Editing Digital AMPS (section)

==Successor technologies==
By 1993 American cellular was again running out of capacity, despite a wide movement to IS-54. The American cellular business continued booming. Subscribers grew from one and a half million customers in 1988 to more than thirteen million subscribers in 1993. Room existed for other technologies to cater to the growing market. The technologies that followed IS-54 stuck to the digital backbone laid down by it.

===IS-136===
A pragmatic effort was launched to improve IS-54 that eventually added an extra channel to the IS-54 hybrid design. Unlike IS-54, IS-136 utilizes time-division multiplexing for both voice and control channel transmissions. Digital control channel allows residential and in-building coverage, dramatically increased battery standby time, several messaging applications, over the air activation and expanded data applications. IS-136 systems needed to support millions of AMPS phones, most of which were designed and manufactured before IS-54 and IS-136 were considered. IS-136 added a number of features to the original IS-54 specification, including text messaging, circuit switched data (CSD), and an improved compression protocol. IS-136 TDMA traffic channels use π/4-DQPSK modulation at a 24.3-[[baud|kilobaud]] channel rate and gives an effective 48.6&nbsp;kbit/s data rate across the six time slots comprising one frame in the 30&nbsp;kHz channel.