Wenye Wang Xinbing Wang Arne Nilsson

Department of Electrical and Computer Engineering, NC State University

March 2005

A New Admission Control Scheme A New Admission Control Scheme under Energy and QoS Constraints under Energy and QoS Constraints

for Wireless Networksfor Wireless Networks

2 A New Admission Control SchemeA New Admission Control Scheme/ Wang et al, INFOCOM’05, Miami, FL

Agenda• Motivations• Relationship between admission control and

energy consumption• New call admission control scheme

– Victim selection algorithm (VSA)– Beneficiary selection algorithm (BSA)– Stochastic adjustment algorithm (SAA)

• Performance analysis– Markov chain model– Blocking probabilities: fixed/dynamic channel holding time– Energy consumption

• Numerical results• Conclusions and future work

3 A New Admission Control SchemeA New Admission Control Scheme/ Wang et al, INFOCOM’05, Miami, FL

Motivations• Two important issues in future wireless networks

– Bandwidth utilization based on call admission control (CAC)

– Energy conservation• Why “another” admission control scheme?

– Existing work on admission control: interference-, mobility-, and priority-based etc.

– Existing work on energy/power management• At physical layer: power control based on channel fading

and interference, joint source and channel coding etc.• At medium access control (MAC) and application layer:

smart on-off schemes are proposed for energy consumption • CAC and energy saving are separate from each other

• Objective: develop a new admission control scheme under develop a new admission control scheme under constraints of energy consumption and QoSconstraints of energy consumption and QoS

4 A New Admission Control SchemeA New Admission Control Scheme/ Wang et al, INFOCOM’05, Miami, FL

Call Admission Control and Energy Consumption

Energy Consumption Rate (ECR): is energy consumption of each successfully transmitted bit

– Total energy consumption E_{total} = ECR * =ECR*T*R

)()(1)( t

bfertbfer

tbt

bEPRR

P

EP

EEECR

⋅−=

−=

Ebt:Energy to transmit one bit

Pfer :Frame error rate,P:Transmission powerR:Transmission rate:Total amount of dataT:Time to transmit data

5 A New Admission Control SchemeA New Admission Control Scheme/ Wang et al, INFOCOM’05, Miami, FL

Relationship between CAC and Energy Consumption: Example

• Energy consumption rates vary with terminals at different trans. rates

• BPSK Modulation

• Reed Soloman (RS) Code

• Consider Retransmission

6 A New Admission Control SchemeA New Admission Control Scheme/ Wang et al, INFOCOM’05, Miami, FL

Admission Control Scheme Energy Consumption

• Victim Selection Algorithm (BSA)– When there is no enough number of channels,

victims are selected according to the lowest energy increasing rate.

• Beneficiary Selection Algorithm (BSA)– When there are some channels released, beneficiaries are chosen based on the highest

energy decreasing rate.• Stochastic Adjustment Algorithm (SAA)

– To achieve fairness among different classes of traffic by pre-block traffic flows

7 A New Admission Control SchemeA New Admission Control Scheme/ Wang et al, INFOCOM’05, Miami, FL

Victim Selection Algorithm (VSA)

• All bandwidth has been allocated to ongoing sessions

• A new/handoff call arrives, how to find (sufficient) bandwidth for it?

– Search for all ongoing sessions, and find a victim, that is, the absolute value of the derivative of rr(R) (R) is the minimum.

– Note that if this terminal is operating at its lower-bound transmission rate, then this terminal cannot be a victim.

– Once a victim is identified, then the amount of BW bandwidth will be reduced.

Victim

8 A New Admission Control SchemeA New Admission Control Scheme/ Wang et al, INFOCOM’05, Miami, FL

Beneficiary Selection Algorithm (BSA)

• Some bandwidth is released when a connection is finished

• Available bandwidth is reallocated to ongoing sessions

– Search for all ongoing sessions, and find a beneficiary terminal, that is, the absolute value of the derivative of rr(R) (R) is the maximum.

– Note that if this terminal is operating at its upper-bound transmission rate, then this terminal cannot be a beneficiary terminal.

– Once a beneficiary terminal is identified, the amount of BW bandwidth will be reallocated.

Beneficiary terminal

9 A New Admission Control SchemeA New Admission Control Scheme/ Wang et al, INFOCOM’05, Miami, FL

Stochastic Adjustment Algorithm (SAA)

• Goal: to couple admission control with QoS requirements to achieve a balance/fairness among multiple classes

• Solution: pre-block some traffic, that is, to determine the rate of arrival requests blocked for each class, k, for a total number of K classes:

• Pricing model is used to create an objective function. For a simplified two-class system, e.g., handoff and new calls, we consider

€

M = [m1,m2,..,mk,....,mK ]

Min { B1 |Q + B2 |Q }s.t. B1 |Q < B2 |Q, m1 0, m2 0

10 A New Admission Control SchemeA New Admission Control Scheme/ Wang et al, INFOCOM’05, Miami, FL

Performance Analysis: System Model

11 A New Admission Control SchemeA New Admission Control Scheme/ Wang et al, INFOCOM’05, Miami, FL

Assumptions

• Poisson arrival process is enforced.

• Exponential service rate is used, which can be relaxed to any arbitrary distribution.

• For new calls and handoff calls, the same admission control scheme will be used.

12 A New Admission Control SchemeA New Admission Control Scheme/ Wang et al, INFOCOM’05, Miami, FL

Analytical Model: Markov Chain

Call blocking probability for multi-class service model is obtained based on multi-dimension Markov Chain.

13 A New Admission Control SchemeA New Admission Control Scheme/ Wang et al, INFOCOM’05, Miami, FL

Blocking Probabilities• Fixed channel holding time:

– The number of channels of a connection session does not affect channel holding time

– The channel holding time is assumed to be exponentially distributed

– The number of channels, or the bandwidth, affects only the quality of service, like the the resolution of an image.

• Dynamic channel holding time– The channel holding time is dependent on the number

of channels– More bandwidth means shorter transmission time

14 A New Admission Control SchemeA New Admission Control Scheme/ Wang et al, INFOCOM’05, Miami, FL

Analysis of Energy Consumption

• The average energy consumption, EE,

– is the probability of each state– is the average energy consumption at

each state

• can be obtained based on the energy consumption rate, ECR matrix (aij is the ECR of class i with j channels,

€

P(N)

€

E(N)

€

E(N)

15 A New Admission Control SchemeA New Admission Control Scheme/ Wang et al, INFOCOM’05, Miami, FL

Simulations• Non-prioritized scheme (NPS): Simplest resource allocation

scheme with least overhead, which determines the admission based on a fixed bandwidth requirement.

• Adaptive resource allocation scheme (AREAS): it determines the admission based on several options of bandwidth requirements.

Parameters Class A Class BArrival Rate (call/min) [1,40] 10

Data Volume (kbyte) 180 180

Transmission Rate (kbps/channel) 8 8

# of Channels for NPS 7 3

# of Channels for AREAS {4, 7, 9} {2, 3, 5}

# of Channels for Our Scheme {4,9} {2,5}

16 A New Admission Control SchemeA New Admission Control Scheme/ Wang et al, INFOCOM’05, Miami, FL

Case I: Blocking Probability • The results of simulations,

analysis of new scheme overlap with the results of AREAS: the energy-based admission control is able to reduce blocking probability as adaptive resource allocation scheme for QoS requirements.

• Adaptive resource allocation schemes are much more effective in reducing blocking probability than non-prioritized scheme

• The lower the bandwidth requirement (e.g., class-B), the lower the blocking probability.

17 A New Admission Control SchemeA New Admission Control Scheme/ Wang et al, INFOCOM’05, Miami, FL

• The throughput of Class-A increases as the arrival rate is increased, whereas the throughput of Class-B decreases because Class-A traffic is dominant for higher A.

• Higher throughput can be achieved by the new scheme

Case I: Throughput

Class-A Class-B

18 A New Admission Control SchemeA New Admission Control Scheme/ Wang et al, INFOCOM’05, Miami, FL

• Dynamic channel holding time is considered as Case II in which data volume is fixed. Thus, the more the bandwidth, the shorter the transmission time.

• The blocking probability of the new scheme is lower than both AREAS and NPS.

• The new scheme yields higher throughput.

Case II: Dynamic Channel Holding Time

Blocking Probability and throughput

Class-B

19 A New Admission Control SchemeA New Admission Control Scheme/ Wang et al, INFOCOM’05, Miami, FL

QoS Adjustment:

Blocking Probability • By sacrificing Class-B,

the blocking probability of Class-A is reduced significantly

• Before using stochastic QoS adjustment algorithm, the difference between blocking probabilities of two classes becomes bigger with increase of arrival rates.

• After the adjustment, the difference of blocking probability of two classes becomes smaller.

20 A New Admission Control SchemeA New Admission Control Scheme/ Wang et al, INFOCOM’05, Miami, FL

Self-Similar Traffic:Blocking Probability and Throughput

• The new scheme is effective in reducing blocking probability and improving throughput for non-Poisson processes such as self-similar traffic

• The simulation takes longer time for self-similar traffic

Blocking Probability Throughput

21 A New Admission Control SchemeA New Admission Control Scheme/ Wang et al, INFOCOM’05, Miami, FL

Energy Consumption

Arrival rate Energy (num. of calls/min)

Consumption Rate

5 20 35

NPS 9.8 9.8 9.8

AREAS 6.2 11.8 12

New Scheme 2.1 3.4 3.6

22 A New Admission Control SchemeA New Admission Control Scheme/ Wang et al, INFOCOM’05, Miami, FL

Conclusions• A new call admission control scheme is designed

based on energy consumption.• Three algorithms: victim selection algorithm (VSA),

beneficiary selection algorithm (BSA), and Stochastic adjustment algorithms (SAA) are proposed to reallocate bandwidth.

• Call blocking probability is analyzed for a multi-class system based on Markov model.

• Lower energy consumption is achieved without the expense of call blocking probability.

Thank you!