Patent ID: 7564909

Claim:
A base station apparatus in a broadband mobile communication system, comprising: a ranging subchannel extractor for extracting subcarrier values with a ranging signal from a fast Fourier transform (FFT) signal; a plurality of multipliers for code-demodulating the subcarrier values by multiplying the subcarrier values by a plurality of ranging codes; a plurality of correlators, each for calculating a plurality of differential correlations in a code-demodulated signal received from a corresponding multiplier; a plurality of inverse fast Fourier transform (IFFT) processors, each for IFFT-processing differential correlations received from a corresponding correlator by mapping the differential correlations to predetermined subcarriers; and a plurality of maximum value detectors, each for detecting a maximum value in an IFFT signal received from a corresponding IFFT processor and calculating a timing offset using an IFFT output index having the maximum value; wherein each of the correlators calculate 2×k max differential correlations (Z k ) by Z k = { ∑ l = 0 5 ⁢ ∑ n = 0 23 - k ⁢ ( Y l , n ⁢ C l , n ) ⁢ ( Y l , m + k ⁢ C l , n + k ) * , l ≤ k ≤ k max Z J - k * , J - k max ≤ k < J ⁢ ⁢ where , ⁢ Z k ⁢ : ⁢ ⁢ J ⁢ - ⁢ point ⁢ ⁢ I ⁢ ⁢ F ⁢ ⁢ F ⁢ ⁢ T ⁢ ⁢ complex ⁢ ⁢ input ⁢ ⁢ value ⁢ ⁢ k ⁢ : ⁢ ⁢ J ⁢ - ⁢ point ⁢ ⁢ I ⁢ ⁢ F ⁢ ⁢ F ⁢ ⁢ T ⁢ ⁢ input ⁢ ⁢ index , 0 ≤ k < J ⁢ - ⁢ point and wherein k is an input index of a J-point IFFT processor, L+1 is a number of subbands, N+1 is a number of subcarriers per subband, Y 1,n is a received signal response of an n th subcarrier in an 1 th subband, C 1,n is a ranging code bit allocated to the n th subcarrier in the 1 th subband, and k max =N.