network layer: non-traditional wireless routing...

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


–  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





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∏−=

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

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

Opportunis?c Rou?ng à 50 transmissions

Loss

Loss

ExOR MORE

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Outline





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

2

1

9s5s+

5

9

…


R1

R2

D 2

1

7s2s+

…

2

1

9s5s+

…

21 s,sSolve 2

equa?ons

Destination decodes by solving linear equations


1s

…

… R1

R2

D

2s2

1

7s2s+

2

7

…

1s

…

…

2s

Routers create random combinations of correct symbols

15s5

0

…


R1

R2

D 2

1

7s2s+

…

15s …

21 s,sSolve 2

equa?ons

Destination decodes by solving linear equations


Destination needs to know which combinations it received

Use run length encoding 5

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Original Packets Coded Packet

5

9

0

9


Use run length encoding


9

5




0

5




Symbol-level Network Coding

5

9


R1


0

9



R1


9

5



R1


0

5



R1


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

0

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





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

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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”

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 R

atio

Average Degree

network layer: non-traditional wireless routing...

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