This ppt includes topics related to telecom technologies such as PCM, CDMA and GSM technologies. It introduces the topics and their subdivisions .

1. PRESENTATION ON :
• PULSE CODE MODULATION
• MULTIPLE ACCESS TECHNIQUES
• GSM

2. MOBILE COMMUNICATIONS

3. Mobile phones send and receive radio signals with any number
of cell site base stations fitted with microwave antennas. These
sites are usually mounted on a tower, pole or building, located
throughout populated areas, then connected to a cabled
communication network and switching system. The phones have
a low-power transceiver that transmits voice and data to the
nearest cell sites, normally not more than 8 to 13 km
(approximately 5 to 8 miles) away. When the mobile phone or
data device is turned on, it registers with the mobile telephone
exchange, or switch, with its unique identifiers, and can then be
alerted by the mobile switch when there is an incoming
telephone call
MOBIE COMMUNICATIONS
:

4. Pulse code modulation
Analog voice data must be translated into a series of binary digits
before they can be transmitted.
With Pulse Code Modulation (PCM), the amplitude of the sound
wave is sampled at regular intervals and translated into a binary
number.
The difference between the original analog signal and the
translated digital signal is called quantizing error.
PCM uses a sampling rate of 8000 samples per
second and each sample is an 8 bit sample resulting in a digital
rate of 64,000 bps (8 x 8000).

5. Steps involved in converting a analog signal to digital sig
PCM consists of four steps to digitize an analog signal:
1. Filtering
2. Sampling
3. Quantization
4. Binary encoding

6. SPECFICATIONS OF PCM :
• Voice Frequency range 0- 4 KHz
• Sampling the Voice Signal @ 8 KHz
(Double the Max. Frequency as per sampling theorem) i.e.
8000s/sec
• Sampling time period Ts=1sec/8000
• Ts= 125 microsecond
• Available for sampling each channel, when we have N
total channels=125/N
• In PCM, Time frame=125microsec ;time available per
chl=125/32 =3.9microsec.

7. MULTIPLE ACCESS TECHNIQUES
A cellular system divides any given area into cells where a
mobile unit in each cell communicates with a base station.
The main aim in the cellular system design is to be able to
increase the capacity of the channel i.e. to handle as many
calls as possible in a given bandwidth with a sufficient level of
quality of service. There are several different ways to allow
access to the channel. These includes mainly the following:
1) Frequency division multiple-access (FDMA)
2) Time division multiple-access (TDMA)
3) Code division multiple-access (CDMA)

8. FREQUENCY DIVISION MULTIPLE ACCESS
(FDMA) :
This was the initial multiple-access
technique for cellular systems in which
each individual user is assigned a pair of
frequencies while making or receiving a
call.

9. TIME DIVISION MULTIPLE ACCESS (TDMA)
:Time division multiple access (TDMA) is
a channel access method for shared
medium networks. It allows several users to
share the same frequency channel by
dividing the signal into different time slots.
The users transmit in rapid succession, one
after the other, each using its own time slot.

10. CODE DIVISION MULTIPLE ACCESS
(CDMA) :
CDMA is a “spread spectrum” technology,
which means that it spreads the information
contained in a particular signal of interest over
a much greater bandwidth than the original
signal.

11. CDMA systems offer services to wide band and narrow band
systems. Wide band systems supports conventional cellular
voice, text and MMS services, but can also carry data at high
speeds, allowing mobile operators to deliver higher
bandwidth applications including streaming and broadband
Internet access.

13. • Multiple Access in CDMA:
o Each user is assigned a unique PN code.
o Each user transmits its information by spreading with
unique code.
o Direct Sequence spread spectrum is used.
o Users are separated by code not by time slot and freq slot.

14. GSM
GSM is the GLOBAL SYSTEM FOR
MOBILE COMMUNICATIONS. It is a cellular network in which the
mobiles are connected to it by searching for cells in the immediate
vicinity.
The GSM system was designed as
a second generation (2G) cellular phone technology. One of the
basic aims was to provide a system that would enable greater
capacity to be achieved than the previous first generation
analogue systems. GSM achieved this by using a digital TDMA
(time division multiple access approach). By adopting this
technique more users could be accommodated within the
available bandwidth.

15. GSM ARCHITECURE

16. The main components of a GSM system are:
1.Mobile Station (MS)
2.Base Station Subsystem (BSS)
3.Network Switching Subsystem(NSS)
MOBILE STATION :
A Mobile Station consists of two main elements:
 The mobile equipment or terminal.
 The Subscriber Identity Module (SIM).

17. Base Station Subsystem (BSS) :
The BSS connects the Mobile
Station and the NSS. It is in charge of the transmission and
reception. The BSS can be divided into two parts:
•The Base Transceiver Station (BTS) or Base Station.
•The Base Station Controller (BSC).
BASE STATION SUBSYSTEM

18. BSC
BTS

19. The network switching subsystem has the following five
important components.
• Mobile Switching Center (MSC)
• Home Location Register (HLR)
• Visitor Location Register (VLR)
• Authentication Center (AUC)
• Equipment Identity Register (EIR)
Network Switching Subsystem(NSS) :
NSS
MSC

20. HLR
AUC

21. SERVICES PROVIDED BY GSM:
Speech or voice calls are obviously the primary function for
the GSM cellular system. To achieve this the speech is
digitally encoded and later decoded using a vocoder.
Besides speech and voice calls, GSM supports different
services like :
1. SMS
2. Voice Mail
3. Advice of Charge
4. Roaming
5. Call hold
6. Call waiting
7. Conference call

22. ADVANTAGES OF GSM :
1. Less signal deterioration inside buildings.
2. Ability to use repeaters.
3. Talk time is generally higher in GSM phones due to the
pulse nature of transmission.
4 .The availability of SIM allows users to switch networks
and handsets at will, aside from a subsidy lock.
5. GSM covers virtually all parts of the world so
international roaming is not a problem.
6. The much bigger number of subscribers globally creates
a better network effect for GSM handset makers, carriers and end
users.

23. CONCLUSION :
The communication development and the increase of living standard
of people are directly related to the more use of cellular mobile
radio- the high end sophisticated technology enables everyone to
communicate anywhere with anybody. The mobile telephony
industry is rapidly growing and that has become back bone for
business success and efficiency and the part of modern life style all
over the world. The features and benefits in the GSM systems are
superior speech quality, low terminal, operational and service costs,
a high level security and providing of international roaming support.
CDMA is radically new concept in wireless communication. It has
gained wide spread international acceptance by cellular radio
system operators as an upgrade that will dramatically increase both
their system capacity and the quality.