Fix PRACH detection sequence generation for NR

lib/src/phy/phch/prach.c

@@ -753,11 +753,16 @@ int srsran_prach_gen(srsran_prach_t* p, uint32_t seq_index, uint32_t freq_offset
     DEBUG(
         "N_zc: %d, N_cp: %d, N_seq: %d, N_ifft_prach=%d begin: %d", p->N_zc, p->N_cp, p->N_seq, p->N_ifft_prach, begin);
 
+    // Fill bottom guard frequency domain with zeros
+    srsran_vec_cf_zero(p->ifft_in, begin);
+
     // Map dft-precoded sequence to ifft bins
-    memset(p->ifft_in, 0, begin * sizeof(cf_t));
-    memcpy(&p->ifft_in[begin], get_precoded_dft(p, seq_index), p->N_zc * sizeof(cf_t));
-    memset(&p->ifft_in[begin + p->N_zc], 0, (p->N_ifft_prach - begin - p->N_zc) * sizeof(cf_t));
+    srsran_vec_cf_copy(&p->ifft_in[begin], get_precoded_dft(p, seq_index), p->N_zc);
+
+    // Fill top guard frequency domain with zeros
+    srsran_vec_cf_zero(&p->ifft_in[begin + p->N_zc], p->N_ifft_prach - begin - p->N_zc);
 
+    // Generate frequency domain signal
     srsran_dft_run(&p->ifft, p->ifft_in, p->ifft_out);
 
     // Copy CP into buffer
@@ -977,7 +982,7 @@ int srsran_prach_detect_offset(srsran_prach_t* p,
     uint32_t N_rb_ul = srsran_nof_prb(p->N_ifft_ul);
     uint32_t k_0     = freq_offset * N_RB_SC - N_rb_ul * N_RB_SC / 2 + p->N_ifft_ul / 2;
     uint32_t K       = DELTA_F / DELTA_F_RA;
-    uint32_t begin   = PHI + (K * k_0) + (K / 2);
+    uint32_t begin   = PHI + (K * k_0) + (p->is_nr ? 1 : (K / 2));
 
     memcpy(p->prach_bins, &p->signal_fft[begin], p->N_zc * sizeof(cf_t));
     int loops = (p->successive_cancellation) ? SUCCESSIVE_CANCELLATION_ITS : 1;