Difference between revisions of "OFDM"
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| − | OFDM Mod GRC block | + | == OFDM Mod GRC block == |
| − | packet_mod_X(ofdm_mod(<options>)) - argument is 'packet_source' | + | ''packet_mod_X(ofdm_mod('''<options>'''))'' - argument is 'packet_source' |
| − | packet_mod: grc/grc_gnuradio/blks2/packet.py | + | ''packet_mod'': |
| − | packet_utils: <core>/python/gnuradio/packet_utils.py | + | grc/grc_gnuradio/blks2/packet.py |
| + | ''packet_utils'': | ||
| + | <core>/python/gnuradio/packet_utils.py | ||
| + | |||
| + | === packet_mod_X === | ||
| + | |||
| + | * Default payload: 512 bytes (if supplied length is default 0, must be multiple of input stream size) | ||
| + | * Input signature: X | ||
| + | * Output signature: inherited from 'packet_source' stream #0 (complex for ofdm) | ||
| − | |||
| − | |||
| − | |||
| − | |||
Starts packet encoder thread that packages incoming data into payload size and submits to 'packet_source' via 'send_pkt' call. | Starts packet encoder thread that packages incoming data into payload size and submits to 'packet_source' via 'send_pkt' call. | ||
| − | packet_utils.make_packet: preamble, access code, length of payload and CRC, (optionally whitened) payload with CRC-32, end byte. | + | ''packet_utils.make_packet'': preamble, access code, length of payload and CRC, (optionally whitened) payload with CRC-32, end byte. |
| − | 'preamble' is fixed. | + | * 'preamble' is fixed. |
| − | 'access code' can be left as default (customisable preamble) | + | * 'access code' can be left as default (customisable preamble) |
| − | ofdm_mod: <core>/python/gnuradio/blks2impl/ofdm.py | + | ''ofdm_mod'': |
| + | <core>/python/gnuradio/blks2impl/ofdm.py | ||
_pkt_input (ofdm_mapper_bcv) -> preambles (ofdm_insert_preamble) -> ifft (fft_vcc) -> cp_adder (ofdm_cyclic prefixer) -> scale (multiply_const_cc) | _pkt_input (ofdm_mapper_bcv) -> preambles (ofdm_insert_preamble) -> ifft (fft_vcc) -> cp_adder (ofdm_cyclic prefixer) -> scale (multiply_const_cc) | ||
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Padded preamble generation (for correlation in time domain): | Padded preamble generation (for correlation in time domain): | ||
| − | zeros_on_left = ceil((FFT length - occupied tones) / 2.0) | + | * zeros_on_left = ceil((FFT length - occupied tones) / 2.0) |
| − | ksfreq = take 'occupied symbols' length from known_symbols_4512_3 (randomly generated fixed list of 1/-1, 4512 items long (=4000+512 ?)) | + | * ksfreq = take 'occupied symbols' length from known_symbols_4512_3 (randomly generated fixed list of 1/-1, 4512 items long (=4000+512 ?)) |
| − | Each item (offset by zeros_on_left) that has an odd index is zeroed. | + | * Each item (offset by zeros_on_left) that has an odd index is zeroed. |
| − | Padded preamble is FFT length, with zeros_on_left, then ksfreq hardcoded symbols, then remaining zeros on right. | + | * Padded preamble is FFT length, with zeros_on_left, then ksfreq hardcoded symbols, then remaining zeros on right. |
| − | ofdm_mapper_bcv: constellation based on modulation, message queue limit (default: 2), occupied tones, FFT length | + | ''ofdm_mapper_bcv'': constellation based on modulation, message queue limit (default: 2), occupied tones, FFT length |
| − | ofdm_insert_preamble (insert 'pre-modulated' preamble symbols before each payload): FFT length, padded preambles | + | ''ofdm_insert_preamble'' (insert 'pre-modulated' preamble symbols before each payload): FFT length, padded preambles |
| − | ofdm_cyclic prefixer (prefix output with CP length from end of input symbols): FFT length, symbol length (= FFT length + cyclic prefix length) | + | ''ofdm_cyclic prefixer'' (prefix output with CP length from end of input symbols): FFT length, symbol length (= FFT length + cyclic prefix length) |
| − | multiply_const_cc: 1.0 / sqrt(FFT length) | + | ''''multiply_const_cc: 1.0 / sqrt(FFT length) |
Revision as of 19:47, 30 January 2012
OFDM Mod GRC block
packet_mod_X(ofdm_mod(<options>)) - argument is 'packet_source'
packet_mod:
grc/grc_gnuradio/blks2/packet.py
packet_utils:
<core>/python/gnuradio/packet_utils.py
packet_mod_X
- Default payload: 512 bytes (if supplied length is default 0, must be multiple of input stream size)
- Input signature: X
- Output signature: inherited from 'packet_source' stream #0 (complex for ofdm)
Starts packet encoder thread that packages incoming data into payload size and submits to 'packet_source' via 'send_pkt' call.
packet_utils.make_packet: preamble, access code, length of payload and CRC, (optionally whitened) payload with CRC-32, end byte.
- 'preamble' is fixed.
- 'access code' can be left as default (customisable preamble)
ofdm_mod:
<core>/python/gnuradio/blks2impl/ofdm.py
_pkt_input (ofdm_mapper_bcv) -> preambles (ofdm_insert_preamble) -> ifft (fft_vcc) -> cp_adder (ofdm_cyclic prefixer) -> scale (multiply_const_cc)
Padded preamble generation (for correlation in time domain):
- zeros_on_left = ceil((FFT length - occupied tones) / 2.0)
- ksfreq = take 'occupied symbols' length from known_symbols_4512_3 (randomly generated fixed list of 1/-1, 4512 items long (=4000+512 ?))
- Each item (offset by zeros_on_left) that has an odd index is zeroed.
- Padded preamble is FFT length, with zeros_on_left, then ksfreq hardcoded symbols, then remaining zeros on right.
ofdm_mapper_bcv: constellation based on modulation, message queue limit (default: 2), occupied tones, FFT length
ofdm_insert_preamble (insert 'pre-modulated' preamble symbols before each payload): FFT length, padded preambles
ofdm_cyclic prefixer (prefix output with CP length from end of input symbols): FFT length, symbol length (= FFT length + cyclic prefix length)
'multiply_const_cc: 1.0 / sqrt(FFT length)
