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“Vertical Handoff in

Heterogeneous Wireless

Networks”

Enrique Stevens Navarro

March 10th, 2006

UBC-IEEE Workshop on Future Wireless Systems

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Presentation Outline

� Heterogeneous Wireless Networks

� Always Best Connected

� Mobility Management

� Handoff Management

� Vertical Handoff

� WLAN/Cellular Interconnection

� Project research at the Communications Group

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Heterogeneous Wireless Networks

� A mix of radio access technologies will co-exist.

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Heterogeneous Wireless Networks

� Different Access Technologies (radio interfaces) and overlapping coverage.

� Different Network Architectures and Protocols for transport, routing and mobility management.

� Different Service Demands from mobile users (low-data-rate, high-data rate, voice, etc)

� Different Operators in the market.

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Always Best Connected (ABC)

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Always Best Connected (ABC) [1]

� The ABC concept allows a person connectivity to applications using the devices and access technologies that best suit his/her communication needs.

� The ABC scenario generates great complexity and a number of requirements.� Technical solutions.

� Business relationships.

� Subscriber handling.

[1] E. Gustafsson and A. Jonsson, “Always Best Connected,” IEEE Wireless Communications, February 2003.

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� Different Wireless Networks are complementary to

each other, their integration will allow mobile users

to be connected using the best available access

network that fits their needs.

� To deal with this problem, Mobility Management

Techniques are required…

Mobility Management

Mobility Management

Handoff Management

Location Management

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Mobility Management

� Location Management: It enables the system to track the locations of mobile terminals (MT).

� Handoff Management: It is the process by which an MT keeps its connection when it moves from one point of attachment (base station or access point) to another.

Handoff or handover

Vertical Handoff (VHO)

Horizontal Handoff (HHO)

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Handoff Management Requirements

� Reduction of signaling and processing overhead.

� Minimize packet loss and delay (seamless HO).

� QoS guarantees during the process and transfer of

context.

� Use of any “triggers” or metrics available to decide

when and where (planned HO).

� Efficient use of network and MT resources.

� Enhanced scalability, reliability and robustness.

� Allow inter-technology handoff (VHO).

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[2] M. Stem and R. Katz “Vertical handoffs in wireless overlay networks,” Mobile Networks and Applications, 1998.

Horizontal vs. Vertical Handoff [2]

Horizontal

Handoff

Vertical

Handoff

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� Horizontal HO – mainly use received signal strength

(RSS) to decide the handoff…

� But Vertical HO?

� RSS?

� Offered bandwidth?

� Price?

� Power consumption?

� Speed?

� ….

Handoff

Metrics

Handoff Metrics

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Vertical Handoff Process

Step 1: “System Discovery”

The MT must know which wireless networks are reachable.

Step 2: “Handoff Decision”

The MT then evaluates the reachable wireless networks to

make a decision.

Step 3: “Handoff Execution”

If the MT decides to perform a VHO, it executes the VHO

procedure required to be associated with the new

wireless network.

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Step 1: System Discovery

� Periodic beacons from AP.

� Signal measurements.

� Database query.

� Handoff metrics gathering.

�Bandwidth, cost, delay, SNR, power, etc.

� Periodic / Adaptive network scanning.

� All interfaces always on.

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Step 2: Handoff Decision

� Fuzzy Logic / Neural Networks.

� Multiple Attribute Decision Making.

� Decision based on utility / cost functions.

� User triggered.

� Decision based on proposed policies:� “Always use the cheapest network”.

� “Always use the interface with lower power consumption”.

� “Always use the WLAN”.

� “Always use the network with more bandwidth”.

� Decision + stability period. (Avoid ping-pong effect)

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Step 3: Handoff Execution

� Network Layer:� Mobile IP v4 vs. Mobile IP v6.

� Transport Layer:� Stream Control Transmission Protocol (SCTP).� Transmission Control Protocol (TCP).

� Application Layer:� Session Initiation Protocol (SIP).� Application-based.

� Infrastructure-based approach

� End-to-end approach.

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WLAN – Cellular Networks

� Important case of heterogeneous wireless

networks integration.

� Two architectures are proposed:

�Tightly-coupled inter-working.

�Loosely-coupled inter-working.

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WLAN – Cellular Networks [3]

[3] M. Buddhikot, G. Chandranmenon, S. Han, Y. Lee, S. Miller and L. Salgarelli, “Integration of 802.11 and 3G Wireless Data Networks” in Proc. of IEEE Infocom’03.

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WLAN – Cellular Networks Integration

Some interoperability open issues:

� When to switch?, VHO policies:

�WLAN to Cellular ≠ Cellular to WLAN

� Seamless handoff (level of integration).

�Packet loss and VHO latency.

� Load balancing between networks.

� QoS guarantees and transfer of context.

� Security and Authentication.

� Billing and revenue sharing.

� Implementation.

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WLAN – Cellular Networks Integration

Standardization efforts:

� Both 3GPP and 3GPP2 are working in the inter-

working with WLAN as an extension of their radio

access networks.

� IEEE 802.21 Media Independent Handover Group is

working toward the seamless handoffs between:

� IEEE 802.XX family.

� IEEE 802.XX and 3G Cellular

� Between 802.11 ESSs.

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Current Research:

� Comparison of different decision algorithms

proposed for vertical handoff.

� Four algorithms:

� SAW (Simple Additive Weighting) [4]

� TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) [4]

� MEW (Multiplicative Exponent Weighting) [5]

� GRA (Grey Relational Analysis) [6]

[4] W. Zhang, “Handover Decision Using Fuzzy MADM in Heterogeneous Networks” in IEEE WCNC’04, March 2004.

[5] K. Yoon and C. Hwang, Multiple Attribute Decision Making: An introduction, Sage Publications, 1995.

[6] Q. Song and A. Jamalipour, “A Network Selection Mechanism for Next Generation Networks” in IEEE ICC’05, May 2005.

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Decision Matrix

MNMM

N

N

xxx

xxx

xxx

...

:...::

...

...

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22221

11211

Networks to Select

- WLAN

- CDMA2000

- GSM/GPRS

M – Number of networks.

N – Number of parameters

Parameters to Consider

- Bandwidth

- Delay

- Jitter

- Bit Error Rate (BER)

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Decision Methods

∑=

∈=

N

j

ijjMi

SAW rwA1

*maxarg

� SAW

∏∈

= jw

ijMi

MEW xA maxarg*

� MEW � GRA

iMi

GRAA ,0

* maxarg Γ=∈

** maxarg iMi

TOP cA∈

=

� TOPSIS

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Performance Comparison

� A set of importance weights are calculated

according to the QoS requirements of the four traffic

classes: conversational, streaming, interactive and

background.

� Simulation: the connection lifetime of the mobile

follows an exponential distribution and each network

evolves according to a Markov chain. Every time

that the status of a network changes the mobile

terminal must decide which network to use.

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1 2 3 4 5 6 7 8 9 1060

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64

(a) Conversational

Avg. bandw

idth

(K

bps)

Avg. connection time (mins)

1 2 3 4 5 6 7 8 9 105600

5800

6000

6200(b) Streaming

Avg. bandw

idth

(K

bps)

Avg. connection time (mins)

1 2 3 4 5 6 7 8 9 104500

5000

5500

6000(c) Interactive

Avg. bandw

idth

(K

bps)

Avg. connection time (mins)

1 2 3 4 5 6 7 8 9 104500

5000

5500

6000(b) Background

Avg. bandw

idth

(K

bps)

Avg. connection time (mins)

SAW MEW TOPSIS GRA

� Average Bandwidth (Kbps)

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1 2 3 4 5 6 7 8 9 1010

12

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16(a) Conversational

Avg

. d

ela

y (

ms)

Avg. connection time (mins)

1 2 3 4 5 6 7 8 9 1058

60

62

64(b) Streaming

Avg

. d

ela

y (

ms)

Avg. connection time (mins)

1 2 3 4 5 6 7 8 9 1060

70

80(c) Interactive

Avg

. d

ela

y (

ms)

Avg. connection time (mins)

1 2 3 4 5 6 7 8 9 1060

70

80(b) Background

Avg

. d

ela

y (

ms)

Avg. connection time (mins)

SAW MEW TOPSIS GRA

� Average Delay (ms)

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Students working in the project:

Pricing StrategiesPhDJun Wang

Vertical HandoffPhDJie Zhang

Vertical HandoffPhDEnrique Stevens

Navarro

AreaProgramName

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Summary:

� Heterogeneous Wireless Networks

� Mobility Management

� Handoff Management and Vertical Handoff

� WLAN/Cellular Inter-working

� Research

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Contact Information:

Enrique Stevens Navarro

Office: Kaiser 4090

Email: enriques@ece.ubc.ca

Thank

You!