Method and apparatus for channel estimation in OFDM
View Patent ↗The present invention relates to methods that can be used in a wireless communication system, and systems adapted to use such methods. In a preferred form the methods are useful in channel estimation in a wireless communication system using orthogonal frequency division multiplexing (OFDM). The system is provided with a control block to optimize channel estimation.
1. A method of controlling an interpolation process in a device of a wireless communications system configured to receive a signal including a plurality of signal positions able to be defined by a time position and sub-carrier frequency, the method including:
comparing a signal quality parameter of the signal to a threshold; and
in the event that the signal quality parameter is less than the threshold, using linear interpolation;
in the event that the signal quality parameter is not less than the threshold:
generating at least one parameter based on the received power of at least a portion of the signal;
comparing each parameter to a respective threshold and, on the basis of said comparison or comparisons, determining at least one of:
a type of interpolation or extrapolation to be used; and
one or more parameters used in said interpolation or extrapolation.
2. A method as claimed in claim 1 wherein the type of interpolation can be linear or linear minimum mean square error (LMMSE).
3. A method as claimed in claim 1 , wherein, when the type of interpolation or extrapolation is determined to be linear minimum mean square error (LMMSE), the method includes determining one or more LMMSE matrices on the basis of a comparison of at least one parameter to its respective threshold.
4. A method as claimed in claim 1 , wherein the generating at least one parameter based on the received power of at least a portion of the signal includes:
parameter determined on the basis of received power is determined for a period greater than the effective delay spread of the signal.
5. A method as claimed in claim 4 , wherein separate parameters are determined for different delay spreads; and
wherein each parameter is compared to a different threshold.
6. A method as claimed in claim 1 , wherein the signal quality parameter comprises a Signal to Noise ratio.
7. A method of controlling an interpolation process in a device of a wireless communications system configured to receive a signal including a plurality of signal positions able to be defined by a time position and sub-carrier frequency, the method including:
comparing a signal quality parameter of the signal to a threshold; and
in the event that the signal quality parameter is less than the threshold, using linear interpolation;
in the event that the signal quality parameter is not less than the threshold:
estimating a Doppler shift affecting at least a portion of the signal;
comparing Doppler estimate to at least two thresholds and, on the basis of said comparisons, determining at least one of:
a type of interpolation or extrapolation to be used; and
one or more parameters used in said interpolation or extrapolation.
8. A method as claimed in claim 7 wherein, in the event that the Doppler estimate is less than a first threshold, using linear interpolation or extrapolation.
9. A method as claimed in claim 8 , wherein, in the event that the Doppler estimate is not less than the first threshold, using linear minimum mean square error (LMMSE) interpolation or extrapolation.
10. A method as claimed in claim 9 wherein in the event that the Doppler estimate is less than a second threshold performing LMMSE, using a corresponding set of parameters.
11. A method as claimed in claim 10 wherein in the event that the Doppler estimate is less than a third threshold performing LMMSE, using a second corresponding set of parameters.