Transcript Vertical Handoff Mechanisms In Integrated WWAN and WLAN

Modularized Two Step
Vertical Handoff Scheme In
Integrated WWAN and
WLAN
Shimin Li
Ying Wang
What is Vertical Handoff
 Vertical handoff is the handoff between
different network
 Horizontal handoff is the handoff within
the same network
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Outline
1. Motivation and Objective
2. Overview of WWAN and WLAN
3. Integration Architecture and Mobile IP
4. Modularized Two Step Handoff Scheme
5. Conclusion
6. Reference
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1. Motivation
 WWAN: low rate, high cost and wide
coverage
 WLAN: high rate, low cost and small
coverage usually deployed at hotspots
 Combines the 3G WWAN and the IEEE
802.11 WLAN together will benefit to
operator and customer
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1. Objective
 To make the integration effective, vertical handoff
between the two networks is necessary
 Major problems in Vertical Handoff in integrate
network
Delay
Loss packet
Billing
 In this presentation, we focus on real time
application. It needs low delay during the vertical
handoff
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1. Related works
 In [1] tight coupling, loose coupling and
Mobile IP were introduced
 [2] and [3] introduce FFT and MAC layer
sensing for handoff decision, but the
solution need improve because handoff
decision does not consider different
situation
 [4] introduce the multi tunnel idea, but did
not get a easy implement solution
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2 Overview of WWAN and
WLAN
 Architecture of WWAN (CDMA 2000)
 Architecture of WLAN
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Architecture of WWAN (CDMA
2000)
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Architecture of WLAN
Internet
Hub/Switch
LAN
Router
Hub/Switch
LAN
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3 Integration Architecture and
Mobile IP
 Tight coupling
 Loose coupling
 Mobile IP
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Internet
CDMA2000
Core Network
Tight
Coupling
Loose
Coupling
CDMA2000
BSC
WLAN
Gateway
BS
WLAN
Gateway
WLAN Access
Point
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Tight coupling
 Basic idea
 disadvantage
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Loose coupling
 Basic idea
 Advantage
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Mobile IP
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4 Modularized Two Step Handoff
Scheme
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Main idea of Modularized Two
Step Handoff Scheme 1
Pre-Handoff
Message
Physical
Signal
Decision
Module
MAC
Signal
Pre-Handoff
Action
Module
Handoff
Message
Handoff
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Main idea of Modularized Two
Step Handoff Scheme 2
 Decision module
Sensing physical layer and MAC layer
Sending message to Action module
 Action module
Receiving message from Decision module
Performing handoff action
 Interface between two modules
Pre-handoff message
Handoff message
 There only two message sequences allowed
Pre-handoff message followed by pre-handoff message
Pre-handoff message followed by handoff message
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Main idea of Modularized Two
Step Handoff Scheme 3
 Handoff process include two step
Pre handoff step
handoff step
 When the HA receives the pre handoff message, it
begins to multi-tunnel the packet. It copies the IP
packet destined to MN and sends them to the FA
in WLAN and WWAN respectively.
 When the mobile node meet the handoff condition,
it execute handoff.
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4.1 Decision Module
 Different with horizontal handoff
 Handoff from WWAN to WLAN
 Handoff from WLAN to WWAN
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Different with horizontal handoff
 No comparable signal strength
 When moves from WWAN to WLAN, can
not be triggered by signal decay
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4.1.1 Handoff decision from
WWAN to WLAN
 Physical-layer sensing
 MAC-Layer Sensing
 Handoff decision scheme
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Physical-layer sensing
 WLAN air interface will be periodically
turned on to scan the signal of WLAN
 Once the user moves into WLAN, a valid
WLAN service set identifier (SSID) will be
detected
 If received signal strength index (RSSI) be
larger than a preset threshold R1 then send
pre-handoff message to Action module
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MAC-Layer Sensing
 Goal: detect the WLAN network condition, such as
available bandwidth and MAC-layer access delay
 NAV (Network Allocation Vector) is the main scheme used
in WLAN to avoid collision by setting a busy duration on
hearing frame transmissions from other mobile hosts
 By listening to and collecting the NAV in MAC layer, we
can obtain the available bandwidth and access delay in
MAC
 Observe the NAV for T times and calculate the average
NAV in this observation window. If the average NAV is
smaller than a threshold N1, roaming into WLAN is
granted; otherwise, the user stays in WWAN
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Relationship between NAV and
Available bandwidth
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Relationship between NAV and
Mean access delay
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Handoff decision scheme from
WWAN to WLAN
 Detecting the RSSI signal, If RSSI>R1,
then begin collect NAV and send prehandoff message to Action module.
 If the average NAV <N1, then send handoff
message to Action module
 Else keep the connection with the WWAN
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4.1.2 Handoff decision from
WLAN to WWAN
 The key problem is how to detect the
unavailability and the decay of the WLAN
signal
 we present an approach that integrate FFTBased Decay Detection, NAV Occupation
and simple physical signal strength for
accurately detecting the unavailability of
WLAN
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FFT-Based Decay Detection
X (1) 
N 1
 x(n) sin( 
n 0
2n
)
N
 Regard sin (-(2πn/N)) as a linear filter applied to the
sequence x(N)
 x (1) is the most smooth metric because sin(-2πn/N))
is the filter with the least high-frequency
component
 This will reduce the variation of x (1) even x (n) may
vary severely
 we can set a threshold F1 for x (1)/N. If x(1)/N is
smaller than F1, the signal is considered to be
decaying
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MAC layer sensing
 From NAV we can obtain the available
bandwidth and access delay in MAC
 Set the threshold of average NAV is N2
 If the average NAV>N2, it mean that the
delay of WLAN is large, so the user send
pre-handoff message to Action module
 After short time T, send handoff message to
Action module
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Physical Signal Sensing
 Some time the signal of WLAN change very
quickly. If the level of the RSSI is small then R3,
the user will lose the connection
 FFT is not very sensitive in this situation
 we select R4=R3+⊿ where ⊿ is the small amount
as a threshold. When the signal is less R4 send
pre-handoff message to Action module, When the
signal is less then R3 then send handoff message
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Handoff decision scheme from
WLAN to WWAN
 a) If RSSI<R4, then send pre-handoff message to
Action module;
If RSSI<R3, send handoff message
In this situation, the user need handoff
immediately because the RSSI is too weak.
 b) If RSSI<R2, then begin FFT and send prehandoff message to Action module
If the X (1)/N< F1 then send handoff message
 c) If the NAV occupation > N2 then send prehandoff message to Action module, after time T
send handoff message
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To avoid Ping-Pong effect
 R1>R2>R4>R3;
 N1<N2
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4.2 Action module
 Will be introduced by shimin
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5 Conclusion and future work
 For real time application a Modularized Two Step
Handoff Scheme is proposed for handoff between
WWAN and WLAN
 In this scheme we design two module and a set of
protocols, compare other scheme, it is clear and
easy to implement
 In this scheme not only physical layer signal but
also MAC layer signal be considered
 Handoff delay is very little and packet loss can be
reduced
 Avoids ping-pong effect
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6 References
 [1]Buddhikot, M.M.; Chandranmenon, G.; Seungjae Han; Yui-
Wah Lee; Miller, S.; Salgarelli, L.; “Design and implementation
of a WLAN/cdma2000 interworking architecture” IEEE Commun.
Mag., Volume: 41 , Issue: 11 , pp. 90–100 Nov. 2003
 [2] Q. Zhang, C. Guo, Z. Guo, and W. Zhu, “Efficient mobility
management for vertical handoff between WWAN and WLAN,” IEEE
Commun. Mag., vol. 41, pp. 102–108, Nov. 2003.
 [3]Guo, C.; Guo, Z.; Zhang, Q.; Zhu, W.; “A Seamless and
Proactive End-to-End Mobility Solution for Roaming Across
Heterogeneous Wireless Networks” Selected Areas in
Communications, IEEE Journal on , Volume: 22 , Issue: 5 , pp.834
- 848 June 2004
 [4]M.Ye, “The mobile IP handoff between hybrid networks”, IEEE,
2002
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Thank you!!!