IS95CDMA

IS-95 CDMA, also known as IS-95 or cdmaOne, is a second-generation (2G) mobile telecommunications standard that uses code-division multiple access (CDMA) on the air interface. Developed by Qualcomm in the 1990s, it was the first widely deployed CDMA-based cellular technology and served as the basis for the cdmaOne family and later CDMA2000.

IS-95 uses direct-sequence spread spectrum with a 1.25 MHz carrier, Walsh codes for channelization, and pseudo-random (PN) codes to separate users. The air interface supports simultaneous conversations by multiplexing users in the same frequency band. The system employs forward (base to mobile) and reverse (mobile to base) links, with bidirectional signaling for control and data.

Key features include dynamic power control to reduce interference (addressing the near–far problem), and soft handoff where a mobile unit communicates with multiple base stations during a transition. These mechanisms improve capacity and call quality in dense networks. The standard was originally designed to operate in 800 MHz and 1900 MHz bands in North America; later variants extended deployments to other bands.

IS-95 has undergone revisions, notably IS-95A, which added improvements to forward-link power control and reliability, and IS-95B, which introduced higher data rates and data services. IS-95 is a precursor to the CDMA2000 family, and its technology influenced the design of subsequent 3G CDMA networks. Today, IS-95-based networks largely transitioned to CDMA2000 and other 3G/4G technologies, but the IS-95 system played a critical role in popularizing CDMA as a mobile access method.