network layer: non-traditional wireless routing localization intro y. richard yang 12/4/2012

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 BR

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Outline




– Motivation– Opportunistic routing: “parallel computing for one

src-dst pair”

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

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 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





src-dst pair”

» ExOR» MORE

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 '

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

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

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

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 Packet loss of 99%

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





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

DSP1P2

P1P2

P1P2

What Should Each Router Forward?

R1

R2

DSP1P2

1) Forward everything Inefficient2) Coordinate Unscalable

P1P2

P1P2

P1P2

P1P2

Forward random combinations of correct symbols

R1

R2

DSP1P2

Symbol Level Network Coding

P1P2

P1P2

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

…


R1

R2

D2

1

7s

2s

…

2

1

9s

5s

…

21 s,sSolve 2

equations

Destination decodes by solving linear equations


1s

…

…R1

R2

D

2s2

1

7s

2s

2

7

…

1s

…

…

2s

Routers create random combinations of correct symbols

15s

5

0

…


R1

R2

D2

1

7s

2s

…

15s …

21 s,sSolve 2

equations

Destination decodes by solving linear equations


Destination needs to know which combinations it received

Use run length encoding5

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Original Packets Coded Packet

5

9

0

9


Use run length encoding


9

5




0

5




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

Throughput (Kbps)

CD

FThroughput Comparison

2.1x3x

Shortest PathMOREMIXIT

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Outline





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

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 goodperformance

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 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”

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

network layer: non-traditional wireless routing localization intro y. richard yang 12/4/2012

Documents

traditional routing

r traditional routing

outline r

rate r

batches r

evaluations r

scheduling r

rule r