Talking about the third generation

3G is a specification developed by the International Telecommunication Union for the third generation of mobile communications technology, (analog cellular was the first generation, digital PCS the second). 3G digital cellular technology promises increased bandwidth: up to 384K bit/sec when a device is stationary or moving at pedestrian speed, 128K bit/sec in a car, and 2M bit/sec in fixed applications.

GSM (Global System for Mobile Communications) is an open, nonproprietary system that is the dominant cellular technology throughout the world today. GSM uses a variation of the Time Division Multiple Access (TDMA) protocol. Data is digitized and compressed, then sent down a channel with two other streams of user data, each in its own time slot. It operates at either the 900-MHz or 1800-MHz and 1900-MHz frequency band.

Another so-called second-generation wireless air interface is CDMA (Code Division Multiple Access). CDMA is a form of multiplexing, which allows numerous signals to occupy a single transmission channel, optimizing the use of available bandwidth. The technology is used in cellular telephone systems in the 800-MHz and 1.9-GHz bands.

How it works
Subscribe to the Tech Update newsletter
Here is a weekly newsletter to help you stay abreast of new networking standards and technologies by providing down-to-earth explanations of how they work.

Current circuit-switched GSM networks transmit data at 9.6K bit/sec or up to 43.2K bit/sec using multitime slot high-speed circuit switched data (HSCSD) upgrades. GSM's 3G counterpart, Wideband Code Division Multiple Access (WCDMA), offers much higher data speeds. WCDMA can support mobile voice, images, data and video communications at up to 2M bit/sec (local-area access) or 384K bit/sec (wide-area access). The input signals are digitized and transmitted in a coded, spread-spectrum mode over a range of frequencies. A 5 MHz-wide carrier is used, compared with 200 KHz-wide carrier for narrowband CDMA.

In fact, 3G technology applies equally to all standards that are being considered, including CDMA2000 in the United States. CDMA2000 can support mobile data communications at speeds ranging from 144K bit/sec to 2M bit/sec. Deployment is in the planning stages.

GSM-based packet radio services (GPRS), already extremely popular in Europe, are being rolled out now in the United States. With GPRS, datastreams are broken up into packets of data rather than the continuous stream of GSM circuit-switched networks. Packetized GPRS offers "always on" connectivity versus GSM, where users pay if they occupy a channel and don't transmit data or voice. GPRS is central to the promise of mobile Internet capability, delivering voice, video and data to subscribers at up to 115K bit/sec. In Europe, GPRS-equipped handsets are projected to be available for the mass market by early 2002.

The next stage in GSM evolution is Enhanced Data rates for Global Evolution (EDGE), with potential 384K bit/sec capability. Developed specifically to meet the bandwidth needs of 3G, EDGE is a new modulation scheme for the air interface that retains the basic frame structure of GSM and uses GPRS packet data protocols. EDGE is more important to GSM providers that have not or could not acquire the 3G license. As such, EDGE may well be a step in which the 3G license holders will skip in their evolution from GPRS to 3G.

Handset manufacturers are racing to deliver entry-level 3G cell phones that will deliver data, e-commerce, wireless Internet and intranet access to users anytime, anywhere and which may eventually replace much of what is now done on a desktop PC, laptop or a simple PDA.

Multimedia Messaging Service (MMS) may be the first killer app. MMS lets users record text messages synchronized with audio and video, and transmit them in non-real-time to cell phones and other hand-held devices. Handset manufacturers and application developers are also teaming to deliver real-time, interactive, multiple player gaming over a wireless device that will support 2.5G and 3G technologies.

Packet-based services present new challenges for carriers that are used to billing calls based on time and distance. Now they're faced with the need to measure, track and bill for information as digital packets of data.

However, since these enhanced service-level strategies are still in development, operators will need to tighten their alliances with infrastructure suppliers to try to distribute the initial costs of their spectrum investment. Their initial concern is to limit the costs for the construction of a new network that supports up to three times the transmission capacity of their existing 2G infrastructure.

A higher-capacity 3G network is a parallel network, requiring different base stations and many new and additional sites. In many cases, 3G base stations will be co-located with existing lower-capacity GSM base stations, thereby leveraging existing sites, towers and backhaul links.

As an interconnect solution for base stations, microwave radio can be installed, commissioned and redeployed easily and quickly, and provides a high degree of flexibility in terms of distance and traffic capacity. Wireless enables newly licensed operators to self-provide backhaul links without the need to rely on leased circuits from competitive, incumbent operators.

Talking about the third generation

Related Links