Tracking system
View Patent ↗The present invention relates to a tracking system comprised in a receiver, which tracking system is operable to track rapid changes in frequency and phase offset. The tracking system comprises a first system operable to perform a pilot-based phase and frequency tracking. The tracking system also comprises a second system operable to perform data-based phase and frequency tracking. The tracking system also comprises a control means connected to said first system and to said second system, which control means is operable to gradually reduce the effect of said first system, i.e. said pilot-based phase and frequency tracking.
1. A method for tracking rapid changes in frequency and phase offset in a receiver, the method comprising:
performing a pilot-based phase and frequency tracking using a pilot-based phase and frequency tracking system;
performing data-based phase and frequency tracking using a data-based phase and frequency tracking system;
gradually reducing an effect of said pilot-based phase and frequency tracking using a control system;
employing gradually decreasing weight factors in order to gradually reduce the effect of said pilot-based phase and frequency tracking using a control system;
performing an estimate of the phase of a received symbol;
calculating a phase increment between two consecutive symbols;
weighting said phase increment with a first weight factor; and
scaling said weighted value to obtain a frequency correction increment output.
2. A method for tracking rapid changes in frequency and phase offset in a receiver according to claim 1 , wherein said method also comprises:
weighting said phase increment with a second weight factor; and
summing together all of said individual phase
increments to obtain a phase error estimate output.
3. A method for tracking rapid changes in frequency and phase offset in a receiver according to claim 2 , wherein said method also comprises:
counting the received symbols in order to use a weight
factor that depends on the symbol number.
4. A method for tracking rapid changes in frequency and phase offset in a receiver according to claim 3 , wherein said method also comprises:
correcting a frequency error of a received symbol;
performing a Fourier transform operation resulting in a number of independently modulated subcarriers;
performing a correction of the symbol phase;
demodulating said phase-corrected symbol to produce a data stream;
remodulating said data stream; and
performing an error correction resulting in a final estimate of the received data symbols.
5. A method for tracking rapid changes in frequency and phase offset in a receiver according to claim 4 , wherein said weight factors are set to 1 up to where the transition from pilot-based phase and frequency tracking to data-based phase and frequency tracking is to occur.
6. A method for tracking rapid changes in frequency and phase offset in a receiver according to claim 5 , wherein said first weight factor and said second weight factor for the same symbol number are equal.
7. A method for tracking rapid changes in frequency and phase offset in a receiver according to claim 5 , wherein said first weight factor and said second weight factor for the same symbol number are unequal.