call admission control schemes in umts
TRANSCRIPT
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?
Universal Mobile Telecommunications Systems
Member if the 3G (3rd Generation) family
Developed by ETSI (European Telecommunications Standards Institute) within the ITU’s (International Telecommunication Union’s) 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 Network’s Resources Must guarantee QoS. Typical QoS parameters maybe: Blocking Probabilities
Transmission RatesDelayReliability
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.
OutlineOutline
Overview of UMTS
Rationale behind CAC schemes
Prevalent CAC Schemes
Conclusions
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
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.
OutlineOutlineOutlineOutline
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 ChannelsCA: 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 callsDN = number of rejected callsDH = 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 admissionOtherwise, DN = DN + 1, and reject}If a call is completed or handoff-ed to another cell{PA = PA – 1}
Results: Fixed Guard Scheme policy
Blocking and Dropping Probabilities with no Guard Channels implemented
Blocking and Dropping Probabilities with 25% Guard Channels
Hand off Blocking Probability
0
0.2
0.4
0.6
0.8
1
1.2
time (sec)
Call Blocking Probability
0
0.1
0.2
0.3
0.4
0.5
0.6
time (sec)
Hand off Blocking Probability
0
0.2
0.4
0.6
0.8
1
time (sec)
Call Blocking Probability
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
time (sec)
Results: Fixed Guard Scheme policy
Phb and Pnb vs # Guard channels
0
0.5
1
1.5
0 20 40 60
# Guard channels
Blo
ckin
g
Pro
bab
ility
: P
hb
an
d P
nb Handoff Blocking
Probability
New Call BlockingProbability
Blocking Probabilities Vs Guard Channels
Capacity Based Schemes2. 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 measurementsH: handoff calls into cells (both rejected and admitted)DH: number of rejected handoff calls in the past τ secondsTH: threshold for handoff call dropping probability
If a handoff call is dropped andDH/H ≥ αuTH thenCH = min {CH + !, Cmax},where αu is the threshold chosen as, e.g. 0.9.
If DH/H <= αdTH for N consecutive handoff calls, thenCH = 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.
Capacity Based Schemes3. Fractional Guard Channel Policy
New calls accepted with probability = βiHandoff Calls accepted with probability = 1
where i is the state of the system
“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:
in total channels ofnumber
channels available ofnumber
cd
g-n i 0
g-niH )/)(85.0(
Hi 1
kniHei
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
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:
call speed low afor ),(
call speedhigh afor ),(),,,(
TtL
TtLTtjiI
lij
hij
||
1
iij N
Sk
kijij TtLI ),(
jNi
ijj RR
Mobility Based Schemes1. Integral MBCR
Variations Conservative: Ceiling value of Rj; may waste resources Aggressive: Floor value of Rj; may increase dropping rate .
2. Fractional MBCR
where RjI is the integral part and Rj
F is the fractional part
newBjRCusedB
newBjRCusedB
newP ~ 0
~ 1
B - R - C B 0
B - R - C B 1
1 - B - R - C B 1
newI
jused
newI
jused
newI
jused
Fjnew RP
Mobility Based Schemes
3. New Call Bounding Scheme
3. Hybrid Scheme
otherwise 0
& 1 newBCused
Bbnd
Nusednew
BnewP
otherwise 0bnd
N usednew
B & newB - j
R~
- C usednew
B 1newP
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 Strategy
uplink admission criterion: Itotal_old + I > Ithreshold
downlink admission criterion: Ptotal_old + Ptotal > Pthreshold curve load the of DerivationL
II
Ul
total
1
Density spectral Noise /bit perenergy Signal /NE
factor activity voice υ user, Jth of rate Bit R Rate, Chip W
ob
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i
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Interference Based Schemes2. Throughput Based Admission Control Strategy
Uplink criterion: UL + L > UL_threshold
Downlink criterion: DL +L > DL_threshold
Density spectral Noise /bit perenergy Signal /NE
factor activity voice υ user, Jth of rate Bit R Rate, Chip W
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Interference Based Schemes3. 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:
i.user by the dexperience nceinterefere : C - I I Gain; Processing : PG
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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] = δ
Acceptable Interference level:
Total interference plus noise power received at the BS:
L)1,....., (k .
.
oI
k)
b(E
k
kk RI
WS
L
kooutkk WnSSNI
1
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:
kcco N
ikckckic
L
kc
L
kkokoko WRRN
11
6
11
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kcco N
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L
k
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k ckokoko RRNC
111
6
1
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