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Glenn Research Center at Lewis Field

NEONet 2006

Investigating 802.16 for

Aeronautical Use

Steven BretmerskyCleveland State University

March 1, 2006

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Glenn Research Center at Lewis Field

Background

The airport surface is a highly dynamic environment that encompasses many diverse users with different needs. Future operations will make more use of data communications and will require a wireless link.

In the technology pre-screening phase of the Future Communication Study (a joint Eurocontrol / FAA study) 802.16 was identified as one possible enabling technology for the airport surface for ATC. This technology could benefit other surface users as well.

This work investigates the possible uses of 802.16 for the airport surface.

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Glenn Research Center at Lewis Field

Uses of a surface wireless network

• As a data link to aircraft for Air Traffic Control (ATC) and Aeronautical Operational Communications (AOC) messages

• As a data link for surface vehicles (fuel trucks, baggage carts, maintenance vehicles)

• As a backup link for existing ATC fixed surface systems (radar sites, voice radio sites, navaid sites)

• As a primary link for new surface systems located in remote or hard-to-reach areas (ASDE-X multilateration sensors, wake vortex sensors)

• As a network connection for airport staff (technicians in the field)

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Glenn Research Center at Lewis Field

Wireless Surface Scenario

Weather Radar

ILS

Aircraft

Emergency Vehicles

FAA

Airlines

PortAuthority

Technicians

Fuel TruckBaggageHandlers

RTR

Radar

Snow Removal Equipment

ALS

Wake Vortex SensorRWSL

ASDE-XSensor

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Glenn Research Center at Lewis Field

Current Communications Systems

• To Aircraft – VHF voice and character-based messaging system (ACARS)

• To surface vehicles – VHF voice to ATC, mobile radios

• To existing surface systems – copper, leased telco lines, microwave wireless links, and/or fiber. All existing surface systems use point-to-point analog interfaces (modems)

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Glenn Research Center at Lewis Field

Future System Requirements

• High reliability• Pre-emption / prioritization (QoS)• Privacy / Security

– Encryption– Authentication

• Mobility• Operate in a protected band (safety of flight)

– C-band identified as good candidate – MLS extension band (5.091 – 5.150 GHz) is unutilized and

currently protected as aeronautical radionavigation

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Glenn Research Center at Lewis Field

802.16 Flavors

✔ ✔Mesh✔ ✔ ✔Mobility✔ ✔ ✔ ✔Spaced Time Coding (STC)✔ ✔ ✔ ✔Adaptive Antenna System (AAS)✔ ✔ ✔ ✔Automatic Repeat Request (ARQ)

10 – 66 GHz

2 - 11 GHz

2 - 11GHz

2 - 11GHz

2 - 11GHz

Frequency

TDDFDD

TDDFDD

TDDFDD

TDDFDD

TDDDuplexing

WirelessMAN-SC

WirelessMAN-SCa

WirelessMAN-OFDM

WirelessMAN-OFDMA

WirelessHUMAN

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Glenn Research Center at Lewis Field

802.16 OFDM Waveform

• 8 Pilot Subcarriers– Used as reference for phase and amplitude

• 192 Data Subcarriers• Combination of all subcarriers creates an OFDM

symbol

Pilot SubcarriersData Subcarriers

Guard Band Guard Band

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Glenn Research Center at Lewis Field

TDD Frame Structure

Downlink Subframe

UL BurstDL Burst iDL Burst 1 UL Burst

DL PHY PDU UL PHY PDU UL PHY PDU

Uplink Subframe

Frame

Preamble

Frame Control Header

DL-MAP, UL-MAP, DCD, UCD

Burst 1 MAC PDU 1

Burst 1 MAC PDU k

Burst i MAC PDU 1

Burst i MAC PDU l

Transmit/Receive Turnaround Gap

Initial Ranging Contention Slot

BW Request Contention Slot

SS 1 PHY PDU Preamble

SS 1 MAC PDU 1

SS 1 MAC PDU m

SS x PHY PDU Preamble

SS x MAC PDU 1

SS x MAC PDU n

Receive/Transmit Turnaround Gap

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Glenn Research Center at Lewis Field

802.16 on High Reliability

• 802.16 uses multiple modulations and FEC rates to offer best performance for link conditions. – Modulation / FEC selection is a tradeoff between robustness and data

rate.

– WirelessMAN-OFDM modulations:• BPSK• QPSK• 16-QAM• 64-QAM

– WirelessMAN-OFDM FEC algorithms• Reed-Solomon-Convolutional Code (RS-CC) at rates of 1/2, 2/3, and 3/4• Block Turbo Coding (BTC) at rates of 1/2, 3/5, 2/3, 3/4, 4/5, and 5/6

(optional)• Convolutional Turbo Codes (CTC) at rates of 1/2, 2/3, and 3/4 (optional)

• 802.16 offers ARQ that can be enabled on a per-service-flow basis

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Glenn Research Center at Lewis Field

802.16 on QoS

• 802.16 offers four types of services– Unsolicited Grant Service

• Real-time fixed-rate flows

– Real Time Polled Service• Real-time variable rate flows

– Non-Real Time Polled Service– Best Effort Service

• QoS for real-time services– Priority (8 levels)– Tolerated jitter– Maximum tolerated latency– Minimum tolerated traffic rate

• 802.16 scheduler is not standardized

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Glenn Research Center at Lewis Field

802.16 on Privacy / Security

• Key management– X.509 digital certificates– RSA public key encryption/authentication– Optional EAP authentication in 802.16e– HMAC with SHA-1 authentication

• Data encryption– DES with 56-bit keys– AES with 64 and 128 bit keys

• Data authentication– AES with 128-bit keys in 802.16e

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Glenn Research Center at Lewis Field

802.16 on Mobility

• 802.16e adds the mobility component to the base standard– Designed to accommodate vehicular speeds (< 120 km/h)– Cannot support takeoff/landing speeds (~250 km/h),

although this is not a big issue since the aircraft will likely be using the terminal area data link during these periods

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Glenn Research Center at Lewis Field

Study Approach

• Identify surface applications and scenarios• Create 802.16 OFDM model to use in OPNET

simulations• Identify and implement appropriate scheduling

algorithm• Evaluate scenario options and verify with simulations

– Single vs. multiple systems – Channel size

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Glenn Research Center at Lewis Field

802.16 Model

• Implementation of 802.16 P2MP protocols in progress– MAC Common Part Sublayer

– Convergence Sublayer

– Overhead from Privacy Sublayer

– Overhead from OFDM PHY

• 802.16e extensions to be added in the future

• Creation of physical layer model to begin soon– Waiting for inputs from Ohio

University Sounding Study

Scope of Standard

Service-SpecificConvergence Sublayer (CS)

MAC Common Part Sublayer(MAC CPS)

Privacy Sublayer

Physical Layer (PHY)

Transmission Convergence (TC)

CS SAP

MAC SAP

PHY SAP

PHY

MAC

Scope of Model

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Glenn Research Center at Lewis Field

Scheduling Algorithm

• Must determine when to grant bandwidth to services to meet QoS requirements– minimum rate– maximum latency– maximum jitter– priority

• Must poll subscribers at appropriate time• Must take into account the current modulation and

FEC rate being used by the subscriber

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Glenn Research Center at Lewis Field

Bandwidth Options

• Channel bandwidth is configurable (between 1.25 and 25 MHz, 802.16e up to 5 MHz)

• Example (OFDM, G = 1/32)– 1.25 MHz channel (minimum)

• BPSK with RS-CC ½ (most robust)– 524 kbps raw data rate

• 64-QAM with RX-CC ¾ (least robust)– 4.7 Mbps raw data rate

– 25 MHz channel• BPSK with RS-CC ½ (most robust)

– 10.5 Mbps raw data rate

• 64-QAM with RX-CC ¾ (least robust)– 94.2 Mbps raw data rate

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Glenn Research Center at Lewis Field

Scenario Options

• Single system scenario– All nodes use same wireless channel(s)

• Multiple system scenarios– Separate wireless channels for fixed nodes and for mobiles– Separate point-to-multipoint and mesh channels

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Glenn Research Center at Lewis Field

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