Enhanced Data for Global Evolution (EDGE) should feature strongly in GSM operators’ network evolution plans — whether or not they are rolling out third-generation (3G) mobile networks based on Wideband Code Division Multiple Access (WCDMA), says Bjorn Samuelsson of Ericsson.
Despite being part of the GSM standard, the role of EDGE as a complementary, cost-effective 3G mobile technology is often overlooked or misunderstood amid all the discussions of WCDMA roll-out.
However, with the financial squeeze that many GSM operators are experiencing, the attraction of EDGE as a fast, cost-effective and future-proofed route to new service revenues is growing. EDGE gives GSM operators real opportunities for revenue generation, whatever their plans for UMTS/WCDMA-based services, and wherever in the world they are based.
Although the Americas initially led the way in EDGE deployment, the powerful economic arguments for EDGE mean that an increasing number of operators in other parts of the world are now looking at the technology as a means to boost the speed and capacity of GSM/General Packet Radio Service (GPRS), or as a complement to WCDMA. Now seems the right time to re-examine the benefits of EDGE, in light of the widespread deployment of GPRS and with 3G on the horizon.
EDGE boosts GPRS
EDGE immediately helps operators to maximize their return on investment in GPRS, because it can be added to an existing GSM/GPRS network quickly, easily and comparatively cost-effectively. EDGE is a radio modulation technique for GSM/GPRS networks that raises user data rates and increases capacity within existing spectrum, using existing infrastructure for the most part. It does this by introducing a new modulation scheme and enhancing the protocol that handles the packet data flow between the mobile handset and the Base Station Controller (BSC), tripling user data rates to 384kbit/s and above. No other part of the GSM/GPRS network is changed by EDGE.
In effect, EDGE ‘turbocharges’ GPRS, so that it can deliver high-quality, content-rich mobile multimedia services — including video clips, multimedia messaging (digital postcards with video attachments, for example), and interactive on-line games — to large-screen mobile devices.
EDGE is also spectrum-efficient: it requires fewer ‘timeslots’ to offer high data rates to individual subscribers. This means that, as well as boosting data rates, EDGE can also be deployed to serve up to three times the number of datacom subscribers as would be possible with GPRS alone, or to free up capacity for still-expanding voice traffic. Operators who have deployed EDGE have typically done so for a combination of these benefits.
EDGE also has the advantage of being a fully-fledged, well-supported technology, developed by Ericsson and other vendors since the 1990s.
EDGE is specified as part of the GSM/GPRS Release 99 standard, also known as EGPRS (Enhanced GPRS). This explains its success in the Americas, where several operators have been deploying GSM/GPRS networks from scratch and consider EDGE to be a fundamental part of the package, and not an add-on.
Full 3G coverage — faster
One of the other benefits of EDGE is that it offers a low-risk, low-cost evolution route for GSM/GPRS networks, enabling initial 3G services, either in specific areas or nationwide. Operators that do not have WCDMA licenses can still compete against those who do, by providing multimedia services over existing radio spectrum. However, even operators with WCDMA licenses are looking at EDGE.
EDGE and WCMDA can co-exist quite naturally. For example, EDGE could be used by operators planning to roll out WCDMA coverage to ensure widespread availability of initial 3G services from day one — quickly and cost-effectively. Subscribers will want, and expect, to be able to use advanced Mobile Internet services anywhere, but it will take time to achieve full UMTS/WCDMA coverage.
In this ‘hybrid’ scenario, operators can roll out UMTS/WCDMA in densely populated areas such as cities — where there is greater early demand for high-performance, data-heavy communications — and use EDGE as a complement to cover areas where there is less demand on the network. In this way, EDGE can deliver initial 3G services at times or in areas where UMTS/WCDMA is not available.
Once network-wide EDGE/WCDMA 3G coverage is in place, deployment of WCDMA can proceed in line with market demand, enabling the operator to control new network investment, manage cash-flow better, and make the best use of resources and expertise.
Some operators may be deterred by the thought of the further expenditure necessary to implement EDGE, particularly after the considerable investments made in GPRS and WCDMA. In fact, the good news for hard-pressed mobile operators is that initial 3G application coverage can be achieved very cost-effectively using EDGE. This is particularly true in the case of existing GSM/GPRS operators, because they are simply adding EDGE to an already established network infrastructure and using existing radio spectrum.
A study by consultancy Northstream (Positioning EDGE in a 3G World, Baskerville Communications, December 2000) showed that deploying EDGE and WCDMA in combination requires only half the capital expenditure (CAPEX) needed for WCDMA-only roll-out.
The Northstream study used the case of a hypothetical European GSM operator with UMTS/WCDMA spectrum for the roll-out of a nationwide 3G network. In one scenario the entire 3G deployment is carried out using only WCDMA; while in the other EDGE is rolled out, as a complement to WCDMA, in suburban and rural areas where traffic volumes are lower.
The main difference between the two scenarios is the number of radio base stations required. The GSM/EDGE 900MHz band provides better coverage characteristics than the higher-frequency 2GHz WCDMA band. WCDMA therefore needs more sites, and that means higher CAPEX (including site acquisition and construction, and hardware and software in the radio access network). Operating expenditure (OPEX) relating to site rental, and power and maintenance requirements is also higher in the WCDMA-only scenario.
Adding EDGE to the network typically requires only the introduction of a transceiver unit into existing radio base stations and a software upgrade of the GSM/GPRS network. This enables new multimedia service coverage to be deployed with minimal verification, and no impact on existing customer traffic, cell plan or number of radio sites. Once implemented, EDGE requires little additional investment, and upgrading the network can also be carried out gradually, with cells made EDGE-compliant over a period of time.
EDGE-compatible handsets are rapidly becoming available. The first GSM/GPRS/EDGE handsets have already entered the market on all GSM frequency bands (800/900/1800/ 1900), with multi-mode GSM/GPRS/EDGE/ WCDMA devices planned for introduction in 2004.
Where next for EDGE?
The next evolutionary stage for the mobile network after the deployment of EDGE is a series of network enhancements to increase alignment with WCDMA. These enhancements are currently being specified for the GSM/EDGE Radio Access Network (GERAN) within the 3GPP (Third Generation Partnership Project). Based on EDGE high-speed transmission techniques, combined with GPRS radio-link interfaces and further enhancements, GERAN will support real-time conversational and streaming services, as defined for WCDMA. This will enable the network to deliver a new range of applications, including IP multimedia applications.
While GERAN activities are ongoing, EDGE itself is quite definitely commercially established. EDGE has now come to the center of the mobile stage, with a variety of operators —with or without WCDMA licenses — now attracted by its impressive list of benefits.