Summary

• Most second-generation systems, including GSM, are based on TDMA.

• CDMA is a more advanced technology, but does not have the installed base of GSM. It is used as the basis for third-generation systems.

• TDMA usually allows each user to transmit or receive only part of the time. The capacity available to each user can be increased by allocating more time slots.

• One-way paging systems are evolving into two-way data networks.

• Metricom's Ricochet system provides high-speed wireless Internet access, but only in U.S. cities.

• PMR has moved from a niche application to a viable alternative to digital cellular. It offers advanced, faster call setup and other features, such as conference calling, though many owners of PMR terminals use them as regular cellphones.