Network Layer: Non-Traditional Wireless Routing Localization Intro

Transcription

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

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

3 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 3

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 4

5 Traditional Routing Q: which route? 5

6 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? 6

7 Inefficiency of Traditional Routing In traditional routing, packets received off the chosen path are useless 7

8 Motivating Scenario Src A sends packet 1 to dst B; src B sends packet 3 to dst A A R B Traditional routing needs to transmit 4 packets Motivating question: can we do better, i.e., serve multiple src-dst pairs? 8

9 Outline Admin. and recap Network layer Intro Location/service discovery Routing Traditional routing Non-traditional routing Motivation Opportunistic routing: parallel computing for one srcdst pair 9

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

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 11

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 12

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 13

14 ExOR: Example N2 N0 N3 N1 14

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 15

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

17 Evaluation: 2x Overall Improvement Cumulative Fraction of Node Pairs ExOR Traditional Throughput (Kbits/sec) Median throughputs: 240 Kbits/sec for ExOR, 121 Kbits/sec for Traditional 17

18 OR uses links in parallel Traditional Routing 3 forwarders 4 links ExOR 7 forwarders 18 links 18

19 OR moves packets farther 58% of Traditional Routing transmissions Fraction of Transmissions ExOR Traditional Routing Distance (meters) 25% of ExOR transmissions ExOR average: 422 meters/transmission Traditional Routing average: 205 meters/tx 19

20 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 20

21 Outline Admin. and recap Network layer Intro Location/service discovery Routing Traditional routing Non-traditional routing Motivation Opportunistic routing: parallel computing for one srcdst pair» ExOR» MORE 21

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

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 p ' j = c p ji i MORE header includes the code vector [c j1, c j2, c jk ] for coded packet p j 23

24 Basic Idea: Source 24

25 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

26 Basic Idea: Destination Decode Send ACK back to src if success 26

27 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

28 Єij: loss probability of the link between i and j Computes z s Compute z s so that at least one forwarder that is closer to destination is expected to have received the packet : zs = 1 (1 ε j sj ) 28

29 Compute z j 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: Lj = i isfurther [z i (1 ε ij ) k closer tod ε ik ] 29

30 Compute z j for forwarder j Lj = i isfurther [z i (1 ε ij ) k closer tod ε ik ] To guarantee at least one forwarder closer to d receives the packet z j = (1 k L j closer to d ε jk ) 30

31 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

32 Throughput 32

33 Improve on MORE? 33

34 Mesh Networks API So Far Network Forward correct packets to destination PHY/LL Deliver correct packets

35 Motivation 10-3 BER R1 S D 10-3 BER R2 570 bytes; 1 bit in 1000 incorrect à Packet loss of 99%

36 Opportunis?c Rou?ng à 50 transmissions Implication S 99% (10-3 BER) 99% (10-3 BER) ExOR MORE R1 Loss Loss R2 D

37 Outline Admin. and recap Network layer Intro Location/service discovery Routing Traditional routing Non-traditional routing Motivation Opportunistic routing: parallel computing for one srcdst pair» ExOR [2005]» MORE [2007]» MIXIT [2008] 37

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

39 What Should Each Router Forward? S P1 P2 R1 P1 P2 R2 P1 P2 D

40 What Should Each Router Forward? S P1 P2 R1 P1 P2 R2 P1 P2 D 1) Forward everything à Inefficient 2) Coordinate à Unscalable

41 Symbol Level Network Coding S P1 P2 R1 P1 P2 R2 P1 P2 D Forward random combinations of correct symbols

42 Symbol Level Network Coding R1 2s 1 + 7s s 1 s 2 R2 D 5s 1 + 9s s 1 s 2 Routers create random combinations of correct symbols

43 Symbol Level Network Coding R1 2s 1 + 7s 2 D 5s 1 + 9s 2 R2 Solve 2 equa?ons s1, s 2 Destination decodes by solving linear equations

44 Symbol Level Network Coding R1 2s 1 + 7s s 1 s 2 R2 D 5s 1 5 s 1 0 s 2 Routers create random combinations of correct symbols

45 Symbol Level Network Coding R1 2s 1 + 7s 2 D 5s 1 R2 Solve 2 equa?ons s1, s 2 Destination decodes by solving linear equations

46 Destination needs to know which combinations it received 5 Use run length encoding Original Packets Coded Packet

47 Destination needs to know which combinations it received Use run length encoding 0 9 Original Packets Coded Packet

48 Destination needs to know which combinations it received Use run length encoding 5 9 Original Packets Coded Packet

49 Destination needs to know which combinations it received Use run length encoding 5 0 Original Packets Coded Packet

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

51 Symbol-level Network Coding Forward random combinations of correct symbols R1 5 9 Original Packets Coded Packet

52 Symbol-level Network Coding Forward random combinations of correct symbols R1 0 9 Original Packets Coded Packet

53 Symbol-level Network Coding Forward random combinations of correct symbols R1 5 9 Original Packets Coded Packet

54 Symbol-level Network Coding Forward random combinations of correct symbols R1 5 0 Original Packets Coded Packet

55 Evaluation Implementa9on on GNURadio SDR and USRP Zigbee (IEEE ) link layer 25 node indoor testbed, random flows Compared to: 1. Shortest path rou9ng based on ETX 2. MORE: Packet- level opportunis9c rou9ng

56 Throughput Comparison CDF x 2.1x MIXIT MORE Shortest Path Throughput (Kbps)

57 Outline Admin. and recap Network layer Intro Location/service discovery Routing Traditional routing Non-traditional routing Motivation Opportunistic routing: parallel computing for one srcdst pair Opportunistic routing: parallel computing for multiple src-dst pairs 57

58 Motivating Scenario A sends pkt 1 to dst B B sends pkt 3 to dst A A R B 58

59 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 59

60 Opportunistic Coding: Example 60

61 Wireless Networking: Summary send receive info info/control status - 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. 61

62 Outline Admin. Network layer Localization overview 62

63 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 63

64 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] 64

65 The Localization Process Location Based Applications Location Computation Localizability (opt) Measurements 65

66 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 66 For a detailed study, see Accuracy Characterization for Metropolitan-scale Wi-Fi Localization, in Mobisys 2005.

67 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 67 iphone 4 GPS (ifixit)

68 Outline Admin. Localization Overview GPS 68

69 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 69

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,

71 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)? 71

72 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 72

73 GPS Basics: Triangulation Measurement: Computes distance t 1 S p = t + c p R 1 p p 1 = c( t R1 t S ) 73

74 GPS Basics: Triangulation In reality, receiver clock is not sync d with satellites Thus need to estimate clock t R1 d c S 1 = t + + δ clock drift p p = c( t t δ R1 S 1 clock drift R1 S = c( t t ) cδ clock drift ) called pseudo range 74

75 75 GPS with Clock Synchronization?

76 GPS Design/Operation Segments (components) user segment: users with receivers control segment: control the satellites space segment: the constellation of satellites transmission scheme 76

77 Control Segment Master Control Station is located at the Consolidated Space Operations Center (CSOC) at Flacon Air Force Station near Colorado Springs 77

78 CSOC Track the satellites for orbit and clock determination Time synchronization Upload the Navigation Message Manage Denial Of Availability (DOA) 78

79 Space Segment: Constellation 79

80 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 80

81 GPS Orbits 81

82 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 82

83 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) 83

84 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 84

85 Basic Scheme 85

86 GPS Control Controlling precision Lower chipping rate, lower precision Control access/anti-spoofing Control chipping sequence 86

87 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 (repeat about one week) P code is encrypted called P(Y) code

88 GPS PHY and MAC Layers 88

89 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 89

90 Military Receiver Decodes both L1 and L2 L2 is more precise L1 and L2 difference allows computing ionospheric delay 90

91 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 91

92 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: BCM

93 GPS: Summary GPS is among the simplest localization technique (in terms topology): one-step trilateration 93

94 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 94

95 Limitation of Trilateration Percentage of localizable nodes localized by Trilateration. Ratio Uniformly random 250 node network. Average Degree 95