Enhanced Data rates for Global Evolution (EDGE)

EDGE Technology

By-

Ramrao Desai

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

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

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

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

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.

EDGE vs GPRS – a comparison of technical data

THE LAYERS …….

Physical layer

RLC/MAC layer

Physical Layer

Channel codingInterleavingIncremental redundancyModulation

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

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

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.

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.

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

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.

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.

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 ).

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.

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.

RLC/MAC layer

Fixed/Dynamic Allocation

Ack/Un-ack Operation

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

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)

RLC

Error correction

Retransmission

Reassembly

Segmentation

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

RLC contd.

Two types of transmissions:

Acknowledgement based

Unacknowledged

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.

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.

Addressing window

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.

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.

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.

For further info……..

www.gsmworld.com

www.ericsson.com

THANK YOU