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