Download - BCS Chapter 09
-
5/25/2018 BCS Chapter 09
1/42
@ McGraw-Hill Education1
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
1
PROPRIETARY MATERIAL. 2010 The McGraw-Hill Companies, Inc. All rights reserved. No part of this PowerPoint slide may be displayed, reproduced ordistributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators
permitted by McGraw-Hill for their individual course preparation. If you are a student using this PowerPoint slide, you are using it without permission.
PowerPoint Slides
-
5/25/2018 BCS Chapter 09
2/42
@ McGraw-Hill Education2
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
2
9
A Basic
Cellular
System
-
5/25/2018 BCS Chapter 09
3/42
@ McGraw-Hill Education3
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
3
A Basic Cellular SystemLimitations of Conventional MobileTelephone System
Consideration of the Componentsof a Cellular System
Operation of a Cellular System
Performance Criteria
Planning a Cellular System
-
5/25/2018 BCS Chapter 09
4/42
@ McGraw-Hill Education4
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
4
Why Cellular Systems?
Operational limitations of conventionalmobile telephone systems:
High transmitter powerin a largeautonomous geographical service area
Limited service capability: nocontinuation of call between service areas
Poor service performance :low capacity,high blocking probabilityduring busy hours
Inefficient frequency spectrumutilization
-
5/25/2018 BCS Chapter 09
5/42
@ McGraw-Hill Education5
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
5
Definition of A Basic Cellular
System
A basic cellular system comprises of many
low power transmitters (LPTs), each
specifically designed to serve only a small area
called a cell.
The same frequency could be reusedin
different cells with sufficient distance, causingnegligible effects of interferencebetween
users of the same channel.
-
5/25/2018 BCS Chapter 09
6/42
@ McGraw-Hill Education6
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
6
A Basic Cellular System
connected to PSTN
-
5/25/2018 BCS Chapter 09
7/42
@ McGraw-Hill Education7
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
7
Parts of a Basic Cellular System
-
5/25/2018 BCS Chapter 09
8/42
@ McGraw-Hill Education8
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
8
Cell-Site Equipment (CSE)
A fixed base station used for wirelesscommunication with mobile subscriber andsignaling/data communication with MTSO
Located at the center or the edge ofcoverage region of a cell
Consists of a number of transreceivers,Tx/Rx antennas mounted on a tall tower, datalinks, and power plant
Transmission data rate on data links varyfrom 10 Kbps to several Mbps
-
5/25/2018 BCS Chapter 09
9/42
@ McGraw-Hill Education9
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
9
Mobile Telephone Switching
Office (MTSO)
The central coordinating element for all the
cell sites connected to it
Interfaces with Public Switch Telephone
Network (PSTN)
Controls call processing and handle billing
activitiesComprises of the switch and the processor
-
5/25/2018 BCS Chapter 09
10/42
@ McGraw-Hill Education10
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
10
Mobile Subscriber Unit (MSU)Comprises of a single antenna,transreceiver, and microprocessor-based
control circuit
Usesaduplexer or RF switch to separate
the transmit and receive signals
GSM mobile subscriber unit consists of
the Mobile Equipment (ME)an electronic smart card called a Subscriber
Identity Module (SIM), which plugs into the ME
-
5/25/2018 BCS Chapter 09
11/42
@ McGraw-Hill Education11
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
11
Operation of a Cellular System
From a users point of view, the
operation can be divided into four parts
and a handoff procedureMobile unit initialization
Mobile originated calls
Network originated calls
Call termination
Handoff procedure
-
5/25/2018 BCS Chapter 09
12/42
@ McGraw-Hill Education12
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
12
Mobile Unit Initialization
When a mobile is switched ON, it scans allcontrol channels and selects the strongest one(usually from the nearest cell site).
This self-location scheme is user-independent and repeated periodically toupdate.
Mobile gets registered itself with the cell site
as being active.The MTSO can then track the location ofthe mobile by paging it on control channel.
@ M G Hill Ed ti13
-
5/25/2018 BCS Chapter 09
13/42
@ McGraw-Hill Education13
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
13
Mobile Originated Calls
The mobile subscriber places the callednumber and press the `sendbutton.
A request for service is sent on a
selected control channel.The cell site receives it and sends a requestto MTSO for allocation of resources.
After authentication, MTSO directs cell
site to allocate a voice channel for the call.
MTSO also connects the called subscriber.
@ M G Hill Ed ti14
-
5/25/2018 BCS Chapter 09
14/42
@ McGraw-Hill Education14
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
14
Call Processing in Cellular
System
@ M G Hill Ed ti15
-
5/25/2018 BCS Chapter 09
15/42
@ McGraw-Hill Education15
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
15
Network Originated Calls
MTSO receives a call request from Network.
It sends a message to certain cell sites,based on called mobile number and search
algorithm.Each cell site transmits the page on itscontrol channel.
The called mobile unit recognizes its ownID, and responds to the cell site.
It locks on to assigned voice channel andinitiate user alert tone.
@ McGraw Hill Education16
-
5/25/2018 BCS Chapter 09
16/42
@ McGraw-Hill Education16
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
16
Call Termination
When the mobile unit terminates the
call, a particular message signal is
transmitted to the cell site.The voice channel is made free.
The mobile unit resumes monitoring
page messages through the strongestcontrol channel.
@ McGraw Hill Education17
-
5/25/2018 BCS Chapter 09
17/42
@ McGraw-Hill Education17
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
17
Handoff Procedure
During the call, when the mobile unit movesout of the coverage area of its cell site, thereceived signal becomes weak.
The present cell site requests a handoff toMTSO.
The MTSO switches the call to a new voicechannel in a new cell site automatically.
The call continues as long as theconversation is on.The mobile user does not notice the handoffoccurrences.
@ McGraw Hill Education18
-
5/25/2018 BCS Chapter 09
18/42
@ McGraw-Hill Education18
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
18
MSUs Operating on Same MTSO
MSU1CSEBSCMSCBSCCSEMSU2
@ McGraw-Hill Education19
-
5/25/2018 BCS Chapter 09
19/42
@ McGraw-Hill Education19
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
19
MSUs Operating on Different MTSOs
MSU1CSE1MTSO-APSTN MTSO-BCSE2MSU2
@ McGraw-Hill Education20
-
5/25/2018 BCS Chapter 09
20/42
@ McGraw Hill Education20
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
20
Performance Criteria
Voice Quality
Grade of Service
Spectral Efficiency
Radio Capacity
Service Quality and SpecialFeatures
@ McGraw-Hill Education21
-
5/25/2018 BCS Chapter 09
21/42
@ McGraw Hill Education21
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
21
Voice Quality (Circuit Merit Level
and MOS)
@ McGraw-Hill Education22
-
5/25/2018 BCS Chapter 09
22/42
@ McGraw Hill Education22
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
22
Trunking and Grade of ServiceOffered traffic load, A av= x H
where = average rate of calls, and H =average holding time per successful call
Total offered traffic intensity, A t= Z x A av
ErlangBformula (also known as theblocked calls cleared formula) provides a
conservative estimate of the GOS for aninfinite number of mobile subscribers
@ McGraw-Hill Education23
-
5/25/2018 BCS Chapter 09
23/42
@
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
23
Spectral EfficiencySpectral efficiency defined in terms ofchannels/MHz/km2can be expressed as
1= (Total number of channels)/ [(system
bandwidth) (total coverage area)]Spectral efficiency defined in terms ofErlangs/MHz/km2can be expressed as
2= (Total traffic load)/ [(system bandwidth)
(total coverage area)]Overall system spectral efficiency,
= 1x 2
@ McGraw-Hill Education24
-
5/25/2018 BCS Chapter 09
24/42
@
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
24
Spectral Efficiency of FDMA SystemThe spectral efficiency of FDMA is the ratio
of total bandwidth available for user data
transmission and allocated system bandwidth
in a cluster, that is,
f= (Ndx Bc) / Bt < 1
1= Nd/cell/ (Btx Acell)channels/MHz/km2
2= (t rx Nd/cell) / (Btx Acell)Erlangs/MHz/km2
@ McGraw-Hill Education25
-
5/25/2018 BCS Chapter 09
25/42
@
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
25
Spectral Efficiency of TDMA System
@ McGraw-Hill Education26
-
5/25/2018 BCS Chapter 09
26/42
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
26
Radio Capacity and C/I
@ McGraw-Hill Education27
-
5/25/2018 BCS Chapter 09
27/42
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
27
Analog AMPS with Digital TDMA Cellular
@ McGraw-Hill Education28
-
5/25/2018 BCS Chapter 09
28/42
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
28
Dropped Call RateThe dropped call is defined as the drop of an
on-going call after the call is established but
before it is properly terminated.
If there is a possibility of a call drop due tonon-availability of voice channel, this is
counted as a blocked call, not a dropped call.
If there is a possibility of a call drop due tothe poor signalof assigned voice channel,
this is considered a dropped call
@ McGraw-Hill Education29
-
5/25/2018 BCS Chapter 09
29/42
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
29
Dropped Call RateEvaluationDropped call can also happen when the
mobile units are at a standstill and the radio
carrier is changed from a strong setup channel
to a weak voice channel due to the selectivefrequency fading phenomenon.
The dropped call rate and the specified
voice quality are inversely proportional.
If voice quality is not to be maintained,
dropped call rate can be set very low.
@ McGraw-Hill Education30
-
5/25/2018 BCS Chapter 09
30/42
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
30
Factors affecting Dropped Call Rate
Provide signal coverage based on theprobability (say 90%) that all the receivedsignals will be above the specified threshold
signal level.Maintain the specified co-channel andadjacent channel interference levels in eachcell during a busy hour i.e. worst case.
The response time for a handoff request hasto be shorter in order to reduce the calldropped rate.
@ McGraw-Hill Education31
-
5/25/2018 BCS Chapter 09
31/42
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
31
Service Quality ParametersCoverage:The cellular system shouldserve an area as large as possible. However,with radio coverage, radio system usually tries
to cover 90% of an area in flat terrain and 75%of an area in hilly terrain.
Required grade of servicemeans lessblocking probability (
-
5/25/2018 BCS Chapter 09
32/42
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
32
Special FeaturesA cellular system would like to provide as
many special features as possible, such as
call forwarding
call waiting
automatic roaming
SMS, etc.
For some special services, the customersmight have to pay extra charges.
@ McGraw-Hill Education33
-
5/25/2018 BCS Chapter 09
33/42
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
33
Planning a Cellular System
A good Plan is necessary to ensure agood service to the Customers.
Objectives of the cellular system
planning are
To find the optimal network solution
Scalability in terms of capacity demand
Future technology evolution
@ McGraw-Hill Education34
-
5/25/2018 BCS Chapter 09
34/42
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
34
Stages of Cellular Planning
Regulations and Market Situations
Engineers Role
Finding Solutions
Become fully familiar with rulesand regulations administered bythe central and state government
agencies Be sure that the plan is workable
@ McGraw-Hill Education35
-
5/25/2018 BCS Chapter 09
35/42
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
35
Market Situations
Prediction of gross incomebased on thepopulation, average income, businesstypes, business zones, etc.
Understanding competitorsincludingtheir area coverage, system performanceand number of customers. Provide aunique and outstanding service.
Decision of geographic coverage,depending upon the type of service to beprovided.
@ McGraw-Hill Education36
-
5/25/2018 BCS Chapter 09
36/42
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
36
Engineers Role Create a plan that uses minimum numbers of cell
sites to cover the given area.
Determine the number of voice channels requiredto handle the traffic load at the busy hours
Study the interference problems.
Study blocking probability at each cell site.
Check that area being covered is importantrevenue area.
Plan to absorb new customers depending onservice charges, system performance andseasons of the year.
@ McGraw-Hill Education37
-
5/25/2018 BCS Chapter 09
37/42
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
37
Finding Solutions
Use practical design tools
to create a plan that uses minimum numbers of
cell sites.
To determine the number of voice channelsrequired to handle the traffic load at the busy hours
Find way to reduce interference problems
Try to minimize blocking problems
Try to develop new technologies to utilize fullythe limited rf spectrum assigned
Request for a large spectrum, if necessary
@ McGraw-Hill Education38
-
5/25/2018 BCS Chapter 09
38/42
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
38
Network Planning Process
@ McGraw-Hill Education39
-
5/25/2018 BCS Chapter 09
39/42
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
39
Nature and Scope of Planning
Areas
Radio network planning
Transmission network planning Signalling network planning
External connectivity network
planning
@ McGraw-Hill Education40
-
5/25/2018 BCS Chapter 09
40/42
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
40
Timing and Information Flow
@ McGraw-Hill Education41
-
5/25/2018 BCS Chapter 09
41/42
T L SINGAL : Wireless Communications McGraw-Hill Education 2010
41
Summary
Essential components of a basic cellular
system are CSE, MTSO and MSU.
Performance determining parametersinclude voice quality, grade of service,
spectrum efficiency, radio capacity,
service quality, and special features.
A good system plan is necessary to provide
a satisfying service to the customers.
@ McGraw-Hill Education42
-
5/25/2018 BCS Chapter 09
42/42
T L SINGAL : Wireless Communications McGraw-Hill Education 2010