Every Stuff about Mobile Telephony

Hello Welcome to Mobile Telephony.

Mobile Communication is now viewed as a fastest growing and most demanding technologies in the world.When discussing the improvements in this industry we can proudly say that we are at the door step of a new generation i.e Forth Generation(4G)

History of wireless Communication
First Generation (1G) systems were fully analog with reasonably reliable networks. But limited services were available in 1G.
Second Generation (2G) systems are digital and came with better options in terms of service sophistication, capacity and quality.The world famous GSM technology is introduced in second generation.
General Packet Radio Service (GPRS) is an improvement of 2G technology enabling mobile phones to use internet.Since it is called 2.5G.
Later on in 2000/2001 period Third Generation (3G) was introduced with more attractive features.People could able to get video calls and browse internet faster than ever before with the 3G technology. 

Global System for Mobile Communication (GSM)
There are many mobile standards in second generation, among them GSM accounts for 70% of the world's market.Since this is a global standard, subscribers can connect with any other PLMN in the world.

GSM Hierarchy

Figure 01: GSM Hierarchy

• MS     : Mobile Station
• BTS    : Base Transceiver Station
• BSC    :Base Station Controller
• MSC   :Mobile Switching Center
• VLR    :Visitor Location Register
• HLR    :Home Location Register
• AuC    :Authentication Center
• EIR     :Equipment Identity Register
• PSTN :Public Switched Telephone Network
• ISDN :Integrated Services Digital Network

1.Mobile Station (MS)

   Mobile Station is the user equipment in GSM network. It consists of two parts
               * Mobile Equipment (ME)
               * Subscriber Identity Module (SIM) 

                      Subscriber Identity module contains identities to identify the user correctly

                      with high security.The GSM identities stored in the SIM are IMSI & Ki.

2.Base Transceiver Station (BTS)

   BTS is the place where the MS connects to the GSM network.

   The main functions of the BTS are

   •    Provide the interface for communication with users in air interface
   •    Encoding/decoding and modulation/demodulation of voice traffic signals
   •    Forwarding voice traffic and necessary signals to the Base Station Controller (BSC)

3. Base Station Controller (BSC)
    Several BTSs are connected to one BSC. The main functions of the BSC are
   •    Assigning free radio channels in the TRx units to new call connections
   •    Control TRx units
   •    Forward the voice traffic and signaling data to Mobile Switching Center

4. Mobile Switching Center (MSC)
    The main task of MSC is to switch calls between the two corresponding mobile stations. Other than that, it handles the management of mobile services such as such as registration, authentication, location updating, handovers, and call routing to a roaming subscriber. MSC’s can be mainly divided in to two different categories by its function.
VMSC: The Visited MSC is the MSC where a subscriber is currently located. The VLR associated with this MSC will have the subscriber's data in it.
GMSC: The Gateway MSC is used when a subscriber in the local network is connecting (dialing or receiving a call) to another operator’s network. GMSC is an interface between the VMSC and other operators.

5. Home Location Register (HLR)
The HLR is a database to store permanent data of subscribers, including a subscriber's service profile, location information, etc.
The information stored includes:
•    Subscriber identity (i.e. IMSI, MSISDN)
•    Subscriber supplementary services (GPRS, WAP)
•    Subscriber location information (i.e. MSC service area)
•    Subscriber authentication information (Ki , Algorithms)
•    Subscriber Status (Attached / Detached)

6. Visitor Location Register (VLR)
    VLR is a database that contains temporary (dynamic) information of subscribers.The VLR is always integrated with the MSC.This helps to avoid interrogating the HLR each time the subscriber make/receive a call.The VLR maintains a copy of the necessary subscription details, including the following information:
• Identity numbers for the subscriber (IMSI , MSISDN)
• Supplementary service information (eg.subscriber has activated call forwarding on busy )
• Activity of MS (e.g. idle)
• Current LA of MS

7. Authentication Center (AUC)
    Authentication Center is used for authentication and ciphering of the radio channel. The AUC protects network operators from different types of fraud found in today's cellular world.

8 . Equipment Identity Register (EIR)
    The EIR is a database that contains a list of all valid mobile equipment on the network, where its International Mobile Equipment Identity (IMEI) identifies each MS. An IMEI is marked as invalid if it has been reported stolen or is not type approved.

GSM Channel concept
The carrier separation is 200 kHz; this provides 124 carriers in the GSM 900 band, 374 carriers in the GSM 1800 band and 299 in the GSM 1900 band. Since each carrier is shared by eight
MSs, the total number of channels is
•    124 x 8 = 992 channels in GSM 900
•    374 x 8 = 2992 channels in GSM 1800
•    299 x 8 = 2392 channels in GSM 1900

Frequency Allocation

Figure 02: Summary of Standards

2G to 3G Technology Evolution

Figure 03:Evolution of Technology