GSoC 2025 · GNU Radio 4.0 Block-Set Expansion

Week-5 check-in (mentor — Josh Morman)

   
Date 12 June 2025, 17:00 IST
Duration 40 min
Participants Josh Morman · Krish Gupta

1 · Repository Transition News

Josh shared important project updates:

  • GNU Radio organization is transitioning from fair-acc/gnuradio4 to gnuradio/gnuradio4
  • Existing PRs will need to be rebased or re-submitted to the new repository
  • This transition impacts our Math PR but creates a clean slate for Analog and Digital submissions

2 · Progress update

  • Math PR Review
    • Received feedback from maintainers on Math PR
    • Made requested changes to improve type safety and documentation
    • Added more comments explaining CRTP implementation
  • Analog Blocks
    • Completed initial implementation of:
      • FrequencyMod.hpp with configurable sensitivity
      • PhaseModulator.hpp with proper phase wrapping
    • Started on QuadratureDemod.hpp implementation
    • All implementations use minimal state and maximize processOne() efficiency

3 · Boost.UT Testing Strategy

Migrated from GoogleTest to Boost.UT for more concise tests:

// Before (GoogleTest)
TEST(FrequencyModTest, BasicModulation) {
    FrequencyMod<float> mod(1.0f);
    EXPECT_NEAR(mod.processOne(1.0f), 0.15915f, 0.0001f);
}

// After (Boost.UT)
"BasicModulation"_test = []{
    FrequencyMod<float> mod(1.0f);
    expect(that % mod.processOne(1.0f) == approx(0.15915f, 0.0001f));
};

Benefits:

  • More concise test code
  • Faster compilation time
  • Better integration with GR4 testing framework

4 · Technical Challenges

Discovered and resolved several technical challenges:

Challenge Solution
Phase wrapping Implemented custom wrapping function that avoids branches for better SIMD vectorization
Complex type handling Created specialized templates for complex I/O types
Gain adaptation rates Implemented smooth gain adjustment with configurable attack/decay rates

5 · Documentation Progress

Major progress on the porting guide:

  • Completed first draft of GR3 → GR4 porting patterns
  • Added specific section on handling complex types
  • Created diagrams showing the lifecycle of a block (initialization → processOne/Bulk → cleanup)
  • Documented reflection macro usage with clear examples

6 · Action items

Owner Task
Krish • Complete QuadratureDemod and AmDemod implementations
• Begin work on AGC blocks
• Rebase Math PR against the new repository when ready
Josh • Coordinate repository transition timeline
• Review Analog block implementations
• Provide feedback on porting guide draft

Next sync: June 19th with focus on completing the Analog demodulators and beginning AGC implementation.

7 · Implementation Insights

Key pattern emerging in our implementations:

template <typename T>
class FrequencyMod : public Block<FrequencyMod<T>> {
private:
    T sensitivity_{1.0};
    // Minimal state, maximum efficiency

public:
    void processOne(const T& in, T& out) {
        // Direct, branch-free implementation
        out = std::sin(sensitivity_ * in);
    }
    
    // Configuration through reflection
    GR_MAKE_REFLECTABLE(FrequencyMod, sensitivity_);
};

GR_REGISTER_BLOCK(FrequencyMod<float>);
GR_REGISTER_BLOCK(FrequencyMod<double>);

This pattern ensures:

  • Minimal memory footprint
  • Maximum vectorization potential
  • Type-safe instantiations
  • Clean configuration via reflection