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#!/usr/bin/env python
#
# Copyright 2005 Free Software Foundation, Inc.
#
# This file is part of GNU Radio
#
# GNU Radio is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3, or (at your option)
# any later version.
#
# GNU Radio 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 General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with GNU Radio; see the file COPYING. If not, write to
# the Free Software Foundation, Inc., 51 Franklin Street,
# Boston, MA 02110-1301, USA.
#
"""
Digital voice Tx and Rx using GSM 13kbit vocoder and GMSK.
Runs channel at 32kbit/sec. Currently uses fake channel coding,
but there's room for a rate 1/2 coder.
"""
from gnuradio import gr, gru
from gnuradio import blocks
from gnuradio.blksimpl.gmsk import gmsk_mod, gmsk_demod
from gnuradio.vocoder import gsm_full_rate
# Size of gsm full rate speech encoder output packet in bytes
GSM_FRAME_SIZE = 33
# Size of packet in bytes that we send to GMSK modulator:
#
# Target: 256kS/sec air rate.
#
# 256kS 1 sym 1 bit 1 byte 0.020 sec 80 bytes
# ---- * ----- * ----- * ------ * --------- = --------
# sec 8 S 1 sym 8 bits frame frame
#
# gr_simple_framer add 10 bytes of overhead.
AIR_FRAME_SIZE = 70
class digital_voice_tx(gr.hier_block):
"""
Hierarchical block for digital voice tranmission.
The input is 8kS/sec floating point audio in the range [-1,+1]
The output is 256kS/sec GMSK modulated complex baseband signal in the range [-1,+1].
"""
def __init__(self, fg):
samples_per_symbol = 8
symbol_rate = 32000
bt = 0.3 # Gaussian filter bandwidth * symbol time
src_scale = blocks.multiply_const_ff(32767)
f2s = blocks.float_to_short()
voice_coder = gsm_full_rate.encode_sp()
channel_coder = gr.fake_channel_encoder_pp(GSM_FRAME_SIZE, AIR_FRAME_SIZE)
p2s = gr.parallel_to_serial(gr.sizeof_char, AIR_FRAME_SIZE)
mod = gmsk_mod(fg, sps=samples_per_symbol,
symbol_rate=symbol_rate, bt=bt,
p_size=AIR_FRAME_SIZE)
fg.connect(src_scale, f2s, voice_coder, channel_coder, p2s, mod)
gr.hier_block.__init__(self, fg, src_scale, mod)
class digital_voice_rx(gr.hier_block):
"""
Hierarchical block for digital voice reception.
The input is 256kS/sec GMSK modulated complex baseband signal.
The output is 8kS/sec floating point audio in the range [-1,+1]
"""
def __init__(self, fg):
samples_per_symbol = 8
symbol_rate = 32000
demod = gmsk_demod(fg, sps=samples_per_symbol,
symbol_rate=symbol_rate,
p_size=AIR_FRAME_SIZE)
s2p = gr.serial_to_parallel(gr.sizeof_char, AIR_FRAME_SIZE)
channel_decoder = gr.fake_channel_decoder_pp(AIR_FRAME_SIZE, GSM_FRAME_SIZE)
voice_decoder = gsm_full_rate.decode_ps()
s2f = blocks.short_to_float ()
sink_scale = blocks.multiply_const_ff(1.0/32767.)
fg.connect(demod, s2p, channel_decoder, voice_decoder, s2f, sink_scale)
gr.hier_block.__init__(self, fg, demod, sink_scale)
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