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Transcript of Enrique SN
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A Vertical Handoff Decision
Algorithm in Heterogeneous
Wireless Networks
Enrique Stevens-Navarro
March 9th, 2007
Second UBC-IEEE Workshop onFuture Wireless Systems
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Presentation Outline
Heterogeneous Wireless Networks
Vertical Handoff
WLAN/Cellular Interconnection
Current research at UBC:
A vertical handoff decision algorithm forheterogeneous wireless networks
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Heterogeneous Wireless Networks
Different Access Technologies (radio interfaces) and overlapping coverage.
Different Network Architectures and Protocols for transport, routing andmobility management.
Different Service Demands from mobile users (low-data-rate, high-datarate, voice, etc)
Different Operators in the market.
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Heterogeneous Wireless Networks
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[1] M. Stem and R. Katz Vertical handoffs in wireless overlay networks, MobileNetworks and Applications, 1998.
Horizontal vs. Vertical Handoff [1]
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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Steps of the 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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WLAN Cellular Networks Important case ofheterogeneous wireless networks integration.
Two architectures are proposed [2]:
Tightly-coupled inter-working.
Loosely-coupled inter-working.
[2] M. Buddhikot, G. Chandranmenon, S. Han, Y. Lee, S. Miller and L. Salgarelli,Integration of 802.11 and 3G Wireless Data Networks in Infocom 03.
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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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Research at UBC: Vertical Handoff Decision Algorithm
The problem is formulated as a Markov Decision Process (MDP) .
There is a link reward function associated with the QoS of the connection
and also a signaling cost function associated with the signaling overhead
and processing load of the vertical handoff.
Both functions are introduced to capture the tradeoffs between the network
resources utilized by a connection and the processing load incurred in the
network.
Objective: determine an optimal policy which maximizes the total expected
reward per connection.
where (s) is the total expected reward, given policy is used with initial state s,
and discount factor .
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An MDP model consists of five elements: decision epochs, states, actions,
rewards and transitions probabilities.
Decision Epochs
Xt denotes the state at decision epoch t.
Ytdenotes the action chosen at decision epoch t.
Ndenotes the time that the connection terminates.
Model Formulation
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Vertical Handoff Decision Epochs
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State Space
NetworkUnits of Bandwidth
Units of Delay
Mdenotes the number of collocated networks.
Bm denotes set of available bandwidth form networkm.
Dm denotes set of delay from networkm.
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Rewards
Link
Reward
Function
Signaling
Cost
Function
Reward Function
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Actions
Transition Probabilities
Given the current state s=[i,b1,d1, ,bm,dm] and the chosen action be a,
the probability function that the next state s=[j,b1,d1, ,bm,dm] is:
where Mis the number of collocated networks.
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Optimality Equations
Let (s) denote the maximum expected reward given initial state s
Then, the optimality equations are given by:
The solutions of the optimality equations correspond to the maximum
expected total reward (s) and the optimal policy *(s).
To solve our problem, the value iteration algorithm was used.
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Numerical Results
Figure 1 (a) Expected total reward and 1 (b) expected number of vertical
handoff versus switching cost Ki,a with =0.975 and =0.25.
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Numerical Results
Figure 2 (a) Expected total reward and 2 (b) expected number of vertical
handoff versus discount factor with switching cost K1,2= K2,1=1 and
=0.25.
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Summary of Results
The MDP scheme gives higher expected total reward and lower expected
number of vertical handoffthan SAW and GRA.
The MDP model can be applied to a wide range of conditions.
Link reward function (e.g. real-time, non-real-time).
Signaling cost function (Ki,a, re-routing complexity, roaming)
Tradeoff between network resources utilized by the connection and the
signaling load incurred in the network.
Extend the MDP model and simulation model.
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Summary:
Heterogeneous Wireless Networks
Vertical Handoff
WLAN/Cellular Inter-working
Research at UBC
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Contact Information:
Enrique Stevens-Navarro
Office: Kaiser 4090
Email: [email protected]
http://www.ece.ubc.ca/~enriques/
Thank
You!