Patent ID: 8194799

Claim:
A cyclic prefix-based enhanced data recovery method, comprising the steps of: receiving data including orthogonal frequency division multiplexed (OFDM) symbols transmitted through a wireless linear channel of length L+1, wherein L is an integer, wherein each symbol has a length N, where N is an integer; transforming the linear channel into a circular sub-channel and a linear sub-channel; in a detector circuit, separating a cyclic prefix from the received orthogonal frequency division multiplexed symbols; establishing a variable y i , wherein y i represents a cyclic prefix of output of the linear sub-channel at a particular time i, wherein y i is given by y i = X i h i + n i , where h i represents a channel effect of the transmitted data at the time i, n i represents noise of the transmitted data, and X i is a matrix given by X i = X Li + X Ui−1 , where X Li is a matrix composed of cyclic prefixes of current unknown OFDM symbols x i and X Ui−1 is a matrix composed of cyclic prefixes of previous known OFDM symbols x i-1 , where X _ Li = ( x _ i ⁡ ( 0 ) 0 … 0 x _ i ⁡ ( 1 ) x _ i ⁡ ( 0 ) … 0 ⋮ ⋱ ⋱ ⋮ x _ i ⁡ ( L - 1 ) … x _ i ⁡ ( 0 ) 0 ) ⁢ ⁢ and X _ Ui - 1 = ( 0 x _ i - 1 ⁡ ( L - 1 ) … x _ i - 1 ⁡ ( 0 ) 0 0 … x _ i - 1 ⁡ ( 1 ) ⋮ ⋱ ⋱ ⋮ 0 … 0 x _ i - 1 ⁡ ( L - 1 ) ) ; establishing a variable x i , wherein x i represents a cyclic prefix of output of the circular sub-channel at the time i, wherein x i is a length-N, zero-padded version of x i ; performing FFT of the received OFDM symbols without the cyclic prefix; recovering the data by maximum likelihood estimation using the cyclic prefix and the received OFDM symbols, wherein a blind method for channel estimation is utilized, thereby making collective use of natural constraints of a wireless communications protocol and channel; refining the data by a refinement method comprising the steps of: obtaining an initial estimate using a plurality of pilots and frequency correlation; establishing an objective function Z; obtaining a gradient of the objective function Z subject to a constant modulus constraint on data given by φ j =|χ i (j)| 2 =E x for integer j=1, 2, 3, . . . N, wherein Z=∥ y i −Bχ i *−Cχ i *∥ 2 , where χ i is an N-point FFT of the x i , χ i * is a convolution of χ i , B=(1/E x ) X Ui−1 Q L+1 D Y and C=(1/E x ) X Li Q L+1 D Y , Q L+1 represents the first L+1 rows of an inverse FFT matrix Q, and D Y is a diagonal matrix with elements on the diagonal being equal to N-point FFT of y i ; obtaining a Hessian of the objective function subjected to the constant modulus constraint on data; using the gradient and the Hessian in Newton's method.