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8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
SP
R 2
020
CELLULAR NETWORK CAPACITY PLANNING
Follow up on lecture 07
1
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
SP
R 2
020
Increase number of users
2
Increase number
of channels
Increase number
of cells
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
SP
R 2
020
Increase number of Channels Per cell
• Increase the BW (buy more channels)
– Very expensive
• Decrease the reuse factor
• Actual carrier to interface equal𝐶
𝐼=3𝑁
𝑛• The actual Carrier to interference
𝐶
𝐼should be smaller than the required
Carrier to interference 𝐶∗
𝐼∗
3𝑁
𝑛≥𝐶∗
𝐼∗
3
There is a limit to decreasing the reuse factor N
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
SP
R 2
020
Increase Number of cell
• Decrease cell size (decrease power)
• Increase the number of cells per area
• C/I remains the same
• Total number of users =users per cell x number of cells
Slides are modified version of Digital Transmission Fundamentals Slides by Leon-Garcia/Widjaja Page 4
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
SP
R 2
020
Practical Solution
• Add more cells in the
same cell location
• Use more antennas on
the same tour
• Use directive antennas
• Split each cell into a
number smaller cells
based on the number
of antennas used
5
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
SP
R 2
020
Sectoring
• Divide each cell into a
number of sectors
• Divide the channels on the
number of sectors
• Sectors could be 180, 120
and 60
a
• Sectoring alone does not increase
number of users
• Sectoring decreases the number
of channels per sector
• This decreases the total Erlang
per sector and hence decrease the
total number of user• In example the Erlang per cell
decreased from 8 to 3
8Tra
nsm
issio
n a
nd
Sw
itch
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M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
Fa
ll 2
02
0
Sectoring
Interfering
cells =23𝑁
𝑛≥𝐶∗
𝐼∗
Number of interferers
decrease because of
sectoring (from 6 to 2 in
example )
This allows for the
decrease of reuse
factor and hence
increase the number of
channels per cell
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
SP
R 2
020
CELLULAR NETWORK
Slides are modified version of Digital Transmission Fundamentals Slides by Leon-Garcia/Widjaja Page 8
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
Fa
ll 2020 AC = authentication center
BSS = base station subsystem
EIR = equipment identity register
HLR = home location register
Wireline
terminal
MSC
PSTN
BSS BSS
STP SS7HLR
VLREIR
AC
MSC = mobile switching center
PSTN = public switched telephone network
STP = signal transfer point
VLR = visitor location register
Cellular Network
Base station
• Transmits to users on
forward channels
• Receives from users on
reverse channels
Mobile Switching Center
• Controls connection
setup within cells & to
telephone network
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
SP
R 2
020
Base Transceiver Station (BTS)
• Establishes and maintains
connections to the MS
• Interface between MS and
BTS is called Um interface.
• Hosts the Antenna and Radio
Frequency hardware
• Contain software for multiple
access
• BTSs and the BS are either
co-located or are connected
together
10 5
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
SP
R 2
020
Base Station Control (BSC)
• Has control Functionality
• Interface between BTS and
BSC is called Abis interface
• Responsible for
– channel assignment
– Maintenance of link quality
– Handover
– Power Control
– Coding
11 5
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
SP
R 2
02
0
Mobile Switching Center (MSC)
• The MSC (mobile switching center) plays a central role in
GSM
– switching functions
– additional functions for mobility support
– management of network resources
– interworking functions via Gateway MSC (GMSC)
– integration of several databases
• Functions of a MSC
– specific functions for paging and call forwarding
– termination of SS7 (signaling system no. 7)
– mobility specific signaling
– location registration and forwarding of location information
– provision of new services (fax, data calls)
– support of short message service (SMS)
– generation and forwarding of accounting and billing information
12 5
8Tra
nsm
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n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
SP
R 2
020
Databases
• Databases (important: scalability, high capacity, low delay)
– Home Location Register (HLR)
central master database containing user data, permanent and semi-
permanent data of all subscribers assigned to the HLR (one provider can
have several HLRs)
– Visitor Location Register (VLR)
local database for a subset of user data, including data about all user
currently in the domain of the VLR
13 5
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
SP
R 2
02
0
5
Operation subsystem
• The OSS (Operation Subsystem) enables centralized operation, management, and maintenance of all GSM subsystems
• Components
– Authentication Center (AUC)
• generates user specific authentication parameters on request of a VLR
• authentication parameters used for authentication of mobile terminals and encryption of user data on the air interface within the GSM system
– Equipment Identity Register (EIR)
• registers GSM mobile stations and user rights
• stolen or malfunctioning mobile stations can be locked and sometimes even localized
– Operation and Maintenance Center (OMC)
• different control capabilities for the radio subsystem and the network subsystem
14
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
Fa
ll 2020
Signaling & Connection Control
• Setup channels set aside for call setup & handoff
– Mobile unit selects setup channel with strongest signal & monitors this
channel
• Incoming call to mobile unit
– MSC sends call request to all BSSs
– BSSs broadcast request on all setup channels
– Mobile unit replies on reverse setup channel
– BSS forwards reply to MSC
– BSS assigns forward & reverse voice channels
– BSS informs mobile to use these
– Mobile phone rings
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
Fa
ll 2
02
0
Mobile Originated Call
• Mobile sends request in reverse setup channel
• Message from mobile includes serial # and possibly authentication
information
• BSS forwards message to MSC
• MSC consults Home Location Register for information about the
subscriber
• MSC may consult Authentication center
• MSC establishes call to PSTN
• BSS assigns forward & reverse channel
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
Fa
ll 2020
Handoff
• Base station monitors signal levels from its mobiles
• If signal level drops below threshold, MSC notified & mobile instructed to transmit on setup channel
• Base stations in vicinity of mobile instructed to monitor signal from mobile on setup channel
• Results forward to MSC, which selects new cell
• Current BSS & mobile instructed to prepare for handoff
• MSC releases connection to first BSS and sets up connection to new BSS
• Mobile changes to new channels in new cell
• Brief interruption in connection (except for CDMA)
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
Fa
ll 2
02
0
Roaming
• Users subscribe to roaming service to use service outside their
home region
• Signaling network used for message exchange between home &
visited network
• Roamer uses setup channels to register in new area
• MSC in visited areas requests authorization from users Home
Location Register
• Visitor Location Register informed of new user
• User can now receive & place calls
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
Fa
ll 2020
GSM Signaling Standard
• Base station– Base Transceiver Station (BTS)
• Antenna + Transceiver to mobile
• Monitoring signal strength
– Base Station Controller• Manages radio resources or 1 or more BTSs
• Set up of channels & handoff
• Interposed between BTS & MSC
• Mobile & MSC Applications– Call Management (CM)
– Mobility Management (MM)
• Radio Resources Management (RRM) concerns mobile, BTS, BSC, and MSC
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
SP
R 2
02
0
Logical Channels
Traffic Channel (TCH) Control Channel (CCH)
Full rate(/F)
Half Rate(/H)
One Eight (/8)
Broadcast
Channel (BCH)
Common
Control Channel
(CCCH) Dedicated
Control Channel (DCCH)
Cell Broadcast
Channel (CBCH)
Frequency
Correction
channel
(FCCH)
Synchronization
Channel (SCH)
Broadcast
Control
Channel (BCCH)
Standalone
Dedicated
Control Channel
(SDCCH)
Slow Associated
Control Channel
(SACCH)
Fast Associated Control Channel (FACCH)
Paging
Channel
(PCH)
Random Access
Channel (RACH)
Access Grant
Channel (AGCH)
20 6
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
SP
R 2
020
Traffic Channels
• Traffic means voice transmission.
– Full Rate:
• 22.8Kbps, and speech coding 13Kbps.
– Half Rate:• 11.4Kbps, and speech coding 6.5Kbps.
– One Eight:• For signaling or SMS’s.
21 6
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
SP
R 2
020
Broadcast Channels BCHs
• Found on the down link
• Serves as beacon signal
• MS uses signal from these channels to establish time and
frequency synchronization
• Provide information about cell identity
• MS has to track information form these channels all the
time for possible Hand Over
22 6
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
SP
R 2
020
Broadcast channels
• Frequency Correction Channel (FCCH)– Provides the MS with a frequency reference
– The MS tunes its frequency to this reference
• Synchronization Channels (SCH)– Define the frame number of the cell and Base Station Identification Code (BSIC)
– The BSIC ensures that the MS synchronizes to the right network.
• Broadcast Control Channel BCCHTransmits cell specific information such as
– Location Area Identity (LAI)
– Maximum permitted signal power
– Actual available traffic channel
– Frequencies of the neighboring BSs that are permanently observed for possible Hand Over
23 6
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
SP
R 2
020
Common Control Channels
Used by the BS to establish a connection to a specific MS• Paging Channel (PCH)
– Used to send the permanent international Mobile Subscriber Identity (IMSI) or the temporary Mobile Subscriber
Identity when a connection arrives to a MS
– May be used to broad cast local messages (street information and commercials)
• Random Access Channel (RACH)
– Found only in the uplink
– Used by MS to request Connection
• To reply on PCH
• Send request for dedicated channel (SDCCH)
• Access Grant Channel (AGCH)
– Used to assign a standalone dedicated control channel in response to request via RACH
– Found only in the uplink
– Reply for the request of SDCCH with the time slot No.
24 6
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
SP
R 2
020
• DCCH :
– SDCCH: standalone dedicated control channel (Downlink)
• For call signaling setup. Operates at TCH/8 or TCH/4.
– SACCH: Slow Association Control Channel
• Downlink to inform the MS power level.
• Uplink to inform the BS with the MS power level.
– FACCH: Fast Association Control Channel
• For handover by stealing 20 ms from the speech.
• CBCH : Cell Broadcast Channel (Downlink)
– Each cell sends a short message to all MS’s every 2
ms to broadcast the users with information from a
service center to mobile stations.
Dedicated Control Channel (DCCHs)
25 6
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itch
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M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
SP
R 2
020
TDMA/FDMA
26
6
Frequency
8Tra
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Sw
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M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
Fa
ll 2020
6
1 2 3 4 5 6 7 8
higher GSM frame structures
935-960 MHz
124 channels (200 kHz)
downlink
890-915 MHz
124 channels (200 kHz)
uplink
time
GSM TDMA frame
GSM time-slot (normal burst)
4.615 ms
546.5 µs577 µs
tail user data TrainingSguard
space S user data tailguard
space
3 bits 57 bits 26 bits 57 bits1 1 3
GSM - TDMA/FDMA
27
8Tra
nsm
issio
n a
nd
Sw
itch
ing
M
oham
ed A
shour
, G
erm
an U
niv
ers
ity in C
airo
Moh
amed
Ash
our
Le
ctu
re
SP
R 2
020
THANK YOU
Page 28
If you have any questions or comments
regarding the lecture please email me at
I will try to answer them the next lecture
