1 / 32

A Distributed Mechanism for Power Saving in IEEE 802.11 Wireless LANs

A Distributed Mechanism for Power Saving in IEEE 802.11 Wireless LANs. LUCIANO BONONI MARCO CONTI LORENZO DONATIELLO ΠΑΡΟΥΣΙΑΣΗ :ΜΑΝΙΑΔΑΚΗΣ ΑΠΟΛΛΩΝ. Introduction(1/1). Power Save-Distributed Contention Control (PS-DCC) used on top of the IEEE 802.11 WLANs

lareina-macias
Download Presentation

A Distributed Mechanism for Power Saving in IEEE 802.11 Wireless LANs

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. A Distributed Mechanism for Power Saving in IEEE 802.11 Wireless LANs LUCIANO BONONI MARCO CONTI LORENZO DONATIELLO ΠΑΡΟΥΣΙΑΣΗ :ΜΑΝΙΑΔΑΚΗΣ ΑΠΟΛΛΩΝ

  2. Introduction(1/1) • Power Save-Distributed Contention Control (PS-DCC) used on top of the IEEE 802.11 WLANs • Power Saving Strategy at the MAC level • Wireless ad hoc networks • Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) • Based on Distributed Coordination Function (DCF) • Maximize channel utilization and QoS • No power wasted due to the collisions and Carrier Sensing • Balancing the power consumed by the NI in the transmission and reception phases • Adaptive to the congestion variations

  3. IEEE 802.11 Standard DCF for WLANs(1/2) • Active stations perform Carrier Sensing activity • DIFS-Basic Access mechanism • Collision Avoidance-Binary Exponential Backoff scheme • Backoff_Counter:number of empty slots station must observe the channel • Rnd(): function returning pseudo-random numbers uniformly distributed in [0,1]

  4. IEEE 802.11 Standard DCF for WLANs(2/2) • Backoff_Counter=0 – successful transmission • ACK after a SIFS • If the transmission generates a collision,the CW_Size is doubled • Num_Att :number of transmission attempts • Low utilization channel • Congested systems-High collision probability

  5. The DCC mechanism(1/3) • Every active station counts (Num_Busy_Slots) and (Num_Available_Slots) • Normalized lower bound for the actual contention level of the channel

  6. The DCC mechanism(2/3) • Each station controls its transmission via Probability of Transmission(P_T(…)) • Privilege old transmission requests (queue-emptying behavior) • When the congestion level grows, the P_T(…) reduces to 0

  7. The DCC mechanism(3/3) • If slot utilization=1, it means no accesses in the next slot • Modifying the P_T(…) • SU_limit :arbitrary upper limit to the slot utilization • DCC mechanism reduces all the P_T(…)

  8. Power consumption analysis(1/10) • M active stations • PTX:power consumed (mW) by the Network Interface (NI) during transmission • PRX:power consumed (mW) by the (NI) during reception • Backoff interval sampled from a geometric distribution with parameter p, p=1/(E[B]+1), E[B]:average backoff time • Payload length sampled from a geometric distribution with parameter q,

  9. Power consumption analysis(2/10)

  10. Power consumption analysis(3/10) • Jth renewal period: time interval between jth and (j+1)th successful transmission • Energy :Energy required to a station to perform a successful transmission • System behavior in virtual transmission time

  11. Power consumption analysis(4/10) • Nc :number of collisions experienced in a virtual transmission time • In each subinterval, there are a number of not used slots (random variables sampled from a geometric distribution) • Station transmits in a slot with probability p

  12. Power consumption analysis(5/10) • N_nusk : number of consecutive not_used_slots • Energynus_k :power consumption during the N_nusk slots • Energytagged_collision_k : power consumption experienced by the tagged station in kth collision • Energytagged_success :power consumption experienced by the tagged station in jth successful transmission

  13. Power consumption analysis(6/10)

  14. Power consumption analysis(7/10) • backoff interval sampled from a geometric distribution (p) • Collision: average length of a collision • τ :maximum propagation delay between 2 WLANs • E[Collnot_tagged]: average length of a collision not involving the tagged station

  15. Power consumption analysis(8/10) • S: average length of a successful transmission • The tagged station average power consumption during a not_used slot is

  16. Power consumption analysis(9/10) • The tagged station average power consumption, when it performs a successful transmission in a slot • The tagged station power consumption, when it experiences a collision while transmitting

  17. Power consumption analysis(10/10) • The average energy requirement (in mJ units) for a frame transmission • popt: the value of p which minimizes the energy consumption • M, q, PTX, PRX :fixed system’s parameters

  18. The PS-DCC mechanism(1/5) • Used to enhance an IEEE 802.11 from the power consumption standpoint • Asymptotical Contention Limit (ACL) :optimal parameter setting for power consumption in a boundary value for the network slot utilization • Each of the M stations uses the optimal backoff value popt Negative 2nd order term • M x popt : tight upper bound of the Slot_Utilization

  19. The PS-DCC mechanism(2/5) • IEEE 802.11 does not depend on payload parameter value and Slot_Utilization greater than optimal values • DCC does not produce the optimal contention level

  20. The PS-DCC mechanism(3/5) • PTX/PRX low, then M x popt quasi-constant for M • A quasi-optimal value for the M x popt as a function of the payload parameter • Represents the optimal level of slot utilization, to guarantee power consumption optimality • PTX/PRX high, M x popt significantly affected by M • Not possible given the influence of M, thus considering only the high values of M

  21. The PS-DCC mechanism(4/5) • DCC mechanism limits the slot utilization by its optimal upper bound asymptotic contention limit (ACL) • New probability of transmission (P_T) • PS-DCC mechanism requires payload and the Slot_Utilization estimations to determine the value of the P_T

  22. The PS-DCC mechanism(5/5) • M=100

  23. Simulation results(1/9) • Average power consumption for a frame transmission • Channel utilization level when varying the contention level on the transmission channel • Number of stations 2 to 200 • PTX/PRX=2 and 100 • Average payload length 2.5 and 100 slot units • Random access schemes with respect to the contention level influence • Confidence level 95%

  24. Simulation results(2/9)

  25. Simulation results(3/9)

  26. Simulation results(4/9) Results show that: • Power consumption in the Standard 802.11 DCF is negatively affected by the congestion level • PS-DCC mechanism counterbalances the congestion growth by maintaining the optimality in the power consumption • Energy saving achieved by PS-DCC is significant and increases with the average frame size

  27. Simulation results(5/9) • Power consumption in the “worst case” for a frame transmission

  28. Simulation results(6/9)

  29. Simulation results(7/9) • MAC access delay: time between the first transmission and the completion of its successful transmission PS-DCC mechanism : • leads to a reduction of the mean access delay • Stations with high Num_Att -High probability of success • Fairness • Queue-emptying behavior of the system

  30. Simulation results(8/9) • Simulation traces of the average energy required for a frame transmission with and without the PS-DCC mechanism • 100 stations initially active • A burst of additional 100 station activates, causing the congestion level to grow up (twice) • PS-DCC mechanism obtains a lower energy requirement (close to the optimal value) for the frame transmissions-fast to adopt new contention scenarios

  31. Simulation results(9/9)

  32. Conclusions and future research PS-DCC: • Effective in implementing a distributed and adaptive contention control • Guarantee the optimal power consumption of a random-access MAC protocol • No additional hardware • Flexibility • Stable behavior • Fair reduction of contention • Queue-emptying behavior of the system • Quasi-optimum channel utilization and power consumption, without affection of the contention level

More Related