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@ -54,45 +54,40 @@ void llr_approx(const _Complex float *in, float *out, int N, int M, int B,
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_Complex float *symbols, uint32_t (*S)[6][32], float sigma2) {
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int i, s, b;
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float num, den;
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float new_num, new_den;
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float idiff0, qdiff0, idiff1, qdiff1;
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int change_sign = -1;
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float x, y, d[64];
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for (s=0; s<N; s++) { /* recevied symbols */
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for (b=0; b<B; b++) {/* bits per symbol*/
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/* initiate num[b] and den[b] */
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idiff0 = __real__ in[s] - __real__ symbols[S[0][b][0]];
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qdiff0 = __imag__ in[s] - __imag__ symbols[S[0][b][0]];
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num = idiff0*idiff0 + qdiff0*qdiff0;
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for (s=0; s<N; s++) { /* recevied symbols */
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/* Compute the distances squared d[i] between the received symbol and all constellation points */
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for (i=0; i<M; i++) {
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x = __real__ in[s] - __real__ symbols[i];
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y = __imag__ in[s] - __imag__ symbols[i];
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d[i] = x*x + y*y;
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}
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idiff1 = __real__ in[s] - __real__ symbols[S[1][b][0]];
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qdiff1 = __imag__ in[s] - __imag__ symbols[S[1][b][0]];
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den = idiff1*idiff1 + qdiff1*qdiff1;
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for (b=0; b<B; b++) {/* bits per symbol*/
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/* initiate num[b] and den[b] */
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num = d[S[0][b][0]];
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den = d[S[1][b][0]];
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/* half the constellation symbols have '1'|'0' at any bit pos. */
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for (i=1; i<M/2; i++) {
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idiff0 = __real__ in[s] - __real__ symbols[S[0][b][i]];
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qdiff0 = __imag__ in[s] - __imag__ symbols[S[0][b][i]];
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new_num = idiff0*idiff0 + qdiff0*qdiff0;
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idiff1 = __real__ in[s] - __real__ symbols[S[1][b][i]];
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qdiff1 = __imag__ in[s] - __imag__ symbols[S[1][b][i]];
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new_den = idiff1*idiff1 + qdiff1*qdiff1;
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if (new_num < num) {
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num = new_num;
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}
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if (new_den < den) {
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den = new_den;
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}
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}
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/* Theoretical LLR and approximate LLR values are positive if
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* symbol(s) with '0' is/are closer and negative if symbol(s)
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* with '1' are closer.
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* Change sign if mapping negative to '0' and positive to '1' */
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out[s*B+b] = change_sign*(den-num)/sigma2;
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}
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/* Minimum distance squared search between recevied symbol and a constellation point with a
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'1' and a '0' for each bit position */
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for (i=1; i<M/2; i++) { /* half the constellation points have '1'|'0' at any given bit position */
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if (d[S[0][b][i]] < num) {
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num = d[S[0][b][i]];
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}
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if (d[S[1][b][i]] < den) {
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den = d[S[1][b][i]];
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}
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}
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/* Theoretical LLR and approximate LLR values are positive if
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* symbol(s) with '0' is/are closer and negative if symbol(s)
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* with '1' are closer.
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* Change sign if mapping negative to '0' and positive to '1' */
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out[s*B+b] = change_sign*(den-num)/sigma2;
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}
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}
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}
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/**
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@ -115,29 +110,32 @@ void llr_exact(const _Complex float *in, float *out, int N, int M, int B,
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_Complex float *symbols, uint32_t (*S)[6][32], float sigma2) {
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int i, s, b;
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float num, den;
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float idiff0, qdiff0, idiff1, qdiff1;
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int change_sign = -1;
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float x, y, d[64];
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for (s=0; s<N; s++) { /* recevied symbols */
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/* Compute exp{·} of the distances squared d[i] between the received symbol and all constellation points */
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for (i=0; i<M; i++) {
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x = __real__ in[s] - __real__ symbols[i];
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y = __imag__ in[s] - __imag__ symbols[i];
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d[i] = exp(-1*(x*x + y*y)/sigma2);
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}
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for (s=0; s<N; s++) { /* recevied symbols */
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for (b=0; b<B; b++) {/* bits per symbol*/
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/* initiate num[b] and den[b] */
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num = 0;
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den = 0;
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/* half the constellation symbols have '1'|'0' at any bit pos. */
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for (i=0; i<M/2; i++) {
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idiff0 = __real__ in[s] - __real__ symbols[S[0][b][i]];
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qdiff0 = __imag__ in[s] - __imag__ symbols[S[0][b][i]];
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num += exp(-1*(idiff0*idiff0 + qdiff0*qdiff0)/sigma2);
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/* Sum up the corresponding d[i]'s for each bit position */
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for (b=0; b<B; b++) {/* bits per symbol*/
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/* initiate num[b] and den[b] */
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num = 0;
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den = 0;
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idiff1 = __real__ in[s] - __real__ symbols[S[1][b][i]];
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qdiff1 = __imag__ in[s] - __imag__ symbols[S[1][b][i]];
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den += exp(-1*(idiff1*idiff1 + qdiff1*qdiff1)/sigma2);
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}
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/* Theoretical LLR and approximate LLR values are positive if
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* symbol(s) with '0' is/are closer and negative if symbol(s)
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* with '1' are closer.
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* Change sign if mapping negative to '0' and positive to '1' */
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out[s*B+b] = change_sign*log(num/den);
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}
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for (i=0; i<M/2; i++) { /* half the constellation points have '1'|'0' at any given bit position */
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num += d[S[0][b][i]];
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den += d[S[1][b][i]];
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}
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/* Theoretical LLR and approximate LLR values are positive if
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* symbol(s) with '0' is/are closer and negative if symbol(s)
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* with '1' are closer.
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* Change sign if mapping negative to '0' and positive to '1' */
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out[s*B+b] = change_sign*log(num/den);
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}
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}
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}
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