a transmitting part including an MP3 audio encoder, an FEC encoder, a modulator, a PN spreader, a high-frequency modulator, a power amplifier, a first controller converting an audio signal inputted through a microphone into an MP3 audio signal, FEC-encoding, and PN-spreading the MP3 audio signal, and then modulating the signal, to transmit it;

a receiving part including a low-noise amplifier, a high-frequency demodulator, a PN despreader, a demodulator, an FEC decoder, an MP3 audio decoder, an audio interface, an oscillator, a PLL circuit, and a second controller receiving the signal transmitted from the transmitting part, PN-despreading, FEC-decoding, and MP3-decoding the received signal, and then converting the signal into the original audio signal,

wherein the MP3 audio encoder does not use psycho-acoustic modeling and, accordingly, performs quantization at a bit rate higher than a predetermined first bit rate without driving an outer repetitive loop of a repetitive loop required for the psycho-acoustic modeling, to thereby convert the audio signal inputted through the microphone into the MP3 audio signal;

wherein the MP3 audio decoder comprises:

a side information extracting part finding a frame synchronous bit pattern from a frame in MPEG audio, reading frame header, extracting side information, and extracting a scale factor;

a Huffman decoder selecting a proper Huffman table to perform Huffman decoding;

an inverse quantifier readjusting constant values created after the Huffman decoding into energy values in the actual frequency domain according to the scale factor;

an aliasing processor adding up frequency values in each frequency band symmetrically to remove aliasing distortion in order to mitigate the aliasing distortion generated during quantization;

a second hybrid converter entering the result of the aliasing process as an input of MDCT, to perform frequency-time conversion; and

a sub-band composite filter bank applying convolution-addition method in order to remove discontinuity generated during inverse MDCT;

wherein a matrix calculation procedure performed by the sub-band composite filter bank is converted into 32-point IDCT so as to reduce the amount of calculation by half; and

wherein the second hybrid converter reduces the amount of matrix calculation using the matrix conversion method applied to the sub-band composite filter bank.