Short Time DFT コンパンダの最適化構造とその雑音抑圧効果

Abstract

Effective utilization of the radio frequency resources is eager to be promised in narrowing spectrum occupancy bandwidth or saving transmission power. Unfortunately, the more efficient in narrowing bandwidth of angular modulation signals the merit of low-noise loses worse in wide-band amplifiers, or the more effective in saving transmission power speech quality is the worse suffered from such noises as thermal and fading. The noise reduction facility of implementing compander or diversity receiving becomes to be inevitable in the narrow band communication systems for preventing frequency resources from exhausting. The short time DFT compander achieves companding on the frequency domain with employing the concept of instantaneous spectrum without detecting the input signal envelopes. Where input signals are analyzed into instantaneous spectrum through the short time DFT, companding is performed via such operations as multiplying or dividing these components of instantaneous spectrum without giving any phase deviation to the vector of the spectrum. The output signal is, therefore, realized with synthesizing from the companded instantaneous spectrums. Noise reduction, which is one of the most important function of the compander, is examined to be sufficient for cellular telephone systems through baseband fading simulation system over 900MHz channel of existing cellular systems.