Basics_of_Mobile_communication.ppt

I Unit Wireless
Communication
By,
C.Janani, AP / IT,
SSMCE
12/8/2022 Mobile Communication

Contents
• Cellular Systems
• Frequency Management and channel assignment
• Types of Handoffs and their characteristics
• Dropped call rates and their evaluation
• MAC
• SDMA
• FDMA
• TDMA
• CDMA
• Cellular Wireless Networks

Introduction
• Communication
• User Mobility
• Device Portability
• Characteristics of communication Devices:
Fixed & Wired
Mobile & Wired
Fixed & Wireless
Mobile & Wireless

Applications
• Vehicles
• Entertainments
• Media
• Networking
• Conversation
• Data Warehousing
• Hospitals
• Vending
• Retail

Mobile and wireless devices categories
• Sensors
• Embedded controllers
• Pager
• Mobile Phones
• PDA
• Pocket computer
• Notebook / Laptop

Evaluation of Cellular Communication
Ancient Day Communication

Alexander Grahambell
1843
Philip Reis
1861
Optical Transmission

Marconi (1874 - 1937)
Telegraphy
Electro magnetic transmission
World Administration Radio
Conference 1906 – Radio Frequencies Robert Von lieben & Lee Deforest

John Bardeen, William Shockley and Walter
Brattain at Bell Labs, 1948.

Sri Lankabhimanya
Sir Arthur C. Clarke

Shiv Ayyadurai (1963)

Cellular Systems

Channel Assignment

Frequency Management

Signals

Antennas
• Isotropic radiator
An isotropic radiator is a theoretical point source of electromagnetic
or sound waves which radiates the same intensity of radiation in all
directions. It has no preferred direction of radiation

• Directive antennas

• Dipole Antenna

• Omni Directional Antenna

• Directional Antenna

• Sectorized Antenna

• Multi Element Multi Array

Signal Propagation
• Transmission range
– communication possible
– low error rate
• Detection range
– detection of the signal
possible
– no communication
possible, high error rate
• Interference range
– signal may not be
detected
– signal adds to the
background noise
Sender
Transmission
Detection
Interference
Distance

• Propagation in free space always like light (straight line)
• Receiving power declines proportional to 1/d2 in vacuum
• (d = distance between sender and receiver)
• Receiving power in real environments additionally affected by
fading due to the atmosphere and large distances
 shadowing
 reflection at large obstacles
 refraction depending on the density of a medium
 scattering at small obstacles
 diffraction at edges
reflection scattering
diffraction

Multipath propagation
• Signals can take many different paths between
sender and receiver arriving at different times
with different signal strength at the receiver

HANDOFFS AND DROPPED
CALLS
Handoff
• Mobiles may move out of coverage area of a cell and into coverage area of
a different cell during a call
• MSC must identify new BS to handle call
– MSC must seamlessly transfer control of call to new BS
– MSC must assign call new forward and reverse channels within the channels of
new BS
• Some important performance metrics in handoff:
– Seamless – user should not know handoff occurring
– Minimum unnecessary Handoff due to short time fading
– Low probability of blocking new calls in the new cell
– Handoff to a good SNR channel so that an admitted call is not dropped

• Handoff Main Steps
1. Initiation
2. Resource reservation
3. Execution
4. Completion
• Important handoff parameter:
– SNRold to initiate handoff based on minimum acceptable quality
– SNRnew of the target channel (SNRnew > SNRold )
– D = SNRnew - SNRold dB
 If D too small, unnecessary handoffs occur
 If D too large, may be insufficient time to complete
handoff before SNRold becomes too weak and signal is
lost

Occurrence of handoff

Types of Handoff
A. Natures of handoff
1. Hard handoff
2. Soft handoff
B. Purposes of handoff
1. Intracell handoff:
2. Intercell handoff:
3. Inter BSC/MSC handoff:
4. Intersystem handoff:
5. Intercarrier handoffs:
6. Intermode handoff:
C. Algorithms of handoff
1. MCHO (Mobile Control Handoff)
2. NCHO (Network Control Handoff)
3. NCHO/MAHO (Network Control Handoff/Mobile Assists Handoff)

Soft Hand off and Hard Hand off

• Hard Handoff: Characterized by an actual break in
the connection while switching from one cell or base
station to another. The switch takes place so quickly
that it can hardly be noticed by the user. Because
only one channel is needed to serve a system
designed for hard handoffs, it is the more affordable
option. It is also sufficient for services that can allow
slight delays, such as mobile broadband Internet.
• Soft Handoff: Entails two connections to the cell
phone from two different base stations. This ensures
that no break ensues during the handoff. Naturally, it
is more costly than a hard handoff.

Intercell handoff

Intracell handoff

Dropped call rates and their
evaluation
• The dropped call is defined as an established call
which leaves the system before it is normally
terminated
• The Dropped Call Rate (DCR) parameter represents
what percentage of all established calls is dropped
during a specified time period
• The DCR and voice quality are inversely proportional
and high DCR may indicate coverage, handoff, or
channels accessibility problems

• The perception of dropped call rate by the
subscribers can be higher due to:
• 1. The subscriber unit not functioning properly
(needs repair).
• 2. The user operating the portable unit in a vehicle
(misused).
• 3. The user not knowing how to get the best
reception from a portable unit (needs education).

Relationship Among Capacity, Voice Quality,
Dropped Call Rate
• Radio Capacity m is expressed as follows:
• Where BT/ BC  total no. of voice channels
• C/I  relation between system capacity & dropped call rate

FORMULA OF DROPPED CALL RATE
• General Formula of Dropped Call Rate
The general formula of dropped call rate P in a
whole system can be expressed as:
Where
And

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