2G networks

1. G Second generation network - GSM
Mobile communication of second generation 2G - standard GSM.
2G started in 1991 with a speed for data transmission 9.6 kbit/s. In 1999, in the GSM
standard is incorporated, the standard GPRS (considered as intermediate generation -
2.5G), which provides mobile Internet with greater speed.
GSM (group name from Groupe Spécial Mobile, later renamed to Global System for
Mobile Communications) is the global standard for digital mobile cellular connection with
the TDMA separation of channel and a high degree of safety, thanks to an open encryption
key. Developed under the auspices of the European Telecommunications Standards Institute
(ETSI) in the 80 years of the twentieth century.
GSM refers to second generation networks (2nd Generation), although in 2006 it entered in
a conditional phase 2,5 G and is the most popular standard for mobile cellular connection in
the world. Mobile phones are manufactured for use in a range of four frequencies: 850 MHz,
900 MHz, 1800 MHz, 1900 MHz. The GSM standard uses GMSK modulation.
Network Architecture
Base station (BS) is connecting your cell phone with a cellular network. Each base station is
called cell, because it has a specific coverage area. All base stations are linked, so you can
get a reliable connection when you move from one cell to another. This process is called
"transfer" (hand-over). With base stations included in the set of Base Stations Controller
(BSC).
The mobile station (terminal) from your cell phone and SIM-module is one type of electronic
signature (which includes your subscriber number) to be sent to the nearest cell as an
application that you want as a subscriber access to the system. BSC submit the application
to the heart of the cellular network - Mobile Switching Center (MSC). MSC takes care of
providing a connection to route incoming and outgoing calls to and from fixed or mobile
networks. MSC contains a critical component called HLR (Home Location Register) -
Internal register (register of inland locations), providing administrative information,
identifying you as an individual subscriber. Once receiving a request from the cellular
phone, HLR instantly compare specific signature in this application, the data for the
subscriber. If your subscription is correct, MSC sent back, via cell phone to your message
that you are admitted to network. Usually at this point on the display is written the name of
the cellular network. From here onwards can receive and make calls. On receipt of a call,
MSC first checks HLR to see your location. At any time, cell phones will send a message to
the nearest cell to inform the network where you are. This process is known as polling.
Each base station uses a purely digital technology to support a massive number of
subscribers simultaneously connected to a cellular network, but also enable them to make
and receive calls. This technique is called multiplexing.
The network is able to redirect your calls to the base station in whose coverage is your
phone, even if other subscribers at the same time are connected to it. When you switch to
another cell (eg. while driving), HLR information is automatically updated to make accurate
routing of signal for your calls.
When you make an outgoing call, another module of the MSC is activated called the VLR
(Visitor Location Register) - register which verify that you are actually allowed to make

2. calls. (For example, your customer number may be banned for international calls). VLR
response is forwarded back to your phone. Voicemail and the Centre for short messages
(SMS) are other services that provide MSC. SMS messages are transmitted on a separate
channel of the conversations, and you can receive short messages even when talking.
Radio interfaces of GSM digital cellular network
Interfaces are of two types:
1. Interface for connection to external networks (signaling system No.7 /SS7/)
o Abis - interface between BS and BSC;
o A - interface between BSC and MSC;
o B - interface between VLR and MSC;
o C - interface between MSC and HLR;
o D - interface between VLR and HLR;
o E - interface between MSC and EIR;
o F - interface between two stations;
o Um - Radio Interface between MS and BS.
2. Species series (burst):
o Normal (normal burst);
o To adjust the frequency;
o For Synchronization;
o For Access series (shortened series);
o Blank (deaf serie).
Logical channels in 2G mobile communication - GSM
Logical
channel
Direction of
transmission
Type of transmitted information
AGCH MS→BS Query for outgoing call
RACH BS←MS
Information for the independent channel (channel
number, time interval)
SDCCH MS→BS Send the number of the called subscriber
SDCCH BS→MS Application authentication
SDCCH MS→BS Responses of checking the authenticity
SDCCH BS→MS
Permission to access the services of mobile network,
appointing a number and time interval for the speech
SDCCH MS→BS Confirmation
SDCCH MS→BS Discharging channel
TCH MS↔BS Transmitting Speech
After the call
BSCH BS→MS Frequency correction and synchronization

3. CCCH MS←BS Exchange of business information for control
2G Cellular Systems
Second-generation (2G) digital cellular systems constitute the majority of cellular communication
infrastructures deployed today. 2G systems such as GSM, whose rollout started in 1987, signaled a
major shift in the way mobile communications is used worldwide. In part they helped fuel the
transition of a mobile phone from luxury to necessity and helped to drive subscriber costs down by
more efficient utilization of air interface and volume deployment of infrastructure components and
handsets.
Major geographical regions adopted different 2G systems, namely TDMA and CDMA in North
America, GSM in Europe, and Personal Digital Cellular (PDC) in Japan. Figure 3.3 depicts the
worldwide subscriber numbers for major 2G cellular systems. It effectively shows how the GSM
system has been successful and why it is now being adopted in geographical areas other than
Europe (such as North America, China, the Asia-Pacific region, and more recently, South America).
CDMA, which originated in North America, has also proliferated in South America and later in the
Asia-Pacific region. TDMA remains to be widely deployed in North and South America regions, but it
is expected to decline mostly because of the decisions taken by few major North American carriers
to convert their TDMA networks to GSM.
Figure 3.3: 2G technologies worldwide
market share in subscribers (2002).
North American TDMA (IS 136)
This second-generation system, widely deployed in the United States, Canada, and South America,
goes by many names, including North American TDMA, IS-136, and D-AMPS (Digital AMPS). For
the sake of clarity, we will refer to it as North American TDMA, as well as simply TDMA, when the
context makes it clear. TDMA has been used in North America since 1992 and was the first digital
technology to be commercially deployed there. As its name indicates, it is based on Time Division
Multiple Access. In TDMA the resources are shared in time, combined with frequency-division
multiplexing (that is, when multiple frequencies are used). As a result, TDMA offers multiple digital
channels using different time slots on a shared frequency carrier. Each mobile station is assigned
both a specific frequency and a time slot during which it can communicate with the base station, as
shown in Figure 3.4.

4. Figure 3.4: Time Division Multiple Access.
The TDMA transmitter is active during the assigned time slot and inactive during other time slots,
which allows for power-saving terminal designs, among other advantages. North American TDMA
supports three time slots, at 30 kHz each, further divided into three or six channels to maximize air
interface utilization. A sequence of time-division multiplexed time slots in TDMA makes up frames,
which are 40 ms long. The TDMA traffic channel total bit rate is 48.6 Kbps. Control overhead and
number of users per channel, which is greater than one, decrease the effective throughput of a
channel available for user traffic to 13 Kbps. TDMA is a dual-band technology, which means it can
be deployed in 800-MHz and 1900-MHz frequency bands. In regions where both AMPS and TDMA
are deployed, TDMA phones are often designed to operate in dual mode, analog and digital, in order
to offer customers the ability to utilize coverage of the existing analog infrastructure.
Global System for Mobile Communications (GSM)
There are still some analog cellular systems in operations in Europe, but their number is declining,
and some regional networks are being completely shut down or converted to Global System for
Mobile Communications. The GSM cellular system initiative was initiated in 1982 by the Conference
of European Posts and Telecommunications Administrations (CEPT) and is currently governed by
European Telecommunications Standards Institute (ETSI), which in turn has delegated GSM
specifications maintenance and evolution to 3GPP (reviewed in part in Chapter 1). The intent behind
GSM introduction was to have a common approach to the creation of digital systems across
European countries, to allow—among other advantages of a common standard—easy international
roaming and better economies of scale by decreasing handset and infrastructure components costs
through mass production. In hindsight, this was a smart political decision, which contributed to the
worldwide success of European cellular infrastructure providers and equipment manufacturers.
Let's look at some details of the GSM air interface technology. The GSM standard, similarly to North
American TDMA, is based on the use of two simultaneous multiplexing technologies, TDMA and
FDMA. Each radio frequency (RF) channel in GSM supports eight time slots (compared to three for
North American TDMA) grouped into TDMA frames, which are in turn grouped
into multiframes consisting of 26 TDMA frames carrying traffic and control channels. Multiframes are
built into superframes and hyperframes. This yields an 8-to-1 capacity increase over NMT or TACS
in the same RF spectrum. The allocation of the time slots is essentially static on a short-term basis;
for instance, the eighth time slot of a given RF channel is assigned to the same user each time it
comes around, whether or not the user has voice or data to send.
The GSM system, emphasizing not only physical properties but also service definitions (unlike some
1G systems), supports three major types of services: bearer services, tele-services, and
supplementary services. GSM bearer services allow for transparent or acknowledged user data
transfer and define access attributes, information transfer attributes, and general attributes with
specific roles. Access attributes define access channel properties and parameters such as bit
rate; transfer attributes define data transfer mode (bidirectional, unidirectional), information type
(speech or data), and call setup mode; general attributes define network-specific services such as
QoS and internetworking options. Tele-services are what GSM subscribers actually use. They are
based on the foundation provided by bearer services and govern user-to-user communications for
voice or data applications. Examples of tele-services include Group 3 Fax, telephony, Short

5. Message Service (SMS), and circuit data IP and X.25 communications. GSM supplementaryservices
provide additional value-added features such as call waiting, call forwarding, call barring, and
conference calling used by wireless operators to further differentiate their offerings. Further
information about GSM can be obtained from a variety of sources such as [Eberspacher 2001].
High-Speed Circuit-Switched Data
High-Speed Circuit-Switched Data (HSCSD) is an option in GSM that allows combining multiple
GSM time slots (traffic channels) each capable of a 14.4-Kbps data rate. The resulting bit rate made
available for a single user might reach as high as 56 Kbps, although probably at a steep price tag. In
fact, owners of the mobiles capable of HSCSD support will have to pay for the combined GSM time
slots being used.
Wireless carriers can achieve the migration to HSCSD by upgrading GSM Mobile Switching Center
(MSC) and Base Transceiver Station (BTS) software. Wireless carriers also have to distribute
handsets capable of receiving HSCSD transmission or firmware upgrades for the GSM mobiles
based on Personal Computer Memory Card International Association (PCMCIA) and CompactFlash
(CF) cards (such as those produced by Nokia). HSCSD can be supported within the existing GSM
mobility management infrastructure, which also enables roaming and other familiar GSM services at
higher data rates.
cdmaOne
Code Division Multiple Access (CDMA) IS-95—or cdmaOne—is one of the popular 2G technologies
being used in the Americas, Asia, and Eastern Europe. CDMA is based on the technique in which
each subscriber is assigned a unique code, also known as pseudorandom code that is used by the
system to distinguish that user from all other users transmitting simultaneously in the same
frequency band. CDMA belongs to the class of systems called spread spectrum systems, and more
specifically to the Direct Sequence Spread Spectrum (DSSS) family. Physical channels in CDMA are
defined in terms of radio frequency of the carrier and a code—that is, a sequence of bits. The digital
signal resulting from the encoding of voice or data, after the application of appropriate framing (or
radio link layers), is digitally scrambled before it modulates the carrier frequency. This is
accomplished by digitally (base 2) adding the signal to the pseudorandom code that is used to
distinguish the user. The entire carrier spectrum is available to each single user, hence the
name spread spectrum.
The receiver, which has a pseudorandom signal decoder, reproduces the original signal by
demodulating the RF and adding (base 2) the same pseudorandom signal used by the transmitter,
thus obtaining the original signal. CDMA is an interference-limited system, meaning that anytime a
user is not transmitting and thereby not interfering with other users sharing the same spectrum, the
effective bandwidth, and hence signal-to-noise ratio, available to other users will increase to some
degree. CDMA properties are as follows:
 Multiple voice channels are available for each radio channel.
 To prevent interference, callers are assigned to different radio frequency channels (or, if
sharing a radio channel, different pseudorandom codes).
 The same radio channel can be used in adjacent cells.
 The number of calls in a sector is "soft" limited, not hard limited.
 Bandwidth usage influences the number of simultaneous users.
To better visualize the CDMA concept, imagine a room filled with pairs of people talking to each
other, each couple in their own language. They would only be able to understand their counterparts

6. but not the rest of the conversations in the room. As the number of pairs with unique language
increases, the noise level will reach its maximum, after which no conversations will be possible (not
unlike in some trendy restaurants and pubs).
The CDMA cellular technology also comes with soft handoff capability— that is, the system specifies
a receiver (RAKE receiver) capable of receiving up to three signals related to the same channel,
because of multipath effects or to multiple sources transmitting the same signal. The system allows
the mobile station to send and receive simultaneously with three base stations, which are defined as
belonging to the "active set" of base stations. This allows for the avoidance of handoff Ping-Pong
effects and also allows for improved performance against multipath or adverse radio conditions.
CDMA was originally deployed under the commercial name cdmaOne based on TIA [IS95], a
mobile-to-base-station compatibility standard for wideband spread-spectrum systems. It is a direct
sequence CDMA scheme in which users are differentiated by unique codes known to both
transmitter and receiver. The IS-95A version of the standard allows for circuit-switched data service
up to 14.4 Kbps. The next generation of IS-95, called IS-95B, requires software and hardware
change in CDMA system elements and mobile stations but will support packet data at a sustained bit
rate of 64 to 115 Kbps. This is achieved mostly through the use of advanced channel and code
aggregation techniques and other modifications to IS-95A. In IS-95B, up to eight CDMA traffic
channels can be aggregated for use by a single subscriber—not unlike HSCSD used in GSM.
2G network allows for much greater penetration intensity. 2G technologies
enabled the various mobile phone networks to provide the services such as
text messages, picture messages and MMS (multi media messages). 2G
technology is more efficient. 2G technology holds sufficient security for both
the sender and the receiver. All text messages are digitally encrypted. This
digital encryption allows for the transfer of data in such a way that only the
intended receiver can receive and read it.
2G Technologies (Second Generation Technologies)
Second generation technologies are either time division multiple access
(TDMA) or code division multiple access (CDMA). TDMA allows for the
division of signal into time slots. CDMA allocates each user a special code to
communicate over a multiplex physical channel. Different TDMA technologies
are GSM, PDC, iDEN, iS-136.CDMA technology is IS-95. GSM has its origin
from the Group special Mobile, in Europe. GSM (Global system for mobile
communication) is the most admired standard of all the mobile technologies.
Although this technology originates from the Europe, but now it is used in
more than 212 countries in the world. GSM technology was the first one to
help establish international roaming. This enabled the mobile subscribers to
use their mobile phone connections in many different countries of the world’s
is based on digital signals ,unlike 1G technologies which were used to
transfer analogue signals. GSM has enabled the users to make use of the
short message services (SMS) to any mobile network at any time. SMS is a
cheap and easy way to send a message to anyone, other than the voice call

7. or conference. This technology is beneficial to both the network operators
and the ultimate users at the same time.
Another use of this technology is the availability of international emergency
numbers, which can be used by international users anytime without having
to know the local emergency numbers. PDC or personal digital cellular
technology was developed in Japan, and is exclusively used in JAPAN as well.
PDC uses 25 KHz frequency. Docomo launched its first digital service of PDC
in 1993.integrated digital enhanced network (iDEN) was developed by
MOTOROLA, as a major mobile technology. It enabled the mobile users to
make use of complex trunked radio and mobile phones. iDEN has a
frequency of about 25Khz.i DEN allows three or six user per mobile
channel.iS-136 is a second generation cellular phone system. It is also
known as digital AMPS. D-AMPS were widely popular in America and Canada.
However now it is in the declining phase. This technology is facing a strong
competition by GSM technologies. Now the network carriers have adopted
GSM and other CDMA 2000 technologies at large. Interim standard 95 is a
first and the foremost CDMA cellular technology. It is most famous by its
brand name known as cdmaOne. It makes use of the CDMA to transfer the
voice signals and data signals from cellular phones to cell sites (cell sites is
cellular network).
Benefits of 2G technology (Second Generation)
Digital signals require consume less battery power, so it helps mobile
batteries to last long. Digital coding improves the voice clarity and reduces
noise in the line. Digital signals are considered environment friendly. The use
of digital data service assists mobile network operators to introduce short
message service over the cellular phones. Digital encryption has provided
secrecy and safety to the data and voice calls. The use of 2G technology
requires strong digital signals to help mobile phones work. If there is no
network coverage in any specific area, digital signals would be weak.
What Is 2G Technology?
2G is shortfor second-generation wireless telephone technology.The prime aim ofthis article is to answer whatis 2g
technologyand give our visitors a true explanation of 2g technology. Read on to know more.
2g technologies are based on whattype of multiplexing is employed,for instance,the procedure of merging multiple
digital data streams into one signal.Classified bywhether they are based on time division multiple access (TDMA) or
code division multiple access (CDMA), the 2G standards mayinclude the following:Integrated Digital Enhanced
Network (IDEN) or Global System for Mobile communications (GSM), used worldwide.Digital Advanced Mobile
Phone System (D-AMPS) is used in North and South America, while Personal Digital Cellular (PDC) is used in Japan.

8. 2G telecom networks were commerciallylaunched in 1991 on the GSM standard in Finland.The 2G systems were
found to be considerablymore efficienton the spectrum,allowing far greater mobile phone penetration levels.
Moreover, the phone conversations were digitallyencrypted.
Getting on with the meaning of2g technology, 2G makes use ofa CODEC or compression-decompression algorithm
for compressing and to multiplexdigital voice data. Using this technology,it is possible for a 2G network to bundle
more calls per amountofbandwidth.As the data is transmitted through digital signals,2Galso offers extra services
such as SMS and e-mail.Moreover the battery lasts longer due to the lower-powered radio signals.Digital voice
encoding,offering a feature of error checking,also improves the sound qualityby reducing dynamic and lowering the
noise floor.
Although 2g technologies have much more benefits to offer over its predecessors,ithas a few disadvantages as well.
The 2G's digital signals are very dependenton location and proximity. A call made from far away may not allow the
digital signal to be strong enough to reach it. Moreover, the digital signals used in 2g technologies have a jagged,
angular curve, which can fail completelyunder unsuitable conditions