Subchannel modulation scheme for carrying management and control data outside the regular data channel

Abstract

A method and apparatus for implementing a subchannel for management and control or other supplemental data on a media shared with a high speed data link. Several FDMA approaches are disclosed including AM, FM, PM, phase, QAM, QPSK etc. modulation of a subcarrier having a frequency which is in the bandwidth provided by the shared media which is not used by the DC balanced high speed data stream. A preferred species which is compatible with existing high speed data transmitters and receivers comprises a subchannel transmitter which frequency shift keys a subchannel carrier of about 1 mHz with the subchannel data. The modulated subchannel carrier is summed by superposition with a DC balanced NRZ format gigabit data stream and coupled onto the media. Injection power levels of the subchannel carrier are controlled so as to not cause excessive jitter in the high speed data receivers but so as to provide sufficient amplitude in the face of noise sources including random variations in transition density to be recovered by a subchannel receiver. At the destination node, the combined signal is directly coupled to the input of the high speed data receiver, but is coupled to the input of the subchannel receiver through a low pass filter. The subchannel receiver is narrowband and includes an FSK demodulator.