AM compatible digital waveform frame timing recovery and frame synchronous power measurement

An apparatus for waveform frame timing recovery from a quadrature phase component signal of a received signal transmitted from a remote source, said received signal including an analog segment and a digital segment, said digital segment comprising an OFDM waveform with at least one pair of constant envelope carriers, wherein the sum of said pair of constant envelope carriers are in phase-quadrature with an analog segment carrier, said apparatus comprising:

• a numerically controlled oscillator for providing a first stable reference signal;
• a phase shifter coupled to receive said first stable reference signal for providing a second stable reference signal, said second stable reference signal being at a fixed 90.degree. phase offset to said first stable reference signal;
• a first mixing means coupled to receive said quadrature phase component signal and said first stable reference signal for producing a first mixed signal;
• a second mixing means coupled to receive said quadrature phase component signal and said second stable reference signal for producing a second mixed signal;
• a first integrator coupled to receive said first mixed signal for producing a first integrator output signal by performing an integration over a time period, said time period being an integer multiple of a frame duration, including a single frame duration;
• a second integrator coupled to receive said second mixed signal for producing a second integrator output signal by performing an integration over said time period;
• a multiplying means coupled to receive said first integrator output signal and said second integrator output signal for producing an error value;
• means also coupled to receive said first integrator output signal for establishing the absolute value of the first integrator output signal;
• means coupled to receive output of said absolute value establishing means for measuring variance of the absolute value of said first integrator output signal;
• and
• means coupled to receive said variance value for comparing said variance value with a threshold value to trigger a command signal to slip integration interval phase by one-half symbol time.

A method for waveform frame timing recovery from a received quadrature phase component of a received signal, said method comprising the steps of:

• generating a first stable reference signal;
• generating a second stable reference signal, said signal being at a fixed 90.degree. phase offset to said first stable reference signal;
• mixing said first stable reference signal with said received quadrature phase component signal to produce a first mixed signal;
• mixing said second stable reference signal with said received quadrature phase component signal to produce a second mixed signal;
• integrating said first mixed signal over an integer multiple of frame intervals, including a single frame interval, to produce a first integrator output signal;
• integrating said second mixed signal over an integer multiple of frame intervals, including a single frame interval, to produce a second integrator output signal;
• multiplying said first and second integrator output signals to produce an error value;
• measuring variance of the absolute value of said first integrator output signal;
• and
• comparing said variance value with a preset threshold value to selectively generate a command signal to slip integration interval phase by one-half symbol time.