From 3a8ac3d4c669a03c92b91b7c8004d97afd95f0ac Mon Sep 17 00:00:00 2001
From: Markus Schmidl <markus.schmidl@mailbox.tu-dresden.de>
Date: Sun, 5 Jan 2025 16:54:22 +0100
Subject: [PATCH] try to compute a channel even if it is as large as the number
 of pilots

---
 CMakeLists.txt            |  4 +++-
 derivation.nix            |  2 ++
 src/iq_stream_decoder.cpp | 17 +++++++++++++++++
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index d65fcbf..432894f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -61,14 +61,16 @@ find_package(fmt REQUIRED)
 find_package(nlohmann_json REQUIRED)
 find_package(prometheus-cpp CONFIG REQUIRED)
 find_package(cpr REQUIRED)
+find_package(Armadillo REQUIRED)
 
+include_directories(${ARMADILLO_INCLUDE_DIRS})
 include_directories(${CMAKE_SOURCE_DIR}/include)
 
 if (NOT NIX_BUILD)
 	target_link_libraries(tetra-decoder-library cxxopts::cxxopts)
 endif()
 
-target_link_libraries(tetra-decoder-library ZLIB::ZLIB fmt::fmt nlohmann_json::nlohmann_json viterbi prometheus-cpp::pull cpr::cpr)
+target_link_libraries(tetra-decoder-library ZLIB::ZLIB fmt::fmt nlohmann_json::nlohmann_json viterbi prometheus-cpp::pull cpr::cpr ${ARMADILLO_LIBRARIES})
 target_link_libraries(tetra-decoder tetra-decoder-library)
 target_link_libraries(tetra-viterbi viterbi)
 
diff --git a/derivation.nix b/derivation.nix
index e33acd3..7bac3d4 100644
--- a/derivation.nix
+++ b/derivation.nix
@@ -8,6 +8,7 @@
 , prometheus-cpp
 , curlFull
 , libcpr
+, armadillo
 }:
 clangStdenv.mkDerivation {
   name = "tetra-decoder";
@@ -23,6 +24,7 @@ clangStdenv.mkDerivation {
     curlFull
     prometheus-cpp
     libcpr
+    armadillo
   ];
 
   cmakeFlags = [ "-DNIX_BUILD=ON" ];
diff --git a/src/iq_stream_decoder.cpp b/src/iq_stream_decoder.cpp
index 0e644ea..cb875f1 100644
--- a/src/iq_stream_decoder.cpp
+++ b/src/iq_stream_decoder.cpp
@@ -9,6 +9,7 @@
 
 #include "iq_stream_decoder.hpp"
 #include "l2/lower_mac.hpp"
+#include <armadillo>
 #include <memory>
 
 IQStreamDecoder::IQStreamDecoder(
@@ -94,6 +95,19 @@ std::vector<std::complex<float>> IQStreamDecoder::channel_estimation(std::vector
     return stream;
 }
 
+static auto solve_channel(const std::vector<std::complex<float>>& pilots,
+                          const FixedQueue<std::complex<float>, 300>& signal_queue, const std::size_t signal_offset)
+    -> arma::cx_fvec {
+    auto arma_pilots = arma::cx_fvec(pilots);
+    auto arma_signal = arma::cx_fvec(pilots.size());
+    for (auto i = 0; i < arma_signal.size(); i++) {
+        arma_signal[i] = signal_queue[signal_offset + i];
+    }
+    auto arma_conj_pilots = arma::conj(arma_pilots);
+    auto h_vec = arma::solve(arma_conj_pilots * arma_pilots, arma_conj_pilots * arma::conj(arma_signal));
+    return h_vec;
+}
+
 void IQStreamDecoder::process_complex(std::complex<float> symbol) noexcept {
     if (is_uplink_) {
         float detectedN;
@@ -123,6 +137,9 @@ void IQStreamDecoder::process_complex(std::complex<float> symbol) noexcept {
         if (detectedX >= SEQUENCE_DETECTION_THRESHOLD) {
             // std::cout << "Potential CUB found" << std::endl;
 
+            auto channel = solve_channel(training_seq_x_, symbol_buffer_hard_decision_, 44);
+            std::cout << channel << std::endl;
+
             auto len = 103;
 
             std::vector<uint8_t> bits(len * 2);