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Network Layer: Non-Traditional Wireless Routing Localization Intro Y. Richard Yang 12/4/2012
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2 Outline r Admin. and recap r Network layer m Intro m Location/service discovery m Routing Traditional routing Non-traditional routing r Localization m Intro
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Admin. r Projects m please use Sign Up on classesv2 for project meetings m project code/<6-page report due Dec. 12 m final presentation date? m First finish a basic version, and then stress/extend your design 3
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4 Recap: Routing r So far, all routing protocols are in the framework of traditional wireline routing m a graph representation of underlying network point-to-point graph, edges with costs m select a best (lowest-cost) route for a src-dst pair
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5 Traditional Routing r Q: which route?
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6 Inefficiency of Traditional Routing r In traditional routing, packets received off the chosen path are useless r Q: what is the probability that at least one of the intermediate nodes will receive from src?
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7 Inefficiency of Traditional Routing r In traditional routing, packets received off the chosen path are useless
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8 Motivating Scenario r Src A sends packet 1 to dst B; src B sends packet 3 to dst A r Traditional routing needs to transmit 4 packets r Motivating question: can we do better, i.e., serve multiple src-dst pairs? ABR
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9 Outline r Admin. and recap r Network layer m Intro m Location/service discovery m 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 10 Key Issue: opportunistic forwarding may lead to duplicates.
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11 Extreme Opportunistic Routing (ExOR) [2005] r Basic idea: avoid duplicates by scheduling r 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 m a background process collects ETX information via periodic link-state flooding r Forwarders are prioritized by ETX-like metric to the destination
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12 ExOR: Forwarding r Group packets into batches r The highest priority forwarder transmits when the batch ends r The remaining forwarders transmit in prioritized order m each forwarder forwards packets it receives yet not received by higher priority forwarders m status collected by batch map
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13 Batch Map r 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 14 N0 N3 N1 N2
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ExOR: Stopping Rule r 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 m the remaining packets transferred with traditional routing 15
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16 Evaluations r 65 Node pairs r 1.0MByte file transfer r 1 Mbit/s 802.11 bit rate r 1 KByte packets r EXOR bacth size 100 1 kilometer
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17 Evaluation: 2x Overall Improvement r 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 0200400600800 Cumulative Fraction of Node Pairs ExOR Traditional
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18 OR uses links in parallel Traditional Routing 3 forwarders 4 links ExOR 7 forwarders 18 links
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19 OR moves packets farther r ExOR average: 422 meters/transmission r Traditional Routing average: 205 meters/tx Fraction of Transmissions 0 0.1 0.2 0.6 ExOR Traditional Routing 01002003004005006007008009001000 Distance (meters) 25% of ExOR transmissions 58% of Traditional Routing transmissions
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20 Comments: ExOR r Pros m takes advantage of link diversity (the probabilistic reception) to increase the throughput m does not require changes in the MAC layer m can cope well with unreliable wireless medium r Cons m scheduling is hard to scale in large networks m overhead in packet header (batch info) m batches increase delay
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21 Outline r Admin. and recap r Network layer m Intro m Location/service discovery m Routing Traditional routing Non-traditional routing –Motivation –Opportunistic routing: “parallel computing for one src- dst pair” »ExOR »MORE
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MORE: MAC-independent Opportunistic Routing & Encoding [2007] r Basic idea: m Replace node coordination with network coding m Trading structured scheduler for random packets combination 22
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Basic Idea: Source r Chooses a list of forwarders (e.g., using ETX) r Breaks up file into K packets (p1, p2, …, pK) r Generate random packets r MORE header includes the code vector [c j1, c j2, …c jK ] for coded packet p j ’ 23
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Basic Idea: Source 24
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Basic Idea: Forwarder r Check if in the list of forwarders r Check if linearly independent of new packet with existing packet r Re-coding and forward 25
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Basic Idea: Destination r Decode r Send ACK back to src if success 26
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Key Practical Question: How many packets does a forwarder send? r Compute zi: the expected number of times that forwarder i should forward each packet 27
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Computes z s 28 Compute z s 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 z j for forwarder j r Only need to forward packets that are m received by j m sent by forwarders who are further from destination m not received by any forwarder who is closer to destination r #such pkts: 29
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Compute z j for forwarder j r To guarantee at least one forwarder closer to d receives the packet 30
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Evaluations r 20 nodes distributed in a indoor building r Path between nodes are 1 ~ 5 hops in length r Loss rate is 0% ~ 60%; average 27% 31
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Throughput 32
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Improve on MORE? 33
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Mesh Networks API So Far NetworkForward correct packets to destination PHY/LLDeliver correct packets
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S R1 R2 D 10 -3 BER Motivation 0% 570 bytes; 1 bit in 1000 incorrect Packet loss of 99%
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S R1 R2 D 99% (10 -3 BER) Implication 0% Opportunistic Routing 50 transmissions Loss ExOR MORE
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37 Outline r Admin. and recap r Network layer m Intro m Location/service discovery m 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 NetworkForward correct symbols to destination
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What Should Each Router Forward? R1 R2 D S P1 P2 P1 P2 P1 P2
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What Should Each Router Forward? R1 R2 D S P1 P2 1)Forward everything Inefficient 2)Coordinate Unscalable P1 P2 P1 P2 P1 P2 P1 P2
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Forward random combinations of correct symbols R1 R2 D S P1 P2 Symbol Level Network Coding P1 P2 P1 P2
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… … R1 R2 D … … … Routers create random combinations of correct symbols … Symbol Level Network Coding
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R1 R2 D … … Solve 2 equations Destination decodes by solving linear equations Symbol Level Network Coding
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… … R1 R2 D … … … Routers create random combinations of correct symbols … Symbol Level Network Coding
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R1 R2 D … … Solve 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 encoding Original Packets Coded Packet
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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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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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Symbol-level Network Coding Original Packets Coded Packet R1 Forward random combinations of correct symbols
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Original Packets Coded Packet Symbol-level Network Coding R1 Forward random combinations of correct symbols
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Original Packets Coded Packet Symbol-level Network Coding R1 Forward random combinations of correct symbols
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Original Packets Coded Packet Symbol-level Network Coding R1 Forward random combinations of correct symbols
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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 ETX 2.MORE: Packet-level opportunistic routing
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Throughput (Kbps) CDF Throughput Comparison 2.1x 3x Shortest Path MORE MIXIT
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57 Outline r Admin. and recap r Network layer m Intro m Location/service discovery m 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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58 Motivating Scenario r A sends pkt 1 to dst B r B sends pkt 3 to dst A ABR
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Opportunistic Coding: Basic Idea r Each node looks at the packets available in its buffer, and those its neighbors’ buffers r It selects a set of packets, computes the XOR of the selected packets, and broadcasts the XOR 59
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60 Opportunistic Coding: Example
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61 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 r Admin. r Network layer r Localization m overview 62
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63 Motivations r The ancient question: Where am I? r Localization is the process of determining the positions of the network nodes r This is as fundamental a primitive as the ability to communicate
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64 Localization: Many Applications r Location aware information services m 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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65 Measurements The Localization Process Localizability (opt) Location Computation Location Based Applications
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66 Classification of Localization based on Measurement Modality r Coarse-grained measurements, e.g., m 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 m Connectivity r Advantages m low cost; measurements do not need line-of-sight r Disadvantages m low precision For a detailed study, see “Accuracy Characterization for Metropolitan-scale Wi-Fi Localization,” in Mobisys 2005.
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67 Classification of Localization based on Measurement Modality (cont’) r Fine-grained localization m distance m angle (esp. with MIMO) r Advantages m high precision r Disadvantages m measurements need line-of-sight for good performance Cricket iPhone 4 GPS (iFixit)
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Outline r Admin. r Localization m Overview m GPS 68
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69 Global Position Systems r US Department of Defense: need for very precise navigation r In 1973, the US Air Force proposed a new system for navigation using satellites r 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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70 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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71 NAVSTAR GPS Goals r What time is it? r What is my position (including attitude)? r What is my velocity? r 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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72 GSP Basics Simply stated: The GPS satellites are nothing more than a set of wireless base stations in the sky r The satellites simultaneously broadcast beacon messages (called navigation messages) r A GPS receiver measures time of arrival to the satellites, and then uses “trilateration” to determine its position
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73 GPS Basics: Triangulation r Measurement: Computes distance
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74 GPS Basics: Triangulation r In reality, receiver clock is not sync’d with satellites r Thus need to estimate clock called pseudo range
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75 GPS with Clock Synchronization?
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76 GPS Design/Operation r Segments (components) m user segment: users with receivers m control segment: control the satellites m space segment: the constellation of satellites transmission scheme
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77 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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78 CSOC r Track the satellites for orbit and clock determination r Time synchronization r Upload the Navigation Message r Manage Denial Of Availability (DOA)
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79 Space Segment: Constellation
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80 Space Segment: Constellation r System consists of 24 satellites in the operational mode: 21 in use and 3 spares 3 other satellites are used for testing r Altitude: 20,200 Km with periods of 12 hr. r Current Satellites: Block IIR- $25,000,000 2000 KG r Hydrogen maser atomic clocks m these clocks lose one second every 2,739,000 million years
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81 GPS Orbits
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82 GPS Satellite Transmission Scheme: Navigation Message r To compute position one must know the positions of the satellites r Navigation message consists of: - satellite status to allow calculating pos - clock info r Navigation Message at 50 bps m each frame is 1500 bits m Q: how long for each message? More detail: see http://home.tiscali.nl/~samsvl/nav2eu.htm
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83 GPS Satellite Transmission Scheme: Requirements r All 24 GPS satellites transmit Navigation Messages on the same frequencies r Resistant to jamming r Resistant to spoofing r Allows military control of access (selected availability)
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84 GPS As a Communication Infrastructure r All 24 GPS satellites transmit on the same frequencies BUT use different codes m i.e., Direct Sequence Spread Spectrum (DSSS), and m Code Division Multiple Access (CDMA) m Using BPSK to encode bits
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85 Basic Scheme
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86 GPS Control r Controlling precision m Lower chipping rate, lower precision r Control access/anti-spoofing m Control chipping sequence
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87 GPS Chipping Seq. and Codes r Two types of codes m C/A Code - Coarse/Acquisition Code available for civilian use on L1 Chipping rate: 1.023 M 1023 bits pseudorandom numbers (PRN) m P Code - Precise Code on L1 and L2 used by the military Chipping rate: 10.23 M PRN code is 6.1871 × 10 12 (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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88 GPS PHY and MAC Layers
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89 Typical GPS Receiver: C/A code on L1 r During the “acquisition” time you are receiving the navigation message also on L1 r The receiver then reads the timing information and computes “pseudo-ranges”
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Military Receiver r Decodes both L1 and L2 m L2 is more precise m L1 and L2 difference allows computing ionospheric delay 90
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91 Denial of Accuracy (DOA) r The US military uses two approaches to prohibit use of the full resolution of the system r Selective availability (SA) m noise is added to the clock signal and m the navigation message has “lies” in it m SA is turned off permanently in 2000 r Anti-Spoofing (AS) - P-code is encrypted
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92 Extensions to GPS r Differential GPS m ground stations with known positions calculate positions using GPS m the difference (fix) transmitted using FM radio m used to improve accuracy r Assisted GPS m put a server on the ground to help a GPS receiver m reduces GPS search time from minutes to seconds m E.g., iPhone GPS: http://www.broadcom.com/products/GPS/GPS- Silicon-Solutions/BCM4750http://www.broadcom.com/products/GPS/GPS- Silicon-Solutions/BCM4750
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93 GPS: Summary r GPS is among the “simplest” localization technique (in terms topology): one-step trilateration
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94 GPS Limitations r Hardware requirements vs. small devices r GPS can be jammed by sophisticated adversaries r 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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95 Percentage of localizable nodes localized by Trilateration. Uniformly random 250 node network. Limitation of Trilateration Ratio Average Degree
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