Patent ID: 7801020

Claim:
A method to estimate a frequency response of a channel for use in a demodulation device, the method comprising: extracting, in the device, scattered pilots of an orthogonal frequency division multiplexed (OFDM) symbol, the OFDM symbol comprising both scattered pilots and continuous pilots, wherein the scattered pilots are spaced a predetermined number (L) of carriers apart with a predetermined period of repetition (M), with the scattered pilot locations shifted in frequency by (L/M) carrier positions from one symbol to the next resulting in a scattered pilot pattern that repeats every M OFDM symbols; calculating a N-point inverse fast Fourier transform of the scattered pilots to generate a first sequence in the device; generating a second sequence from the first sequence in the device; generating an impulse response mask in the device, the impulse response mask comprising: quantizing a phase difference between current and previous symbols to multiples of 2π/M, wherein the quantizing step comprises the following steps when M=4: obtaining phase angles θ 4 , θ 5 , θ 6 , and θ 7 , from a row of a two-dimensional array U; subtracting set, θ 4 , from each of the phase angles, θ 4 , θ 5 , θ 6 , and θ 7 , resulting in angles φ 4 , φ 5 , φ 6 , and φ 7 , where φ 4 has a value of zero; computing three phase differences (φ 5 −φ 4 ), (φ 6 −φ 5 ), and (φ 7 −φ 6 ) to produce Δ φ54 , Δ φ65 , Δ φ76 ; and rounding Δ φ54 , Δ φ65 , Δ φ76 to the nearest π/2; accumulating the phase difference with other quantized phase differences; thresholding amplitudes of the samples to eliminate a noise floor; and setting remaining non-zero amplitudes equal to one; wherein a resulting third sequence comprises entries in a set {0, exp(j2π/M) where p=0, 1, . . . , (M−1)} which in the case M=4 turns out to be {0, 1, −1, j, −j}, where j is the imaginary number square root of −1; and applying the impulse response mask to the second sequence, enabling the device to produce an estimate of the channel impulse response of the transmission channel, wherein the estimate is produced without consideration of the continuous pilots.