an experimental mobile ad hoc networking testbed

CMU/GM Collaborative Research Lab

An Experimental Mobile Ad Hoc Networking Testbed

Project Kick-off MeetingMarch 1, 2004


Mobile Network Connections

Internet

Connect via 3G

Ad hoc relaying

Connect via Hotspot

3G coverage

Hot spot coverage

Car range


Peer-to-Peer Networking

• Exchange of emergency/traffic information• Exchange of diagnostic information• Active safety applications• Allow one vehicle to function as a network portal for

nearby vehicles• Vehicle as sensor


IETF Draft Protocols• On Demand Protocols

– Pro: minimize network overhead since routes are refreshed only when needed

– Con: excess latency when invoking seldom-used routes– IETF Drafts:

• Dynamic Source Routing (DSR)• Ad Hoc On Demand Distance Vector Routing (AODV)

• Proactive Protocols– Pro: minimize latency since routes are fresh– Con: excess network overhead to update routes even if not used– IETF Drafts:

• Optimized Link State Routing Protocol (OLSRP)• Topology Dissemination Based on Reversed-Path Forwarding (TBRPF)


Specific Requirements for Telematics Applications

• Epidemic Flood-Fill protocols with hop limits– Perhaps more appropriate than protocols used with specific

destinations in mind• May not want to propagate to near-by but

distinct roads/highways (e.g., highway crossings without interconnects, etc.)

• Proprietary Solutions– MeshNetworks?

• Implementations of IETF protocols are almost all in UNIX (BSD, Linux, etc.)


Proposed Ad Hoc Testbed

V

GPS

Internet

1XRTT

MN

Site Office

DGPS reference station beacons

Network can operate wherever DGPS beacons and 1XRTT are available

http://ghoul.flipcode.com/3dm/s-car01/s-car-03.jpg






Network Components• Mobile Node

– 5.8 GHz 802.11a (Represents DSRC)– 1XRTT Cellular/PCS 3G data– Ad Hoc Protocol (DSR?)– Differential GPS

• Site Office– Bird’s eye view of test track (tests not limited to track,

however)– Visualizer & Analysis tools


Vizualizer Example


Video


Example Measured & Modeled Signal Strength

-120

-100

-80

-60

-40

0 100 200 300 400 500 600

sign

al s

tren

gth

(dBW

)

Time (s)(Data from Prior Ad Hoc Network supported by Caterpillar)


Example Dropped Packet Performance

(Data from Prior Ad Hoc Network supported by Caterpillar)


Research Objectives: Physical & Link Layers

a. Collect extensive peer-to-peer channel RSSI data and extract path loss exponents for classes of environments (e.g., Urban, suburban, rural, etc.).

b. Investigate the expected range, reliability, throughput of 802.11a/DSRC in this mobile environment

c. Implement the capability of real-time power control for sparse/dense traffic, and evaluate performance

d. Management of channels, e.g., control & datae. Collaborate with HRL to integrate findings with their

simulations


Improved Channel Measurement Options:Sliding Correlator Method

• N=code sequence length• Rc=transmit chip rate

• Rc-d = receive chip rate

• Time resolution ~1/Rc

• E.g., Rc=12.5 Mbps, gives resolution ~ 80 ns

• Gives measurement of RMS delay spread

time

N/d

time

N/d Devasirvatham ‘86


Sliding Correlator Implementation Possibilities

• Without pilot locking: phase drift is 90 deg/s

• Should also permit analysis of Doppler

Bandpassfilter

Low noise amplifier

Local oscillator

Agilent 89610A vector signal analyzer

Matlab post-processing

Agilent E4433B digital signal generator

Bandpassfilter

Low noise amplifier

Local oscillator



Agilent E4433B digital signal generator BPSK + CW pilot


Multi-carrier Probing

Bandpassfilter

Low noise amplifier

Local oscillator




Bandpassfilter

Low noise amplifier

Local oscillator




MCM


Research Objectives: Network & Higher Layers

a. Evaluate the performance of leading ad hoc protocols for the automotive/ITS application environment

b. Develop suite of protocols for active safety/telematics applications

c. Define latency requirements d. Explore multi-hop relaying, and attempt to determine the

limiting factors to the range (i.e., number of hops)e. Identify and implement “hooks” throughout the stack that

will facilitate delivery of the required QoSf. Collaborate with HRL to integrate findings with their

simulations


GM Contributions• Application concepts• Antenna and mounting issues• System and vehicle integration architecture• Standards activities• Vehicles


TimelinePhase I Tasks Q1-04 Q2-04 Q3-04 Q4-04 Q1-05 Q2-05 Q3-05 Q4-051. Construction a. Site selection b.Protocol select c. Vehicle acq. d. MN integ. e. MN install f. SO integ. g. SO install h. Visualizer i. System integ. 2. Layer 1,2 Res. a. Chan. Model b. Ch. Mod. Opt c. 802.11a perf. d. Power control 3. Layer 3-6 Res. a.Platform select b. Protocol Eval c. Protocol Suite d. Latency Req. e. Hop limits f. Hooks in stack 4. MANET stds 5. HRL collab.


Summary• Ad hoc network using 5-6 vehicles to be constructed• Network capable of operation anywhere DGPS

beacons are available (also 1XRTT for site office connectivity)

• Develop 5-6 GHz peer-peer propagation model• Develop suite of protocols optimized for

telematics/active safety applications• Collect real data on network operation to use in

validating simulations• Timeline: construct in ~ 9 mo; operate for 15+ mo

an experimental mobile ad hoc networking testbed

Documents