Absfract-Toward the goal of providing digital radio services, thispaper describes the joint development of a medium bit rate speech coderalong with an effective channel coding technique to provide a robust,spectrally ...
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Absfract-Toward the goal of providing digital radio services, this
paper describes the joint development of a medium bit rate speech coder
along with an effective channel coding technique to provide a robust,
spectrally efficient, high quality mobile communication system. The
speech coder employed is a subband coder operating at 12 kbit/s which,
in the absence of channel errors, provides speech quality comparable
to current analog land-mobile radio systems. In addition, the subbandcoder design incorporates a unique coding of the side information to
facilitate the use of forward error-correction coding without the need
to code the entire bit stream. The use of excessive overhead for redun-
dancy is avoided while still mitigating the harsh effects of frequent
channel errors. These techniques have been employed in an experi-
mental FDMA digital land-mobile radio system. The combined speech
and channel coder operates at 15 kbit/s and provides intelligible speech
at fading channel error rates up to 8 percent.
This paper presents a new design technique for obtaining optimum M channel orthogonal subband coders where M equals 2i. All filters that constitute the subband coder are FIR type filters with linear phase. We carry ou...
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ISBN:
(纸本)081941638X
This paper presents a new design technique for obtaining optimum M channel orthogonal subband coders where M equals 2i. All filters that constitute the subband coder are FIR type filters with linear phase. We carry out the design in time domain, based on time domain orthonormality constraints that the filters must satisfy. Once a suitable low pass filter h0(n) is found, the remaining (M-1) filters of the coder are obtained through the use of shuffling operators on that filter. Since all resulting subband filters use the same numerical coefficient values (in different shift positions), this technique leads to a set of filters that can be implemented very efficiently. If, on the other hand, maximization of the coding gain is more important consideration than efficient implementation, the set of impulse responses obtained through shuffling can be further processed to remove the correlation between the subbands. This process leads to a new set of orthonormal linear phase filters that no longer share the same numerical coefficient values. In general, coding gain performance for this new set is better compared to the initial design. This uncorrelated decomposition can be thought of as counterpart of Karhunen-Loeve transform in an M channel filter bank.
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