Short Time DFTフィードフォワードシラビックコンパンダの特性と構成

Abstract

Reducing the spectrum occupancy over radio channels is as well known as important to prevent from exhausting radio spectrum resources. The syllabic compandor provides with indispensable function both to improve speech quality and reduce fading noise over radio channels against to saving transmission power and narrowing spectrum occupancy. Therefore, many invesitigations are keenly studied on realizing the syllabic compandors. Unfortunatelly, most of them have been concerned with approximation in the way of AM demodulation to estimate envelope component with certain intermodulation error between input signals and their envelopes. When such approximating envelope detector is adopted to compressor/expander, the intermodulation error in the approximately estimated envelopes induces harmonic distortions to expand spectrum occupancy and to degrade speech quality in the aprior communication systems. An exact compandor is succesfully discussed with employing instantaneous spectrum analysis insted of AM demodulation approximations in realizing the envelope detectors, which is based on that compressing/expanding is precisely performed on the frequency domain. After being decomposed into instantaneous spectrum, input signals are processed via dividing/multiplying along each vector of the instantaneous spectrum components. The output signals are synthesized from the compressed/expanded instantaneous spectrum without alomost any harmonic distortions.