Method and apparatus for determining transmit power levels for data transmission and reception

A modem for data transmission and reception, the modem having an initial training period for determining a transmit power level from a transmitted probe signal received via a channel, the transmitted probe signal having a sequence of a plurality of tones having predetermined frequency, amplitude and phase characteristics, the transmitted probe signal having a first power level and a second power level, the transmitted probe signal received for a minimum duration for each of the first and second power levels to form a plurality of sets of transmitted tones, the modem comprising:

• a data access arrangement coupleable to the channel to receive the transmitted probe signal, to form a received probe signal;
• an analog-digital converter coupled to the data access arrangement to sample and convert the received probe signal to form a plurality of sets of received probe tones;
• and
• a processor coupled to the analog-digital converter to receive the plurality of sets of received probe tones, the processor responsive to determine an average probe signal level for each tone frequency of the plurality of sets of received probe tones for the first power level, to form a first set of probe signal average power levels, and for the second power level, to form a second set of probe signal average power levels, and to determine an average noise level for a plurality of noise frequencies for the first power level, to form a first set of average noise levels, and for the second power level, to form a second set of average noise levels;
• the processor further responsive to determine a harmonic content parameter of the plurality of sets of received probe tones, for the first power level and for the second power level and to determine a receive signal power parameter from the second set of probe signal average power levels;
• the processor further responsive to determine a plurality of signal to distortion ratios, each of the plurality of signal to distortion ratios corresponding to a symbol rate and carrier frequency combination from a plurality of combinations of symbol rates and carrier frequencies, to form a set of signal to distortion ratios, and to determine a proportional noise parameter and a signal to distortion threshold parameter from the set of signal to distortion ratios;
• and the processor further responsive to determine a transmit power level from the signal to distortion threshold parameter, the harmonic content parameter, the receive signal power parameter, and the proportional noise parameter.