Implemented initial NR cell search

lib/include/srsran/phy/common/phy_common_nr.h

@@ -181,6 +181,11 @@ extern "C" {
  */
 #define SRSRAN_NID_2_NR(N_ID) ((N_ID) % SRSRAN_NOF_NID_2_NR)
 
+/**
+ * @brief Compute Physical Cell Identifier (PCI) N_id from N_id_1 and N_id_2
+ */
+#define SRSRAN_NID_NR(NID_1, NID_2) (SRSRAN_NOF_NID_2_NR * (NID_1) + (NID_2))
+
 /**
  * @brief SSB number of resource elements, described in TS 38.211 section 7.4.3.1 Time-frequency structure of an SS/PBCH
  * block

lib/include/srsran/phy/sync/pss_nr.h

@@ -46,4 +46,14 @@ SRSRAN_API int srsran_pss_nr_put(cf_t ssb_grid[SRSRAN_SSB_NOF_RE], uint32_t N_id
  */
 SRSRAN_API int srsran_pss_nr_extract_lse(const cf_t* ssb_grid, uint32_t N_id_2, cf_t lse[SRSRAN_PSS_NR_LEN]);
 
+/**
+ * @brief Find the best PSS sequence given the SSB resource grid
+ * @attention Assumes the SSB is synchronized and the average delay is pre-compensated
+ * @param ssb_grid The SSB resource grid to search
+ * @param norm_corr Normalised correlation of the best found sequence
+ * @param found_N_id_2 The N_id_2 of the best sequence
+ * @return SRSLTE_SUCCESS if the parameters are valid, SRSLTE_ERROR code otherwise
+ */
+SRSRAN_API int srsran_pss_nr_find(const cf_t ssb_grid[SRSRAN_SSB_NOF_RE], float* norm_corr, uint32_t* found_N_id_2);
+
 #endif // SRSRAN_PSS_NR_H

lib/include/srsran/phy/sync/ssb.h

@@ -43,7 +43,7 @@ typedef struct SRSRAN_API {
   bool                        enable_correlate; ///< Enables PSS/SSS correlation and peak search (UE cell search)
   bool                        enable_encode;    ///< Enables PBCH Encoder (intended for gNb)
   bool                        enable_decode;    ///< Enables PBCH Decoder (intented for UE)
-  bool                        enable_measure;   ///< Enables PSS/SSS CSI measurements
+  bool                        enable_measure;   ///< Enables PSS/SSS CSI measurements and frequency domain search
 } srsran_ssb_args_t;
 
 /**
@@ -121,6 +121,18 @@ SRSRAN_API int srsran_ssb_decode_pbch(srsran_ssb_t* q, const cf_t* in, srsran_pb
 SRSRAN_API int
 srsran_ssb_add(srsran_ssb_t* q, uint32_t N_id, const srsran_pbch_msg_nr_t* msg, const cf_t* in, cf_t* out);
 
+/**
+ * @brief Perform cell search and measurement
+ * @note This function assumes the SSB transmission is aligned with the input base-band signal
+ * @param q NR PSS object
+ * @param in Base-band signal buffer
+ * @param N_id Physical Cell Identifier of the most suitable cell identifier
+ * @param meas SSB-based CSI measurement of the most suitable cell identifier
+ * @return SRSLTE_SUCCESS if the parameters are valid, SRSLTE_ERROR code otherwise
+ */
+SRSRAN_API int
+srsran_ssb_csi_search(srsran_ssb_t* q, const cf_t* in, uint32_t* N_id, srsran_csi_trs_measurements_t* meas);
+
 /**
  * @brief Perform Channel State Information (CSI) measurement from the SSB
  * @param q NR PSS object

lib/src/phy/sync/pss_nr.c

@@ -94,3 +94,52 @@ int srsran_pss_nr_extract_lse(const cf_t* ssb_grid, uint32_t N_id_2, cf_t lse[SR
 
   return SRSRAN_SUCCESS;
 }
+
+int srsran_pss_nr_find(const cf_t ssb_grid[SRSRAN_SSB_NOF_RE], float* norm_corr, uint32_t* found_N_id_2)
+{
+  // Verify inputs
+  if (ssb_grid == NULL || norm_corr == NULL || found_N_id_2 == NULL) {
+    return SRSRAN_ERROR_INVALID_INPUTS;
+  }
+
+  const cf_t* pss_ptr = &ssb_grid[SRSRAN_PSS_NR_SYMBOL_IDX * SRSRAN_SSB_BW_SUBC + PSS_NR_SUBC_BEGIN];
+
+  // Measure PSS region average power
+  float avg_power = srsran_vec_avg_power_cf(pss_ptr, SRSRAN_PSS_NR_LEN);
+
+  // If no energy detected or invalid, consider zero correlation
+  if (!isnormal(avg_power)) {
+    *norm_corr    = 0.0f;
+    *found_N_id_2 = 0;
+    return SRSRAN_SUCCESS;
+  }
+
+  // Search state
+  float    max_corr = -INFINITY; //< Stores best correlation
+  uint32_t N_id_2   = 0;         //< Best N_id_2
+
+  // Iterate over all possible N_id_2
+  for (uint32_t N_id_2_candidate = 0; N_id_2_candidate < SRSRAN_NOF_NID_2_NR; N_id_2_candidate++) {
+    uint32_t m   = PSS_NR_SEQUENCE_M(N_id_2_candidate);
+    cf_t     acc = 0.0f;
+
+    // Correlate d sequence fist part
+    acc += srsran_vec_dot_prod_ccc(&pss_nr_d[m], &pss_ptr[0], SRSRAN_PSS_NR_LEN - m);
+
+    // Correlate d sequence second part
+    acc += srsran_vec_dot_prod_ccc(&pss_nr_d[0], &pss_ptr[SRSRAN_PSS_NR_LEN - m], m);
+
+    // Correlate
+    float corr = SRSRAN_CSQABS(acc);
+    if (corr > max_corr) {
+      N_id_2   = N_id_2_candidate;
+      max_corr = corr;
+    }
+  }
+
+  // Copy found result
+  *norm_corr    = max_corr / avg_power / SRSRAN_PSS_NR_LEN;
+  *found_N_id_2 = N_id_2;
+
+  return SRSRAN_SUCCESS;
+}

lib/src/phy/sync/ssb.c

@@ -241,23 +241,8 @@ int srsran_ssb_add(srsran_ssb_t* q, uint32_t N_id, const srsran_pbch_msg_nr_t* m
   return SRSRAN_SUCCESS;
 }
 
-int srsran_ssb_csi_measure(srsran_ssb_t* q, uint32_t N_id, const cf_t* in, srsran_csi_trs_measurements_t* meas)
+static int ssb_demodulate(srsran_ssb_t* q, const cf_t* in, cf_t ssb_grid[SRSRAN_SSB_NOF_RE])
 {
-  // Verify inputs
-  if (q == NULL || N_id >= SRSRAN_NOF_NID_NR || in == NULL || meas == NULL || !isnormal(q->scs_hz)) {
-    return SRSRAN_ERROR_INVALID_INPUTS;
-  }
-
-  if (!q->args.enable_measure) {
-    ERROR("SSB is not configured for measure");
-    return SRSRAN_ERROR;
-  }
-
-  uint32_t N_id_1                      = SRSRAN_NID_1_NR(N_id);
-  uint32_t N_id_2                      = SRSRAN_NID_2_NR(N_id);
-  cf_t     ssb_grid[SRSRAN_SSB_NOF_RE] = {};
-
-  // Demodulate
   const cf_t* in_ptr = in;
   for (uint32_t l = 0; l < SRSRAN_SSB_DURATION_NSYMB; l++) {
     // Get CP length
@@ -297,6 +282,15 @@ int srsran_ssb_csi_measure(srsran_ssb_t* q, uint32_t N_id, const cf_t* in, srsra
     }
   }
 
+  return SRSRAN_SUCCESS;
+}
+
+static int
+ssb_measure(srsran_ssb_t* q, const cf_t ssb_grid[SRSRAN_SSB_NOF_RE], uint32_t N_id, srsran_csi_trs_measurements_t* meas)
+{
+  uint32_t N_id_1 = SRSRAN_NID_1_NR(N_id);
+  uint32_t N_id_2 = SRSRAN_NID_2_NR(N_id);
+
   // Extract PSS LSE
   cf_t pss_lse[SRSRAN_PSS_NR_LEN];
   cf_t sss_lse[SRSRAN_SSS_NR_LEN];
@@ -313,14 +307,17 @@ int srsran_ssb_csi_measure(srsran_ssb_t* q, uint32_t N_id, const cf_t* in, srsra
   float delay_avg_us   = 1e6f * delay_avg_norm / q->scs_hz;
 
   // Pre-compensate delay
+  cf_t ssb_grid_corrected[SRSRAN_SSB_NOF_RE];
   for (uint32_t l = 0; l < SRSRAN_SSB_DURATION_NSYMB; l++) {
-    srsran_vec_apply_cfo(
-        &ssb_grid[SRSRAN_SSB_BW_SUBC * l], delay_avg_norm, &ssb_grid[SRSRAN_SSB_BW_SUBC * l], SRSRAN_SSB_BW_SUBC);
+    srsran_vec_apply_cfo(&ssb_grid[SRSRAN_SSB_BW_SUBC * l],
+                         delay_avg_norm,
+                         &ssb_grid_corrected[SRSRAN_SSB_BW_SUBC * l],
+                         SRSRAN_SSB_BW_SUBC);
   }
 
   // Extract LSE again
-  if (srsran_pss_nr_extract_lse(ssb_grid, N_id_2, pss_lse) < SRSRAN_SUCCESS ||
-      srsran_sss_nr_extract_lse(ssb_grid, N_id_1, N_id_2, sss_lse) < SRSRAN_SUCCESS) {
+  if (srsran_pss_nr_extract_lse(ssb_grid_corrected, N_id_2, pss_lse) < SRSRAN_SUCCESS ||
+      srsran_sss_nr_extract_lse(ssb_grid_corrected, N_id_1, N_id_2, sss_lse) < SRSRAN_SUCCESS) {
     ERROR("Error extracting LSE");
     return SRSRAN_ERROR;
   }
@@ -361,5 +358,81 @@ int srsran_ssb_csi_measure(srsran_ssb_t* q, uint32_t N_id, const cf_t* in, srsra
   meas->delay_us   = delay_avg_us; // Convert the delay to microseconds
   meas->nof_re     = SRSRAN_PSS_NR_LEN + SRSRAN_SSS_NR_LEN;
 
+  return SRSRAN_SUCCESS;
+}
+int srsran_ssb_csi_search(srsran_ssb_t* q, const cf_t* in, uint32_t* N_id, srsran_csi_trs_measurements_t* meas)
+{
+  // Verify inputs
+  if (q == NULL || in == NULL || N_id == NULL || meas == NULL || !isnormal(q->scs_hz)) {
+    return SRSRAN_ERROR_INVALID_INPUTS;
+  }
+
+  if (!q->args.enable_measure) {
+    ERROR("SSB is not configured for search");
+    return SRSRAN_ERROR;
+  }
+
+  cf_t ssb_grid[SRSRAN_SSB_NOF_RE] = {};
+
+  // Demodulate
+  if (ssb_demodulate(q, in, ssb_grid) < SRSRAN_SUCCESS) {
+    ERROR("Error demodulating");
+    return SRSRAN_ERROR;
+  }
+
+  // Find best N_id_2
+  uint32_t N_id_2   = 0;
+  float    pss_corr = 0.0f;
+  if (srsran_pss_nr_find(ssb_grid, &pss_corr, &N_id_2) < SRSRAN_SUCCESS) {
+    ERROR("Error searching for N_id_2");
+    return SRSRAN_ERROR;
+  }
+
+  // Find best N_id_1
+  uint32_t N_id_1   = 0;
+  float    sss_corr = 0.0f;
+  if (srsran_sss_nr_find(ssb_grid, N_id_2, &sss_corr, &N_id_1) < SRSRAN_SUCCESS) {
+    ERROR("Error searching for N_id_2");
+    return SRSRAN_ERROR;
+  }
+
+  // Select N_id
+  *N_id = SRSRAN_NID_NR(N_id_1, N_id_2);
+
+  // Measure selected N_id
+  if (ssb_measure(q, ssb_grid, *N_id, meas)) {
+    ERROR("Error measuring");
+    return SRSRAN_ERROR;
+  }
+
+  return SRSRAN_SUCCESS;
+}
+
+int srsran_ssb_csi_measure(srsran_ssb_t* q, uint32_t N_id, const cf_t* in, srsran_csi_trs_measurements_t* meas)
+{
+  // Verify inputs
+  if (q == NULL || N_id >= SRSRAN_NOF_NID_NR || in == NULL || meas == NULL || !isnormal(q->scs_hz)) {
+    return SRSRAN_ERROR_INVALID_INPUTS;
+  }
+
+  if (!q->args.enable_measure) {
+    ERROR("SSB is not configured for measure");
+    return SRSRAN_ERROR;
+  }
+
+  cf_t ssb_grid[SRSRAN_SSB_NOF_RE] = {};
+
+  // Demodulate
+  if (ssb_demodulate(q, in, ssb_grid) < SRSRAN_SUCCESS) {
+    ERROR("Error demodulating");
+    return SRSRAN_ERROR;
+  }
+
+  // Actual measurement
+  if (ssb_measure(q, ssb_grid, N_id, meas)) {
+    ERROR("Error measuring");
+    return SRSRAN_ERROR;
+  }
+
   return SRSRAN_SUCCESS;
 }

lib/src/phy/sync/sss_nr.c

@@ -142,7 +142,7 @@ int srsran_sss_nr_find(const cf_t ssb_grid[SRSRAN_SSB_NOF_RE],
                        uint32_t*  found_N_id_1)
 {
   // Verify inputs
-  if (ssb_grid == NULL || N_id_2 >= SRSRAN_NOF_NID_2_NR) {
+  if (ssb_grid == NULL || N_id_2 >= SRSRAN_NOF_NID_2_NR || norm_corr == NULL || found_N_id_1 == NULL) {
     return SRSRAN_ERROR_INVALID_INPUTS;
   }
 
@@ -154,9 +154,8 @@ int srsran_sss_nr_find(const cf_t ssb_grid[SRSRAN_SSB_NOF_RE],
 
   // If the measured power is invalid or zero, consider no SSS signal
   if (!isnormal(avg_power)) {
-    if (norm_corr) {
-      *norm_corr = 0.0f;
-    }
+    *norm_corr    = 0.0f;
+    *found_N_id_1 = 0;
     return SRSRAN_SUCCESS;
   }
 
@@ -176,19 +175,18 @@ int srsran_sss_nr_find(const cf_t ssb_grid[SRSRAN_SSB_NOF_RE],
     srsran_vec_prod_ccc(&sss_ptr[SRSRAN_SSS_NR_LEN - m1], &sss_nr_d1[0], &sss_seq_m1[SRSRAN_SSS_NR_LEN - m1], m1);
 
     // Iterate over all N_id_1 with the given m1 sequence
-    for (uint32_t N_id_1_blind = m1; N_id_1_blind < SRSRAN_NOF_NID_1; N_id_1_blind += SSS_NR_NOF_M1) {
-      uint32_t m0 = SSS_NR_SEQUENCE_M0(N_id_1_blind, N_id_2);
-
-      cf_t sss_seq_m0[SRSRAN_SSS_NR_LEN];
+    for (uint32_t N_id_1_blind = m1; N_id_1_blind < SRSRAN_NOF_NID_1_NR; N_id_1_blind += SSS_NR_NOF_M1) {
+      uint32_t m0  = SSS_NR_SEQUENCE_M0(N_id_1_blind, N_id_2);
+      cf_t     acc = 0.0f;
 
-      // Apply d0 sequence fist part
-      srsran_vec_prod_ccc(&sss_seq_m1[0], &sss_nr_d0[m0], &sss_seq_m0[0], SRSRAN_SSS_NR_LEN - m0);
+      // Correlate d0 sequence fist part
+      acc += srsran_vec_dot_prod_ccc(&sss_seq_m1[0], &sss_nr_d0[m0], SRSRAN_SSS_NR_LEN - m0);
 
-      // Apply d0 sequence second part
-      srsran_vec_prod_ccc(&sss_seq_m1[SRSRAN_SSS_NR_LEN - m0], &sss_nr_d0[0], &sss_seq_m0[SRSRAN_SSS_NR_LEN - m0], m0);
+      // Correlate d0 sequence second part
+      acc += srsran_vec_dot_prod_ccc(&sss_seq_m1[SRSRAN_SSS_NR_LEN - m0], &sss_nr_d0[0], m0);
 
-      // Correlate
-      float corr = SRSRAN_CSQABS(srsran_vec_acc_cc(sss_seq_m0, SRSRAN_SSS_NR_LEN)) / avg_power;
+      // Normalise
+      float corr = SRSRAN_CSQABS(acc);
       if (corr > max_corr) {
         N_id_1   = N_id_1_blind;
         max_corr = corr;
@@ -196,13 +194,9 @@ int srsran_sss_nr_find(const cf_t ssb_grid[SRSRAN_SSB_NOF_RE],
     }
   }
 
-  if (norm_corr) {
-    *norm_corr = max_corr;
-  }
-
-  if (found_N_id_1) {
-    *found_N_id_1 = N_id_1;
-  }
+  // Copy found result
+  *norm_corr    = max_corr / avg_power / SRSRAN_SSS_NR_LEN;
+  *found_N_id_1 = N_id_1;
 
   return SRSRAN_SUCCESS;
 }

lib/src/phy/sync/test/ssb_measure_test.c

@@ -77,13 +77,25 @@ static void run_channel()
   srsran_channel_awgn_run_c(&awgn, buffer, buffer, sf_len);
 }
 
+static int assert_measure(const srsran_csi_trs_measurements_t* meas)
+{
+  TESTASSERT(fabsf(meas->rsrp_dB - 0.0f) < RSRP_MAX_ERROR);
+  TESTASSERT(fabsf(meas->epre_dB - 0.0f) < EPRE_MAX_ERROR);
+  TESTASSERT(fabsf(meas->n0_dB - n0_dB) < N0_MAX_ERROR);
+  TESTASSERT(fabsf(meas->snr_dB + n0_dB) < SNR_MAX_ERROR);
+  TESTASSERT(fabsf(meas->cfo_hz - cfo_hz) < CFO_MAX_ERROR);
+  TESTASSERT(fabsf(meas->delay_us + delay_us) < DELAY_MAX_ERROR);
+  return SRSRAN_SUCCESS;
+}
+
 static int test_case_1(srsran_ssb_t* ssb)
 {
-  uint64_t         t_usec  = 0;
-  srsran_ssb_cfg_t ssb_cfg = {};
-  ssb_cfg.srate_hz         = srate_hz;
-  ssb_cfg.freq_offset_hz   = 0.0;
-  ssb_cfg.scs              = ssb_scs;
+  uint64_t         t_find_usec = 0;
+  uint64_t         t_meas_usec = 0;
+  srsran_ssb_cfg_t ssb_cfg     = {};
+  ssb_cfg.srate_hz             = srate_hz;
+  ssb_cfg.freq_offset_hz       = 0.0;
+  ssb_cfg.scs                  = ssb_scs;
 
   TESTASSERT(srsran_ssb_set_cfg(ssb, &ssb_cfg) == SRSRAN_SUCCESS);
 
@@ -102,13 +114,26 @@ static int test_case_1(srsran_ssb_t* ssb)
     // Run channel
     run_channel();
 
+    // Find
+    gettimeofday(&t[1], NULL);
+    uint32_t                      N_id_found  = 0;
+    srsran_csi_trs_measurements_t meas_search = {};
+    TESTASSERT(srsran_ssb_csi_search(ssb, buffer, &N_id_found, &meas_search) == SRSRAN_SUCCESS);
+    gettimeofday(&t[2], NULL);
+    get_time_interval(t);
+    t_find_usec += t[0].tv_usec + t[0].tv_sec * 1000000UL;
+
+    // Assert find and measurements
+    TESTASSERT(N_id_found == pci);
+    TESTASSERT(assert_measure(&meas_search) == SRSRAN_SUCCESS);
+
     // Measure
     gettimeofday(&t[1], NULL);
     srsran_csi_trs_measurements_t meas = {};
     TESTASSERT(srsran_ssb_csi_measure(ssb, pci, buffer, &meas) == SRSRAN_SUCCESS);
     gettimeofday(&t[2], NULL);
     get_time_interval(t);
-    t_usec += t[0].tv_usec + t[0].tv_sec * 1000000UL;
+    t_meas_usec += t[0].tv_usec + t[0].tv_sec * 1000000UL;
 
     // Print measurement
     char str[512];
@@ -116,15 +141,12 @@ static int test_case_1(srsran_ssb_t* ssb)
     INFO("test_case_1 - pci=%d %s", pci, str);
 
     // Assert measurements
-    TESTASSERT(fabsf(meas.rsrp_dB - 0.0f) < RSRP_MAX_ERROR);
-    TESTASSERT(fabsf(meas.epre_dB - 0.0f) < EPRE_MAX_ERROR);
-    TESTASSERT(fabsf(meas.n0_dB - n0_dB) < N0_MAX_ERROR);
-    TESTASSERT(fabsf(meas.snr_dB + n0_dB) < SNR_MAX_ERROR);
-    TESTASSERT(fabsf(meas.cfo_hz - cfo_hz) < CFO_MAX_ERROR);
-    TESTASSERT(fabsf(meas.delay_us + delay_us) < DELAY_MAX_ERROR);
+    TESTASSERT(assert_measure(&meas) == SRSRAN_SUCCESS);
   }
 
-  INFO("test_case_1 - %.1f usec/measurement", (double)t_usec / (double)SRSRAN_NOF_NID_NR);
+  INFO("test_case_1 - %.1f usec/search; %.1f usec/measurement",
+       (double)t_find_usec / (double)SRSRAN_NOF_NID_NR,
+       (double)t_meas_usec / (double)SRSRAN_NOF_NID_NR);
 
   return SRSRAN_SUCCESS;
 }