Introduction to EDGE

8/7/2019 Introduction to EDGE

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EDGEINT delta

Introduction to EDGE

Training Document

Issue 1© Nokia Networks Oy 1 (24)




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Contents

1 Objectives....................................................................................4

2 EDGE Key Features....................................................................5 2.1 General.........................................................................................5 2.2 Benefits for GSM Operators .........................................................8 2.3 Benefits for End Users..................................................................9 2.3.1 Web Browsing...............................................................................9 2.3.2 Mobile Video Applications...........................................................10 2.3.3 Consumer Applications...............................................................10 2.3.4 Remote LAN & Intranet Access..................................................10 2.4 EDGE Phases.............................................................................11 2.4.1 EDGE Phase 1 (3GPP Release 99) ...........................................11 2.4.2 EDGE Phase 2 (3GPP Release 4/5) ..........................................11

3.1 Modulation..................................................................................12 3 EDGE Basics.............................................................................12

3.1.1 GMSK Modulation.......................................................................12 3.1.2 8-PSK Modulation.......................................................................14 3.1.3 8-PSK Bursts ..............................................................................15 3.1.4 EGPRS Modulation and Coding Schemes .................................15 3.2 EGPRS Link Quality Control.......................................................18 3.2.1 Link Adaptation for EGPRS ........................................................18 3.2.2 Incremental Redundancy............................................................19 3.2.3 Combined LA / IR .......................................................................21

4 Review Questions.....................................................................23





1 Objectives

At the end of this module the participant will be able to:

• Describe the benefits for 2G network operators and end users

• Describe the different services in EDGE Phase 1 and 2

• Explain EGPRS modulation and coding schemes

• Describe EGPRS link quality control




EDGE Key Features

2 EDGE Key Features

2.1 General

Market analysts estimate that the amount of packet data traffic will dramatically

increase in the future. Nokia has also estimated that mobile Internet connections

will exceed normal fixed Internet connections already this year (2002).

Figure 1: Mobile Data Traffic Increase

Industry experts predict that by 2005, more than 65 percent of employees

worldwide will be equipped and trained for mobile work. As mobile equipment

gets more and more performance acceptance increases to integrate mobile

devices in ever more parts of professional and private life. Every month,

between five and seven million subscribers sign up for mobile services

including mobile data services.

And - the SMS success story will continue with short messages enriched by still pictures, audio clips or short video sequences.

Pair this phenomenal growth with subscriber demand for new services, such as

the ability to access and send data, is the need to move mobile services to the

next level of performance:

3G mobile networks.

With the rapid deployment of mobile use and the need for third-generation

capabilities, Nokia understands that faster network speed and data transmission





capabilities are crucial. To help operators enhance their existing networks to

provide new services and add new networks with the latest technologies, Nokia

is moving to the next level in mobile transmission:

Nokia Enhanced Data Rates for Global Evolution.

EDGE is not alternative for UMTS but a complementing technology that will be

used in parallel with WCDMA. By a smooth upgrade, 3G services can be

offered at a lower, but similar data rate as UMTS (Universal Mobile

Telecommunication System) does but earlier than in UMTS by using the

existing GSM infrastructure. Thus 3G-like services will maximize the usage of

the existing GSM investments.

In order to offer a 3G alternative to UMTS for network operators without any

3G license, e.g., Telia of Sweden, Bouygues Telecom in France (a.o.) GSMinfrastructure is being evolved to support mobile services with radio interface

data rates of approx. 500kbps. In the U.S., EDGE was chosen as a 3G

alternative for 2G GSM800 / 1900 and IS-136 TDMA networks.

Specification work has been shifted from ETSI (European Telecommunication

Standards Institute) to 3GPP (3rd

Generation Partnership Project) in order to

align the development of both GSM evolution and UMTS development. EDGE

is being specified in such a way that it will enhance the throughput per time slot

for both High-speed Circuit-switched Data (HSCSD) and General Packet

Radio Service (GPRS).

The enhancement of HSCSD is called ECSD (Enhanced Circuit-switched

Data), whereas the enhancement of GPRS is called EGPRS (Enhanced

GPRS).

EDGE can be applied to 2G networks using different frequency ranges

identified as

• GSM900

• GSM1800

• GSM900/1800 (dual-band networks)

• GSM1900 (U.S.)

• GSM800 (U.S., Asia)

• E-GSM (Extended GSM band, 880-890 / 925-935MHz)

• GSM-R (non-public GSM for railway control at 876-880 / 921-925MHz)

• IS-136 (D-AMPS) in 700MHz, 800MHz, 1900MHz




EDGE Key Features

The idea is to provide this increased data rate without major changes to the

existing GSM network infrastructure by introducing a new modulation

scheme, known as 8-PSK (Phase Shift Keying). This will not replace, but will

co-exist with the current GMSK (Gaussian Minimum Shift Keying) modulation.

8-PSK comprises 3 bits of the modulation signal and allocates it to one out of 8so-called symbols that are controlling the modulator.

As a GSM evolution, EDGE will provide significantly higher data rates on the

current 200 kHz GSM carrier. Data rates being specified by 3GPP would bring

• ECSD rates up to 48kbps / timeslot and

• EGPRS rates up to 60kbps / timeslot.

Thus, data throughput per carrier increases to

• 8 x 48kbps = 384kbps for ECSD and

• 8 x 60kbps = 480kbps for EGPRS.

For ECSD, it is possible to support an ISDN-type 64 kbps real -time service

with a low bit error ratio (BER) by allocating two time slots with 32kbps each.

The EDGE modulation will adapt to radio circumstances and hence offer the

highest data rates in good propagation conditions, whilst ensuring wider area

coverage at lower data speeds per timeslot.

Nokia EDGE uses 200 kHz radio channels, which are the same as current GSM

channel bandwidths. From a technical perspective, Nokia EDGE allows the

GSM network to offer a set of new radio access bearers to its core network.

Nokia EDGE is designed to improve spectral efficiency through link quality

control. Increased data traffic requires wider terrestrial transmission channel

widths. Nokia EDGE features flexible time slot allocation to mix and match all

forms of communications, including voice, data and video.

Introducing Nokia EDGE to a GSM network has little technical impact, since it

is fully based on and evolved from GSM, and requires relatively small

changes to network hardware and software, as Figure 1.1-3 shows.

© Nokia Networks Oy 7 (24)Issue 1




Figure 2: ETSI Release 99 EDGE Implementation

Nor do operators have to make any changes to the network structure or invest in

new regulatory licenses.

Nokia is dedicated to supporting GSM operators with wireless data solutions

that help create value in the marketplace, both now and in the future. Using the

new Nokia EDGE solution, Nokia strengthens market share by offering a wide

selection of modern 3G value-added services for network operators’ businesses.

Nokia EDGE was created to give operators a competitive edge, to help generate

more revenues, and to strengthen market share. Nokia’s aim is to protect

operators’ existing investments, while providing a smooth migration path to the

next generation of mobile telephony. Backed by Nokia’s long, solid expertise in

GSM systems and comprehensive knowledge of 3G systems, the Nokia EDGE

solution provides standardised EDGE features from the very beginning. Nokia

EDGE offers a cost-efficient evolution for GSM to move to 3G. Nokia EDGEoffers greater capacity and a higher Quality of Service (QoS) functionality

with existing site densities and frequency plans. Nokia EDGE is compatible

with GSM equipment and services and with all new emerging 3G services.

As one major driver within a small community of infrastructure suppliers,

Nokia is committed to moving the EDGE standard forward, with the main

driver being the Nokia All-IP Strategy. The design target is to deliver 3G

services as cost efficiently as possible by optimising the use of the radio

resources with the existing infrastructure platform as a basis.

2.2 Benefits for GSM Operators

The Nokia EDGE solution provides an unlimited EDGE growth path, not only

for macro-cellular and micro-cellular solutions, but also for local area solutions,

such as indoor configurations. It improves operators’ competitiveness in those

segments with the most demanding subscribers. Nokia EDGE is especially

attractive for GSM 900, GSM 1800, GSM800 and GSM 1900 operators who

wish to offer mobile multimedia applications at an early stage.

Compared to the data services currently available from GSM, Nokia EDGE

provides significantly higher capacity than GPRS. For operators, Nokia

EDGE offers the most cost-effective means to provide 3G services within theexisting spectrum. With Nokia EDGE, operators realise their full revenue

potential through incorporating international roaming in a convenient and cost-

effective manner.

With Nokia EDGE, operators with UMTS licenses can offer 3G capabilities to

all end users in a cost-effective manner. Wide-band Code Division Multiple

Access (WCDMA) combines well with Nokia EDGE for data intensive

applications, since Nokia EDGE is the most cost-effective service delivery




EDGE Key Features

vehicle for voice and data applications that require data user rates up to 128

kbps.

Nokia EDGE capability is available with Nokia MetroSite EDGE Base

Transceiver Station (BTS) and Nokia UltraSite EDGE BTS solutions as an easyunit upgrade. Since it houses both EDGE and WCDMA carriers, Nokia

UltraSite EDGE BTS also provides site evolution to WCDMA.

Operators can look forward to:

• Seamless delivery of all services across GSM / EDGE / WCDMA

• More revenue by 3G service delivery in GSM frequencies with EDGE

• Higher capacity and coverage

• Full global GSM / EDGE footprint and roaming as the Americas now

also go for GSM / EDGE - higher roaming incomes globally• GSM / EDGE roll-out already on-going

• EDGE and WCDMA with equal QoS support and complementing data

rates thus GSM / EDGE and WCDMA optimally complement each other

• 3G services delivery at lowest cost of coverage and capacity

• Shorter 3G services time to market enables faster 3G services penetration

2.3 Benefits for End Users

End users can look forward to:

• Improved service quality through increased data capacity and higher data

throughput that decreases response times for all data services

• New multimedia services

• A pathway to future 3G services.

WAP Applications

EGPRS will provide the necessary fast bearer to help WAP services to become

a success – finally. WAP based services would see EGPRS as a carrier enabling

User Datagram Protocol transmission. Wireless Mark-up Language (WML)

based services can be accessed in EDGE using the standard WAP gateways.

2.3.1 Web Browsing

All web applications running on some form of TCP/IP that is by nature a

protocol family for packet switched networks may use EGPRS as an ideal





bearer. Any packet switched application such as Internet connection offering

user data rates of more than 100kbps are supported.

2.3.2 Mobile Video Applications

Mobile imaging applications require a constant data throughput for high-quality

images. Transparent services enabled by ECSD with up to 64 kbps with two

air interface time slots provide a good platform for any mobile video

applications, e.g., video messaging, site surveillance, video telephony and video

on demand.

2.3.3 Consumer Applications

• Web browsing

• E-mail

• Chats

• News push

• Networked games

• Electronic commerce

• Digital Photo Post Card

2.3.4 Remote LAN & Intranet Access

• E-mail

• Database access

• File transfer

• Corporate information exchange

• Collaborative working

• Electronic Business Card

• Video Conferences




EDGE Key Features

2.4 EDGE Phases

2.4.1 EDGE Phase 1 (3GPP Release 99)

Phase1 of EDGE standardization was completed by early 2000 and includes

both ECSD and EGPRS services. EDGE Phase 1 will provide the following

services and main features:

• ECSD at 28.8kbps in transparent and non-transparent mode in one time

slot

• ECSD at 43.2kbps in transparent and non-transparent mode in one time

slot

•

ECSD at 57.6kbps in non-transparent mode in two time slots• ECSD at 64kbps in transparent mode in two time slots

• EGPRS at 8.8...59.2 kbps in up to 8 time slots

• Modulation and Coding Schemes (MCS 1...9

• Link adaptation combined with Incremental Redundancy (LA / IR).

Although EDGE specifies circuit-switched and packet-switched enhancements

for GSM networks actual infrastructure development and implementation focus

on EGPRS. At the moment (spring 2002) ECSD is likely to play no role.

Having EDGE-capable infrastructure equipment available, Nokia presently

focuses on EGPRS only.

2.4.2 EDGE Phase 2 (3GPP Release 4/5)

EDGE Phase 2 will bring improvements for voice and possibly data services.

The following items are seen as important in the evolution towards IP-based 3G

services:

• Introduction of real time packet services such as VoIP and Video over

IP.

• Handover for packet-switched connections to enable real time services.• "Enhanced AMR" and "Hi-Fi" speech codecs

• Multi-call utilizing simultaneous voice and data.

• Co-operation with UMTS Radio Access Networks

EDGE phase key characteristics will be presented in detail in Chapter 9.





3 EDGE Basics

3.1 Modulation

The basic concept to provide a higher data rate on the 200kHz carrier is using

an 8-PSK modulation that enables 3 times higher gross data rate of 69.2 kbps

per radio time slot by transmitting 3 bits/symbol with the existing symbol rate.

With multi-slot reservation, EDGE offers an evolution path for GSM to support

medium rate multimedia applications.

Table 2.1-1 below compares the currently used GMSK modulation with 8-PSK

modulation.

EDGE GSM

Modulation 8-PSK, 3bit / symbol GMSK, 1bit / symbol

Symbol rate 270.833 ksps 270.833 ksps

Payload / burst

(information part)

116 symbols

(2*3*58-2 = 346 bits)

114 symbols

(2*57 = 114bits)

Gross rate / time slot

(channel codingincluded)

4*346bits = 1,384bits / 20ms

(add.interleaving) = 69.2 kbps

22.8kbps

Table 1: 8-PSK and GMSK modulation details comparison

3.1.1 GMSK Modulation

To assure high speech quality and a maximum spectral efficiency, standard

GSM uses a phase continuous type of modulation: Gaussian Minimum Shift

Keying. It is a phase modulation that represents a serial bit stream as sliding

phase shift of the RF carrier.

The main processing steps in the modulator / demodulator are:

• Base-band filtering by a Gaussian low pass filter

• Differential coding to avoid reference signal for demodulation




EDGE Basics

• I / Q phase modulation

• Amplification

GMSK modulated signals have four different phase states, n*90° (n = 1...4).

The resulting vector of the modulated signal slides from one position to an other

avoiding hard “jumps” that would increase the modulation spectrum. The

amplitude of the vector is a constant one, a big advantage that requires less

accuracy of sub-sequent power amplifier.

The big disadvantage of this modulation type is the non-efficient usage of thephase modulator. For speech transmission, that GSM was developed for,

GMSK is a good modulation type.

In order to transmit higher data rates, it is necessary to describe more than only

one bit with one symbol. On the air interface, the symbol rate must be constant

and the same like in GSM. EDGE applications use the same air interface like

GSM application

Figure 3: GMSK phase trajectory

The big disadvantage of this modulation type is the non-efficient usage of the

phase modulator. For speech transmission, that GSM was developed for,

GMSK is a good modulation type.

In order to transmit higher data rates, it is necessary to describe more than only

one bit with one symbol. On the air interface, the symbol rate must be constant

and the same like in GSM. EDGE applications use the same air interface like

GSM applications.





3.1.2 8-PSK Modulation

An 8-PSK signal is able to carry three bits per modulated symbol over the

radio path, while a GMSK signal carries only one bit per symbol. A number of

possible transitions from one particular phase state to another are defined.

(0,0,1)

(1,0,1)

(0,0,0) (0,1,0)

(0,1,1)

(1,1,1)

(1,1,0)

(1,0,0)

(0,0,1)

(1,0,1)

(0,0,0) (0,1,0)

(0,1,1)

(1,1,1)

(1,1,0)

(1,0,0)

Figure 4: 8-PSK vector diagram

In order to avoid any transition through “0”, an additional rotation of the phase

states of 3π/8 per phase transition is applied.

As a result, an additional amplitude modulation is obtained that puts some problems to both, the MS and the network.

GMSK Modulated Burst 8-PSK Modulated Burst

Amplitude

Time

± 0.5dB

± 8dB

Figure 5:GMSK vs. 8-PSK burst




EDGE Basics

The major problems are:

• Higher requirements on linearity of all RF components involved, mostly

the amplifier

• Higher battery capacity required to ensure state-of-the-art handset stand- by and talk times

• Dissipation of heat

3.1.3 8-PSK Bursts

With EDGE, the air interface is the same as in GSM. The carrier spacing is 200

kHz and the length of each burst is 156.25bits in a time of 0.577ms, too. But

now, one 8-PSK-modulated bit is called one symbol that describes 3 original

bits. Thus, the EDGE burst looks like that:

8.2558 symbols58 symbols 26 33

Figure 6: EDGE Normal Burst

Tail symbols, “Payload” (2 x 58 symbols), including signalling symbols

(stealing flags, fast power control bits) and the training sequence are all 8-PSK

modulated. As GMSK is only a subset of 8-PSK, EDGE BTSs and MSs can process GMSK-modulated signals as well.

The 26 training sequence symbols are defined in a way that the additional

amplitude modulation is at a minimum level.

3.1.4 EGPRS Modulation and Coding Schemes

EGPRS will be built on top of GPRS using 9 different modulation and coding

schemes (MCS) which processes user bit rates from 8.8kbps up to 59.2kbps on

the radio interface and a bundling of up to 8 timeslots per user.

Thus, user data rates of 8 * 59,2kbps = 473kbps are achieved.

It should be noted that GPRS is not a subset of EGPRS, i.e., GPRS coding

schemes CS1 to CS4 are different to EGPRS GMSK MCS1 to 4.





Scheme Modulation Data Rate (kbps)

MCS-9

MCS-8

MCS-7

MCS-6MCS-5

8PSK

59.2

54.4

44.8

29.622.4

MCS-4

MCS-3

MCS-2

MCS-1

GMSK

17.6

14.8

11.2

8.8

P

r o t e c t i on

+

Scheme Modulation Data Rate (kbps)

MCS-9

MCS-8

MCS-7

MCS-6MCS-5

8PSK

59.2

54.4

44.8

29.622.4

MCS-4

MCS-3

MCS-2

MCS-1

GMSK

17.6

14.8

11.2

8.8

P

r o t e c t i on

+

Figure 7: Modulation and coding schemes

EDGE uses an enhanced 8-PSK modulation in addition to GMSK. Hence,

different protection sets are available in GMSK and 8-PSK, as thesemodulations do not have the same robustness to the propagation channel.

Nine protection schemes are designed for EGPRS: MCS1 - MCS9. The

information is encoded to resist channel degradation and modulated before

transmission over the air interface. MCS1 to MCS9 range from high protection

with low bit rate to no protection with high bit rate, as summarized in the table

below.

Table 2: EGPRS Modulation and Coding Schemes

GMSK modulation provides the robust mode for wide area coverage while 8-

PSK provides higher data rates. The MCSs are organized in families in order

to allow re-segmentation of the data block for link adaptation.

The protection that best fits the channel condition is chosen for maximum

throughput, as higher protection means lower throughput.




EDGE Basics

In general, a higher coding scheme has higher coding rate, and consequently

higher peak throughput, but it also tolerates less noise or interference.

0

10

20

30

40

50

60

0 5 10 15 20 25 30

MCS-1

MCS-2

MCS-3

MCS-4

MCS-5

MCS-6

MCS-7

MCS-8

MCS-9

Figure 8: Throughput Vs. C/i

Figure 8 shows throughput vs. C/I of EGPRS coding schemes in TU50iFH,

without incremental redundancy.

The basic unit of transmission is radio block (= 4 bursts = 20 ms on average),

which contains one or two RLC blocks.

From one data block to another, it is possible to switch between any of the

MCSs, as it is in GPRS. However, in GPRS, once a data block is segmented to

fit one particular coding scheme, it is not possible to switch the coding scheme

on reception failure and the retransmission takes place with exactly the same

protection as for its initial transmission. In EGPRS, it is possible to change the

MCS, i.e., the data block can be sent again but with better protection than for

its initial transmission.





3.2 EGPRS Link Quality Control

EGPRS LQC has been designed around two fundamental mechanisms:

• Link Adaptation (LA) and

• Incremental Redundancy (IR).

3.2.1 Link Adaptation for EGPRS

EDGE not only increases efficiency and speed, but also improves data

protection through link quality control. The system uses various measurements

of the past link to predict up coming channel quality. This prediction determines

the relevant protection of the information to be sent. The Link Adaptation (LA)

mechanism works to provide the highest throughput and lowest delay available by adapting the protection of the information to be sent, according to the link

quality.

MCS-7

MCS-1

22

MCS-2

28

MCS-3

37

MCS-4

44

MCS-6

74

5656

MCS-8

6868

MCS-5

56

MCS-9

74 74

Family AFamily C

Family B

Figure 9: EGPRS Link Adaptation

Enabling LA requires accurate link quality measurements and a set of

modulation and coding schemes (MCSs) with different degrees of protection.

The use of new, efficient EGPRS measurement provides accurate prediction of

upcoming link quality. The link quality measurements are Bit Error Probability

estimates (BEP). Nokia uses a link adaptation algorithm to work in co-operation




EDGE Basics

with IR. While IR improves throughput by adapting the total amount of

transmitted redundancy to the radio channel conditions, LA selects the amount

of redundancy for each individual transmission. This helps reduce the number

of re-transmissions, and thus keeps the transfer delay reasonably low.

Nine Modulation and Coding Schemes (MCSs) are designed for EGPRS as

described earlier. When an RLC data block is sent, the information is encoded

using one of the MCSs to resist channel degradation and modulated before

transmission over the air-interface. Since the resources are limited, the higher

the level of protection for information, the less information is sent. MCS-1 to

MCS-9 ranges from a high protection / low bit rate, to a no protection/high bit

rate. In EGPRS, it is possible to switch between any of the MCSs, from one

data block to another, as it is not the case in GPRS. The GPRS re-transmission

would take place with exactly the same protection as for its initial transmission.

In GPRS, retransmissions are in the same CS as the original trans-mission,

which causes problems if too high a CS has been selected. EGPRS allows a

retransmission to be performed in a lower MCS than original. For this, theMCSs are divided in three families:A, B and C. The payload of different MCSs

in a family (A,B or C) is chosen in such a way that resegmentation is possible

(the payloads are simply multiples of 2 or 4 of each other within a family). The

coding scheme can be changed within the family

MCS 7

MCS 5 MCS 5

MCS 7

MCS 5 MCS 5

Figure 10:Change of coding scheme

3.2.2 Incremental Redundancy

Incremental Redundancy (IR) is an efficient combination of two techniques,

Automatic Repeat request (ARQ) and Forward Error Correction (FEC). In the

ARQ method, when the receiver detects the presence of errors in a received

RLC block, it requests and receives a re-transmission of the same RLC block

from the transmitter. The process continues until an uncorrupted copy reaches

the destination. The Forward Error Correction (FEC) method adds redundant





information to the user information at the transmitter, and the receiver uses the

information to correct errors caused by disturbances in the radio channel.

In the IR scheme (also known as Type II Hybrid ARQ scheme), all the

redundancy is not sent right away. Rather, only a small amount is sent first,which yields a high user throughput if the decoding is successful. However, if

decoding fails, a re-transmission takes place according to the ARQ method.

Using IR, the transmitter transmits a different set of FEC information from the

same RLC block. These sets are called puncturing schemes, and there are two

(P1 and P2) or three (P1, P2 and P3) of them in each of the nine MCSs of

EGPRS. Supporting IR, the receiver is able to combine the necessary amount of

error correcting information. This mechanism is illustrated in Figure 2.6-1.

Since the combination includes more information than any individual

transmission, the probability of correct reception is increased. IR co-operates

with link adaptation, which selects the amount of redundancy information

transmitted in each transmission.

The benefits of IR are increased throughput due to better and automatic

adaptation to different and varying channel conditions and reduced sensitivity to

link quality measurements.

The IR mechanism in EGPRS is designed with the nine MCSs described earlier.

The basic characteristic of each MCS is its fixed data rate, hence a fixed

protection level. For each of the MCSs, it is possible to reach the same data rate

with the same protection level but with another punctering scheme.

Interference > corruption of data Store blockTransmission of GPSR data block

Puncturing

scheme 1

Puncturingscheme 2

Soft combiningRe-transmission Interference > corruption of data Block accepted

Interference > corruption of data

Interference > corruption of dataTransmission of GPSR data block

Re-transmission Block not accepted

Re-transmission Interference > corruption of data Block not accepted

•EGPRS "send and minimize re-sending"

•GPRS "send and pray" "


Puncturing

scheme 1

Puncturingscheme 2



Puncturing

scheme 1

Puncturingscheme 2










•EGPRS "send and minimize re-sending"

•GPRS "send and pray" "

Figure 11: Incremental Redundancy




EDGE Basics

original data

1/3 coded data

1st xmission

2nd xmission

3rd xmission

1st decoding attempt

2nd decoding attempt

3rd decoding attempt

r = 1/3

r = 1/2

r = 1/1

r = 1/1

r = 1/1

r = 1/1

Figure 12: IR example

Figure 12shows an example of IR transmission and combining with different

puncturing schemes for different transmissions. The shown case corresponds to

MCS-4 or MCS-9, where the basic code rate is 1. There are 3 punctering

schemes P1, P 2 and P3 for MCS-9 (MSC-4). The data block is first protected

with the P1 and sent over the air to the receiver, which tries to recover the data.

If this phase fails, the received P1 is stored in the receiver's memory for future

use, and the transmitter sends the data block protected with the P2 of the same

MCS. The receiver combines the received P2 with the stored P1 and tries to

recover the data from the combination of P1, P2 and so on. If after P3, the data

still cannot be recovered, P1 is sent again, and combined with the stored P1, P2

and P3 (which reaches a protection level of about 4 times the protection level of

P1), and so on.

3.2.3 Combined LA / IR

IR needs no information about the link quality to protect the data, as the right

protection is obtained incrementally and therefore, automatically. However, in

for example severe channel conditions, it may be that many retransmissions areneeded before getting the data through, hence consuming a lot of time and

resources. To avoid this phenomenon, the data block is protected with the MCS

selected after processing the measurements about the link quality, and the IR

mechanism takes place (P1, P2 and eventually P3, depending on the MCS).

When talking about EGPRS IR , we assume combined LA/IR . This

combination allows some very powerful protection levels, which could not be

achieved in a simple acknowledged mode (either IR only, or acknowledged

LA).





As the EDGE standard is not yet complete, the following figure is based on

preliminary simulations and do not include incremental redundancy, which is

expected to increase the link performance.

In order to show the tremendous benefit of EGPRS in contrast to existingcircuit-switched data at a max. speed of 14.4kbps the graph below indicates data

rate throughput vs. air interface interference (C/I ratio).

In a quite realistic situation of 18db more than double the speed can be achieved

with EGPRS.

Throughput vs C/I

0

10

20

30

40

50

60

0 5 10 15 20 25 30

dB

kbps

EGPRS

GSM

Figure 13: Data throughput vs. C/I




Review Questions

4 Review Questions

In the following questions, please select one or more answers that fit best.

1. What are the drivers for EDGE?

a) To provide 3G-like data services prior to UMTS operation

b) To provide regional enhancements to UMTS

c) To implement 3G services in the Americas

2. Which services are likely to be implemented?

a) ECSD because customers are used to circuit-switched services

b) EGPRS because packet-switched services are billed according to the

amount of transported data volume

3. What are the differences between EDGE implementation in the Americas and

in other regions of the world?

a) In the Americas, EDGE can use 2G spectrum to offer 3G-like services

b) As many U.S. operators actually replaces IS-136 infrastructure by

GSM900 / GSM1900 networks a smooth transition to 3G is possible

c) As many U.S. operators actually replaces IS-136 infrastructure by

GSM800 / GSM1900 networks a smooth transition to 3G is possible

d) In other regions, EDGE must not be implemented in GSM1900 networks

4. What are the advantages of GMSK?

a) Simple to implement, supports high data rates

b) Simple to implement, robust, with only low data rate support

c) During GSM development in the 80s’ of last century, it was one of the

most performing modulation technologies that could technically be

implemented

5. What are the key features of 8-PSK?

a) To enable an approx. 3 times higher user bit rate

b) Air interface gross bit rate has tripled

c) More resistant against air interface interferences

d) GMSK can be seen as an 8-PSK subset





6. What can be done to ensure a certain EDGE QoS level per region?

a) Use LA

b) Use IR

c) Use LA and IR

d) Restrict to a max. MCS level

7. What can be done to ensure a certain EDGE coverage per region?

a) Use LA

b) Use IR

c) Use LA and IR

d) Restrict to a max. MCS level

( ) © O

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Introduction to EDGE

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