Resampling module for USRP. Not completed. In progress.

git-svn-id: http://svn.eurecom.fr/openair4G/trunk@5085 818b1a75-f10b-46b9-bf7c-635c3b92a50f
2014-02-25 08:23:00 +00:00
parent 18e4f19e54
commit 791d449b6d
8 changed files with 1928 additions and 0 deletions
@@ -0,0 +1,61 @@
+#include "polyphaseResample.h"
+#include <iostream>
+#include <stdio.h>
+using namespace std;
+
+// table_len should be decied by the length of the filter output
+// but a default value of 50000 is adequate for our app
+void buildPolyphaseCache(const int P, const int Q, int *&branch_table, int *&offset_table, const int table_len) {
+	branch_table = new int[table_len];
+	offset_table = new int[table_len];
+	for (int i = 0; i < table_len; ++i) {
+		branch_table[i] = (i * Q) % P;
+		offset_table[i] = (i * Q - branch_table[i]) / P;
+	}
+}
+
+void polyphaseResample(short *in_data, unsigned int in_sample_count,
+		short *out_data, unsigned int out_sample_count,
+		short *filter_coeff, unsigned int filter_len,
+		const int P, const int Q, const unsigned int fix_shift,
+		int *branch_table, int *offset_table) {
+	buildPolyphaseCache( P, Q, branch_table, offset_table, 50000);
+	// calculate the sample count of output
+	out_sample_count = (int)(in_sample_count * (float)P / (float)Q);
+
+	short *output_ptr = out_data;
+	unsigned int output_ix = 0;
+	short const *input_end = in_data + in_sample_count * 2;
+	short const *output_end = out_data + out_sample_count * 2;
+	short const *filter_end = filter_coeff + filter_len;
+	while (output_ptr < output_end) 
+	{
+		int output_branch = branch_table[output_ix];
+		int input_offset = offset_table[output_ix];
+
+		short *input_ptr = in_data + 2 * input_offset;
+		short *filter_ptr = filter_coeff + output_branch;
+
+		while (input_ptr >= input_end) {
+			input_ptr -= 2;
+			filter_ptr += P;
+		}
+
+		int sum_real = 0, sum_imag = 0;
+		while ((input_ptr >= in_data) && (filter_ptr < filter_end)) {
+			sum_real += (int)(*input_ptr) * (int)(*filter_ptr);
+			sum_imag += (int)(*(input_ptr + 1)) * (int)(*filter_ptr);
+			input_ptr -= 2;
+			filter_ptr += P;
+		}
+
+		*output_ptr = (short)(sum_real >> fix_shift);
+		*(output_ptr + 1) = (short)(sum_imag >> fix_shift);
+
+		output_ptr += 2;
+		output_ix++;
+	}
+}
+
+
+