High resolution timing advance estimation based on PRACH
Systems, methods and computer software are disclosed for providing high resolution timing advance estimation based on Physical Random Access Channel (PRACH). An example method includes receiving a preamble signal r(n) having a predetermined sampling frequency and a predetermined length; correlating a down sampled version of the received preamble with a reference preamble sequence c(n) using an FFT method to provide correlation output Ryc; using a peak value P of the correlation output Ryc to detect a preamble ID and a timing advance at a resolution of 24Ts; zero padding sequences Y(k) and C(k) so that they have a predetermined length resulting in sequences Y_hat(k) and C_hat(k), which are 1024-point FFT of y(n) and c(n); performing a maximum likelihood estimation (MLE) to estimate a timing offset; and detecting a peak value out of the R_hat(m) and using a corresponding index Q to provide a timing advance with an accuracy of 2Ts.
1. A method for improving a telecommunications system, comprising:
receiving, at a 4G or 5G capable base station, a preamble y(n) from a user equipment in a frequency domain;
performing, using a microprocessor at the 4G or 5G capable base station, a Fourier transform on the received preamble y(n) to generate a received time-domain preamble y(k);
performing, using the microprocessor at the 4G or 5G capable base station, a Fourier transform on a reference preamble c(n) to generate a time-domain reference preamble c(k);
performing, using the microprocessor at the 4G or 5G capable base station, an inverse Fourier transform on a dot product of the received time-domain preamble y(k) and the reference time-domain preamble c(k) to generate a correlation function R;
padding the received time-domain preamble y(k) and the reference time-domain preamble c(k) to a certain length with zeroes;
using a peak value P of the correlation function R to detect a preamble identifier;
performing, using the microprocessor at the 4G or 5G capable base station, an inverse discrete Fourier transform on the dot product of the received time-domain preamble y(k) and the reference time-domain preamble c(k) at a plurality of positions within a sparse timing hypothesis window L, the sparse timing hypothesis window L based on the preamble identifier, to generate a second correlation function R_hat; and
using a peak value Q of the second correlation function R_hat to determine a timing advance value,
wherein the preamble y(n) is a preamble of a Long Term Evolution (LTE) or 5G Physical Random Access Channel (PRACH) radio signal, and further comprising retrieving a PRACH preamble format table to interpret the preamble identifier.
2. The method of claim 1 , wherein the timing advance value has a resolution of 2 Ts or finer.
3. The method of claim 1 , further comprising performing a grouped FFT algorithm for selective transformed outputs to generate the second correlation function R_hat.
4. The method of claim 1 , further comprising performing cyclic prefix removal, frequency shifting, and downsampling on the received preamble.
5. The method of claim 1 , wherein the preamble is a portion of a orthogonal frequency division multiplexed (OFDM) signal.
6. The method of claim 1 , further comprising retrieving the reference preamble or the reference time-domain preamble from a storage medium.