matc fall lecture series: hamid sharif

UNIVERSITY OF NEBRASKA – LINCOLN COLLEGE OF ENGINEERING

Advanced Telecommunications Engineering Laboratory (TEL)

State of Wireless Communications in North American Freight Railroads

Hamid SharifComputer and Electronics Engineering Department


University of Nebraska – LincolnSeptember 28, 2012



Wireless in Railroads

• The Five-Year US Federal Railroad Administration (FRA) Strategic Plan for Railroad Research and Development

identifies mobile wireless communication as one of the most critical areas to collect, process, and disseminate information to improve the safety, security, and operational effectiveness of railroads. *

* From: The vision for the future of intelligent railroad systems



• Voice – Portions of the voice wireless infrastructure are

more than 30+ years old.• Data

– The Advanced Train Control System (ATCS) wireless data networks (developed in 80s) are only supporting at best 4800/9600 bps and not designed to support today’s multimedia and Internet type applications.

State of Wireless in Railroads



Project’s Objectives

• Study the suitable wireless technology for current and future of mobile railroads to support:

– high-speed data network for moving trains

– real-time Internet accessibility for trains’ crews, passengers, and ground crews

– improving railroad operating safety and effective operations



Industry Partners

• Federal Railroad Administration (FRA)• American Association of Railroad (AAR)• Freight Railroads of North America:

– Union Pacific Railroad– BNSF Railway– CSX Transportation– Norfolk Southern Railway– Canadian National Railway– Canadian Pacific Railway



Research MethodologyReal-World

Test Bed Experiments

Detailed Simulation

ModelsAnalytical

Models

• Build comprehensive simulation models to complement our theoretical study for wireless standard protocols.

• Testbed experiments to study and evaluate the implementation of these technologies for the railroad environments.



PHASE 1 - WIFI



Overview of WiFi Project Phase

• Feasibility of WiFi in mobile railroad environment

• Performance evaluations of WiFi throughput in mobile railroad scenarios

• Study of handoff and Quality of Service (QoS) in WiFi for mobile railroad applications

• Performance evaluations of multimedia applications over WiFi in railroad environments



• Investigation of the mobility impact on performance of the 802.11x system with fading under different client velocities

• Analysis of the impact of Doppler shift caused by the velocity of transmitter and receiver

• The multipath interference due to reflections and diffractions from terrain and objects in the radio coverage area and other serious impairment factors

• Study of the bit error rate performances for various velocities with different data rates

Theoretical Approach



Simulation Models

• 802.11x features designed and implemented:• PHY:

– Determines the impact of noise, fading and Doppler shift– Calculates effects of shadowing, Rician and Rayleigh

fading• MAC:

– Fragmentation and Defragmentation, Data Retransmission– Multirate support (fixed as well as rate adaptation)– Multiple channels, Channel scanning– Synchronization, Power management– Authentication, Association, Re-Association, Handoff



WiFi Test bed

• A 3.5 mile section of BNSF track at Crete Nebraska was chosen for it’s close proximity to the UNL, low traffic volumes, and challenging environment (heavy foliage, curves, surrounding hills).

• Test bed utilizes the 802.11 technology to support wireless connectivity between moving trains and fixed Access Points.

• Involved with the design of Testbed were: AAR, BNSF, UP, CSX and CN



BNSF WAN

Microwave Link

VPN into BNSF WAN

DSL Link

CC

Router/Gateway

BNSF Core Network

Router/Gateway

AP7 AP6 AP5 AP4 AP3 AP2

NC

NCNCNC CCCCCCCCNCNCNCNC CCCCCC

AP8Crete Depot

AP1Berks East

Internet

Microwave Microwave

Test Bed



Test Bed Area Map



• GPS with real-time mapping– GPS integrated into user interface– Retrieves current location in test bed from GPS device, displays location

of test client and all APs in test bed, calculates distances to all APs and records all information

• WifiPoll with real-time plotting– WifiPoll measures all Wifi adapter information, such as link speed and

status, signal strength, channel, current associated AP, throughput, etc.– Real-time plotting of these results allows real-time evaluation of testing

progress– Graphs include: Tput vs. Time, Tput vs. Distance, Tput histogram, RSSI

(signal strength) vs. Time, RSSI vs. Distance, RSSI histogram, AP association vs. Time

WifiTools Features



Developed test tools (WifiViz)



Antenna Field Pattern



Comparison of Test Bed Results and Simulation

12:21:01 12:23:54 12:26:47 12:29:39 12:32:32 12:35:25 12:38:18 12:41:110

1000

2000

3000

4000

5000

6000

7000

Comparison of Field Test Results and Simulation Results using GPS Log Information

Field Test 04/27/2006 Simulation using GPSLog

Time

Thro

ughp

ut (k

bps)



Throughput vs. Time

0

1

2

3

4

5

6

7

10:33:36 11:45:36 12:57:36 14:09:36 15:21:36

Time

Th

rou

gh

pu

t (M

bp

s)

Throughput

Velocity vs Time

0

10

20

30

40

50

60

70

10:33:36 11:45:36 12:57:36 14:09:36 15:21:36

Time

Vel

ocity

(mph

)

Velocity

Mobility test results



Throughput vs Distance Comparison - 802.11b 1 Mbps

0

100

200

300

400

500

600

700

800

900

1000

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Distance (meters)

Th

rou

gh

pu

t (k

bp

s)

NS-2

Qualnet

Theory

Field Cutoff

Throughput vs. Distance Comparisons



Summary of Findings• Benefits of WiFi:

– Operates in unlicensed frequency band, easily accessible for railroads– Good network throughput (about 6 Mbps in good channel)– Supports mobility (tested up to 70 mph)– Inexpensive and readily available equipment and setups– Supports real time multimedia applications

• Drawbacks of WiFi:– Communication Distance limited to only a mile (under excellent LOS conditions

only)– Limited number of channels in unlicensed band creates competition among all

WiFi networks in an area• Interference becomes a problem

– Contention-based multiuser access scheme creates problems for coexistence– No Quality-of-Service mechanism for multimedia applications– No standardized approach for interconnecting WiFi access points



PHASE 2 – MOBILE WIMAX



Mobile WiMAX - Overview

• Is designed to be a 4G network technology– All-IP network infrastructure, based on IEEE 802.16e

• 802.16e/802.16-2007 is air interface only

• Mobile WiMAX defines end-to-end system

– Supports large communication distances• Initial target distance for Mobile WiMAX was 30 miles

– Supports high throughput• 20 MHz channel provides up to 70 Mbps throughput

– Supports mobility• Mobile nodes are supported even at 120 mph

– Supports QoS and streaming applications• Mobile WiMAX has robust QoS for video and voice applications over wireless

channels



• UNL has 5 EBS licenses, centered around Omaha, Lincoln, Kearney (35 miles radius), among them:

Mobile WiMAX – RF Frequency Space

WCG671 – around Lincoln WHR724 – around Omaha



Mobile WiMAX Simulation Model

Results from Lab Testing and Computer Simulations



WiMAX Simulation Model ComparisonFeatures QualNet 4.0 OPNet NS-2 Models:

Taiwan Italy NIST TEL (our model)

Air Interface 802.16e 802.16e 802.16-2004 802.16d 802.16e 802.16-2009

Duplex TDD n/a TDD n/a TDD TDD

PHY Mode OFDMA OFDMA OFDMA n/a OFDM OFDM, OFDMA

ARQ, Hybrid-ARQ Y, N Y, N N, Y N, N N, N Y, Y

Multihop Backhaul n/a n/a N Y N Y

QoS Y Y Y N N I/P

Flow Scheduling Y Y Y N N Y

AMC Support n/a n/a N n/a N Y

Mode Pt-to-MPt n/a Pt-to-MPt Mesh Pt-to-MPt Pt-to-MPt

Realistic RF model n/a n/a N n/a N Y

Mobility Support Y Y N N Y Y

Handoff Schemes Y Y, limited n/a n/a Y Y

Multimedia Support n/a n/a N n/a N Y

Device Emulation n/a n/a N n/a N Y

ASN-GW Support N n/a N N N I/P



Mobile WiMAX Simulation Results



Comparison of Theory, Simulation, Tests

qpsk-1/2 qpsk-3/4 16qam-1/2 16qam-3/4 64qam-2/3 64qam-3/40

5000000

10000000

15000000

20000000

25000000

Total Throughput for Simulation, Lab-Test, and Theory

Simu-wimax Test-pBst Theory

Thro

ughp

ut (k

bps)



Predicted Distance for Test Equipment

0 2000 4000 6000 8000 10000 12000 140000

2000

4000

6000

8000

10000

12000

14000

16000

18000

Mobile WiMAX Throughput vs Distance

64QAM34 DL64QAM23 DL16QAM34 DL16QAM12 DLQPSK34 DLQPSK12 DL

Distance (meters)

Thro

ughp

ut (k

bps)



Sample Simulation Scenarios we are studying



Event Recorder Data UploadKey Parameters:• 70 mph train speed• 5 km AP Spacing (~3.1 miles)• Total length of 20 km• Uses maximum data transfer rate

0 50 100 150 200 2500

1000

2000

3000

4000

5000

6000

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Event Recorder UL - Throughput

TCP Throughput AP Association

Time (s)

Data

Thr

ough

put (

kbps

)

AP ID

0 50 100 150 200 2500

20

40

60

80

100

120

140

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Event Recorder UL – File Size

FTPFileSize AP Association

Time (s)

File

Size

(Mby

te)

AP ID



Video Streaming Fairness Comparison

Fairness Impact on Image Quality

0 2 4 6 8 10 12 14 160.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

Total Station Number

PS

NR

Fai

rnes

s In

dex

802.16

802.11

Fairness Impact on Throughput

0 2 4 6 8 10 12 14 160.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

Total Station Number

Thr

ough

put

Fai

rnes

s In

dex

Throughput Fairness vs. Total Station Number

802.16

802.11



Mobile WiMAX Video: PKI Neighborhood

Drive around the new Aksarben Neighborhood: Distance to PKI is about 0.5 milesSeveral signal obstructions from buildings in the area.

This is all done under the coverage of a SINGLE WiMAX Base Station!



Mobile WiMAX Video: Park

Drive around Elmwood Park: Distance to PKI is about 0.4 miles at farthest pointExtreme signal obstruction and scattering from trees in park!

WiFi would fail after the first few yards into the park area!



Mobile WiMAX Video: Speed and Distance

Drive on West Center road: Distance to PKI is between 0.6 miles and 1.0 miles at end!Signal obstructions from buildings between road and PKI, Doppler shift from 60 mph!

Under the coverage of a SINGLE WiMAX Base Station, with LOS RSSI=-66dBm at 1 mile!



Multiuser Comparison – WiFi and WiMAX

• WiMAX exhibits more efficiency (less overhead)– WiFi degrades with increased

no. of subscribers– Outcome of contention-based

operation in WiFi– Central resource management

eliminates these issues for downlink, drastically reduces its impact for uplink

• WiMAX also demonstrates better fairness among multiple subscribers

0 2 4 6 8 10 12 14 164

5

6

7

8

9

10

11

12

13

Station Number

Thr

ough

put(

Mbp

s)

Uplink Performance under N STAs

802.11

802.16

Total Throughput vs. No. of Subscribers



Mobile WiMAX Field Tests



Field Tests - Overview

• Field tests designed to provide real-world performance data– Maximum communication distance

– Maximum throughput at different velocities

– Handover performance with and w/o ASN-GW

– Latency, Packet Loss, Quality-of-Service, etc.

• We are utilizing microwave tower sites made available to us by Union Pacific and BNSF

• Preliminary Field Tests have been performed around our campus



Test Site 1 – UP: Logan, IA

Logan, IA - Tower

Road for WiMAX Tests

Main Antenna Direction Indicator

120degree coverage area of antenna (shaded area)

3 miles (approx.)



Test Site 2 – BNSF: Ashland, NE

Ashland, NE - TowerRoad for WiMAX Tests

Main Antenna Direction Indicator

120degree coverage area of antenna (shaded area)

3 miles (approx.)



Summary

• High-speed data networks is critical for effective railroad operations in mobile environments.

• One technology may not be the solution for all railroad needs.

• Combination of WiFi and WiMAX is a promising solution.

• An integrated solution is needed to support audio and video (multimedia type) applications.



Contact Information

• Hamid Sharif• Email: [email protected]• Phone: (402) 554-3628• Web: www.tel.unl.edu

• Thank you!

mailto:[email protected]

http://www.tel.unl.edu/

matc fall lecture series: hamid sharif

Documents

railroad research

railroad operating safety

suitable wireless technology

railroads voice portions

wireless standard protocols

ourtheoretical study

trains crews

impact of doppler shift