Comparison of DPCM and Subband Codec performance in the presence of burst errors Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/r207tr996

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  • This thesis is a preliminary study of the relative performance of the major speech compression techniques, Differential Pulse Code Modulation (DPCM) and Subband Coding (SBC) in the presence of transmission distortion. The combined effect of the channel distortions and the channel codec including error correction is represented by bursts of bit errors. While compression is critical since bandwidth is scarce in a wireless channel, channel distortions are greater and less predictable. Little to no work has addressed the impact of channel errors on perceptual quality of speech due to the complexity of the problem. At the transmitter, the input signal is compressed to 24 kbps using either DPCM or SBC, quantized, binary encoded and transmitted over the burst error channel. The reverse process is carried out at the receiver. DPCM achieves compression by removing redundant information in successive time domain samples, while SBC uses lower resolution quantizer to encode frequency bands of lower perceptual importance. The performance of these codecs is evaluated for BERs of 0.001 and 0.05, with the burst lengths varying between 4 and 64 bits. Two different speech segments - one voiced and one unvoiced are used in testing. Performance measures include two objective tests signal to noise ratio (SNR) & segmental SNR, and a subjective test of perceptual quality - the Mean Opinion Score (MOS). The results obtained show that with a fixed BER and increasing burst length in bits, the total errors reduce in the decoded speech thereby improving its perceptual quality for both DPCM and SBC. Informal subjective tests also demonstrate this trend as well as indicate distortion in DPCM seemed to be less perceptually degrading than SBC.
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