1XRTT

Technology for introducing packet data to IS-95 CDMA to improve the standard toward 3G. (Cingular)

CDMA2000 1x

CDMA2000 1x, the core CDMA2000 wireless air interface standard, is known by many terms: 1x, 1xRTT, IS-2000, CDMA2000 1X, 1X, and cdma2000 (lowercase). The designation "1xRTT" (1 times Radio Transmission Technology) is used to identify the version of CDMA2000 radio technology that operates in a pair of 1.25-MHz radio channels (one times 1.25 MHz, as opposed to three times 1.25 MHz in 3xRTT). 1xRTT almost doubles voice capacity over IS-95 networks. Although capable of higher data rates, most deployments have limited the peak data rate to 144 kbit/s. While 1xRTT officially qualifies as 3G technology, 1xRTT is considered by some to be a 2.5G (or sometimes 2.75G) technology. This has allowed it to be deployed in 2G spectrum in some countries which limit 3G systems to certain bands.

The main differences between IS-95 and IS-2000 signaling are: the use of a pilot signal on the IS-2000 reverse link to permit the use of coherent modulation, and 64 more traffic channels on the forward link that are orthogonal to the original set. Some changes were also made to the data link layer to accommodate the greater use of data services—IS-2000 has media and link access control protocols and QoS control. In IS-95, none of these were present, and the data link layer basically consisted of a "best effort delivery" RLP—this arrangement is still used for voice.

In the United States, Verizon Wireless, Sprint PCS, Alltel, and U.S. Cellular use 1x, and it is in use in Canada by Bell Mobility and TELUS Mobility. (Wikipedia)