Here are the answers to your questions, based on the information from the provided
documents:
1. Basics of Cellular Network
A cellular network is a radio-based technology where radio waves are propagated by antennas,
primarily in the 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz frequency bands. Base stations
transmit to and receive from mobile devices at an assigned spectrum. The service area of each
base station is called a "cell". Multiple base stations can use the same spectrum, a concept
known as "spectral reuse" or "frequency reuse". Mobile terminals are typically served by the
closest base station, and a "handoff" occurs when terminals move between cells.
In a cellular system, the operator's covering area is divided into cells, each covered by one or a
small collection of transmitters. The frequency reuse method allows frequencies to be reused
outside the range of a transmitter, where the signal level falls below a usable limit and will not
cause significant interference. While often shown as hexagonal shapes diagrammatically, real
cell boundaries are irregular due to terrain, buildings, and other objects that attenuate signals
differently.
2. Generation of Cellular Network
Cellular networks are categorized into generations based on their technological advancements:
* 0G (Zero Generation): Briefly mentioned as briefcase-size mobile radio telephones.
* 1G (First Generation): Characterized by analog voice communication.
* 2G (Second Generation): Introduced digital voice communication. GSM is a prime example of
a 2G digital cellular communications system.
* 3G (Third Generation): Added capabilities for digital voice and data services.
* 4G (Fourth Generation): Focused on higher speed internet access for mobile devices and
data-centric communication. LTE (Long-Term Evolution) is the standard for 4G technology.
3. GSM Services
GSM (Global System for Mobile communications) is a digital cellular system designed to be
compatible with ISDN services. Key features and criteria for GSM include good subjective
speech quality, low terminal and service cost, support for international roaming, ability to
support handheld terminals, and support for a range of new services and facilities. GSM also
ensures spectral efficiency and ISDN compatibility.
GSM services can be broadly classified into:
* Tele Services: These include voice calls, emergency calls, and short message service (SMS).
* Bearer Services: These enable data transmission capabilities, allowing for various
applications.
* Supplementary Services: These enhance tele and bearer services, offering features like call
forwarding, call waiting, call holding, multi-party calls, call barring, and advice of charge.
4. Base Station Subsystem (BSS)
The Base Station Subsystem (BSS) is one of the three main parts of the GSM architecture. It is
responsible for managing the radio interface between the mobile station and the network. The
BSS consists of two main components:
* Base Transceiver Station (BTS): This component houses the radio transceivers that define a
cell. Its primary function is to handle the radio-link protocols with the Mobile Station (MS).
* Base Station Controller (BSC): The BSC manages the radio resources for one or more BTSs. It
handles radio-channel setup, frequency hopping, and handovers. It also acts as the connection
between the mobile station and the Mobile services Switching Center (MSC).
5. Network and Switching Subsystem (NSS)
The Network and Switching Subsystem (NSS) is the core of the GSM network, responsible for
handling switching functions for mobile users, managing subscriber databases, and connecting
the mobile network to other fixed networks. It comprises several key components:
* Mobile services Switching Center (MSC): The central component of the NSS, acting like a
normal switching node of the Public Switched Telephone Network (PSTN) or Integrated Services
Digital Network (ISDN). It manages mobile-specific operations such as registration,
authentication, location updates, handovers, and call routing.
* Home Location Register (HLR): A permanent database containing all the administrative
information of each subscriber registered in the GSM network, along with the current location
of the mobile.
* Visitor Location Register (VLR): A temporary database that contains selected administrative
information from the HLR, necessary for call control within the current MSC service area.
* Equipment Identity Register (EIR): A database that contains a list of all valid mobile
equipment (IMEIs) on the network.
* Authentication Center (AuC): A protected database that stores a copy of the secret key found
in each subscriber's SIM card, used for authentication and encryption over the radio channel.
6. Handover
"Handover" (used in Europe) or "Handoff" (used in North America) is the process of seamlessly
transferring an active call from the base station of one cell to another as a mobile handset
moves, without any noticeable disruption to the call. This ensures continuous connectivity and
mobility for the user.
Handovers are determined by several parameters, including:
* The signal strength of the current base station.
* The signal strengths of the surrounding stations.
* The availability of channels in the target cell.
There are different types of handovers:
* Hard Handover: An existing connection must be broken before the new one is established
(break-before-make).
* Soft Handover: A new connection is established before the old one is released (make-before-
break), providing a smoother transition.
* Softer Handover: A signal is replaced by a stronger signal from a different sector under the
same base station.
7. Roaming. NIJE PORO
Information specifically defining "Roaming" is not available in the provided documents.
8. Evolution from 2G to 3G
& 9. GSM Evolution to 3G
The evolution from 2G (like GSM) to 3G (like UMTS) primarily focused on transitioning from
digital voice to supporting both digital voice and data services.
Key steps in the evolution:
* GPRS (General Packet Radio Service): This was an enhancement to GSM networks, providing a
packet-switched connectivity solution based on Internet Protocols. GPRS enabled a wide range
of enterprise and consumer applications with throughput rates of up to 40 kbit/s, offering
speeds similar to a dial-up modem. It was considered a significant step towards 3GSM (or
wideband-CDMA) networks and services.
* EDGE (Enhanced Data rates for GSM Evolution): Further enhanced GSM networks by
providing up to three times the data capacity of GPRS. EDGE allowed operators to handle more
subscribers, triple data rates per subscriber, or add extra voice capacity. It used the same TDMA
frame structure and carrier bandwidth as GSM, allowing it to be easily overlaid onto existing
GSM networks, often through a simple software upgrade. EDGE enabled advanced mobile
services like video and music downloads, multimedia messaging, and high-speed internet
access.
* UMTS (Universal Mobile Telecommunication System): This is a 3G mobile cellular system that
evolved from the GSM standard. UMTS brought significantly higher data rates and support for
multimedia services.
10. UMTS?
UMTS stands for Universal Mobile Telecommunication System. It is a 3G mobile cellular system
that evolved from the GSM standard. UMTS is part of the IMT-2000 family of 3G technologies.
Basic services that an IMT-2000 (3G) network, including UMTS, should provide include high-
quality voice, messaging, multimedia, and internet access.
11. UMTS Architecture
The provided documents mention UTRAN (Universal Terrestrial Radio Access Network), which is
a collective term for the Node B's and Radio Network Controllers (RNCs) that make up the UMTS
radio access network.
However, a complete detailed architecture of UMTS beyond UTRAN is not fully described across
the provided slides.
12. Define Node B, GGSN, SGSN
* Node B: In UMTS, Node B is equivalent to the Base Transceiver Station (BTS) in GSM. It is part
of the UTRAN (Universal Terrestrial Radio Access Network) and handles the radio interface for
UMTS.
* SGSN (Serving GPRS Support Node): The SGSN is a key component in a GPRS/UMTS network.
Its main functions include:
* Routing and forwarding user data packets.
* Performing mobility management, such as attaching/detaching mobiles from the network,
and managing location updates.
* Authenticating users and managing logical links.
* Collecting charging data.
* GGSN (Gateway GPRS Support Node): The GGSN acts as the gateway between the
GPRS/UMTS network and external packet data networks, such as the internet. Its main
functions include:
* Interfacing with external packet data networks.
* Routing and tunneling data packets to the correct SGSN.
* Maintaining subscriber sessions.
* Dynamic allocation of IP addresses.
13. Features of LTE (4G)
LTE (Long-Term Evolution) is the standard for 4G cellular technology. While a detailed list of
features is not provided, 4G networks generally aim for higher speed internet access for mobile
devices and are characterized by being entirely IP-based, focusing on data-centric
communication.
14. 2G-4G Data Rate
The provided documents offer the following general indications of data rates:
* 2G (GPRS): Throughput rates of up to 40 kbit/s.
* 2G (EDGE): Provides up to three times the data capacity of GPRS. This implies rates potentially
up to ~120 kbit/s, though not explicitly stated.
* 3G: Not a specific data rate mentioned, but 3G networks brought significantly higher data
rates compared to 2G, enabling multimedia and internet access.
* 4G (LTE): Generally characterized by "high speed internet access for mobile devices". Specific
speeds are not detailed in the provided content.
