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

CSNDSP 20062/23 Introduction Wireless LAN Broadband Application Quality of Service Mobility

CSNDSP 20063/23 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 20064/23 Goal Defining of Power Saving schema aiming to reduce the power consumption of a mobile IEEE e device while guaranteeing QoS requirements for delay-sensitive applications like multimedia streaming.

CSNDSP 20065/23 IEEE e APSD

CSNDSP 20066/23 IEEE e APSD IEEE e 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 20067/23 IEEE e APSD Unscheduled APSD Scheduled APSD The stations sends a trigger to the AP in order to begin a Service Period The Service Periods are repeated every Service Interval

CSNDSP 20068/23 IEEE e 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 20069/23 IEEE e 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 /23 Our Proposal Defining of an Enhanced APSD Scheduler

CSNDSP /23 A novel APSD Scheduler has been designed for WLAN IEEE e, 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. Proposal Enhanced APSD Scheduler Th max

CSNDSP /23 According to the value of PS-Buffer occupancy (n), at the end of every Service Period, the E-APSD behaves as follow: If n < Th max, 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 ≥ Th max, 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. Proposal Enhanced APSD Scheduler

CSNDSP /23 Enhanced APSD Scheduler Buffered MSDU Mean Data Rate Maximum number of MSDU sent during a SP

CSNDSP /23 Enhanced APSD Scheduler 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. Time Service Interval

CSNDSP /23 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 Th max, the AP will assign to 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. Enhanced APSD Scheduler

CSNDSP /23 Time Station A: SI 10 msStation B: SI 10 msStation C: SI 10 ms Occupied Slots STA-A jumps one Service Period. STA-B has more than Th max 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. Enhanced APSD Scheduler

CSNDSP /23 Enhanced APSD Scheduler Th max represents the minimum amount of data in a PS-Buffer that allows a Station to use an additional slot, reducing the sleep time.

CSNDSP /23 Simulation Model Streaming Server Access Point Client wireless

CSNDSP /23 Simulation Hypothesis Hypotesis Audio/Video Streaming Traffic 13 Stations in the WLAN IEEE a 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%. A comparison between the proposed E-APSD scheduler and that presented in Appendix H of Draft 10 of IEEE e specifications is been performed.

CSNDSP /23 CBRVBR 1VBR 2 Simulation Hypothesis Traffic Generators Packet size512 byte Data rate128 Kbps Service Interval30 ms Delay Bound200 ms Thmax14 R7 N° of streams9 Packet size512 byte Minimum rate320 Kbps Maximum rate1.5 Mbps Rate time4 sec Burst time1 sec Time deviation0.5 Rate deviation0.25 Number of changes10 Service Interval30 ms Delay Bound200 ms Thmax14 R7 N° of streams2 Packet size512 byte Minimum rate1 Mbps Maximum rate6 Mbps Rate time1.5 sec Burst time1 sec Time deviation0.5 Rate deviation0.25 Number of changes10 Service Interval10 ms Delay Bound200 ms Thmax12 R7 N° of streams2

CSNDSP /23 Simulations Results Energy Bit Ratio up to 50% of energy less …

CSNDSP /23 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 e compatible Access Point or network adapter. Conclusions

CSNDSP /23 Thank for your attention 1 Giovanni Ciccarese, 2 Gabriella Convertino, 1 Mario De Blasi, 1 Sebastiano Elia, 1 Cosimo Palazzo, 1 Luigi Patrono 1 Dep. of Innovation Engineering, University of Lecce, Via Monteroni, Lecce, Italy {cosimo.palazzo, mario.deblasi, gianni.ciccarese, luigi.patrono, 2 STMicroelecronics, Lecce, Italy

CSNDSP /23 Simulations Results Mean Packet Delay