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
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
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38 A CROSS-LAYER SCHEME FOR HANDOVER IN 802.16E NETWORK WITH F-HMIPV6 MOBILITY
Core Network
Core Network
AAA
HA
BS 1
BS 3
BS 2
AR3 AR2
AR1
ASN
Gateway
ASN
Gateway
Intra-MAP
handover Inter-MAP
handover
MN
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( )_
 
L
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()_
2
223
2( )
7
 


 
totalFMIPvPARNAR DAD tunnelPARNAR Lc
MN HAMN CNMNAR
PAR NARNAR HANAR CNhop

D
ADtunnelPAR NARLcMNAR
TTTTT
TTT
NNN
TTT T
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
)
22
max( ,2(1)
)
22


 


 

total CLFSLoDADPMAPNAR
PMAP PARtunnelMAP AR
MNNARMNNMAPMNHA
LoDADPAR NARMAPAR
hoptunnelMAP ARMN NAR
MN NMAPMN HA
TTTT
TT
TT T
TT NN
TT T
TT

(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
C opyright © 2009 SciRes CN

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() _
F
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)
T
FMIPv6
T
CLFS
Figure 6. Handover latency for different frame durations
024681012 14 16 1820
0
50
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.
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