CELLULAR CONCEPTS

By

Syed Mohammed Abrar

III Year-ECE-MEC.

Transmitting/receiving voice and data using electromagnetic waves in open space.

The information from sender to receiver is carried over a well defined frequency band(channel).

Each channel has a fixed frequency bandwidth & capacity(bit rate).

Different channels can be used to transmit information in parallel and independently.

Transmitting signalReceived signal

satellite

Transmitting antenna

Receivingantenna

FM RADIO 88 MHZ

TV BROADCAST 200 MHZ

GSM PHONES 900 MHZ

GPS 1.2 GHZ

PCS PHONES 1.8 GHZ

BLUETOOTH 2.4 GHZ

Wi-Fi 2.4 GHZ

Freedom from wires.

No bunch of wires running from here and there.

“Auto Magical” instantaneous communication without physical connection setup e.g.- Bluetooth, Wi-Fi.

Global coverage

Communication can reach where wiring is infeasible or costly

e.g.- rural areas,buildings,battlefield,outerspace.

Stay connected,flexiblity to connect multiple devices.

RADIO TRANSMISSION:- easily generated, Omni-directional , travel long distance , easily penetrates buildings.

PROBLEMS:- frequency dependent , relatively low bandwidth for data communication , tightly licensed by government.

MICROWAVE TRANSMISSION:- widely used for long distance communication , give high S/N ratio , relatively inexpensive.

PROBLEMS:- don’t pass through buildings , whether and frequency dependent.

INFRARED AND MILIMETER WAVES:-

widely used for short range communication , unable to pass through solid objects , used for indoor wireless LANs , not for outdoors.

LIGHT WAVE TRANSMISSION:- unguided optical signal such as laser , unidirectional , easy to install , no license required.

PROBLEMS:- unable to penetrate rain or thick fog , laser beam can be easily diverted by air.

CELLULAR SYSTEM

WIRELESS LANs

SATELLITE SYSTEM

PAGING SYSTEM

PANs(BLUETOOTH)

Definition

Wireless communication technology in which several small exchanges (called cells) equipped with low-power radio antennas (strategically located over a wide geographical area) are interconnected through a central exchange. As a receiver (cell phone) moves from one place to the next, its identity, location, and radio frequency is handed-overby one cell to another without interrupting a call.

Practical

High capacity is achieved by limiting the coverage of each base station to a small geographic region called a cell.

Same frequencies timeslots/codes are reused by spatially separated base stations.

A switching technique called handoff enables a call to proceed uninterrupted when one user moves from one cell to another.

Neighboring base stations are assigned different group of channels so as to minimize the interference.

By systematically spacing base stations and the channel groups may be reuse as many number of times as necessary.

MSC

CELLS

PSTN

SUBSCRIBER UNIT

BASE STATIONS

Coverage area

BSC

BS1

BS2BS3

Connect to Bs1 & start calling

Out of BS1 coverage & connect to BS2

Out of BS2 coverage & connect to BS3

Call ended

Cellular radio systems rely on intelligent allocation and reuse of channels throughout the coverage area.

Each base station is allocated a group of radio channels to be used within the same geographical area of its cell.

Neighboring base stations are given different channel allocation from each other.

The design procedure of allocating channel groups for all of the cellular BS within a system is called frequency reuse or frequency planning.

Co channel cells

Co channel cells

Co channels

60 degree

u

v

D

Axes u and v intersect at 60 degree.

Unit scale is the distance between center cells.

If cell radius to point of hexagon is R then 2Rcos30=1

Or R = 1/√3. to find the distance of a point P(u , v) from the origin we use x-y to u-v coordinate transformation.

R² = x² + y²

x=ucos30˚

y=u+vsin30˚

r=√(v²+uv+u²)

Using this equation to locate co-channel cells we start from reference cell and moves i hexagon along u axis then j hexagon along the v axis.

Hence the distance between co-channel cells in

adjacent cluster is given by D = √(i²+ij+j²)

The number of cells in a cluster N is given by

N = √(i²+ij+j²) where i and j are integers.

Hence the possible values of N are 1 , 3 , 4 , 7 , 12……

Formation of cluster for N=7

Suppose i=2 and j=1 will give co channel cell

Same color showing co-channel cells.

i=2

j-=1

Co channel cells

Global system for mobile communication is a set of ETSI standards specifying the infrastructure for a digital cellular services.

GSM networks are structured hierarchically it consist of one administrative region which is assigned to a MSC.

Each administrative region is made up of at least one location area (LA). LA is also called the visited area.

An LA consists of several cell groups.

Each cell group is assigned to a base station controller (BSC)

GSM NETWORK

MSC REGION

LOCATION AREA (LA)

BS CONTROLLER

CELL CELL

LA

LA

BS CONTROLLER

BS CONTR-OLLER

MSC REGION

MSC REGION

BSC

MSCEIR

AUCHLR VLR

ISDN

PSTN

OTHER NETWORKSBSS

NSS NMS

Mobile station

Consist of two main elements.

1. The mobile equipment

2. Subscriber identity module(SIM).

BSS = BSC + BTS

1. RADIO PATH CONTROL

2. AIR INTERFACE SIGNALLING

1. CENTRAL N/W ELEMENT OF BSS

2. CALL ESTABLISHMENT

3. MOBILITY MGMT

4. STATISTICAL RAW DATA COLLECTION

1. SPEECH PROCESSING

2. MODULATION/DEMODULATION

3. TRANSCODER

4. MINIMIZE TRANSMISSION PROBLEM

5. AIR INTERFACE MANAGEMENT

NSS = MSC + HLR + VLR + AUC + EIR

MANAGECOMMUNICATION B/W USERS

INCLUDEDATABASE TO

STORE INFORMATION OF USER

CALL CONTROL

MOBILITYMGMT

SUBSCRIBERDATA HANDLING

CHECK IDENTITY OF USER

PERMANENT STORAGE OF USER INFORMATION

STORE A COPY OF HLR

CHECK ROAMING

PROVIDE AUTHENTICATION

SECURITY

CHECK IMEI NUMBER OF MOBILE

1. MONITORING

2. MANAGE

3. OPERATION

4. MAINTANENCE

NMS

USE TDMA + FDMA

MODULATION USED = GMSK(Gaussian minimum shift keying)

UPLINK FREQUENCY = 890 – 915 MHZ

DOWNLINK FREQUENCY = 935 – 960 MHZ

WLAN connect local computers

Range (100 m) confined region

Break data into packets

Channel access is shared

Backbone internet provides best service

Poor performance in some application like videos

Low mobility

Global coverage

Different orbit height

Optimized for good transmission

Expensive base stations.

Voice and data transmission

Telecommunication application

GPS , global telephone connection

TV broadcasting , military , whether broadcasting

Broad coverage for short messages

Message broadcast from all base stations

Simple terminals

Optimized for one way transmission

Answer back hard

Overtaken by cellular

Pager system

PSTNPaging control center

Paging terminal

Paging terminal

Paging terminal

Terrestrial link

Terrestrial link

Satellite link

City 1

City 2

City N

Base station

Base station

Base station

Bluetooth

Cable replacement RF technology

Short range(10m)

2.4 GHz band

TDD duplex scheme

1 Mbps data rate shared b/w 7 devices

Polling based multiple access

Work on frequency hopping spread spectrum technology

Peer to peer communication

No backbone infrastructure

Routing can be multihop

Topology is dynamic

Fully connected with different link SINRs.

Ad-hoc network provides a flexible network infrastructure for many emerging applications.

The capacity of such networks is generally unknown.

Transmission , access and routing strategies for these networks are generally ad-hoc.

Cross layer design is very critical and challenging.

Energy constraints impose interesting design for trade offs communication and networking.