Method of compensating for systemic impairments in a telecommunications network

A method of determining systemic impairments in a telecommunications network, comprising:

• sending digital symbols from a digital modem to an analog modem;
• receiving an analog representation of the digital symbols in the analog modem;
• training a receiver of the analog modem to recognize changes in the analog signals that correspond to known changes in digital symbols from the digital modem to the analog modem;
• transmitting a candidate set of digital symbols from a digital modem to an analog modem;
• receiving an analog representation of the candidate set of digital symbols by the analog modem;
• deriving a set of data information symbols from the analog representation of the candidate set of digital symbols;
• and
• transmitting a representation of the data information symbols from the analog modem to the digital modem.

A method of determining systemic impairments in an analog modem of a telecommunications network comprising:

• receiving an analog representation of a candidate set of digital symbols sent by a digital modem to said analog modem;
• deriving a mapping table relating the candidate set of digital symbols to the received analog representation of the candidate set of symbols;
• and
• transmitting a representation of said mapping table from said analog modem to said digital modem.

A method in a digital modem for improved spectral shaping using a transmit shaping transfer function comprising:

• transforming, by a mapping table, symbols to be transmitted into corresponding analog codes received upon transmission of said symbols through a telecommunications network, wherein the mapping table represents transformations of transmitted symbols resulting from systemic impairments in the telecommunications network;
• applying said corresponding analog codes as inputs to said transmit shaping transfer function;
• and
• performing spectral shaping using an output of the transmit shaping transfer function.

In a telecommunications network where PCM codes are transmitted by a digital modem and are attenuated or otherwise transformed by the telecommunications network, converted to analog signals and subsequently received by an analog modem, a method in a digital modem of compensating for robbed bits in said telecommunications network, wherein a robbed bit is defined as one or more least significant bits of said PCM code within a frame of multiple PCM codes that are used for carrying telephone system signaling information and are therefore unavailable for other use, and wherein said robbed bit may occur at any one of a number of positions within said frame, comprising:

• transmitting a candidate set of digital symbols to the analog modem;
• receiving a plurality of mapping tables, each of said respective mapping tables representing respective transformations resulting from systemic impairments that occur for each position within said frame when the one or more robbed bits are in given positions within said frame;
• and
• selecting mapping tables from the plurality of mapping tables, where said selection is dependent upon the position of said one or more robbed bits within said frame, to compensate for said robbed bits.

In a telecommunications network where PCM codes are transmitted by a digital modem and are attenuated or otherwise transformed by the telecommunications network, converted to analog signals and subsequently received by an analog modem, a method in an analog modem of compensating for robbed bits in said telecommunications network, wherein a robbed bit is defined as one or more least significant bits of said PCM code within a frame of multiple PCM codes that are used for carrying telephone system signaling information and are therefore unavailable for other use, and wherein said robbed bit may occur at any one of a number of positions within said frame, comprising:

• receiving an analog representation of a candidate set of digital symbols transmitted by the digital modem;
• deriving a plurality of mapping tables from said analog representation, each of said respective mapping tables representing respective transformations resulting from systemic impairments that occur for each position within said frame when the one or more robbed bits are in given positions within said frame;
• and
• transmitting representations of the plurality of mapping tables to the digital modem.