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1
Service Charge and Energy-Aware Vertical Handoff in
Integrated IEEE 80216e80211 Networks
Youngkyu Choi and Sunghyun Choi School of Electrical Engineering and INMC Se
oul National University Seoul KoreaIEEE INFOCOM 2007
2
Outline
bull Introductionbull System Model
ndash Handling MSTArsquos Mobility-Related Issuesndash IEEE 80216e-Assisted 80211 Scanning
bull Scanning Rule for WLANSndash 80211 Active Scan and Energy Consumptionndash Analytical Model for Scanning in Mobile Environmentndash Optimal Scanning Rule
bull Conclusion
3
Introduction
bull Vertical handoff (VHO) ie handoff across heterogeneous access networks is considered a key feature to bring the next generation wireless communication era
bull Three generalized steps of handoffndash Finding candidate networksndash Deciding a handoffndash Executing a handoff
4
Introduction
bull Comparison of ndash VHO between WLAN and 3G system
bull The discovery of the available WLANs has not taken much attention
bull MSTA monitors available WLANs by attempting to detect the WLAN signal or MSTA is located at the specific region
bull Battery-powered
ndash VHO between WLAN and 80216ebull not throughput
5
Introduction
bull Issues considered in this paperndash Do not consider many protocol related to the
VHO execution itselfndash Finding a possible network (discovery WLAN
APs)ndash Making a decision (MSTArsquos speed)
6
System Model
bull Assumptionsndash The 80216e network is assumed to be alway
s reachable by MSTAsndash The 80211 WLAN is opportunistically reacha
ble since the BS of the 80216e is deployed to support seamless mobility
ndash The 80216e network can assist MSTAs to search available 80211 networks
7
Handling MSTArsquos Mobility-Related Issues
bull The velocity of an MSTA is one of the important factors in VHO
bull The ping-pong effect
bull MSTA does not consider a VHO into WLANs when its speed exceeds a certain threshold Vmax
8
Handling MSTArsquos Mobility-Related Issues
bull Proposition 1ndash Vmax should satisfy the condition
Prob(sgt k ) gt ψbull VHO execution timebull s MSTArsquos sojourn time in a WLAN bull k constant chosen by the userbull ψ target probability controllable by the user
bull Vmax=
ndash r radius of the WLAN coverage
bull Ex ndash r=50m =500ms k=100 ψ=09ndash Vmax= 087 ms
212
k
r
9
IEEE 80216e-Assisted 80211 Scanning
bull How do MSTAs find 80211 APs
bull A simple method is that MSTAs should keep its WLAN interface turned on or switch it on periodically at a pre-determined time interval to detect a WLAN signal
bull Not energy-efficient
10
IEEE 80216e-Assisted 80211 Scanning
bull Which information will the 80216e network provide to aid MSTAs to discovery available 80211 APs
bull The more detailed the information is the more efficient scheme can be devised
bull Precious bandwidth resources
11
IEEE 80216e-Assisted 80211 Scanning
bull 1-octet overhead indicating the 80211 AP density
bull Modify a MAC management message called MOB_NBR-ADV
12
13
Scanning Rule for WLANS
bull Proposition 2 ndash If ρgt ρmin an MSTA attempts to scan WLANs
Otherwise turn off the WLAN interface until ρis newly given by another 80216e BS
bull 80211 active scan amp passive scan
14
80211 Active Scan and Energy Consumption
bull An active scan trial operates as followsndash After broadcasting a Probe Request frame at a specifi
c frequency channel if the channel stays idle for min-ChannelTime declare the channel as empty
ndash If the channel becomes busy within in minChannelTime waits for maxChannelTime in the receiving MAC state and then handles Probe Response frames received afterwards
ndash Moving to the next channel repeat the same procedures until there is no frequency channel to scan
15
80211 Active Scan and Energy Consumption
16
80211 Active Scan and Energy Consumption
bull If a nonempty channel is examined the scan time Tu is1048708ndash Tu = Tp_req + maxChannelTime
bull if an empty channel is examined the scan time Te isndash Te = Tp_req + minChannelTime
17
80211 Active Scan and Energy Consumption
bull For total n frequency channels each channel is sequentially examined by transmitting a Probe Request frame1048708
bull A scan trial is completed if n sequential scans are completed1048708
bull A scan trial is successful or failed1048708
bull A scan interval gtgtnTe=23 ms for n = 11 since Te 212 ms
s
18
80211 Active Scan and Energy Consumption
bull is lower-bounded by 1048708
bull For the energy consumption is minimized by changing MSTArsquos MAC state to sleep or off state
s
s
sec230min ss
19
80211 Active Scan and Energy Consumption
bull A scan trial failed the energy consumption is1048708
bull Obviously
lfail PeChannelTimaCW
DIFS )min2
min(
treqp PaCW
DIFST )2
min( _
failsuccess
20
21
80211 Active Scan and Energy Consumption
bull ε(k) the energy consumption after k scan trials1048708
bull is the lower bound of ε(k) ie the energy consumption when all k trials failed1048708
bull When scanning is done during time t
kPnk ssfailfail )()(
senT
tk
)(kfail
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
2
Outline
bull Introductionbull System Model
ndash Handling MSTArsquos Mobility-Related Issuesndash IEEE 80216e-Assisted 80211 Scanning
bull Scanning Rule for WLANSndash 80211 Active Scan and Energy Consumptionndash Analytical Model for Scanning in Mobile Environmentndash Optimal Scanning Rule
bull Conclusion
3
Introduction
bull Vertical handoff (VHO) ie handoff across heterogeneous access networks is considered a key feature to bring the next generation wireless communication era
bull Three generalized steps of handoffndash Finding candidate networksndash Deciding a handoffndash Executing a handoff
4
Introduction
bull Comparison of ndash VHO between WLAN and 3G system
bull The discovery of the available WLANs has not taken much attention
bull MSTA monitors available WLANs by attempting to detect the WLAN signal or MSTA is located at the specific region
bull Battery-powered
ndash VHO between WLAN and 80216ebull not throughput
5
Introduction
bull Issues considered in this paperndash Do not consider many protocol related to the
VHO execution itselfndash Finding a possible network (discovery WLAN
APs)ndash Making a decision (MSTArsquos speed)
6
System Model
bull Assumptionsndash The 80216e network is assumed to be alway
s reachable by MSTAsndash The 80211 WLAN is opportunistically reacha
ble since the BS of the 80216e is deployed to support seamless mobility
ndash The 80216e network can assist MSTAs to search available 80211 networks
7
Handling MSTArsquos Mobility-Related Issues
bull The velocity of an MSTA is one of the important factors in VHO
bull The ping-pong effect
bull MSTA does not consider a VHO into WLANs when its speed exceeds a certain threshold Vmax
8
Handling MSTArsquos Mobility-Related Issues
bull Proposition 1ndash Vmax should satisfy the condition
Prob(sgt k ) gt ψbull VHO execution timebull s MSTArsquos sojourn time in a WLAN bull k constant chosen by the userbull ψ target probability controllable by the user
bull Vmax=
ndash r radius of the WLAN coverage
bull Ex ndash r=50m =500ms k=100 ψ=09ndash Vmax= 087 ms
212
k
r
9
IEEE 80216e-Assisted 80211 Scanning
bull How do MSTAs find 80211 APs
bull A simple method is that MSTAs should keep its WLAN interface turned on or switch it on periodically at a pre-determined time interval to detect a WLAN signal
bull Not energy-efficient
10
IEEE 80216e-Assisted 80211 Scanning
bull Which information will the 80216e network provide to aid MSTAs to discovery available 80211 APs
bull The more detailed the information is the more efficient scheme can be devised
bull Precious bandwidth resources
11
IEEE 80216e-Assisted 80211 Scanning
bull 1-octet overhead indicating the 80211 AP density
bull Modify a MAC management message called MOB_NBR-ADV
12
13
Scanning Rule for WLANS
bull Proposition 2 ndash If ρgt ρmin an MSTA attempts to scan WLANs
Otherwise turn off the WLAN interface until ρis newly given by another 80216e BS
bull 80211 active scan amp passive scan
14
80211 Active Scan and Energy Consumption
bull An active scan trial operates as followsndash After broadcasting a Probe Request frame at a specifi
c frequency channel if the channel stays idle for min-ChannelTime declare the channel as empty
ndash If the channel becomes busy within in minChannelTime waits for maxChannelTime in the receiving MAC state and then handles Probe Response frames received afterwards
ndash Moving to the next channel repeat the same procedures until there is no frequency channel to scan
15
80211 Active Scan and Energy Consumption
16
80211 Active Scan and Energy Consumption
bull If a nonempty channel is examined the scan time Tu is1048708ndash Tu = Tp_req + maxChannelTime
bull if an empty channel is examined the scan time Te isndash Te = Tp_req + minChannelTime
17
80211 Active Scan and Energy Consumption
bull For total n frequency channels each channel is sequentially examined by transmitting a Probe Request frame1048708
bull A scan trial is completed if n sequential scans are completed1048708
bull A scan trial is successful or failed1048708
bull A scan interval gtgtnTe=23 ms for n = 11 since Te 212 ms
s
18
80211 Active Scan and Energy Consumption
bull is lower-bounded by 1048708
bull For the energy consumption is minimized by changing MSTArsquos MAC state to sleep or off state
s
s
sec230min ss
19
80211 Active Scan and Energy Consumption
bull A scan trial failed the energy consumption is1048708
bull Obviously
lfail PeChannelTimaCW
DIFS )min2
min(
treqp PaCW
DIFST )2
min( _
failsuccess
20
21
80211 Active Scan and Energy Consumption
bull ε(k) the energy consumption after k scan trials1048708
bull is the lower bound of ε(k) ie the energy consumption when all k trials failed1048708
bull When scanning is done during time t
kPnk ssfailfail )()(
senT
tk
)(kfail
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
3
Introduction
bull Vertical handoff (VHO) ie handoff across heterogeneous access networks is considered a key feature to bring the next generation wireless communication era
bull Three generalized steps of handoffndash Finding candidate networksndash Deciding a handoffndash Executing a handoff
4
Introduction
bull Comparison of ndash VHO between WLAN and 3G system
bull The discovery of the available WLANs has not taken much attention
bull MSTA monitors available WLANs by attempting to detect the WLAN signal or MSTA is located at the specific region
bull Battery-powered
ndash VHO between WLAN and 80216ebull not throughput
5
Introduction
bull Issues considered in this paperndash Do not consider many protocol related to the
VHO execution itselfndash Finding a possible network (discovery WLAN
APs)ndash Making a decision (MSTArsquos speed)
6
System Model
bull Assumptionsndash The 80216e network is assumed to be alway
s reachable by MSTAsndash The 80211 WLAN is opportunistically reacha
ble since the BS of the 80216e is deployed to support seamless mobility
ndash The 80216e network can assist MSTAs to search available 80211 networks
7
Handling MSTArsquos Mobility-Related Issues
bull The velocity of an MSTA is one of the important factors in VHO
bull The ping-pong effect
bull MSTA does not consider a VHO into WLANs when its speed exceeds a certain threshold Vmax
8
Handling MSTArsquos Mobility-Related Issues
bull Proposition 1ndash Vmax should satisfy the condition
Prob(sgt k ) gt ψbull VHO execution timebull s MSTArsquos sojourn time in a WLAN bull k constant chosen by the userbull ψ target probability controllable by the user
bull Vmax=
ndash r radius of the WLAN coverage
bull Ex ndash r=50m =500ms k=100 ψ=09ndash Vmax= 087 ms
212
k
r
9
IEEE 80216e-Assisted 80211 Scanning
bull How do MSTAs find 80211 APs
bull A simple method is that MSTAs should keep its WLAN interface turned on or switch it on periodically at a pre-determined time interval to detect a WLAN signal
bull Not energy-efficient
10
IEEE 80216e-Assisted 80211 Scanning
bull Which information will the 80216e network provide to aid MSTAs to discovery available 80211 APs
bull The more detailed the information is the more efficient scheme can be devised
bull Precious bandwidth resources
11
IEEE 80216e-Assisted 80211 Scanning
bull 1-octet overhead indicating the 80211 AP density
bull Modify a MAC management message called MOB_NBR-ADV
12
13
Scanning Rule for WLANS
bull Proposition 2 ndash If ρgt ρmin an MSTA attempts to scan WLANs
Otherwise turn off the WLAN interface until ρis newly given by another 80216e BS
bull 80211 active scan amp passive scan
14
80211 Active Scan and Energy Consumption
bull An active scan trial operates as followsndash After broadcasting a Probe Request frame at a specifi
c frequency channel if the channel stays idle for min-ChannelTime declare the channel as empty
ndash If the channel becomes busy within in minChannelTime waits for maxChannelTime in the receiving MAC state and then handles Probe Response frames received afterwards
ndash Moving to the next channel repeat the same procedures until there is no frequency channel to scan
15
80211 Active Scan and Energy Consumption
16
80211 Active Scan and Energy Consumption
bull If a nonempty channel is examined the scan time Tu is1048708ndash Tu = Tp_req + maxChannelTime
bull if an empty channel is examined the scan time Te isndash Te = Tp_req + minChannelTime
17
80211 Active Scan and Energy Consumption
bull For total n frequency channels each channel is sequentially examined by transmitting a Probe Request frame1048708
bull A scan trial is completed if n sequential scans are completed1048708
bull A scan trial is successful or failed1048708
bull A scan interval gtgtnTe=23 ms for n = 11 since Te 212 ms
s
18
80211 Active Scan and Energy Consumption
bull is lower-bounded by 1048708
bull For the energy consumption is minimized by changing MSTArsquos MAC state to sleep or off state
s
s
sec230min ss
19
80211 Active Scan and Energy Consumption
bull A scan trial failed the energy consumption is1048708
bull Obviously
lfail PeChannelTimaCW
DIFS )min2
min(
treqp PaCW
DIFST )2
min( _
failsuccess
20
21
80211 Active Scan and Energy Consumption
bull ε(k) the energy consumption after k scan trials1048708
bull is the lower bound of ε(k) ie the energy consumption when all k trials failed1048708
bull When scanning is done during time t
kPnk ssfailfail )()(
senT
tk
)(kfail
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
4
Introduction
bull Comparison of ndash VHO between WLAN and 3G system
bull The discovery of the available WLANs has not taken much attention
bull MSTA monitors available WLANs by attempting to detect the WLAN signal or MSTA is located at the specific region
bull Battery-powered
ndash VHO between WLAN and 80216ebull not throughput
5
Introduction
bull Issues considered in this paperndash Do not consider many protocol related to the
VHO execution itselfndash Finding a possible network (discovery WLAN
APs)ndash Making a decision (MSTArsquos speed)
6
System Model
bull Assumptionsndash The 80216e network is assumed to be alway
s reachable by MSTAsndash The 80211 WLAN is opportunistically reacha
ble since the BS of the 80216e is deployed to support seamless mobility
ndash The 80216e network can assist MSTAs to search available 80211 networks
7
Handling MSTArsquos Mobility-Related Issues
bull The velocity of an MSTA is one of the important factors in VHO
bull The ping-pong effect
bull MSTA does not consider a VHO into WLANs when its speed exceeds a certain threshold Vmax
8
Handling MSTArsquos Mobility-Related Issues
bull Proposition 1ndash Vmax should satisfy the condition
Prob(sgt k ) gt ψbull VHO execution timebull s MSTArsquos sojourn time in a WLAN bull k constant chosen by the userbull ψ target probability controllable by the user
bull Vmax=
ndash r radius of the WLAN coverage
bull Ex ndash r=50m =500ms k=100 ψ=09ndash Vmax= 087 ms
212
k
r
9
IEEE 80216e-Assisted 80211 Scanning
bull How do MSTAs find 80211 APs
bull A simple method is that MSTAs should keep its WLAN interface turned on or switch it on periodically at a pre-determined time interval to detect a WLAN signal
bull Not energy-efficient
10
IEEE 80216e-Assisted 80211 Scanning
bull Which information will the 80216e network provide to aid MSTAs to discovery available 80211 APs
bull The more detailed the information is the more efficient scheme can be devised
bull Precious bandwidth resources
11
IEEE 80216e-Assisted 80211 Scanning
bull 1-octet overhead indicating the 80211 AP density
bull Modify a MAC management message called MOB_NBR-ADV
12
13
Scanning Rule for WLANS
bull Proposition 2 ndash If ρgt ρmin an MSTA attempts to scan WLANs
Otherwise turn off the WLAN interface until ρis newly given by another 80216e BS
bull 80211 active scan amp passive scan
14
80211 Active Scan and Energy Consumption
bull An active scan trial operates as followsndash After broadcasting a Probe Request frame at a specifi
c frequency channel if the channel stays idle for min-ChannelTime declare the channel as empty
ndash If the channel becomes busy within in minChannelTime waits for maxChannelTime in the receiving MAC state and then handles Probe Response frames received afterwards
ndash Moving to the next channel repeat the same procedures until there is no frequency channel to scan
15
80211 Active Scan and Energy Consumption
16
80211 Active Scan and Energy Consumption
bull If a nonempty channel is examined the scan time Tu is1048708ndash Tu = Tp_req + maxChannelTime
bull if an empty channel is examined the scan time Te isndash Te = Tp_req + minChannelTime
17
80211 Active Scan and Energy Consumption
bull For total n frequency channels each channel is sequentially examined by transmitting a Probe Request frame1048708
bull A scan trial is completed if n sequential scans are completed1048708
bull A scan trial is successful or failed1048708
bull A scan interval gtgtnTe=23 ms for n = 11 since Te 212 ms
s
18
80211 Active Scan and Energy Consumption
bull is lower-bounded by 1048708
bull For the energy consumption is minimized by changing MSTArsquos MAC state to sleep or off state
s
s
sec230min ss
19
80211 Active Scan and Energy Consumption
bull A scan trial failed the energy consumption is1048708
bull Obviously
lfail PeChannelTimaCW
DIFS )min2
min(
treqp PaCW
DIFST )2
min( _
failsuccess
20
21
80211 Active Scan and Energy Consumption
bull ε(k) the energy consumption after k scan trials1048708
bull is the lower bound of ε(k) ie the energy consumption when all k trials failed1048708
bull When scanning is done during time t
kPnk ssfailfail )()(
senT
tk
)(kfail
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
5
Introduction
bull Issues considered in this paperndash Do not consider many protocol related to the
VHO execution itselfndash Finding a possible network (discovery WLAN
APs)ndash Making a decision (MSTArsquos speed)
6
System Model
bull Assumptionsndash The 80216e network is assumed to be alway
s reachable by MSTAsndash The 80211 WLAN is opportunistically reacha
ble since the BS of the 80216e is deployed to support seamless mobility
ndash The 80216e network can assist MSTAs to search available 80211 networks
7
Handling MSTArsquos Mobility-Related Issues
bull The velocity of an MSTA is one of the important factors in VHO
bull The ping-pong effect
bull MSTA does not consider a VHO into WLANs when its speed exceeds a certain threshold Vmax
8
Handling MSTArsquos Mobility-Related Issues
bull Proposition 1ndash Vmax should satisfy the condition
Prob(sgt k ) gt ψbull VHO execution timebull s MSTArsquos sojourn time in a WLAN bull k constant chosen by the userbull ψ target probability controllable by the user
bull Vmax=
ndash r radius of the WLAN coverage
bull Ex ndash r=50m =500ms k=100 ψ=09ndash Vmax= 087 ms
212
k
r
9
IEEE 80216e-Assisted 80211 Scanning
bull How do MSTAs find 80211 APs
bull A simple method is that MSTAs should keep its WLAN interface turned on or switch it on periodically at a pre-determined time interval to detect a WLAN signal
bull Not energy-efficient
10
IEEE 80216e-Assisted 80211 Scanning
bull Which information will the 80216e network provide to aid MSTAs to discovery available 80211 APs
bull The more detailed the information is the more efficient scheme can be devised
bull Precious bandwidth resources
11
IEEE 80216e-Assisted 80211 Scanning
bull 1-octet overhead indicating the 80211 AP density
bull Modify a MAC management message called MOB_NBR-ADV
12
13
Scanning Rule for WLANS
bull Proposition 2 ndash If ρgt ρmin an MSTA attempts to scan WLANs
Otherwise turn off the WLAN interface until ρis newly given by another 80216e BS
bull 80211 active scan amp passive scan
14
80211 Active Scan and Energy Consumption
bull An active scan trial operates as followsndash After broadcasting a Probe Request frame at a specifi
c frequency channel if the channel stays idle for min-ChannelTime declare the channel as empty
ndash If the channel becomes busy within in minChannelTime waits for maxChannelTime in the receiving MAC state and then handles Probe Response frames received afterwards
ndash Moving to the next channel repeat the same procedures until there is no frequency channel to scan
15
80211 Active Scan and Energy Consumption
16
80211 Active Scan and Energy Consumption
bull If a nonempty channel is examined the scan time Tu is1048708ndash Tu = Tp_req + maxChannelTime
bull if an empty channel is examined the scan time Te isndash Te = Tp_req + minChannelTime
17
80211 Active Scan and Energy Consumption
bull For total n frequency channels each channel is sequentially examined by transmitting a Probe Request frame1048708
bull A scan trial is completed if n sequential scans are completed1048708
bull A scan trial is successful or failed1048708
bull A scan interval gtgtnTe=23 ms for n = 11 since Te 212 ms
s
18
80211 Active Scan and Energy Consumption
bull is lower-bounded by 1048708
bull For the energy consumption is minimized by changing MSTArsquos MAC state to sleep or off state
s
s
sec230min ss
19
80211 Active Scan and Energy Consumption
bull A scan trial failed the energy consumption is1048708
bull Obviously
lfail PeChannelTimaCW
DIFS )min2
min(
treqp PaCW
DIFST )2
min( _
failsuccess
20
21
80211 Active Scan and Energy Consumption
bull ε(k) the energy consumption after k scan trials1048708
bull is the lower bound of ε(k) ie the energy consumption when all k trials failed1048708
bull When scanning is done during time t
kPnk ssfailfail )()(
senT
tk
)(kfail
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
6
System Model
bull Assumptionsndash The 80216e network is assumed to be alway
s reachable by MSTAsndash The 80211 WLAN is opportunistically reacha
ble since the BS of the 80216e is deployed to support seamless mobility
ndash The 80216e network can assist MSTAs to search available 80211 networks
7
Handling MSTArsquos Mobility-Related Issues
bull The velocity of an MSTA is one of the important factors in VHO
bull The ping-pong effect
bull MSTA does not consider a VHO into WLANs when its speed exceeds a certain threshold Vmax
8
Handling MSTArsquos Mobility-Related Issues
bull Proposition 1ndash Vmax should satisfy the condition
Prob(sgt k ) gt ψbull VHO execution timebull s MSTArsquos sojourn time in a WLAN bull k constant chosen by the userbull ψ target probability controllable by the user
bull Vmax=
ndash r radius of the WLAN coverage
bull Ex ndash r=50m =500ms k=100 ψ=09ndash Vmax= 087 ms
212
k
r
9
IEEE 80216e-Assisted 80211 Scanning
bull How do MSTAs find 80211 APs
bull A simple method is that MSTAs should keep its WLAN interface turned on or switch it on periodically at a pre-determined time interval to detect a WLAN signal
bull Not energy-efficient
10
IEEE 80216e-Assisted 80211 Scanning
bull Which information will the 80216e network provide to aid MSTAs to discovery available 80211 APs
bull The more detailed the information is the more efficient scheme can be devised
bull Precious bandwidth resources
11
IEEE 80216e-Assisted 80211 Scanning
bull 1-octet overhead indicating the 80211 AP density
bull Modify a MAC management message called MOB_NBR-ADV
12
13
Scanning Rule for WLANS
bull Proposition 2 ndash If ρgt ρmin an MSTA attempts to scan WLANs
Otherwise turn off the WLAN interface until ρis newly given by another 80216e BS
bull 80211 active scan amp passive scan
14
80211 Active Scan and Energy Consumption
bull An active scan trial operates as followsndash After broadcasting a Probe Request frame at a specifi
c frequency channel if the channel stays idle for min-ChannelTime declare the channel as empty
ndash If the channel becomes busy within in minChannelTime waits for maxChannelTime in the receiving MAC state and then handles Probe Response frames received afterwards
ndash Moving to the next channel repeat the same procedures until there is no frequency channel to scan
15
80211 Active Scan and Energy Consumption
16
80211 Active Scan and Energy Consumption
bull If a nonempty channel is examined the scan time Tu is1048708ndash Tu = Tp_req + maxChannelTime
bull if an empty channel is examined the scan time Te isndash Te = Tp_req + minChannelTime
17
80211 Active Scan and Energy Consumption
bull For total n frequency channels each channel is sequentially examined by transmitting a Probe Request frame1048708
bull A scan trial is completed if n sequential scans are completed1048708
bull A scan trial is successful or failed1048708
bull A scan interval gtgtnTe=23 ms for n = 11 since Te 212 ms
s
18
80211 Active Scan and Energy Consumption
bull is lower-bounded by 1048708
bull For the energy consumption is minimized by changing MSTArsquos MAC state to sleep or off state
s
s
sec230min ss
19
80211 Active Scan and Energy Consumption
bull A scan trial failed the energy consumption is1048708
bull Obviously
lfail PeChannelTimaCW
DIFS )min2
min(
treqp PaCW
DIFST )2
min( _
failsuccess
20
21
80211 Active Scan and Energy Consumption
bull ε(k) the energy consumption after k scan trials1048708
bull is the lower bound of ε(k) ie the energy consumption when all k trials failed1048708
bull When scanning is done during time t
kPnk ssfailfail )()(
senT
tk
)(kfail
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
7
Handling MSTArsquos Mobility-Related Issues
bull The velocity of an MSTA is one of the important factors in VHO
bull The ping-pong effect
bull MSTA does not consider a VHO into WLANs when its speed exceeds a certain threshold Vmax
8
Handling MSTArsquos Mobility-Related Issues
bull Proposition 1ndash Vmax should satisfy the condition
Prob(sgt k ) gt ψbull VHO execution timebull s MSTArsquos sojourn time in a WLAN bull k constant chosen by the userbull ψ target probability controllable by the user
bull Vmax=
ndash r radius of the WLAN coverage
bull Ex ndash r=50m =500ms k=100 ψ=09ndash Vmax= 087 ms
212
k
r
9
IEEE 80216e-Assisted 80211 Scanning
bull How do MSTAs find 80211 APs
bull A simple method is that MSTAs should keep its WLAN interface turned on or switch it on periodically at a pre-determined time interval to detect a WLAN signal
bull Not energy-efficient
10
IEEE 80216e-Assisted 80211 Scanning
bull Which information will the 80216e network provide to aid MSTAs to discovery available 80211 APs
bull The more detailed the information is the more efficient scheme can be devised
bull Precious bandwidth resources
11
IEEE 80216e-Assisted 80211 Scanning
bull 1-octet overhead indicating the 80211 AP density
bull Modify a MAC management message called MOB_NBR-ADV
12
13
Scanning Rule for WLANS
bull Proposition 2 ndash If ρgt ρmin an MSTA attempts to scan WLANs
Otherwise turn off the WLAN interface until ρis newly given by another 80216e BS
bull 80211 active scan amp passive scan
14
80211 Active Scan and Energy Consumption
bull An active scan trial operates as followsndash After broadcasting a Probe Request frame at a specifi
c frequency channel if the channel stays idle for min-ChannelTime declare the channel as empty
ndash If the channel becomes busy within in minChannelTime waits for maxChannelTime in the receiving MAC state and then handles Probe Response frames received afterwards
ndash Moving to the next channel repeat the same procedures until there is no frequency channel to scan
15
80211 Active Scan and Energy Consumption
16
80211 Active Scan and Energy Consumption
bull If a nonempty channel is examined the scan time Tu is1048708ndash Tu = Tp_req + maxChannelTime
bull if an empty channel is examined the scan time Te isndash Te = Tp_req + minChannelTime
17
80211 Active Scan and Energy Consumption
bull For total n frequency channels each channel is sequentially examined by transmitting a Probe Request frame1048708
bull A scan trial is completed if n sequential scans are completed1048708
bull A scan trial is successful or failed1048708
bull A scan interval gtgtnTe=23 ms for n = 11 since Te 212 ms
s
18
80211 Active Scan and Energy Consumption
bull is lower-bounded by 1048708
bull For the energy consumption is minimized by changing MSTArsquos MAC state to sleep or off state
s
s
sec230min ss
19
80211 Active Scan and Energy Consumption
bull A scan trial failed the energy consumption is1048708
bull Obviously
lfail PeChannelTimaCW
DIFS )min2
min(
treqp PaCW
DIFST )2
min( _
failsuccess
20
21
80211 Active Scan and Energy Consumption
bull ε(k) the energy consumption after k scan trials1048708
bull is the lower bound of ε(k) ie the energy consumption when all k trials failed1048708
bull When scanning is done during time t
kPnk ssfailfail )()(
senT
tk
)(kfail
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
8
Handling MSTArsquos Mobility-Related Issues
bull Proposition 1ndash Vmax should satisfy the condition
Prob(sgt k ) gt ψbull VHO execution timebull s MSTArsquos sojourn time in a WLAN bull k constant chosen by the userbull ψ target probability controllable by the user
bull Vmax=
ndash r radius of the WLAN coverage
bull Ex ndash r=50m =500ms k=100 ψ=09ndash Vmax= 087 ms
212
k
r
9
IEEE 80216e-Assisted 80211 Scanning
bull How do MSTAs find 80211 APs
bull A simple method is that MSTAs should keep its WLAN interface turned on or switch it on periodically at a pre-determined time interval to detect a WLAN signal
bull Not energy-efficient
10
IEEE 80216e-Assisted 80211 Scanning
bull Which information will the 80216e network provide to aid MSTAs to discovery available 80211 APs
bull The more detailed the information is the more efficient scheme can be devised
bull Precious bandwidth resources
11
IEEE 80216e-Assisted 80211 Scanning
bull 1-octet overhead indicating the 80211 AP density
bull Modify a MAC management message called MOB_NBR-ADV
12
13
Scanning Rule for WLANS
bull Proposition 2 ndash If ρgt ρmin an MSTA attempts to scan WLANs
Otherwise turn off the WLAN interface until ρis newly given by another 80216e BS
bull 80211 active scan amp passive scan
14
80211 Active Scan and Energy Consumption
bull An active scan trial operates as followsndash After broadcasting a Probe Request frame at a specifi
c frequency channel if the channel stays idle for min-ChannelTime declare the channel as empty
ndash If the channel becomes busy within in minChannelTime waits for maxChannelTime in the receiving MAC state and then handles Probe Response frames received afterwards
ndash Moving to the next channel repeat the same procedures until there is no frequency channel to scan
15
80211 Active Scan and Energy Consumption
16
80211 Active Scan and Energy Consumption
bull If a nonempty channel is examined the scan time Tu is1048708ndash Tu = Tp_req + maxChannelTime
bull if an empty channel is examined the scan time Te isndash Te = Tp_req + minChannelTime
17
80211 Active Scan and Energy Consumption
bull For total n frequency channels each channel is sequentially examined by transmitting a Probe Request frame1048708
bull A scan trial is completed if n sequential scans are completed1048708
bull A scan trial is successful or failed1048708
bull A scan interval gtgtnTe=23 ms for n = 11 since Te 212 ms
s
18
80211 Active Scan and Energy Consumption
bull is lower-bounded by 1048708
bull For the energy consumption is minimized by changing MSTArsquos MAC state to sleep or off state
s
s
sec230min ss
19
80211 Active Scan and Energy Consumption
bull A scan trial failed the energy consumption is1048708
bull Obviously
lfail PeChannelTimaCW
DIFS )min2
min(
treqp PaCW
DIFST )2
min( _
failsuccess
20
21
80211 Active Scan and Energy Consumption
bull ε(k) the energy consumption after k scan trials1048708
bull is the lower bound of ε(k) ie the energy consumption when all k trials failed1048708
bull When scanning is done during time t
kPnk ssfailfail )()(
senT
tk
)(kfail
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
9
IEEE 80216e-Assisted 80211 Scanning
bull How do MSTAs find 80211 APs
bull A simple method is that MSTAs should keep its WLAN interface turned on or switch it on periodically at a pre-determined time interval to detect a WLAN signal
bull Not energy-efficient
10
IEEE 80216e-Assisted 80211 Scanning
bull Which information will the 80216e network provide to aid MSTAs to discovery available 80211 APs
bull The more detailed the information is the more efficient scheme can be devised
bull Precious bandwidth resources
11
IEEE 80216e-Assisted 80211 Scanning
bull 1-octet overhead indicating the 80211 AP density
bull Modify a MAC management message called MOB_NBR-ADV
12
13
Scanning Rule for WLANS
bull Proposition 2 ndash If ρgt ρmin an MSTA attempts to scan WLANs
Otherwise turn off the WLAN interface until ρis newly given by another 80216e BS
bull 80211 active scan amp passive scan
14
80211 Active Scan and Energy Consumption
bull An active scan trial operates as followsndash After broadcasting a Probe Request frame at a specifi
c frequency channel if the channel stays idle for min-ChannelTime declare the channel as empty
ndash If the channel becomes busy within in minChannelTime waits for maxChannelTime in the receiving MAC state and then handles Probe Response frames received afterwards
ndash Moving to the next channel repeat the same procedures until there is no frequency channel to scan
15
80211 Active Scan and Energy Consumption
16
80211 Active Scan and Energy Consumption
bull If a nonempty channel is examined the scan time Tu is1048708ndash Tu = Tp_req + maxChannelTime
bull if an empty channel is examined the scan time Te isndash Te = Tp_req + minChannelTime
17
80211 Active Scan and Energy Consumption
bull For total n frequency channels each channel is sequentially examined by transmitting a Probe Request frame1048708
bull A scan trial is completed if n sequential scans are completed1048708
bull A scan trial is successful or failed1048708
bull A scan interval gtgtnTe=23 ms for n = 11 since Te 212 ms
s
18
80211 Active Scan and Energy Consumption
bull is lower-bounded by 1048708
bull For the energy consumption is minimized by changing MSTArsquos MAC state to sleep or off state
s
s
sec230min ss
19
80211 Active Scan and Energy Consumption
bull A scan trial failed the energy consumption is1048708
bull Obviously
lfail PeChannelTimaCW
DIFS )min2
min(
treqp PaCW
DIFST )2
min( _
failsuccess
20
21
80211 Active Scan and Energy Consumption
bull ε(k) the energy consumption after k scan trials1048708
bull is the lower bound of ε(k) ie the energy consumption when all k trials failed1048708
bull When scanning is done during time t
kPnk ssfailfail )()(
senT
tk
)(kfail
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
10
IEEE 80216e-Assisted 80211 Scanning
bull Which information will the 80216e network provide to aid MSTAs to discovery available 80211 APs
bull The more detailed the information is the more efficient scheme can be devised
bull Precious bandwidth resources
11
IEEE 80216e-Assisted 80211 Scanning
bull 1-octet overhead indicating the 80211 AP density
bull Modify a MAC management message called MOB_NBR-ADV
12
13
Scanning Rule for WLANS
bull Proposition 2 ndash If ρgt ρmin an MSTA attempts to scan WLANs
Otherwise turn off the WLAN interface until ρis newly given by another 80216e BS
bull 80211 active scan amp passive scan
14
80211 Active Scan and Energy Consumption
bull An active scan trial operates as followsndash After broadcasting a Probe Request frame at a specifi
c frequency channel if the channel stays idle for min-ChannelTime declare the channel as empty
ndash If the channel becomes busy within in minChannelTime waits for maxChannelTime in the receiving MAC state and then handles Probe Response frames received afterwards
ndash Moving to the next channel repeat the same procedures until there is no frequency channel to scan
15
80211 Active Scan and Energy Consumption
16
80211 Active Scan and Energy Consumption
bull If a nonempty channel is examined the scan time Tu is1048708ndash Tu = Tp_req + maxChannelTime
bull if an empty channel is examined the scan time Te isndash Te = Tp_req + minChannelTime
17
80211 Active Scan and Energy Consumption
bull For total n frequency channels each channel is sequentially examined by transmitting a Probe Request frame1048708
bull A scan trial is completed if n sequential scans are completed1048708
bull A scan trial is successful or failed1048708
bull A scan interval gtgtnTe=23 ms for n = 11 since Te 212 ms
s
18
80211 Active Scan and Energy Consumption
bull is lower-bounded by 1048708
bull For the energy consumption is minimized by changing MSTArsquos MAC state to sleep or off state
s
s
sec230min ss
19
80211 Active Scan and Energy Consumption
bull A scan trial failed the energy consumption is1048708
bull Obviously
lfail PeChannelTimaCW
DIFS )min2
min(
treqp PaCW
DIFST )2
min( _
failsuccess
20
21
80211 Active Scan and Energy Consumption
bull ε(k) the energy consumption after k scan trials1048708
bull is the lower bound of ε(k) ie the energy consumption when all k trials failed1048708
bull When scanning is done during time t
kPnk ssfailfail )()(
senT
tk
)(kfail
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
11
IEEE 80216e-Assisted 80211 Scanning
bull 1-octet overhead indicating the 80211 AP density
bull Modify a MAC management message called MOB_NBR-ADV
12
13
Scanning Rule for WLANS
bull Proposition 2 ndash If ρgt ρmin an MSTA attempts to scan WLANs
Otherwise turn off the WLAN interface until ρis newly given by another 80216e BS
bull 80211 active scan amp passive scan
14
80211 Active Scan and Energy Consumption
bull An active scan trial operates as followsndash After broadcasting a Probe Request frame at a specifi
c frequency channel if the channel stays idle for min-ChannelTime declare the channel as empty
ndash If the channel becomes busy within in minChannelTime waits for maxChannelTime in the receiving MAC state and then handles Probe Response frames received afterwards
ndash Moving to the next channel repeat the same procedures until there is no frequency channel to scan
15
80211 Active Scan and Energy Consumption
16
80211 Active Scan and Energy Consumption
bull If a nonempty channel is examined the scan time Tu is1048708ndash Tu = Tp_req + maxChannelTime
bull if an empty channel is examined the scan time Te isndash Te = Tp_req + minChannelTime
17
80211 Active Scan and Energy Consumption
bull For total n frequency channels each channel is sequentially examined by transmitting a Probe Request frame1048708
bull A scan trial is completed if n sequential scans are completed1048708
bull A scan trial is successful or failed1048708
bull A scan interval gtgtnTe=23 ms for n = 11 since Te 212 ms
s
18
80211 Active Scan and Energy Consumption
bull is lower-bounded by 1048708
bull For the energy consumption is minimized by changing MSTArsquos MAC state to sleep or off state
s
s
sec230min ss
19
80211 Active Scan and Energy Consumption
bull A scan trial failed the energy consumption is1048708
bull Obviously
lfail PeChannelTimaCW
DIFS )min2
min(
treqp PaCW
DIFST )2
min( _
failsuccess
20
21
80211 Active Scan and Energy Consumption
bull ε(k) the energy consumption after k scan trials1048708
bull is the lower bound of ε(k) ie the energy consumption when all k trials failed1048708
bull When scanning is done during time t
kPnk ssfailfail )()(
senT
tk
)(kfail
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
12
13
Scanning Rule for WLANS
bull Proposition 2 ndash If ρgt ρmin an MSTA attempts to scan WLANs
Otherwise turn off the WLAN interface until ρis newly given by another 80216e BS
bull 80211 active scan amp passive scan
14
80211 Active Scan and Energy Consumption
bull An active scan trial operates as followsndash After broadcasting a Probe Request frame at a specifi
c frequency channel if the channel stays idle for min-ChannelTime declare the channel as empty
ndash If the channel becomes busy within in minChannelTime waits for maxChannelTime in the receiving MAC state and then handles Probe Response frames received afterwards
ndash Moving to the next channel repeat the same procedures until there is no frequency channel to scan
15
80211 Active Scan and Energy Consumption
16
80211 Active Scan and Energy Consumption
bull If a nonempty channel is examined the scan time Tu is1048708ndash Tu = Tp_req + maxChannelTime
bull if an empty channel is examined the scan time Te isndash Te = Tp_req + minChannelTime
17
80211 Active Scan and Energy Consumption
bull For total n frequency channels each channel is sequentially examined by transmitting a Probe Request frame1048708
bull A scan trial is completed if n sequential scans are completed1048708
bull A scan trial is successful or failed1048708
bull A scan interval gtgtnTe=23 ms for n = 11 since Te 212 ms
s
18
80211 Active Scan and Energy Consumption
bull is lower-bounded by 1048708
bull For the energy consumption is minimized by changing MSTArsquos MAC state to sleep or off state
s
s
sec230min ss
19
80211 Active Scan and Energy Consumption
bull A scan trial failed the energy consumption is1048708
bull Obviously
lfail PeChannelTimaCW
DIFS )min2
min(
treqp PaCW
DIFST )2
min( _
failsuccess
20
21
80211 Active Scan and Energy Consumption
bull ε(k) the energy consumption after k scan trials1048708
bull is the lower bound of ε(k) ie the energy consumption when all k trials failed1048708
bull When scanning is done during time t
kPnk ssfailfail )()(
senT
tk
)(kfail
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
13
Scanning Rule for WLANS
bull Proposition 2 ndash If ρgt ρmin an MSTA attempts to scan WLANs
Otherwise turn off the WLAN interface until ρis newly given by another 80216e BS
bull 80211 active scan amp passive scan
14
80211 Active Scan and Energy Consumption
bull An active scan trial operates as followsndash After broadcasting a Probe Request frame at a specifi
c frequency channel if the channel stays idle for min-ChannelTime declare the channel as empty
ndash If the channel becomes busy within in minChannelTime waits for maxChannelTime in the receiving MAC state and then handles Probe Response frames received afterwards
ndash Moving to the next channel repeat the same procedures until there is no frequency channel to scan
15
80211 Active Scan and Energy Consumption
16
80211 Active Scan and Energy Consumption
bull If a nonempty channel is examined the scan time Tu is1048708ndash Tu = Tp_req + maxChannelTime
bull if an empty channel is examined the scan time Te isndash Te = Tp_req + minChannelTime
17
80211 Active Scan and Energy Consumption
bull For total n frequency channels each channel is sequentially examined by transmitting a Probe Request frame1048708
bull A scan trial is completed if n sequential scans are completed1048708
bull A scan trial is successful or failed1048708
bull A scan interval gtgtnTe=23 ms for n = 11 since Te 212 ms
s
18
80211 Active Scan and Energy Consumption
bull is lower-bounded by 1048708
bull For the energy consumption is minimized by changing MSTArsquos MAC state to sleep or off state
s
s
sec230min ss
19
80211 Active Scan and Energy Consumption
bull A scan trial failed the energy consumption is1048708
bull Obviously
lfail PeChannelTimaCW
DIFS )min2
min(
treqp PaCW
DIFST )2
min( _
failsuccess
20
21
80211 Active Scan and Energy Consumption
bull ε(k) the energy consumption after k scan trials1048708
bull is the lower bound of ε(k) ie the energy consumption when all k trials failed1048708
bull When scanning is done during time t
kPnk ssfailfail )()(
senT
tk
)(kfail
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
14
80211 Active Scan and Energy Consumption
bull An active scan trial operates as followsndash After broadcasting a Probe Request frame at a specifi
c frequency channel if the channel stays idle for min-ChannelTime declare the channel as empty
ndash If the channel becomes busy within in minChannelTime waits for maxChannelTime in the receiving MAC state and then handles Probe Response frames received afterwards
ndash Moving to the next channel repeat the same procedures until there is no frequency channel to scan
15
80211 Active Scan and Energy Consumption
16
80211 Active Scan and Energy Consumption
bull If a nonempty channel is examined the scan time Tu is1048708ndash Tu = Tp_req + maxChannelTime
bull if an empty channel is examined the scan time Te isndash Te = Tp_req + minChannelTime
17
80211 Active Scan and Energy Consumption
bull For total n frequency channels each channel is sequentially examined by transmitting a Probe Request frame1048708
bull A scan trial is completed if n sequential scans are completed1048708
bull A scan trial is successful or failed1048708
bull A scan interval gtgtnTe=23 ms for n = 11 since Te 212 ms
s
18
80211 Active Scan and Energy Consumption
bull is lower-bounded by 1048708
bull For the energy consumption is minimized by changing MSTArsquos MAC state to sleep or off state
s
s
sec230min ss
19
80211 Active Scan and Energy Consumption
bull A scan trial failed the energy consumption is1048708
bull Obviously
lfail PeChannelTimaCW
DIFS )min2
min(
treqp PaCW
DIFST )2
min( _
failsuccess
20
21
80211 Active Scan and Energy Consumption
bull ε(k) the energy consumption after k scan trials1048708
bull is the lower bound of ε(k) ie the energy consumption when all k trials failed1048708
bull When scanning is done during time t
kPnk ssfailfail )()(
senT
tk
)(kfail
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
15
80211 Active Scan and Energy Consumption
16
80211 Active Scan and Energy Consumption
bull If a nonempty channel is examined the scan time Tu is1048708ndash Tu = Tp_req + maxChannelTime
bull if an empty channel is examined the scan time Te isndash Te = Tp_req + minChannelTime
17
80211 Active Scan and Energy Consumption
bull For total n frequency channels each channel is sequentially examined by transmitting a Probe Request frame1048708
bull A scan trial is completed if n sequential scans are completed1048708
bull A scan trial is successful or failed1048708
bull A scan interval gtgtnTe=23 ms for n = 11 since Te 212 ms
s
18
80211 Active Scan and Energy Consumption
bull is lower-bounded by 1048708
bull For the energy consumption is minimized by changing MSTArsquos MAC state to sleep or off state
s
s
sec230min ss
19
80211 Active Scan and Energy Consumption
bull A scan trial failed the energy consumption is1048708
bull Obviously
lfail PeChannelTimaCW
DIFS )min2
min(
treqp PaCW
DIFST )2
min( _
failsuccess
20
21
80211 Active Scan and Energy Consumption
bull ε(k) the energy consumption after k scan trials1048708
bull is the lower bound of ε(k) ie the energy consumption when all k trials failed1048708
bull When scanning is done during time t
kPnk ssfailfail )()(
senT
tk
)(kfail
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
16
80211 Active Scan and Energy Consumption
bull If a nonempty channel is examined the scan time Tu is1048708ndash Tu = Tp_req + maxChannelTime
bull if an empty channel is examined the scan time Te isndash Te = Tp_req + minChannelTime
17
80211 Active Scan and Energy Consumption
bull For total n frequency channels each channel is sequentially examined by transmitting a Probe Request frame1048708
bull A scan trial is completed if n sequential scans are completed1048708
bull A scan trial is successful or failed1048708
bull A scan interval gtgtnTe=23 ms for n = 11 since Te 212 ms
s
18
80211 Active Scan and Energy Consumption
bull is lower-bounded by 1048708
bull For the energy consumption is minimized by changing MSTArsquos MAC state to sleep or off state
s
s
sec230min ss
19
80211 Active Scan and Energy Consumption
bull A scan trial failed the energy consumption is1048708
bull Obviously
lfail PeChannelTimaCW
DIFS )min2
min(
treqp PaCW
DIFST )2
min( _
failsuccess
20
21
80211 Active Scan and Energy Consumption
bull ε(k) the energy consumption after k scan trials1048708
bull is the lower bound of ε(k) ie the energy consumption when all k trials failed1048708
bull When scanning is done during time t
kPnk ssfailfail )()(
senT
tk
)(kfail
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
17
80211 Active Scan and Energy Consumption
bull For total n frequency channels each channel is sequentially examined by transmitting a Probe Request frame1048708
bull A scan trial is completed if n sequential scans are completed1048708
bull A scan trial is successful or failed1048708
bull A scan interval gtgtnTe=23 ms for n = 11 since Te 212 ms
s
18
80211 Active Scan and Energy Consumption
bull is lower-bounded by 1048708
bull For the energy consumption is minimized by changing MSTArsquos MAC state to sleep or off state
s
s
sec230min ss
19
80211 Active Scan and Energy Consumption
bull A scan trial failed the energy consumption is1048708
bull Obviously
lfail PeChannelTimaCW
DIFS )min2
min(
treqp PaCW
DIFST )2
min( _
failsuccess
20
21
80211 Active Scan and Energy Consumption
bull ε(k) the energy consumption after k scan trials1048708
bull is the lower bound of ε(k) ie the energy consumption when all k trials failed1048708
bull When scanning is done during time t
kPnk ssfailfail )()(
senT
tk
)(kfail
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
18
80211 Active Scan and Energy Consumption
bull is lower-bounded by 1048708
bull For the energy consumption is minimized by changing MSTArsquos MAC state to sleep or off state
s
s
sec230min ss
19
80211 Active Scan and Energy Consumption
bull A scan trial failed the energy consumption is1048708
bull Obviously
lfail PeChannelTimaCW
DIFS )min2
min(
treqp PaCW
DIFST )2
min( _
failsuccess
20
21
80211 Active Scan and Energy Consumption
bull ε(k) the energy consumption after k scan trials1048708
bull is the lower bound of ε(k) ie the energy consumption when all k trials failed1048708
bull When scanning is done during time t
kPnk ssfailfail )()(
senT
tk
)(kfail
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
19
80211 Active Scan and Energy Consumption
bull A scan trial failed the energy consumption is1048708
bull Obviously
lfail PeChannelTimaCW
DIFS )min2
min(
treqp PaCW
DIFST )2
min( _
failsuccess
20
21
80211 Active Scan and Energy Consumption
bull ε(k) the energy consumption after k scan trials1048708
bull is the lower bound of ε(k) ie the energy consumption when all k trials failed1048708
bull When scanning is done during time t
kPnk ssfailfail )()(
senT
tk
)(kfail
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
20
21
80211 Active Scan and Energy Consumption
bull ε(k) the energy consumption after k scan trials1048708
bull is the lower bound of ε(k) ie the energy consumption when all k trials failed1048708
bull When scanning is done during time t
kPnk ssfailfail )()(
senT
tk
)(kfail
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
21
80211 Active Scan and Energy Consumption
bull ε(k) the energy consumption after k scan trials1048708
bull is the lower bound of ε(k) ie the energy consumption when all k trials failed1048708
bull When scanning is done during time t
kPnk ssfailfail )()(
senT
tk
)(kfail
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
22
80211 Active Scan and Energy Consumption
bull Proposition 3ndash At a given time t is a decreasing functio
n of )(kfails
)()( 2 esfailses
fail TPnT
nt
d
d
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
23
Analytical Model for Scanning in Mobile Environment
bull ΔC(k) the additional area examined at the k-th scan trial1048708
bull Letting1048708
bull the cumulative probability Ps(k) of a successful scan after k trials can be represented 1048708
bull Ps(k) is proportional to k
k
i
iCkS1
)()(
)(1)0(1)( kSs ePkP
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
24
Analytical Model for Scanning in Mobile Environment
bull The profiles of the simulation1048709ndash The side of the square that is assumed to be the cove
rage of the 80216e single-cell is m1048708ndash At time t = 0 and an MSTA are placed randomly in th
e square1048708ndash The MSTA starts to move according to the random wa
ypoint model[19] and moves linearly with the constant speed1048708
ndash A run of simulation is finished if the scan trial is successful or the simulation time reaches tmax
310
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
25
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
26
Optimal Scanning Rule
bull Problem 1 ndash Scanning Problem in WLAN
bull where the constraint is interpreted that the scan should succeed with a probability larger than Ptar
get
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
27
Optimal Scanning Rule
bull Proposition 4ρmin is the minimum ρ which satisfies Ps ≧Ptarget using1048708
bull For a given ρgt ρmin we solve Problem 1 using the energy efficient scan policy (ESP) algorithm
minss
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
28
Energy-efficient Scan Policy (ESP)
bull a small is preferred for a given k to minimize ε from 1048708
bull According to Proposition 3 k should be minimized to maximize
senT
tk
max
max minmaxses nT
k
t
)1ln(
)(|min argmin
ettPkSkk
s
s
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
29
Energy-efficient Scan Policy (ESP)
bull Finally the optimal scan interval τs is represented as
max min
min
maxses nT
k
t
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
30
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
31
Conclusion
bull 80211 active scan develop a mathematical model which shows the successful scan probability in terms of the AP density and the scan interval
bull Energy-efficient scan Policy (ESP) algorithm
bull Under a practical service charge plan it is beneficial for user to control the usage of the 80216e network
