EDGE – a currently vanishing 3G technology

All these years I have been looking up for that small `E` on my mobile screen so that I was sure about the connectivity on my nokia phone. I use the Airtel service for my mobile net and while there was no EDGE network over Vasai, I was used to the `G` symbol on same place before!

After the `G` came the `E`, which is still in use by most of India and is slowly fading out while `3G` is trying to replace it. 3G has already been rolled out on to BSNL-MTNL network, which is a very sad and un-corporate deed by the Government, I think. The other day I had to present about EDGE technology in my class and this is what I had!

`Note: this is total theroy with no practical example`

Enhanced Data rates for GSM Evolution
Enhanced Data rates for Global Evolution
Enhanced Data GSM Environment
Enhanced GPRS (EGPRS)
IMT Single Carrier (IMT-SC)

EDGE is a digital mobile phone technology that allows improved data transmission rates as a backward-compatible extension of GSM. EDGE is considered a 3G radio technology and is part of ITU’s 3G definition. EDGE was deployed on GSM networks beginning in 2003 — initially by Cingular (now AT&T) in the United States
EDGE/EGPRS is an enhancement for 2.5G GSM/GPRS networks, making it easier for existing GSM carriers to upgrade to it.

 

Edge History

Release ’97 of the GSM standard added packet data capabilities by means of General Packet Radio Service (GPRS). Then the Release ’99 introduced higher speed data transmission using Enhanced Data Rates for GSM Evolution (EDGE).
EDGE was actually deployed on GSM networks beginning in 2003 — initially by Cingular (now AT&T) in the US. All newer versions of the standard were backward-compatible with the original GSM system.

 

GSM EDGE evolution specification overview

Parameter Details
Multiple Access Technology FDMA / TDMA
Duplex Technique FDD
Channel Spacing 200 kHz
Modulation GMSK, 8PSK*
Slots per channel 8
Frame duration 4.615 ms
Latency Below 100 ms
Overall symbol rate 270 k symbols/s
Overall modulation bit rate 810 kbps
Radio data rate per time slot 69.2 kbps
Max user data rate per time slot 59.2 kbps (MCS-9)
Max user data rate when using 8 time slots 473.6 kbps **

Note:** A maximum user data rate of 384 kbps is often seen quoted as the data rate for GSM EDGE. This data rate corresponds to the International Telecommunications Union (ITU) definition of the data rate limit required for a service to fulfill the International Mobile Telecommunications-2000 (IMT-2000) standard(i.e. 3G) in a pedestrian environment.

*Uses 8-PSK in addition to GMSK

In addition to Gaussian minimum-shift keying (GMSK), EDGE uses higher-order PSK/8 phase shift keying (8PSK) for the upper five of its nine modulation and coding schemes. EDGE produces a 3-bit word for every change in carrier phase. This effectively triples the gross data rate offered by GSM. EDGE, like GPRS, uses a rate adaptation algorithm that adapts the modulation and coding scheme (MCS) according to the quality of the radio channel, and thus the bit rate and robustness of data transmission. It introduces a new technology not found in GPRS, Incremental Redundancy, which, instead of retransmitting disturbed packets, sends more redundancy information to be combined in the receiver. This increases the probability of correct decoding.

 

GSM EDGE time slots

EDGE, GPRS and GSM have to all operate along side each other in a network. It is a primary requirement that the evolutionary technologies are able to all operate on the same network. This ensures the service offered to existing customers using older phones along with those paying additional rates for the premium EDGE services. This means that the network has to support both services operating simultaneously.

Accordingly different slots within the traffic frames will need to be able to support different structures and different types of modulation dependent upon the phones being used, the calls being made and the prevailing conditions. It is quite possible that one slot may be supporting a GSM call, the next a GPRS data connection, and the third an EDGE connection using GMSK or 8PSK.

Using all 8 slots, can reach a max of 547 Kbps per user; practically 384 Kbps per user per carrier

 

GSM EDGE network architecture

GSM EDGE network architecture upgrades

Although in practice a variety of elements are required within the network architecture, the main new network architecture entities that are needed for the EDGE upgrade are:

•          SGSN:   GPRS Support Node – this forms a gateway to the services within the network.

•          GGSN:   Gateway GPRS Support Node which forms the gateway to the outside world.

•          PCU:   Packet Control Unit which differentiates whether data is to be routed to the packet switched or circuit switched networks.

A simplified view of the GSM EDGE network architecture can be seen in the diagram below. From this it can be seen that it is very similar to the more basic GSM network architecture, but with additional elements.

 

EDGE - network architecture

 

SGSN

The SGSN or Serving GPRS Support Node element of the GPRS network provides a number of takes focused on the IP elements of the overall system. It provides a variety of services to the mobiles:

•          Packet routing and transfer

•          Mobility management

•          Authentication

•          Attach/detach

•          Logical link management

•          Charging data

There is a location register within the SGSN and this stores location information (e.g., current cell, current VLR). It also stores the user profiles (e.g., IMSI, packet addresses used) for all the GPRS users registered with the particular SGSN.

GGSN

The GGSN, Gateway GPRS Support Node is one of the most important entities within the GSM EDGE network architecture.

The GGSN organises the inter-working between the GPRS / EDGE network and external packet switched networks to which the mobiles may be connected. These may include both Internet and X.25 networks.

The GGSN can be considered to be a combination of a gateway, router and firewall as it hides the internal network to the outside. In operation, when the GGSN receives data addressed to a specific user, it checks if the user is active, then forwarding the data. In the opposite direction, packet data from the mobile is routed to the right destination network by the GGSN.

PCU

The PCU or Packet Control Unit is a hardware router that is added to the BSC. It differentiates data destined for the standard GSM network (circuit switched data) and data destined for the EDGE network (Packet Switched Data). The PCU itself may be a separate physical entity, or more often these days it is incorporated into the base station controller, BSC, thereby saving additional hardware costs.

The EDGE network architecture can be viewed as an evolution of the GSM network carrying both circuit switched and packet data. The EDGE network architecture was also used as the basis for the 3G UMTS network. In this way network operators could evolve their networks GSM, to GPRS then EDGE and finally to the full 3G networks without having to replace and install more new equipment than was absolutely necessary

EDGE is four times as efficient as GPRS. GPRS uses four coding schemes (CS-1 to 4) while EDGE uses nine Modulation and Coding Schemes (MCS-1 to 9).

Coding and modulation
scheme (MCS)
Bit Rate
(kbit/s/slot)
Modulation
MCS-1 8.80 GMSK
MCS-2 11.2 GMSK
MCS-3 14.8 GMSK
MCS-4 17.6 GMSK
MCS-5 22.4 8-PSK
MCS-6 29.6 8-PSK
MCS-7 44.8 8-PSK
MCS-8 54.4 8-PSK
MCS-9 59.2 8-PSK

Services

Among the various possibilities offered by the GPRS include:

* “Chat”. Internet is full of chat rooms, which are discussed all the issues imaginable. It will be possible to access chat rooms from existing mobile terminals.

* Sailing on the network. With GPRS it will be possible to directly access pages on the World Wide Web written in HTML and have access to all contents of sites, including images.

* WAP over GPRS. The technology can be used to complement access to WAP services, enabling almost instant ligation and downloads of information faster.

* Images. It will be possible to receive and display photos, cards, and send pictures taken with digital cameras.

* Transfer documents. Access FTPs, etc.

* “E-mail”. The emails are received at the time the mobile does not require connecting to the server to check for new e-mails.

* Audio. Voice and sound files can be sent using the GPRS

* Other possible applications include using the mobile to control appliances equipped with Bluetooth technology from anywhere, and so on.

 

Evolved EDGE

Evolved EDGE improves on EDGE in a number of ways. Latencies are reduced by lowering the Transmission Time Interval by half (from 20 ms to 10 ms). Bit rates are increased up to 1 MBit/s peak bandwidth and latencies down to 800 ms using dual carriers, higher symbol rate and higher-order modulation (32QAM and 16QAM instead of 8-PSK), and turbo codes to improve error correction. And finally signal quality is improved using dual antennas improving average bit-rates and spectrum efficiency. EDGE Evolution can be gradually introduced as software upgrades, taking advantage of the installed base. With EDGE Evolution, end-users will be able to experience mobile internet connections corresponding to a 500 kbit/s ADSL service.

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