Non-Traditional Routing, Transport and Localization Y. Richard Yang 3/3/2009

2 Admin. r Project proposal: m March 6 by to and r Exam date?

Outline r Admin. r Opportunistic routing r Transport overview r Localization overview 3

Recap: Opportunistic Routing r Basic idea: m Take advantage of spatial diversity r Key issue m Avoid redundancy and interference r Techniques m ExOR: coordination m MORE: coordination -> random network coding 4

S R1 R2 D 99% (10 -3 BER) Problem of MORE 0% Opportunistic Routing  50 transmissions Loss

MIXIT: Revisiting Link/ Network API PHY + LLDeliver correct symbols to higher layer NetworkForward correct symbols to destination R1 R2 S P1 P2 P1 P2 P1 P2

Key Question: What Should Each Router Forward? R1 R2 D S P1 P2 P1 P2 P1 P2

Key Question: What Should Each Router Forward? R1 R2 D S P1 P2 Forward everything  Inefficient 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

… … R1 R2 D … … … Routers create random combinations of correct symbols … Symbol Level Network Coding

R1 R2 D … … Solve 2 equations Destination decodes by solving linear equations Symbol Level Network Coding

… … R1 R2 D … … … Routers create random combinations of correct symbols … Symbol Level Network Coding

R1 R2 D … … Solve 2 equations Destination decodes by solving linear equations Symbol Level Network Coding

Problem: Mixed Correct and Incorrect Symbols Original Packets

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

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

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

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

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

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

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

Outline r Admin. r Opportunistic routing r Transport overview 22

23 Transport Layer vs. Network Layer r Provide logical communication between app’ processes r Transport protocols run in end systems r Transport vs. network layer services: m network layer data transfer between end systems m transport layer data transfer between processes relies on, enhances, network layer services application transport network data link physical application transport network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical logical end-end transport

24 Transport Layer Services and Protocols r Transport services m multiplexing/demultiplexing m flow control m reliable data transfer m congestion/rate control r Transport protocols in the Internet m UDP m TCP

25 flow 2 (5 Mbps) flow 1 router 1 10 Mbps 5 Mbps 20 Mbps Key Challenge in Transport: Rate /Congestion Control Assume m flow 2 fixed at 5 Mbps m no retransmission m the link from router 1 to router 2 has finite buffer 5 Mbps 20 Mbps sending rate by flow 1 (Mbps) throughput of flows 1 & 2 (Mbps) r when packet dropped at the link from router 2 to router 5, the upstream transmission from router 1 to router 2 used for that packet was wasted! 0 router 3 router 4 router 2 router 5 router 6

26 TCP Reliability/Rate Control m End-to-end, sliding window-based reliability m Use the AIMD algorithm to adjust the sliding window size dynamically m after receiving an ACK for a packet, increase cwin by 1/cwin m if any loss, reduce cwin to half cwnd w

27 TCP/Reno: Cwin Time cwnd congestion avoidance Loss congestion avoidance Loss congestion avoidance Q: Is TCP rate control effective in wireless networks?

28 TCP/Reno Throughput as a Function of Loss Rate r Given mean packet loss rate p, mean round- trip time RTT, packet size S

29 Example r Assume a TCP flow with S = 1000 bits, RTT = 10 ms r Assume the link bandwidth is 11 Mbps r If there is only one flow, then the (congestion) loss rate to fully utilize the link r Assume a wireless network with packet (corruption) loss rate of 4%, m then the maximum achievable rate using TCP/Reno is 700 Kbps r If we increase RTT = 200 ms (satellite) m the rate is 35 Kbps

Discussion r Does TCP perform really that bad in wireless? 30 mobile host base station “wired“ Internet

31 Wireless Networking: Summary send receive status info info/control - The ability to communicate is a foundational support of wireless mobile networks - Unfortunately, the capacity of such networks using current techniques is limited - Much progress has been made, but still more are coming.

Outline r Admin. r Opportunistic routing r Transport overview r Localization m overview 32

33 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

34 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]

35 Measurements The Localization Process Localizability (opt) Location Computation Applications Using Location

36 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 ( at different locations match to the signature m connectivity r Usage m e.g., Microsoft “Locate Me” m Place lab: 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.

37 Classification of Localization based on Measurement Modality (cont’) r Fine-grained localization m distance m angle (esp. with MIMO) r Usage m GPS, sensor networks r Advantages m high precision r Disadvantages m measurements need line-of-sight for good performance Cricket

Outline r Admin. r Opportunistic routing r Transport overview r Localization m Overview m GPS 38

39 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

40 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

41 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?

42 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

43 GPS Basics: Triangulation r Measurement: Computes distance

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

45 Why Do I Need To See 4 Satellites?

46 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

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

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

49 Space Segment: Constellation

50 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, KG r Hydrogen maser atomic clocks m these clocks lose one second every 2,739,000 million years

51 GPS Orbits

52 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

53 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)

54 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

55 GPS PHY and MAC Layers

56 GPS Identifying Codes r Two types of codes m C/A Code - Coarse/Acquisition Code available for civilian use on L1 m P Code - Precise Code on L1 and L2 used by the military encrypted P code (called Y code) provides selected availability and anti-spoofing

57 GPS Receiver r Typical 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 the “pseudo- ranges”

58 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

59 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 receivers m reduces GPS search time from minutes to seconds

iPhone GPS r Hammerhead™ II 60

61 GPS: Summary r GPS is among the “simplest” localization technique (in terms topology): one-step trilateration r Russia has a system known as GLONASS r The EU is deploying GALLIOS

62 GPS Limitations r Hardware requirements vs. small devices r GPS 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

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

Backup Slides 64