mobile cellular telecommunication system-revised

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Mobile Communications

Assistant Prof.Dr.Tamer M. Barakat

Electronics & Communications Dept.



Course Contents

PART I: Introduction

• Conventional mobile system against cellularsystem.

•

Objectives in design of cellular system.• Basic cellular system.

• Operation of cellular systems.

• Call supervision.

• Modern Wireless Communication Systems:Second Generation (2G - GSM) Cellular Networks.

Third Generation (3G - UMTS) Wireless Networks.

4/10/2011 Assistant Prof.Dr.Tamer M. Barakat 2



Course Contents (Cont…)

PART II: GSM Cellular Networks.

• GSM parts.

•

Hanover process.• Digital services:

Caller Identification.

Short Message Services (SMS).FAX services.





PART III: Multiple Access Techniques for

Wireless Communications.

• Introduction to Multiple Access.

• FDMA.

• TDMA.

• Spread Spectrum Multiple Access (SSMA).

– Frequency Hopped Multiple Access (FHMA).

– Code Division Multiple Access ( CDMA).

– Hybrid Spread Spectrum Techniques.





– Space Division Multiple Access (SDMA).

– Packet Radio.





PART IV: Cellular Configuration

• Properties of Cellular Geometry.

•

Capacity of Cellular Systems.• Description of Mobile Transmission Medium.

• Co-channel Interference.

• Channel Assignment.




References

• “Wireless Communications: Principles &

Practices – 2nd edition” Theodore S. Rappaport

• “Mobile Communications”, Lee.




Lecture #1

Mobile Cellular Telecommunication System




Conventional mobile system against

cellular mobile system

• One of many reasons for developing a cellular

mobile telephone system is the operational

limitations of conventional mobile telephone

system:

1. Limited service capability.

problem of the handoff process.

The number of active users is limited to the

number of channels assigned to a particular

frequency zone.




2. Poor service performance; the large number

of subscribers created a high blockingprobability during busy hours.

3. Inefficient frequency spectrum utilization;

In conventional system:

=

Where : the maximum number of customers

that could be served by one channel at the busy

hour.4/10/2011 Assistant Prof.Dr.Tamer M. Barakat 10



• For example:

If given: = 53 customers/channel

average calling time= 1.76 min

the number of channels = 6

∴ =

= × # 60

=

1. 76× 53× 6

60= 9.33

∴ from the table we can find the blocking prob. =

B =50 %




Objectives in the design of cellular

systems

1. Large subscriber capability.

2. Spectrum utilization.

3. Compatibility.4. Adoptability to traffic density.

5. Quality of service and affordability.




Basic cellular system


MRMTSO MR

Cell #1

voice

datadata

voice

Cell #2

A basic cellular system consists of three parts:

I. Mobile units.

II. Cell site; it contains a control unit, a radio cabinets, antennas, data terminal andpower planet.

III. MTSO; Mobile Telecommunication Switching Office. It is the central

coordinating element for all cell sites and contains the cellular processor and a

cellular switch



Operation of cellular systems

1) Mobile unit initialization

- The user activates the of the mobile unit.

- The receiver scan 21 set-up channels from designed 333channels.

- It then selects the strongest (the nearest) cell sites. This iscalled self-location scheme.

2) Mobile originated call

- The user place the called number into an originated registerin the mobile unit which checked that the number is correct.

- A request for service is sent on a selected set-up channelobtained from a self-location scheme.




Operation of cellular systems Cont.

- The cell site, which is directional antenna, selectsthe best directive antenna for the voice channel touse.

- At the same time the cell site sends the request toMTSO via a high-speed data link.

- The MTSO selects an appropriate voice channelfor the cell and then the cell site acts on it through

the best directive antenna to link the mobile unit.- The MTSO also connects the wire-line party

through the telephone company.





3) Network originated call

- A land-line party dials a mobile unit number.

The telephone company office recognizes that the numberis mobile and forwards the call to the MTSO.

- The MTSO sends a paging message to certain cell sitesbased on the mobile unit number and the searchalgorithm.

- Each cell site transmits the page on its own set-upchannel.

- The mobile unit recognizes its own identification on aset-up channel and responds to the cell site.





4) Call termination.

5) Handoff procedure.

- when the mobile unit moves out of coverage area of a

particular cell site, the reception becomes weak.- The present cell site request a handoff.

- The system switches the call to a new frequencychannel in a new cell site without either interrupting the

call or altering the user.- The call continuous as long as the user is talking.

- The user does not notice the handoff procedures.




Call supervision

• On the voice channel, one of the three tones is used forsupervision.

• These tones are centered at 6 KHz and calledSupervisory Audio Tones (SAT).

• The SAT is added to the voice transmission by a landstation.

• The three frequencies used are:

5970, 6000, and 6030 Hz.

• The other tones is known as Signaling Tone (ST).• ST is transmitted at 10 KHz and it is used to indicate

the mobile user on-hook and off-hook conditions




End of Lecture #1




Lecture #2

GSM




Base Station Subsystem (BSS)

- The radio part of the GSM network equipment

are contained within the BSS.

- It is consists of two main parts:

a) The base Transceiver Station (BTS).

b) The Base Station Controller (BSC).




Base Station Subsystem (BSS) Cont….

a) Base Transceiver Station (BTS):

the BTS consists of transmitters, receivers,antenna, power supply and test circuit.

b) Base Station Controller (BSC):

The BSC comprises:

1. A control computer ( typically a microprocessor

control processing unit with memory).2. Data communication facilities.

3. Multiplexing and de-multiplexing equipment.




Base Station Subsystem (BSS) Cont….

•

The basic function of BSC:1) It can control the radio power levels of the various

transceiver in the BTS.

2) It can autonomously control the mobile stations radiotransmitter power level as well.

3) The BSC passes certain type of control messagesbetween the BTS and the mobile Switching Center.

4) The BSC handles certain types of control messages itself under appropriate conditions.

Note:

A single BSC can control several BTS radio equipmenttransmitters.

The BSC can be located in a base station or at anotherremote site.




Network and Switching Subsystem (SS)


BTSBSC

OMC MSC

VLR

HLR

EIR

MS

BSS

Basic parts of GSM network



Network and Switching Subsystem

(SS) Cont….

• Mobile Services Switching Centre: (MSC):

- A number of BSC are served by a MSC which controlscalls to and from other telephony and datacommunication system such as PSTN, ISDN, PLMN orPublic Data Network.

- It is consists of switching Centre and power supplies.

- The switches allow connection between each base

station and PSTN. Basically, these switches use anElectronic Switching System (ESS) which uses processcalled Time Slot Interchange (TSI) to connect incomingand outgoing digital lines together through the use of temporary memory locations.





Cont….

• home location register (HLR)

It contains subscriber information such as

supplementary services and authentication

parameters.

• authentication center (AUC)

- It is connected to the HLR.

- Its function is to provide the HLR with the

authentication parameter and ciphering keys.




Network and Switching Subsystem

(SS) Cont….

• visitor location register (VLR)

- It is a database containing information about allthe MSs currently located in the MSC area.

- If the MS wants to make a call, the VLR will haveall the information needed about call set upwithout having to interrogate the HLR each time.

- The VLR can be seen as distributed HLR.

- The VLR will also contain more exact informationabout the location of MS in MSC area.





Cont….

• equipment identity register (EIR)

—The EIR is a database that contains

information about the identity of mobile

equipment that prevents calls from stolen,

unauthorized, or defective mobile stations. The

AUC and EIR are implemented as stand-alone

nodes or as a combined AUC/EIR node.




Mobile Station

- The term mobile station is taken to mean

equipment necessary to access the GSM

PLMN.

- It consists of:

a) Mobile equipment. It being the actual phone

which identified by its identity number IMEI

(International Mobile Equipment Identity).b) SIM card. It being a card with information a bout

the subscription.




Mobile Station Cont…

• Different types of MS:

a) Vehicle mounted station.

b) Portable station.

c) Hand-held station.

• Mobile station classes


CLASS TYPE MAX OUTPUT POWER

1 ---------------------------- ----------------------------

2 Vehicle mounted 8 WATT

3 Portable 5 WATT

4 Handheld 2 WATT

5 Handheld 0.8 WATT



Handover (Hand off) Process

• It is a means to continue a call even when amobile station crosses the border of one cell intoanother.

•

In a cellular network, one cell has a setneighboring cells. The system has to determinewhich cell the mobile station should be passed.

• The difference in the procedure can be

determined from the different names; thehandoff comes from the analog system whereasthe handover was introduced by GSM.




Handover (Hand off) Process Cont…

• In analog system, the MS is the passive participant inthe handoff process. All measurements and work aredone in the base station and the network.

• In GSM system, the MS continuously monitor the

neighboring cells perceived power levels:

i. The base station gives the mobile a list of basestations channels on which to perform powermeasurements.

ii. The MS performs continuous measurements on thequality and the power level of the serving cell andoff the power levels of the adjacent cells.





iii. The measurement results are put into ameasurement report, which are periodically sentback to the BS.

iv. The BS itself may also be performing measurements

on the quality and power of the link to the MS.

v. If these measurements indicate the necessary for ahandover, as appropriate BS for a handover isalready known.

vi. The GSM system distinguishes different types of handover depending on what type of cell border theMS is crossing.





vii. If a handover has to be performed within the

area of a BSC, it can be controlled by BSC

without consulting the MSC. This handover is

called a simple handover between BTSs.viii. If instead, a MS is crossing the border of a BSC

(rather than a BTS), then, the MSC has to

control the procedure in order to ensure thesmooth transition of the conversation. This

type is called a handover between two MSCs.




Cellular Digital Services

1. Caller Identification


MSC

MS

1. Dial mobile

telephone2. Decode digits

from phone

company

BS

3. Send dialed digit

message

4. Lockup name from memory

+ display number

5. Customer decides if

necessary to answercall.

Telephone Line



Cellular Digital Services Cont…

2. Short Message Services (SMS):

The SMS can be divided into three general

categories:

i. Point to Point.

ii. Point to Multi-point.iii. Broadcast.




Cellular Digital Services Cont…

i. Point to Point Messaging:


MSC

MS

1. send message

2. Store Message

BS

3. Locate Mobile

Telephone

5. Acknowledge

Message

Telephone Line

Message

Centre

4. Deliver Message

6. Display Message



Celluler Configuration

• The coverage planning depend on:

1. Power planning (the adjustement of cells

power)

2. Frequency planning ( the assignment of

frequency to cells)

3. Traffic planning.




Celluler Configuration Cont…

• Properties of cellular geometry:- The main purpose of cells in a portable radio telephone

system is to define an area in which either specific channelsor the specific cell sites will be used.

- The proper positioning of cell site equipment and properselection of equipment to service each cell made isnecessary to realize the advantage of the designed cellpattern.

- To achive this end, a geometry patterned structure is used

rather than irregular strucure.- The use of irregular cell structure lead to an inefficient useof spectrum due to an inability to reuse frequenciesbecause of co-channel interference.




Celluler Configuration Cont…

• To assure complete area coverage with no

dead spots, a series of regular polygons have

been adopted by Advanced Mobile Phone

Service (AMPS).

• The defualt cell structure is the hexagonal

shape which has the maximum area coverage.


R RR

= 2

60°

ℎ = 6 × 1 2 × 30 =2.6

= 1.3



Cellular Geometry

• The distance between two cells:

= +

2 120°

∴ = +

+


V, ju,

x

= °



Cellular Geometry Cont…

• Let , = 0, 0 the origin

• Let , = , the shifting

parameters

• Hence, = + +

• Thus, the center-to-center distance of the

adjacent hexagon is 230 = 3 R

• ∴ = + + General

Form




i i f b f ll



Determination of number of cells per

cluster Cont…

• ∵The distance between two co-cells

= 3 + + radius of large hexagon

∴ the area of hexagon is proportional to the square of theradius

∴ the area enclosed in large hexagon is

= = K 3 + +

From symmetry, large hexagon encloses

+ 1 3 × 6 = 3 cells

Where:

- N: No. of cells /cluster for 1 cluster.

-1 3 : No. of cells associated with other six clusters


D i i f b f ll



Determination of number of cells per

cluster Cont… • The area enclosed in the small hexagon:

=

∴

=

= 3 + +

∴ = + +

Where : the frequency re-use pattern;

No. of cells /cluster; or

cell re-use factor∴ = =

=

Where: : co-channel re-use ratio




Co-channel interference ratio

• As no. of cluster/area system capacity•

• But i.e. co-channel interference

• So we must select the value of to optimize both system

capacity and co-channel interference.• ∴

=

−

= −

Where: : cell radius

: distance to the co-located channel

: propagation decay; 2 ≤ ≤ 4


D i i f bil i i



Description of mobile transmission

medium

• Free space loss

- According to poynting theorem, the power fluxdensity is given by:

∅ = × ∗

2

But, ∅ =

Where, : power tranmitted: distance between isotropic transmiting

and receiving antennas.

mobile cellular telecommunication system-revised

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