The path to 3G began in earnest in the mid-1990s as first-generation (1G) analog systems yielded to second-generation (2G) digital systems. But this path isn't a straight line—it's more of a convergence, since there are many varieties of 2G systems (see the figure). The top and bottom paths of the diagram represent the U.S. systems: code-division multiple access (CDMA), also known as IS-95, and time-division multiple access (TDMA), also known as IS-136. (IS denotes an interim standard.)
Second from the top in the diagram is the Japanese path. It starts with Pacific Digital Cellular (PDC), which also is a TDMA implementation. The remaining path is the European model, Global System for Communications (GSM). This is a TDMA technology with frequency hopping. GSM is the fastest-growing system in absolute terms, while CDMA has the fastest growth on a percentage basis.
Continuing along the top path, IS-95 transitions to IS-95-B, which has higher data rates (64 kbits/s) for mobile data. This entire section of the diagram represents 2.5G systems, an intermediate step along the path to 3G. It's also essentially where we are now in time. IS-95-B will eventually shift to IS-2000 (also called cdma2000) and to multicarrier wideband CDMA (MC W-CDMA).
The second path begins at PDC, skips the intermediate 2.5G section, and continues in the 3G area with the NTT DoCoMo trials. NTT DoCoMo refers to the NTT Mobile Communications Network, which is the Japanese cellular company. NTT, of course, is Nippon Telegraph and Telecom. Interestingly enough, the DoCoMo moniker comes from the Japanese word for anywhere—doko mo. It's a reference to the anywhere/anytime goals of 3G systems. Next, this path leads to Japan's Association of Radio Industries and Business wideband CDMA (ARIB W-CDMA), a direct-sequence, spread-spectrum technology.
Initially, the two bottom paths go their separate ways. GSM changes to High-Speed Circuit Switched Data and General Packet Radio Service (HSCSD/GPRS). HSCSD uses the existing infrastructure with speeds up to 56 kbits/s. GPRS utilizes the existing circuit-switched GSM network infrastructure for voice traffic while adding a new packet-switched network for data traffic. The result is an improved data rate of up to 160 kbits/s, versus the 9.6-kbit/s rate of standard GSM networks.
On the bottom path, IS-136 upgrades to IS-136+ and IS-136 High Speed (IS-136 HS). IS-136+ improves the data rates to 43.2 kbits/s, while IS-136 HS jacks them up to 384 kbits/s. The two bottom paths eventually should come together with the Enhanced Data Rates for GSM Environments and the Universal Wireless Communications 136 standards (EDGE/UWC-136). EDGE employs a modified 8PSK (phase shift keying) modulation scheme to attain its 384-kbit/s data rate.
EDGE/UWC-136 is expected to become the UTRA W-CDMA system, which stands for UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access Wideband CDMA. This also is a direct-sequence, spread-spectrum technology.
Finally, all these paths are slated to join together this year as the International Mobile Telecommunication 2000 system (IMT-2000), with trials set to begin in 2001.
This entire transition is being driven by market pressure for enhanced data delivery and telephony services, global roaming, Internet access, e-mail, and even video. The evolution from 2G to 3G will supply the bandwidth to meet these demands.
