Kind of Prequel to my earlier post EDGE Evolution - Part 1
This will revisit the fundamentals of GPRS & EDGE (i.e. EGPRS)....
What is EDGE?
To enable data services in more improved manner to meet the
traffic explosion towards internet by mobile phone users, ETSI standardized
GPRS - General Packet Radio Service by Release-97 as an overlaid technology on
existing GSM networks which was supporting only 9.6 Kbps data rate at that time.Even though HSCSD was in trial and running commercially in few networks, GPRS brought minimum impact to the existing radio access
network to achieve higher than HSCSD data rates.Additional network elements (PCU/SGSN/GGSN) were introduced to
handle this traffic as shown in Figure 1.
The basic concept is some of the time-slots from GSM TRX is configured as GPRS channels and based on service request they are allotted to
users.
Unlike one channel for one voice call concept Note-1,
in case of GPRS the engineering is done in a way to allot more channels as per
demand for one user. This is already done in CSD/HSCSD implementation. But for
GPRS mobile handsets to use specific coding scheme in order to achieve higher
data rate compare to traditional 9.6 kbps per channel.
Due to further data services explosion, the demand for more
data higher data speed went up then 3GPPNote-2 who succeeded
ETSI in standardizations included EDGE in its portfolio as pre-step towards 3G
Networks. This was commercially deployed by Cingular in 2003
GPRS was considered as 2.5G and EDGE was considered as 2.75
G.
The date rate was brought from 9.6 kbps (CSD mode) to 43.2
Kbps by HSCSD. Then GPRS brought it up to 80 Kbps using GMSK Coding Scheme and
then EDGE brought it to revolutionizing 236.8 Kbps by using QPSK Coding Scheme. Note
that all these are theoretical calculations. To achieve this Mobile Equipment, BTS
& BSC-PCU required extensive SW & HW upgrades to support the rate.
Figure 2 shows various formats of data services using GPRS/EDGE network.
Figure 3 & 4 shows the data rates & Modulation schemes used by GPRS/EDGE Networks.
This also pushed the Gb interface from conventional FRAME RELAY type link towards IP link to achieve more flexibility, capacity
& redundancy. This is the step which laid the foundation for all IP network
at a later stage.
Then further 3G was introduced from which the data rate
grown from 384 kbps to 42 Mbps and looking at further evolutions like career
aggregation etc. Also 4G came in to play and data rate started from 42 Mbps and
touching 1.6 Gbps as recently demonstrated by NSN.
Note 1 : Earlier it was one call per one TS then it become 2-HR calls in one channel. There are substantial developments in the form of VAMOS in order to double the capacity once again.
Note 2 : 3GPP is the owner of all developments and standardization authority. It woeks closely with ETSI/ANSI and other regional standardizations bodies.
Figure 1 GPRS Standard Architecture
Figure 2 Data Service types during GPRS/EDGE Deployments
Figure 3 Data rates & Packet Data Technologies
Figure 4 GPRS & EDGE - Coding Schemes & Modulation Techniques
What is EDGE Evolution / EDGE II / Evolved EDGE?
During the 3G deployment & evolution experience higher
order modulation like 16 QAM / 32 QAM were found yielding more benefits in
terms of Spectral Efficiency/Higher Data Rate/reduced latency.
Mean time there were many operators left out to run only 2G Networks
or a bigger pie of their network is still in 2G mode ( i.e. reasons like due to
regulatory/investment/returns etc.). In order to utilize that 2G Network and
enable higher speed for customers who actually in no need of 3G+ level speeds, they
addressed to Vendors & 3GPP to look at some possibilities on the existing
2G Network evolution (Actually the story even continues post 4G auctions also).
So to achieve spectral efficiency/higher speed/low latency
using higher order modulation in EDGE enabled network become the final decision.
16QAM,32 QAM & 64QAM are inducted in EDGE Coding Schemes as part of 3GPP Release-7.
Figure 5 EGPRS2-A -Coding Schemes & Modulation Techniques
Figure 5 EGPRS2-B -Coding Schemes & Modulation Techniques
EDGE II is split as 2 phases to help operators and vendors to optimize the roll out & investment.EGPRS2A is only software enhancement in BTS & BSC-PCU with addition of HOM-Higher Order Modulation & Turbo Codes.
EGPRS2B is adding HSR-Higher Symbol Rate to increase the data rate from EGPRS2A. HW changes/upgrades required at BSS network to support the same.There is no architectural change from Figure-1.
To Summarize it...
- EGPRS-2A downlink: 8-PSK+16/32QAM+Turbo Codes
- EGPRS-2A uplink: 16QAM
- EGPRS-2B downlink: QPSK+16/32QAM+Turbo Codes+Higher Symbol Rate
- EGPRS-2B uplink: 16/32QAM+Higher Symbol Rate
So by enabling 5 Time slots we can achieve a data rate of 5 * 118.4 Kbps = 592 kbps.
References :
- EDGE Evolution (EDGE II or Evolved EDGE) – Definitions
Available From:
- A
Sharper EDGE for GSM by Mark Pecen, VP, Research in Motion
Limited Available
From:
- EDGE
Evolution Technology Introduction, Application Note 1MA129 by Rohde &
Schwarz
GSM/EDGE:
evolution and performance by Mikko Saily, Guillaume S´ebire , Eddie
Riddington.
Pages:
155,160 & 165
Available
From: Google Books for reference / Wiley Books
Important Enhancements
during GPRS to EDGE/EDGE II
Comparison of data rate & latency
Some enhancements that can be part of
EDGE II
Why EDGE II is needed now? and for whom?
Figure 2 : 3G to 4G Technology/Architecture Evolution 
