phy: redduce EVM calculator memory footprint

Author: xavierarteaga

lib/phy/upper/channel_modulation/evm_calculator_generic_impl.cpp

@@ -19,15 +19,42 @@ float evm_calculator_generic_impl::calculate(span<const log_likelihood_ratio> so
                                              span<const cf_t>                 symbols,
                                              modulation_scheme                modulation)
 {
-  // Perform hard-decision.
-  bit_buffer hard_bits = temp_hard_bits.first(soft_bits.size());
-  hard_decision(hard_bits, soft_bits);
+  // Get modulation order.
+  unsigned bits_per_symbol = get_bits_per_symbol(modulation);
 
-  // Modulate.
-  span<cf_t> modulated = temp_modulated.first(symbols.size());
-  modulator->modulate(modulated, hard_bits, modulation);
+  // Verify that soft bits and symbols dimensions are consistent.
+  srsran_assert(soft_bits.size() == symbols.size() * bits_per_symbol,
+                "The number of soft bits (i.e., {}) is not consistent with the number of symbols (i.e., {}) and "
+                "modulation (i.e., {}).",
+                soft_bits.size(),
+                symbols.size(),
+                to_string(modulation));
 
-  // Calculate EVM.
-  srsvec::subtract(modulated, symbols, modulated);
-  return std::sqrt(srsvec::average_power(modulated));
+  unsigned nof_symbols = symbols.size();
+  float    avg_power   = 0.0;
+
+  while (!soft_bits.empty()) {
+    unsigned block_nof_symbols = std::min(static_cast<unsigned>(symbols.size()), MAX_NOF_SYMBOLS);
+    unsigned block_nof_bits    = block_nof_symbols * bits_per_symbol;
+
+    // Perform hard-decision.
+    bit_buffer hard_bits = temp_hard_bits.first(block_nof_bits);
+    hard_decision(hard_bits, soft_bits.first(block_nof_bits));
+
+    // Modulate.
+    span<cf_t> modulated = temp_modulated.first(block_nof_symbols);
+    modulator->modulate(modulated, hard_bits, modulation);
+
+    // Calculate EVM.
+    srsvec::subtract(modulated, symbols.first(block_nof_symbols), modulated);
+
+    // Accumulate power.
+    avg_power += std::real(srsvec::dot_prod(modulated, modulated));
+
+    // Pop bits and symbols.
+    symbols   = symbols.last(symbols.size() - block_nof_symbols);
+    soft_bits = soft_bits.last(soft_bits.size() - block_nof_bits);
+  }
+
+  return std::sqrt(avg_power / static_cast<float>(nof_symbols));
 }

lib/phy/upper/channel_modulation/evm_calculator_generic_impl.h

@@ -34,7 +34,7 @@ class evm_calculator_generic_impl : public evm_calculator
 
 private:
   /// Maximum number of symbols assuming 156 RE/RB, 275 RB and 4 layers.
-  static constexpr unsigned MAX_NOF_SYMBOLS = 156 * 275 * 4;
+  static constexpr unsigned MAX_NOF_SYMBOLS = 4096;
   /// Maximum number of bits.
   static constexpr unsigned MAX_NOF_BITS = MAX_NOF_SYMBOLS * 8;
   /// Internal modulator.