Phase tracking apparatus and method for continuous phase modulated signals

An apparatus for demodulating data signals CPM modulated onto a carrier, said apparatus comprising:

• a source of phase reference signals;
• a source of symbol timing estimates;
• a trellis demodulator coupled to said source of phase reference signals and to said source of symbol timing estimates, for demodulating received modulated signals using said phase reference signals together with said symbol timing estimates, by calculating branch metrics signals representative of the likelihood that the branch was in the modulator path;
• a phase shifter for phase shifting said branch metrics signals by π/2, to thereby generate phase shifted branch metrics signals associated with each path;
• a decoder using said branch metrics signals to select the path through said trellis having the highest probability, representing a best estimate of said data signals and for, at each symbol interval, for that one of said paths having the highest probability, selecting the associated phase shifted branch metric;
• and
• adjustment means coupled to said source of phase reference signals and to said decoder, for applying said selected phase shifted branch metric to adjust the value of said phase reference signals.

A method for establishing a phase reference signal for demodulating received data signals CPM modulated onto a carrier, said method comprising the steps of:

• trellis demodulating received modulated signals using phase reference signal and symbol timing estimates, by calculating branch metrics signals representative of the likelihood that the branch was in the modulator path, to produce estimated data;
• estimating at least a form of the transmitted signal from said estimated data, said phase reference signal and said symbol timing estimates;
• phase shifting said form of said transmitted signal to thereby produce phase-shifted estimated transmitted signals;
• correlating said phase-shifted estimated transmitted signals with at least a form of the received data signals, to produce phase error signals;
• and
• applying said phase error signals to correct said phase reference signal.

An apparatus for demodulating received data signals CPM modulated onto a carrier, said apparatus comprising:

• a controllable source of phase reference signals;
• a source of symbol timing estimates;
• a trellis demodulator coupled to said source of phase reference signals and to said source of symbol timing estimates, for demodulating at least signals having the same form as said received data signals modulated onto a carrier, using said phase reference signals together with said symbol timing estimates, by calculating branch metrics signals representative of the likelihood that the branch was in the modulator path, to thereby generate estimated data signals
• a transmitter signal reconstituting arrangement coupled to said trellis demodulator for receiving said estimated data signals, to said source of phase reference signals, and to said source of symbol timing estimates, for generating an estimate of the transmitted signals;
• a phase shifter coupled to said transmitter signal reconstituting arrangement, for phase shifting said estimate of said transmitted signals by π/2, to thereby generate phase shifted estimated transmitted signals;
• a correlator coupled to said phase shifter for receiving said phase shifted estimated transmitted signals, and also coupled to receive said signals having the same form as said received data signals modulated onto a carrier, for correlating said phase shifted estimated transmitted signals with said signals having the same form as said received data signals modulated onto a carrier to produce a phase error signal;
• and
• adjustment means coupled to said correlator and to said source of phase reference signals, for applying said phase error signal to said source of phase reference signals, for adjusting the value of said phase reference signals.