Wireless Communications

Cellular Network
• A cellular network or mobile network is a communication network
where the last link is wireless
• Base stations transmit to and receive from mobiles at the assigned
spectrum
– Multiple base stations use the same spectrum (spectral reuse)
• The service area of each base station is called a cell
• Each mobile terminal is typically served by the ‘closest’ base stations
– Handoff when terminals move

Frequency reuse
The key characteristic of a cellular network is the ability to re-use
frequencies
• Increase both coverage and capacity
• adjacent cells must use different frequencies,
• The elements that determine frequency reuse are the reuse
distance and the reuse factor.
The reuse distance, D is calculated as
• D=R√3N
where R is the cell radius and N is the number of cells per cluster
3

The Multiple Access Problem
• The base stations need to serve many mobile
terminals at the same time (both downlink
and uplink)
• All mobiles in the cell need to transmit to the
base station
• Interference among different senders and
receivers
• So we need multiple access scheme

Multiple Access Schemes
• Frequency Division Multiple Access (FDMA)
• Time Division Multiple Access (TDMA)
• Code Division Multiple Access (CDMA)
3 orthogonal Schemes:

Cellular Network Generations
• It is useful to think of cellular Network/telephony in
terms of generations:
– 0G: Briefcase-size mobile radio telephones
– 1G: Analog cellular telephony
– 2G: Digital cellular telephony
– 3G: High-speed digital cellular telephony (including video
telephony)
– 4G: “anytime, anywhere” voice, data, and multimedia
telephony at faster data rates than 3G

2 G, The Second Generation
• Second generation 2G cellular telecom networks were
commercially launched on the (global system for mobile
communications ) GSM standard in Finland
• Widely used in 90’s-2000
• allows multiple users on a single channel.
• Supports voice as well as data.
• radio signals on 2G networks are digital, which can be
compressed and multiplexed easily.
• 2G technologies can be divided into TDMA-based and CDMA-
based standards depending on the type of multiplexing used.
• Speed 9.6 Kbps .
• Carrier frequency is of 200 KHz.
7

GSM Services
• Voice, 3.1 kHz
• Short Message Service (SMS)
– 1985 GSM standard that allows messages of at most 160 chars. (incl.
spaces) to be sent between handsets and other stations
– Over 2.4 billion people use it; multi-billion $ industry
• General Packet Radio Service (GPRS)
– GSM upgrade that provides IP-based packet data transmission up to
114 kbps
– Users can “simultaneously” make calls and send data
– GPRS provides “always on” Internet access and the Multimedia
Messaging Service (MMS) whereby users can send rich text, audio,
video messages to each other
– Performance degrades as number of users increase
– GPRS is an example of 2.5G telephony

GSM Channels
• Physical Channel: Each timeslot on a carrier is referred to as a
physical channel
• Logical Channel: Variety of information is transmitted between the
Mobile Station (MS) and Base Transverse system (BTS). Different
types of logical channels:
– Traffic channel
– Control Channel
Downlink
Uplink
Channels

GSM Architecture
Public
Switched
Telephone
Network

Mobile Station (MS)
• MS is the user’s handset and has two parts
• Mobile Equipment
– Radio equipment
– User interface
– Processing capability and memory required for various
tasks
• Call signalling
• Encryption
• SMS
– Equipment IMEI number
• SIM
International Mobile Equipment Identity
Subscriber Identity Module

Base Station Subsystem
• Base Station Controller (BSC)
– Controls the channel (time slot) allocation
implemented by the BTSes
– Manages the handovers
– Knows which mobile stations are within the cell and
provide information as required
• Base Transceiver System (BTS)
– Controls several transmitters
– Each transmitter has 8 time slots, some used for
signaling, on a specific frequency

Network and Switching Subsystem
• The backbone of a GSM network is a telephone network with
additional cellular network capabilities
• Mobile Switching Center (MSC)
– An typical telephony exchange, Integrated Services Digital Network
(ISDN exchange) which supports mobile communications
– Visitor Location Register (VLR):contains information about the
subscribers roaming within a mobile switching center's
• A database, part of the MSC
• Contains the location of the active Mobile Stations
• Home Location Register (HLR)
– Contain subscriber information, including authentication information
in Authentication Center (AuC)
• Equipment Identity Register (EIR)
– International Mobile Station Equipment Identity (IMEI) codes for e.g.,
blacklisting stolen phones
carries out call switching and mobility management functions

Home Location Register
• One database per operator
• Contains all the permanent subscriber information
– MSISDN (Mobile Subscriber ISDN number) is the telephone
number of the subscriber
– International Mobile Subscriber Identity (IMSI) is a 15 digit code
used to identify the subscriber
• It incorporates a country code and operator code
– IMSI code is used to link the MSISDN number to the subscriber’s
SIM (Subscriber Identity Module)
– Charging information
– Services available to the customer
• Also the subscriber’s present Location Area Code, which
refers to the MSC, which can connect to the MS.

Other Systems
• Operations Support System
– The management network for the whole GSM network
– Usually vendor dependent
– Very loosely specified in the GSM standards
• Value added services
– Voice mail
– Call forwarding
– Group calls
• Short Message Service Center
– Stores and forwards the SMS messages
– Like an E-mail server
– Required to operate the SMS services

Location Updates
• The cells overlap and usually a mobile station
can ‘see’ several transceivers (BTSes)
• The MS monitors the identifier for the BSC
controlling the cells
• When the mobile station reaches a new BSC’s
area, it requests an location update
• The update is forwarded to the MSC, entered
into the VLR, the old BSC is notified and an
acknowledgement is passed back

Handoff (Handover)
• When a call is in process, the changes in location
need special processing
• Within a BSS, the BSC, which knows the current
radio link configuration (including feedbacks from
the MS), prepares an available channel in the new
BTS
• The MS is told to switch over to the new BTS
• This is called a hard handoff
– In a soft handoff, the MS is connected to two BTSes
simultaneously

Roaming
• When a MS enters another operators network, it
can be allowed to use the services of this
operator
– Operator to operator agreements and contracts
– Higher billing
• The MS is identified by the information in the SIM
card and the identification request is forwarded
to the home operator
– The home HLR is updated to reflect the MS’s current
location

❑ 3G technology has taken the gaming to the next level.
❑ Real-time multiplayer gaming is possible in 3G system.
❑ Innovative new services are being added by developer daily.
 Came into picture during 2004-2005.
 High speed (2Mbps) and increased bandwidth.
 Carrier frequency is 5 MHz.

❑Not simply rebroadcast of TV or website
❑Enhanced existing service for mobile
environment.
❑Multi-faceted – 24*7 access to multiple
live streams , video , image & text content ,
voting , messaging.
❑User interaction on multiple levels.
❑Fully integrated in browser – one click access.

Also known as “Mobile Broadband Everywhere”
One of the terms used to describe 4G is:
Mobile Multimedia
Anytime Anywhere
Global mobility Support
Integrated wireless solution and
Customized personal service.

For the customer
❑ Video streaming , TV broadcast
❑ Video calls , video clips- news , music , sports
❑ Enhanced gaming , chat , location services…
For Business
❑ High speed Tele-working
❑ Sales force automation, is a technique of using software to automate the
business tasks of sales.
❑ Video conferencing
❑ Real-time financial information

Specifications 3G 4G
Frequency band 1.5- 2.8 GHz 2-8 GHz
Access CDMA Multi-carrier-CDMA or
OFDM(TDMA)
FEC, Forward Error
correction
Turbo codes concatenated codes
Switching Circuit/ Packet Packet
Top speeds 200kmph 200kmph

COMPARISON BETWEEN 3G Vs 4G
Technology 3G 4G
Data Transfer Rate 3.1 MB/sec 100 MB/sec
Internet Services Broadband Ultra Broadband
Mobile - TV Resolution Low High
Bandwidth 5-20 MHz 100MHz
Download and upload 5.8 Mbps 14 Mbps
The basic difference between 3G and 4G is in data transfer and signal
quality.

5G TECHNOLOGY
5G technology refer to short name of fifth Generation
Complete wireless communication
with almost no limitations.
It is highly supportable to WWWW
(Wireless World Wide Web).

COMPARISON BETWEEN 4G Vs 5G
The following basic differences between 4G and 5G are:

LTE (Long-Term Evolution)
• It is based on the GSM/EDGE and UMTS/HSPA network
technologies
• a registered trademark owned by ETSI (European
Telecommunications Standards Institute)
• goal of LTE was to increase the capacity and speed of
wireless data networks using new DSP (digital signal
processing)
• A further goal was the redesign and simplification of
the network architecture with significantly reduced
transfer latency compared to the 3G architecture.
28

LTE Features
• The LTE specification provides downlink peak
rates of 300 Mbit/s
• uplink peak rates of 75 Mbit/s
• QoS provisions permitting a transfer latency of
less than 5 ms in the radio access network.
• LTE has the ability to manage fast-moving mobiles
and supports multi-cast and broadcast streams
• supports seamless handovers for both voice and
data to cell towers with older network technology
29

Advantages of LTE

Comparison of LTE Speed

Major LTE Radio Technologies
• Uses Orthogonal Frequency Division
Multiplexing (OFDM) for downlink
• Uses Single Carrier Frequency Division
Multiple Access (SC-FDMA) for uplink
• Uses Multi-input Multi-output(MIMO) for
enhanced throughput
• Reduced power consumption
• Higher RF power amplifier efficiency (less
battery power used by handsets)

LTE-A
• Formally submitted as a candidate 4G system in late
2009, was approved into ITU, International
Telecommunications Union, and was finalized in March
2011.
• Data rate is expected as 2Gbps.
• It targets faster switching between power states and
improved performance at the cell edge.
• Improves the capacity and coverage, and ensures user
fairness.
• Also introduces multicarrier to be able to use ultra wide
bandwidth, up to 100 MHz of spectrum supporting very
high data rates.