Vector sum excited linear prediction (VSELP) is a
speech coding
Speech coding is an application of data compression of digital audio signals containing speech. Speech coding uses speech-specific parameter estimation using audio signal processing techniques to model the speech signal, combined with generic d ...
method used in several cellular standards. The VSELP algorithm is an analysis-by-synthesis coding technique and belongs to the class of speech coding algorithms known as
CELP
Code-excited linear prediction (CELP) is a linear predictive speech coding algorithm originally proposed by Manfred R. Schroeder and Bishnu S. Atal in 1985. At the time, it provided significantly better quality than existing low bit-rate algori ...
(Code Excited Linear Prediction).
[ETSI]
EN 300 969 - Half rate speech transcoding (GSM 06.20 version 8.0.1 Release 1999)
Retrieved on 2009-07-11
Variations of this
codec
A codec is a device or computer program that encodes or decodes a data stream or signal. ''Codec'' is a portmanteau of coder/decoder.
In electronic communications, an endec is a device that acts as both an encoder and a decoder on a signal or ...
have been used in several
2G cellular telephony standards, including
IS-54
IS-54 and IS-136 are second-generation ( 2G) mobile phone systems, known as Digital AMPS (D-AMPS), and a further development of the North American 1G mobile system Advanced Mobile Phone System (AMPS). It was once prevalent throughout the Americ ...
,
IS-136
IS-54 and IS-136 are second-generation ( 2G) mobile phone systems, known as Digital AMPS (D-AMPS), and a further development of the North American 1G mobile system Advanced Mobile Phone System (AMPS). It was once prevalent throughout the America ...
(D-AMPS),
GSM
The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such ...
(
Half Rate
Half Rate (HR or GSM-HR or GSM 06.20) is a speech coding system for GSM, developed in the early 1990s.
Since the codec, operating at 5.6 kbit/s, requires half the bandwidth of the Full Rate codec, network capacity for voice traffic is doubled, at ...
speech) and
iDEN. It was also used in the first version of
RealAudio
RealAudio, or also spelled as Real Audio is a proprietary audio format developed by RealNetworks and first released in April 1995. It uses a variety of audio codecs, ranging from low-bitrate formats that can be used over dialup modems, to high-fi ...
for audio over the
Internet
The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...
. The IS-54 VSELP standard was published by the
Telecommunications Industry Association
The Telecommunications Industry Association (TIA) is accredited by the American National Standards Institute (ANSI) to develop voluntary, consensus-based industry standards for a wide variety of Information and Communication Technologies ( ICT) ...
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. In an actual TDMA cell phone, the
vocoder
A vocoder (, a portmanteau of ''voice'' and ''encoder'') is a category of speech coding that analyzes and synthesizes the human voice signal for audio data compression, multiplexing, voice encryption or voice transformation.
The vocoder was ...
output is packaged with error correction and signaling information, resulting in an over-the-air data rate of 16.2 kbit/s. For internet audio, each 159-bit frame is stored in 20 bytes, leaving 1 bit unused. The resulting file thus has a data rate of exactly 8 kbit/s.
GSM half-rate VSELP (GSM 06.20) uses 20 ms frames with 112 bits per frame, giving a raw data rate of 5.6 kbit/s. The iDEN VSELP coder has three modes:
* 30 ms frames at 126 bits per frame with a raw data rate of 4.2 kbit/s,
* 22.5 ms frames at 99 bits per frame with a raw data rate of 4.4 kbit/s and
* 22.5 ms frames at 180 bits per frame with a raw data rate of 8.0 kbit/s.
A major drawback of VSELP is its limited ability to encode non-speech sounds, so that it performs poorly when encoding speech in the presence of background noise. For this reason, use of VSELP has been gradually phased out in favor of newer codecs.
VSELP is also the encoding method used in some early Motorola Type II trunking systems. It was phased out in favor of the newer
IMBE method.
References
* Ira A. Gerson and Mark A. Jasiuk, ''Vector Sum Excited Linear Prediction (VSELP),'' IEEE Workshop on Speech Coding for Telecommunications, September 1989, pp. 66–68
* Ira A. Gerson and Mark A. Jasiuk, ''Vector sum excited linear prediction (VSELP) speech coding at 8 kbps,'' Proceedings of the 1990 IEEE
(ICASSP-90), April 1990, pp. 461–464
{{reflist
External links
Telecommunications Industry Association web site Speech codecs