Transmission Media -Cont

ƒ     Geosynchronous Satellite o    Line of sight propagation requires the sending and receiving antennas must be locked into each other o    To ensure continuous communication, satellites must move with the same speed as earth. So that they seem fixes w.r.t earth o    These satellites are called Geosynchronous Satellites

Figure shows 3 satellites in geosynchronous orbit each 120 degree from one another so that whole earth can be covered ƒ     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 Cellular Telephony o    Each service area is divided into small ranges called cells o    Each cell office is controlled by a switching office called MTSO Operations of Cellular Telephony Transmitting -Mobile phone sends the number to the closest cell office -Cell office Æ MTSO Æ Telephone office -MTSO assigns an unused voice channel 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 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