DATA COMMUNICATION Lecture

Overview of Lecture 27  Frequency Ranges  Microwave Communication  Satellite Communication  Cellular 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 BandDownlink Uplink C GHz GHz Ku GH GHz Ka GHz 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