3l Satellite communications systems

3l Satellite communications systems

1. GPS

   • Applications
     • SatNav
       • Offers maps, directions and warnings ETC
     • GeoCaching
     • GeoTagging
   • How it works
     • 24 satellites in NAVSTAR constellation.
     • Always at least 4 satellites in line of sight
       • Uses 3 satellites to do trilateration, using distance from each station
     • Orbit earth twice a year
   • Advantages
     • O- No need for large maps
     • O- Time saved planning journeys
     • O- Calculates new route if error is made
     • O- very accurate (as good as +- 30cm)
     • O- Maps can be updated via internet
     • O- GPS on phone can be used to find lost people
   • Disadvantages
     • X- Blind-spots due to tunnels or building
     • X- Maps may not up-to-date
     • X- Atmospheric conditions can affect accuracy of GPS
     • X- Drivers may become lost if GPS breaksdown
     • X- Desired destination may not be recognised
     • X- Setting destination and looking at SatNav may distract from driving

2. Weather

   • Applications
     • Monitor cloud formations to predict direction of weather fronts
     • Collect data on snow ad ice cover, pollution effects, fires, smog, dust and ocean currents
   • How it works
     • Can have geostationary orbit 35,000 km over one spot on the equator
       • Used by TV companies to provide cloud formation photos
     • Polar orbit, orbits over the poles 850km above earth
       • Higher quality pictures
       • Can use thermal and infrared images to find land and water temperatures
   • Advantages
     • O- Can monitor fires, hurricanes and sand clouds to give warnings
     • O- Can track energy usage and light pollution
   • Disadvantages
     • X- Expensive to build and launch satellites
     • X- Weather forecasts may not always be accurate
     • X- Concern over use of equipment for spying

3. Television

   • Applications
     • Can watch more channels than with aerial due to high bandwidth
     • Can be free to air or subscription
     • Can be used with set top box to see TV guide
   • How it works
     • TV companies send signals fro earth to a geosychronous satellite
       • Direct Broadcast satellite (DBS) encrypt signal so homes can only receive channels they have paid for
         • Signal compressed so more channels can be broadcast with same frequency
           • Satellite dish receives microwave signals from space
             • Receicer, set top box, decodes and decrypts signals to receive subscribed channels and decompress signal to find individual channel
   • Advantages
     • O- High bandwidth=> Hundreds of channels available
     • O- Can be received in remote areas where antenna signal is weak
     • O- Encrypted signals so viewers can pay for one-off programmes or subscriptins
   • Disadvantages
     • X- Equipment/ subscription is initially expensive
     • X- Need extra set top boxes to have satellite TV in other rooms
     • X- Weather conditions affects satellite signal
     • X- Signal dish is unsightly