Zack Lane ReCAP Coordinator August 5, 2011 ReCAP Columbia University.
Admin. Recap: Routing - Zoo | Yale...
Transcript of Admin. Recap: Routing - Zoo | Yale...
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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
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 B R
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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”
Key Issue in Opportunistic Routing
10 Key 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 order ❍ each 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
ExOR: Example
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N0
N3
N1
N2
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 nodes ❍ the 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
0 0 200 400 600 800
Cum
ulat
ive
Frac
tion
of N
ode
Pai
rs
ExOR Traditional
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OR uses links in parallel
Traditional Routing 3 forwarders
4 links
ExOR 7 forwarders
18 links
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OR moves packets farther
❒ ExOR average: 422 meters/transmission ❒ Traditional Routing average: 205 meters/tx
Frac
tion
of T
rans
mis
sion
s
0
0.1
0.2
0.6 ExOR Traditional 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
MORE: MAC-independent Opportunistic 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 '
Basic Idea: Source
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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 ε∏−=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
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 εε∑ ∏−=
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 εε∑ ∏−=
)1(d closer to jk
k
jLjz ε∏−=
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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
S
R1
R2
D
10-3 BER
10-3 BER
Motivation
0%
0%
570 bytes; 1 bit in 1000 incorrect à Packet loss of 99%
S
R1
R2
D
99% (10-3 BER)
99% (10-3 BER)
Implication
0%
0%
Opportunis?c Rou?ng à 50 transmissions
Loss
Loss
ExOR MORE
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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]
New API
PHY + LL
Deliver correct symbols to higher layer
Network Forward correct symbols to destination
What Should Each Router Forward?
R1
R2
D S P1 P2
P1 P2
P1 P2
What Should Each Router Forward?
R1
R2
D S P1 P2
1) Forward everything à Inefficient 2) Coordinate à Unscalable
P1 P2
P1 P2
P1 P2
P1 P2
Forward random combinations of correct symbols
R1
R2
D S P1 P2
Symbol Level Network Coding
P1 P2
P1 P2
1s
…
… R1
R2
D
2s2
1
7s2s+
2
7
…
1s
…
…
2s
Routers create random combinations of correct symbols
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1
9s5s+
5
9
…
Symbol Level Network Coding
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R1
R2
D 2
1
7s2s+
…
2
1
9s5s+
…
21 s,sSolve 2
equa?ons
Destination decodes by solving linear equations
Symbol Level Network Coding
1s
…
… R1
R2
D
2s2
1
7s2s+
2
7
…
1s
…
…
2s
Routers create random combinations of correct symbols
15s5
0
…
Symbol Level Network Coding
R1
R2
D 2
1
7s2s+
…
15s …
21 s,sSolve 2
equa?ons
Destination decodes by solving linear equations
Symbol Level Network Coding Destination needs to know which combinations it received
Use run length encoding 5
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Original Packets Coded Packet
5
9
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Original Packets Coded Packet
Use run length encoding
Destination needs to know which combinations it received
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Original Packets Coded Packet
Destination needs to know which combinations it received
Use run length encoding
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5
Original Packets Coded Packet
Destination needs to know which combinations it received
Use run length encoding
Destination needs to know which combinations it received
Use run length encoding
Symbol-level Network Coding
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Original Packets Coded Packet
R1
Forward random combinations of correct symbols
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9
Original Packets Coded Packet
Symbol-level Network Coding
R1
Forward random combinations of correct symbols
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5
Original Packets Coded Packet
Symbol-level Network Coding
R1
Forward random combinations of correct symbols
0
5
Original Packets Coded Packet
Symbol-level Network Coding
R1
Forward random combinations of correct symbols
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Evaluation
• Implementa9on on GNURadio SDR and USRP • Zigbee (IEEE 802.15.4) link layer • 25 node indoor testbed, random flows • Compared to:
1. Shortest path rou9ng based on ETX 2. MORE: Packet-‐level opportunis9c rou9ng
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0.2
0.4
0.6
0.8
1
0 20 40 60 80 100 Throughput (Kbps)
CD
F
Throughput Comparison
2.1x
3x
Shortest Path MORE MIXIT
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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 B R
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.
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 good performance
Cricket
iPhone 4 GPS (iFixit)
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 the Secretary of Defense at 00:01 hours on July 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 cpp
tt SR 11 −+=
)( 11
SR ttcpp −=−
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GPS Basics: Triangulation
❒ In reality, receiver clock is not sync’d with satellites
❒ Thus need to estimate clock
driftclockSR
cdtt −++= δ11 )( 1
1 driftclockSR ttcpp −−−=− δ
driftclockSR cttc −−−= δ)( 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 near Colorado 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) code
http://www.navcen.uscg.gov/gps/geninfo/IS-GPS-200D.pdf
http://www.gmat.unsw.edu.au/snap/gps/gps_survey/chap3/chap3.htm 88
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”
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 Trilateration
Rat
io
Average Degree