ers worldwide and a growing popula- tion of subscribers in both North America and Latin America. UWC uses TDMA and Time Division Duplex (TDD) schemes, and it offers a total of six time slots. Because it employs TDD, one time slot is required for each end of the conversation, which means it can carry three conversations per channel. It operates in the 800MHz frequency band, uses AMPS for signaling to reserve resources, and transfers speech in digital form; therefore, it is a digital overlay that is interoperable with the analog AMPS infrastructure. TDMA can now support a 10-fold increase over AMPS capacity, using microcell and hierarchical cell engi- neering. In terms of data capabilities, the IS-136 standards that exist today include the following: IS-136 currently allows data rates up to 30Kbps. IS-136+ provides 43.2Kbps to 64Kbps. IS-136 HS (high-speed) ranges from 384Kbps to 2Mbps. It is looking toward the same sorts of data rates that 3G promises, it supports EDGE, and it uses the eight phase-shift keying (8-PSK) modulation scheme as well as GPRS (for packet data). UWC-136, an enhancement of IS-136, uses EDGE technology. It allows the U.S. TDMA community to migrate from 1G (IS-136) to 3G (UWC-136) sys- items. UWC-136 uses a wideband TDMA technique. cdmaOne cdmaOne is the CDMA Development Group's (CDG's; www.cdg.org) name for cel- lular carriers that use 2G CDMA technology (IS-95), and it offers a data rate range of 9.6Kbps to 14.4Kbps. cdmaOne describes a complete wireless system based on the TIA/EIA IS-95 CDMA standard, including the IS-95A, IS-95B, and IS-95 HDR revisions. It represents the end-to-end wireless system and all the necessary specifi- cations that govern its operation. cdmaOne provides a family of related services, including cellular, PCS, and fixed wireless (i.e., wireless local loop). The TIA/EIA IS-95 standard makes use of the spread spectrum technologies discussed in Chapter 13, "Wireless Communications Basics." It operates in the 800MHz and 1,900MHz frequency bands but can work on other fr