Voice control of the pan-European digital mobile radio system

Abstract

An important mode of operation for mobile radio systems is known as discontinuous transmission (DTX). In this mode the transmitter is switched on when a user begins to talk and switched off again when he stops.There are two reasons for using DTX: to increase the number of radio channels (by 100% or more) which can be accommodated in a given bandwidth and to reduce the power drain in hand portable equipment.Since system operators rely on the DTX working efficiently (to avoid excessive co-channel interference) it is also necessary to find ways of specifying and measuring the performance.This paper describes the DTX system which has been standardized by the CEPT for the Pan-European digital mobile radio system.

A multichannel speech/silence detector based on time delay estimation and fuzzy classification

“…So, the Fuzzy VAD proposed returns a continuous output ranging from 0 (Non-Activity) to 1 (Activity), which does not depend on whether the single inputs have exceeded a threshold or not, but on an overall evaluation of the values they have assumed (defuzzyfication process). The final decision is made by comparing the output of the fuzzy system, which varies in a range between 0 and 1, with a fixed threshold experimentally chosen by minimizing the sum of Front End Clipping (FEC), Mid Speech Clipping (MSC), OVER, Noise Detected as Speech (NDS) [12] and the standard deviation of the MSC and NDS parameters. In this way we found an appropriate value for the hangover module that satisfies the MSC and NDS statistics, reducing the total error.…”

“…As regards the objective parameters, the performance was evaluated considering the total contribution of FEC (Front End Clipping) and MSC (Mid Speech Clipping) in active voice frames to calculate the amount of clipping introduced, and the total contribution of OVER and NDS (Noise Detected as Speech) [12] in non-active voice frames to calculate the increase in activity. To estimate the amount of clipping which causes most perceived degradation in quality we propose considering the following three subclasses of objective parameters as well:…”

Subjective performance evaluation of the RPE-LTP codec for the pan-European cellular digital mobile radio system

“…the speech performance by the Voice-activity detector are not the subject of this paper but information relating to this topic can be found in [2].…”