Osmocom GSM/GPRS/EGPRS transceiver, originally forked from OpenBTS transceiver. For building SDR based GSM BTS with osmo-bts-trx.
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/*
* Rational Sample Rate Conversion
* Copyright (C) 2012, 2013 Thomas Tsou <tom@tsou.cc>
*
* SPDX-License-Identifier: LGPL-2.1+
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*/
#ifndef _RESAMPLER_H_
#define _RESAMPLER_H_
#include <vector>
#include <complex>
class Resampler {
public:
/* Constructor for rational sample rate conversion
* @param p numerator of resampling ratio
* @param q denominator of resampling ratio
* @param filt_len length of each polyphase subfilter
*/
Resampler(size_t p, size_t q, size_t filt_len = 16);
~Resampler();
/* Initialize resampler filterbank.
* @param bw bandwidth factor on filter generation (pre-window)
* @return false on error, zero otherwise
*
* Automatic setting is to compute the filter to prevent aliasing with
* a Blackman-Harris window. Adjustment is made through a bandwidth
* factor to shift the cutoff and/or the constituent filter lengths.
* Calculation of specific rolloff factors or 3-dB cutoff points is
* left as an excersize for the reader.
*/
bool init(float bw = 1.0f);
/* Rotate "commutator" and drive samples through filterbank
* @param in continuous buffer of input complex float values
* @param in_len input buffer length
* @param out continuous buffer of output complex float values
* @param out_len output buffer length
* @return number of samples outputted, negative on error
*
* Input and output vector lengths must of be equal multiples of the
* rational conversion rate denominator and numerator respectively.
*/
int rotate(const float *in, size_t in_len, float *out, size_t out_len);
/* Get filter length
* @return number of taps in each filter partition
*/
size_t len();
private:
size_t p;
size_t q;
size_t filt_len;
std::vector<size_t> in_index;
std::vector<size_t> out_path;
std::vector<std::complex<float> *> partitions;
void initFilters(float bw);
};
#endif /* _RESAMPLER_H_ */