By- Abhishek sinha

Introduction to CDMA & GSMMobile Communication

( E&C Engg.) Email- aksinha246@gmail.com

It all started like this

Contents:-• History• Generations• CDMA• TDMA• FDMA• GSM- TDMA+FDMA• What is cellular ?• Cellular principles• GSM Conclusion.

CDMA History:-• CDMA is based around a form of transmission known as Direct Sequence

Spread Spectrum.• The CDMA history can be directly linked back to the 1940s when this form

of transmission was first envisaged.• it is difficult to decipher without the knowledge of the right codes• The first CDMA system was launched in September 1995 by Hutchison

Telephone Co. Ltd. in Hong Kong• And SK Telecom in Korea soon followed along with networks in the USA.• This was only one cellular telecommunications system, although it was the

first. Its development lead on to the CDMA2000 series of standards.• Multiple access: - The use of the spreading codes which are independent

for each user along with synchronous reception allow multiple users to access the same channel simultaneously.

GSM History:-• 1982- Group Special Mobile (GSM) is formed by the (CEPT)

to design a pan-European mobile technology.• CEPT -Confederation of European Posts and

Telecommunications• 1984-France & Germany sign a joint development

agreement for GSM.• 1986-EU Heads of State endorse the GSM project. • The European Commission initiatitive proposes to reserve

900MHz spectrum band for GSM.• agreed in the EC Telecommunications Council.• 1987-Basic parameters of the GSM standard agreed in

February.

GSM History:-

• 1988-Completion of first set of detailed GSM specifications for infrastructure tendering purposes.

• 1990-GSM adaptation work started for the DCS1800 band.

• 1991-First GSM call made by Radiolinja in Finland.

GSM History:-

• 1992-First international roaming agreement signed between Telecom Finland and Vodafone (UK).

• 1992-First SMS sent.• 1996-First GSM networks in Russia and China

go live.• 1996-Pre-paid GSM SIM cards launched.• And now a days……………

Generations of mobile:-

1st generation (1-G) :-• 1979-80 (America)• AMPS- Advance mobile phone service• TCS- Total communnication system• NMI- Nordic mobile telephony• Nature of the system was Analog

2nd generation (2-G) :-• In 1990s • DAMPS- Digital advance mobile phone service• GSM- Global system for mobile communication• CDMA- Code division multiple access• Digital in nature• Technology used TDMA+FDMA• TDMA- Time division multiple access• FDMA- Frequency division multiple access

3rd generation (3-G) :-• WLL- Wireless in local loop• Technology used is, “CDMA”

Information

>0 Seperation code (DIGITAL)• Data speed will increase and go for 144 kbps to 384 kbps

>0>0>0>0>0>0>0>0>0>0>0>0………..………………….>0>0>0>0>0>0>0>0…………….

CDMA:- • CDMA- Code division multiple access• CDMA is green mobile• Used in 3-G & WLL• All information of the customers are on the same

frequency/seperation.• Each information is seperated by a digital code• Digital codes separate one information to another

to avoid interference of call/talk.

CDMA:- • The technology employed shall depend upon various radio access techniques,

like FDMA, TDMA and CDMA• Frequency of operation: 824-849Mhz and 869-894 Mhz• Duplexing Mehtod: Frequency Division Duplexing (FDD)• Access Channel per carrier: Maximum 61 Channels• RF Spacing: 1.25 Mhz• Coverage: 5 Km with hand held telephones and approx. • 20 Km with fixed units

• The various technological options available are as follows :- 1. Multi Access Radio Relay 2. Wireless In Local Loop 3. Fibre In the Local Loop

CDMA:-

• WLL - wireless in local loop:-• Fixed Wireless telephony in the subscriber access network also known

as (WLL)

• WLL is generally used as “the last mile solution” to deliver basic phone service

• It is also used in remote areas• The technology employed shall depend upon various radio

access techniques, like FDMA, TDMA and CDMA

CDMA:-

• WLL:-

BTS BSC MSC• BTS, BSC & MSC are the Units of mobile

Units of mobile:-Units of mobile:-1. BTS- Base transceiver station

BTS

Base transceiver station

• A base transceiver station (BTS) is a piece of equipment that facilitates wireless communication between user equipment (UE) and a network.

Trans + Receiver

Transceiver

BTS:-• BTS is also known as CELL• Its size and shape are hexagonal• BTS range upto 35 km Max. QUES- WHAT IS CELL ?ANS- Cell is unit• In Battery, cell is made up of carbon which generate

radiation in mobile phone/cell phone. CELL PHONE- Area covered by a BTS is called cell And the

device which is used in communication between a cell is known as Cell phone.

2. BSC:-

• BSC- Base station controller

BSC• A base station controller (BSC) is a critical mobile network component that

controls one or more base transceiver stations (BTS),• also known as base stations or cell sites • Key BSC functions include radio network management (such as radio

frequency control), BTS handover management and call setup.

3. MSC:-

• MSC- Mobile switching center

MSC

• Mobile-services Switching Center (MSC) performs the switching functions for all mobile stations located in the geographic area

MSC:- Functions of the MSC include:- • Call handling that copes with mobile nature of subscribers (e.g., paging)• Management of required logical radio-link channel during calls• Management of MSC-BSS signalling protocol• Handling location registration and ensuring interworking between

Mobile Station and VLR• Control of inter-BSS and inter-MSC handovers• Acting as a gateway MSC to interrogate the HLR• Exchange of signalling information with other system entities• Standard functions of a local exchange switch in the fixed network

(example: charging)

Connections :-

BSC

BTS

BTSBTS

BTS

OFC

OFC

OFC OFC

Connections :-• BTS are connected with BSC• BSC is the controller of BTS• Each BSC will be connected with the MSC

• MSC- Mobile switching center• It is a responsible center for setting of a cell• When this all connected with optical fibre cable

(OFC) it will be becomes GSM Exchange.

Connections :-

TDMA:-• Time Division Multiple Access• Each channel is divided into timeslots, each conversation uses

one timeslot.• Many conversations are multiplexed into a single channel. • In a TDMA system each channel is split up into time segments• And a transmitter is given exclusive use of one or more

channels only during a particular time period. • Shares single carrier frequency with multiple users• Higher synchronization overhead than CDMA• Used in GSM

FDMA:-• FDMA- Frequency Division Multiple Access• FDMA is a familiar method of allocating bandwidth• FDMA can be used with both analog and digital signal• FDMA requires high-performing filters in the radio

hardware, in contrast to TDMA and CDMA.• Used in GSM• where a base station is allowed to transmit on one or more

number of preassigned carrier frequencies• and a mobile unit transmits on corresponding reverse

channels.

GSM:-• GSM- Global system for mobile communication• The GSM network is called Public Land Mobile Network (PLMN)

• It is organised in three subsystems: - 1. Base Station Subsystem (BSS) 2. Network Switching Subsystem (NSS) 3. Network Management Subsystem (NMS)

GSM:-

DWDM DWDM (BHOPAL) (DELHI) •DWDM- Dense wavelength division multiplexer

DDWWDDMM

OFC DDWWDDMM

GSM Overview

GSM Architecture

GSM Architecture:-• HLR- Home location registers• The Home Location Register (HLR) contains the identities of mobile subscribers

(called International Mobile Subscriber Identities or IMSIs)– Main customer database– It is a subscriber data unit and it it is responsible

In summary, the HLR contains:-• Identity of mobile subscriber• ISDN directory number of mobile station• Subscription information on teleservices and bearer services• Service restrictions (if any)• Supplementary services• Location information for call routing

GSM Architecture:-Vlr- visitor location registers• The Visitor Location Register (VLR) contains the subscriber parameters and

location • information for all mobile subscribers currently located in the geographical area

(i.e., cells) controlled by that VLR.• It is a private secretary of HLR and it define the Roaming of mobile In summary, the VLR contains:-• Identity of mobile subscriber• Any temporary mobile subscriber identity• ISDN directory number of mobile• A directory number to route calls to a roaming station• Location area where the mobile station is registered• Copy of (part of) the subscriber data from the HLR

GSM Architecture:-

• EIR- Equipment identity registers• The Equipment Identity Register (EIR) is accessed during the equipment

validation procedure when a mobile station accesses the system.• It contains the identity of mobile station equipment (called International

Mobile Station Equipment Identity or IMEI)

This contains:• White or Valid list - List of valid MS equipment identities• Grey or Monitored list - List of suspected mobiles under observation• Black or prohibited list - List of mobiles for which service is barred.

GSM Architecture:-

AUC- Authentication centre• Stores encryption keys necessary for secure

communications• Contains subscriber authentication data called

Authentication Keys (Ki)• Generates security related parameters needed to

authorize service using Ki• Generates unique data pattern called a Cipher Key

(Kc) needed for encrypting user speech and data

GSM Architecture:-

At a time 128 BTS can be connected with a BSC

• BSS means Base Station Subsystem • LINK- When two or more different thing are

connected with each other is known as “link”

BSS:-

• BSS:- Base station subsystem

BTS + BSC

BSS

BSS:- • The Base Station Subsystem is responsible for managing the

radio network• and it is controlled by an MSC The BSS consists of the following elements: -• • BSC Base Station Controller • • BTS Base Transceiver Station • • TRAU Transcoder and Rate Adaptation Unit (often referred

to as TC (Transcoder)

LINK:-

•Mobile to BTS BTS to Mobile•FRQ- 824-849 mhz FRQ- 869-889 mhz•Frequency never penetrate any solid body. It expand as like baloon.

link

Up link Dwn link

GSM Architecture:-

• SIM – Subscriber Identity Module.– Allows you to switch phones.– Stores your phonebook and

ringtones.• ME – Mobile Equipment.

– Your cellphone• UM – User Mobile Frequency– The actual radio frequency you

are using.

GSM Architecture:-

• BTS – Base Transceiver Stations.– The radio antennas.– In GSM, 1 sends and 1 receives.

• Only 2 are necessary.• BSC – Base Station Controller.

– Packages up all the radio signals and sends them to the switch.

– Handles handoffs and some other low-level functionality.

– Manages up to 50 or so radio antennas• Provides better network segmentation.

• Abis – Typically a T1 SS7 connection using ISUP

GSM Architecture:-

RF/RT:-• RF/RT- Radio frequencies OR Terminals It works as a carrier to carry our voice or data.• Radio frequency is always be in BTS• The mobile journey is start from the BTS• One RF have only 8 slot

1 2 3 4 5 6 7 8

SLOT

Radio Frequencies:-

• Operates in the 1850 MHz band and from:-– 1850 to 1910 MHz Mobile to Base– 1930 – 1990 MHz Base to Mobile

• There are 300 forward/reverse channels in this band.

• Each channel is 200 KHz• GSM uses TDMA to fit 8 conversations on a

channel.• So, technically, GSM is TDMA and FDMA

based.

Speech Coding:-

• GSM uses LPC – Linear Predictive Coding.– Uses interpolation.– Basically, previous samples, which don’t change very

quickly, are used to predict current samples.• So, instead of actually sending the voice sample, the

delta in the voice sample is sent.• Also, silence is not transmitted.– This increases throughput by about 40%.– This bits can be used for other conversations.

Power Requirements:-

• Since GSM is purely digital • It requires a lot less power since it doesn’t

have to transmit an analog wave.• The maximum output power of a GSM phone

is only 2 watts.– And this can be notched down by the controlling

cell phone tower.– The minimum power is only 20 mW.

Difference B/W CDMA & GSM:-

CDMA GSM• More reliable • Less reliable

• Code division • Time & Frequency division

• More comfortable • Less comfortable

• Maintenance cost less • Maintenance cost more

• Reused factor • No reused factor

But what’s cellular ?

HLR, VLR, AC, EIR

MSC

PSTN

BTS B S

• Public Switched Telephone Network

Cellular principles:-Cellular principles:-

• Frequency reuse – same frequency in many cell sites• Cellular expansion – easy to add new cells • Handover – moving between cells• Roaming between networks

GSM conclusion:-• Widely used.– Upwards of 70% of phones.

• Uses SIM cards so customers can use any phone and for security.

• Allows more customers than analog.• Worse voice quality than analog.• Purely digital.• Open source, very complex standard.• Uses TDMA & FDMA.

Presented By

ABHISHEK SINHA THANKS A LOT.