EDGE-ing Towards 3G
By Carlo Longino, Thu Feb 20 12:00:00 GMT 2003

While many carriers eschewed EDGE to go directly to WCDMA, its many benefits - and low cost - make it worth a second look.

Enhanced Data Rates for Global Evolution, or EDGE, has been something of an ignored technology. While it's found favor in North America, it has generally been ignored by European and Asian carriers. Perhaps it's been lost in the furor surrounding 3G, but mobile operators worldwide would do well to give it a second look - and some are doing just that.

EDGE offers carriers similar benefits to 3G - increased capacity and higher data rates. While the 474kbps theoretically offered by the technology doesn't approach the highest theoretical speeds of 3G, it's sufficient for most every existing application and opens the door for plenty of envisioned 3G services. But its most compelling attribute is that it can attain these advantages at a much lower capital expenditure and technical effort than 3G, and without any additional spectrum.

Three Is a Magic Number

EDGE is basically an enhancement to existing GSM/GPRS networks, using the same core network and requiring base station modifications (both hardware and software) to improve the radio interface between a user's device and a network's base stations. The basic technical upshot of EDGE is that it reduces by one-third the time slots used for data transmissions, thereby freeing up additional capacity for other voice or data users. This reduction in necessary time slots can also be used to support the same number of subscribers with higher data speeds.

EDGE accomplishes this by using a different modulation technique than standard GPRS: eight phase shift keying (8-psk). It allows the transmission of 3 bits per symbol as opposed to the one allowed by the Gaussian minimum shift keying modulation used by GPRS. So imagine a typical GSM network where a single frequency is split up into 8 time slots. Five of these slots are used for voice, and three for GPRS data. When using EDGE, subscribers using those three data slots could be handled in only one time slot, freeing up the other two to increase capacity or speed.

In a practical application, assuming fairly thorough and ambitious network planning, 150kbps (triple the speed of GPRS in a similar application) is guaranteed on cell borders in an EDGE network, with higher speeds in other parts of the cell.

Strong Business Case

EDGE has found its first and strongest acceptance in North America, where most carriers don't have sufficient spectrum for WCDMA, and regulators are still debating exactly what spectrum to allocate for 3G, and how and when to clear it. But EDGE offers these carriers the opportunity to launch 3G services in their existing spectrum, and launch those services on a much quicker timescale than if using WCDMA. The economics are pretty stunning - AT&T Wireless in the US said built out its national GSM/GPRS network covering a population of 221 million people at a cost of USD 15 per person, and the cost to add EDGE to that was only USD 2 per person.

The technology also lets carriers hedge their bets on WCDMA. EDGE offers speeds that should be sufficient for most every application in the short- and medium-term future, and EDGE networks can stand on their own or operate as part of an evolution to WCDMA. But EDGE also lets North American carriers make the best use of their existing spectral resources, allowing them to add more customers and drive voice and data service revenues without adding additional spectrum.

But EDGE also has a lot to offer European and Asian carriers. It can be used as a tool to remain competitive with carriers that will soon be launching WCDMA networks, allowing operators to build out high-speed networks at much lower comparative costs since existing cell sites can be used and little network re-planning is required.

But perhaps the most advantageous use of EDGE is as a supplement to WCDMA networks. Building WCDMA networks in urban areas is much more financially viable as opposed to suburban or rural ones, thanks to the tight concentration of users, and the tremendous cost of setting up the huge number of base stations to blanket less densely-populated areas is quite an obstacle.

But since EDGE can simply be added to existing base stations and doesn't require additional sites, it offers a cost-effective alternative to blanket these areas with high-speed coverage. The fact that it can operate at any GSM frequency means that 900-mHz networks, which offers greater cell coverage radius than 2-GHz WCDMA, will reduce costs. Indeed, Swedish consultancy Northstream estimates that European carriers can cut their capital expenditure in half by using such an approach.

Look Again

The low cost and relative technical simplicity of adding EDGE to GSM/GPRS networks should warrant a second look from carriers around the globe. In the face of the rising cost of 3G and growing customer frustration with the hype surrounding it, EDGE offers carriers a quick and simple way forward to higher data speeds and resultant higher revenues.

EDGE offers carriers a greatly cost-efficient evolution to 3G that maximizes their current network and spectral resources, delivering the benefits of new high-speed services while boosting network capacity.

Carlo Longino is a freelance writer based in Austin, Texas. His previous experience includes work for The Wall Street Journal, Dow Jones Newswires, and Hoover's Online.