gsm seminar on technology. md. omar ali shamim ahmed nasrin akter khandakar menhaz morshed speakers
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GSMSEMINAR
ON
TECHNOLOGY
Md. Omar AliShamim Ahmed Nasrin Akter
Khandakar Menhaz Morshed
Speakers
# What’s a cellular phone?
Now all of these mobile devices are shining in your hands.
# Why it calls cellular?
> Uses hexagonal Cells
# Why use cells?
• # If there was no cell• Limited frequency spectrum for available Mobile
Communication• Frequency utilization is inefficient • Single high power antenna => limited number of
users
# Why use cells?
# Benefits of cellular technology• Smaller cells => frequency reuse possible =>
more number of users• As demand increases (more channels needed)
– Number of base stations is increased (by reducing cell size)
– Transmitter power is decreased correspondingly to avoid interference (to eliminate adjacent-channel interference)
# Frequency reuse:
• Adjacent cells assigned different frequencies to avoid interference or crosstalk.
• The same frequency is reused in different areas for different transmissions
• In GSM networks a frequency reuse patternwith k = 3, 4, 7, 12 or 21.
Here, k= Frequency reuse factor• Each ‘k’ number of cells make a cluster.
# Frequency reuse:
>Reuse factor = 33 cell Cluster
>Reuse factor = 44 cell Cluster
# Frequency reuse:
>Reuse factor = 77 cell Cluster
# Frequency Reuse Problems:
• Adjacent-channel interference
• Co-channel Interference
# Adjacent-channel interference
• Comes from imperfect filters that allow frequency leakage into the band
• Serious problem if interferer is nearby, near-far effect– Nearby mobile transmits on a frequency near to that
of a weak mobile
• Base station receivers need high-Q filters to reject adjacent channel interference.
# Adjacent-channel interference
# Co-channel Interference
• One of the primary forms of man-made signal degradation associated with digital radio, co-channel interference occurs when the same carrier frequency reaches the same receiver from two separate transmitters
# Co-channel Interference
F1 F1
F1
F1
F1MS
# Co-channel Interference
# Sectored Cells
• To reduce the adjacent channel interference & co-channel interference a cell can divide into 3 or 6 sectors according to the demand.
• 3 sectors per cell• 3 cells per cluster
1
2
3
2
3
1
2
3
2
3
2
3
• 3 sectors per cell• 4 cells per cluster
3
12
43
2
41
3
12
4
3
12
4
41
21
• 6 sectors per cell
• 2 cells per cluster
12
121
11
2
22
# Original view of sectors
# Multiplexing & Access Methods
SDMASDM
CDMACDM
TDMATDM
FDMAFDM
Access MethodMultiplexing
# FDM & FDMA
Time
Fre
qu
enc
y
F3
F2
F1
# TDM & TDMA
Time
Am
pli
tud
e
T3T2T1
Frequen
cy
# CDM & CDMA
Time
Co
de
Code3
Code2
Code1
Frequen
cy
# SDM & SDMA
# Frequency Spectrum
Down link 935~960MHz
Up link 890~915MHz
MS
BTS
# Channels
• GSM 900 uses 25 MHz frequency spectrum with 124 channels for uplink & downlink.
• Each channels have 200 KHz bandwidth.
• Each two channels are separated by 1.6 KHz guard band.
• Each channel have 8 time slots which allows 8 subscribers to use same frequency by TDMA.
# Channels
1 2 4 5 6 123 1243
1 42 3 5 86 7
Channels with 200 KHz bandwidth
Time slots
4.615 ms
# Cell Types
Cells can be classified into three types
according to cell size
• Macro cell
• Micro cell
• Pico cell
# Cell Types
# Antenna
Two types of antenna used
• Unidirectional antenna
• Omni directional antenna
# Unidirectional antenna
# Omni directional antenna
Semi omni directional antenna
# Modulation Technique
BPSK Two phases represent two binary digits
# Modulation Technique
QPSK & OQPSK Each signal element representing more than one bit
# Modulation Technique
MSK Just like OQPSK, but the rectangular pulses are replaced by half-sinusoids
# Modulation Technique
GMSK Using FSK modulation
On the next session
Shamim Ahmedwill with you
BSS — Base Station System
BTS — Base Transceiver Station
BSC — Base Station Controller
MS — Mobile Station
NSS — Network Sub-System
MSC — Mobile-service Switching Controller
VLR — Visitor Location Register
HLR — Home Location Register
AuC — Authentication Server
GMSC — Gateway MSC
GSM 2G Architecture
SS7BTS
BSCMSC
VLR
HLRAuC
GMSC
BSS
PSTN
NSS
AE
CD
PSTNAbis
B
H
MS
GSM — Global System for Mobile communication
GSMSub-Systems
• Radio Sub System (RSS)
• RSS = MS + BSS
• BSS = BTS+ BSC
• Network Sub System (NSS)
• NSS = MSC+ HLR + VLR + GMSC
• Operation Sub System
• OSS = EIR + AuC
GSM network layer
#Radio resource management (RR) sublayer– Establishment, maintenance, and termination
of radio channel connections
#Mobility management (MM) sublayer– Registration, authentication, and location
tracking
#Call control (CC) sublayer– Establishment, maintenance, and termination
of circuit-switched calls
SS7BTS
BSCMSC
VLR
HLRAuC
GMSC
BSS
PSTN
NSS
AE
CD
PSTNAbis
B
H
MS
BSS — Base Station System
BTS — Base Transceiver Station
BSC — Base Station Controller
NSS — Network Sub-System
MSC — Mobile-service Switching Controller
VLR — Visitor Location Register
HLR — Home Location Register
AuC — Authentication Server
GMSC — Gateway MSC
2.5G Architectural Detail
SGSN — Serving GPRS Support Node
GGSN — Gateway GPRS Support Node
GPRS — General Packet Radio Service
IP
2G+ MS (voice & data)
PSDNGi
SGSN
Gr
Gb
Gs
GGSN
Gc
Gn
2G MS (voice only)
3G rel99 Architecture (UMTS) — 3G Radios
SS7
IP
BTS
BSCMSC
VLR
HLRAuC
GMSC
BSS
SGSN GGSN
PSTN
PSDN
CN
CD
GcGr
Gn Gi
Abis
Gs
B
H
BSS — Base Station System
BTS — Base Transceiver Station
BSC — Base Station Controller
RNS — Radio Network System
RNC — Radio Network Controller
CN — Core Network
MSC — Mobile-service Switching Controller
VLR — Visitor Location Register
HLR — Home Location Register
AuC — Authentication Server
GMSC — Gateway MSC
SGSN — Serving GPRS Support Node
GGSN — Gateway GPRS Support Node
AE PSTN
2G MS (voice only)
2G+ MS (voice & data)
UMTS — Universal Mobile Telecommunication System
Gb
3G UE (voice & data)
Node B
RNC
RNS
Iub
IuCS
ATM
IuPS
3G rel4 Architecture (UMTS) — Soft Switching
SS7
IP/ATM
BTS
BSCMSC Server
VLR
HLRAuC
GMSC server
BSS
SGSN GGSN
PSTN
PSDN
CN
CD
GcGr
Gn Gi
Gb
Abis
Gs
B
H
BSS — Base Station System
BTS — Base Transceiver Station
BSC — Base Station Controller
RNS — Radio Network System
RNC — Radio Network Controller
CN — Core Network
MSC — Mobile-service Switching Controller
VLR — Visitor Location Register
HLR — Home Location Register
AuC — Authentication Server
GMSC — Gateway MSC
SGSN — Serving GPRS Support Node
GGSN — Gateway GPRS Support Node
ANc
2G MS (voice only)
2G+ MS (voice & data)
Node B
RNC
RNS
Iub
IuCS
IuPS
3G UE (voice & data)
Mc
CS-MGW
CS-MGWNb
PSTNMc
ATM
GSM Speech Coding
Low-passfilter
Analogspeech
A/DRPE-LTPspeechencoder
Channelencoder
8000 samples/s,13 bits/sample
104 kbps 13 kbps
MS Hands off
GSM Call Routing For Incoming Call 1. MSISDN
2. MSISDN
VLRHLR
AUCEIR
GMSC/IWF
MSC
BSC
BSC
BTS
BTS
BTS
ISDN
3. MSRN
4. MSRN
5. MSRN
6. TMSI
7. TMSI
7. TMSI
7. TMSI
8. TMSI
LA2
LA1
MS
MS
PSTN-to-Mobile Call
(STP)
(SCP)
PSTNPLMN
(SSP)(SSP)BSSMS
PLMN(Home)(Visitor)
(STP)
HLR
GMSC
(SSP)
VMSC
VLR
IAM
6
2
Where is the subscriber?
5Routing Info
3Provide Roaming
4
SCP
1
IAM
514 581 ...
ISUP
MAP/ IS41 (over TCAP)
Signalingover SS7
Mobile-Terminated Short Message Example (MTSM)
Mobile-Originated Short Message Example (MOSM)
GSM Security
• Fetched triplets are stored in VLR– Every call uses up one triplet (discarded)– Another set must be fetched when exhausted
Visited system
Registration requestIMSI/TMSI identifies user, LAI points to old VLR,requests data toauthenticate user
IMSI/TMSI + LAI
Subscriber data
Old VLR
GSM Security
Visited system
Challenge
Requests tripletsfrom home system,chooses a tripletCalculates
responseby authen-
ticationalgorithm
Challenge response Compares to storedresponse in triplet, registration successfulif matches
New TMSI
Acknowledge
Assigns new TMSI
GSM Security
Visited system
Registrationcancel
Location update
AcknowledgeHLR
Old VLR
Next Speaker
Nasrin Akter
Enhancing GSM• Speech coder
– Trade off speech and error correction bits– Fewer dropped calls
• DTX — discontinuous transmission– Less interference (approach 0 bps during silences)– More calls per cell
Data transfer over GSM
• Four enhancements to GSM for data– HSCSD - High Speed Circuit Switched Data– GPRS - General Packet Radio Service– EGPRS: Enhanced GPRS– EDGE: Enhanced Data rates for the GSM
Evolution• Technically EGPRS and EDGE are same
GPRS — 2.5G for GSM
• General packet radio service– First introduction of packet technology
• Aggregate radio channels– Support higher data rates (115 kbps)– Subject to channel availability– From 1 to 8 time slot / TDMA frame can be allocated for particular
service – Physical Channel are taken from common pool of available
channel in the cell
• Share aggregate channels among multiple users• No changes to voice network, but only new GPRS logical
channels are defined
GPRS features
• Radio resources are allocated for only one or a few packets at a time, so GPRS enables– many users to share radio resources, and
allow efficient transport of packets– fast setup/access times– connectivity to external packet data networks
• GPRS also carries SMS in data channels rather than signaling channels as in GSM
EDGE
• Enhanced Data rates for Global Evolution
• Increased data rates with GSM compatibility– Still 200 KHz bands; still TDMA– 8-PSK modulation: 3 bits/symbol give 3X data rate– Shorter range (more sensitive to
noise/interference)– New GSM/ EDGE radios but evolved ANSI-41
core network
• The EDGE technology uses the same bandwidth allocated for GSM voice and GPRS data services,
• but It delivers a higher capacity and fast data services to the mobile network by using a new modulation scheme called 8 PSK (8-level Phase Shift Keying). With this 8 PSK modulation, there are eight distinct phase changes. Each phase represents a symbol and carries three bits of information.
GPRS and EGPRS Modulation Principles
GSM Evolution for Data Access
1997 2000 2003 2003+
GSM
GPRS
EDGE
UMTS
9.6 kbps
115 kbps
384 kbps
2 Mbps
GSM evolution 3G
SS7BTS
BSCMSC
VLR
HLRAuC
GMSC
BSS
PSTN
NSS
AE
CD
PSTNAbis
B
H
MS
BSS Base Station System
BTS Base Transceiver Station
BSC Base Station Controller
NSS Network Sub-System
MSC Mobile-service Switching Controller
VLR Visitor Location Register
HLR Home Location Register
AuC Authentication Server
GMSC Gateway MSC
GPRS architectural detail
SGSN Serving GPRS Support Node
GGSN Gateway GPRS Support Node
GPRS General Packet Radio Service
IP
2G+ MS (voice & data)
PSDNGi
SGSN
Gr
Gb
Gs
GGSN
Gc
Gn
2G MS (voice only)
GSM to GPRS
Element Software Hardware
MS Upgrade required Upgrade required
BTS Upgrade required No Change
BSC Upgrade required PCU Interface
TRAU No Change No Change
MSC/VLR Upgrade required No Change
HLR Upgrade required No Change
SGSN New New
GGSN New New
GPRS capacity
• Difficult to estimate actual bandwidth available to the GPRS user - will vary a lot– depending on time of day– total number of active users– current geographical location and others...
• Technical Limitations to capacity– Allocation of time slots - between GSM and GPRS
and which multislot classes available– Restrictions in terminals– Availability of coding schemes
GPRS charging• Can be based on
– data volume– duration of call– type of service– destination point
• Charging data output from SGSN and GGSN is encoded in ASN.1/BER and transferred via ftp to a Charging Gateway Function (CGF) node (Billing Gateway)
Modem Modem
Email Server
Auth. Server
InternetGSM PSTN
User
Email via GSM
Email via GPRSEmail Server
GPRS
User
Auth. Server
Internet
Authenticated path to Email server
Virtual GPRS Data Tunnel
GSM v/s GPRS
Next Speaker
Khandaker Menhaz Morshed
Types Of Billing System
• Post Paid:
Pay After Use
• Pre Paid:
Pay Before Use
Prepaid
Advantages:• operator has the money • operator saves• customer: no need for credit worthiness.• prepaid fits well with the expectation of
these customers• many customers will never use up all their
balance
Difference Between Mobile And Fixed Prepaid
• Mobile servers needs: more complex billing system due to more
complex tariffs
complex taxation
real-time usage metering
complexity of customer care
Four Alternatives For Mobile Prepaid
• Wireless Intelligent Network (WIN)
• Service Node
• Hot Billing
• Handset-Based
BTSMS BSC MSC
IntelligentPeripheral
SSP
P-SCP
Wireless Intelligent Network (WIN)
SignalingVoice Trunk
WIN Call termination when called party pays
BTSMS BSC MSC SSP
P-SCP
GMSC
SignalingVoice Trunk
Service Node
BTSMS BSC MSC
ServiceNode
SSP
PBP
SignalingVoice Trunk
Hot Billing
BTSMS BSC MSC SSP
PSCHLR/AuCDatabase
SignalingVoice Trunk
Handset-Based
BTSMSBSC MSC SSP
SignalingVoice Trunk
GSM Summary
Uplink frequencies 890-915 MHz
Downlink frequencies 935-960 MHz
Total GSM bandwidth 25 MHz up + 25 MHz down
Channel bandwidth 200 kHz
Number of RF carriers 124
Multiple access TDMA
Users/carrier 8
Number of simul. users 992
Speech coding rate 13 kb/s
FEC coded speech rate 22.8 kb/s
GSM service quality requirements
Speech intelligibility 90%
Max one-way delay 90 ms
Max handoff gap 150 ms if intercell
Time to alert mobile ofinbound cell
4 sec first attempt, 15 sec final attempt
Release time to callednetwork
2 sec
Connect time to callednetwork
4 sec
GSM 900 and GSM 1800
GSM 900 GSM 1800Frequency band 890-915 MHz
935-960 MHz1710-1785 MHz1805-1880 MHz
Border spacing 25 MHz 75 MHzDuplex spacing 45 MHz 95 MHzCarrier spacing 200 kHz 200 kHzCarriers 124 374Timeslots per carrier 8 8Multiple access TDMA/FDMA TDMA/FDMATypical cell range <300m – 35 km <100m – 15 kmHandset Power 0.8 & 8 W 0.25 & 1 W
THANKS TO ALL
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