1. Hybrid Power Saving Mechanism for VoIP Services with Silence Suppression in IEEE 802.16e Systems Hyun-Ho Choi, Jung-Ryun Lee, and Dong-Ho Cho IEEE Communications Letters Volume 11, Issue 5, May 2007 Page(s):455 - 457

2. Outline Introduction Proposed Hybrid Power Saving Mechanism Numerical Analysis Simulation Results Conclusion

3. Introduction IEEE 802.16e (mobile WiMAX) is targeting for Mobile Subscriber Stations (MSSs) To efficiently manage energy in IEEE 802.16e systems  Sleep-mode operation

4. Power saving classes (PSCs) PSC I is used for nonreal-time traffic with bursty behavior PSC II is designed for real-time traffic, such as VoIP services Enhanced voice codecs, can use a silence suppression scheme It is known that silent periods occupy about 60 percent of the total duration of a VoIP call

5. The overview of the IEEE 802.16e power management (PSC I) 2 n until reach its T max Fixed size

6. The overview of the IEEE 802.16e power management (PSC II) BS MSs L T k-1 Sleep mode LLL Fixed length

7. When some data to transmit in IEEE 802.16e sleep mode BS MSs L TkTk a SDU want to transmit MOB-TRF-IND L T k-1 awake mode Data BS MSs TkTk a SDU want to transmit L MOB-TRF-IND T k-1 awake mode Data Request Response delay SDU transmission interarrival time T I

8. Hybrid Power Saving Mechanism Silence Insertion Descriptor (SID) frame

9. Sleep Interval PSC I PSC II  The MS sleeps during a sleep interval with fixed size T S T i : the length of the i-th sleep interval T L : listening interval with fixed size T max : a maximum sleep cycle T P : a minimum sleep cycle

10. Numerical Analysis Brady proposed a general six-state model that provides good statistical analysis of two- way conversation 19%

11. Numerical Analysis Each MAC SDU is assumed to arrive at an MSS with Poisson process with rate λ (MAC SDUs per unit of time)  1/λ, equal to T I M: the value of k when T k = T max

12. Numerical Analysis (cont.) The probability that there is a arriving SDU during t At least one arriving MAC SDU in w i sleep cycle

13. Numerical Analysis (cont.) The average duration of PSC I The average buffering delay

14. Energy Consumption The energy consumption per unit time in PSC I The energy consumption per unit time in PSC II

15. Simulation Results the frame length is 5 ms T P =4 frames, T S =3 frames, T L =1 frame, E S =0.045 W, E L =1.5 W VoIP end-to-end delay requirement: 270 ms delay constraint: 88 ms We change the value of T max from 4 to 1024

16. Energy consumption and drop probability vs. T max

17. Conclusion the proposed HPSM can result  energy being saved by up to 20%,  maintaining a low drop probability of less than 1.9% The results can be used to select an appropriate value of T max according to the various delay constraints to current IEEE 802.16e systems.

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