static void impulse_response(int rnk, dim_stuff *d, R impulse_amp,
R *A, int N)
{
if (rnk == 0)
A[0] = impulse_amp;
else {
int i;
N /= d->n;
for (i = 0; i < d->n; ++i) {
impulse_response(rnk - 1, d + 1,
impulse_amp * d->ti(d->i0, d->k0 + i, d->n0),
A + i * N, N);
}
}
}
static double rimpulse(dim_stuff *d, R impulse_amp,
int n, int vecn, info *nfo,
R *inA, R *inB, R *inC,
R *outA, R *outB, R *outC,
R *tmp, int rounds, double tol)
{
double e = 0.0;
int N = n * vecn;
int i;
int j;
/* test 2: check that the unit impulse is transformed properly */
for (i = 0; i < N; ++i) {
/* pls */
inA[i] = 0.0;
}
for (i = 0; i < vecn; ++i) {
inA[i * n] = (i+1) / (double)(vecn+1);
/* transform of the pls */
impulse_response(nfo->probsz->rnk, d, impulse_amp * inA[i * n],
outA + i * n, n);
}
dofft(nfo, inA, tmp);
e = dmax(e, racmp(tmp, outA, N, "impulse 1", tol));
for (j = 0; j < rounds; ++j) {
rarand(inB, N);
rasub(inC, inA, inB, N);
dofft(nfo, inB, outB);
dofft(nfo, inC, outC);
raadd(tmp, outB, outC, N);
e = dmax(e, racmp(tmp, outA, N, "impulse", tol));
}
return e;
}
void SISO::gen_chtrellis(void)
// generate trellis for precoded FIR channels with real coefficients
{
//get parameters
int mem_len = impulse_response.cols()-1;//memory length of the channel
int p_order = prec_gen.length()-1;//order of the precoder polynomial
//other variables
register int n,k,j;
double inputs[] = {1.0,-1.0};//1->-1, 0->+1
int index;
double feedback[2];
//create channel trellis
int equiv_ch_mem_len = std::max(mem_len, p_order);
chtrellis.stateNb = (1<<equiv_ch_mem_len);
chtrellis.output = new double[2*chtrellis.stateNb];
chtrellis.nextState = new int[2*chtrellis.stateNb];
chtrellis.prevState = new int[2*chtrellis.stateNb];
chtrellis.input = new int[2*chtrellis.stateNb];
//initialize trellis
itpp::ivec enc_mem(equiv_ch_mem_len);
#pragma omp parallel for private(n,enc_mem,k,feedback,j)
for (n=0; n<chtrellis.stateNb; n++) //initial state
{
enc_mem = 1-2*itpp::to_ivec(itpp::dec2bin(equiv_ch_mem_len, n));//1->-1, 0->+1
//output
for (k=0; k<2; k++)
{
feedback[k] = inputs[k];
for (j=1; j<=p_order; j++)
if (prec_gen[j])
feedback[k] *= enc_mem[j-1];//xor truth table must remain the same
chtrellis.output[n+k*chtrellis.stateNb] = feedback[k]*impulse_response(0,0);
for (j=1; j<=mem_len; j++)
chtrellis.output[n+k*chtrellis.stateNb] += (enc_mem[j-1]*impulse_response(0,j));
}
//next state
for (j=(equiv_ch_mem_len-1); j>0; j--)
enc_mem[j] = enc_mem[j-1];
for (k=0; k<2; k++)
{
enc_mem[0] = int(feedback[k]);
chtrellis.nextState[n+k*chtrellis.stateNb] = itpp::bin2dec(itpp::to_bvec((1-enc_mem)/2), true);//-1->1, +1->0
}
}
#pragma omp parallel for private(j,index,n,k)
for (j=0; j<chtrellis.stateNb; j++)
{
index = 0;
for (n=0; n<chtrellis.stateNb; n++)
{
for (k=0; k<2; k++)
{
if (chtrellis.nextState[n+k*chtrellis.stateNb]==j)
{
chtrellis.prevState[j+index*chtrellis.stateNb] = n;
chtrellis.input[j+index*chtrellis.stateNb] = k;//this is an index to the channel input
index++;
}
}
}
}
}
