Method and apparatus for channel estimation in OFDM receivers
View Patent ↗An efficient channel estimation system and method provides good performance under high Doppler conditions and is suitable for OFDM systems such as DVB-T. A number of different pilot interpolations techniques enable the estimation of channel for the OFDM systems. For 2 k and 4 k modes, the channel is estimated using the preceding symbol, the present symbol, and two succeeding symbols. For an 8 k mode, only one future symbol is used to estimate the channel.
1. A computer-implemented method of interpolating pilot positions to estimate a channel of a wireless communication receiver, the computer-implemented method comprising:
estimating pilot position i+3 of a current symbol as a weighted average of pilot position i+3 of a symbol having an index that is smaller than the current symbol's index by one and pilot position i+3 of a symbol having an index that is greater than the current symbol's index by one; wherein i refers to a pilot position of a symbol and is defined as
i=3*(l mod 4)+12n, wherein l defines a symbol's index and wherein n is an integer greater than or equal to zero;
estimating pilot position i+6 of a current symbol as a weighted average of pilot position i+9 of a symbol having an index that is smaller than the current symbol's index by one and pilot position i+3 of a symbol having an index that is greater than the current symbol's index by one; and
estimating pilot position i+9 of a current symbol as a weighted average of pilot position i+9 of a symbol having an index that is smaller than the current symbol's index by one and pilot position i+9 of a symbol having an index that is greater than the current symbol's index by 1.
2. The computer-implemented method of claim 1 wherein pilot position i+3 of the symbol whose index is one less than the current symbol's index is an estimated pilot position.
3. The computer-implemented method of claim 2 wherein pilot position i+9 of the symbol whose index is one less than the current symbol's index is an estimated pilot position.
4. The computer-implemented method of claim 3 wherein pilot position i+9 of the symbol whose index is one higher than the current symbol's index is a weighted average of pilot position i+6 of a symbol whose index is two higher greater than the current symbol's and pilot position i+12 of the current symbol.
5. The computer-implemented method of claim 4 wherein pilot position i+9 of the symbol whose index is one higher than the current symbol's index is a weighted average of pilot position i+3 of a symbol whose index is one higher than the current symbol's index and pilot position i+15 of a symbol whose index is one higher than the current symbol's index.
6. The computer-implemented method of claim 5 further comprising:
discarding at least one of the estimated pilot positions if the at least one of the estimate pilot positions is a continuous pilot position.
7. The computer-implemented method of claim 5 wherein each of a plurality of coefficients used in determining the weighted average of the pilot positions i+3, i+6 and i+9 of the current symbol has a value between 0.25 and 0.75.
8. The computer-implemented method of claim 7 wherein each of the plurality of coefficients used in determining the weighted average of the pilot positions i+3, i+6 and i+9 of the current symbol has a value of 0.5.
9. A receiver of a wireless communication system adapted to interpolate pilot positions to estimate a channel, the system comprising:
a memory adapted to store pilot positions; and
a processor adapted to:
estimate pilot position i+3 of a current symbol as a weighted average of pilot position i+3 of a symbol having an index that is smaller than the current symbol's index by one and pilot position i+3 of a symbol having an index that is greater than the current symbol's index by one; wherein i refers to a pilot position of a symbol and is defined as
i=3*(l mod 4)+12n, wherein l defines a symbol's index and wherein n is an integer greater than or equal to zero;
estimate pilot position i+6 of a current symbol as a weighted average of pilot position i+9 of a symbol having an index that is smaller than the current symbol's index by one and pilot position i+3 of a symbol having an index that is greater than the current symbol's index by one; and
estimate pilot position i+9 of a current symbol as a weighted average of pilot position i+9 of a symbol having an index that is smaller than the current symbol's index by one and pilot position i+9 of a symbol having an index that is greater than the current symbol's index by 1.
10. The receiver of claim 9 wherein pilot position i+3 of the symbol whose index is one less than the current symbol's index is an estimated pilot position.
11. The receiver of claim 10 wherein pilot position i+9 of the symbol whose index is one less than the current symbol's index is an estimated pilot position.
12. The receiver of claim 11 wherein pilot position i+9 of the symbol whose index is one higher than the current symbol's index is a weighted average of pilot position i+6 of a symbol whose index is two higher greater than the current symbol's and pilot position i+12 of the current symbol.
13. The receiver of claim 12 wherein pilot position i+9 of the symbol whose index is one higher than the current symbol's index is a weighted average of pilot position i+3 of a symbol whose index is one higher than the current symbol's index and pilot position i+15 of a symbol whose index is one higher than the current symbol's index.
14. The receiver of claim 13 wherein said processor is further adapted to discard at least one of the estimated pilot positions if the at least one of the estimate pilot positions is a continuous pilot position.
15. The receiver of claim 13 wherein each of a plurality of coefficients used in determining the weighted average of the pilot positions i+3, i+6 and i+9 of the current symbol has a value between 0.25 and 0.75.
16. The computer-implemented method of claim 15 wherein each of the plurality of coefficients used in determining the weighted average of the pilot positions i+3, i+6 and i+9 of the current symbol has a value of 0.5.