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 providing high resolution timing advance estimation based on Physical Random Access Channel (PRACH), the method comprising:
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 Inverse Fast Fourier Transform (IFFT) 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 24 Ts;
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), wherein Y(k) and C(k) are 1024-point Fast Fourier Transform (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.
2. The method of claim 1 wherein the preamble signal predetermined sampling frequency comprises 30.72M samples per second (sps).
3. The method of claim 1 wherein the preamble signal predetermined length comprises 24576 samples in length.
4. The method of claim 1 further comprising conditioning the preamble signal after the receiving a preamble signal.
5. The method of claim 4 wherein conditioning the preamble includes removing a cyclic prefix and extracting only a preamble sequence.
6. The method of claim 1 wherein sequences Y_hat(k) and C_hat(k) are 12288 bits long.
7. The method of claim 1 further comprising positioning of the signal in the frequency domain by a factor n_PRB_Offset, wherein the signal is shifted in frequency by the n_PRB_Offset so that the signal is centered about Direct Center (DC).
8. The method of claim 1 further comprising filtering the signal with an anti-aliasing filter and down sampling the result by a factor of 24 providing a resulting sequence y(n) having a sequence length of 1024 samples.
9. The method of claim 1 further comprising correlating the sequence y(n) with the reference preamble sequence c(n) using the FFT method Ryc=ifft[Y(k),C*(k)], where Y(k) and C(k) are 1024-point FFT of y(n) and c(n) respectively.
10. The method of claim 1 wherein the MLE is based on the correlation of the received preamble at Fs=30.72Msps with the reference received preamble that is also at the same sampling rate and performing 12288 point circular correlation at multiple positions in a timing hypothesis window L.
11. The method of claim 10 further comprising computing a selective IDFT transformed outputs of R_hat(m)=IDFT{Y_hat(k),C_hat*(k)}wherein (P*12−L/2)≤m ≤(P*12+L/2).
12. A non-transitory computer-readable medium containing instructions for providing high resolution timing advance estimation based on Physical Random Access Channel (PRACH), which, when executed, cause a processing device to perform steps comprising:
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 Inverse Fast Fourier Transform (IFFT) 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), wherein Y(k) and C(k) 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.
13. A system for providing for providing high resolution timing advance estimation based on Physical Random Access Channel (PRACH), the system including a processing circuitry which performs steps comprising:
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 Inverse Fast Fourier Transform (IFFT) 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), wherein Y(k) and C(k) are 1024-point Fast Fourier Transform (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.