Vendors and carriers are working to develop and deploy the next generation of wireless systems, often referred to as 2.5G, which is packet-based and increases data communication speeds to as high as 384 Kbps.
Upgrading will involve a newer radio network for modified air interface, cell planning, and modifications to the core and backbone network. However, 2.5G systems can use many existing infrastructure elements. CDMA-based carriers say they'll have a less expensive migration path than GSM/ TDMA-based carriers. For newer CDMA equipment, CDMA-based carriers may have only to change channel cards in their base stations and upgrade the network software, while GSM/ TDMA-based networks may require close to an entire network overlay.
3G technology would join the different 2G wireless systems into a global system providing data rates of about 2 Mbps. CDMA has emerged as the multiple access scheme of choice for 3G. The proposed 3G evolution path for TDMA-based systems, including GSM, is W-CDMA (Wideband CDMA), a standard proposed by Ericsson, while CDMA systems will evolve to CDMA 2000 systems. W-CDMA will incorporate an airlink that uses a 5-MHz-wide carrier to enable systems to support speeds of up to 2 Mbps; CDMA 2000 will combine three 1.25-MHz carriers to accomplish its rates.
In March 1999, Ericsson and Qualcomm ended a two-year patent dispute over W-CDMA by entering into cross-licensing agreements. This settlement was reached to foster the development of a single 3G CDMA-based standard. Today, almost all wireless equipment manufacturers have signed patent licenses with Qualcomm for CDMA products, including those that incorporate W-CDMA (see "Getting to 3G: Migration Path for Existing 2G and 2.5G Systems").
Many analysts expect the next-generation technology's cost and subscribers' lack of enthusiasm to keep it from becoming widespread in the United States until 2003 or later. However, many prominent service providers, like AT&T Wireless, Cingular, Sprint PCS and Verizon, have developed migration plans. These companies plan to deploy 2.5G networks this year and migrate to 3G networks in the next few years. AT&T had a TDMA-based network. After forming an alliance with NTT DoCoMo, however, AT&T began migrating to a GSM-based network, en route to deploying a GPRS (General Packet Radio Service) network. A few 2.5G deployments can be found in China, Europe, Japan, Korea and a few U.S. cities.
How soon migration to 3G will actually happen is a big question. The answer depends on the maturity of the technology and the appeal of mobile data applications, as well as the costs of implementation. It also depends on how well subscribers respond to 2.5G offerings. There is also the issue of frequency spectrum availability, which is an acute problem in the United States. The FCC plans to hold auctions for 3G licenses in September 2002. NTT DoCoMo expects to launch some 3G services in the coming months.
GPRS
GPRS was introduced as a packet-switched intermediate step to transport high-speed data efficiently over GSM- and TDMA-based networks. GPRS uses eight time slots in the 200-KHz channel and can support IP-based packet data speeds up to about 115 Kbps.
The two main additional infrastructure elements here are the SGSN (Serving GPRS Service Node) and the GGSN (Gateway GPRS Service Node). GPRS packetizes the user data and transports it using an IP backbone, with the GGSN acting as the gateway between the GPRS network and other packet-based networks, like the Internet. These GGSNs also connect to other GPRS networks to provide GPRS roaming.
The SGSN can be considered a mobile switching center. It enables mobility management by keeping track of all the mobile stations on the network, and it provides mobile-data packet routing to and from an SGSN service area.
GPRS uses the GSM network to look up the location-register databases to obtain subscriber-profile data. Enabling GPRS on a GSM network will also require a new air interface for packet-switched traffic.
With GPRS offering speeds between 14.4 Kbps and 115 Kbps, it should allow for better wireless Internet access. However, achieving the theoretical maximum GPRS data transmission speed of about 170 Kbps would require a single user to take over all eight time slots without any error protection.
Another standard, called EDGE (Enhanced Data Rates for Global Evolution), has been specified to improve the throughput per time slot in GPRS to support data rates of up to 384 Kbps using the same 200-KHz TDMA carrier.
CDMA Moves to 3G
Next-generation CDMA networks will come in two phases. The first is CDMA 2000 1X, and the second is CDMA 2000 3X. The "1X" and "3X" refer to the number of 1.25-MHz-wide air interface channels used.
CDMA 2000 1X would enable CDMA systems to improve data performance by providing IP-based packet data speeds of about 144 Kbps in the 1.25-MHz channel. Through modulation improvements and better power control, these systems would more than double the capacity of the earlier IS-95 systems.
CDMA 2000 1X uses a PDSN (Packet Data Serving Node) as the packet data gateway and the Mobile IP protocol to allow mobility management between the cellular network and a packet data network (see "Cellular Technology Comparison").
The newer generation of wireless technologies represents one of the biggest opportunities for equipment vendors and carriers to provide both businesses and users with value-added, location-independent services while opening up new sources of revenue.
Blesson Mathews is a research associate with the Center for Emerging Network Technologies at Syracuse University.
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