Mobile users continue to demand higher data rates. With the continued growth in cellular services, laptop computer use and the Internet, wireless network providers are beginning to pay an increasing amount of attention to packet data networks. Enhanced Global Packet Radio Service (EGPRS) offers a substantial improvement in performance and capacity over existing GPRS services, in return for a relatively minimal additional investment. EGPRS, commonly called EDGE, achieves these enhancements to the GPRS system primarily by implementing changes to the Physical layer and to the Medium Access Control/Radio Link Control (MAC/RLC) layer. The significant improvements are a new modulation technique, additional modulation coding schemes, a combined Link Adaptation and Incremental Redundancy technique, re-segmentation of erroneously received packets, and a larger transmission window size.

1. EDGE Technology
By-
Ramrao Desai

2. Introduction
 EDGE – Enhanced Data rates for Global
Evolution
 Objective:
– to increase data transmission rates and
spectral efficiency
- to facilitate new applications and
increased capacity for mobile use

3. EDGE better than GPRS ,
how?
 GPRS – allows 115 kbps
theoretically up to 160 kbps
 EDGE – allows 384 kbps
theoretically up to 473.6 kbps
 new modulation technique
 error tolerant tx methods
 improved link adaptation mechanisms

5. Base Station Subsystem
(BSS)
 Composed of Base Station Transceiver
(BTS) and Base station controller (BSC)
 BTS – radio transmission and reception
equipment. It provides coverage to a
particular geographic area and is controlled
by the BSC
 BSC -- handles the medium access and radio
resource scheduling

6. Serving GPRS Support
Node (SGSN)
 Controls GPRS service in a particular geographical
coverage area
– provides a point of attachment for the GPRS
mobiles. A logical link is established between the
mobile station and the SGSN, via the base
station
– responsible for the transport and delivery of
packets to and from the user
– is responsible for validating the mobile stations,
before they are allowed access to the GPRS
system, and also performing security functions
such as authentication and ciphering

7. Gateway GPRS Support
Node (GGSN)
 provides connectivity to the external packet data
networks
 primary role is to route data to the mobile stations
at their current points of attachment
 Once the mobile station activates its packet data
address, the mobile station is registered with the
corresponding GGSN. The GGSN maintains a
routing table associating the active GPRS mobiles in
the system with a particular SGSN.

8. EDGE vs GPRS – a
comparison of technical
data

9. THE LAYERS …….
Physical layer
RLC/MAC layer

10. Physical Layer
Channel coding
Interleaving
Incremental redundancy
Modulation

11. Channel Coding
 Both the networks support adaptive channel
coding—
 for good channel conditions maximum
throughput is aimed at
 for poorer channel conditions error control
bits are used to reduce errors and hence
reduce the number of re transmissions

12. Coding Schemes
 GPRS – 4 coding schemes – CS1 to CS4
Each has different amounts of error
correcting coding that is optimized for
different radio environments.
 EDGE – 9 coding schemes – MCS1 to MCS9
– MCS1 to MCS4 – use GMSK
– MCS5 to MCS9 – use 8PSK

14. Interleaving
 Blocks are broken up and interleaved between
bursts. To receive the whole data all the bursts
need to be received.
 For GPRS – 1 in 4 bursts.
 For EDGE – 1 in 2 bursts.

15. Incremental Redundancy
 Initially uses MCS9 – little error correction
 Information received incorrectly - additional
coding is transmitted and then combined in
the receiver with the previously received
information.
 Procedure is repeated until information is
successfully decoded.

16. Modulation technique
 Modulation technique in GPRS – Gaussian
Minimum Shift Keying
 Every symbol that is transmitted represents
one bit; that is, each shift in phase
represents one bit

17. Modulation technique
 Modulation standard for EDGE – 8-Phase
shift Keying (8PSK).
 8PSK – linear modulation technique – three
consecutive bits are mapped onto one
symbol.
 The symbol rate remains the same but each
symbol represents 3 bits instead of one.
 Total data rate increases by a factor of
three.

19. Modulation Technique
( cont. )
 Distance between different symbols is
shorter using 8PSK.
 Increases misinterpretation.
 Under poor radio conditions extra bits will
be added for error correcting.
 Only under very poor conditions GMSK is
more efficient.

20. Link Adaptation –
Measurement Accuracy
 GPRS measure radio environment by
analyzing channel for carrier strength, bit
error rate……..
 Here measurements for interference are
performed during idle bursts ( twice during
a 240 ms period ).

21. Measurement
accuracy……..
 EDGE – measurements are taken on each and
every burst within the equalizer of the terminal
resulting in an estimate of the bit error
probability (BEP).
 Estimated for every burst, the BEP is a
reflection of the current C/I, the time
dispersion of the signal
 The variation of the BEP value over several
bursts will also provide additional information
regarding velocity and frequency hopping.

22. Measurement
accuracy……..
 This results in highly accurate
measurements even during short
measurement periods. Short measurement
periods, in turn, enable quick reaction to
changes in the radio environment. It is
therefore possible to achieve a better and
more flexible link adaptation for EDGE.

23. RLC/MAC layer
Fixed/Dynamic Allocation
Ack/Un-ack Operation

24. MAC (Allocation)
 Aids in queuing and sequencing during multiple
attempts
 Provides sequence numbers and headers
 Follows contention algorithms
 Signal data is given more priority to user data

25. Allocation contd.
 Channels are held as PDCHs (Packet data
channels) and released according to priority
(dynamic)
 Exclusive allocation of certain channels for
particular purposes (fixed)

26. RLC
 Error correction
 Retransmission
 Reassembly
 Segmentation

27. RLC contd.
 Error correction is done by selective
retransmission of only the erroneous frames
 The correctly received frames are buffered until
the erroneous frames are correctly received

28. RLC contd.
Two types of transmissions:
 Acknowledgement based
 Unacknowledged

29. Packet Handling
 EDGE – Has the ability to retransmit an
erroneous packet with a more robust coding
scheme
 GPRS -- Once packets have been sent, they
must be retransmitted using the original
coding scheme even if the radio environment
has changed.

31. Addressing window
 Tx addresses packets with a identification number.
 GPRS packets are numbered from 1 to 128.
Addressing window is 64.
 If an erroneously decoded packet must be
retransmitted, it may have the same number as a
new packet in the queue. If so, the protocol
between the terminal and the network stalls, and all
the packets belonging to the same low-layer
capability frame must be retransmitted.

32. Addressing window

33. EDGE benefits
 Short-term benefits –
– EDGE triples the capacity of GPRS.
– Boosts performance of existing
application and enables services such as
multimedia…..
– Enables transceiver to carry more
voice/data traffic.

34. EDGE benefits
 Mid-term benefits – Complementary Technology
– EDGE and WCDMA are complementary
technology.
– EDGE is designed to integrate into the existing
network – base not replaced or installed from
scratch making implementation seamless.
– With EDGE, operators can offer more wireless
data applications, including wireless multimedia,
e-mail, web infotainment and positioning services,
for both consumer and business users.

35. EDGE benefits
 Long term benefits – Harmonization with
WCDMA
– EDGE can be seen as a foundation toward one
seamless GSM and WCDMA network with a
combined core network and different access
methods that are transparent to the end user.
– Subscribers will be able to browse the Internet
on their mobile phones, personal digital assistants
or laptops at the same speed as on stationary
personal computers.

36. For further info……..
www.gsmworld.com
www.ericsson.com

37. THANK YOU