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Volume 20 (Apr 19, 2004)

3G BTS Systems and NEC Electronics (1/2)

3G mobile phone service area expansion

The mobile phone has become an indispensable item in both our business and personal lives. Mobile communications are making rapid advancement toward the realization of multimedia telecommunications services such as videophone and Internet access as well as still- and moving-picture e-mail. Supporting this advancement are 3G mobile phones that employ a frequency band with high transmission efficiency (2GHz) and aim to achieve 2Mbit/s (2G: 384Kbit/s) high-speed telecommunications. Revolutionary new telecommunications services are expected to make their debut in the near future.

However, even the most groundbreaking telecommunications services will not lead to an increase in the number of users if their service areas are limited. This is why service providers are expanding their service areas and working to create an environment in which multimedia telecommunications services can be realized anytime and anywhere. 3G mobile phone services already cover approximately 96% of Japan's population. Moreover, service providers are expanding 3G service areas through the installation of base transceiver stations (BTS) in tunnels, airports, subways, underground malls and other indoor areas where radio signals could not reach up until now.

Mobile phone system structure

Service area expansion is achieved by installing wireless BTS, which receive radio signals from mobile phones, in numerous locations. The range within which radio signals from mobile phones can reach a BTS is referred to as a cell. This is why mobile phones are sometimes called cell phones. Even if a mobile phone moves from one cell to another, the call is handed off to the BTS that controls the next cell (handoff function) so that it can be continued without interruption.

BTS convert the radio signals received from mobile phones to asynchronous transfer mode (ATM) protocol and then send them to a radio network controller (RNC) that controls multiple BTS. These signals pass through a mobile services switching center (MSC), which controls mobile phone connections and various services, and are then sent on to an existing public telephone network. This is how calls are made on a mobile phone (Figure 1).

With the advent of 3G mobile networking, further reduction in BTS size and weight is being called for since BTS must be set up in numerous locations to form a network that can be likened to a mesh net. In addition, plans are now under way to make the transition to full IP, whereby it will become possible for communications to be carried out using the same system employed by IP networks, which are representative of the Internet. Moreover, the smooth transition from ATM to IP systems has become an issue that must be addressed. Thus, various efforts are currently being made to further the evolution of 3G mobile phone systems.

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