3k Cellular and Satellite phones

Cellular Phones
1. How it works
  1. Mobile -> Landline
    1. Caller dials number
      1. Request sent to BST by microwaves
        Request passed to MSC
        MSC checks status of caller e.g. if there is credit to make the call, if dialled number is allowed (e.g. international numbers)
        Call connected to PSTN and frequency for call allocated.
  2. Receiving call
    1. MSC receive request to call a number
      1. MSC identifies which BSC the mobile is connected to
        Request passed to BSC
        Request to dail number broadcasted by all BST under the BSC
        Mobile Phone receive requests. Call is connected
  3. Moving Phone
    1. Database stores all cell locations of moibles
      1. Phone registers with new cell as it moves, database is update
        If area is covered by 2 cell, phone registers with the strongest signal
2. Applications
  1. Business, social, or emergencies.
  2. Phone and video calls
  3. SMS (text) and MMS (sound/video/image) messages
  4. WWw
  5. Email
  6. Smart Phones with apps, such as music players, or games
3. Country is broken in regions called cells
4. Infrastructure
  1. Mobile stations (MS) such as a mobile phone
  2. Base Station Transceivers (BST) for each cell. e.g. mobile phone mast- Gives signal coverage to cell
  3. Base Station Controller (BSC)- Manages communication between BSTs and a MSC
  4. Mobile Switching Centre (MSC)- Controls all calls taking place on a telephone network
  5. Public Switched Telephone Network (PSTN)- Transfers calls from one phone company to another
5. Advatanges
  1. O- User isn't restricted to one place
  2. O- Can be used to summon help in emergencies
  3. O- Can be used for other activities due to apps
  4. O- Text messages can be used by people with hearing/speaking impairments
  5. O- can access the WWW
6. Disadvantages
  1. X- Battery runs out
  2. X- Weak signals makes conversations break or can't make conversation
  3. X- Cyber bullying
  4. X- Texting and driving can cause accidents
  5. X- Can disturb events, such as films
Satellite Phones
1. How it works
  1. Connects directly to satellites orbiting earth rather than land-based BST
  2. Low earth orbit (LEO)
    1. e.g. iridium
    2. Many satellites at 900 km altitude
    3. Orbit earth 2 times an hour to offer global coverage
    4. Obstacles overcome as next satellite moves into line of sight
  3. Geosynchronous Earth Orbit (GEO)
    1. e.g Thuraya
    2. A few satellites orbit at 35,000 km
      1. X- latency in calls due to long distance
    3. Satellites remain in fixed position above earth
      1. X- Obstacles can prevent calls in certain locations
  4. Making phone call
    1. Number dialled from satellite phone
      1. Request transmitted by microwaves to satellite in space
        Request passed to other satellite using different frequency until it can be sent to correct satellite receiver on earth
        Call connected through PSTN
        Signal bounced back to satellite if call is to another satellite phone.
2. Applications
3. Advantage
  1. Communication in remote areas/ countryside/ ships/ mountains
  2. Less likely to get tapped as it doesn't go through PSTN
    1. used by military
  3. O- Global coverage
  4. O- Now as small a mobile phones
  5. O- Can be used when mobile phone system is unavailable.
4. Disadvantage
  1. X- Expensive phone and call rate
  2. X- limited battery life, hinders long expedition
  3. X- Requires line of sight
  4. X- Limited data transfer rates

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3k Cellular and Satellite phones

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	Created by Gladys Mba almost 8 years ago