant issues for providing high quality application, as it

is crucial to minimize handover latency and maintain ses-

sion continuity. The IEEE 802.16e standard only defines

a frame work in MAC layer (L2) without considering

upper layer handover performance. But from the IP based

service point of view, simply reducing the L2 latency

does not adequately reduce the overall handover latency.

The whole handover procedure shall not include L2 only

but also the IP layer. So in order to improve the IP layer

(L3) handover performance, a number of standards of

MIPv6 are proposed by IETF. Fast Handovers for Mobile

IPv6 (FMIPv6) [3], aim to reduce the handover latency by

configuring new IP addresses before entering the new

subnet. Hierarchical MIPv6 mobility management

(HMIPv6) [4] introduces a hierarchy of mobile agents to

reduce the registration latency and the possibility of an

outdated care-of address. FMIPv6 and HMIPv6 can also

be used together as suggested in [5] to reduce the latency

related to Movement Detection and CoA configuration/

Verification and cut down the signaling overhead and

delay concerned with Binding Update (BU). Fast Hand-

over for Hierarchical MIPv6 (F-HMIPv6) [5] also intro-

duces the Mobility Anchor Point (MAP) to provide a bet-

ter solution for micro mobility.

In order to provide seamless services during handover,

in this paper, we study the process that shall be performed

in L2 and L3 and the related message of 802.16e and F-

HMIPv6 to propose a cross layer handoff scheme. In or-

der to speed up the total handover process, we also use the

proposed scheme in [6] to optimize the 802.16e network

entry procedure and reduce the L2 handover delay. This

paper is organized as follows. In Section 2 we briefly in-

troduce the relevant protocols and related proposals. In

Section 3 we present our cross-layer handover scheme,

while Section 4 validates its performance. We finally con-

clude the paper in Section 5.

2. Background and Related Works

2.1 Handover Process of 802.16e

Figure 1 shows the handover process of 802.16e. The

802.16e handover (HO) procedure includes several phases,

namely, network topology acquisition and advertisement,

target BS scanning procedure, HO decision and initiation,

and network re-entry [7]. We provide details about these

36 A CROSS-LAYER SCHEME FOR HANDOVER IN 802.16E NETWORK WITH F-HMIPV6 MOBILITY

stages, explaining what is their role in the overall MAC-

layer HO latency.

In network topology acquisition stage, a BS periodi-

cally broadcasts the system information of the

neighboring BSs using Neighbour Advertisement mes-

sage. The Serving BS may unicast MOB_NBR-ADV

message based on the cell types of neighbor cells, in

order to achieve overhead reduction and facilitate

scanning priority for MS. Then MS may use any un-

available intervals assigned by the serving BS to per-

form scanning. The BS or MS may prioritize the

neighbor BSs to be scanned based on various metrics,

such as cell type, loading, RSSI and location. MS

measures the selected scanning candidate BSs and re-

ports the measurement result back to the serving BS by

using Neighbour Advertisement message.

The handover algorithm is a network-controlled, MS-

assisted handover. Although handover procedure may be

initiated by either MS or BS, the final HO decision and

target BS(s) selection are performed by the serving BS

or the network. MS executes the HO as directed by the

BS or cancels the HO procedure through HO cancella-

tion message. The network re-entry procedure with the

target BS may be optimized by target BS possession of

MS information obtained from serving BS over the

backbone network. MS may also maintain communication

with serving BS while performing network re-entry at

target BS as directed by serving BS.

2.2 Fast Handover for Hierarchical MIPv6

(F-HMIPv6)

The handover process of 802.16e mainly deals with

layer2 hop-by-hop connection issues. However, fast

Handover for Hierarchical MIPv6 (F-HMIPv6) protocol

takes the advantage of FMIPv6 and HMIPv6, which is the

most popular layer3 protocol. The HMIPv6 introduces the

Mobility Anchor Point (MAP) to reduce the signaling

overhead and delay concerned with Binding Update for

micro mobility. Therefore HMIPv6 still needs a further

handover enhancement to support the real-time applica-

tions. Currently FMIPv6 is the typical protocol to reduce

the handover latency. Then F-HMIPv6 integrates these

two protocols and provides a scheme for effective inte-

gration. Figure 2 illustrates the generic procedures for F-

HMIPv6 operations.

Based on L2 handover anticipation, the mobile node

(MN) sends RtSolPr message to MAP. The RtSolPr

should include information about the link layer address or

identifier of the concerned New Access Router (NAR). In

response to the RtSolPr message, the MAP sends the

PrRtAdv message contain information about New on-link

Care of Address (NLCoA) to the MN. At this time, MAP

Figure 1. A general flow for HO

A CROSS-LAYER SCHEME FOR HANDOVER IN 802.16E NETWORK WITH F-HMIPV6 MOBILITY 37

Figure 2. Procedures of F-HMIPv6

has already known the network prefix and link layer ad-

dress of the associated NAR. Subsequently, MN will up-

date MAP by sending Fast Binding Update (FBU) mes-

sage which contains previous on-link CoA (PLCoA) and

IP address of the NAR. After receiving the FBU message

from MN, the MAP will send a Handover Initiate (HI)

message to the NAR so as to establish a bi-directional

tunnel. If Handover Acknowledgement (HACK) message

from NAR indicates the validity of new NLCoA by Du-

plicate Address Detection (DAD) procedure, the bi-direc-

tional tunnel between MAP and NAR will set up. All data

packets are intercepted by MAP and delivered over this

tunnel. The MN sends Fast Neighbor Advertisement

(FNA) messages to NAR, when it detects that it is moved

in the link layer, and the NAR delivers the buffered data

packets to the MN over NLCoA. When the MAP receives

the new Local Binding Update with NLCoA from the MN,

it will stop the packet forwarding to NAR and then clear

the tunnel established for fast handover. When MN sends

Local Binding Update (LBU) to MAP, MAP will respond

with Local Binding ACK (LBACK), and forward packet

directly to the MN (at NAR).

3. Proposed Cross-Layer Handover Scheme

In this section, we propose our cross layer handover

scheme (CLHS). The CLHS achieves seamless handover

by exploiting the L2 handover indicators and designing

an efficient interleaving scheme of the 802.16e and the

F-HMIPv6 handover procedures. The basic idea of

CLHS is as follows: 1) integrate the correlated messages

of 802.16e and F-HMIPv6. 2) reorder/combine L2 and

L3 signaling messages and minimize the required control

flow. Thus we can get shorter handover latency and

higher throughput.

Figure 3 shows network architecture of CLFS in

802.16e.To achieve hierarchical handover, we propose a

MAP in ASN (Access Service Network) Gateway. The

MAP acts as an aggregation mobile anchor residing in

ASN Gateway and connecting with Access Router (AR).

If MN moves between subnets in the same MAP domain,

it should be in intra-MAP handover status. If MN moves

from one MAP domain to another, it should be in in-

ter-MAP handover status. If MN moves between subnets

in the same AR domain, it should be in L2 handover

status.

Identical with HMIPv6 scheme, a MN has two CoAs,

on-link CoA (LCoA) and Regional CoA (RCoA).When

MN enters a new MAP domain, firstly it performs the

HMIPv6 registrations procedures with HA and MAP.

Then MN will bind its LCoA with an address on the

MAP’s RCoA. If the MN changes its current address

within a local MAP domain (LCoA), such as from AR1 to

AR2, it only needs to register the new address with the

38 A CROSS-LAYER SCHEME FOR HANDOVER IN 802.16E NETWORK WITH F-HMIPV6 MOBILITY

Core Network

AAA

BS 1

BS 3

BS 2

AR3

AR2

AR1

ASN

Gateway

ASN

Gateway

Intra-MAP

handover Inter-MAP

handover

BS 4

Layer 2

handover

Figure 3. Network architecture of CLFS in 802.16e

MAP, following the Local Binding Update procedures of

HMIPv6. As long as MN moves from AR2 to AR3 in the

picture, the Regional CoA (RCoA) needs to be registered

with correspondent nodes and the HA. When MN moves

from BS3 to BS4, it only needs the MAC Layer handover.

In Figure 4, we design F-HMIPv6 handover informa-

tion integrate with 802.16e and make some modifications.

The “MOB_NBR_ADV” message is periodically sent by

BS and its function is similar to the “PrRtAdv” message

in F-HMIPv6. So, these two periodical advertisement

messages can be combined together. We can deliver the

L3 information of target network which MN moves to in

MOB_NBR_ADV message, and RtSol/RtAdv messages

can be omitted. By combining 802.16e with F-HMIPv6,

and employing the former’s new BS discovery ability

with the RtSol/RtAdv messages, MN movement could be

detected. In addition to modifying these two messages,

we can make a little modification and combine the mes-

sage of FBU in layer 3 and the message of MOB_

HO_IND in layer 2. It is indicate that L2’handover when

MS sends MOB_HO_IND message; And FBU message is

to inform MAP for the initiation of L3’ handover. There-

fore, it’s reasonable to send MOB_HO_IND together with

FBU.

In the first place, S-BS shall broadcast a MOB_NBR

-ADV including L3 information of RtSol/RtAdv to MN

periodically. If the MN discovers a new neighbor BS in

this message, it may perform scanning for the T-BS.

When the MN decides to change links based on its policy

such as the degrading signal strength or increasing packet

loss rate, it will initiate handover by sending a

MOB_MSHO-REQ to the BS and will receive a MOB_

BSHO-RSP from the BS as a response. Alternatively, the

BS may initiate handover by sending a MOB_BSHO

-REQ to the MN. Then MN sends MOB_ HO_IND to-

gether with FBU to S-BS, and S-BS will forward FBU

message to MAP. After that, messages of HI and HACK

occur between the MAP and NAR to implement DAD

and establish a bi-directional tunnel. As soon as the tun-

nel is set up, MAP sends FBACK messages over previ-

ous LCoA (PLCoA) and new LCoA (NLCoA), and in-

tercepting packets destined for the MN to NAR over this

tunnel. After switching links, the MN synchronizes

Figure 4. CLFS mechanism for 802.16e

A CROSS-LAYER SCHEME FOR HANDOVER IN 802.16E NETWORK WITH F-HMIPV6 MOBILITY 39

with the target BS and performs the 802.16e network en-

try procedure. In this process, MN will acquaint of NCoA

by Fast_DL_MAP_IE message [7]. Once the network

entry procedure is completed, the L2 signals L3 with a

LINK_UP (LUP) which report MN establish L2 connec-

tion with T-BS. In this stage, MN issues an FNA to NAR

by using NLCoA as a source IP address. When the NAR

receives the FNA from MN, it delivers the buffered pack-

ets to the MN through the tunnel. Then MN sends LBU

message to NMAP to bind the NRCoA and NLCoA, and

NMAP replies LBACK. In the end, NMAP delivers the

buffered packets to MN through the tunnel. Thus, the

whole handover operation is completed.

The above is the general flow of CLFS mechanism, in

practice, different cases need different processes. When

MN from one AR to another with micro mobility, there

will be only needs to register the new address with the

MAP, following the Local Binding Update procedures of

HMIPv6. Therefore, we don’t detail here.

4. Performance Analysis

In this section, we provide a performance analysis for the

concept described in Section 3. The performance evalua-

tion here provided is performed by means of simulations

carried out with Matlab.

4.1 Analytical Models

In this paper, we consider that the handover latency starts

with MN send MOB_HO_IND together with FBU, and

completes with MN can normally communicate with CN.

To analyze the performance of proposed scheme, we

define some parameters in the Table 1 as following:

If we assume TL2 is the L2 handover delay, the conven-

tional L2 handover delay is

2( )_

 

csynccont resolrngauthregframe

TTT TTTT



In Formula (1), Tsync can be done within 2 frames.

Tcont_resol typically needs minimum of 6 frames roundtrip

delay plus a random handling duration. Tauth needs 2

Table 1. Notations of performance parameters

Symbol Descriptions

Ta_b Delay between node a and node b;

Tframe Frame duration of IEEE802.16e PHY

TDAD Average delay of the DAD procedure;

Ttunnel a_b Latency for Tunneled packets;

Thop Delay of each hop in a wired backbone network

Na_b Number of hops between node a and node b;

Tsync Average time required to synchronize with new downlink;

Tcont_resol Average time required for contention resolution procedure;

Trng Average time required for ranging process during HO;

Tauth Average time required for re-authorization during HO;

Treg average time required for re-registration;

frames plus a handling duration of about 100ms. Treg al-

ways needs 2 frames plus a handling duration of about

10ms. And Tframe means the duration of MN send

MOB_HO_IND together with FBU message which takes

1 frame.

We also give the L2 and L3 total handover delay Ttotal

of conventional FMIPv6 in [8] as follow:

(6)__ 2()

___

_2()_

223

2( )

 





 

totalFMIPvPARNAR DAD tunnelPARNAR Lc

MN HAMN CNMNAR

PAR NARNAR HANAR CNhop



ADtunnelPAR NARLcMNAR

TTTTT

TTT

NNN

TTT T



From the Formula (1), we may see that it takes a long

time for handover procedures in conventional L2 scheme.

That’s mainly because, in case of network entry produce,

MS fails to receive Fast RNG_IE and conducts contention

based ranging. The MS performs random backoff and

sends CDMA codes instead of RNG-REQ message on the

link. Furthermore, the MS should perform re-authoriza-

tion and re-registration processes. If we use the proposed

scheme in [8], the downlink packet could be transmitted

just after synchronization to the new downlink and total

L2 handover delay is cut down. So we can get optimized

L2 handover delay as follow:

2( ) 

Losyncframe

TTT



The total handover latency of the CLHSmechanism is

calculated as follow:

() 2()_

__ _

2( )__

max( ,2

)

max( ,2(1)

)





 





 



total CLFSLoDADPMAPNAR

PMAP PARtunnelMAP AR

MNNARMNNMAPMNHA

LoDADPAR NARMAPAR

hoptunnelMAP ARMN NAR

MN NMAPMN HA

TTTT

TT T

TT NN

TT T



(4)

Then we list the delay period and packet disruption

time with CLFS based 802.16e in Figure 5. Apart from

handover disruption and delay period, we also note how

the time point of trigger influences these operations, as

well as the time point at which CN can send packet di-

rectly to MN.

Trigger

MOB_NBR-ADV

RtSoLPr PrRtAdvFBU FBack

Forward

packet to NAR

MOB_HO-IND

LUP

Trigger

FNA Buffered Packet

from NAR to MN

Total

Disruption

Time

Figure 5. Handover disruption time and delay period

40 A CROSS-LAYER SCHEME FOR HANDOVER IN 802.16E NETWORK WITH F-HMIPV6 MOBILITY

Related to Figure 5, we can calculate the disruption

time of CLFS and conventional way are derived below.

2( )_CLFHLoMNNAR

DTT (5)

62() _

MIPvLcMN NAR

DTT (6)

4.2 Simulation Results

We now present the results based on previous analysis.

To evaluate the schemes, we assume the parameters as the

below table. The NAR and PAR are assumed the same

distance from the HA. We assume ,

and the DAD time is chosen from Poisson distribution:

[400ms, 600ms].

0.5

hop frame

TT ms

The simulation results are divided into two parts.

The first part is mainly related to the handover latency

and the second part is related to the service disruption

time for the proposed scheme and the conventional

scheme.

0246810 121416 18 20

400

500

600

700

800

900

1000

1100

1200

IEEE 802.16e frame duration(ms)

Handover Latency(ms)

FMIPv6

CLFS

Figure 6. Handover latency for different frame durations

024681012 14 16 1820

100

150

200

250

300

IEEE 802.16e frame duration(ms)

Handover Disruption Time(ms)

DFMIPv6

DCLFS

Figure 7. Handover disruption time for different frame durations

A CROSS-LAYER SCHEME FOR HANDOVER IN 802.16E NETWORK WITH F-HMIPV6 MOBILITY 41

Figure 6 compares the handover delay of the proposed

CLHS and the conventional scheme. It’s noted that the

delay time is mainly reduced in CLHS mechanism. The

reason is that our scheme needs less number of messages

and L2 and L3 signaling messages are properly arranged

for parallelism. When performing handover, the CLHS

mechanism can greatly reduce the handover latency and

optimize the performance.

In Figure 7, we can find the same situation as Figure 6.

When the frame duration increases, the FMIPv6 disrup-

tion time grows sharply, whereas our scheme only has a

slight increase. It’s mainly because that no more registra-

tion procedure and authorization procedure are needed in

this optimized scheme. Therefore, optimized L2 handover

scheme reduce the disruption time.

Table 2. Simulation parameter setting

Parameter Value Parameter Value

NPAR_NAR 6 TNAR_CN 10

NNAR_HA 8 Ttunnel a_b 10 msec

5. Conclusions

In this paper, we have proposed a cross-layer optimiza-

tion with F-HMIP for WiMAX. Our CLHS mechanism

reduces the number of signaling messages by combining

L2 and L3 messages and parallelizing L2 and L3 signal-

ing messages. In our CLHS mechanism, we use an opti-

mized L2 handover scheme with a Fast_DL_MAP_IE

message to enhance the performance and reduce network

entry messages. In addition, we compare our scheme

with the previous scheme through exhaustive simulations.

However, the selection mechanism of an appropriate BS

is not within our consideration for simulation simplifica-

tion. So future research will extend the concept of cross

layer to cover the complete handover procedure and op-

timize the utilization of network resources.

REFERENCES

[1] BEHESHTI B D. Software implementation and performance

analysis of the LTE physical layer blocks on a next generation

baseband processor platform. 2008 IEEE Long Island, May 2008,

1-1.

[2] WANG F, GHOSH A, SANKARAN C, FLEMING P, HSIEH F,

BENES S. Mobile WiMAX systems: Performance and evolution.

IEEE Communications Magazine, Oct. 2008, 46(10): 41-49.

[3] KOODLI R. Mobile IPv6 fast handovers. IETF RFC5268, June

2008.

[4] SOLIMAN H, CASTELLUCCIA C, MALKI K E, ET AL.

Hierarchical mobile IPv6 mobility management (HMIPv6). IETF

RFC5380, Oct. 2008.

[5] JUNG H Y. Fast handover for hierarchical MIPv6. IETF

Internet-draft, draft-jung-mobopts-fhmipv6-00.txt, 2005.

[6] CHOI S, HWANG G H, KWON T, LIM A R, CHO D H. Fast

handover scheme for real-time downlink services in IEEE

802.16e BWA system. VTC 2005-Spring, 3: 2028-2032.

[7] IEEE 802.16e. Amendment 2: Physical and medium access

control layers for combined fixed and mobile operation in

licensed bands and corrigendum 1. Feb. 28, 2006.

[8] JANG H J. Mobile IPv6 fast handovers over IEEE 802.16e

networks. IETF RFC5270, June 2008.