sched: derive PRACH config index based on provided TDD pattern

Author: frankist

include/srsran/ran/prach/prach_helper.h

@@ -0,0 +1,36 @@
+/*
+ *
+ * Copyright 2021-2023 Software Radio Systems Limited
+ *
+ * By using this file, you agree to the terms and conditions set
+ * forth in the LICENSE file which can be found at the top level of
+ * the distribution.
+ *
+ */
+
+#pragma once
+
+#include "rach_config_common.h"
+#include "srsran/adt/expected.h"
+#include "srsran/adt/interval.h"
+
+namespace srsran {
+
+struct tdd_ul_dl_config_common;
+
+namespace prach_helper {
+
+/// \brief Finds whether a PRACH config index fits in the provided TDD pattern.
+/// \return In case of failure, returns the range of PRACH slots that did not fit in the TDD pattern. If the PRACH
+/// configuration is invalid, an empty interval of slots is returned.
+error_type<interval<uint8_t>> prach_fits_in_tdd_pattern(subcarrier_spacing             pusch_scs,
+                                                        bool                           cp_extended,
+                                                        uint8_t                        prach_cfg_idx,
+                                                        const tdd_ul_dl_config_common& tdd_cfg);
+
+/// \brief Finds a PRACH configuration index that ensures that PRACH falls in an TDD UL slot.
+optional<uint8_t>
+find_valid_prach_config_index(subcarrier_spacing pusch_scs, bool cp_extended, const tdd_ul_dl_config_common& tdd_cfg);
+
+} // namespace prach_helper
+} // namespace srsran

include/srsran/ran/prach/rach_config_common.h

@@ -0,0 +1,57 @@
+/*
+ *
+ * Copyright 2021-2023 Software Radio Systems Limited
+ *
+ * By using this file, you agree to the terms and conditions set
+ * forth in the LICENSE file which can be found at the top level of
+ * the distribution.
+ *
+ */
+
+#pragma once
+
+#include "restricted_set_config.h"
+#include "srsran/adt/bounded_integer.h"
+#include "srsran/adt/optional.h"
+#include "srsran/ran/subcarrier_spacing.h"
+
+namespace srsran {
+
+/// \remark See TS 38.331, RACH-ConfigGeneric.
+struct rach_config_generic {
+  /// Values: {0,...,255}.
+  uint8_t prach_config_index;
+  /// Msg2 RAR window length in #slots. Network configures a value < 10msec. Values: (1, 2, 4, 8, 10, 20, 40, 80).
+  unsigned ra_resp_window;
+  /// Number of PRACH occasions FDMed in one time instance as per TS38.211, clause 6.3.3.2.
+  unsigned msg1_fdm;
+  /// Offset of lowest PRACH transmission occasion in frequency domain respective to PRB 0,
+  /// as per TS38.211, clause 6.3.3.2. Possible values: {0,...,MAX_NOF_PRB - 1}.
+  unsigned msg1_frequency_start;
+  /// Zero-correlation zone configuration number as per TS38.331 "zeroCorrelationZoneConfig", used to derive N_{CS}.
+  uint16_t zero_correlation_zone_config;
+  /// \brief \c preambleReceivedTargetPower, part of \c RACH-ConfigGeneric, TS 38.311.
+  /// Target power level at the network receiver side, in dBm. Only values multiple of 2 are valid.
+  bounded_integer<int, -202, -60> preamble_rx_target_pw;
+};
+
+/// Used to specify the cell-specific random-access parameters as per TS 38.331, "RACH-ConfigCommon".
+struct rach_config_common {
+  rach_config_generic rach_cfg_generic;
+  /// Total number of prambles used for contention based and contention free RA. Values: (1..64).
+  optional<unsigned> total_nof_ra_preambles;
+  /// PRACH Root Sequence Index can be of 2 types, as per \c prach-RootSequenceIndex, \c RACH-ConfigCommon, TS 38.331.
+  /// We use \c true for l839, while \c false for l139.
+  bool is_prach_root_seq_index_l839;
+  /// PRACH root sequence index. Values: (1..839).
+  /// \remark See TS 38.211, clause 6.3.3.1.
+  unsigned prach_root_seq_index;
+  /// \brief Subcarrier spacing of PRACH as per TS38.331, "RACH-ConfigCommon". If invalid, the UE applies the SCS as
+  /// derived from the prach-ConfigurationIndex in RACH-ConfigGeneric as per TS38.211 Tables 6.3.3.1-[1-3].
+  subcarrier_spacing    msg1_scs;
+  restricted_set_config restricted_set;
+  /// Enables the transform precoder for Msg3 transmission according to clause 6.1.3 of TS 38.214.
+  bool msg3_transform_precoder;
+};
+
+} // namespace srsran

include/srsran/scheduler/config/bwp_configuration.h

@@ -19,6 +19,7 @@
 #include "srsran/ran/pcch/pcch_configuration.h"
 #include "srsran/ran/pdcch/coreset.h"
 #include "srsran/ran/pdcch/search_space.h"
+#include "srsran/ran/prach/rach_config_common.h"
 #include "srsran/ran/prach/restricted_set_config.h"
 #include "srsran/ran/pucch/pucch_configuration.h"
 #include "srsran/ran/resource_block.h"
@@ -106,43 +107,6 @@ struct bwp_downlink_common {
   pdsch_config_common pdsch_common;
 };
 
-/// \remark See TS 38.331, RACH-ConfigGeneric.
-struct rach_config_generic {
-  /// Values: {0,...,255}.
-  uint8_t prach_config_index;
-  /// Msg2 RAR window length in #slots. Network configures a value < 10msec. Values: (1, 2, 4, 8, 10, 20, 40, 80).
-  unsigned ra_resp_window;
-  /// Number of PRACH occasions FDMed in one time instance as per TS38.211, clause 6.3.3.2.
-  unsigned msg1_fdm;
-  /// Offset of lowest PRACH transmission occasion in frequency domain respective to PRB 0,
-  /// as per TS38.211, clause 6.3.3.2. Possible values: {0,...,MAX_NOF_PRB - 1}.
-  unsigned msg1_frequency_start;
-  /// Zero-correlation zone configuration number as per TS38.331 "zeroCorrelationZoneConfig", used to derive N_{CS}.
-  uint16_t zero_correlation_zone_config;
-  /// \brief \c preambleReceivedTargetPower, part of \c RACH-ConfigGeneric, TS 38.311.
-  /// Target power level at the network receiver side, in dBm. Only values multiple of 2 are valid.
-  bounded_integer<int, -202, -60> preamble_rx_target_pw;
-};
-
-/// Used to specify the cell-specific random-access parameters as per TS 38.331, "RACH-ConfigCommon".
-struct rach_config_common {
-  rach_config_generic rach_cfg_generic;
-  /// Total number of prambles used for contention based and contention free RA. Values: (1..64).
-  optional<unsigned> total_nof_ra_preambles;
-  /// PRACH Root Sequence Index can be of 2 types, as per \c prach-RootSequenceIndex, \c RACH-ConfigCommon, TS 38.331.
-  /// We use \c true for l839, while \c false for l139.
-  bool is_prach_root_seq_index_l839;
-  /// PRACH root sequence index. Values: (1..839).
-  /// \remark See TS 38.211, clause 6.3.3.1.
-  unsigned prach_root_seq_index;
-  /// \brief Subcarrier spacing of PRACH as per TS38.331, "RACH-ConfigCommon". If invalid, the UE applies the SCS as
-  /// derived from the prach-ConfigurationIndex in RACH-ConfigGeneric as per TS38.211 Tables 6.3.3.1-[1-3].
-  subcarrier_spacing    msg1_scs;
-  restricted_set_config restricted_set;
-  /// Enables the transform precoder for Msg3 transmission according to clause 6.1.3 of TS 38.214.
-  bool msg3_transform_precoder;
-};
-
 struct pusch_time_domain_resource_allocation {
   /// Values: (0..32).
   unsigned         k2;

lib/ran/CMakeLists.txt

@@ -24,6 +24,7 @@ add_library(srsran_ran
         prach/prach_cyclic_shifts.cpp
         prach/prach_frequency_mapping.cpp
         prach/prach_preamble_information.cpp
+        prach/prach_helper.cpp
         precoding/precoding_codebooks.cpp
         pusch/pusch_mcs.cpp
         pusch/pusch_uci_beta_offset.cpp

lib/ran/prach/prach_helper.cpp

@@ -0,0 +1,65 @@
+/*
+ *
+ * Copyright 2021-2023 Software Radio Systems Limited
+ *
+ * By using this file, you agree to the terms and conditions set
+ * forth in the LICENSE file which can be found at the top level of
+ * the distribution.
+ *
+ */
+
+#include "srsran/ran/prach/prach_helper.h"
+#include "srsran/ran/prach/prach_configuration.h"
+#include "srsran/ran/prach/prach_preamble_information.h"
+#include "srsran/ran/tdd_ul_dl_config.h"
+
+using namespace srsran;
+
+error_type<interval<uint8_t>> srsran::prach_helper::prach_fits_in_tdd_pattern(subcarrier_spacing pusch_scs,
+                                                                              bool               cp_extended,
+                                                                              uint8_t            prach_cfg_idx,
+                                                                              const tdd_ul_dl_config_common& tdd_cfg)
+{
+  const unsigned symbols_per_slot = cp_extended ? NOF_OFDM_SYM_PER_SLOT_EXTENDED_CP : NOF_OFDM_SYM_PER_SLOT_NORMAL_CP;
+  const unsigned nof_slots_per_subframe = get_nof_slots_per_subframe(pusch_scs);
+
+  const prach_configuration prach_cfg = prach_configuration_get(frequency_range::FR1, duplex_mode::TDD, prach_cfg_idx);
+  if (prach_cfg.format == prach_format_type::invalid) {
+    return interval<uint8_t>{};
+  }
+  const prach_symbols_slots_duration dur = get_prach_duration_info(prach_cfg, pusch_scs);
+
+  // For each subframe with PRACH, check if all slots are UL.
+  for (uint8_t subframe_index : prach_cfg.subframe) {
+    // There are configuration for which the PRACH starts in an odd slot within the subframe
+    // (for numerologies > mu(SCS 15kHz)); the addition of start_slot_pusch_scs compensate for this.
+    uint8_t start_slot_index = subframe_index * nof_slots_per_subframe + dur.start_slot_pusch_scs;
+    for (uint8_t prach_slot_idx = 0; prach_slot_idx != dur.prach_length_slots; ++prach_slot_idx) {
+      uint8_t           slot_index        = start_slot_index + prach_slot_idx;
+      ofdm_symbol_range active_ul_symbols = get_active_tdd_ul_symbols(tdd_cfg, slot_index, cp_extended);
+
+      // Note: For now, PRACH in special slots is not supported.
+      if (active_ul_symbols.length() != symbols_per_slot) {
+        // No UL symbols exist in this slot.
+        return interval<uint8_t>{start_slot_index, start_slot_index + dur.prach_length_slots};
+      }
+    }
+  }
+
+  return {};
+}
+
+optional<uint8_t> srsran::prach_helper::find_valid_prach_config_index(subcarrier_spacing             pusch_scs,
+                                                                      bool                           cp_extended,
+                                                                      const tdd_ul_dl_config_common& tdd_cfg)
+{
+  static constexpr size_t NOF_PRACH_CONFIG_INDEXES = 256;
+
+  // Iterate over different PRACH configuration indexes until a valid one is found.
+  for (unsigned prach_cfg_idx = 0; prach_cfg_idx != NOF_PRACH_CONFIG_INDEXES; ++prach_cfg_idx) {
+    if (prach_fits_in_tdd_pattern(pusch_scs, cp_extended, prach_cfg_idx, tdd_cfg).has_value()) {
+      return prach_cfg_idx;
+    }
+  }
+  return nullopt;
+}

lib/ran/tdd_ul_dl_config.cpp

@@ -39,10 +39,11 @@ nof_active_symbols(const tdd_ul_dl_config_common& cfg, unsigned slot_index, bool
   }
 
   // UL case.
-  const unsigned ul_pattern_start = period_slots - pattern->nof_ul_slots;
+  const unsigned ul_pattern_start = pattern->dl_ul_tx_period_nof_slots - pattern->nof_ul_slots;
   if (slot_idx_period >= ul_pattern_start) {
     return cp_extended ? NOF_OFDM_SYM_PER_SLOT_EXTENDED_CP : NOF_OFDM_SYM_PER_SLOT_NORMAL_CP;
-  } else if (slot_idx_period == ul_pattern_start - 1) {
+  }
+  if (slot_idx_period == ul_pattern_start - 1) {
     return pattern->nof_ul_symbols;
   }
   return 0;

lib/scheduler/config/scheduler_cell_config_validator.cpp

@@ -14,6 +14,7 @@
 #include "srsran/ran/duplex_mode.h"
 #include "srsran/ran/prach/prach_configuration.h"
 #include "srsran/ran/prach/prach_frequency_mapping.h"
+#include "srsran/ran/prach/prach_helper.h"
 #include "srsran/ran/prach/prach_preamble_information.h"
 #include "srsran/scheduler/sched_consts.h"
 
@@ -61,28 +62,26 @@ static error_type<std::string> validate_rach_cfg_common(const sched_cell_configu
                               rach_cfg_cmn.rach_cfg_generic.prach_config_index);
   VERIFY(prach_cfg.format < prach_format_type::invalid, "Invalid PRACH format");
 
-  subcarrier_spacing           pusch_scs           = msg.ul_cfg_common.init_ul_bwp.generic_params.scs;
-  prach_symbols_slots_duration prach_duration_info = get_prach_duration_info(prach_cfg, pusch_scs);
-  prach_subcarrier_spacing     prach_scs           = is_long_preamble(prach_cfg.format)
-                                                         ? get_prach_preamble_long_info(prach_cfg.format).scs
-                                                         : to_ra_subcarrier_spacing(pusch_scs);
+  subcarrier_spacing       pusch_scs = msg.ul_cfg_common.init_ul_bwp.generic_params.scs;
+  prach_subcarrier_spacing prach_scs = is_long_preamble(prach_cfg.format)
+                                           ? get_prach_preamble_long_info(prach_cfg.format).scs
+                                           : to_ra_subcarrier_spacing(pusch_scs);
 
   // Check if the PRACH preambles fall into UL slots
   if (msg.tdd_ul_dl_cfg_common.has_value()) {
     const cell_configuration cell_cfg{msg};
-    // For each subframe with PRACH, check if all slots are UL.
-    for (unsigned subframe_idx : prach_cfg.subframe) {
-      // There are configuration for which the PRACH starts in an odd slot within the subframe
-      // (for numerologies > mu(SCS 15kHz)); the addition of start_slot_pusch_scs compensate for this.
-      const unsigned start_slot_idx =
-          subframe_idx * (1U << to_numerology_value(pusch_scs)) + prach_duration_info.start_slot_pusch_scs;
-      for (unsigned sl = 0; sl < prach_duration_info.prach_length_slots; ++sl) {
-        VERIFY(
-            cell_cfg.is_fully_ul_enabled(slot_point{to_numerology_value(pusch_scs), sl + start_slot_idx}),
-            "PRACH configuration index {} not supported with current TDD pattern. Slot indexes used for PRACH {} fall "
-            "outside TDD UL slots",
-            rach_cfg_cmn.rach_cfg_generic.prach_config_index,
-            interval<unsigned>{start_slot_idx, start_slot_idx + prach_duration_info.prach_length_slots});
+
+    auto ret = prach_helper::prach_fits_in_tdd_pattern(pusch_scs,
+                                                       msg.ul_cfg_common.init_ul_bwp.generic_params.cp_extended,
+                                                       rach_cfg_cmn.rach_cfg_generic.prach_config_index,
+                                                       *msg.tdd_ul_dl_cfg_common);
+    if (ret.is_error()) {
+      std::string s = fmt::format("PRACH configuration index {} not supported with current TDD pattern.",
+                                  rach_cfg_cmn.rach_cfg_generic.prach_config_index);
+      if (ret.error().empty()) {
+        return s + fmt::format(" Cause: PRACH configuration is not valid");
+      } else {
+        return s + fmt::format(" Cause: Slot indexes used for PRACH {} fall outside TDD UL slots", ret.error());
       }
     }
   }

tests/unittests/scheduler/scheduler_tdd_test.cpp

@@ -15,6 +15,7 @@
 #include "test_utils/indication_generators.h"
 #include "test_utils/result_test_helpers.h"
 #include "test_utils/scheduler_test_bench.h"
+#include "srsran/ran/prach/prach_helper.h"
 #include <gtest/gtest.h>
 
 using namespace srsran;
@@ -49,6 +50,13 @@ class base_scheduler_tdd_tester : public scheduler_test_bench
       // TDD params.
       sched_cfg.tdd_ul_dl_cfg_common = tdd_cfg;
 
+      // RACH config
+      optional<uint8_t> chosen_prach_cfg_idx =
+          prach_helper::find_valid_prach_config_index(sched_cfg.ul_cfg_common.init_ul_bwp.generic_params.scs,
+                                                      sched_cfg.ul_cfg_common.init_ul_bwp.generic_params.cp_extended,
+                                                      *sched_cfg.tdd_ul_dl_cfg_common);
+      sched_cfg.ul_cfg_common.init_ul_bwp.rach_cfg_common->rach_cfg_generic.prach_config_index = *chosen_prach_cfg_idx;
+
       return sched_cfg;
     }());
 
@@ -68,13 +76,13 @@ class base_scheduler_tdd_tester : public scheduler_test_bench
 
 using test_params = tdd_ul_dl_config_common;
 
-class scheduler_tdd_tester : public base_scheduler_tdd_tester, public ::testing::TestWithParam<test_params>
+class scheduler_dl_tdd_tester : public base_scheduler_tdd_tester, public ::testing::TestWithParam<test_params>
 {
 public:
-  scheduler_tdd_tester() : base_scheduler_tdd_tester(GetParam()) {}
+  scheduler_dl_tdd_tester() : base_scheduler_tdd_tester(GetParam()) {}
 };
 
-TEST_P(scheduler_tdd_tester, all_dl_slots_are_scheduled)
+TEST_P(scheduler_dl_tdd_tester, all_dl_slots_are_scheduled)
 {
   // Enqueue enough bytes for continuous DL tx.
   dl_buffer_state_indication_message dl_buf_st{ue_idx, ue_drb_lcid, 10000000};
@@ -83,7 +91,6 @@ TEST_P(scheduler_tdd_tester, all_dl_slots_are_scheduled)
   const unsigned MAX_COUNT = 1000;
   for (unsigned count = 0; count != MAX_COUNT; ++count) {
     this->run_slot();
-    ASSERT_TRUE(this->last_sched_res->success);
 
     // For every DL slot.
     // Note: Skip special slots in test for now.
@@ -105,7 +112,13 @@ TEST_P(scheduler_tdd_tester, all_dl_slots_are_scheduled)
   }
 }
 
-TEST_P(scheduler_tdd_tester, all_ul_slots_are_scheduled)
+class scheduler_ul_tdd_tester : public base_scheduler_tdd_tester, public ::testing::TestWithParam<test_params>
+{
+public:
+  scheduler_ul_tdd_tester() : base_scheduler_tdd_tester(GetParam()) {}
+};
+
+TEST_P(scheduler_ul_tdd_tester, all_ul_slots_are_scheduled)
 {
   // Enqueue enough bytes for continuous UL tx.
   ul_bsr_indication_message bsr{
@@ -120,7 +133,6 @@ TEST_P(scheduler_tdd_tester, all_ul_slots_are_scheduled)
   const unsigned MAX_COUNT = 1000;
   for (unsigned count = 0; count != MAX_COUNT; ++count) {
     this->run_slot();
-    ASSERT_TRUE(this->last_sched_res->success);
 
     // For every UL slot.
     // Note: Skip special slots in test for now.
@@ -146,13 +158,21 @@ TEST_P(scheduler_tdd_tester, all_ul_slots_are_scheduled)
 
 INSTANTIATE_TEST_SUITE_P(
     scheduler_tdd_test,
-    scheduler_tdd_tester,
+    scheduler_dl_tdd_tester,
     testing::Values(
         // clang-format off
   // test_params{ref_scs, pattern1={slot_period, DL_slots, DL_symbols, UL_slots, UL_symbols}, pattern2={...}}
   test_params{subcarrier_spacing::kHz30, {10, 6, 4, 3, 4}, nullopt}));
-  // Note: Not working because some PDSCHs fail due to insufficient PUCCH resources.
-  //test_params{subcarrier_spacing::kHz30, {10, 7, 4, 2, 4}, nullopt},
-  // Note: Not working because PRACH configuration needs to be adjusted.
-  //test_params{subcarrier_spacing::kHz30, {6, 3, 4, 2, 4}, tdd_ul_dl_pattern{4, 4, 0, 0, 0}}));
+  // TODO: Support more TDD patterns.
+// clang-format on
+
+INSTANTIATE_TEST_SUITE_P(
+    scheduler_tdd_test,
+    scheduler_ul_tdd_tester,
+    testing::Values(
+        // clang-format off
+        // test_params{ref_scs, pattern1={slot_period, DL_slots, DL_symbols, UL_slots, UL_symbols}, pattern2={...}}
+        test_params{subcarrier_spacing::kHz30, {10, 6, 4, 3, 4}, nullopt},
+        test_params{subcarrier_spacing::kHz30, {10, 7, 4, 2, 4}, nullopt},
+        test_params{subcarrier_spacing::kHz30, {6, 3, 4, 2, 4}, tdd_ul_dl_pattern{4, 4, 0, 0, 0}}));
 // clang-format on

tests/unittests/scheduler/test_utils/scheduler_test_bench.h

@@ -75,7 +75,6 @@ class scheduler_test_bench
     srsran_assert(cell_cfg_list.size() > cell_idx, "Invalid cellId={}", cell_idx);
     logger.set_context(next_slot.sfn(), next_slot.slot_index());
     last_sched_res = &sched->slot_indication(next_slot, cell_idx);
-    srsran_assert(last_sched_res->success, "No scheduler output was provided");
     test_scheduler_result_consistency(cell_cfg_list[cell_idx], next_slot, *last_sched_res);
     ++next_slot;
   }