Editor’s note: Each Monday, technical writer Ed Crockett tries to unravel the geek speak and alphabet soup surrounding technology which can make buying decisions more difficult than they need be. This week, Ed takes a look at 2.5G services. Getting wireless technology from second generation (2G), which represents most cell phones in use today, to third generation (3G) is proving to be quite a technology leap for some wireless operators.

A 2G-3G transitional zone known as 2.5G is bringing improvements in existing data transmission and services, and 2.5G may prove to be a fertile testing ground for the wonders of 3G.

The subject of this, the second of three articles on wireless technology is an examination of 2.5G from each of two perspectives: GSM and CDMA. (We’ll spell out the acronyms in just a moment.)

Extending existing technology with 2.5G

2.5G is an extension to existing infrastructure to improve Internet access, data transmission rates and services without forcing a total overhaul of wireless infrastructure, and to provide a testing environment for the present and future developments.
Two dissimilar digital mobile radio technologies (airlinks) dominate global wireless infrastructures in 2.5G: Global System for Mobile communications (GSM)…a Time Division Multiple Access (TDMA) implementation…and Code Division Multiple Access (CDMA).
By far, the greater of the two primary wireless technologies…in terms of customer base…is GSM. The phenomenal global popularity of GSM is due to an extensive backbone network that spans Europe and much of the rest of the world, including the Americas. Unfortunately, this vast infrastructure must undergo considerable change for 3G.
GSM operators and customers face many challenges in moving to 3G, which is essentially a move to CDMA. Challenges facing GSM operators include extensive infrastructure overhaul. Customer challenges include the need to upgrade to new mobile phones as technology advances in several phases.

Interim solutions that lead GSM to 3G include, in order of implementation: High Speed Circuit Switched Data (HSCSD), General Packet Radio Service (GPRS), Enhanced Data for Global Evolution (EDGE), and Universal Mobile Telephone System (UMTS). *

GSM — HSCSD: The first of four stages of GSM enhancement toward 3G, HSCSD theoretically boosts the rate of data transmission from 14.2 to 57.6 thousand bits per second (kbps) by using multiple time slots. Skeptics say 28.8 to 43.2 Kbps is a realistic range due to the realities of mobile traffic, which would restrict the number of time slots available under normal traffic conditions. **
GSM — GRPS :The second of four stages of GSM enhancement toward 3G, GRPS theoretically boosts the rate of data transmission to 171.2 Kbps. Again, the skeptics are saying that reality brings this rate down considerably, to little more than a quarter of the theoretical rate. ***

GSM — EDGE : EDGE is an enhancement to GSM that boosts theoretical data transmission to 384 kbps while remaining compatible with existing GSM networks. More conservative estimates give this new technology no more than 70 Kbps throughput.

GSM — UMTS : A product of the International Telecommunications Union (ITU), UMTS represents a vision for the future of wireless. The vision is 3G, where things come together at last, where global roaming is reality, and where functionality of the mobile phone is super-enhanced.


Employed extensively in the Americas, CDMA is smaller in customer base but better suited to accommodate the demands of 3G. Designed originally for the U.S. military, and further developed by Qualcom, CDMA now provides the foundation for the future of mobile communications.

Like its counterpart, complete achievement of 3G goals involves several phases, albeit different ones, including 95A, 95B, MC 1X, and MC 3X.

CDMA…IS-95A. Referred to as cdmaOne, this technology is based on Internet Protocol (IP); therefore, IS-95 mode has great advantage over GSM. Data transmission rate is the basic channel rate of 14.4 Kbps.

CDMA…95B : The upgrade to 95B requires only an upgrade to base station software and no redesign of phones. A data transmission rate of up to 114 Kbps is expected.

CDMA…MC 1X : Ushering in the pre-3G CDMA phase is multi-carrier technology labeled MC 1X. This IMT-2000 standard brings dramatic improvement in Internet connectivity and increases data transmission speed to a maximum of 307 Kbps.****

CDMA…MC 3X : Finally, 3G arrives with multi-carrier 3X technology in the form of MC 3X. Under optimal conditions…latest phone set, upgraded network, moderate traffic…users can enjoy maximum data transmission rates up to two megabytes per second (2 Mbps).

Global standardization, global roaming, fast Internet and messaging are elements of the grand vision that is 3G. As Internet technology advances toward full broadband, mobile radio technology evolves to take advantage.

Next week: The promising world of 3G

(Note: Thanks to Mobile Data Evolution for having developed a resource-rich web. Visit them. www.mobiledataevolution.com/camparison.asp


* www.mobiledataevolution.com/comparison.asp

** www.wirelessclueless.com/data.asp

*** www.wirelessclueless.com/data.asp

**** www.wirelessclueless.com/data.asp