A distributed mechanism for power saving in ieee 802 11 wireless lans
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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

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A distributed mechanism for power saving in ieee 802 11 wireless lans

A Distributed Mechanism for Power Saving in IEEE 802.11 Wireless LANs





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

Ieee 802 11 standard dcf for wlans 1 2
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]

Ieee 802 11 standard dcf for wlans 2 2
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

The dcc mechanism 1 3
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

The dcc mechanism 2 3
The DCC mechanism(2/3)

  • Each station controls its transmission via Probability of Transmission(P_T(…))

  • Privilege old transmission

    requests (queue-emptying


  • When the congestion level

    grows, the P_T(…) reduces to 0

The dcc mechanism 3 3
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(…)

Power consumption analysis 1 10
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,

Power consumption analysis 3 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

Power consumption analysis 4 10
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

Power consumption analysis 5 10
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

Power consumption analysis 7 10
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

Power consumption analysis 8 10
Power consumption analysis(8/10)

  • S: average length of a successful transmission

  • The tagged station average power consumption during a not_used slot is

Power consumption analysis 9 10
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

Power consumption analysis 10 10
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

The ps dcc mechanism 1 5
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

The ps dcc mechanism 2 5
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

The ps dcc mechanism 3 5
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

The ps dcc mechanism 4 5
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

Simulation results 1 9
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%

Simulation results 4 9
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

Simulation results 5 9
Simulation results(5/9)

  • Power consumption in the “worst case” for a frame transmission

Simulation results 7 9
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

Simulation results 8 9
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

Conclusions and future research
Conclusions and future research


  • 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