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An Improved Version of Algebraic Codebook Search Algorithm for an AMR-WB Speech Coder
Volume 28, Issue 2 (2017), pp. 403–414
Pub. online: 1 January 2017      Type: Research Article      Open accessOpen Access
Received
1 October 2015
Accepted
1 May 2016
Published
1 January 2017

Abstract

An adaptive multi-rate wideband (AMR-WB) speech codec with a sampling rate of 16 kHz is known as one of the speech codecs employed in handheld devices that support 4G mobile communication systems. When applied to smartphones, it provides a superior speech quality relative to conventional speech codecs. Nonetheless, a major disadvantage is that an algebraic codebook search occupies a significant computational load in an AMR-WB encoder. In other words, the high computational complexity accounts for the high power consumption on a smartphone battery. This paper presents an improved version of depth-first tree search (DF) algorithm as a means to considerably reduce the complexity of an algebraic codebook search in an AMR-WB speech codec. This proposed search algorithm firstly involves the choice of a specified number of candidate pulses according to a pulse contribution ranking. Subsequently, a DF search is performed on the candidate pulses for a set of best pulses. Consequently, the target of the search and computational complexity reduction can be reached as expected. With a well maintained speech quality, this proposal demonstrates a search performance superiority over a DF and a global pulse replacement approach. Furthermore, with DF as a benchmark, a computational load reduction above 73% is reached in all coding modes.

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Biographies

Yeh Ming-Che
tp26610@gmail.com

M.-C. Yeh received the BS and MS degrees in electrical engineering from National Taipei University of Technology, Taipei, Taiwan, in 2012 and 2013, respectively. He is currently pursuing a PhD degree at the National Taipei University of Technology. His major area of research is speech processing and voice over IP, especially the NAT traversal algorithm and firewall traversal method.

Yeh Cheng-Yu
cy.yeh@ncut.edu.tw

C.-Y. Yeh received the BS and MS degrees in electrical engineering and the PhD degree in Graduate Institute of Mechanical and Electrical Engineering from National Taipei University of Technology, Taipei, Taiwan, in 2000, 2002, and 2006, respectively. Currently, he is an associate professor at the Department of Electrical Engineering, National Chin-Yi University of Technology, Taichung, Taiwan. His research interests include speech and image signal processing, network communication, and embedded system applications.

Hwang Shaw-Hwa
hsf@ntut.edu.tw

S.-H. Hwang received the BS and MS degrees in communication engineering and a PhD degree in electronic engineering from National Chiao Tung University, Hsinchu, Taiwan, in 1989, 1991, and 1996, respectively. He is currently a professor at the Department of Electrical Engineering, National Taipei University of Technology, Taipei, Taiwan. His major area of research is speech processing and voice over IP, especially video streaming over IP and NAT traversal method.


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© 2017 Vilnius University
Open access article under the CC BY license.

Keywords
speech codec algebraic code-excited linear-prediction (ACELP) algebraic codebook search depth-first tree search VoIP

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