System and method for reducing phase errors in multiple sub-carrier communication systems
View Patent ↗This disclosure is directed to systems and methods that compensate for a phase change that results from a change in RF gain, a “phase glitch,” that would otherwise degrade the performance of a multiple sub-carrier communication system, such as OFDM. Pilot symbols are used to estimate the phase change, allowing the pilot and data symbols to be compensated by the estimated phase change. Preferably, the compensated pilots are used to per form a second iteration of phase change estimation that determines residual phase glitch. Thus, following the second estimation of phase change, data symbols can be compensated for the estimated residual phase change.
1. A method for equalizing phase change in a multiple sub-carrier digital communication receiver comprising the steps of:
receiving a set of pilot symbols;
generating a first channel estimate and equalizing the set of pilot symbols;
estimating a first phase glitch using the equalized set of pilot symbols;
reducing phase error based upon the estimated first phase glitch from the set of pilot symbols and a plurality of data symbols to generate a set of compensated pilot symbols corresponding to the set of pilot symbols;
estimating a residual phase glitch using the set of compensated pilot symbols; and
generating a second channel estimate using the set of compensated pilots and equalizing the set of compensated pilot symbols before estimating the residual phase glitch.
2. The method of claim 1 , further comprising the step of reducing phase error based upon the residual phase glitch from the plurality of data symbols.
3. The method of claim 1 , wherein the steps of estimating the first phase glitch and the residual phase glitch comprise applying a Wiener filter to the pilot symbols.
4. The method of claim 1 , further comprising the step of reducing inter-channel interference from the set of compensated pilot symbols.
5. The method of claim 1 , further comprising the step of reducing inter-channel interference from the plurality of data symbols based upon the first channel estimate.
6. The method of claim 2 , further comprising the step of reducing inter-channel interference from the plurality of data symbols based upon the second channel estimate.
7. The method of claim 1 , wherein the pilot symbols comprise scattered pilot symbols.
8. An apparatus in a multiple sub-carrier digital communication receiver for reducing phase noise, the apparatus comprising:
a first interpolation block configured to equalize a set of pilot symbols:
a first phase glitch block configured to estimate phase glitch using the equalized set of received pilot symbols;
a first equalization block configured to reduce phase error based on estimated phase glitch from the set of received pilot symbols and a plurality of data symbols and generate a set of compensated pilot symbols;
a second phase glitch block configured to estimate residual phase glitch using the set of compensated pilot symbols; and
a second interpolation block configured to equalize the set of compensated pilot symbols prior to being fed to the second phase glitch block.
9. The apparatus of claim 8 , further comprising a second equalization block configured to reduce phase error based upon the residual phase glitch from the plurality of data symbols.
10. The apparatus of claim 8 , wherein the first and second phase glitch estimation blocks are configured to apply a Wiener filter to the pilot symbols.
11. The apparatus of claim 8 , wherein the first equalization block is configured to reduce inter-channel interference from the set of compensated pilot symbols and the plurality of data symbols.
12. The apparatus of claim 9 , wherein the second equalization block is configured to reduce inter-channel interference from the plurality of data symbols based upon the second channel estimate.