Bit-stream-arranged weighted modulation scheme for low delay spread frequency selective fading channels

Kiyoshi Kobayashi, Shuji Kubota

Research output: Contribution to journalArticlepeer-review


This paper proposes a bit-stream-arranged weighted modulation scheme to improve voice quality in low delay spread frequency selective fading channels. The proposed modulation scheme employs an input bit stream arrangement method that changes the bit stream order for significant bits so that they are not adjacent to each other over time; a mapping method that controls the amplitude of the modulation signals according to the importance of the bits; and modified differential encoding to prevent the error propagation from insignificant to significant bits. Computer simulations clarify that the proposed bit-stream-arranged weighted modulation scheme shows a S/N improvement of 8 dB in an 8-bit linear pulse code modulation (PCM) voice signal compared with the conventional non-weighted nf 4-shift quadrature phase shift keying (QPSK) modulation scheme. The proposed scheme also shows 3.5 dB improvement in a 4-bit adaptive differential pulse code modulation (ADPCM) voice signal. In this case, occurence of 'click noise' in recovered voice signal is halved. Although the proposed scheme increases the peak power of the modulated signals, the non-linearity of the power amplifier is not fatal.

Original languageEnglish
Pages (from-to)1452-1458
Number of pages7
JournalIEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences
Issue number7
Publication statusPublished - 1998
Externally publishedYes


  • Frequency selective fading
  • Microcell system
  • PCM
  • Weighted modulation

ASJC Scopus subject areas

  • Signal Processing
  • Computer Graphics and Computer-Aided Design
  • Electrical and Electronic Engineering
  • Applied Mathematics


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