presented by hasan sozer1 a pseudo random coordinated scheduling algorithm for bluetooth scatternets...
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presented by Hasan SOZER 1
A Pseudo Random Coordinated Scheduling Algorithm forBluetooth Scatternets
Andras Racz, Gyorgy Miklos, Ferenc Kubinszky, Andras Valko
Traffic Analysis and Network Performance Lab.,
Ericsson Research
MobiHOC 2001, Long Beach, CA, USA © ACM 2001
presented by Hasan SOZER 2
Outline Introduction PCSS Algorithm
Overview Operation Dynamic adjustment in responce to varying traffic
Simulation Reference algorithms Scenarios
Conclusion
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Introduction Switching between piconets on a
time division basis Two important phenomenas
unnecessary polls & waiting nodes absence of nodes (slaves & masters)
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Introduction (cont’d) Scatternet wide communication
problem Scheduling orders may lead to
conflicts Variation of traffic intensity Two approaches
Hard coordination schemes Soft coordination schemes
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Introduction (cont’d) Hard coordination schemes
Time slots are allocated in advance Complex, explicit signalling Reallocation in case of changes
Soft coordination schemes Based on local information Reduced complexity Cannot guarantee conflict-free
participation
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Introduction (cont’d) Key components of the algorithm
Check Points (Meeting points): Specific to particular links Pseudo-random distribution for avoiding
systematic conflicts Dynamic adjustment of checking intensity
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PCSS Algorithm checkpoint -> Bluetooth frame
check: being present at the check point
Link becomes active at the check point
Link remains active until; there is no user data or, one leaves for another checkpoint
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PCSS Algorithm (cont’d) Randomness in assigning
checkpoints avoids systematic collusions
Sequence is generated based on Bluetooth clock of the master MAC address of the slave
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PCSS Algorithm (cont’d) Base checking interval: T Checking intensity: 1/T
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PCSS Algorithm (cont’d) Checkpoints may collide or overlap
There may be non-present neighbours Each node performs traffic
measurements for each of its link Checking intensity for each link is
increased or decreased accordingly
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PCSS Algorithm (cont’d) ??? Two nodes on a given link may
select different base checking periods
Pseudo random generation of checkpoint sequence guarantees; Set of checkpoint positions at a lower
checking intensity is a subset of checkpoint positions at any higher checking intensities
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PCSS Algorithm - Operation Initialization
No specific procedure required Communication
Starts at the checkpoint If there is no data
nodes remain idle until next checkpoint One may leave because of another
checkpoint Other node would realize the situation worst case: 5+1 slots after
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PCSS Algorithm - Operation Inputs to pseudo random
generator Current value of the master’s clock Base checking period length MAC address of the slave
Base checking period T = 2n
2fmin >= T >= 2fmax
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Dynamic Adjustment of Checking Intensity
L: number of links of the node
Avgerage Number ofcheckpoints in Tmax
Avgerage time betweentwo consecutive checkpoints
Share of a link, j from total capacity
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Dynamic Adjustment of Checking Intensity (cont’d) Measurement of utilization of
checkpoints p(i) on the ith link Moving average method
If checkpoint is utilized;
If checkpoint is not utilized;
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Dynamic Adjustment of Checking Intensity (cont’d) Total utilization p(node):
P(win): fraction of time slots in the past time window of length Nuti,win where the node has been active over the total number of time slots
If p(node) < plower, T(i) is doubled After increase or decrease, p(i) is reset
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Dynamic Adjustment of Checking Intensity (cont’d) Communication continues despite
the decrease in the checking intensity
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Dynamic Adjustment of Checking Intensity (cont’d) If p(i) > pupper, T(i) is divided by 2 Typical values for pupper and plower
for avoiding oscillation;
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Dynamic Adjustment of Checking Intensity (cont’d) Communication in case of a
checking intensity increase
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Simulation – Reference Algorithms Reference Algorithms
Ideal Coordinated Scatternet Scheduler (ICSS)
Uncoordinated Greedy Scatternet Scheduler (UGSS)
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Simulation – Reference Algorithms (cont’d) Scheduling list of a node pair in
case of the ICSS algorithm
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Simulation - Scenarios Simulation Scenarios
Network Access Point (NAP) Several forwarding hops Bridging node with varying bridging
degrees
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Simulation - NAP Checking intensities are fixed for
mouse delay requirement As laptops increase, sum of laptop
throughputs do notdecrease in case ofPCSS & ICSSalgorithms
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Simulation – Several Forwarding Hops Background traffic provided
PCSS lies between ICSS & UGSS
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Simulation – Varying bridging degrees Dynamic PCSS scheme matches
quite closely the throughput achieved by the ICSS algorithm
Perform much betterthan fixed PCSS