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GPRS
Before GPRS: HSCSD
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HSCSD or High Speed Circuit Switched Data was the
first upgrade to be standardized by ETSI to bring high
speed data to GSM
The standardization process started as early as 1994
and therefore, HSCSD was the first high speed data
extension to be ready for implementation in 1999
Channel coding to increase the data rate from 9.6
kbps to 14.4 kbps
Up to 4 time slots combined per user.
HSCSD is able to reach throughput rates of up to 57.6
kbps
HSCSD Network Infrastructure
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HSCSD is a circuit-switched technology
One of its major advantages is that the existing core
network, mainly the MSC is able to handle HSCSD
traffic.
As opposed to GPRS, HSCSD neither requires
hardware upgrade within the network, nor does it
introduces new channel coding methodologies.
HSCSD is a rather simple upgrade of the standard
GSM, particularly in comparison with GPRS and
EDGE.
GPRS
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GPRS is a packet switched transmission
 Provides
the transmission of data in packet form
 Switches data at packet level
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Can always be online and users can be charged
based on the amount of transmitted data rather than
network time.
The radio and network resources are only accessed
when data actually needs to be transmitted between
the mobile user and the network
In between alternating transmissions, no network
resources need to be allocated
GPRS
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In circuit-switched transaction where resources are
being accessed permanently, regardless of whether
or not transmission is actually taking place
GPRS
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Therefore, packet-switching saves resources,
especially in the case of bursty transactions
GPRS
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Packet overlay over existing GSM digital circuit
switched network
Using packet-switching and is more suitable for bursty
traffic
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“Always on” / “Always connected”
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TCP/IP based (Allows data packets to be conveyed across
network using packet switching
After initial log-on, user is permanently connected to IP
services
Bandwidth on demand
Network resources only used when data is ready to be
transmitted
 More efficient utilization of air time
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Performance
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GPRS offers bandwidths up to 160 kbit/s
GPRS applies timeslot bundling and new channel
coding schemes have been defined, compared to
GSM
With 8 timeslots and coding scheme 4, GPRS is able
to provide a net throughput rate of 160 kbit/s
The channel coding schemes that provide for higher
data transmission rates per slot sacrifices data
protection for speed.
Performance
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The new coding schemes CS-2, CS-3 and CS-4
make less provision for forward error correction
and can only be applied when radio conditions
are good to excellent
1 timeslot
2 timeslots
8 timeslots
CS-1
8.0 kbit/s
16.0 kbit/s
64.0 kbit/s
CS-2
12.0 kbit/s
24.0 kbit/s
96.0 kbit/s
CS-3
14.4 kbit/s
28.8 kbit/s
115.2 kbit/s
CS-4
20.0 kbit/s
40.0 kbit/s
160.0 kbit/s
GPRS/GSM network architecture
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Network architecture
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For GPRS, the existing network switching
infrastructure cannot be reused. An entirely new core
network architecture is required.
The base station subsystem or BSS can be used for
both circuit-switched and GPRS packet-switched
services.
BSS needs to be upgraded with the so-called Packet
Control Unit or PCU
The new network elements within the GPRS core
network are the serving GPRS node (SGSN) and the
Gateway GPRS Support Node (GGSN)
GPRS, compared to GSM
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GPRS
GSM
2.5 G
2G
Packet switched network
Circuit switched network
Higher transmission rate –
160kb/s
Transmission rate only 9.6
kb/s
Allow direct connection to
internet
No direct connection to
internet
Charging per data volume
Charging per amount of time
connection
GPRS architecture differ from GSM
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Different
Mobile Station
New mobile station is needed for accessing GPRS
services. Backward compatible for voice calls
Base Transceiver Station Software upgrade is needed in the existing BTS
Base Station Controller
Software upgrade and new hardware, needed
packet control unit
GPRS support nodes
Installation of new core network elements – GPRS
support node, gateway GPRS node
Databases
Requires software upgrade to handle new models
and functions to handle databases involved in the
network
EDGE
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Formerly, EDGE was the abbreviation for Enhanced Data
Rates for GSM Evolution
With EDGE being adopted by the North American market,
EDGE is the acronym for Enhanced Data Rate for Global
Evolution
EDGE introduces a new modulation scheme which is an 8-PSK
in addition to GMSK in the case of GSM
GPRS and HSCSD works with the normal GSM modulation
scheme which is GMSK.
GMSK has lots of advantages, the most important of which
being that it does not contain any amplitude modulation.
Its low speed is one disadvantage.
In GMSK, only 1 bit can be transmitted per symbol, as
opposed to 8-PSK where 3 bits are transmitted per symbol
This makes 8-PSK three times faster than GMSK
EDGE requires a major hardware
upgrade
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EDGE is mainly concerned with the modulation
scheme on the Air-interface.
Adding 8-PSK as a new modulation scheme
requires all base stations to receive hardware
upgrades of their RF-parts to support the EDGE
technology.
This is a major undertaking which is risky, and
most importantly, costly to the operator.
EDGE (cont...)
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Require h/w and s/w upgrade of both BS and MS
Used 8-PSK in addition to GMSK
Uses 9 air interface formats, known a multiple
Modulation
and
Coding
Schemes
(MCS)
autonomously and rapidly selectable for each time
slot or user. Controlled by a feedback loop for
maximum throughput with an acceptable outage
performance
Using all 8 slots, can reach a max of 547 Kbps per
user, practically 384Kbps per user per carrier.