diff options
Diffstat (limited to 'gr-fec/lib/viterbi/metrics.cc')
| -rw-r--r-- | gr-fec/lib/viterbi/metrics.cc | 136 |
1 files changed, 69 insertions, 67 deletions
diff --git a/gr-fec/lib/viterbi/metrics.cc b/gr-fec/lib/viterbi/metrics.cc index c94133be15..9ec2f37e17 100644 --- a/gr-fec/lib/viterbi/metrics.cc +++ b/gr-fec/lib/viterbi/metrics.cc @@ -37,94 +37,96 @@ /* Symbols are offset-binary, with 128 corresponding to an erased (no * information) symbol */ -#define OFFSET 128 +#define OFFSET 128 -#include<gnuradio/math.h> +#include <gnuradio/math.h> #include <cstdlib> #include <cmath> /* Normal function integrated from -Inf to x. Range: 0-1 */ -#define normal(x) (0.5 + 0.5*erf((x)/GR_M_SQRT2)) +#define normal(x) (0.5 + 0.5 * erf((x) / GR_M_SQRT2)) /* Logarithm base 2 */ -#define gr_log2(x) (log(x)*GR_M_LOG2E) +#define gr_log2(x) (log(x) * GR_M_LOG2E) -namespace gr{ - namespace fec{ +namespace gr { +namespace fec { /* Generate log-likelihood metrics for 8-bit soft quantized channel * assuming AWGN and BPSK */ - void - gen_met(int mettab[2][256], /* Metric table, [sent sym][rx symbol] */ - int amp, /* Signal amplitude, units */ - double esn0, /* Es/N0 ratio in dB */ - double bias, /* Metric bias; 0 for viterbi, rate for sequential */ - int scale) /* Scale factor */ - { - double noise; - int s,bit; - double metrics[2][256]; - double p0,p1; - - /* Es/N0 as power ratio */ - esn0 = pow(10.,esn0/10); - - noise = 0.5/esn0; /* only half the noise for BPSK */ - noise = sqrt(noise); /* noise/signal Voltage ratio */ - - /* Zero is a special value, since this sample includes all - * lower samples that were clipped to this value, i.e., it - * takes the whole lower tail of the curve - */ - p1 = normal(((0-OFFSET+0.5)/amp - 1)/noise); /* P(s|1) */ - - /* Prob of this value occurring for a 0-bit */ /* P(s|0) */ - p0 = normal(((0-OFFSET+0.5)/amp + 1)/noise); - metrics[0][0] = gr_log2(2*p0/(p1+p0)) - bias; - metrics[1][0] = gr_log2(2*p1/(p1+p0)) - bias; - - for(s=1;s<255;s++){ +void gen_met(int mettab[2][256], /* Metric table, [sent sym][rx symbol] */ + int amp, /* Signal amplitude, units */ + double esn0, /* Es/N0 ratio in dB */ + double bias, /* Metric bias; 0 for viterbi, rate for sequential */ + int scale) /* Scale factor */ +{ + double noise; + int s, bit; + double metrics[2][256]; + double p0, p1; + + /* Es/N0 as power ratio */ + esn0 = pow(10., esn0 / 10); + + noise = 0.5 / esn0; /* only half the noise for BPSK */ + noise = sqrt(noise); /* noise/signal Voltage ratio */ + + /* Zero is a special value, since this sample includes all + * lower samples that were clipped to this value, i.e., it + * takes the whole lower tail of the curve + */ + p1 = normal(((0 - OFFSET + 0.5) / amp - 1) / noise); /* P(s|1) */ + + /* Prob of this value occurring for a 0-bit */ /* P(s|0) */ + p0 = normal(((0 - OFFSET + 0.5) / amp + 1) / noise); + metrics[0][0] = gr_log2(2 * p0 / (p1 + p0)) - bias; + metrics[1][0] = gr_log2(2 * p1 / (p1 + p0)) - bias; + + for (s = 1; s < 255; s++) { /* P(s|1), prob of receiving s given 1 transmitted */ - p1 = normal(((s-OFFSET+0.5)/amp - 1)/noise) - - normal(((s-OFFSET-0.5)/amp - 1)/noise); + p1 = normal(((s - OFFSET + 0.5) / amp - 1) / noise) - + normal(((s - OFFSET - 0.5) / amp - 1) / noise); /* P(s|0), prob of receiving s given 0 transmitted */ - p0 = normal(((s-OFFSET+0.5)/amp + 1)/noise) - - normal(((s-OFFSET-0.5)/amp + 1)/noise); + p0 = normal(((s - OFFSET + 0.5) / amp + 1) / noise) - + normal(((s - OFFSET - 0.5) / amp + 1) / noise); #ifdef notdef - printf("P(%d|1) = %lg, P(%d|0) = %lg\n",s,p1,s,p0); + printf("P(%d|1) = %lg, P(%d|0) = %lg\n", s, p1, s, p0); #endif - metrics[0][s] = gr_log2(2*p0/(p1+p0)) - bias; - metrics[1][s] = gr_log2(2*p1/(p1+p0)) - bias; - } - /* 255 is also a special value */ - /* P(s|1) */ - p1 = 1 - normal(((255-OFFSET-0.5)/amp - 1)/noise); - /* P(s|0) */ - p0 = 1 - normal(((255-OFFSET-0.5)/amp + 1)/noise); - - metrics[0][255] = gr_log2(2*p0/(p1+p0)) - bias; - metrics[1][255] = gr_log2(2*p1/(p1+p0)) - bias; -#ifdef notdef - /* The probability of a raw symbol error is the probability - * that a 1-bit would be received as a sample with value - * 0-128. This is the offset normal curve integrated from -Inf to 0. - */ - printf("symbol Pe = %lg\n",normal(-1/noise)); + metrics[0][s] = gr_log2(2 * p0 / (p1 + p0)) - bias; + metrics[1][s] = gr_log2(2 * p1 / (p1 + p0)) - bias; + } + /* 255 is also a special value */ + /* P(s|1) */ + p1 = 1 - normal(((255 - OFFSET - 0.5) / amp - 1) / noise); + /* P(s|0) */ + p0 = 1 - normal(((255 - OFFSET - 0.5) / amp + 1) / noise); + + metrics[0][255] = gr_log2(2 * p0 / (p1 + p0)) - bias; + metrics[1][255] = gr_log2(2 * p1 / (p1 + p0)) - bias; +#ifdef notdef + /* The probability of a raw symbol error is the probability + * that a 1-bit would be received as a sample with value + * 0-128. This is the offset normal curve integrated from -Inf to 0. + */ + printf("symbol Pe = %lg\n", normal(-1 / noise)); #endif - for(bit=0;bit<2;bit++){ - for(s=0;s<256;s++){ - /* Scale and round to nearest integer */ - mettab[bit][s] = floor(metrics[bit][s] * scale + 0.5); -#ifdef notdef - printf("metrics[%d][%d] = %lg, mettab = %d\n", - bit,s,metrics[bit][s],mettab[bit][s]); + for (bit = 0; bit < 2; bit++) { + for (s = 0; s < 256; s++) { + /* Scale and round to nearest integer */ + mettab[bit][s] = floor(metrics[bit][s] * scale + 0.5); +#ifdef notdef + printf("metrics[%d][%d] = %lg, mettab = %d\n", + bit, + s, + metrics[bit][s], + mettab[bit][s]); #endif } - } } - } } +} // namespace fec +} // namespace gr |