Blind signal separation in ISDN local loop

To unobtrusively tap into an ISDN line local loop, for eavesdropping or testing purposes, requires the ability to blindly separate and recover the duplex signals in the transmission line. An observer has no access to timing or channel information. The only a priori information is a general pulse shape used for transmission and the format of the digital data. The receiver must combat multiuser interference, intersymbol interference, near and far-end echoes, and additive noise. A subspace algorithm is used in conjunction with the well-known JADE blind-beamforming algorithm followed by iterations of the ILSE algorithm. Symbol error rates for simulated and real data are presented.