network layer: non-traditional wireless routing localization intro y. richard yang 12/4/2012
TRANSCRIPT
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Network Layer: Non-Traditional Wireless Routing
Localization Intro
Y. Richard Yang
12/4/2012
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Outline
Admin. and recap Network layer
Intro Location/service discovery Routing
• Traditional routing• Non-traditional routing
Localization Intro
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Admin. Projects
please use Sign Up on classesv2 for project meetings
project code/<6-page report due Dec. 12 final presentation date? First finish a basic version, and then
stress/extend your design
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Recap: Routing
So far, all routing protocols are in the framework of traditional wireline routing a graph representation of underlying
network• point-to-point graph, edges with costs
select a best (lowest-cost) route for a src-dst pair
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Traditional Routing
Q: which route?
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Inefficiency of Traditional Routing
In traditional routing, packets received off the chosen path are useless Q: what is the probability that at least one of the intermediate nodes
will receive from src?
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Inefficiency of Traditional Routing
In traditional routing, packets received off the chosen path are useless
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Motivating Scenario
Src A sends packet 1 to dst B; src B sends packet 3 to dst A
Traditional routing needs to transmit 4 packets
Motivating question: can we do better, i.e., serve multiple src-dst pairs?
A BR
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Outline
Admin. and recap Network layer
Intro Location/service discovery Routing
• Traditional routing• Non-traditional routing
– Motivation– Opportunistic routing: “parallel computing for one
src-dst pair”
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Key Issue in Opportunistic Routing
10Key Issue: opportunistic forwarding may lead to duplicates.
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Extreme Opportunistic Routing (ExOR) [2005]
Basic idea: avoid duplicates by scheduling
Instead of choosing a fix sequential path (e.g., src->B->D->dst), the source chooses a list of forwarders (a forwarder list in the packets) using ETX-like metric a background process collects ETX
information via periodic link-state flooding
Forwarders are prioritized by ETX-like metric to the destination
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ExOR: Forwarding
Group packets into batches
The highest priority forwarder transmits when the batch ends
The remaining forwarders transmit in prioritized ordereach forwarder forwards packets it
receives yet not received by higher priority forwarders
status collected by batch map
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Batch Map
Batch map indicates, for each packet in a batch, the highest-priority node known to have received a copy of that packet
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ExOR: Example
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N0
N3
N1
N2
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ExOR: Stopping Rule
A nodes stops sending the remaining packets in the batch if its batch map indicates over 90% of this batch has been received by higher priority nodesthe remaining packets transferred
with traditional routing
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Evaluations
65 Node pairs 1.0MByte file
transfer 1 Mbit/s 802.11
bit rate 1 KByte packets EXOR bacth size
100
1 kilometer
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Evaluation: 2x Overall Improvement
Median throughputs: 240 Kbits/sec for ExOR, 121 Kbits/sec for Traditional
Throughput (Kbits/sec)
1.0
0.8
0.6
0.4
0.2
00 200 400 600 800Cum
ula
tive F
ract
ion o
f N
ode P
air
s
ExORTraditional
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OR uses links in parallel
Traditional Routing3 forwarders
4 links
ExOR7 forwarders
18 links
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OR moves packets farther
ExOR average: 422 meters/transmission Traditional Routing average: 205 meters/tx
Fract
ion o
f Tra
nsm
issi
ons
0
0.1
0.2
0.6 ExORTraditional Routing
0 100 200 300 400 500 600 700 800 900 1000
Distance (meters)
25% of ExOR transmissions
58% of Traditional Routing transmissions
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Comments: ExOR
Pros takes advantage of link diversity (the
probabilistic reception) to increase the throughput
does not require changes in the MAC layer can cope well with unreliable wireless
medium
Cons scheduling is hard to scale in large networks overhead in packet header (batch info) batches increase delay
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Outline
Admin. and recap Network layer
Intro Location/service discovery Routing
• Traditional routing• Non-traditional routing
– Motivation– Opportunistic routing: “parallel computing for one
src-dst pair”
» ExOR» MORE
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MORE: MAC-independentOpportunistic Routing & Encoding [2007]
Basic idea: Replace node coordination with network
coding Trading structured scheduler for random
packets combination
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Basic Idea: Source
Chooses a list of forwarders (e.g., using ETX)
Breaks up file into K packets (p1, p2, …, pK)
Generate random packets
MORE header includes the code vector [cj1, cj2, …cjK] for coded packet pj’
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ijij pcp '
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Basic Idea: Forwarder
Check if in the list of forwarders Check if linearly independent of new
packet with existing packet Re-coding and forward
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Basic Idea: Destination
Decode
Send ACK back to src if success
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Key Practical Question: How many packets does a forwarder send?
Compute zi: the expected number of times that forwarder i should forward each packet
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Computes zs
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)1(1
sjj
sz Compute zs so that at least one forwarder that is closer to destination is expected to have received the packet :
Єij: loss probability of the link between i and j
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Compute zj for forwarder j
Only need to forward packets that are received by j sent by forwarders who are further from
destination not received by any forwarder who is closer
to destination
#such pkts:
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])1([zfurther is d closer to
i iki k
ijjL
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Compute zj for forwarder j
To guarantee at least one forwarder closer to d receives the packet
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])1([zfurther is d closer to
i iki k
ijjL
)1(d closer to
jkk
jL
jz
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Evaluations
20 nodes distributed in a indoor building Path between nodes are 1 ~ 5 hops in
length Loss rate is 0% ~ 60%; average 27%
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Throughput
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Improve on MORE?
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Mesh Networks API So Far
Network
Forward correct packets to destination
PHY/LL Deliver correct packets
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S
R1
R2
D
10-3 BER
10 -3 BER
Motivation
0%
0%
570 bytes; 1 bit in 1000 incorrect Packet loss of 99%
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S
R1
R2
D
99% (10-3
BER)
99% (10 -3 BER)
Implication
0%
0%
Opportunistic Routing 50 transmissions
Loss
Loss
ExORMORE
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Outline
Admin. and recap Network layer
Intro Location/service discovery Routing
• Traditional routing• Non-traditional routing
– Motivation– Opportunistic routing: “parallel computing for one
src-dst pair”
» ExOR [2005]» MORE [2007]» MIXIT [2008]
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New API
PHY + LL
Deliver correct symbols to higher layer
Network Forward correct symbols to destination
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What Should Each Router Forward?
R1
R2
DSP1P2
P1P2
P1P2
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What Should Each Router Forward?
R1
R2
DSP1P2
1) Forward everything Inefficient2) Coordinate Unscalable
P1P2
P1P2
P1P2
P1P2
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Forward random combinations of correct symbols
R1
R2
DSP1P2
Symbol Level Network Coding
P1P2
P1P2
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1s
…
…R1
R2
D
2s2
1
7s
2s
2
7
…
1s
…
…
2s
Routers create random combinations of correct symbols
2
1
9s
5s
5
9
…
Symbol Level Network Coding
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R1
R2
D2
1
7s
2s
…
2
1
9s
5s
…
21 s,sSolve 2
equations
Destination decodes by solving linear equations
Symbol Level Network Coding
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1s
…
…R1
R2
D
2s2
1
7s
2s
2
7
…
1s
…
…
2s
Routers create random combinations of correct symbols
15s
5
0
…
Symbol Level Network Coding
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R1
R2
D2
1
7s
2s
…
15s …
21 s,sSolve 2
equations
Destination decodes by solving linear equations
Symbol Level Network Coding
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Destination needs to know which combinations it received
Use run length encoding5
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Original Packets Coded Packet
5
9
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0
9
Original Packets Coded Packet
Use run length encoding
Destination needs to know which combinations it received
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5
Original Packets Coded Packet
Destination needs to know which combinations it received
Use run length encoding
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0
5
Original Packets Coded Packet
Destination needs to know which combinations it received
Use run length encoding
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Destination needs to know which combinations it received
Use run length encoding
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Evaluation
• Implementation on GNURadio SDR and USRP• Zigbee (IEEE 802.15.4) link layer• 25 node indoor testbed, random flows• Compared to:
1. Shortest path routing based on ETX2. MORE: Packet-level opportunistic routing
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Throughput (Kbps)
CD
FThroughput Comparison
2.1x3x
Shortest PathMOREMIXIT
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Outline
Admin. and recap Network layer
Intro Location/service discovery Routing
• Traditional routing• Non-traditional routing
– Motivation– Opportunistic routing: “parallel computing for one
src-dst pair”
– Opportunistic routing: “parallel computing for multiple src-dst pairs”
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Motivating Scenario
A sends pkt 1 to dst B B sends pkt 3 to dst A
A BR
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Opportunistic Coding: Basic Idea Each node looks at the packets
available in its buffer, and those its neighbors’ buffers
It selects a set of packets, computes the XOR of the selected packets, and broadcasts the XOR
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Opportunistic Coding: Example
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Wireless Networking: Summary
send receive
status
info info/control
- The ability to communicate is a foundational support of wireless mobile networks-The capacity of such networks is continuously being challenged as demand increases (e.g., Verizon LTE-based home broadband)- Much progress has been made, but still more are coming.
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Outline
Admin. Network layer Localization
overview
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Motivations The ancient question:
Where am I?
Localization is the process of determining the positions of the network nodes
This is as fundamental a primitive as the ability to communicate
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Localization: Many Applications
Location aware information services e.g., E911, location-based search,
advertisement, inventory management, traffic monitoring, emergency crew coordination, intrusion detection, air/water quality monitoring, environmental studies, biodiversity, military applications, resource selection (server, printer, etc.)
“Sensing data without knowing the location is meaningless.” [IEEE Computer, Vol. 33, 2000]
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Measurements
The Localization Process
Localizability (opt)
Location Computation
Location Based Applications
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Classification of Localization based on Measurement Modality Coarse-grained measurements, e.g.,
signal signature • a database of signal signature (e.g. pattern of received
signal, visible set of APs (http://www.wigle.net/)) at different locations
• match to the signature Connectivity
Advantages low cost; measurements do not need line-of-sight
Disadvantages low precision
For a detailed study, see “Accuracy Characterization for Metropolitan-scale Wi-Fi Localization,” in Mobisys 2005.
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Classification of Localization based on Measurement Modality (cont’) Fine-grained localization
distance angle (esp. with MIMO)
Advantages high precision
Disadvantages measurements need
line-of-sight for goodperformance
Cricket
iPhone 4 GPS (iFixit)
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Outline
Admin. Localization
Overview GPS
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Global Position Systems
US Department of Defense: need for very precise navigation
In 1973, the US Air Force proposed a new system for navigation using satellites
The system is known as: Navigation System with Timing and Ranging: Global Positioning System or NAVSTAR GPS
http://www.colorado.edu/geography/gcraft/notes/gps/gps_f.html
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GPS Operational Capabilities
Initial Operational Capability - December 8,
1993
Full Operational Capability declared by theSecretary of Defense at 00:01 hours onJuly 17, 1995
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NAVSTAR GPS Goals
What time is it? What is my position (including attitude)? What is my velocity? Other Goals: - What is the local time? - When is sunrise and sunset? - What is the distance between two
points? - What is my estimated time arrival
(ETA)?
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GSP Basics
Simply stated: The GPS satellites are nothing more than a set of wireless base stations in
the sky
The satellites simultaneously broadcast beacon messages (called navigation messages)
A GPS receiver measures time of arrival to the satellites, and then uses “trilateration” to determine its position
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GPS Basics: Triangulation
Measurement:
Computes distance
c
pptt SR 11
)( 11
SR ttcpp
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GPS Basics: Triangulation
In reality, receiver clockis not sync’d with satellites
Thus need to estimate clock
driftclockSR
c
dtt 11 )( 1
1 driftclockSR ttcpp
driftclockSR cttc )( 1
called pseudo range
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GPS with Clock Synchronization?
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GPS Design/Operation
Segments (components)user segment: users with receivers
control segment: control the satellites
space segment: • the constellation of satellites• transmission scheme
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Control Segment
Master Control Station is located at the Consolidated Space Operations Center (CSOC) at Flacon Air Force Station nearColorado Springs
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CSOC
Track the satellites for orbit and clock determination
Time synchronization
Upload the Navigation Message
Manage Denial Of Availability (DOA)
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Space Segment: Constellation
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Space Segment: Constellation
System consists of 24 satellites in the operational mode: 21 in use and 3 spares
3 other satellites are used for testing Altitude: 20,200 Km with periods of 12 hr. Current Satellites: Block IIR- $25,000,000
2000 KG Hydrogen maser atomic clocks
these clocks lose one second every 2,739,000 million years
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GPS Orbits
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GPS Satellite Transmission Scheme: Navigation Message
To compute position one must know the positions of the satellites
Navigation message consists of: - satellite status to allow calculating pos - clock info
Navigation Message at 50 bps each frame is 1500 bits Q: how long for each message?
More detail: see http://home.tiscali.nl/~samsvl/nav2eu.htm
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GPS Satellite Transmission Scheme: Requirements
All 24 GPS satellites transmit Navigation Messages on the same frequencies
Resistant to jamming
Resistant to spoofing
Allows military control of access (selected availability)
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GPS As a Communication Infrastructure
All 24 GPS satellites transmit on the same frequencies BUT use different codes i.e., Direct Sequence Spread Spectrum
(DSSS), and Code Division Multiple Access (CDMA) Using BPSK to encode bits
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Basic Scheme
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GPS Control
Controlling precision Lower chipping rate, lower precision
Control access/anti-spoofing Control chipping sequence
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GPS Chipping Seq. and Codes
Two types of codes C/A Code - Coarse/Acquisition Code
available for civilian use on L1• Chipping rate: 1.023 M• 1023 bits pseudorandom numbers (PRN)
P Code - Precise Code on L1 and L2 used by the military
• Chipping rate: 10.23 M• PRN code is 6.1871 × 1012 (repeat about one
week)• P code is encrypted called P(Y) codehttp://www.navcen.uscg.gov/gps/geninfo/IS-GPS-200D.pdf
http://www.gmat.unsw.edu.au/snap/gps/gps_survey/chap3/chap3.htm
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GPS PHY and MAC Layers
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Typical GPS Receiver: C/A code on L1
During the “acquisition” time you are receiving the navigation message also on L1
The receiver then reads the timing information and computes “pseudo-ranges”
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Military Receiver
Decodes both L1 and L2 L2 is more precise L1 and L2
difference allows computing ionospheric delay
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Denial of Accuracy (DOA)
The US military uses two approaches to prohibit use of the full resolution of the system
Selective availability (SA) noise is added to the clock signal and the navigation message has “lies” in it SA is turned off permanently in 2000
Anti-Spoofing (AS) - P-code is encrypted
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Extensions to GPS Differential GPS
ground stations with known positions calculate positions using GPS
the difference (fix) transmitted using FM radio used to improve accuracy
Assisted GPS put a server on the ground to help a GPS receiver reduces GPS search time from minutes to seconds E.g., iPhone GPS:
http://www.broadcom.com/products/GPS/GPS-Silicon-Solutions/BCM4750
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GPS: Summary
GPS is among the “simplest” localization technique (in terms topology): one-step trilateration
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GPS Limitations
Hardware requirements vs. small devices
GPS can be jammed by sophisticated adversaries
Obstructions to GPS satellites common• each node needs LOS to 4 satellites • GPS satellites not necessarily overhead, e.g., urban
canyon, indoors, and underground
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Percentage of localizable nodes localized by Trilateration.
Uniformly random 250 node network.
Limitation of TrilaterationR
atio
Average Degree