A Novel APSD Scheduler for WLAN IEEE 802.11e

1. COMMUNICATION SYSTEMS, NETWORKS AND DIGITAL SIGNAL PROCESSING University of Lecce A Novel APSD Scheduler for WLAN IEEE 802.11e Speaker: Sebastiano Elia CSNDSP 2006 Fifth International Symposium

2. Introduction Wireless LAN Broadband Application Mobility Quality of Service CSNDSP 2006

3. Power Management Device with limited battery capacity Limited time in action Need of Power Saving mechanisms in order to increase the life time of batteries CSNDSP 2006

4. Goal Defining of Power Saving schema aiming to reduce the power consumption of a mobile IEEE 802.11e device while guaranteeing QoS requirements for delay-sensitive applications like multimedia streaming. CSNDSP 2006

5. IEEE 802.11e APSD CSNDSP 2006

6. IEEE 802.11e APSD IEEE 802.11e defines a new method to deliver the frames buffered at the AP while the station is in PS Mode, the Automatic Power Save Delivery (APSD) With APSD the station in PS mode remains in awake state for the duration of a Service Period. CSNDSP 2006

7. IEEE 802.11e APSD The Service Periods are repeated every Service Interval The stations sends a trigger to the AP in order to begin a Service Period Unscheduled APSD Scheduled APSD CSNDSP 2006

8. IEEE 802.11e APSD APSD scheduler The channel time is slotted into APSD channels repeating at fixed time intervals equal to the Basic Service Interval. An APSD channel may be assigned to a single APSD station with service interval equal to the Basic Service Interval, or can be shared by two or more PS stations with TSs having longer SI. CSNDSP 2006

9. IEEE 802.11e APSD APSD scheduler Fixed Service Interval Short life time of battery in presence of Variable Bit Rate traffic The transition between sleep to awake wastes energy CSNDSP 2006

10. Our Proposal Defining of an Enhanced APSD Scheduler CSNDSP 2006

11. Proposal Enhanced APSD Scheduler • A novel APSD Scheduler has been designed for WLAN IEEE 802.11e, referred as Enhanced APSD (E-APSD) scheduler. • The E-APSD scheduler is able to exploit information related to PS-Buffer statistics in order to optimize (growing up or down) the duration of sleep periods for the stations in APSD mode. Thmax CSNDSP 2006

12. Proposal Enhanced APSD Scheduler • According to the value of PS-Buffer occupancy (n), at the end of every Service Period, the E-APSD behaves as follow: • If n < Thmax, then the AP communicates to the APSD Station the number of SI that the Station must jump, by using the QAP PS Buffer State subfield of the QoS Control field included into the header of the QoS Null frame. • If n ≥ Thmax, then the E-APSD scheduler tries to assign additional free slots to the admitted APSD reducing the time that the APSD Station spends in sleep state. CSNDSP 2006

13. Mean Data Rate Buffered MSDU Maximum number of MSDU sent during a SP Enhanced APSD Scheduler CSNDSP 2006

14. Enhanced APSD Scheduler 1 1 1 1 1 Time Service Interval • After the end of the first SP the number of buffered packets is less than Thmax. • The AP calculates N (equal to two SI in this example) and communicates how many SIs the PS-Station must jump. CSNDSP 2006

15. Enhanced APSD Scheduler • A slot is considered free when another Station will jump it or when it has not yet been assigned to any APSD stream. The presence of free APSD channels is always known to AP. • At the end of a Service Period, if the number of MSDU buffered at the AP is higher than Thmax,the AP will assignto the STA the first free slot among next m, where m is the number of APSD channel before the next slot regurarly assigned to the STA after a SI. CSNDSP 2006

16. Enhanced APSD Scheduler Station A: SI 10 ms Station B: SI 10 ms Station C: SI 10 ms Occupied Slots 2 3 4 5 6 7 1 2 3 1 Time • STA-A jumps one Service Period. • STA-B has more than Thmax packets stored into the PS-Buffer, so the AP tries to assign to STA-B one extra-slot. • STA-B gains the slot released by STA-A, in addition to that one assigned after a SI. • STA-C wakes up. CSNDSP 2006

17. Enhanced APSD Scheduler • Thmax represents the minimum amount of data in a PS-Buffer that allows a Station to use an additional slot, reducing the sleep time. CSNDSP 2006

18. Simulation Model Client wireless Streaming Server Access Point CSNDSP 2006

19. Simulation Hypothesis A comparison between the proposed E-APSD scheduler and that presented in Appendix H of Draft 10 of IEEE 802.11e specifications is been performed. Hypotesis • Audio/Video Streaming Traffic • 13 Stations in the WLAN • IEEE 802.11a phisyc layer • SNR: from 22 dB to 26 dB • No mobility and no congestion • All simulation results, obtained using the Network Simulator v2 (ns2) tool, are characterized by a 95% confidence interval whose maximum relative error is equal to 5%. CSNDSP 2006

20. Simulation Hypothesis Traffic Generators CBR VBR 1 VBR 2 CSNDSP 2006

21. Simulations Results Energy Bit Ratio up to 50% of energy less … CSNDSP 2006

22. Conclusions Conclusions • The simulation results have shown that adapting the duration of sleep period according to the current traffic load together with the absence of triggers are very effective in terms of power saving. • Moreover, the proposed scheduler is very simple and should be very easily implemented in a IEEE 802.11e compatible Access Point or network adapter. CSNDSP 2006

23. Thank for your attention 1Giovanni Ciccarese, 2Gabriella Convertino, 1Mario De Blasi, 1Sebastiano Elia, 1Cosimo Palazzo, 1Luigi Patrono 1 Dep. of Innovation Engineering, University of Lecce, Via Monteroni, 73100 Lecce, Italy e-mail: {cosimo.palazzo, mario.deblasi, gianni.ciccarese, luigi.patrono, sebastiano.elia} @unile.it 2 STMicroelecronics, Lecce, Italy gabriella.convertino@st.com CSNDSP 2006

24. Simulations Results Mean Packet Delay CSNDSP 2006