Trường Đại học Bách Khoa Hà Nội Hanoi University of Science and Technology
Hệ thông Thông tin Hàng Không
TS. Đỗ Trọng Tuấn Bộ môn Kỹ thuật thông tin
© HUST 2012
Trường Đại học Bách Khoa Hà Nội Hanoi University of Science and Technology
Hệ thống Thông tin Hàng Không
Chương 3
Phân mạng HF
© HUST 2012
Teminologies
AM(R)S: Aeronautical Mobile (Route) Service AM(OR)S: Aeronautical Mobile (Off-Route) Service DSB-AM: Double Side Band - Amplitude Modulation WRC: World Radio Conference SARP: Standard And Recommended Practices
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Introduction
4
Introduction
Airline Host System
Satcom
Aviation Communication Services
ARINC Ground Network (AviNet®)
HFDL
FAA/CAA Tower Systems
ARINC Central Processing System (CPS)
ACARS/AOA
VHF
ATN
Air Traffic Service Provider
GLOBALinkSM by ARINC
Air/Ground Router
http://www.arinc.com/products/globalink/index.html
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GLOBALink/HF Flight Tracks (9/00)
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GLOBALink/HF Flight Tracks (2003)
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HF Range
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GLOBALink/HFDL Global Coverage @2000
HF Ground Stations (12) Alaska Bolivia California + Guam (12/5) Hawaii Iceland Ireland New York New Zealand Russia South Africa Thailand
Legend
HFDL ground station
Areas of Primary coverage
Areas of Secondary coverage
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GLOBALink/HFDL Global Coverage @2001
HF Ground Stations (14) Alaska + Bahrain Bolivia California + Canary Islands Guam Hawaii Iceland Ireland New York New Zealand Russia South Africa Thailand
Legend
HFDL ground station
Areas of Primary coverage
Areas of Secondary coverage
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GLOBALink/HFDL Global Coverage @2003
HFDL Ground Stations Alaska Bahrain Bolivia California Canary Islands Guam Hawaii Iceland Ireland New York New Zealand Russia South Africa Thailand
Legend
HFDL ground station
Areas of Primary coverage
Areas of Secondary coverage
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ARINC GLOBALink World Wide VHF Coverage
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GLOBALink/HFDL Global Coverage
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High Frequency Data Link: HFDL
High Frequency Data Link, or HFDL, is part of ARINC’s
GLOBALink end-to-end communication system
The HFDL system
is a segment of
the Aircraft Communications Addressing and Reporting System (ACARS) used to exchange Airline Operational Control (AOC) and Air Traffic Control (ATS) messagesbetween aircraft end systems and corresponding ground-based stations.
GLOBALink/HF provides HF-based, air-to-ground digital communications with aircraft using ARINC 635 protocol.
The HFDL system uses the principles of geographic to optimize HF frequency diversity
diversity and propagation
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High Frequency Data Link: HFDL
HFDL is currently the only truly global aeronautical data link capability, and the only data link for flight routes over the North Pole.
Inmarsat satellite SATCOM coverage becomes marginal
around 80 degrees north and south latitude.
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LINE OF SIGHT, GROUND WAVE, SKY WAVE
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KNOWLEDGE CHECK
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IONOSPHERE REGIONS
The ionosphere is the uppermost part of the atmosphere and is ionized by solar radiation.
Ionization is the conversion of
atoms or molecules into an ion by light (heating up or charging) from the sun on the upper atmosphere.
Ionization also creates a
horizontal set of stratum (layer) where each has a peak density and a definable width or profile that influences radio propagation.
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IONOSPHERE REGIONS
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IONOSPHERE REGIONS
The F layer: or region, is 120 km to 400 km above the surface of the Earth. It is the top most layer of the ionosphere. Here extreme ultraviolet (UV) (10-100 nm) solar radiation ionizes atomic oxygen (O). The F region is the most important part of the ionosphere in terms of HF communications. The F layer combines into one layer at night, and in the presence of sunlight (during daytime), it divides into two layers, the F1 and F2. The F layers are responsible for most skywave propagation of radio waves, and are thickest and most reflective of radio on the side of the Earth facing the sun.
The E layer: is the middle layer, 90 km to 120 km above the surface of the Earth. This layer can only reflect radio waves having frequencies less than about 10 MHz. It has a negative effect on frequencies above 10 MHz due to its partial absorption of these waves. At night the E layer begins to disappear because the primary source of ionization is no longer present. The increase in the height of the E layer maximum increases the range to which radio waves can travel by reflection from the layer
The D layer: is the innermost layer, 50 km to 90 km above the surface of the Earth. when the sun is active with 50 or more sunspots, During the night cosmic rays produce a residual amount of ionization as a result high-frequency (HF) radio waves aren't reflected by the D layer. The D layer is mainly responsible for absorption of HF radio waves, particularly at 10 MHz and below, with progressively smaller absorption as the frequency gets higher. The absorption is small at night and greatest about midday. The layer reduces greatly after sunset. A common example of the D layer in action is the disappearance of distant AM broadcast band stations in the daytime.
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HF Propagation
Due to variations in height and intensities of the ionised regions, different frequencies must be used at different times of day and night and for different paths. There is also some seasonal variation (particularly between winter and summer). Propagation may also be disturbed and enhanced during periods of intense solar activity. The upshot of this is that HF propagation has considerable vagaries and is far less predictable than propagation at VHF. Frequencies chosen for a particular radio path are usually set roughly mid-way between the lowest usable frequency (LUF) and the maximum usable frequency (MUF). The daytime LUF is usually between 4 to 6 MHz during the day, falling rapidly after sunset to around 2 MHz. The MUF is dependent on the season and sunspot cycle (11 years) but is often between 8 MHz and 20 MHz. Hence a typical daytime frequency for aircraft communication might be 8 MHz whilst this might be as low as 3 MHz during the night.
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HF Propagation
HF bands are allocated to the aeronautical service
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HF Propagation
Each HGS operates on 2-3 channels and is equipped with a family of HF frequencies ranging from 2-30 MHz.
solar
and
Adaptive Frequency Management techniques are employed to obtain weekly Active Frequency Tables (AFT). These tables are derived from a combination of real-time ionospheric monitoring, geomagnetic observational data and HF propagation models.
Each week, an updated AFT is uploaded to each HGS from the ARINC Operations Center (AOC) in Annapolis, Maryland, USA.
The AFT instructs the ground station on which frequencies to operate over the course of each 24-hour period
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HF Modulation: SSB modulation
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KNOWLEDGE CHECK
1. Explain why HF radio is used on trans-oceanic
routes.
2. Explain why different frequencies are used for HF aircraft communications during the day and at night.
1. State TWO advantages of using SSB modulation
for aircraft HF communications.
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Selective calling (SELCAL)
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Selective calling (SELCAL)
SELCAL codes are uniquely allocated to particular aircraft by Air Traffic Control (ATC).
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Selective calling (SELCAL)
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HF data link
Aircraft operational control at various ‘out-off-on-in’ (OOOI) stages
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HF data link
HFDL messages sent from the four aircraft shown to the Shannon HFDL ground station using the same communications channel
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HF data link
The radio path from one of the aircraft (LH8409) - Shannon HGS
Log-on requests and the maximum bit rate is specified in the header.
In each log-on request, the aircraft is identified by its unique 24-bit ICAO address.
Once logged on, the aircraft is allocated an 8-bit address code (AF hex in the case of the third message and AD hex in the case of the fourth message).
Each aircraft also transmits its current location data (longitude and latitude).
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HF data link
The system used for HFDL data exchange is specified in ARINC 635.
Each Ground Station transmits a frame called a ‘squitter’ every 32 seconds.
The squitter frame informs aircraft of the system status, provides a timing reference and provides protocol control.
Each Ground Station has a time offset for its squitters. This allows aircraft to jump between ground stations finding the best one before logging on. When passing traffic, dedicated TDM time slots are used. This prevents two aircraft transmitting at the same time causing data collisions
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A simple SSB transmitter/receiver
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HF radio equipment
Aircraft HF radio specifications
HF radio control unit
HF antenna location
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