HF COMMUNICATION : PAST, PRESENT,
FUTURE
HF COMMUNICATION: PAST, PRESENT, FUTURE 1
CONTENTS
INTRODUCTION
BRIEF PRELIMINARIES ON HF COMMUNICATION
HISTORICAL REVIEW OF HF COMMUNICATION
KEY CHALLENGES
FUTURE DIRECTION
SUMMARY
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INTRODUCTION
An electromagnetic frequency defined by ITU for radio and radar comm.
Operates in a range of 3 to 30 MHz.
Wavelength 10 to 100m.
Important wireless comm. Practice.
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USES OF HF COMMUNICATION
Emergency comm. In disaster area.
Remote comm. With ships, aircrafts.
International and regional broadcasting.
Amateur radio.
Maritime sea-to-shore service.
Air-to-ground communication.
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BRIEF PRELIMINARIES ON HF COMMUNICATION
Surface/Ground wave propagation
Sky wave propagation
Line of sight
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SURFACE WAVE PROPAGATION
A wave which guided along the surface of the earth.
Produced by vertically polarized antennas.
Propagates with absorption and reflection.
Attenuation increases as frequency increases.
Propagates low frequencies(VLF,LF,MF) upto 2 MHz.
Short distance communication
Ex:- AM broadcasting, ship-to-ship comm.
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SKY WAVE PROPAGATION
A wave that is refracted/reflected towards the earth from ionosphere.
Ionization is possible due to presence of sun energy.
Propagates middle range frequencies(HF,VHF).
Used for long distance transmission.
Ex:- Military communication, international broadcasting.
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LINE OF SIGHT
LOS operates in a range of 15 to 85kms.
Transmitting and receiving antenna must be within line of sight
Radio band changes due to change in refractive index of atmosphere.
Height of tower should be high from obstecles.
Ex:- TV, Satellite, optical comm.
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HISTORICAL REVIEW OF HF COMMUNICATION
Starts around 1985
Marconi & other radio pioneers began to use long wavelengths
HF were given for experiments until 1921
HF band’s long distance transmission capability
Lower transmit power and smaller antennas.
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FIRST GENERATION HF COMMUNICATION(1920-
1970)
Spark gap transmitter
Manual frequency selection
Invention of continuous wave oscillator
Analogy voice service
Point-to-point communication
MSK, FSK, PSK gives better performance
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SECOND GENERATION HF COMMUNICATION(1980-
1990)
Automatic link establishment.
Digital voice/data service.
Point-to-multipoint communication.
Asynchronous process requires long time.
Voice service lack of data.
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THIRD GENERATION HF COMMUNICATION(2000-
2010)
Automatic link establishment
High performance data transmission
Channel for link establishment and transmission separated.
Higher data rate,lower SNR, faster link establishment
Synchronous technique reduced scanning time.
Integrated service from analogy to digital voice.
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NEXT GENERATION HF COMMUNICATION(2010- )
Intelligent operations
Wideband data transmission
Heterogeneous networking
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KEY CHALLENGES
Reliability
High Data Rates
Massive Remote Access
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RELIABILITY
Due to complex and unpredictable factor of Nature
Ex:-changing in ionospheric refrection
Unintentional interference
Intentional jamming
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HIGH DATA RATES
For supporting video and image transmissions.
Voice and data with less cost
Transmission of large data files
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MASSIVE REMOTE ACCESS
Increasing in worldwide applications like ships, aircrafts etc.
Massive :-huge no. of concurrent connection comm.
Remote:-distance bw HF transceivers is large.
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FUTURE DIRECTION
Intelligent HF radio
Wideband HF
Heterogeneous Networking
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INTELLIGENT HF RADIOS
Improve self adaptability.
Proactive ALE
Pre selection of favourable freq. based on spectrum prediction.
Smart anti-jamming
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WIDEBAND HF
Increase data rates for supporting diverse services.
Design a new waveform utilizing current 3 KHz allocation.
Multichannel approach.
Increase data rates using wider contiguous waveform.
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HETEROGENEOUS NETWORK
Improve reliability by diverse combining.
Centralized access control to coordinate massive connections.
Integrated space-air-marine-ground comm. Network.
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SUMMARY
Presents a general tutorial on HF comm.
Technical evolution of HF comm.
Key challenges.
Future directions.
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