Call Admission Control Schemes in UMTSKamala

SubramaniamAdvisor

Dr.

Arne A. Nilsson

Outline Overview of UMTS Rationale behind CAC schemes Prevalent CAC Schemes Conclusions

What is UMTS?

Universal Mobile Telecommunications Systems Member if the 3G (3rd Generation) family Developed by ETSI (European Telecommunications Standards Institute) within the ITUs (International Telecommunication Unions) IMT (International Mobile Telecommunications ) framework.

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

UMTS Quality of Service (QoS) Classes3GPP (3rd Generation 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

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 Networks 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.

Outline Overview of UMTS Rationale behind CAC schemes Prevalent CAC Schemes Conclusions

Rationale behind CAC schemesA 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-Bs

CAC Terminology

New Call: When a mobile user wants to communicate to another, the Mobile Terminal (MT) obtains anew 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 isnot 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 achannel 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 attemptfrom 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.

Outline Overview of UMTS Rationale behind CAC schemes Prevalent CAC Schemes Conclusions

CAC Schemes

Capacity Based Schemes Mobility Based Schemes Interference Based Schemes Adaptive Call Admission Control (ACAC)

Capacity Based Schemes1.

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}

Results: Fixed Guard Scheme policyHand off Blocking Probability Call Blocking Probability1 .2 0.6 0.5 0.4 0.3 0.2 0.1 0 1 0.8 0.6 0.4 0.2 0 time ( sec ) time ( sec )

Blocking and Dropping Probabilities with no Guard Channels implemented

Hand off Blocking Probability1 0.8 0.6 0.4 0.2 0 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

Call Blocking Probability

time ( sec )

time ( sec )

Blocking and Dropping Probabilities with 25% Guard Channels

Results: Fixed Guard Scheme policyPhb and Pnb vs # Guard channels Blocking Probability : Phb and Pnb 1.5 1 0.5 0 0 20 40 60 # Guard channels Handoff Blocking Probability New Call Blocking Probability

Blocking Probabilities Vs Guard Channels

Capacity Based Schemes1.

Adaptive Fixed Guard Channel Scheme.Dropping rate Increases, increase number of guard channels Keep Dropping rate below Threshold at all times : Time period for updating measurements H: handoff calls into cells (both rejected and admitted) DH: number of rejected handoff calls in the past seconds TH: threshold for handoff call dropping probability If a handoff call is dropped and DH/H uTH then CH = min {CH + !, Cmax}, where u is the threshold chosen as, e.g. 0.9. If DH/H 0, e.g., 0.2,0.25 and 0.3 dc h, cold cell: lots of available channels, i = 1 number of available channels for new calls = (n - g) i i H, hot cell: lower resources, i = 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: 1 i = (0.85 + e( H i) / n )k 0

i n -g

Results: Fractional Guard Channel Policy

Blocking Probability of new calls as a function of the offered traffic load

Dropping Probability of handoff calls as a function of the offered traffic load

Rationale: Mobility Based SchemesUsers 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 1 Directional Factor: ij = ; Ni is the set of neighboring cells to cell i | Ni | Influence curves: ij Lh (t , T ) I (i , j , t , T ) = ij Ll (t , T ) for a high speed call for a low speed call

Total Influence that all ongoing calls exert on cell j: I ij = ij L(t k , T )kS

At time T, cell j needs to reserve: Rj =iN j

R

ij

Mobility Based Schemes1.

Integral MBCR1 Pnew = 0 Variations

~ B C R j Bnew used ~ B > C R j Bnew used

Conservative: Ceiling value of Rj; may waste resources Aggressive: Floor value of Rj; may increase dropping rate.

13.

Fractional MBCR1 F = 1 R j 0 B used C - R j - B new - 1 B used = C - R j - B new B used > C - R j - B newI I I

Pnew

where RjI is the integral part and RjF is the fractional part

Mobility Based Schemes1.

New Call Bounding SchemePnew =1 0

B N &B C Bnew usednew bnd used otherwise

Hybrid Scheme~ B C - R - Bnew & B N usednew j usednew bnd otherwise

1 Pnew = 0

Results: Mobility Based Schemes

Handoff Call Blocking Probability

New Call Blocking Probability

Interference Based Schemes

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

Interference Based Schemes1.

Wideband Power-Based Admission Control Strategyuplink admission criterion: Itotal_old + I > Ithreshold

downlink admission criterion: Ptotal_old + Ptotal > PthresholdI = Itotal L 1 Ul Derivation of the load curve

UL = (1 + i ).

1 uplink load W j =1 1+ ( Eb / N o ).Ri .i

N

W = Chip Rate,R j = Bit rateof Jth user, i = voiceactivity factor E b /No = Signal energy per bit / Noise spectralDensity

L =

1 W 1+ .Eb / N o .R

Interference Based Schemes1.

Throughput Based Admission Control StrategyUplink criterion: UL + L > UL_thresholdUL = (1 + i ).1 uplink load W j =1 1+ ( Eb / N o ).Ri .iN

W = Chip Rate,R j = Bit rateof Jth user, i = voiceactivity factor E b /No = Signal energy per bit / Noise spectralDensity

Downlink criterion: DL +L > DL_threshold DL = j =1 R j .N

j ( Eb / N o ) j .[(1 av )+ iav ] W av : average orthogonality of the cell i av : the average downlink other - to - own cell interference ration of the cell

Interference Based Schemes1.

CAC Based on Signal to Noise Interference Ratiouplink algorithm:Eb Ci / Ri C PG = = i i N o ( N + I Ci ) / W ( N + I i ) PG i : Processing Gain; I i = I - Ci : intereference experienced by the user i.

M-1 users in system, Mth user requesting access, minimum required power for new user is:~ ( Eb / No ) target , M ( IM + N ) CM = PGM I M : interference seen by new user if accepted I M +N : total power that the BS is receiving

downlink algorithm: power with which the ith user channel is received at the ith MT:Ci = (1 + N ) i 1+( PGi /( Eb / N o ) i )

estimation of needed received power for Mth MT:~ CM = (1 + N ) M 1 + ( PGM /( Eb / No) target , M

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.

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] = Acceptable Interference level:k (E ) b k = S k .W I I .R k o (k = 1,....., L)

Total interference plus noise power received at the BS:I = N k S k + S out + noWk =1 L

ACAC

Constraint on the number of users:

N ko Rko ko + k =1 c =1

Lo

6

k =1 i =1

Lc

N kc

kic

Rkc kc < W (1 )

where = upper bound on the total received interference (0.1 < < 0.25)

Bandwidth utilized by a user of class k: Lo

C N ko Rko ko + k =1 c =1

6

k =1 i =1

Lc

N kc

kic

Rkc kc

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 CACs which may be a combination of the above CACs are best for a system design