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