1. Network Layer: Non-Traditional Wireless Routing Localization Intro
Y. Richard Yang
12/4/2012

2. Outline Admin. and recap Network layer Localization Intro
Location/service discovery
Routing
Traditional routing
Non-traditional routing
Localization

3. Admin. Projects please use Sign Up on classesv2 for project meetings
final presentation date?
First finish a basic version, and then stress/extend your design

4. 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
Problems: don’t fully exploit path (spatial) diversity and wireless broadcast opportunities
commit to a specific route before forwarding
each node forwards a received packet as it is to next hop

5. Traditional Routing
Q: which route?

6. Inefficiency of Traditional Routing
Motivating question: can we take advantage of transmissions that reach unexpectedly far or unexpectedly short?
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?

7. Inefficiency of Traditional Routing
Motivating question: can we take advantage of transmissions that reach unexpectedly far or unexpectedly short?
In traditional routing, packets received off the chosen path are useless

8. 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 R B

9. 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”

10. Key Issue in Opportunistic Routing
Key Issue: opportunistic forwarding may lead to duplicates.

11. 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

12. 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

13. Batch Map
Batch map indicates, for each packet in a batch, the highest-priority node known to have received a copy of that packet

14. ExOR: Example N2 N0 N3 N1

15. 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

16. Evaluations 65 Node pairs 1.0MByte file transfer
1 Mbit/s bit rate
1 KByte packets
EXOR bacth size 100
1 kilometer

17. Evaluation: 2x Overall Improvement
1.0
0.8
0.6
Cumulative Fraction of Node Pairs
0.4
0.2
ExOR
Traditional
spend a little more time on the 240 x say this is just for the median, and it’s a factor of 2!
200
400
600
800
Throughput (Kbits/sec)
Median throughputs: Kbits/sec for ExOR,
121 Kbits/sec for Traditional

18. OR uses links in parallel
possible question – why are there only 7 forwarders.(just say we thin out...)
ExOR
7 forwarders
18 links
Traditional Routing
3 forwarders
4 links

19. OR moves packets farther
58% of Traditional Routing transmissions
0.6
ExOR
Traditional Routing
Fraction of Transmissions
0.2
25% of ExOR transmissions
0.1
lower is better. right circle – using lots of longer links, sum them up and it’s 25%. so, like ex 1, using lots of long links. zeros: before many packets made no progress, with exor at least some.
100
200
300
400
500
600
700
800
900
1000
Distance (meters)
ExOR average: 422 meters/transmission
Traditional Routing average: 205 meters/tx

20. Comments: ExOR Pros Cons
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

21. 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

22. MORE: MAC-independent Opportunistic Routing & Encoding [2007]
Basic idea:
Replace node coordination with network coding
Trading structured scheduler for random packets combination

23. 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’

24. Basic Idea: Forwarder Check if in the list of forwarders
Check if linearly independent of new packet with existing packet
Re-coding and forward

25. Basic Idea: Destination
Decode
Send ACK back to src if success

26. Key Practical Question: How many packets does a forwarder send?
Compute zi: the expected number of times that forwarder i should forward each packet

27. Computes zs
Єij: loss probability of the link between i and j
Compute zs so that at least one forwarder that is closer to destination is expected to have received the packet :

28. 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:

29. Compute zj for forwarder j
To guarantee at least one forwarder closer to d receives the packet

30. Evaluations 20 nodes distributed in a indoor building
Path between nodes are 1 ~ 5 hops in length
Loss rate is 0% ~ 60%; average 27%

31. Throughput

32. Improve on MORE?

33. Mesh Networks API So Far
Forward correct packets to destination
PHY/LL
Deliver correct packets

34. 570 bytes; 1 bit in 1000 incorrect
Motivation R1
10-3 BER 0% S D 0%
10-3 BER R2
570 bytes; 1 bit in 1000 incorrect
 Packet loss of 99%

35. Opportunistic Routing  50 transmissions
Implication R1
99% (10-3 BER)
ExOR
MORE
Loss 0% S D
Loss 0%
99% (10-3 BER) R2
Opportunistic Routing  50 transmissions

36. 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]

37. New API PHY + LL Deliver correct symbols to higher layer Network
Forward correct symbols to destination

38. What Should Each Router Forward?P1 P1 P2 R2 P2 P1 P2

39. What Should Each Router Forward?P1 P2 P1 P1 P2 R2 P2 P1 P2 P1 P2
Forward everything  Inefficient
Coordinate  Unscalable

40. Symbol Level Network CodingP1 P2 P1 R2 P2 P1 P2
Forward random combinations of correct symbols

41. Symbol Level Network Coding… … D R2 … …
Routers create random combinations of correct symbols

42. Symbol Level Network Coding… D R2 …
Solve 2
equations
Destination decodes by solving linear equations

43. Symbol Level Network Coding… … D R2 … …
Routers create random combinations of correct symbols

44. Symbol Level Network Coding… D R2 …
Solve 2
equations
Destination decodes by solving linear equations

45. Destination needs to know which combinations it received
Use run length encoding
Original Packets
Coded Packet

46. Destination needs to know which combinations it received
Use run length encoding
Original Packets
Coded Packet

47. Destination needs to know which combinations it received
Use run length encoding
Original Packets
Coded Packet

48. Destination needs to know which combinations it received
Use run length encoding
Original Packets
Coded Packet

49. Destination needs to know which combinations it received
Use run length encoding

50. Evaluation Implementation on GNURadio SDR and USRP
Zigbee (IEEE ) link layer
25 node indoor testbed, random flows
Compared to:
Shortest path routing based on ETX
MORE: Packet-level opportunistic routing

51. Throughput Comparison
CDF
2.1x
MIXIT 3x
MORE
Shortest Path
Throughput (Kbps)

52. 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”

53. Motivating Scenario A sends pkt 1 to dst B B sends pkt 3 to dst A A B

54. 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

55. Opportunistic Coding: Example

56. 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.

57. Outline
Admin.
Network layer
Localization
overview

58. 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

59. 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]

60. The Localization Process
Location Based Applications
Location Computation
Localizability (opt)
Measurements

61. 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 ( 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.

62. 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)

63. Outline
Admin.
Localization
Overview
GPS

64. 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

65. 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

66. 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)?

67. 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

68. GPS Basics: Triangulation
Measurement:
Computes distance

69. GPS Basics: Triangulation
In reality, receiver clock is not sync’d with satellites
Thus need to estimate clock
called pseudo range

70. GPS with Clock Synchronization?

71. GPS Design/Operation Segments (components)
user segment: users with receivers
control segment: control the satellites
space segment:
the constellation of satellites
transmission scheme

72. Control Segment Master Control Station is located at the
Consolidated Space Operations Center
(CSOC) at Flacon Air Force Station near
Colorado Springs

73. CSOC Track the satellites for orbit and clock determination
Time synchronization
Upload the Navigation Message
Manage Denial Of Availability (DOA)

74. Space Segment: Constellation

75. 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, KG
Hydrogen maser atomic clocks
these clocks lose one second every 2,739,000 million years

76. GPS Orbits

77. 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

78. 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)

79. 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

80. Basic Scheme

81. GPS Control Controlling precision Control access/anti-spoofing
Lower chipping rate, lower precision
Control access/anti-spoofing
Control chipping sequence

82. GPS Chipping Seq. and Codes
Two types of codes
C/A Code - Coarse/Acquisition Code available for civilian use on L1
Chipping rate: M
1023 bits pseudorandom numbers (PRN)
P Code - Precise Code on L1 and L2 used by the military
Chipping rate: M
PRN code is × 1012 (repeat about one week)
P code is encrypted called P(Y) code

83. GPS PHY and MAC Layers

84. 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”

85. Military Receiver Decodes both L1 and L2 L2 is more precise
L1 and L2 difference allows computing ionospheric delay

86. 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

87. Extensions to GPS Differential GPS Assisted 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:

88. GPS: Summary
GPS is among the “simplest” localization technique (in terms topology): one-step trilateration

89. 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

90. Limitation of Trilateration
Percentage of localizable nodes localized by Trilateration.
Ratio
Average Degree
Uniformly random 250 node network.

91. Backup Slides