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Call Admission Control in Wireless Networks What Why and How

2. CAC

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Call Admission Control in Wireless Networks What Why and How

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    1. Call Admission Control in Wireless Networks What? Why? and How? By Mohamed H. Ahmed BCWS, Carleton University, Ottawa, Canada

    2. 2 CAC..what? CAC can be defined as a process for managing the arriving traffic (at the call, session, or connection level) based on some predefined criteria.

    3. 3 CAC.what? Example 1 (Uncontrolled CDMA Network) Assumptions: BW=1.25 MHz, Rb=8 kbps. Exponential path loss model (n=4) with a log-normal shadowing (s=8). 3 sector/cell. Number of users in a sector N(t0) is equal to 36. From [1], Pout, defined as P(BER>10-3), is less than 1%.

    4. 4 CAC.what? 2 more users arrived at the same sector by the moment t1 (t1> t0). Therefore, Pout in that sector jumps to 2.7% [1]. Result: Outage probability is almost tripled by admitting the two new user, and some calls (including the new ones) might be dropped. Conclusion: Admitting these 2 users was not a good decision.

    5. 5 CAC.what? Example 2 (Uncontrolled TDMA Network) Assumptions: Number of channels per cell=20. The network consists of 3 cells. At instant (t0), number of users Ni(t0) (i=1,2,3) is equal to (18, 17, 19) At instant (t1), a new user arrived at cell 3. Then Ni(t2) will be (18, 17,20).

    6. 6 CAC.what? At instant (t2), one of the 17 active users in cell 2 is leaving cell 2 heading cell 3. This user has to be handedover to cell 3, but cell 3 is fully loaded. Result: This user will be rejected by cell 3 and the call will be dropped. Conclusion: Admitting the new user in cell 2 at instant (t1) was not a good decision. Guard band concept by Hong and Rappaport [2].

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