Method and apparatus compensating for effects of digital loss insertion

Abstract

The present invention provides a method and apparatus for minimizing quantization noise in signal transmissions between modems coupled together via a digital network resulting from the performance of digital loss insertion in .mu.-law encoded signal transmissions when the receiving modem is coupled to the digital network via an analog subscriber loop. In a preferred embodiment, the minimization of quantization noise is effected by providing in a digital modem means for .mu.-law encoding and decoding of signal transmissions, means for scaling the amplitude levels of signals generated by the first modem down by a predetermined reduction factor to obtain factored signals in addition to means for performing an inversion mapping comprising a scaling of the amplitude level of the factored, .mu.-law encoded signals up by a predetermined inversion factor to obtain a gain in the amplitude level of the factored signals corresponding to the predetermined loss inserted in the amplitude levels of the transmitted .mu.-law encoded signals. In accordance with an alternate embodiment, the minimization of quantization noise is effected independently of the transmitting modem through an inversion mapping of .mu.-law encoded signals forming .mu.-law code words when transmitted through an interexchange (IEC) digital network. The inversion mapping is performed by scaling the amplitude levels of .mu.-law code words up by a predetermined inversion factor to obtain a gain corresponding to the predetermined loss subsequently inserted in the amplitude levels of the .mu.-law code words. This is accomplished by providing within a digital switch of the IEC network means for detecting one of the existence of a terminating analog subscriber loop and the occurrence of loss insertion over the digital network, means for determining the amount of loss inserted in the signal transmissions, means for performing a .mu.-law code word-to-code word inversion mapping.