Chapter 3

Help you understand how cellular phones and satellite phones operate.

You should be able to understand the advantages and disadvantages of both methods and understand when and where they should be used.

Mobile technology has allowed us to make calls whilst being mobile.

Gone are the days of having to find a pay phone when someone has beeped us...

Gone are the days of trekking for miles when your car breaks down...

Gone are the days...oh you get the point!

Cell

BST

MS

BSCBSC BSCBSC

MSCMSC PSTNPSTN

Connection Established

Calls taking place to a landline involves the following stages:

◦ The call is passed from the mobile device to the BST.

◦ The BST then transfers the call to the MSC.

◦ The MSC checks: There is enough credit on the phone to make the call The dialled number is valid

◦ The MSC connects the call through the PSTN and allocates a frequency to the MS.

Calls taking place to other mobiles involves the following stages:

◦ The MSC receives a request to establish a connection to another mobile phone.

◦ The MSC uses it’s active database to find out which BSC the mobile phone is connected to and the request is past to that BSC.

◦ The dialling request is then broadcast through all the BSTs that are connected to the BSC.

◦The mobile phone being called receives the request and acknowledges this to the BST.

◦ The call is then connected by the MSC using a frequency allocated to voice calls.

What happens if a mobile phone passes from one cell to another?

The mobile phone will connect to the new BST.

Sometimes BST’s signals can overlap...in which case the mobile phone will connect to the strongest signal.

Keeping a call active whilst moving through different cells requires the MSC to constantly update...

The MSC has an active database meaning that it constantly updates itself as a mobile phone registers to new BSCs.

The only time you can really notice a change is when you move from a strong signal to a low signal area.

This is how people can track where you are using your mobile phone.

Mobile phones are so popular these days that the UK is almost saturated with them!

In fact...there are more mobile phones in the UK than there are people! (Approx 1.6 mobiles for every 1 person)

So how are they used?◦ Business calls◦ Contacting friends and family to organise events◦ Texting and picture messaging◦ Browsing the internet and checking emails.

Smart phones also allow you to:◦ Listen to music and radio◦ Built in navigation software allows you to use your phone as a SatNav system.◦ Taking pictures and videos.◦ Playing games

Pros Cons

Incredibly convenient! Can be used anywhere you have a good enough signal.

Rubbish battery on a lot of phones means you have to be careful how long you use your phone for!

Can be used in am emergencyEmergency calls can be placed on any available network.

Signals are not strong everywhere and some phones provide better signal strength than others.

Additional applications can often be installed which allow you to make your phone into something more than just a device for calling and texting!

People often walk around with mobiles on them meaning they are always contactable – parents always stress out if their kids don’t have their phones on them!

Texting is great for those who have hearing disabilities!

Can cause massive distractions – big problem with driving and texting!!

Access to the internet is often possible wherever there is a good enough signal.

Bullying via mobiles is increasing which can be difficult to stop.

Using the diagram of the cell phone network, create a series of slides which show the process of calling another mobile phone on a different BSC.

Your animation should show the processes but also should contain a text box explaining what is happening during the process.

When you have done that try creating another version which makes a call to a landline number.

Satellite calls are similar to those on the mobile phone network but with a difference...the calls are connected via satellite! DUH.

There are two types of connections which can be made:◦ Low Earth Orbit (LEO)◦ Geosynchronous Earth Orbit (GEO)

The Iridium network consists of 66 satellites that orbit Earth at altitudes of about 900 km.

Each satellite orbits Earth about twice every hour!

Because of this global coverage is always ensured as the satellites move over.

This means that obstacles, such as mountains, do not interfere with calls.

Note: Iridium is just one example of a LEO satellite

This diagram shows how calls can be made via satellite phones to a mobile phone.

The satellite phone connects to a iridium satellite, which passes the call to other satellites.

The call is then passed back down to a gateway which connects to the wireless switch...the rest you know!

These are satellites which orbit Earth in a fixed location at an altitude of approximately 35,000 km.

Because of the great distance there is often a short delay between sending and receiving the communication.

Thuraya satellites are an example of this type of satellite connection.

Because of their fixed location, obstacles such as mountains can impede communications.

The Thuraya satellites provide cover for:◦ Europe◦ Africa◦ The Middle East◦ Australia

If a call is placed to a landline from a satellite phone then the connection must go through the PSTN.

If the call is placed to another satellite phone then the call is passed back to the satellite in space and sent down to the receiving phone.

If you are in a remote place then satellite phones are the must have accessory!

The army make use of them because there aren’t many mobile phone masts out in the desert!

Natural disasters often knock out mobile phone communications but satellite phones are unaffected.

Using satellite phones also makes it difficult to ‘tap’ calls. Its why it is used by naughty people!

The text book mentioned terrorists...but I couldn’t find any information on this! How about you try looking!

Pros Cons

Global coverage! The cost of these mobile phones is very expensive!

Phones aren’t that much bigger than mobile phones.

Battery life is not very good – which is an issue if you are in the middle of the desert or up a mountain!

Conversations can’t be monitored. Requires line of sight in order to work.

Can be used in emergencies when there is no mobile phone signal.

Data transfer rates are really slow(10 kbps is the norm).

Latency is an issue...especially when using GEO satellites.

Method Advantage Disadvantage Where is it used?

Mobile Phone

Satellite Phone

Describe the five components of a cellular network.

Identify the limitations of using a mobile phone to make an emergency call.

Identify three ways in which a while might use a mobile phone.

Why would a user use a satellite phone instead of a mobile phone?

Give two reasons why a user would prefer to use a mobile phone rather than a satellite phone.