Column

Evolved EDGE and the Future of TDMA

Network Computing Mobile Observer, October 18, 2006

By Peter Rysavy

Late last month I attended an analyst meeting in Boston hosted by 3G Americas, an organization that promotes GSM/UMTS-based technology in the Americas. One area of emphasis at the meeting was the likely evolution of 3GPP wireless technologies, including continued improvements
in UMTS such as High Speed Downlink Packet Access and High Speed Uplink Packet Access (with the combination referred to simply as High Speed Packet Access or HSPA), enhancements to HSPA called HSPA+ and the eventual move by the end of the decade to 3GPP Long Term Evolution--an OFDMA (Orthogonal Frequency Division Multiple Access) technology that shares a number of attributes with Mobile WiMAX. There are no surprises in this area, but information about the continued evolution of technologies based on TDMA (Time Division Multiple Access), including Evolved EDGE (Enhanced Data Rates for GSM Evolution), was new to many attendees. Evolved EDGE is a technology I studied fairly closely as part of a white paper I developed for 3G Americas. Published last month, "Mobile Broadband: EDGE, HSPA and LTE" was distributed at the meeting and is available at http://www.3gamericas.com.

GSM with EDGE today is by far the most broadly deployed and used wireless voice and data service. Globally, GSM has over two billion subscribers, gaining a whopping 500 million of these during the 12 months from the second quarter 2005 to the second quarter 2006. As of September 15, 2006, 160 operators in 91 countries are offering commercial EDGE services. It's likely that most GPRS (General Packet Radio Service) networks eventually will be upgraded to EDGE. Some operators were originally skeptical of EDGE, with UMTS coming online. However, there is an emerging realization that UMTS--because it requires a sizeable investment at every base station-- won't be deployed everywhere for quite some time. Additionally, providers don't want to drop UMTS/HSDPA users all the way to GPRS when they roam out of UMTS coverage. As described by a wireless architect I know, it's kind of like a car that goes only 100 mph or 10 mph. EDGE provides better service continuity between the two services. Hence, even many UMTS operators that were never going to deploy EDGE are now doing so.

Evolved EDGE enters the picture because continued radio technology improvements now make it possible to take EDGE to a whole new performance level. One such enhancement is duplexer technology, which allows simultaneous send/receive. Current devices cannot send and receive
simultaneously, thus limiting the number of time slots an EDGE device can use in the radio channel. Another enhancement is mobile receive diversity, where two radio receive chains operate in parallel on the device. Outputs are combined to extract a better signal, thus facilitating lower coding overhead and higher order modulation. Higher order 16-QAM modulation is yet another enhancement, as is simultaneously receiving on two radio channels. Add all these up and you get Evolved EDGE in 3GPP Release 7, which will have peak throughput rates of 1.3 Mbps with achievable user data rates of over 1 Mbps--previously the domain of technologies such as HSDPA. Of course, peak rates with new versions of HSDPA devices are now projected as high as 7.2 Mbps and, eventually, with HSPA+ as high as 28 Mbps. That's all well and good, but a super- charged version of EDGE actually could be very attractive for a number of operators.

First, there are quite a few GSM operators globally that have not yet committed to 3G deployment. These operators are doing just fine selling voice and lower-speed data services such as wireless e-mail. With the whole business model for mobile broadband somewhat up in the air, Evolved EDGE could be a much lower-cost way of beefing up data service while waiting for the mobile broadband business to mature. Even for operators offering 3G service, Evolved EDGE could allow 3G deployments to be focused in higher-density areas while a lower-cost alternative for higher-speed data service is offered in rural areas. All this will be especially attractive because some Evolved EDGE features will be a relatively straight-forward software upgrade to the network. In addition, Evolved EDGE devices are not likely to cost much more than EDGE devices. For price sensitive market segments, a single radio solution based on GSM/EDGE will be less expensive than a UMTS device that must also support GSM/EDGE, thus requiring two radios. The one radio solution brings power consumption benefits, too.

So, even as most attention focuses on 3G, evolved 3G and Mobile WiMAX technologies, TDMA-based GSM--along with its data service EDGE--will constitute the majority of subscriber usage through at least the end of the decade. Efforts like Evolved EDGE also show that it does not so much matter what the underlying radio technology is, but what service and benefits it can offer users.

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