Method for pilot-aided channel estimation in ofdm systems regardless of the frequency selectivity severity of the channel

A method for pilot-aided channel estimation in orthogonal frequency division multiplexing (OFDM) system regardless of frequency selectively severity of a channel, the method comprising:

• estimating the channel in a transceiver by the step of:
• converting M OFDM symbols as Sm(k), k=1, . . . , N, m=1, . . . , M;
• inverse discrete Fourier transforming N orthogonal subcarriers from a frequency-domain to xm(n), n=1, . . . , N in time-domain;
• using a first symbol of the M OFDM symbols containing N known pilots for channel estimation;
• using a remainder of the N orthogonal subcarriers for data transmission;
• applying M-block inverse discrete Fourier transforms (DFT) to M subsymbols;
• applying parallel to serial;
• adding a cyclic prefix (CP);
• and
• passing to a transmitter through the channel;
• enhancing channel estimation in the transceiver by the steps of;
• discarding the CP;
• writing the received signal as:
• y=Hc{circumflex over (x)}+z=HcBM−1x+z, wherein y is the received signal after discarding the cyclic prefix, Hc is a circulant channel matrix of MN×MN size representing the channel, {circumflex over (x)} is a transmitted data vector stacked from all OFDM symbols after an M-point block-IDFT operator, z=an additive white Gaussian noice vector, Bm−1 is an inverse block-discrete Fourier transform;
• applying the M-block discrete Fourier transform (DFT) to a received signal (y1 wherein
• y
• 1
• =
• B
• M
• ⁢
• H
• c
• ⁢
• B
• M
• -
• 1
• ⁢
• x
• +
• B
• M
• ⁢
• z
• =
• H
• D
• ⁢
• x
• +
• B
• M
• ⁢
• z
• ,
• where BM is an M-point block DFT operator, HD is a block-diagonalized channel matrix after applying the block-DFT transform;
• applying an N-DFT process to a first subsymbol (y1) in accordance with, y2=FNFN−1p+FNz1, where y2 is an output after applying the N-point DFT on the first subsymbol, FN is an N-point DFT matrix, is a time domain circulant channel matrix of size N×N, FN−1 is an inverse N-point DFT matrix, p is a pilot vector of the first subsymbol, z1 is a noise vector corresponding to the first subsymbol after block DFT;
• estimating the channel using:
• =DFT(FN−1P−1y2,K)=DFT(FN−1P−1(PN+FNz1),K)=DFT(FN−1N+FN−1P−1FNz1,K)=N+{tilde over (z)}1 where {tilde over (z)}1=DFT(FN−1p−1FNz1,K).
• where {tilde over (z)}1=DFT(FN−1p−1FNz1, K),
• where is a channel frequency response of MN×1 length, K is N×M, P is a pilot-symbol diagonal matrix where known pilot symbols are inserted, hN is a channel impulse response of N×1 length;
• {tilde over (z)}1 is an equivalent noise after pilot-based channel estimation;
• applying an equalization process;
• and
• demodulating the symbols.