Digital signal processing apparatus and a communication system using the same

A communication system comprising:

• a base station side equipment connected to a public telephone line;
• and
• at least one terminal side equipment coupled to said base station side equipment via a radio communication line,
• wherein said base station side equipment comprises:
• a base station side signal processing means corresponding to each of a plurality of massage channels, said base station side signal processing means converting, on a digital-to-digital basis, a digital signal having a first transmission rate and applied from said public telephone line into a digital signal having one of a plurality of second transmission rates, each of said plurality of second transmission rates being less than the first transmission rate, and converting, on a digital-to-digital basis, a digital signal having one of said plurality of second transmission rates and applied from said terminal side equipment, into a digital signal having the first transmission rate;
• a plurality of storage means for respectively storing a plurality of different low bit rate coding/decoding programs;
• temporary storage means for temporarily storing any of said plurality of different low bit rate coding/decoding programs;
• control means for determining a low bit rate coding/decoding method of said applied digital signal to select a storage means, from one of the plurality of storage means, storing a low bit rate coding/decoding program corresponding to the determined low bit rate coding/decoding method and transfer the low bit rate coding/decoding program stored therein to said temporary storage means,
• wherein said base station side signal processing means carries out the digital to digital conversion according to the low bit rate coding/decoding program transferred to and stored in said temporary storage means, and
• wherein said terminal side equipment comprises a terminal side signal processing means for converting, on a digital-to-digital basis, a digital signal, having one of the plurality of second transmission rates received from said base station side equipment into a digital signal of a higher transmission rate according to the low bit rate coding/decoding program, and converting, on a digital-to-digital basis, a digital signal, having the higher transmission rate and to be transmitted to the based station side equipment into a digital signal having one of the plurality of second transmission rates.