Queueing Analysis for Access Points with Failures and Handoffs of

Mobile Stations in Wireless Networks

Chen Xinyu and Michael R. Lyu

The Chinese Univ. of Hong Kong

2004-03-08

Big Sky, MT

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Outline

Wireless network architecture

System model and assumptions

Five dispatch strategies

Analytical results and comparisons

Conclusions

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Cell

Wireless Network Architecture

Access Point Mobile Station Static Host

Radio LinkWired Link

Handoff: a mechanism for a Mobile Station to seamlessly

change a connection from one Access Point to another

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State Transition Diagram

Three states for a mobile station State 0 – Normal, State 1 – Recovery, State 2 – Handoff

0

2 1

R: Recovery time H: Handoff time

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Stationary State Probability

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System Model and Assumptions

Communications among all three components are by message-passing

The message arrival process for each Mobile Station is with a constant rate

The message dispatch requirement D is an exponentially distributed random variable with rate

The Access Point itself does not undergo failures

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Undispatchable Message

Undispatchable message a message reaches the dispatch facility, however,

its target mobile station is not in the normal state, i.e., in the recovery or handoff state

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Expected Sojourn Time

Sojourn time the time period between that a message enters an

Access Point and that the message leaves it

Objective Derive the expected message sojourn time in an

Access Point with different dispatch strategies in the presence of failures and handoffs of Mobile Stations.

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Dispatch Model (1)

Basic Dispatch Model

n

q0

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Message Sojourn Time (1)

Conditioned message dispatch time

Expected message sojourn time

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Dispatch Model (2)

Static Processor-Sharing Dispatch Model

/n

q1

/n

q2

/n

qn

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Message Sojourn Time (2)

Conditioned message dispatch time

Expected message sojourn time

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Dispatch Model (3)

Dynamic Processor-Sharing Dispatch Model

q1 q2 qn

/K /K /K K

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K Dispatchable Messages

When a message enters the dispatch facility

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Message Sojourn Time (3)

Conditioned message dispatch time

Expected message sojourn time

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Dispatch Model (4)

Round-Robin Dispatch Model

q1 q2 qn

No swap time

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Message Sojourn Time (4)

Conditioned message dispatch time

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Dispatch Model (5)

Feedback Dispatch Model

n

q0

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Possion Arrivals See Time Averages

Possion Arrivals See Time Averages (PASTA) The probability of having M messages in the

system at a random epoch is equal to the steady state probability of having M messages in the system at any random time

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Message Sojourn Time (5)

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Analytical Results and Comparisons (1)

Number of mobile stations

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Analytical Results and Comparisons (2)

Failure rate

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Analytical Results and Comparisons (3)

Message arrival rate

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Analytical Results and Comparisons (4)

Expected message dispatch requirement

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Conclusions

Analyze the message sojourn time within an Access Point in the presence of failures and handoffs of mobile stations in wireless networks

Consider five dispatch strategies Obtain analytical results and comparisons