APPARATUS FOR TRANSMITTING DTMF TONE SIGNALS USING VOCODER IN WIRELESS LOCAL LOOP

摘要

PURPOSE: An apparatus for transmitting DTMF(Dual Tone Multi Frequency) tone signals using a vocoder in a WLL(Wireless Local Loop) is provided to prevent a distortion from being generated by not executing echo cancellation, in case that a DTMF tone signal is detected by a DTMF tone signal detector. CONSTITUTION: A hybrid(110), connected with a terminal directly, makes signals transmitted and received without loss. A tone detector(120) detects a DTMF signal among the signals supplied from the hybrid(110) and outputs control signals through another path. A matching part(12) matches the signals supplied from the tone detector(120) with the signals supplied from another path. A vocoder(14) codes the signals supplied from the matching part(12) into digital signals and supplies them to an RF(Radio Frequency) transceiver(15). The RF transceiver(15) up-converts the signals supplied from the vocoder(14) into RF signals and transmits the up-converted signals to a site(200) through a connected antenna. An echo canceling part(13) extracts part of the signals outputted from the vocoder(14) and supplies the extracted signals to the matching part(12) using the signal of the phase contrary to the phase of an echo signal supplied to the matching part(12) from the tone detector(120). An on/off controller(130) controls the on/off of the echo canceling part(13) according to the control signals outputted from the tone detector(120). An adjusted detector(160) detects and outputs a distorted DTMF tone signal among the signals outputted from the vocoder(14). A DTMF tone generator(140) receives the distorted DTMF tone signal, outputs it into a normal DTMF tone signal, and supplies it to the hybrid(110). A silence generator(150) generates a silence signal by a control signal of the adjusted detector(160) for a given time in order to discriminate the normal DTMF tone signal from the next DTMF tone signal.