Transcript Document

Enhanced Data
GSM Environment
Justin Champion
Room C208 - Tel: 3273
www.staffs.ac.uk/personel/engineering_and_technology/jjc1
Enhanced Data GSM Environment

Contents
 Why

do we need it?
Increased Data Rate

Video-on-Demand
 EDGE
 Benefits
over GPRS
 Movement towards 3G


Quality of Service
Packet Switched Voice
Enhanced Data GSM Environment
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Increased Data Use
3G UMTS
 As
discussed last lecture the
introduction of increased data rates
technology will take place over time.
 Each of these introductions will then
allow development towards 3G.

2.5 G
EDGE
GPRS
Each of these technologies will be built
upon to allow 3G



Last lecture we introduced GPRS
This time we are looking at EDGE
Both are referred to as 2.5G technology
2G
GSM
Enhanced Data GSM Environment
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Edge


Will allow another step towards the use of 3G
This will allow the infrastructure to grow and improve

Consider what would happen if a network went from 9.6 Kbps data access
to 2Mbps in a short time


It would not be able to cope as the companies would not be available to update
the entire network infrastructure that quickly
The network infrastructure would not cope and upgrades will be required.



This is already a consideration with EDGE level access
20 devices receiving a football stream at 200 (reasonable quality) Kbps in a
town centre
 Base station needs 20 * 200 = 4 Mbps
Now consider how many other base stations are also requesting the same
data?
Enhanced Data GSM Environment
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Edge
 Is
now being considered as a replacement for 3G
 Vodafone are intending to allow EDGE services this
year

Vodafone are pushing Edge now as a 3G technology

It will be available later this year via a data card attached to your
laptops
 Intended for business data users only initially
 Manchester, Liverpool and London are the cities it will operate
within
 (www.computerweekly.com/Article127287.htm, 2004)
Enhanced Data GSM Environment

The amount of value added services is predicted
to increase
 To
allow a greater choice of these services a higher
throughput will be required for the devices
 Device will always have limited storage in comparison
to what is available for them


A solution to this is to provide those services on-demand and
download them.
After use these can be deleted with no impact on the actual
device


Video on Demand is an example of this
Location based services i.e. show me a web cam of the inside
of the “Peking Temple” restaurant now!
Enhanced Data GSM Environment
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Video-on-Demand (VOD)
 Two choices for VOD
 Stream the entire film across the network in real-time


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
Download parts of the film in the background to the device and
play it when the film is in the storage of the device

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
Sensitive to any delays in the network
A powerful enough server would be needed to supply the demand
Does not need a large amount of storage on the actual device
Device will need sufficient storage
Some method would be needed to know what a person might be
interested in
 A pre-registration scheme for example with a football match
A scheme somewhere between the two would be ideal

Part of the video would be downloaded to get the viewer watching
whilst the rest would be downloaded in real-time
Enhanced Data GSM Environment
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EDGE

Developed by Erricson for the benefit of the loser in the 3G spectrum bidding
 Operates at a theoretical 384 Kbps within the current GSM transmission bands



This means that a company who has not paid for out 3G can still provide fast data
services
Companies that have bought 3G spectrum, will benefit from the infrastructure put in
place for EDGE, as this will be used for UMTS
Current infrastructure

The current Base stations will require a new transceiver and a software upgrade to
allow EDGE transmission



This can take place as and when the normal BS are being serviced
This allows for a wider coverage than will be available at least initially with the
UMTS network.
Obviously there are still the same issues as GPRS in respect that a channel that is
used for EDGE takes one away from a voice call
Enhanced Data GSM Environment
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EDGE continued
 The
data transferred is transferred using 8 Phase
shifting Key (8 PSK)



This can change and will be discussed further in a further
slide
This allows the transfer of 3 bits in each modulation
Three times GPRS and one of the reason why EDGE is 3x
faster

EDGE is more sensitive to errors and as such needs to be
close to the transmitter to allow maximum throughput of data
Enhanced Data GSM Environment
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EDGE continued
 Works
the same as GPRS as in a single GSM frame
is divided between the transmission
Channel
Use of the Channel
1
Voice
2
AAAABBABBAAAAFA
3
Voice
4
AAABAABAAAFAAAA
5
AAAFAFAFFFAFFFFB
6
BBBBABABAFFFFFFF
7
Voice
8
FFAFFAFFABABBBBB
Data Users
A = User 1
B = User 2
F = User 3
In this instance we
have 3 voice calls and
5 users receiving data
Enhanced Data GSM Environment
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EDGE
 As
with GSM and GPRS will have separate downlink
and uplink channels
 A discussion is currently taking place regarding the use
of 8-PSK
 As the internet is a download intensive environment


8-psk may only be used in the downlink
Uplink may well remain as the GSM GMSK
 This
will reduce the overhead of the 8-PSK
Enhanced Data GSM Environment
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Quality

EDGE uses packets which are physically closer together than the
GPRS system


This increases the likelihood of error taking place
Coding Scheme

As with GPRS, EDGE has a number of coding schemes to allow for
these errors


They range from
 MSC1 to MCS4 (using GMSK modulation)
 MSC5 to MSC9 (using the 8PSK modulation)
As with other wireless technologies

The best transmission rate is used to start and then a lower one will be
selected until successful communications can take place
Enhanced Data GSM Environment
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Quality

The code rate indicates how much of the packet is data
(including headers) and how much is error checking code

MCS3 indicates that 15% of the packet is error checking code
Modulation
Data Rate
Modulation Technique
Code Rate
MSC1
8.8 Kbps
GMSK
0.53
MSC2
11.2 Kbps
GMSK
0.66
MSC3
14.8 Kbps
GMSK
0.85
MSC4
17.6 Kbps
GMSK
1
MSC5
22.4 Kbps
8PSK
0.37
MSC6
29.6 Kbps
8PSK
0.49
MSC7
44.8 Kbps
8PSK
0.76
MSC8
54.4 Kbps
8PSK
0.92
MSC9
59.2 Kbps
8PSK
1
Enhanced Data GSM Environment
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Packet Handling improvements over GPRS
 If
a packet is sent which arrives corrupted


GPRS will send the packet again using the same modulation
technique
EDGE will lower the modulation technique used and send the
packet again.



The lowering of the modulation is a problem
 The available data in a new packet is reduced
EDGE allows for resegmentation and the packet being sent again
This allows EDGE to send packets at a rate which would normally
corrupted and then resend them again when a error takes place
Enhanced Data GSM Environment
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Error checking continued

Receipts for frames
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In GPRS a maximum addressing number is 128




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The window for receipts is a maximum of 64
This means that after a sequence of packets are sent an acknowledgement
for the last (at most) 64 packets is sent
If one of these packets were in error that packet must be resent based on the
addressing number
This can be an issue with large amounts of data being sent in error as the
addressing window will restart again at 0
 Indicating that an incorrect packet maybe resent
 In this event the entire frame sequence would need sending again to the
device
EDGE

Has increased the addressing number to 2048 and the window is now 1024
 Thereby reducing the chance of lost packets
Enhanced Data GSM Environment
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Error checking continued
 Forward Error Checking (FEC)
 As discussed previously it is better to send some redundant bits
with each packet, which in the event of error can be used to
mathematically recreate the original packet


EDGE


Alternative is to send each packet again with an increased rate of
FEC
Will send the packet again, but the new packet will be combined with
the original packet to recreate the corrupted part of the packet
 No increase in the amount of FEC bits are sent the same
number are sent again, but using different bits.
Correctly received packets

The FEC bits are a waste of available bandwidth!
Enhanced Data GSM Environment
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Working out the correct sending rate
 This
is a particular issue for data communications, rather
than voice
 To carry this out the radio environment needs measuring

Measuring for Bit error rate, carrier strength, interference, etc.
 Once
measurements are made the correct coding
scheme can be selected

Measurements can be taken on every burst of data sent


These measurements are used to generate the Bit Error Probability
(BEP)
Several of these taken can be used to give an accurate reading of
the quality of the signal and to calculate the velocity of the device
Enhanced Data GSM Environment
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Rollout Stages
 Phase 1
 Introduce single and multi-slot packet switched services
 Introduce single and Multi-slot circuit switched services
 Phase 2
 Web Use
 Email
 Real-time services


VOIP
Video Conferencing
Enhanced Data GSM Environment
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Interleaving of data

The data is sent in bursts



These bursts refer to the amount of information sent
If one of the bursts arrives corrupted the entire burst sequence
needs sending again
A radio block


The sequence of the packets being sent is referred to as a radio
block
GRPS


EDGE


The radio block are interleaved into 4
The radio block are interleaved into 2
Increased throughput

The potential for interference in the EDGE system has now been
reduced by a half

Assuming all other factors remain the same
Enhanced Data GSM Environment
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Infrastructure
 will
not need adding to from the GPRS environment
(www.ericsson.com/products/white_papers_pdf/edge_wp_technical.pdf, 2003)
Enhanced Data GSM Environment
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Infrastructure
 Changes
 Base station System GRPS Protocol (BSSGP)


Different quality of services are required require minor changes to
the GPRS standards
The other changes are obviously taking place in the layers 0 and 1
of the device and the base station
 A EDGE
Based device will be able to communicate with
GPRS

If a EDGE based service is not available at the time
Enhanced Data GSM Environment
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QOS classes
 The
classes which are supported by EDGE are the same
as UMTS
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Conversational


Streaming


Video – audio files, time dependent
 One way communication
Interactive


Real-Time communications highest priority
 Two way communications
WWW usage, telnet etc
 Reduced request response time
Background

SMS, email, MMS
 Best effort delivery
 Each
of the communications will be issued with one of
these classes.

This will depend ion the technology being used for EDGE
Enhanced Data GSM Environment
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Problem with the installation of EDGE
 No

Killer App YET !
There is no reason at this stage for user to want a EDGE based
phone
 Potential killer app maybe the downloading of music
 Apples i-pod (http://www.apple.com/ipod/, 2003)
 Allows the downloading of music onto the device, with 20Gb of
storage




Consider if these songs were downloaded in the background of
your phone and you pay for them.
You specify and pay for the album a few days in advance
Albums available to you the second they are released
Massive potential, with records that shops usually sell out of
Enhanced Data GSM Environment

Key Points
 Builds upon GSM and GPRS
 EDGE allows a theoretical 384 Kbps
 8-PSK
 Improved error handling over GPRS
 Will operate at GPRS, GSM data rates in EDGE is not available
Enhanced Data GSM Environment

Summary
 Why do we need it?
 Video-on-Demand
 EDGE
 Benefits over GPRS