Using factor of average instead of absolute detection threshold, added fixes for high-speed sequence generation (detection still not supported), added tests for multiplexed PRACH sequences

lte/phy/include/liblte/phy/prach/prach.h

@@ -36,7 +36,9 @@
 #include "liblte/phy/utils/dft.h"
 
 typedef _Complex float cf_t;
-#define PRACH_DETECT_THRESH 0.3 // Should be a value in [0,1]
+
+//PRACH detection threshold is PRACH_DETECT_FACTOR*average
+#define PRACH_DETECT_FACTOR 10
 
 /** Generation and detection of RACH signals for uplink.
  *  Currently only supports preamble formats 0-3.

lte/phy/lib/prach/src/prach.c

@@ -182,7 +182,7 @@ int prach_gen_seqs(prach_t *p)
 {
   uint32_t u = 0;
   uint32_t v = 1;
-  uint32_t v_max = 0;
+  int v_max = 0;
   uint32_t p_ = 0;
   uint32_t d_u = 0;
   uint32_t d_start = 0;
@@ -238,7 +238,9 @@ int prach_gen_seqs(prach_t *p)
                 N_neg_shift = N_shift;
         }
         v_max = N_shift*N_group + N_neg_shift - 1;
-
+        if(v_max < 0){
+          v_max = 0;
+        }
       }else{
         // Normal cell
         if(0 == p->N_cs){
@@ -253,7 +255,11 @@ int prach_gen_seqs(prach_t *p)
 
     // Shift root and add to set
     if(p->hs){
+      if(N_shift==0){
+        C_v = 0;
+      }else{
         C_v = d_start*floor(v/N_shift) + (v % N_shift)*p->N_cs;
+      }
     }else{
       C_v = v*p->N_cs;
     }
@@ -439,6 +445,7 @@ int prach_detect(prach_t *p,
       memset(p->corr_spec, 0, sizeof(cf_t)*p->N_zc);
       memset(p->corr, 0, sizeof(float)*p->N_zc);
       float corr_max = 0;
+      float corr_ave = 0;
 
       cf_t *root_spec = p->dft_seqs[p->root_seqs_idx[i]];
 
@@ -451,7 +458,9 @@ int prach_detect(prach_t *p,
       float norm = sqrtf(p->N_zc);
       for(int j=0;j<p->N_zc;j++){
         p->corr[j] = cabsf(p->corr_spec[j])/norm;
+        corr_ave += p->corr[j];
       }
+      corr_ave /= p->N_zc;
 
       uint32_t winsize = 0;
       if(p->N_cs != 0){
@@ -469,7 +478,7 @@ int prach_detect(prach_t *p,
             corr_max = p->corr[k];
           }
         }
-        if(corr_max > PRACH_DETECT_THRESH){
+        if(corr_max > PRACH_DETECT_FACTOR*corr_ave){
           indices[*n_indices] = (i*n_wins)+j;
           (*n_indices)++;
         }

lte/phy/lib/prach/test/CMakeLists.txt

@@ -50,5 +50,12 @@ ADD_TEST(prach_zc0 prach_test -z 0)
 ADD_TEST(prach_zc2 prach_test -z 2)
 ADD_TEST(prach_zc3 prach_test -z 3)
  
+ADD_EXECUTABLE(prach_test_multi prach_test_multi.c)
+TARGET_LINK_LIBRARIES(prach_test_multi lte_phy)
 
+ADD_TEST(prach_test_multi prach_test_multi)
 
+ADD_TEST(prach_test_multi_n32 prach_test_multi -n 32)
+ADD_TEST(prach_test_multi_n16 prach_test_multi -n 16)
+ADD_TEST(prach_test_multi_n8 prach_test_multi -n 8)
+ADD_TEST(prach_test_multi_n4 prach_test_multi -n 4)

lte/phy/lib/prach/test/prach_test_multi.c

@@ -0,0 +1,114 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <math.h>
+#include <time.h>
+#include <complex.h>
+
+#include "liblte/phy/prach/prach.h"
+
+#define MAX_LEN  70176
+typedef _Complex float cf_t;
+
+uint32_t N_ifft_ul        = 128;
+uint32_t preamble_format  = 0;
+uint32_t root_seq_idx     = 0;
+uint32_t zero_corr_zone   = 1;
+uint32_t n_seqs           = 64;
+
+void usage(char *prog) {
+  printf("Usage: %s\n", prog);
+  printf("\t-N Uplink IFFT size [Default 128]\n");
+  printf("\t-f Preamble format [Default 0]\n");
+  printf("\t-r Root sequence index [Default 0]\n");
+  printf("\t-z Zero correlation zone config [Default 1]\n");
+  printf("\t-n Number of sequences used for each test [Default 64]\n");
+}
+
+void parse_args(int argc, char **argv) {
+  int opt;
+  while ((opt = getopt(argc, argv, "Nfrzn")) != -1) {
+    switch (opt) {
+    case 'N':
+      N_ifft_ul = atoi(argv[optind]);
+      break;
+    case 'f':
+      preamble_format = atoi(argv[optind]);
+      break;
+    case 'r':
+      root_seq_idx = atoi(argv[optind]);
+      break;
+    case 'z':
+      zero_corr_zone = atoi(argv[optind]);
+      break;
+    case 'n':
+      n_seqs = atoi(argv[optind]);
+      break;
+    default:
+      usage(argv[0]);
+      exit(-1);
+    }
+  }
+}
+
+int main(int argc, char **argv) {
+  parse_args(argc, argv);
+
+  prach_t *p = (prach_t*)malloc(sizeof(prach_t));
+
+  bool high_speed_flag      = false;
+
+  cf_t preamble[MAX_LEN];
+  memset(preamble, 0, sizeof(cf_t)*MAX_LEN);
+  cf_t preamble_sum[MAX_LEN];
+  memset(preamble_sum, 0, sizeof(cf_t)*MAX_LEN);
+
+  prach_init(p,
+             N_ifft_ul,
+             preamble_format,
+             root_seq_idx,
+             high_speed_flag,
+             zero_corr_zone);
+
+  uint32_t seq_index = 0;
+  uint32_t frequency_offset = 0;
+
+  uint32_t indices[64];
+  uint32_t n_indices = 0;
+  for(int i=0;i<64;i++)
+    indices[i] = 0;
+
+  for(seq_index=0;seq_index<n_seqs;seq_index++)
+  {
+    prach_gen(p,
+              seq_index,
+              frequency_offset,
+              preamble);
+
+    for(int i=0;i<p->N_cp+p->N_seq;i++)
+    {
+      preamble_sum[i] += preamble[i];
+    }
+  }
+
+  uint32_t prach_len = p->N_seq;
+  if(preamble_format == 2 || preamble_format == 3)
+    prach_len /= 2;
+  prach_detect(p, 0, &preamble_sum[p->N_cp], prach_len, indices, &n_indices);
+
+  if(n_indices != n_seqs)
+    return -1;
+
+  for(int i=0;i<n_seqs;i++)
+  {
+    if(indices[i] != i)
+      return -1;
+  }
+
+  prach_free(p);
+  free(p);
+
+	printf("Done\n");
+	exit(0);
+}