* Digital AMPS ( IS-54 and IS-136 ), a 2G mobile-phone standard that uses Time division multiple access

IS-54 stands for Interim Standard-54, which is a mobile communication standard employing digital technology.

The ANSI designation of IS-54 is ANSI / TIA / EIA-627, but this standard is still popularly referred to as IS-54.

The quest resulted in IS-54, the first American 2G standard.

The access method used for IS-54 is Time Division Multiple Access ( TDMA ), which was the first U. S. digital standard to be developed.

Time Division Multiple Access or TDMA was initially defined by the IS-54 standard and is now specified in the IS-13x series of specifications of the EIA / TIA.

IS-54 security features is also a matter of interest as it was the first standard to specify some security measures.

The IS-54 VSELP standard was published by the Telecommunications Industry Association in 1989.

D-AMPS ( IS-54 and IS-136 ) VSELP specifies an encoding of each 20 ms of speech into 159-bit frames, thus achieving a raw data rate of 7. 95 kbit / s.

To maintain compatibility with the existing AMPS cellular telephone system, the primary forward and reverse control channels in IS-54 cellular systems use the same signaling techniques and modulation scheme ( binary FSK ) as AMPS.

Using IS-54, a cellular carrier could convert any of its system's analog voice channels to digital.

IS-54 was, in fact, backward compatible with analog cellular and indeed co-exists on the same radio channels as AMPS.

That name is based on the abbreviation for time division multiple access, a common multiple access technique which is used by multiple protocols, including GSM, as well as in IS-54 and IS-136.

IS-54 is the first mobile communication system which had provision for security, and the first to employ TDMA technology.

IS-54 and IS-136 are second-generation ( 2G ) mobile phone systems, known as Digital AMPS ( D-AMPS ).

IS-54 maintains compatibility with Advanced Mobile Phone System ( AMPS ) in many ways.

IS-54 employs the same 30 kHz channel spacing and frequency bands ( 824-849 and 869-894 MHz ) as AMPS.

An AMPS / IS-54 infrastructure can support use of either analog AMPS phones or D-AMPS phones.

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-54, on the other hand, increased capacity by digital means using TDMA protocols.

IS-54 also supported authentication, a help in preventing fraud.

The IS-54 system has different synchronization sequences for each of the six time slots making up the frame, thereby allowing each receiver to synchronize to its own preassigned time slots.

The modulation scheme for IS-54 is 7C / 4 differential quaternary phase shift keying ( DQPSK ), otherwise known as differential 7t / 4 4-PSK or π / 4 DQPSK.

IS-54 uses the CAVE ( Cellular Authentication, Voice Privacy and Encryption ) algorithm for authentication and the CMEA ( Cellular Message Encryption Algorithm ) for encryption.

Variations of this codec have been used in several 2G cellular telephony standards, including IS-54, IS-136 ( D-AMPS ), GSM ( Half Rate speech ) and iDEN.

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