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Call Admission Control Schemes in UMTS

Call Admission Control Schemes in UMTS. Kamala Subramaniam Advisor Dr. Arne A. Nilsson. Outline. Overview of UMTS Rationale behind CAC schemes Prevalent CAC Schemes Conclusions. What is UMTS ?. U niversal M obile T elecommunications S ystems

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Call Admission Control Schemes in UMTS

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  1. Call Admission Control Schemes in UMTS Kamala Subramaniam Advisor Dr. Arne A. Nilsson

  2. Outline • Overview of UMTS • Rationale behind CAC schemes • Prevalent CAC Schemes • Conclusions

  3. What is UMTS? • Universal Mobile Telecommunications Systems • Member if the 3G (3rdGeneration) family • Developed by ETSI (European Telecommunications Standards Institute) within the ITU’s (International Telecommunication Union’s) IMT (International Mobile Telecommunications ) framework.

  4. Why UMTS? • Today consumers use the Internet to access integrated services such as voice, data and multimedia. • Next logical step is to provide the same services with the added feature of mobility • UMTS provides data up to 2Mbps making portable videophones a reality

  5. UMTS Quality of Service (QoS) Classes 3GPP (3rdGeneration Partnership Project) defines four classes for UMTS • Conversation Class:Delay Constrained / Connection Oriented/ Constant Bit Rate • Streaming Class:Delay Constrained / Connection Oriented / Variable Bit rate • Interactive Class:Longer Delay Constraints / Connectionless • Background Class:Best Effort Connectionless Services

  6. Importance of Call Admission Control (CAC) Schemes in UMTS • Need to admit calls selectively into the system minimizing call dropping and call blocking • Must make efficient use of Network’s Resources • Must guarantee QoS. Typical QoS parameters maybe: Blocking Probabilities Transmission Rates Delay Reliability • Need to multiplex a non-homogeneous mix of traffic within a limited set of resources and various propagation characteristics. • Need to incorporate mobility complications and handoff procedures.

  7. Outline Outline • Overview of UMTS • Rationale behind CAC schemes • Prevalent CAC Schemes • Conclusions

  8. Rationale behind CAC schemes A UMTS network showing cellular architecture, where each cell is served by the Node-B and the Radio Network Controller (RNC) serving a bunch of Node-B’s

  9. CAC Terminology • New Call: When a mobile user wants to communicate to another, the Mobile Terminal (MT) obtains a new channel from the Base Station (BS) it hears best. If a channel is available, the BS grants it and a new call originates • New Call Blocking Probability (or simply blocking probability): If all channels are busy, the MT is not granted the channel and the call is blocked. • Handoff Call: The procedure of moving between cells when a call is in progress is called a “handoff”. During handoff the MT requests resources from the BS in the cell it is moving to. • Handoff Call Dropping Probability (or simply dropping probability): When the MT is denied a channel in the cell it is moving to, the call is dropped. • Priority: Forced termination of a call in progress is more annoying than blocking of a new calling attempt from the users point of view. Clearly, handoff calls must be given a higher priority. • Cell Dwell Time: After entering a cell, the time a MT resides in it.

  10. Outline Outline Outline Outline • Overview of UMTS • Rationale behind CAC schemes • Prevalent CAC Schemes • Conclusions

  11. CAC Schemes • Capacity Based Schemes • Mobility Based Schemes • Interference Based Schemes • Adaptive Call Admission Control (ACAC)

  12. Capacity Based Schemes • Fixed Guard Channel / Cutoff Priority Scheme. C = CA + CH; C: Total Number of Channels CA: Channels allocated to handle admitted calls (handoff and new) CH: Guard channels allocated to handle handoff calls New Call Admitted: if total number of calls (handoff and new) < CA Handoff Call Admitted: if CA + CH < C PA= number of on-going calls DN = number of rejected calls DH = number of rejected handoff calls If handoff call request { If PA < C, PA = PA + 1, and grant admission Otherwise, DH = DH + 1, and reject} If new call request { If PA < C, then PA = PA + 1, and grant admission Otherwise, DN = DN + 1, and reject} If a call is completed or handoff-ed to another cell {PA = PA – 1}

  13. Results: Fixed Guard Scheme policy Blocking and Dropping Probabilities with no Guard Channels implemented Blocking and Dropping Probabilities with 25% Guard Channels

  14. Results: Fixed Guard Scheme policy Blocking Probabilities Vs Guard Channels

  15. Capacity Based Schemes • Adaptive Fixed Guard Channel Scheme. • Dropping rate Increases, increase number of guard channels • Keep Dropping rate below Threshold at all times τ: Time period for updating measurements H: handoff calls into cells (both rejected and admitted) DH: number of rejected handoff calls in the past τ seconds TH: threshold for handoff call dropping probability If a handoff call is dropped and DH/H ≥ αuTH then CH = min {CH + !, Cmax}, where αu is the threshold chosen as, e.g. 0.9. If DH/H <= αdTH for N consecutive handoff calls, then CH = max {CH – 1, Cmin}, where αd is another threshold chosen as e.g., 0.6 and N is an integer chosen as e.g.,10.

  16. Capacity Based Schemes • Fractional Guard Channel Policy New calls accepted with probability = βi Handoff Calls accepted with probability = 1 where i is the state of the system

  17. “Hot” Vs “Cold” • Define threshold h >0, e.g., 0.2,0.25 and 0.3 • dc» h, “cold cell”: lots of available channels, βi = 1 number of available channels for new calls = (n - g) – i • i » H, “hot cell”: lower resources, βi = 0 where i : state of the system g: number of guard channels n: total number of channels H = (1 – h) n - g New Call Acceptance Probability:

  18. Results: Fractional Guard Channel Policy Blocking Probability of new calls as a function Dropping Probability of handoff calls of the offered traffic load as a function of the offered traffic load

  19. Rationale: Mobility Based Schemes • Users of two types: Low Speed (Pedestrian) users and High Speed (Vehicular) users • Cell Dwell Times = F (elapsed time in cell, velocity class) • Pr (call will request a handoff sometime after T) = Lh (t,T) for high-speed ; Ll (t,T) for low-speed • Directional Factor: ; Ni is the set of neighboring cells to cell i • Influence curves: • Total Influence that all ongoing calls exert on cell j: • At time T, cell j needs to reserve:

  20. Mobility Based Schemes • Integral MBCR Variations • Conservative: Ceiling value of Rj; may waste resources • Aggressive: Floor value of Rj; may increase dropping rate. • Fractional MBCR where RjI is the integral part and RjF is the fractional part

  21. Mobility Based Schemes • New Call Bounding Scheme • Hybrid Scheme

  22. Results: Mobility Based Schemes Handoff Call Blocking Probability New Call Blocking Probability

  23. Interference Based Schemes • Admit user into system only if Interference threshold not passed • CAC scheme: guarantee dropping probability below threshold at high offered loads.

  24. Interference Based Schemes • Wideband Power-Based Admission Control Strategy uplinkadmission criterion: Itotal_old + I > Ithreshold downlink admission criterion: Ptotal_old + Ptotal > Pthreshold

  25. Interference Based Schemes • Throughput Based Admission Control Strategy Uplink criterion: UL + L > UL_threshold Downlink criterion: DL +L > DL_threshold

  26. Interference Based Schemes • CAC Based on Signal to Noise Interference Ratio uplink algorithm: M-1 users in system, Mth user requesting access, minimum required power for new user is: downlink algorithm: power with which the ith user channel is received at the ith MT: estimation of needed received power for Mth MT:

  27. Results: Interference Based Schemes Power-based CAC, downlink, homogeneous traffic distribution: offered traffic vs. accepted traffic and maximum dropping probability for different values of the ratio Pthr/Pmax. Interference-based CAC, uplink, homogeneous traffic distribution: offered traffic vs. accepted traffic and maximum dropping probability for different values of the threshold level.

  28. Adaptive Call Admission Control (ACAC) • Limit on acceptable interference threshold ↔ number of users of each service class in local and neighboring cells • Obtain tradeoff between the number of voice and data users according to outage/blocking probability. • Outage Probability: P[C ≥ W] = δ • Acceptable Interference level: • Total interference plus noise power received at the BS:

  29. ACAC • Constraint on the number of users: where η = upper bound on the total received interference (0.1 < η < 0.25) • Bandwidth utilized by a user of class k:

  30. Conclusions • Summarized UMTS CAC schemes from open literature • CAC schemes classified as capacity based, interference based, mobility based and adaptive • CAC schemes efficiently utilize system resources in order to: Guarantee QoS Minimize Blocking/Dropping Probabilities Minimize Interference Provide priority to Handoff Calls Handle Mobility • Adaptive CAC’s which may be a combination of the above CAC’s are best for a system design

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