LTE Channel Estimation
A method for channel estimation in LTE, the method comprising decoding a received LTE signal comprising a message, and when a CRC of the decoder indicates successful decoding of a subframe, estimating the content of the message transmitted to the decoder, de-rotating the received LTE signal based on the estimated content of the message transmitted to the decoder to calculate pseudo pilot signals for all resource elements on which the corresponding physical downlink shared channel ‘PDSCH’ is mapped.
1 . A method for channel estimation in LTE, the method comprising:
decoding a received LTE signal comprising a message, and when a CRC of the decoder indicates successful decoding of a subframe;
estimating the content of the message transmitted to the decoder;
de-rotating the received LTE signal based on the estimated content of the message transmitted to the decoder to calculate pseudo pilot signals for all resource elements on which the corresponding physical downlink shared channel ‘PDSCH’ is mapped.
2 . The method of claim 1 wherein the estimating comprises reconstructing the content of the message transmitted to the decoder by emulating the transmit chain of the eNodeB that transmitted the received signal and passing the decoded received signal through the emulated transmit chain
3 . The method of claim 1 wherein de-rotation comprises for each symbol and subcarrier of the received signal, de-rotating using the estimated content of the message transmitted to the decoder.
4 . The method of claim 3 wherein de-rotation comprises calculating each pseudo pilot signal as
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5 . The method of claim 1 further comprising estimating the channel at a pre-defined time and frequency by averaging neighboring de-rotated pseudo pilot signals.
6 . The method of claim 1 further comprising reducing the noise in the cell-specific reference signals ‘CRS’ by averaging neighboring and non-overlapping de-rotated pseudo pilot signals.
7 . The method of claim 1 further comprising reducing the noise in the Doppler frequency and phase error measurements of the channel by using the pseudo pilot signals to calculate a mean correlation by averaging the correlation between all combinations of symbols carrying data spaced by a pre-defined time delay.
8 . The method of claim 5 further comprising, when in a low Doppler environment wherein the channel can be assumed to be constant between two consecutive subframes, using the channel estimation of the previous subframe when decoding the subsequent subframe if the previous subframe was successfully decoded, and using a channel estimation from the CRS of the subsequent subframe when decoding the subsequent subframe if the previous subframe was not successfully decoded.
9 . The method of claim 5 further comprising, in relation to two consecutive subframes and when in a high Doppler environment, using both the channel estimation of the previous subframe if the previous subframe was successfully decoded, and using a channel estimation from the CRS of the current subframe to decode the current subframe.
10 . The method of claim 5 further comprising, in relation to two consecutive subframes, when decoding of a previous subframe has failed and the previous subframe is located in the same narrowband as the current subframe, performing alpha filtering on the CRS of the de-rotated pseudo pilot signals to minimize the mean square error of the channel estimation.
11 . The method of claim 10 wherein the alpha filtering comprises:
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12 . The method of claim 5 further comprising in relation to two consecutive subframes, when the transport block of a subsequent subframe is different to the transport block of a previous subframe, using the channel estimation of the previous subframe when decoding the subsequent subframe if the previous subframe was successfully decoded, and using a channel estimation from the CRS of the previous subframe when decoding the subsequent subframe if the previous subframe was not successfully decoded.
13 . The method of claim 12 further comprising calculating the pseudo pilot signals for subsequent subframes even if the data has been successfully decoded to allow enhanced channel estimation across transport blocks.
14 . A non-transitory computer readable medium comprising computer readable instructions that when executed by a processor, cause the processor to carry out the method of claim 1 .
15 . A device comprising a receiver and a processor, the processor being operable to carry out the method of claim 1 .