View
219
Download
0
Category
Tags:
Preview:
Citation preview
DATA DATA COMMUNICATIONCOMMUNICATION
Lecture
Overview of Lecture 27
Frequency RangesMicrowave CommunicationSatellite CommunicationCellular Telephony
Frequency Ranges
The type of propagation used in radio transmission depends upon the frequency of the signal
Very Low Frequency (VLF)
Contd…
• VLF waves are propagated as surface waves through air
• Do not suffer much attenuation in TX but are susceptible to high levels of atmospheric noise I.e. electricity and heat
• Used for Long-range radio navigation and Submarine Communication
Low Frequency (LF)
Also propagated as surface waves Used for Long-range radio and for
navigational locators Attenuation is greater
Middle Frequency (MF)
– The distance they cover is limited by the angle needed to get the signal reflect
– Used for AM Radio
High Frequency (HF)
– Used for International Broadcasting, Military Communication, Telephone, Telegraph and Fax
Very High Frequency (VHF)
–Most VHF waves use line-of-sight propagation
–Used for VHF Television, FM Radio, Aircraft AM Radio
Ultra High Frequency (UHF)
– Always use line-of-sight propagation– Used for UHF Television, Mobile
Telephone, Cellular Radio, Paging, Microwave Links
– Note that microwave communication begins at 1GHz in UHF and continues into SHF and EHF band
Super High Frequency (SHF)
– SHF waves are TX using mostly line-of-sight and some Space propagation
– Used for Terrestrial and Satellite Microwave and Radar Communication
Extremely High Frequency (EHF)
–Used for Radar , Satellite and Experimental Communication
Terrestrial Microwave
Microwaves do not follow the curvature of earth
Line-of-sight transmission
Height allows the signal to travel farther
Terrestrial Microwave
Satellite Communication
Line-of-sight microwave communication using satellite
Satellite acts as a very tall antenna
and a repeater
Satellite Communication
Geosynchronous Satellites
Satellite Frequency Bands
Each satellite sends and receives over two bands
–Uplink: From the earth to the satellite
–Downlink: From the satellite to the earth
Satellite Frequency Bands
Band Downlink UplinkC 3.7-4.2 GHz 5.925-6.425
GHz
Ku 11.7-12.2 GH 14-14.5 GHz
Ka 17.7-21 GHz 27.5-31 GHz
Cellular Telephony
Each service area is divided into small ranges called cells
Each cell office is controlled by a switching office called MTSO
Cellular Telephony
Operations of Cellular Telephony
Transmitting– Mobile phone sends the number to the
closest cell office
– Cell office MTSO Telephone office
– MTSO assigns an unused voice channel
Operations of Cellular Telephony
Receiving– Telephone office sends the signal to
MTSO
– MTSO sends queries to each cell (paging)
– If mobile phone is found and available, assigns a channel
Operations of Cellular Telephony
Handoff–MTSO monitors the signal level
every few seconds
– If the strength diminishes, MTSO seeks a new cell and changes the channel carrying the call
Recommended