9. 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.
4/10/2011 Assistant Prof.Dr.Tamer M. Barakat 9
10. 2. Poor service performance; the large number
of subscribers created a high blocking
probability during busy hours.
3. Inefficient frequency spectrum utilization;
In conventional system:
𝑀 𝜊 =
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑢𝑠𝑡𝑜𝑚𝑒𝑟𝑠
𝑐𝑎𝑛𝑛𝑒𝑙
Where 𝑀 𝜊: 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
11. • For example:
If given: 𝑀 𝜊 = 53 customers/channel
average calling time= 1.76 min
the number of channels = 6
∴ 𝐴 = 𝑜𝑓𝑓𝑒𝑟𝑒𝑑 𝑙𝑜𝑎𝑑
=
𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑐𝑎𝑙𝑙𝑖𝑛𝑔 𝑡𝑖𝑚𝑒 × #𝑡𝑜𝑡𝑎𝑙 𝑐𝑢𝑠𝑡𝑜𝑚𝑒𝑟𝑠
60 𝑚𝑖𝑛
𝐴 =
1.76 × 53 × 6
60
= 9.33 𝑒𝑟𝑙𝑎𝑛𝑔
∴ from the table we can find the blocking prob. =
B =50 %
4/10/2011 Assistant Prof.Dr.Tamer M. Barakat 11
12. 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.
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13. Basic cellular system
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MR
MTSO MR
Cell #1
voice
data data
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 and
power 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
14. 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 333
channels.
- It then selects the strongest (the nearest) cell sites. This is
called self-location scheme.
2) Mobile originated call
- The user place the called number into an originated register
in the mobile unit which checked that the number is correct.
- A request for service is sent on a selected set-up channel
obtained from a self-location scheme.
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15. Operation of cellular systems Cont.
- The cell site, which is directional antenna, selects
the best directive antenna for the voice channel to
use.
- At the same time the cell site sends the request to
MTSO via a high-speed data link.
- The MTSO selects an appropriate voice channel
for 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.
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16. Operation of cellular systems Cont.
3) Network originated call
- A land-line party dials a mobile unit number.
The telephone company office recognizes that the number
is mobile and forwards the call to the MTSO.
- The MTSO sends a paging message to certain cell sites
based on the mobile unit number and the search
algorithm.
- Each cell site transmits the page on its own set-up
channel.
- The mobile unit recognizes its own identification on a
set-up channel and responds to the cell site.
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17. Operation of cellular systems Cont.
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 frequency
channel 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.
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18. Call supervision
• On the voice channel, one of the three tones is used for
supervision.
• These tones are centered at 6 KHz and called
Supervisory Audio Tones (SAT).
• The SAT is added to the voice transmission by a land
station.
• 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
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19. End of Lecture #1
4/10/2011 Assistant Prof.Dr.Tamer M. Barakat 19
21. GSM Parts
A GSM network comprised of several major portions:
• A mobile radio part.
• Subscriber information part.
• A radio network.
• A switching system.
• A network intelligence (primarily data base).
• Mobile phone which called Mobile Station (MS).
• An electronic card which called Subscriber Identity
Module (SIM).
• Mobile stations communicate with nearest radio power
called Base Station Subsystem (BSS).
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22. 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).
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23. 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.
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24. 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 radio
transmitter power level as well.
3) The BSC passes certain type of control messages
between 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 equipment
transmitters.
The BSC can be located in a base station or at another
remote site.
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25. Network and Switching Subsystem (SS)
4/10/2011 Assistant Prof.Dr.Tamer M. Barakat 25
BTS
BSC
OMC MSC
VLR
HLR
EIR
MS
BSS
Basic parts of GSM network
26. Network and Switching Subsystem (SS)
Cont….
The switching system includes the following functional unit:
i. Mobile Services Switching Centre (MSC).
ii. Visitor Location Register (VLR).
iii. Home Location Register (HLR).
iv. Authentication Centre (AUC).
v. Equipment Identity Register (EIR).
Note:
- Operations and Maintenance Centre (OMC); is connected to
all equipment in the switching system and to the BSC. The
purpose of OMC is to offer the customer cost-effective
support for centralized, regional, and local operational and
maintenance activities that are required for a GSM network.
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27. Network and Switching Subsystem
(SS) Cont….
• Mobile Services Switching Centre: (MSC):
- A number of BSC are served by a MSC which controls
calls to and from other telephony and data
communication system such as PSTN, ISDN, PLMN or
Public 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 an
Electronic Switching System (ESS) which uses process
called Time Slot Interchange (TSI) to connect incoming
and outgoing digital lines together through the use of
temporary memory locations.
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28. Network and Switching Subsystem (SS)
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.
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29. Network and Switching Subsystem
(SS) Cont….
• visitor location register (VLR)
- It is a database containing information about all
the MSs currently located in the MSC area.
- If the MS wants to make a call, the VLR will have
all the information needed about call set up
without having to interrogate the HLR each time.
- The VLR can be seen as distributed HLR.
- The VLR will also contain more exact information
about the location of MS in MSC area.
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30. Network and Switching Subsystem (SS)
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.
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31. 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.
4/10/2011 Assistant Prof.Dr.Tamer M. Barakat 31
32. Mobile Station Cont…
• Different types of MS:
a) Vehicle mounted station.
b) Portable station.
c) Hand-held station.
• Mobile station classes
4/10/2011 Assistant Prof.Dr.Tamer M. Barakat 32
CLASS TYPE MAX OUTPUT POWER
1 ---------------------------- ----------------------------
2 Vehicle mounted 8 WATT
3 Portable 5 WATT
4 Handheld 2 WATT
5 Handheld 0.8 WATT
33. Handover (Hand off) Process
• It is a means to continue a call even when a
mobile station crosses the border of one cell into
another.
• In a cellular network, one cell has a set
neighboring cells. The system has to determine
which cell the mobile station should be passed.
• The difference in the procedure can be
determined from the different names; the
handoff comes from the analog system whereas
the handover was introduced by GSM.
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34. Handover (Hand off) Process Cont…
• In analog system, the MS is the passive participant in
the handoff process. All measurements and work are
done 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 base
stations channels on which to perform power
measurements.
ii. The MS performs continuous measurements on the
quality and the power level of the serving cell and
off the power levels of the adjacent cells.
4/10/2011 Assistant Prof.Dr.Tamer M. Barakat 34
35. Handover (Hand off) Process Cont…
iii. The measurement results are put into a
measurement report, which are periodically sent
back 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 a
handover, as appropriate BS for a handover is
already known.
vi. The GSM system distinguishes different types of
handover depending on what type of cell border the
MS is crossing.
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36. Handover (Hand off) Process Cont…
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 the
smooth transition of the conversation. This
type is called a handover between two MSCs.
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37. Cellular Digital Services
1. Caller Identification
4/10/2011 Assistant Prof.Dr.Tamer M. Barakat 37
MSC
MS
1. Dial mobile
telephone
2. Decode digits
from phone
company
BS
3. Send dialed digit
message
4. Lockup name from memory
+ display number
5. Customer decides if
necessary to answer
call.
Telephone Line
38. 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.
4/10/2011 Assistant Prof.Dr.Tamer M. Barakat 38
39. Cellular Digital Services Cont…
i. Point to Point Messaging:
4/10/2011 Assistant Prof.Dr.Tamer M. Barakat 39
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
40. End of Lecture #2
4/10/2011 Assistant Prof.Dr.Tamer M. Barakat 40
41. 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.
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42. 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 channels
or the specific cell sites will be used.
- The proper positioning of cell site equipment and proper
selection of equipment to service each cell made is
necessary to realize the advantage of the designed cell
pattern.
- To achive this end, a geometry patterned structure is used
rather than irregular strucure.
- The use of irregular cell structure lead to an inefficient use
of spectrum due to an inability to reuse frequencies
because of co-channel interference.
4/10/2011 Assistant Prof.Dr.Tamer M. Barakat 42
43. 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.
4/10/2011 Assistant Prof.Dr.Tamer M. Barakat 43
R R
R
𝐴 𝑠𝑞 = 2𝑅2
60°
𝐴ℎ𝑒𝑥 = 6 × 1 2 𝑅 × 𝑅𝑐𝑜𝑠 30
=2.6𝑅2
𝐴 𝑡𝑟𝑖 = 1.3𝑅2
45. Cellular Geometry Cont…
• Let 𝑢1, 𝑣1 = 0, 0 the origin
• Let 𝑢2, 𝑣2 = 𝑖, 𝑗 the shifting
parameters
• Hence, 𝐷2
= 𝑖2
+ 𝑗2
+ 𝑖𝑗
• Thus, the center-to-center distance of the
adjacent hexagon is 2𝑅𝑐𝑜𝑠30 = 3 R
• ∴ 𝑫 𝟐
= 𝟑𝑹 𝟐
𝒊 𝟐
+ 𝒋 𝟐
+ 𝒊𝒋 General
Form
4/10/2011 Assistant Prof.Dr.Tamer M. Barakat 45
46. Determination of number of cells per
cluster
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47. Determination of number of cells per
cluster Cont…
• ∵The distance between two co-cells
𝐷 = 3 𝑅 𝑖2 + 𝑗2 + 𝑖𝑗 radius of large hexagon
∴ the area of hexagon is proportional to the square of the
radius
∴ the area enclosed in large hexagon is
𝐴 = 𝐾𝐷2 = K 3𝑅2 𝑖2 + 𝑗2 + 𝑖𝑗
From symmetry, large hexagon encloses
𝑁 + 1 3 𝑁 × 6 = 3𝑁 cells
Where:
- N: No. of cells /cluster for 1 𝑠𝑡 cluster.
-1 3 𝑁: No. of cells associated with other six clusters
4/10/2011 Assistant Prof.Dr.Tamer M. Barakat 47
48. Determination of number of cells per
cluster Cont…
• The area enclosed in the small hexagon:
𝐴 𝑠𝑚𝑎𝑙𝑙 = 𝐾𝑅2
∴
𝐴𝑙𝑎𝑟𝑔𝑒
𝐴 𝑠𝑚𝑎𝑙𝑙
=
𝐷2
𝑅2
= 3 𝑖2
+ 𝑗2
+ 𝑖𝑗
∴ 𝑁 = 𝑖2
+ 𝑗2
+ 𝑖𝑗
Where 𝑁: the frequency re-use pattern;
No. of cells /cluster; or
cell re-use factor
∴ 𝑫 = 𝑹 𝟑𝑵 𝒒 =
𝑫
𝑹
= 𝟑𝑵
Where: 𝒒: co-channel re-use ratio
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49. Co-channel interference ratio
• As 𝑁 no. of cluster/area system capacity
•
• But 𝑁 𝐷 𝑞 i.e. co-channel interference
• So we must select the value of 𝑁 to optimize both system
capacity and co-channel interference.
• ∴
𝑰
𝑺
=
𝟏𝟎 𝒍𝒐𝒈 𝟏𝟎 𝟔
𝑫 − 𝑹
𝑹
−𝒏
= 𝟏𝟎 𝒍𝒐𝒈 𝟏𝟎 𝟔 𝟑𝑵 − 𝟏
−𝒏
Where: 𝑅: cell radius
𝐷: distance to the co-located channel
𝑛: propagation decay; 2 ≤ 𝑛 ≤ 4
4/10/2011 Assistant Prof.Dr.Tamer M. Barakat 49
50. Description of mobile transmission
medium
• Free space loss
- According to poynting theorem, the power flux
density is given by:
∅ =
𝐸 × 𝐻∗
2
But, ∅ =
𝑃𝑡
4𝜋𝑑2
Where, 𝑃𝑡: power tranmitted
𝑑: distance between isotropic transmiting
and receiving antennas.
4/10/2011 Assistant Prof.Dr.Tamer M. Barakat 50
