Skip to content

Commit

Permalink
Add decoding algorithm for the BEC
Browse files Browse the repository at this point in the history
  • Loading branch information
@heat1q
heat1q committed Dec 21, 2020
1 parent 1a558a1 commit 7e942fb
Show file tree
Hide file tree
Showing 7 changed files with 163 additions and 21 deletions.
32 changes: 20 additions & 12 deletions src/core/ldpc.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ namespace ldpc
{

ldpc_code::ldpc_code(const std::string &pcFileName)
: mMaxDC(0),
: mMaxDegree(0),
mH(),
mG()
{
Expand Down Expand Up @@ -43,7 +43,8 @@ namespace ldpc
std::string line;
int skipLines = 0;

if (!infile.good()) throw std::runtime_error("can not open file for reading");
if (!infile.good())
throw std::runtime_error("can not open file for reading");

while (getline(infile, line))
{
Expand All @@ -53,15 +54,17 @@ namespace ldpc
{
int index;
auto token = line.substr(0, i);
std::istringstream record(line.substr(i+1));
std::istringstream record(line.substr(i + 1));

if (token.find("puncture") != std::string::npos)
{
while (record >> index) mPuncture.push_back(index);
}
while (record >> index)
mPuncture.push_back(index);
}
else if (token.find("shorten") != std::string::npos)
{
while (record >> index) mShorten.push_back(index);
while (record >> index)
mShorten.push_back(index);
}

++skipLines;
Expand All @@ -76,17 +79,22 @@ namespace ldpc

mH.read_from_file(pcFileName, skipLines);

// maximum check node degree
auto tmp = std::max_element(mH.row_neighbor().begin(), mH.row_neighbor().end(), [](const auto &a, const auto &b) { return (a.size() < b.size()); });
mMaxDC = tmp->size();
// maximum node degree
auto cd = std::max_element(mH.row_neighbor().begin(), mH.row_neighbor().end(),
[](const auto &a, const auto &b) { return (a.size() < b.size()); });
auto vd = std::max_element(mH.col_neighbor().begin(), mH.col_neighbor().end(),
[](const auto &a, const auto &b) { return (a.size() < b.size()); });
mMaxDegree = std::max(cd->size(), vd->size());

// position of transmitted bits
for (int i = 0; i < nc(); i++)
{
auto tmp = std::find(mShorten.cbegin(), mShorten.cend(), i);
if (tmp != mShorten.cend()) continue; // skip if current index shortened
if (tmp != mShorten.cend())
continue; // skip if current index shortened
tmp = std::find(mPuncture.cbegin(), mPuncture.cend(), i);
if (tmp != mPuncture.cend()) continue; // skip if current index punctured
if (tmp != mPuncture.cend())
continue; // skip if current index punctured

mBitPos.push_back(i);
}
Expand All @@ -111,7 +119,7 @@ namespace ldpc
os << "K : " << code.kc() << "\n";
os << "NNZ : " << code.nnz() << "\n";
//os << "Rank: " << code.mRank << "\n";
//os << "max dc : " << code.max_dc() << "\n";
//os << "max dc : " << code.max_degree() << "\n";
os << "puncture[" << code.puncture().size() << "] : " << code.puncture() << "\n";
os << "shorten[" << code.shorten().size() << "] : " << code.shorten() << "\n";
os << "Rate : " << rate << "\n";
Expand Down
6 changes: 3 additions & 3 deletions src/core/ldpc.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -61,8 +61,8 @@ namespace ldpc
const vec_int &puncture() const { return mPuncture; };
// Array of shorten indices
const vec_int &shorten() const { return mShorten; };
// Maximum check node degree
int max_dc() const { return mMaxDC; };
// Maximum node degree
int max_degree() const { return mMaxDegree; };
// Index position of transmitted bits
const vec_int &bit_pos() const { return mBitPos; }
// Parity-check matrix
Expand All @@ -73,7 +73,7 @@ namespace ldpc
private:
vec_int mPuncture; /* array pf punctured bit indices */
vec_int mShorten; /* array of shortened bit indices */
int mMaxDC;
int mMaxDegree;

// position of transmitted bits, i.e. puncture/shorten exluded
vec_int mBitPos;
Expand Down
105 changes: 104 additions & 1 deletion src/decoding/decoder.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -83,8 +83,111 @@ namespace ldpc
{
}

int ldpc_decoder_bec::decode()
int ldpc_decoder_bec::decode()
{
return 0;
}

int ldpc_decoder_bec::decode(const vec_bits_t &channelInput)
{
auto &edges = mLdpcCode->H().nz_entry();

//initialize
for (int i = 0; i < mLdpcCode->nnz(); ++i)
{
mLv2c[i] = mLLRIn[edges[i].colIndex];
}

u32 I = 0;
while (I < mDecoderParam.iterations)
{
// CN update
for (int i = 0; i < mLdpcCode->mc(); ++i)
{
auto cw = mLdpcCode->H().row_neighbor()[i].size();
auto &cn = mLdpcCode->H().row_neighbor()[i];

mExMsgF[0] = mLv2c[cn[0].edgeIndex];
mExMsgB[cw - 1] = mLv2c[cn[cw - 1].edgeIndex];
for (u64 j = 1; j < cw; ++j)
{
mExMsgF[j] = cn_update(mExMsgF[j - 1], mLv2c[cn[j].edgeIndex]);
mExMsgB[cw - 1 - j] = cn_update(mExMsgB[cw - j], mLv2c[cn[cw - j - 1].edgeIndex]);
}

mLc2v[cn[0].edgeIndex] = mExMsgB[1];
mLc2v[cn[cw - 1].edgeIndex] = mExMsgF[cw - 2];
for (u64 j = 1; j < cw - 1; ++j)
{
mLc2v[cn[j].edgeIndex] = cn_update(mExMsgF[j - 1], mExMsgB[j + 1]);
}
}

// VN update
for (int i = 0; i < mLdpcCode->nc(); ++i)
{
// id channel output is no erasure
// propagate output
if (mLLRIn[i] != ERASURE)
{
auto &vn = mLdpcCode->H().col_neighbor()[i]; //neighbours of VN
for (const auto &hi : vn)
{
mLv2c[hi.edgeIndex] = channelInput[i].value;
}

mLLROut[i] = channelInput[i].value;
mCO[i] = channelInput[i];
}
else // channel output is erasure
{
auto vw = mLdpcCode->H().col_neighbor()[i].size();
auto &vn = mLdpcCode->H().col_neighbor()[i];

mExMsgF[0] = mLc2v[vn[0].edgeIndex];
mExMsgB[vw - 1] = mLc2v[vn[vw - 1].edgeIndex];
for (u64 j = 1; j < vw; ++j)
{
mExMsgF[j] = vn_update(mExMsgF[j - 1], mLc2v[vn[j].edgeIndex], channelInput[i]);
mExMsgB[vw - 1 - j] = vn_update(mExMsgB[vw - j], mLc2v[vn[vw - j - 1].edgeIndex], channelInput[i]);
}

mLv2c[vn[0].edgeIndex] = mExMsgB[1];
mLv2c[vn[vw - 1].edgeIndex] = mExMsgF[vw - 2];
for (u64 j = 1; j < vw - 1; ++j)
{
mLv2c[vn[j].edgeIndex] = vn_update(mExMsgF[j - 1], mExMsgB[j + 1], channelInput[i]);
}

// final decision
mLLROut[i] = mExMsgF[vw - 1]; //mExMsgB[0]
// if all incoming messages are erasures set the wrong bit
mCO[i] = (mLLROut[i] == ERASURE) ? -channelInput[i] : channelInput[i];
}
}

if (mDecoderParam.earlyTerm)
{
// stop decoding when no erasures are left
bool erasure_found = false;
for (auto llr : mLLROut)
{
if (llr == ERASURE)
{
erasure_found = true;
break;
}
}

if (!erasure_found)
{
break;
}
}

++I;
}

return I;
}
} // namespace ldpc
19 changes: 17 additions & 2 deletions src/decoding/decoder.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -34,14 +34,14 @@ namespace ldpc
mCNApprox(ldpc::jacobian),
mCO(code->nc()),
mLv2c(code->nnz()), mLc2v(code->nnz()),
mExMsgF(code->max_dc()), mExMsgB(code->max_dc()),
mExMsgF(code->max_degree()), mExMsgB(code->max_degree()),
mLLRIn(code->nc()), mLLROut(code->nc())
{
set_param(decoderParam);
}
virtual ~ldpc_decoder_base() = default;

virtual int decode();
virtual int decode() { return 0; }

// Verifies whether mCO is a codeword or not
bool is_codeword()
Expand Down Expand Up @@ -138,5 +138,20 @@ namespace ldpc
virtual ~ldpc_decoder_bec() = default;

int decode() override;
int decode(const vec_bits_t& channelInput);

// BEC Decoder VN update
// if neither of the values equals the channel input then the output is an erasure
static inline constexpr u8 vn_update(const u8 l, const u8 r, const bits_t xi)
{
return ((xi.value == l) || (xi.value == r)) ? xi.value : ERASURE;
}

// BEC Decoder CN update
// if any value is an erasure then the output is an erasure
static inline constexpr u8 cn_update(const u8 l, const u8 r)
{
return ((l == ERASURE) || (r == ERASURE)) ? ERASURE : (bits_t(l) + bits_t(r)).value;
}
};
} // namespace ldpc
2 changes: 2 additions & 0 deletions src/sim/channel.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,8 @@ namespace ldpc
void channel::encode_and_map() {}
void channel::simulate() {}
void channel::calculate_llrs() {}
int channel::decode() { return 0; }
const vec_bits_t &channel::estimate() const { return mCodeWord; }

channel_awgn::channel_awgn(const std::shared_ptr<ldpc_code> &code,
const decoder_param &decoderParams,
Expand Down
2 changes: 1 addition & 1 deletion src/sim/channel.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -225,7 +225,7 @@ namespace ldpc
*/
int decode() override
{
return mLdpcDecoder->decode();
return mLdpcDecoder->decode(mCodeWord);
}

/**
Expand Down
18 changes: 16 additions & 2 deletions src/sim/ldpcsim.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -55,6 +55,19 @@ namespace ldpc
)
);
}
else if (mChannelParams.type == std::string("BEC"))
{
mChannel.push_back(
std::make_shared<channel_bec>(
channel_bec(
mLdpcCode,
mDecoderParams,
mChannelParams.seed + i,
0.
)
)
);
}
else
{
throw std::runtime_error("No channel selected.");
Expand All @@ -63,7 +76,8 @@ namespace ldpc
}
catch (std::exception &e)
{
std::cout << "Error: ldpc_sim::ldpc_sim() " << e.what() << "\n";
std::cout << "Error: ldpc_sim::ldpc_sim() " << e.what() << std::endl;
exit(EXIT_FAILURE);
}
}

Expand Down Expand Up @@ -100,7 +114,7 @@ namespace ldpc
auto maxFrames = mSimulationParams.maxFrames;
std::string xValType = "SNR";

if (mChannelParams.type == std::string("BSC"))
if (mChannelParams.type == std::string("BSC") || mChannelParams.type == std::string("BEC"))
{
xValType = "EPS";
// reverse the epsilon values, since we should start at the worst
Expand Down

0 comments on commit 7e942fb

Please sign in to comment.