Fix NR PBCH encoding/decoding

lib/src/phy/phch/pbch_nr.c

@@ -180,18 +180,33 @@ void srsran_pbch_nr_free(srsran_pbch_nr_t* q)
 static const uint32_t G[PBCH_NR_A] = {16, 23, 18, 17, 8,  30, 10, 6,  24, 7,  0,  5,  3,  2,  1,  4,
                                       9,  11, 12, 13, 14, 15, 19, 20, 21, 22, 25, 26, 27, 28, 29, 31};
 
+#define PBCH_SFN_PAYLOAD_BEGIN 1
+#define PBCH_SFN_PAYLOAD_LENGTH 6
+#define PBCH_SFN_2ND_LSB_G (G[PBCH_SFN_PAYLOAD_LENGTH + 2])
+#define PBCH_SFN_3RD_LSB_G (G[PBCH_SFN_PAYLOAD_LENGTH + 1])
+
 static void
 pbch_nr_pbch_msg_pack(const srsran_pbch_nr_cfg_t* cfg, const srsran_pbch_msg_nr_t* msg, uint8_t a[PBCH_NR_A])
 {
   // Extract actual payload size
   uint32_t A_hat = SRSRAN_PBCH_MSG_NR_SZ;
 
+  // Put actual payload
+  uint32_t j_sfn   = 0;
+  uint32_t j_other = 14;
+  for (uint32_t i = 0; i < A_hat; i++) {
+    if (i >= PBCH_SFN_PAYLOAD_BEGIN && i < (PBCH_SFN_PAYLOAD_BEGIN + PBCH_SFN_PAYLOAD_LENGTH)) {
+      a[G[j_sfn++]] = msg->payload[i];
+    } else {
+      a[G[j_other++]] = msg->payload[i];
+    }
+  }
+
   // Put SFN in a_hat[A_hat] to a_hat[A_hat + 3]
-  uint32_t j_sfn = 0;
+  a[G[j_sfn++]] = (uint8_t)((msg->sfn_4lsb >> 3U) & 1U); // 4th LSB of SFN
-  a[G[j_sfn++]]  = (uint8_t)((msg->sfn_4lsb >> 3U) & 1U); // 4th LSB of SFN
+  a[G[j_sfn++]] = (uint8_t)((msg->sfn_4lsb >> 2U) & 1U); // 3th LSB of SFN
-  a[G[j_sfn++]]  = (uint8_t)((msg->sfn_4lsb >> 2U) & 1U); // 3th LSB of SFN
+  a[G[j_sfn++]] = (uint8_t)((msg->sfn_4lsb >> 1U) & 1U); // 2th LSB of SFN
-  a[G[j_sfn++]]  = (uint8_t)((msg->sfn_4lsb >> 1U) & 1U); // 2th LSB of SFN
+  a[G[j_sfn++]] = (uint8_t)((msg->sfn_4lsb >> 0U) & 1U); // 1th LSB of SFN
-  a[G[j_sfn++]]  = (uint8_t)((msg->sfn_4lsb >> 0U) & 1U); // 1th LSB of SFN
 
   // Put HRF in a_hat[A_hat + 4]
   a[G[10]] = (msg->hrf ? 1 : 0);
@@ -207,16 +222,6 @@ pbch_nr_pbch_msg_pack(const srsran_pbch_nr_cfg_t* cfg, const srsran_pbch_msg_nr_
     a[G[13]] = 0;                       // Reserved
   }
 
-  // Put actual payload
-  uint32_t j_other = 14;
-  for (uint32_t i = 0; i < A_hat; i++) {
-    if (i > 0 && i < 7) {
-      a[G[j_sfn++]] = msg->payload[i];
-    } else {
-      a[G[j_other++]] = msg->payload[i];
-    }
-  }
-
   if (srsran_verbose >= SRSRAN_VERBOSE_DEBUG && !handler_registered) {
     PBCH_NR_DEBUG_TX("Packed PBCH bits: ");
     srsran_vec_fprint_byte(stdout, a, PBCH_NR_A);
@@ -233,9 +238,19 @@ pbch_nr_pbch_msg_unpack(const srsran_pbch_nr_cfg_t* cfg, const uint8_t a[PBCH_NR
   // Extract actual payload size
   uint32_t A_hat = SRSRAN_PBCH_MSG_NR_SZ;
 
+  // Get actual payload
+  uint32_t j_sfn   = 0;
+  uint32_t j_other = 14;
+  for (uint32_t i = 0; i < A_hat; i++) {
+    if (i >= PBCH_SFN_PAYLOAD_BEGIN && i < (PBCH_SFN_PAYLOAD_BEGIN + PBCH_SFN_PAYLOAD_LENGTH)) {
+      msg->payload[i] = a[G[j_sfn++]];
+    } else {
+      msg->payload[i] = a[G[j_other++]];
+    }
+  }
+
   // Put SFN in a_hat[A_hat] to a_hat[A_hat + 3]
-  uint32_t j_sfn = 0;
+  msg->sfn_4lsb = 0;
-  msg->sfn_4lsb  = 0;
   msg->sfn_4lsb |= (uint8_t)(a[G[j_sfn++]] << 3U); // 4th LSB of SFN
   msg->sfn_4lsb |= (uint8_t)(a[G[j_sfn++]] << 2U); // 3th LSB of SFN
   msg->sfn_4lsb |= (uint8_t)(a[G[j_sfn++]] << 1U); // 2th LSB of SFN
@@ -254,16 +269,6 @@ pbch_nr_pbch_msg_unpack(const srsran_pbch_nr_cfg_t* cfg, const uint8_t a[PBCH_NR
   } else {
     msg->k_ssb_msb = a[G[11]];
   }
-
-  // Put actual payload
-  uint32_t j_other = 14;
-  for (uint32_t i = 0; i < A_hat; i++) {
-    if (i > 0 && i < 7) {
-      msg->payload[i] = a[G[j_sfn++]];
-    } else {
-      msg->payload[i] = a[G[j_other++]];
-    }
-  }
 }
 
 static void pbch_nr_scramble(const srsran_pbch_nr_cfg_t* cfg, const uint8_t a[PBCH_NR_A], uint8_t a_prime[PBCH_NR_A])
@@ -282,7 +287,7 @@ static void pbch_nr_scramble(const srsran_pbch_nr_cfg_t* cfg, const uint8_t a[PB
   }
 
   // Select value v
-  uint32_t v = 2 * a[G[1]] + a[G[2]];
+  uint32_t v = 2 * a[PBCH_SFN_3RD_LSB_G] + a[PBCH_SFN_2ND_LSB_G];
 
   // Advance sequence
   srsran_sequence_state_advance(&sequence_state, M * v);
@@ -292,12 +297,14 @@ static void pbch_nr_scramble(const srsran_pbch_nr_cfg_t* cfg, const uint8_t a[PB
   srsran_sequence_state_apply_bit(&sequence_state, c, c, PBCH_NR_A);
 
   while (i < PBCH_NR_A) {
-    // a i corresponds to any one of the bits belonging to the SS/PBCH block index, the half frame index, and 2 nd and 3
-    // rd least significant bits of the system frame number
     uint8_t s_i = c[j];
 
-    // else
+    // Check if i belongs to a SS/PBCH block index which is only multiplexed when L_max is 64
-    if (i == G[11] || i == G[12] || i == G[13] || i == G[10] || i == G[1] || i == G[2]) {
+    bool is_ssb_idx = (i == G[11] || i == G[12] || i == G[13]) && cfg->Lmax == 64;
+
+    // a i corresponds to any one of the bits belonging to the SS/PBCH block index, the half frame index, and 2 nd and 3
+    // rd least significant bits of the system frame number
+    if (is_ssb_idx || i == G[10] || i == PBCH_SFN_2ND_LSB_G || i == PBCH_SFN_3RD_LSB_G) {
       s_i = 0;
     } else {
       j++;

lib/src/phy/sync/test/CMakeLists.txt

@@ -150,4 +150,4 @@ target_link_libraries(ssb_file_test srsran_phy)
 
 # File test 1
 # Captured with command: lib/examples/usrp_capture -a type=x300,clock=external,sampling_rate=46.08e6,rx_subdev_spec=B:0 -g 20 -r 46.08e6 -n 460800  -f 3502.8e6 -o /tmp/n78.fo35028.fs2304M.data
-add_nr_test(ssb_file_test ssb_file_test -i ${CMAKE_CURRENT_SOURCE_DIR}/n78.fo35028.fs4608M.data -v -r 46.08e6 -f 3502.8e6 -F 3512.64e6 -n 460800 -A 500 357802 5 0 0 0)
+add_nr_test(ssb_file_test ssb_file_test -i ${CMAKE_CURRENT_SOURCE_DIR}/n78.fo35028.fs4608M.data -v -r 46.08e6 -f 3502.8e6 -F 3512.64e6 -n 460800 -A 500 357802 2 0 1 0)

srsue/src/phy/nr/cc_worker.cc

@@ -43,6 +43,7 @@ cc_worker::cc_worker(uint32_t cc_idx_, srslog::basic_logger& log, state& phy_sta
 
   srsran_ssb_args_t ssb_args = {};
   ssb_args.enable_measure    = true;
+  ssb_args.enable_decode     = true;
   if (srsran_ssb_init(&ssb, &ssb_args) < SRSRAN_SUCCESS) {
     ERROR("Error initiating SSB");
     return;
@@ -381,6 +382,37 @@ bool cc_worker::measure_csi()
         logger.debug("SSB-CSI: %s", str.data());
       }
 
+      bool                 hrf      = (dl_slot_cfg.idx % SRSRAN_NSLOTS_PER_FRAME_NR(phy.cfg.carrier.scs) >
+                  SRSRAN_NSLOTS_PER_FRAME_NR(phy.cfg.carrier.scs) / 2);
+      srsran_pbch_msg_nr_t pbch_msg = {};
+      if (srsran_ssb_decode_pbch(&ssb, phy.cfg.carrier.pci, hrf, ssb_idx, rx_buffer[0], &pbch_msg) < SRSRAN_SUCCESS) {
+        logger.error("Error decoding PBCH");
+        return false;
+      }
+
+      // Check if PBCH message was decoded
+      if (pbch_msg.crc) {
+        // Unpack MIB
+        srsran_mib_nr_t mib = {};
+        if (srsran_pbch_msg_nr_mib_unpack(&pbch_msg, &mib) < SRSRAN_SUCCESS) {
+          logger.error("Error unpacking PBCH-MIB");
+          return false;
+        }
+
+        // Check if the SFN matches
+        // ...
+
+        // Log MIB information
+        if (logger.debug.enabled()) {
+          std::array<char, 512> str = {};
+          srsran_pbch_msg_nr_mib_info(&mib, str.data(), (uint32_t)str.size());
+          logger.debug("PBCH-MIB: sfn_4lsb=%d; %s", (dl_slot_cfg.idx / 10) & 0xf, str.data());
+        }
+      } else {
+        // CRC shall never fail if the UE is in sync
+        logger.warning("PBCH-MIB: CRC failed");
+      }
+
       // Report SSB candidate channel measurement to the PHY state
       phy.new_csi_trs_measurement(meas);
     }