Adaptive Filters - Digital Signal Processing and Applications with the C6713 and C6416 DSK - page 281

// Adaptpredict_2IN.c Adaptive predictor->cancel narrowband interference
#include "DSK6713_AIC23.h" //codec-DSK support file
Uint32 fs=DSK6713_AIC23_FREQ_8KHZ;//set sampling rate
#define beta 1E-13 //rate of convergence
#define N 60 //# of coefficients of adapt FIR
#define NS 256 //size of wideband's buffer
#define LEFT 0 //left channel
#define RIGHT 1 //right channel
const short bufferlength = NS; //buffer length for wideband signal
float splusn[N+1]; //buffer wideband signal+interference
float w[N+1]; //buffer for weights of adapt FIR
float delay[N+1]; //buffer for input to adapt FIR
volatile union {unsigned int uint; short channel[2];}AIC23_data;

interrupt void c_int11() //ISR
{
static short buffercount=0; //init buffer
short i;
float yn, E; //yn=out adapt FIR, error signal

float wb_signal; //wideband desired signal

float noise; //external interference

AIC23_data.uint = input_sample();//input left and right as 32-bit
wb_signal = AIC23_data.channel[LEFT]; //desired on left channel
noise = AIC23_data.channel[RIGHT]; //noise on right channel
splusn[0] = (wb_signal + noise); //wideband signal + interference
delay[0] = splusn[3]; //delayed input to adaptive FIR
yn = 0; //init output of adaptive FIR
for (i = 0; i < N; i++)
yn += (w[i] * delay[i]); //output of adaptive FIR filter
E = splusn[0] - yn; //(wideband + noise)-out adapt FIR
for (i = N-1; i >= 0; i--)
{
w[i] = w[i]+(beta*E*delay[i]); //update weights of adapt FIR
delay[i+1] = delay[i]; //update buffer delay samples
splusn[i+1] = splusn[i]; //update buffer corrupted wideband
}
buffercount++; //incr buffer count of wideband
if(buffercount>=bufferlength) buffercount=0; //reinit count
output_sample((short)E); //overall output from left channel
return;
}

void main()
{
int T = 0;
for (T = 0; T < N; T++) //init variables
{
w[T] = 0.0; //init weights of adaptive FIR

delay[T] = 0.0; //init buffer for delay samples

splusn[T] = 0; //init wideband+interference

}
comm_intr(); //init DSK, codec, McBSP
while(1); //infinite loop
}

FIGURE 7.26. Adaptive predictor program for cancellation of narrowband interference in
the presence of a wideband signal using external inputs ( adaptpredict_2IN.c ).