#
# Copyright 2013 Free Software Foundation, Inc.
#
# This file is part of GNU Radio
#
# SPDX-License-Identifier: GPL-3.0-or-later
#
#
"""
OFDM Transmitter / Receiver hier blocks.
For simple configurations, no need to connect all the relevant OFDM blocks
to form an OFDM Tx/Rx--simply use these.
"""
# Reminder: All frequency-domain stuff is in shifted form, i.e. DC carrier
# in the middle!
import numpy
from gnuradio import gr, blocks, fft, analog
from . import digital_python as digital
_def_fft_len = 64
_def_cp_len = 16
_def_frame_length_tag_key = "frame_length"
_def_packet_length_tag_key = "packet_length"
_def_packet_num_tag_key = "packet_num"
# Data and pilot carriers are same as in 802.11a
_def_occupied_carriers = (list(range(-26, -21)) + list(range(-20, -7)) + list(range(-6, 0)) + list(range(1, 7)) + list(range(8, 21)) + list(range(22, 27)),)
_def_pilot_carriers=((-21, -7, 7, 21,),)
_pilot_sym_scramble_seq = (
1,1,1,1, -1,-1,-1,1, -1,-1,-1,-1, 1,1,-1,1, -1,-1,1,1, -1,1,1,-1, 1,1,1,1, 1,1,-1,1,
1,1,-1,1, 1,-1,-1,1, 1,1,-1,1, -1,-1,-1,1, -1,1,-1,-1, 1,-1,-1,1, 1,1,1,1, -1,-1,1,1,
-1,-1,1,-1, 1,-1,1,1, -1,-1,-1,1, 1,-1,-1,-1, -1,1,-1,-1, 1,-1,1,1, 1,1,-1,1, -1,1,-1,1,
-1,-1,-1,-1, -1,1,-1,1, 1,-1,1,-1, 1,1,1,-1, -1,1,-1,-1, -1,1,1,1, -1,-1,-1,-1, -1,-1,-1
)
_def_pilot_symbols= tuple([(x, x, x, -x) for x in _pilot_sym_scramble_seq])
_seq_seed = 42
def _get_active_carriers(fft_len, occupied_carriers, pilot_carriers):
""" Returns a list of all carriers that at some point carry data or pilots. """
active_carriers = list()
for carrier in list(occupied_carriers[0]) + list(pilot_carriers[0]):
if carrier < 0:
carrier += fft_len
active_carriers.append(carrier)
return active_carriers
def _make_sync_word1(fft_len, occupied_carriers, pilot_carriers):
""" Creates a random sync sequence for fine frequency offset and timing
estimation. This is the first of typically two sync preamble symbols
for the Schmidl & Cox sync algorithm.
The relevant feature of this symbols is that every second sub-carrier
is zero. In the time domain, this results in two identical halves of
the OFDM symbols.
Symbols are always BPSK symbols. Carriers are scaled by sqrt(2) to keep
total energy constant.
Carrier 0 (DC carrier) is always zero. If used, carrier 1 is non-zero.
This means the sync algorithm has to check on odd carriers!
"""
active_carriers = _get_active_carriers(fft_len, occupied_carriers, pilot_carriers)
numpy.random.seed(_seq_seed)
bpsk = {0: numpy.sqrt(2), 1: -numpy.sqrt(2)}
sw1 = [bpsk[numpy.random.randint(2)] if x in active_carriers and x % 2 else 0 for x in range(fft_len)]
return numpy.fft.fftshift(sw1)
def _make_sync_word2(fft_len, occupied_carriers, pilot_carriers):
""" Creates a random sync sequence for coarse frequency offset and channel
estimation. This is the second of typically two sync preamble symbols
for the Schmidl & Cox sync algorithm.
Symbols are always BPSK symbols.
"""
active_carriers = _get_active_carriers(fft_len, occupied_carriers, pilot_carriers)
numpy.random.seed(_seq_seed)
bpsk = {0: 1, 1: -1}
sw2 = [bpsk[numpy.random.randint(2)] if x in active_carriers else 0 for x in range(fft_len)]
sw2[0] = 0j
return numpy.fft.fftshift(sw2)
def _get_constellation(bps):
""" Returns a modulator block for a given number of bits per symbol """
constellation = {
1: digital.constellation_bpsk(),
2: digital.constellation_qpsk(),
3: digital.constellation_8psk()
}
try:
return constellation[bps]
except KeyError:
print('Modulation not supported.')
exit(1)
class ofdm_tx(gr.hier_block2):
"""Hierarchical block for OFDM modulation.
The input is a byte stream (unsigned char) and the
output is the complex modulated signal at baseband.
Args:
fft_len: The length of FFT (integer).
cp_len: The length of cyclic prefix in total samples (integer).
packet_length_tag_key: The name of the tag giving packet length at the input.
occupied_carriers: A vector of vectors describing which OFDM carriers are occupied.
pilot_carriers: A vector of vectors describing which OFDM carriers are occupied with pilot symbols.
pilot_symbols: The pilot symbols.
bps_header: Bits per symbol (header).
bps_payload: Bits per symbol (payload).
sync_word1: The first sync preamble symbol. This has to be with
| zeros on alternating carriers. Used for fine and
| coarse frequency offset and timing estimation.
sync_word2: The second sync preamble symbol. This has to be filled
| entirely. Also used for coarse frequency offset and
| channel estimation.
rolloff: The rolloff length in samples. Must be smaller than the CP.
debug_log: Write output into log files (Warning: creates lots of data!)
scramble_bits: Activates the scramblers (set this to True unless debugging)
"""
def __init__(self, fft_len=_def_fft_len, cp_len=_def_cp_len,
packet_length_tag_key=_def_packet_length_tag_key,
occupied_carriers=_def_occupied_carriers,
pilot_carriers=_def_pilot_carriers,
pilot_symbols=_def_pilot_symbols,
bps_header=1,
bps_payload=1,
sync_word1=None,
sync_word2=None,
rolloff=0,
debug_log=False,
scramble_bits=False
):
gr.hier_block2.__init__(self, "ofdm_tx",
gr.io_signature(1, 1, gr.sizeof_char),
gr.io_signature(1, 1, gr.sizeof_gr_complex))
### Param init / sanity check ########################################
self.fft_len = fft_len
self.cp_len = cp_len
self.packet_length_tag_key = packet_length_tag_key
self.occupied_carriers = occupied_carriers
self.pilot_carriers = pilot_carriers
self.pilot_symbols = pilot_symbols
self.bps_header = bps_header
self.bps_payload = bps_payload
self.sync_word1 = sync_word1
if sync_word1 is None:
self.sync_word1 = _make_sync_word1(fft_len, occupied_carriers, pilot_carriers)
else:
if len(sync_word1) != self.fft_len:
raise ValueError("Length of sync sequence(s) must be FFT length.")
self.sync_words = [self.sync_word1,]
if sync_word2 is None:
self.sync_word2 = _make_sync_word2(fft_len, occupied_carriers, pilot_carriers)
else:
self.sync_word2 = sync_word2
if len(self.sync_word2):
if len(self.sync_word2) != fft_len:
raise ValueError("Length of sync sequence(s) must be FFT length.")
self.sync_word2 = list(self.sync_word2)
self.sync_words.append(self.sync_word2)
if scramble_bits:
self.scramble_seed = 0x7f
else:
self.scramble_seed = 0x00 # We deactivate the scrambler by init'ing it with zeros
### Header modulation ################################################
crc = digital.crc32_bb(False, self.packet_length_tag_key)
header_constellation = _get_constellation(bps_header)
header_mod = digital.chunks_to_symbols_bc(header_constellation.points())
formatter_object = digital.packet_header_ofdm(
occupied_carriers=occupied_carriers, n_syms=1,
bits_per_header_sym=self.bps_header,
bits_per_payload_sym=self.bps_payload,
scramble_header=scramble_bits
)
header_gen = digital.packet_headergenerator_bb(formatter_object.base(), self.packet_length_tag_key)
header_payload_mux = blocks.tagged_stream_mux(
itemsize=gr.sizeof_gr_complex*1,
lengthtagname=self.packet_length_tag_key,
tag_preserve_head_pos=1 # Head tags on the payload stream stay on the head
)
self.connect(
self,
crc,
header_gen,
header_mod,
(header_payload_mux, 0)
)
if debug_log:
self.connect(header_gen, blocks.file_sink(1, 'tx-hdr.dat'))
### Payload modulation ###############################################
payload_constellation = _get_constellation(bps_payload)
payload_mod = digital.chunks_to_symbols_bc(payload_constellation.points())
payload_scrambler = digital.additive_scrambler_bb(
0x8a,
self.scramble_seed,
7,
0, # Don't reset after fixed length (let the reset tag do that)
bits_per_byte=8, # This is before unpacking
reset_tag_key=self.packet_length_tag_key
)
payload_unpack = blocks.repack_bits_bb(
8, # Unpack 8 bits per byte
bps_payload,
self.packet_length_tag_key
)
self.connect(
crc,
payload_scrambler,
payload_unpack,
payload_mod,
(header_payload_mux, 1)
)
### Create OFDM frame ################################################
allocator = digital.ofdm_carrier_allocator_cvc(
self.fft_len,
occupied_carriers=self.occupied_carriers,
pilot_carriers=self.pilot_carriers,
pilot_symbols=self.pilot_symbols,
sync_words=self.sync_words,
len_tag_key=self.packet_length_tag_key
)
ffter = fft.fft_vcc(
self.fft_len,
False, # Inverse FFT
(), # No window
True # Shift
)
cyclic_prefixer = digital.ofdm_cyclic_prefixer(
self.fft_len,
self.fft_len+self.cp_len,
rolloff,
self.packet_length_tag_key
)
self.connect(header_payload_mux, allocator, ffter, cyclic_prefixer, self)
if debug_log:
self.connect(allocator, blocks.file_sink(gr.sizeof_gr_complex * fft_len, 'tx-post-allocator.dat'))
self.connect(cyclic_prefixer, blocks.file_sink(gr.sizeof_gr_complex, 'tx-signal.dat'))
class ofdm_rx(gr.hier_block2):
"""Hierarchical block for OFDM demodulation.
The input is a complex baseband signal (e.g. from a UHD source).
The detected packets are output as a stream of packed bits on the output.
Args:
fft_len: The length of FFT (integer).
cp_len: The length of cyclic prefix in total samples (integer).
frame_length_tag_key: Used internally to tag the length of the OFDM frame.
packet_length_tag_key: The name of the tag giving packet length at the input.
occupied_carriers: A vector of vectors describing which OFDM carriers are occupied.
pilot_carriers: A vector of vectors describing which OFDM carriers are occupied with pilot symbols.
pilot_symbols: The pilot symbols.
bps_header: Bits per symbol (header).
bps_payload: Bits per symbol (payload).
sync_word1: The first sync preamble symbol. This has to be with
| zeros on alternating carriers. Used for fine and
| coarse frequency offset and timing estimation.
sync_word2: The second sync preamble symbol. This has to be filled
| entirely. Also used for coarse frequency offset and
| channel estimation.
"""
def __init__(self, fft_len=_def_fft_len, cp_len=_def_cp_len,
frame_length_tag_key=_def_frame_length_tag_key,
packet_length_tag_key=_def_packet_length_tag_key,
packet_num_tag_key=_def_packet_num_tag_key,
occupied_carriers=_def_occupied_carriers,
pilot_carriers=_def_pilot_carriers,
pilot_symbols=_def_pilot_symbols,
bps_header=1,
bps_payload=1,
sync_word1=None,
sync_word2=None,
debug_log=False,
scramble_bits=False
):
gr.hier_block2.__init__(self, "ofdm_rx",
gr.io_signature(1, 1, gr.sizeof_gr_complex),
gr.io_signature(1, 1, gr.sizeof_char))
### Param init / sanity check ########################################
self.fft_len = fft_len
self.cp_len = cp_len
self.frame_length_tag_key = frame_length_tag_key
self.packet_length_tag_key = packet_length_tag_key
self.occupied_carriers = occupied_carriers
self.bps_header = bps_header
self.bps_payload = bps_payload
n_sync_words = 1
if sync_word1 is None:
self.sync_word1 = _make_sync_word1(fft_len, occupied_carriers, pilot_carriers)
else:
if len(sync_word1) != self.fft_len:
raise ValueError("Length of sync sequence(s) must be FFT length.")
self.sync_word1 = sync_word1
self.sync_word2 = ()
if sync_word2 is None:
self.sync_word2 = _make_sync_word2(fft_len, occupied_carriers, pilot_carriers)
n_sync_words = 2
elif len(sync_word2):
if len(sync_word2) != fft_len:
raise ValueError("Length of sync sequence(s) must be FFT length.")
self.sync_word2 = sync_word2
n_sync_words = 2
if scramble_bits:
self.scramble_seed = 0x7f
else:
self.scramble_seed = 0x00 # We deactivate the scrambler by init'ing it with zeros
### Sync ############################################################
sync_detect = digital.ofdm_sync_sc_cfb(fft_len, cp_len)
delay = blocks.delay(gr.sizeof_gr_complex, fft_len+cp_len)
oscillator = analog.frequency_modulator_fc(-2.0 / fft_len)
mixer = blocks.multiply_cc()
hpd = digital.header_payload_demux(
n_sync_words+1, # Number of OFDM symbols before payload (sync + 1 sym header)
fft_len, cp_len, # FFT length, guard interval
frame_length_tag_key, # Frame length tag key
"", # We're not using trigger tags
True # One output item is one OFDM symbol (False would output complex scalars)
)
self.connect(self, sync_detect)
self.connect(self, delay, (mixer, 0), (hpd, 0))
self.connect((sync_detect, 0), oscillator, (mixer, 1))
self.connect((sync_detect, 1), (hpd, 1))
if debug_log:
self.connect((sync_detect, 0), blocks.file_sink(gr.sizeof_float, 'freq-offset.dat'))
self.connect((sync_detect, 1), blocks.file_sink(gr.sizeof_char, 'sync-detect.dat'))
### Header demodulation ##############################################
header_fft = fft.fft_vcc(self.fft_len, True, (), True)
chanest = digital.ofdm_chanest_vcvc(self.sync_word1, self.sync_word2, 1)
header_constellation = _get_constellation(bps_header)
header_equalizer = digital.ofdm_equalizer_simpledfe(
fft_len,
header_constellation.base(),
occupied_carriers,
pilot_carriers,
pilot_symbols,
symbols_skipped=0,
)
header_eq = digital.ofdm_frame_equalizer_vcvc(
header_equalizer.base(),
cp_len,
self.frame_length_tag_key,
True,
1 # Header is 1 symbol long
)
header_serializer = digital.ofdm_serializer_vcc(
fft_len, occupied_carriers,
self.frame_length_tag_key
)
header_demod = digital.constellation_decoder_cb(header_constellation.base())
header_formatter = digital.packet_header_ofdm(
occupied_carriers, 1,
packet_length_tag_key,
frame_length_tag_key,
packet_num_tag_key,
bps_header,
bps_payload,
scramble_header=scramble_bits
)
header_parser = digital.packet_headerparser_b(header_formatter.formatter())
self.connect(
(hpd, 0),
header_fft,
chanest,
header_eq,
header_serializer,
header_demod,
header_parser
)
self.msg_connect(header_parser, "header_data", hpd, "header_data")
if debug_log:
self.connect((chanest, 1), blocks.file_sink(gr.sizeof_gr_complex * fft_len, 'channel-estimate.dat'))
self.connect((chanest, 0), blocks.file_sink(gr.sizeof_gr_complex * fft_len, 'post-hdr-chanest.dat'))
self.connect((chanest, 0), blocks.tag_debug(gr.sizeof_gr_complex * fft_len, 'post-hdr-chanest'))
self.connect(header_eq, blocks.file_sink(gr.sizeof_gr_complex * fft_len, 'post-hdr-eq.dat'))
self.connect(header_serializer, blocks.file_sink(gr.sizeof_gr_complex, 'post-hdr-serializer.dat'))
### Payload demod ####################################################
payload_fft = fft.fft_vcc(self.fft_len, True, (), True)
payload_constellation = _get_constellation(bps_payload)
payload_equalizer = digital.ofdm_equalizer_simpledfe(
fft_len,
payload_constellation.base(),
occupied_carriers,
pilot_carriers,
pilot_symbols,
symbols_skipped=1, # (that was already in the header)
alpha=0.1
)
payload_eq = digital.ofdm_frame_equalizer_vcvc(
payload_equalizer.base(),
cp_len,
self.frame_length_tag_key
)
payload_serializer = digital.ofdm_serializer_vcc(
fft_len, occupied_carriers,
self.frame_length_tag_key,
self.packet_length_tag_key,
1 # Skip 1 symbol (that was already in the header)
)
payload_demod = digital.constellation_decoder_cb(payload_constellation.base())
self.payload_descrambler = digital.additive_scrambler_bb(
0x8a,
self.scramble_seed,
7,
0, # Don't reset after fixed length
bits_per_byte=8, # This is after packing
reset_tag_key=self.packet_length_tag_key
)
payload_pack = blocks.repack_bits_bb(bps_payload, 8, self.packet_length_tag_key, True)
self.crc = digital.crc32_bb(True, self.packet_length_tag_key)
self.connect(
(hpd, 1),
payload_fft,
payload_eq,
payload_serializer,
payload_demod,
payload_pack,
self.payload_descrambler,
self.crc,
self
)
if debug_log:
self.connect((hpd, 1), blocks.tag_debug(gr.sizeof_gr_complex*fft_len, 'post-hpd'))
self.connect(payload_fft, blocks.file_sink(gr.sizeof_gr_complex*fft_len, 'post-payload-fft.dat'))
self.connect(payload_eq, blocks.file_sink(gr.sizeof_gr_complex*fft_len, 'post-payload-eq.dat'))
self.connect(payload_serializer, blocks.file_sink(gr.sizeof_gr_complex, 'post-payload-serializer.dat'))
self.connect(payload_demod, blocks.file_sink(1, 'post-payload-demod.dat'))
self.connect(payload_pack, blocks.file_sink(1, 'post-payload-pack.dat'))
self.connect(self.crc, blocks.file_sink(1, 'post-payload-crc.dat'))