2. Outline
• Overview of Cellular Network Generations
• Development and History of Digital Cellular
Technology
• Digital Wireless Advantages over Analog
Cellular Systems
• Global System for Mobile Communication
Technology
2
8. 2.5G and 2.75G Networks
• 2.5G:
– Included GPRS and CDMA2000 1x technologies
– Data rates up to about 144 Kbps
• 2.75G:
– GSM-based EDGE wireless data technology
– Sometimes also labeled as “2.9G”
8
9. 3G Networks
• Third generation networks.
• Having data rates of 384 Kbps and higher.
• Prominent 3G networks:
– UMTS (Universal Mobile Telecommunication Service)
• In United States:
– UMTS and CDMA2000 1xEV-DO have been deployed
• FDD means different frequencies are used.
• TDD means one frequency is used in both up and
down links.
9
10. 3.5G and 3.75G Networks
• 3.5G (HSPA – High-speed packet access):
– Evolved from UMTS
• 3.75G (HSPA+)
10
11. 4G Networks
• Consists of WiMAX and Long-term evolution
(LTE).
• WiMAX never really “caught on” in the
industry.
• True 4G technology is LTE Advanced (LTE-A).
11
12. Development and History of Digital
Cellular Technology
• GSM and CDMA are still operational within
carrier networks:
– Not the first-choice technology to carry traffic
– Hanging around for multiple regulatory and
operational reasons
• By around 2016, most wireless carriers will
officially “sunset” 2G technologies.
12
13. Performance of Cellular Systems
• Performance of cellular systems is restricted
primarily by co-channel interference.
• Until around 1992, cellular carriers had always
used analog technology and 850-MHz
spectrum in their networks.
13
14. Early Problems to Cellular Carriers
• By the mid-1990s, the critical problem for 850-
MHz cellular carriers became system capacity.
• Frequency division multiple access (FDMA), an
earliest multiple-access methods used to
derive more capacity.
14
15. Cell Splits
• From 1983 until the early 1990s, the only
option to increase the system capacity was to
do cell splits.
• This method still didn’t produce enough
additional capacity, wireless carriers turned to
digital wireless technologies to augment
network capacity.
15
16. Illustrating Cell Splits
Notice that the coverage area stays the same; yet there are three base stations
in place after the cell split instead of two. So there is a 33 percent increase in
coverage and capacity in the same geographic area after the cell split occurs.
16
17. Digital Wireless Technology
• In 1992, the first digital wireless technology in
the US, known as IS-54 or “D-AMPS” (digital
AMPS):
– used time division multiple access (TDMA)
technology in order to increase system capacity
17
18. Digital-Radio Technology
• In the early-to-mid-1990s, three types of digital-
radio technology were used around the world:
– IS-136 (TDMA), which evolved from IS-54 D-AMPS,
global system for mobile (GSM) communication, and
code division multiple access (CDMA). IS-136 is now a
dead technology
– GSM has evolved over the years into more advanced
digital wireless technologies such as UMTS and HSPA
– CDMA technology, like GSM, has evolved into more
advanced digital wireless technologies as well
18
19. Digital Wireless Advantages over
Analog Cellular Systems
• Support substantially larger amounts of
capacity than the legacy analog (AMPS)
system.
• Digital base stations cost far less than analog
base stations.
• Produce cleaner and quieter signals.
• Provide greater security:
– Nearly impossible to hack, especially CDMA
systems.
19
20. Digital Wireless Advantages over
Analog Cellular Systems (2)
• No cloning fraud. Fraudsters could access AMPS
control channel transmissions.
• Smaller and more lightweight handsets.
• Mobile handset has a role in determining when a
call-handoff is required, and to what cell or cells
the handoff occurs:
– Decreases the potential for dropped calls during the
handoff process
• Use bit error rate (BER) and frame error rate (FER)
measurements instead of dB to assess
interference.
20
21. Global System for Mobile
Communication Technology
• GSM technology is a TDMA technology:
– TDMA systems assign both different frequencies
(FDMA) and different time slots (TDMA) to each
transmission. Separate channels exist for uplink
and downlink transmissions.
21
22. GSM and Incompatible Cellular Systems
• At the time GSM was developed:
– Six incompatible cellular systems were in operation
throughout Europe
– A mobile phone designed for one system could not be
used with another system
• Groupe Special Mobile (GSM) to develop a digital
cellular standard for the European market.
• Later, GSM = Global System for Mobile
communications
22
23. Initial Era of GSM
• The first systems were activated in 1991.
• Commercial service began in 1992 and, by
1996, there were over 35 million GSM
customers being served by over 200 GSM
networks.
• GSM has been deployed in the 900-, 1800-,
and 1900-MHz frequency bands.
23
24. Initial Era of GSM (2)
• Many of the American PCS carriers chose GSM
as their digital radio wireless standard in late
1995.
• A full-rate vocoder allows for eight users
(conversations) over a 200-kHz channel
(carrier):
– Each channel occupies 25 kHz
– Each GSM channel transports eight calls
simultaneously
24
26. GSM Architecture
• Multiple 200-kHz channels will be assigned to
each base station.
• One time slot must be allocated for control
channel purposes:
– Up to seven subscribers can use a 200-kHz
channel simultaneously
26
27. GSM Subsystems
• GSM networks are divided into four
subsystems:
1. The base station subsystem (BSS)
2. The network subsystem (NSS)
3. The operations and support subsystem (OSS)
4. The mobile station subsystem
27
28. 1 - The Base Station Subsystem
• The base station subsystem is comprised of:
– Base station controller (BSC)
– Base transceiver station (BTS)
– The air interface
• The BTS consists of the antenna and the radio
transceiver at the base station.
28
29. GSM Network Architecture
The GSM network architecture. Note the various subsystems. MSCs can always connect to other
MSCs. In this diagram, it’s assumed that it’s an MSC of the same wireless carrier. OSS = operations
and support subsystem. 29
30. Base Station Controller (BSC)
• The BSC is the control computer that manages
many BTSs:
– Usually housed at the MTSO location
– Manages which radio channels are being used by
which BTSs
– Also manages the call-handoff process between
BTSs
– Regulates the transmit power levels of the base
stations and mobile handsets
30
31. Base station controller (2)
– As a handset gets closer (farther from) to the
tower, the BSC signals the mobile to lower
(increase) its transmitter power levels.
– Handle overheads associated with frequency
management, call setup, and call-handoff
31
32. 2 - The Network Subsystem
• The MTSO-based switch is the central
component of the network.
• Authentication center:
– Equipment Identity Register (EIR)
32
33. MTSO-based Switch
• Provides connection to the landline PSTN.
• Provides subscriber management functions:
– Mobile registration
– Location updating
– Authentication
– Call routing to a roaming subscriber
• Houses the home location register (HLR):
– HLR is a database that registers users in a cellular
network
– VLR: database that registers visitors
33
34. GSM Network Architecture
The GSM network architecture. Note the various subsystems. MSCs can always connect to other
MSCs. In this diagram, it’s assumed that it’s an MSC of the same wireless carrier. OSS = operations
and support subsystem. 34
35. Authentication Center (AuC)
• Part of the network subsystem
• Provides the parameters needed for
authentication and encryption functions.
• The Equipment Identity Register (EIR) is a
database used for security and holds records
for three types of mobile phones:
– Black: barred (e.g., stolen)
– Grey: to be tracked; may be used in network
– White: valid phones
35
36. IMEI (International Mobile Equipment Identity)
• When a mobile phone requests service from the
network, its IMEI is checked against the EIR to assess
which category the mobile phone is placed in.
• Every GSM handset manufactured has a unique
identification number known as IMEI.
• The IMEI number is a unique 15-character number
for every valid phone that a GSM network uses to
identify a mobile phone.
36
37. IMEI (2)
• It is assigned to the phone in the factory.
• If a subscriber’s phone gets stolen, the IMEI
number can be blocked, rendering it useless.
• It is unique and no two cell phones will have the
same original number.
– The word “original” is used here because the IMEI can
be changed with special software and a unique cable.
• New IMEIs can be programmed into stolen
handsets
– 10% of IMEIs are not unique, per BT-Cellnet.
37
38. IMEI (3)
• You can see the IMEI number of your phone
by dialing *#06# from the keypad.
• The IMEI number of each handset is stored in
the EIR:
– If the handset has been lost or stolen, the IMEI is
placed on the black list of the EIR and will not
work on the network.
38
39. 3 - The Operations and Support
Subsystem (OSS)
• It is the command center that is used to
monitor and control the GSM network.
• If a major outage occurs at a base station, the
OSS can determine where that BTS is located,
what type of failure occurred, and what
equipment the site engineer will need to
repair the failure.
39
40. GSM Network Architecture
The GSM network architecture. Note the various subsystems. MSCs can always connect to other
MSCs. In this diagram, it’s assumed that it’s an MSC of the same wireless carrier. OSS = operations
and support subsystem. 40
41. 4 - The Mobile Station Subsystem
• Consists of two components:
– The mobile handset
– The subscriber identity module (SIM)
41
42. The Mobile Handset
• The handset in a GSM network is different
from analog phones.
• The identification information of the
subscriber is programmed into the SIM
module and not the handset itself.
42
43. The SIM
• The SIM is a microcontroller embedded into a small
piece of plastic, which holds the GSM operating
program and customer and carrier-specific data.
• Identification information of the subscriber is
programmed into the SIM.
• The SIM card provides:
– Authentication
– Information storage
– Subscriber account information
– Data encryption
43
44. GSM Authentication
• The GSM system used authentication
technology to thwart wireless fraud.
• To date, there has been no cloning fraud on
GSM systems, mainly due to the fact that
authentication technology was incorporated
into the original standard.
44
45. Mobile-Assisted Handoff (MAHO)
• The mobile phone plays an active part in the handoff
process:
– The mobile phone, not the switch at the MTSO,
continuously monitors adjacent (neighboring) base
stations, measuring signal strength of adjacent cell’s
control channels.
• Identities of the 6 best BSs are sent to the switch.
• The network decides when to initiate a call handover.
45
46. GSM Network Architecture
The GSM network architecture. Note the various subsystems. MSCs can always connect to other
MSCs. In this diagram, it’s assumed that it’s an MSC of the same wireless carrier. OSS = operations
and support subsystem. 46
47. GSM Adjunct Systems
• The gateway MSC (GMSC):
– Query the HLR (home location register) to
determine the location of subscribers
– Calls from other networks (i.e., the PSTN) will first
terminate into the GMSC before being routed to
other network elements for processing (i.e., the
switch, or the voice mail system)
• Short message service center (SMS-SC): processes
text messages (160 characters max)
• Equipment identity register (EIR): identifies what
handsets are acceptable in a GSM network
47
48. GSM Adjunct Systems (2)
• Gateway GPRS support node (GGSN): gateway
providing access to external hosts wishing to
communicate with mobile subscribers
– GPRS will be discussed next.
• Service GPRS support node (SGSN):
– mediate access to network resources
– implements packet scheduling policy between different
QoS classes
48
49. GSM Data Communication
Technologies: GPRS and EDGE
• General packet radio service (GPRS) is not
really in use anymore in GSM networks today.
• GPRS has been replaced by its successor
technology EDGE (Enhance Data rates for
Global Evolution).
49
50. General Packet Radio Service (GPRS)
• It’s been known over the years as “2.5G”.
• It implemented a packet-switched domain in
addition to the circuit-switched domain that
existed in GSM networks.
• Theoretical maximum speeds of up to 171.2
kilobits per second (Kbps) were achievable
with GPRS using all eight GSM timeslots at the
same time.
50
51. GPRS Architecture
• Before GPRS, existing MTSOs were designed to
support circuit-switched traffic and could not
process packetized traffic.
• The two GPRS support nodes, required in a
GPRS-enabled wireless network:
– The serving GPRS support node (SGSN)
– The gateway GPRS support node (GGSN)
51
52. GPRS Network Architecture
The GSM/GPRS network architecture. Note how circuit-switched and packet-switched (data) traffic
domains are separated for processing. Note that this architecture is very similar when EDGE
technology is deployed.
52
53. The serving GPRS support node (SGSN)
• SGSN performs mobility management functions such
as mobile subscriber attach/detach and location
management.
• The SGSN is connected to the base station subsystem
(BSS) via a connection to the packet control unit (PCU)
in the BSC.
• Handles all packet-switched data within the GSM
network.
• The SGSN performs the same functions as the MTSO-
based switch for voice traffic.
• The SGSN is connected to the BSC, and is the service
access point to the GPRS network for mobile users.
53
55. The gateway GPRS support node (GGSN)
• The GGSN is used as an interface to external IP
networks.
• Connect to other GPRS networks to facilitate
GPRS roaming operations.
• GGSNs maintain routing information that’s
necessary to tunnel the protocol data units
(PDUs) to the SGSNs.
55
56. Other Network Nodes for
Implementation of GPRS Service
• PCU (packet control unit):
– a separate hardware element associated with the BSC
– decides whether data to be routed to the circuit
switched or packet-switched network
• Mobility management to locate the GPRS mobile
station.
• A new air interface for packet traffic.
• New security features such as ciphering.
• New GPRS-specific signaling systems.
56
57. GPRS Base Station Subsystem
• When either voice or data traffic is originated by
a wireless GPRS/GSM subscriber:
– It is transported over the air interface to the BTS
– From the BTS to the BSC in the same way as a
standard GSM call
• However, at the output ports of the BSC, the
traffic was separated:
– Voice traffic is sent to the mobile switch (at the MTSO)
per standard GSM voice call processing
– Data is sent to the SGSN via the PCU over a frame
relay interface
57
58. EDGE: Enhanced Data GSM
Environment
• EDGE is occasionally called E-GPRS (enhanced GPRS).
• Also known as “2.75G” technology.
• It’s mainly used as a fallback option in areas where
3G UMTS capacity or technology is unavailable
– A bridge between legacy GSM systems and W-CDMA
• EDGE is introduced within existing specifications and
descriptions rather than by creating new ones.
58
59. Data: GPRS vs EDGE
• Each GPRS time slot can handle:
– A maximum of 20 Kbps of user data for a
theoretical peak rate of 172 Kbps when all eight
time slots are used simultaneously
• EDGE squeezes more data into each time slot:
– A single EDGE time slot can handle up to 59.2
Kbps, for a total of 473.6 Kbps with all eight time
slots in use
59
60. GPRS and EDGE: Technical Differences
• GPRS introduced packet-switched data into
GSM networks.
• EDGE introduces a new modulation technique
and new channel coding:
– EDGE is an add-on to GPRS and GSM-based
wireless carrier cannot deploy EDGE unless they
have first deployed GPRS
60
62. GPRS and EDGE: Technical Differences (2)
• GPRS and EDGE have different protocols and
different behavior on the base station system
side.
• GPRS and EDGE share the same packet-
handling protocols on the core network side.
• EDGE increased capacity:
– The same GSM time slot can support more users
with EDGE
62
63. Table Showing Functional Differences
between GPRS and EDGE Technologies
Feature/Function GPRS EDGE
Modulation GMSK 8-PSK/GMSK
Modulation bit rate 270 Kbps 810 Kbps
Radio data rate, per time slot 22.8 Kbps 69.2 Kbps
User data rate per time slot
(radio data rate – packet headers)
20 Kbps 59.2 Kbps
User data rate (all 8 time
slots)
160 Kbps 473.6 Kbps
63
64. EDGE Impact on GSM/GPRS Networks
• The base station was affected by the new
transceiver unit capable of handling EDGE
modulation.
• The core GSM network does not require any
modifications.
• EDGE technology could be deployed with
limited investments and within a short-time
frame.
64
Editor's Notes
Chapter 3 – Bedell’s book
Chapter 3 – Bedell’s book
MSC: mobile switching center
BSC: base station controller (house at the MTSO location)
VLR: visitor location register
NSS: network subsystem
BSS: base station subsystem
MTSO: mobile telephone switching office
MSC: mobile switching center
BSC: base station controller (house at the MTSO location)
VLR: visitor location register
NSS: network subsystem
BSS: base station subsystem
MSC: mobile switching center
BSC: base station controller (house at the MTSO location)
VLR: visitor location register
NSS: network subsystem
BSS: base station subsystem
MSC: mobile switching center
BSC: base station controller (house at the MTSO location)
VLR: visitor location register
NSS: network subsystem
BSS: base station subsystem
BTS: base transceiver station
BSC: base station controller
PCU: packet control unit
