An optimal power-saving class II for VoIP traffic and its performance evaluations in IEEE 802.16e...

An optimal power-saving class II for VoIP traffic and its performance evaluations in

IEEE 802.16e

JungRyun LeeSchool of Electrical and Electronics Eng,Chung-Ang University, Korea

DongHo ChoDepartment of Electrical Engineering and Computer, Korea

ACM Computer Communications 2008

Outline

Introduction Delay model for VoIP traffic The optimal sleep interval decision algorithm Simulation Conclusion

Introduction

Since an MSS is powered by a limited battery, the energy conservation of an MSS in IEEE 802.16e PSM is a key factor in WiMAX application.

Under the PSM, an MS goes to the sleep state, and wakes up during predetermined listening period in order to verify the existence of buffered packet destined for it.

Since PSCII can adjust the length of sleep intervals according to the period of VoIP packet generation, we apply a PSC II to VoIP service.

Motivation

The large packet buffering delay of a VoIP packet may lead to a high packet drop rate, the quality of service (QoS) of VoIP services can deteriorate when long sleep interval length is employed.

BS

MS

BS

MS

DL/UL

DL/UL

Goal

To find the optimal length of sleep intervals under the PCS II while satisfying the delay constraint of a VoIP connection.

Delay model for VoIP traffic

Codec-induced delay ( G.729 Codec )– Encoding delay / Decoding delay– Packetization delay / depacketization delay

Playout delay by de-jitter buffering in a receiver– Playout Delay: 語音播放延遲– De-jitter : jitter = 0 ( 封包 delay 為定值 )

Network delay– Routing delay of IP Router

Variable delay and fixed delay – Buffering delay in BS

PSC II leads to another additional packet buffering delay caused by periodic sleep intervals in the BS

Definitions

τ = 37.5 msρ = 22 msT = 20 ms

Reference “Voice over internet protocol”


VoIP Sender

BS

VoIP Receiver

Encoding delay

Routing delay of IP Router

Packetization delay

Buffering delay in BS

Depacketization delay

Decoding delay

T

T

p1 p2

p1 p1 p2

p1 p2p1

P1 end-to-end delay

P2 end-to-end delay

Sender-to-BS delay


Routing delay of IP Router

Sender-to-BS delay

Fixed Variable

Transmission delay

Fixed Variable Fixed Variable

Router 1 Router 2 Router 3

Queuing delay with the rate λi

For the service time in each router, the evaluation begins with an exponentially distributed queuing delay with rate λi at the i-th router and the sum of the exponential random variables follows

a hypoexponential distribution.

The Optimal Sleep Interval Decision Algorithm

Assumption– Only one party ( VoIP users ) is under the PSC II– Sender-to-BS is N hop– The transmission delay for a router is fixed


Definitions– T : Packet generation interval

– α : the length of listening interval

– β : the length of sleep interval

– (α + β) : a power-saving unit α + β= kT for positive integer k

BS

α β

VoIP sender

Tα + β= 2T


Definitions– m : the m-th slot – p : the p-th power-saving unit – mT + pkT ( 0 <= m < k) : the m-th slot in p-th power-savi

ng unit

BS

α β

VoIP sender

T

α + β= 2T

mT + pkT = 1 x T + 1 x 2 x T


Definitions– ρ : Sum of decoding delay and depacketization delay– Ym : sender-to-BS delay of the VoIP packet generated at the m-t

h slot– : sender-to-BS delay + packet buffering delay

– Wm : end-to-end delay of the packet generated at the m-th slotα + β= 2T

mY


Delay Constraint – W : end-to-end delay of a packet

– Dthr :delay threshold

– δ : the maximum tolerable packet loss probability


Proposition:– The delay constraint δ <=1/k is satisfied if and only if, for each pack

et generated at the m-th slot of each power-saving unit, there exists some positive integer l that satisfies the following two inequalities simultaneously:


lm :indicates the smallest value of n such that the packet generated at the m-th slot of the p-th power-saving unit satisfies Proposition simultaneously in the ( n + p )-th power-saving unit.

fY(t) : Probability Density Function of Y

: cdf of fY(t)


Prove the position is true

Example

Dthr - ρ is larger than 8T, l = 4

the smallest l satisfying proposition becomes 3 for m = 0.

The smallest l satisfying proposition is 4 for m =1,

Simulations ITU-T defines an object model to estimate the perceived quality of V

oIP session Dthr is set to 285 ms

The packet loss threshold, d, is set to 0.03. ai is assumed to be 10 ms

The framing interval in IEEE 802.16e is 5 ms and the length of the listening interval is set to one frame duration.

shows an example of the available values of l with increasing k when N=3 and λi= i / 30.

Thus, the longest power saving unit satisfying the delay constraint becomes 3 x 20 = 60ms and the longest sleep interval becomes 55 ms.

Simulations

As the average end-to-end delay of VoIP packet increases, the optimal sleep interval length decreases in order to maintain the packet drop probability within the given threshold.

Simulations

As expected, the energy consumption of an MS decreases and the average packet buffering delay increases as k increases.

Conclusions

In this work, we studied the methodology on how to choose the optimal sleep interval of the PSC II while satisfying the given end-to-end delay constraint of a VoIP connection, in the context of IEEE 802.16e standard.

An optimal power-saving class II for VoIP traffic and its performance evaluations in IEEE 802.16e...

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