Patent ID: 8634288

Claim:
A method ( 400 ) for extracting a random access channel (RACH) preamble from a signal received in a base station ( 110 ) from a user device ( 120 ), in a (Long Term Evolution) LTE system ( 100 ), wherein prior to executing the method the base station removes an initial cyclic prefix (symbol CP) portion from the signal, and performs a ½ subcarrier frequency shift, the method comprising: for a predetermined number of successive symbols of the signal (S 405 , S 472 , S 474 ) after the symbol CP portion has been removed performing (S 410 ) a Fast Fourier Transformation (FFT) of a symbol, generating (S 420 ), from the FFT of the symbol, a baseband signal corresponding to a RACH frequency band all other non-RACH frequency bins having been set to zero, performing (S 430 ) an inverse FFT on the baseband signal to yield a time domain signal, adjusting (S 440 ) a phase of the time domain signal to compensate for group delays due to symbol CP gaps occurring during the generating, wherein a phase adjustment is determined individually for each symbol, padding zeros (S 450 ) at a beginning of the phase-adjusted time domain signal to account for the symbol CP portion that was removed, down-sampling (S 460 ) the phase-adjusted time domain signal, and storing (S 470 ) the down-sampled signal to form a time sequence by concatenation; selecting (S 480 ) the RACH preamble from the stored sequence; and performing (S 490 ) a FFT on the RACH preamble using at least 1024 points, wherein the FFT of the RACH preamble is further used for identifying and synchronizing between the user device ( 120 ) with the base station ( 110 ).