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 Big Sky, MT

2 CUHK Outline Wireless network architecture System model and assumptions Five dispatch strategies Analytical results and comparisons Conclusions

3 CUHK Cell Wireless Network Architecture Access Point Mobile Station Static Host Radio Link Wired Link Handoff: a mechanism for a Mobile Station to seamlessly change a connection from one Access Point to another

4 CUHK State Transition Diagram Three states for a mobile station  State 0 – Normal, State 1 – Recovery, State 2 – Handoff 0 21    R: Recovery time  H: Handoff time

5 CUHK Stationary State Probability

6 CUHK 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

7 CUHK 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

8 CUHK 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.

9 CUHK Dispatch Model (1) Basic Dispatch Model n  q0q0

10 CUHK Message Sojourn Time (1) Conditioned message dispatch time Expected message sojourn time

11 CUHK Dispatch Model (2) Static Processor-Sharing Dispatch Model  /n q1q1 q2q2 qnqn

12 CUHK Message Sojourn Time (2) Conditioned message dispatch time Expected message sojourn time

13 CUHK Dispatch Model (3) Dynamic Processor-Sharing Dispatch Model q1q1 q2q2 qnqn  /K K

14 CUHK K Dispatchable Messages When a message enters the dispatch facility

15 CUHK Message Sojourn Time (3) Conditioned message dispatch time Expected message sojourn time

16 CUHK Dispatch Model (4) Round-Robin Dispatch Model q1q1 q2q2 qnqn     No swap time

17 CUHK Message Sojourn Time (4) Conditioned message dispatch time

18 CUHK Dispatch Model (5) Feedback Dispatch Model n  q0q0

19 CUHK 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

20 CUHK Message Sojourn Time (5)

21 CUHK Analytical Results and Comparisons (1) Number of mobile stations

22 CUHK Analytical Results and Comparisons (2) Failure rate

23 CUHK Analytical Results and Comparisons (3) Message arrival rate

24 CUHK Analytical Results and Comparisons (4) Expected message dispatch requirement

25 CUHK 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