Quorum-Based Asynchronous Power-Saving Protocols for IEEE 802.11 Ad Hoc Networks Presented by...
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Quorum-Based Asynchronous Power-Saving Protocols for
IEEE 802.11 Ad Hoc Networks
Presented by
Jehn-Ruey Jiang
Department of Computer Science and Information Engineering
National Central University
To Rest, to Go Far!
Outline IEEE 802.11 Ad hoc Network Power Saving Problem Asynchronous Quorum-based PS Protocols Optimal Asyn. Quorum-Based PS Protocols Analysis and Simulation Conclusion
Outline IEEE 802.11 Ad hoc Network Power Saving Problem Asynchronous Quorum-based PS Protocols Optimal Asyn. Quorum-Based PS Protocols Analysis and Simulation Conclusion
IEEE 802.11 Overview
Approved by IEEE in 1997
Extensions approved in 1999 (High Rate)
Standard for Wireless Local Area Networks ( WLAN )
IEEE 802.11 Family(1/2)
802.11a (1999)(WiFi5):6 to 54 Mbps in the 5 GHz band
802.11b (1999)(WiFi, Wireless Fidelity):5.5 and 11 Mbps in the 2.4 GHz band
802.11g (2001):54 Mbps in the 2.4 GHz band
802.11n (2006)(MIMO):160 Mbps in the 2.4 and the 5 GHz bands
IEEE 802.11 Family(2/2) 802.11c: support for 802.11 frames 802.11d: new support for 802.11 frames 802.11e: QoS enhancement in MAC 802.11f: Inter Access Point Protocol 802.11h: channel selection and power control 802.11i: security enhancement in MAC 802.11j: 5 GHz globalization
Infrastructure vs Ad-hoc Modesinfrastructure network
ad-hoc network
APAP
AP
wired network
ad-hoc network
Multi-hop ad hoc network
Ad hoc Network (1/3)
A collection of wireless mobile hosts forming a temporary network without the aid of established infrastructure or centralized administration(by D. B. Johnson et al.)
Also called MANET (Mobile Ad hoc Network)(by Internet Society IETF)
Ad hoc Network (2/3)
Single-Hop Each node is within each other’s transmission
rangeFully connected
Multi-HopA node reaches another node via a chain of
intermediate nodesNetworks may partition and/or merge
Ad hoc Network (3/3)
Applications:
Battlefields
Disaster rescue
Spontaneous meetings
Outdoor activities
Outline IEEE 802.11 Ad hoc Network Power Saving Problem Asynchronous Quorum-based PS Protocols Optimal Asyn. Quorum-Based PS Protocols Analysis and Simulation Conclusion
Power Saving
Battery is a limited resource for portable devices
Battery technology does not progress fast enough
Power saving becomes a critical issue in MANETs, in which devices are all supported by batteries
Solutions to Power Saving
PHY Layer: transmission power controlHuang (ICCCN’01), Ramanathan (INFOCOM’00)
MAC Layer: power mode managementTseng (INFOCOM’02), Chiasserini (WCNC’00)
Network Layer: power-aware routingSingh (ICMCN’98), Ryu (ICC’00)
Transmission Power Control
Tuning transmission energy for higher channel reuse
Example:A is sending to B (based on IEEE 802.11)Can (C, D) and (E, F) join?
A
BCD
F E
No!Yes!
Power Mode Management
doze mode vs. active mode Example:
A is sending to BDoes C need to stay awake?
A
B
C
No!It can turn off its radio to save energy!
But it should turn on its radio periodiclally for possible data comm.
Power-Aware Routing
Routing in an ad hoc network with energy-saving (prolonging network lifetime) in mind
Example:
+
–
+
–
+
–
+
–
+
–
+
–
SRCN1 N2
DEST
N4N3
Better!!
Our Focus
Among the three solutions:PHY Layer: transmission power controlMAC Layer: power mode managementNetwork Layer: power-aware routing
IEEE 802.11 PS Mode(2/2)
Environments: Infrastructure (O)
Ad hoc (infrastructureless)Single-hop (O)Multi-hop
IEEE 802.11 PS Mode(1/2)An IEEE 802.11 Card is allowed to turn off its radio to be in the PS mode to save energyPower Consumption:(ORiNOCO IEEE 802.11b PC Gold Card)
Vcc:5V, Speed:11Mbps
PS for 1-hop Ad hoc Networks (1/3)
Host
ATIM Window
Beacon Interval
Power Saving Mode
Beacon Interval Beacon Interval Beacon Interval
Beacon
Time axis is divided into equal-length intervals called beacon intervals
In the beginning of a beacon interval, there is ATIM window, in which hosts should wake up and contend to send a beacon frame with the backoff mechanism for synchronizing clocks
PS for 1-hop Ad hoc Networks (2/3)
A possible sender also sends ATIM (Ad hoc Traffic Indication Map) message with DCF procedure in the ATIM window to its intended receivers in the PS mode
ATIM demands an ACK. And the pair of hosts receiving ATIM and ATIM-ACK should keep themselves awake for transmitting and receiving data
ATIM Window
ATIM Window
PS for 1-hop Ad hoc Networks (3/3)
Beacon Interval Beacon Interval
ATIM Window
ATIM Window
Host A
Host B
Beacon
BTA=2, BTB=5
power saving mode
power saving mode
Beacon
ATIM
ACK
active state
data frame
ACK
Target Beacon Transmission Time (TBTT)
No ATIM means no data to send
or to receive
PS: m-hop Ad hoc NetworkProblems:
Clock Synchronizationit is hard due to communication delays and mobility
Network Partitionunsynchronized hosts with different wakeup times may not recognize each other
Clock Drift Example
Max. clock drift for IEEE 802.11 TSF (200 DSSS nodes, 11Mbps, aBP=0.1s)
Network-Partitioning Example
Host A
Host B
A
B
C D
E
F
Host C
Host D
Host E
Host F
╳
╳
ATIM window
╳
╳
Network Partition
The blue ones do not know the existence of the red ones, not to
mention the time when they are awake.
The red ones do not know the existence of the blue ones, not to
mention the time when they are awake.
Asynchronous PS Protocols (1/2)
Try to solve the network partitioning problem to achieveNeighbor discoveryWakeup prediction
without synchronizing hosts’ clocks
Asynchronous PS Protocols (2/2)
Three existent asyn. PS protocols:Dominating-Awake-IntervalPeriodical-Fully-Awake-IntervalQuorum-BasedRef:
“Power-Saving Protocols for IEEE 802.11-BasedMulti-Hop Ad Hoc Networks,”Yu-Chee Tseng, Chih-Shun Hsu and Ten-Yueng HsiehInfoCom’2002
Outline IEEE 802.11 Ad hoc Network Power Saving Problem Asynchronous Quorum-based PS Protocols Optimal Asyn. Quorum-Based PS Protocols Analysis and Simulation Conclusion
Numbering beacon intervals
0 1 2 3
4 5 6 7
8 9 10 11
12 13 14 15
And they are organized
as a n n array
n consecutive beacon intervals are numbered as 0 to n-1
201514131211109876543210 …
Beacon interval
Quorum Intervals (1/4)
Intervals from one row and one column are called
quorum intervals
0 1 2 3
4 5 6 7
8 9 10 11
12 13 14 15
Example:Quorum intervals arenumbered by2, 6, 8, 9, 10, 11, 14
Quorum Intervals (2/4)
Intervals from one row and one column are called
quorum intervals
0 1 2 3
4 5 6 7
8 9 10 11
12 13 14 15
Example:Quorum intervals arenumbered by0, 1, 2, 3, 5, 9, 13
Quorum Intervals (3/4)
Any two sets of quorum intervals have two common members
For example:The set of quorum intervals {0, 1, 2, 3, 5, 9, 13} and the set of quorum intervals{2, 6, 8, 9, 10, 11, 14} have two common members:
2 and 915141312
111098
7654
3210
Quorum Intervals (4/4)
1514131211109876543210
2 151413121110987654310
2 overlapping quorum intervals
Host DHost C
2 151413121110987654310Host D
1514131211109876543210Host C
Even when the beacon interval numbers are not aligned (they are rotated), there are always at least two overlapping quorum intervals
Structure of quorum intervals
Networks Merge Properly
Host A
Host B
A
B
C D
E
F
Host C
Host D
Host E
Host F
ATIM window
Beacon window
Monitor window
Short Summary
There is an asynchronous power-saving protocol that achievesasynchronous neighbor discovery
Hearing beacons twice or more in every n consecutive beacon intervals
wakeup predictionvia a simple quorum concept.
Observation 1
It is a simple grid quorum system [Maekawa 1985] in Tseng’s work.
There are many more complicated quorum systems in the literature of distributed systems:FPP [Maekawa 1985], Tree [Agrawal 1990],
Hierarchical[Kumar 1991], Cohorts [Jiang 1997], Cyclic [Luk 1997], Torus [Lang 1998], etc.
Question: Can these quorum systems be directly applied to solve the power-saving problem in a MANET?
The Answer Is … Not all quorum systems can be used here!
Counter example: { {1}} under {1,2,3}
Only those quorum systems with the rotation closure property can be used!
Observation 2
Smaller quorums are better because they imply lower active ratio (better energy-efficiency)
But quorums cannot be too small less the quorum system does not satisfy the rotation closure property
Question 1: What is the smallest quorum size? Question 2: Is there any quorum systems to have
the smallest quorum size?
Outline IEEE 802.11 Ad hoc Network Power Saving Problem Asynchronous Quorum-based PS Protocols Optimal Asyn. Quorum-Based PS Protocols Analysis and Simulation Conclusion
What are quorum systems?Quorum system:
a collection of mutually intersecting subsets of a universal set U, where each subset is called a quorumE.G. {{1, 2},{2, 3},{1,3}} is a quorum system
under U={1,2,3}
A quorum system is a collection of sets satisfying the intersection property
Rotation Closure Property (1/3)Definition. Given a non-negative integer i and a quorum H in a quorum system Q under U = {0,…, n1}, we define rotate(H, i) = {j+ijH} (mod n).
E.G. Let H={0,3} be a subset of U={0,…,3}. We have rotate(H, 0)={0, 3}, rotate(H, 1)={1,0}, rotate(H, 2)={2, 1}, rotate(H, 3)={3, 2}
Rotation Closure Property (2/3)
Definition. A quorum system Q under U = {0,…, n1} is said to have the rotation closure property ifG,H Q, i {0,…, n1}: G rotate(H, i) .
Rotation Closure Property (3/3)
For example,Q1={{0,1},{0,2},{1,2}} under U={0,1,2}
Q2={{0,1},{0,2},{0,3},{1,2,3}} under U={0,1,2,3}
Because {0,1} rotate({0,3},3) =
{0,1} {3, 2} =
Closure
Examples of quorum systems
Majority quorum system Tree quorum system Hierarchical quorum system Cohorts quorum system ………
Optimal Quorum System (1/2)
Quorum Size Lower Bound for quorum systems satisfying the rotation closure property:k, where k(k-1)+1=n, the cardinality of the universal set, and k-1 is a prime power(k n )
Optimal Quorum System (2/2)
Optimal quorum systemFPP quorum system
Near optimal quorum systemsGrid quorum systemTorus quorum systemCyclic (difference set) quorum system
Outline IEEE 802.11 Ad hoc Network Power Saving Problem Asynchronous Quorum-based PS Protocols Optimal Asyn. Quorum-Based PS Protocols Analysis and Simulation Conclusion
Analysis (1/3)
Active Ratio:the number of quorum intervals over n,where n is cardinality of the universal set
Neighbor Sensibility (NS)the worst-case delay for a PS host to detect the existence of a newly approaching PS host in its neighborhood
Analysis (2/3)
Analysis (3/3)
Optimal!
Simulation Model
Area: 1000m x 1000m Speed: 2Mbps Radio radius: 250m Battery energy: 100J. Traffic load: Poisson Dist. , 1~4 routes/s,
each having ten 1k packets Mobility: way-point model (pause time: 20s) Routing protocol: AODV
Simulation ParametersUnicast send 454+1.9 * L
Broadcast send 266+1.9 * L
Unicast receive 356+0.5 * L
Broadcast receive 56+0.5 * L
Idle 843
Doze 27 L: packet length
Unicast packet size 1024 bytes
Broadcast packet size 32 bytes
Beacon window size 4ms
MTIM window size 16ms
Simulation Metrics
Survival ratioNeighbor discovery timeThroughputAggregate throughput
Simulation Results (1/10)
Survival ratio vs. mobility (beacon interval = 100 ms, 100 hosts, traffic load = 1 route/sec).
Cyclic quorum systemE-torus quorum system
Always Active
Simulation Results (2/10)
Neighbor discovery time vs. mobility(beacon interval =100 ms, 100 hosts, traffic load = 1 route/sec).
0
500
1000
1500
2000
2500
3000
0 5 10 15 20
Moving speed (m/sec)
Neig
hb
or
dis
covery
tim
e (
ms)
C(98)
E(7x14)
A faster host can be discovered in
shorter time.
Simulation Results (3/10)
Throughput vs. mobility(beacon interval = 100 ms, 100 hosts, traffic load = 1 route/sec).
For the aggregate throughput: C(98)>E(7x74)>AA
For the throughput: AA>E(7x74)>C(98)
Simulation Results (4/10)
Survival ratio vs. beacon interval length(100 hosts, traffic load = 1 route/sec, moving speed = 0~20 m/sec with
mean = 10m/sec).
Simulation Results (5/10)
Neighbor discovery time vs. beacon interval length(100 hosts, traffic load = 1 route/sec, moving speed = 0~20 m/sec with
mean = 10m/sec).
0
2000
4000
6000
8000
10000
12000
14000
16000
100 200 300 400
Beacon interval (ms)
Nei
ghbor disco
ver
y tim
e (m
s)
C(98)
E(7x14)
Simulation Results (6/10)
Throughput vs. beacon interval length(100 hosts, traffic load = 1 route/sec, moving speed = 0~20 m/sec with
mean =10m/sec).
Simulation Results (7/10)
Survival ratio vs. traffic load(beacon interval = 100 ms, 100 hosts, mobility = 0~20 m/sec with mean =
10 m/sec).
Simulation Results (8/10)
Throughput vs. traffic load(beacon interval =100 ms, 100 hosts, mobility = 0~20 m/sec with mean =
10 m/sec).
Simulation Results (9/10)
Survival ratio vs. host density(beacon interval = 100ms, traffic load 1 route/sec, mobility = 0~20 m/sec
with mean= 10 m/sec).
Simulation Results (10/10)
Throughput vs. host density (beacon interval = 100ms, traffic load 1 route/sec, mobility = 0~20m/sec
with mean= 10 m/sec).
Outline IEEE 802.11 Ad hoc Network Power Saving Problem Asynchronous Quorum-based PS Protocols Optimal Asyn. Quorum-Based PS Protocols Analysis and Simulation Conclusion
Conclusion Quorum systems with the rotation closure
property can be translated to an asyn. PS protocol.
The active ratio is bounded by 1/ n, where n is the number of a group of consecutive beacon intervals.
Optimal, near optimal and adaptive AQPS protocols save a lot of energy w/o degrading performance significantly
Publication
ICPP’03 Best Paper Award
ACM Journal on Mobile Networks and Applications
Future work To incorporate the clustering concept into the
design of hybrid (syn. and asyn.) power saving protocols (NSC 93-2213-E-008-046-)
To design more flexible adaptive asyn. power saving protocols with the aid of the expectation quorum system (a novel quorum system which is a general form of probabilistic quorum systems) (93CAISER-中央大學分部計畫 )
To incorporate power saving mode management to wireless sensor networks with comm. and sensing coverage in mind (中大新進教師學術研究經費補助計畫 )
Thanks!
FPP quorum system
Proposed by Maekawa in 1985 For solving distributed mutual exclusion Constructed with a hypergraph
An edge can connect more than 2 vertices FPP:Finite Projective Plane
A hypergraph with each pair of edges having exactly one common vertex
Also a Singer difference set quorum system
FPP quorum system Example
0 1 2
3 4
5
6
A FPP quorum system:{ {0,1,2}, {1,5,6}, {2,3,6}, {0,4,6}, {1,3,4}, {2,4,5}, {0,3,5} }
0
3
5
Torus quorum system
For a tw torus, a quorum contains all elements from some column c, plus w/2 elements, each of which comes from column c+i, i=1.. w/2
171615141312
11109876
543210
One full column
One half column cover in a wrap around manner
{ {1,7,13,8,3,10}, {5,11,17,12,1,14},…}
Cyclic (difference set) quorum system
Def: A subset D={d1,…,dk} of Zn is called a difference set if for every e0 (mod n), thereexist elements di and djD such that di-dj=e.
{0,1,2,4} is a difference set under Z8
{ {0, 1, 2, 4}, {1, 2, 3, 5}, {2, 3, 4, 6}, {3, 4, 5, 7},{4, 5, 6, 0}, {5, 6, 7, 1}, {6, 7, 0, 2}, {7, 0, 1, 3} }
is a cyclic (difference set) quorum system C(8)
E-Torus quorum systemTrunk
Branch
Branch
Branch
Branch
cyclic
cyclic
E(t x w, k)