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diff --git a/octave/fmfsk.m b/octave/fmfsk.m
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-%
-% fmfsk.m
-% Author: Brady O'Brien 3 Feb 2016
-% Copyright 2016 David Rowe
-%
-% All rights reserved.
-%
-% This program is free software; you can redistribute it and/or modify
-% it under the terms of the GNU Lesser General Public License veRbion 2, as
-% published by the Free Software Foundation. This program 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 Lesser General Public License
-% along with this program; if not, see <http://www.gnu.org/licenses/>.
-
-% mancyfsk.m modem, extracted and made suitable for C implementation
-
-fm;
-pkg load signal;
-pkg load parallel;
-1;
-
-% Init fmfsk modem
-%Fs is sample frequency
-%Rb is pre-manchester bit rate
-function states = fmfsk_init(Fs,Rb)
- assert(mod(Fs,Rb*2)==0);
-
- %Current fixed processing buffer size, in non-ME bits
- nbit = 96;
-
- states.Rb = Rb;
- states.Rs = Rb*2; % Manchester-encoded bitrate
- states.Fs = Fs;
- states.Ts = Fs/states.Rs;
- states.N = nbit*2*states.Ts;
- states.nin = states.N; % Samples in the next demod cycle
- states.nstash = states.Ts*2; % How many samples to stash away between proc cycles for timing adjust
- states.nmem = states.N+(4*states.Ts);
- states.nsym = nbit*2;
- states.nbit = nbit;
-
- %tates.nsym = floor(states.Rs*.080);
- %states.nbit = floor(states.Rb*.080)
- %Old sample memory
-
- states.oldsamps = zeros(1,states.nmem);
-
- %Last sampled-stream output, for odd bitstream generation
- states.lastint = 0;
-
- %Some stats
- states.norm_rx_timing = 0;
-
-endfunction
-
-%Generate a stream of manchester-coded bits to be sent
-% to any ordinary FM modulator or VCO or something
-function tx = fmfsk_mod(states,inbits)
- Ts = states.Ts;
- tx = zeros(1,length(inbits)*2);
- for ii = 1:length(inbits)
- st = 1 + (ii-1)*Ts*2;
- md = st+Ts-1;
- en = md+Ts;
- if inbits(ii)==0
- tx(st:md) = -ones(1,Ts);
- tx(md+1:en) = ones(1,Ts);
- else
- tx(st:md) = ones(1,Ts);
- tx(md+1:en) = -ones(1,Ts);
- end
- end
-endfunction
-
-%Demodulate a bag of bits from the output of an FM demodulator
-% This function produces nbits output bits and takes states.nin samples
-function [rx_bits states] = fmfsk_demod(states,rx)
- Ts = states.Ts;
- Fs = states.Fs;
- Rs = states.Rs;
- nin = states.nin;
- N = states.N;
- nsym = states.nsym;
- nbits = states.nsym/2;
- nmem = states.nmem;
- nstash = states.nstash;
-
- nold = nmem-nin;
- ssamps = states.oldsamps;
-
-
- %Shift in nin samples
- ssamps(1:nold) = ssamps(nmem-nold+1:nmem);
- ssamps(nold+1:nmem) = rx;
- states.oldsamps = ssamps;
-
- rx_filt = zeros(1,(nsym+1)*Ts);
- %Integrate Ts input samples at every offset
- %This is the same thing as filtering with a filter of all ones
- % out to Ts.
- % It's implemented like this for ease of C-porting
- for ii=(1:(nsym+1)*Ts)
- st = ii;
- en = st+Ts-1;
- rx_filt(ii) = sum(ssamps(st:en));
- end
- states.rx_filt = rx_filt;
- % Fine timing estimation ------------------------------------------------------
-
- % Estimate fine timing using line at Rs/2 that Manchester encoding provides
- % We need this to sync up to Manchester codewords.
- Np = length(rx_filt);
- w = 2*pi*(Rs)/Fs;
- x = (rx_filt .^ 2) * exp(-j*w*(0:Np-1))';
- norm_rx_timing = angle(x)/(2*pi)-.42;
-
- rx_timing = round(norm_rx_timing*Ts);
-
- %If rx timing is too far out, ask for more or less sample the next time
- % around to even it all out
- next_nin = N;
- if norm_rx_timing > -.2;
- next_nin += Ts/2;
- end
- if norm_rx_timing < -.65;
- next_nin -= Ts/2;
- end
-
- states.nin = next_nin;
- states.norm_rx_timing = norm_rx_timing;
- %'Even' and 'Odd' manchester bitstream.
- % We'll figure out which to produce later
- rx_even = zeros(1,nbits);
- rx_odd = zeros(1,nbits);
- apeven = 0;
- apodd = 0;
-
- sample_offset = (Ts/2)+Ts+rx_timing-1;
-
- symsamp = zeros(1,nsym);
-
- % Figure out the bits of the 'even' and 'odd' ME streams
- % Also sample rx_filt offset by what fine timing determined along the way
- % Note: ii is a zero-indexed array pointer, for less mind-breaking c portage
- lastv = states.lastint;
- for ii = (0:nsym-1)
- currv = rx_filt(sample_offset+(ii*Ts)+1);
- mdiff = lastv-currv;
- lastv = currv;
- mbit = mdiff>0;
- symsamp(ii+1) = currv;
- if mod(ii,2)==1
- apeven += abs(mdiff);
- rx_even( floor(ii/2)+1 ) = mbit;
- else
- apodd += abs(mdiff);
- rx_odd( floor(ii/2)+1 ) = mbit;
- end
- end
- states.symsamp = symsamp;
- % Decide on the correct ME alignment
- if(apeven>apodd)
- rx_bits = rx_even;
- else
- rx_bits = rx_odd;
- end
-
- states.lastint = lastv;
-endfunction
-
-% run_sim copypasted from fsk_horus.m
-% simulation of tx and rx side, add noise, channel impairments ----------------------
-
-function fmfsk_run_sim(EbNodB,timing_offset=0,de=0,of=0,hpf=0)
- test_frame_mode = 2;
- frames = 70;
- %EbNodB = 3;
- %timing_offset = 0.0; % see resample() for clock offset below
- %fading = 0; % modulates tx power at 2Hz with 20dB fade depth,
- % to simulate balloon rotating at end of mission
- df = 0; % tx tone freq drift in Hz/s
- dA = 1; % amplitude imbalance of tones (note this affects Eb so not a gd idea)
-
- more off
- rand('state',1);
- randn('state',1);
-
- Fs = 48000;
- Rbit = 2400;
-
- % ----------------------------------------------------------------------
-
- fm_states.pre_emp = 0;
- fm_states.de_emp = de;
- fm_states.Ts = Fs/(Rbit*2);
- fm_states.Fs = Fs;
- fm_states.fc = Fs/4;
- fm_states.fm_max = 3E3;
- fm_states.fd = 5E3;
- fm_states.output_filter = of;
- fm_states = analog_fm_init(fm_states);
-
- % ----------------------------------------------------------------------
-
- states = fmfsk_init(Fs,Rbit);
-
- states.verbose = 0x1;
- Rs = states.Rs;
- nsym = states.nsym;
- Fs = states.Fs;
- nbit = states.nbit;
-
- EbNo = 10^(EbNodB/10);
- variance = states.Fs/(states.Rb*EbNo);
-
- % set up tx signal with payload bits based on test mode
-
- if test_frame_mode == 1
- % test frame of bits, which we repeat for convenience when BER testing
- test_frame = round(rand(1, states.nbit));
- tx_bits = [];
- for i=1:frames+1
- tx_bits = [tx_bits test_frame];
- end
- end
- if test_frame_mode == 2
- % random bits, just to make sure sync algs work on random data
- tx_bits = round(rand(1, states.nbit*(frames+1)));
- end
- if test_frame_mode == 3
- % repeating sequence of all symbols
- % great for initial test of demod if nothing else works,
- % look for this pattern in rx_bits
-
- % ...10101...
- tx_bits = zeros(1, states.nbit*(frames+1));
- tx_bits(1:2:length(tx_bits)) = 1;
-
- end
-
- load fm_radio_filt_model.txt
-
- [b, a] = cheby1(4, 1, 300/Fs, 'high'); % 300Hz HPF to simulate FM radios
-
- tx_pmod = fmfsk_mod(states, tx_bits);
- tx = analog_fm_mod(fm_states, tx_pmod);
-
- tx = tx(10:length(tx));
-
- if(timing_offset>0)
- tx = resample(tx, 1000,1001); % simulated 1000ppm sample clock offset
- end
-
-
- noise = sqrt(variance)*randn(length(tx),1);
- rx = tx + noise';
-
- %Demod by analog fm
- rx = analog_fm_demod(fm_states, rx);
-
- %High-pass filter to simulate the FM radios
- if hpf>0
- printf("high-pass filtering!\n")
- rx = filter(b,a,rx);
- end
- rx = filter(filt,1,rx);
-
- figure(4)
- title("Spectrum of rx-ed signal after FM demod and FM radio channel");
- plot(20*log10(abs(fft(rx))))
- figure(5)
- title("Time domain of rx-ed signal after FM demod and FM radio channel");
- plot(rx)
- %rx = real(rx);
- %b1 = fir2(100, [0 4000 5200 48000]/48000, [1 1 0.5 0.5]);
- %rx = filter(b1,1,rx);
- %[b a] = cheby2(6,40,[3000 6000]/(Fs/2));
- %rx = filter(b,a,rx);
- %rx = sign(rx);
- %rx(find (rx > 1)) = 1;
- %rx(find (rx < -1)) = -1;
-
- % dump simulated rx file
-
- timing_offset_samples = round(timing_offset*states.Ts);
- st = 1 + timing_offset_samples;
- rx_bits_buf = zeros(1,2*nbit);
- x_log = [];
- timing_nl_log = [];
- norm_rx_timing_log = [];
- f_int_resample_log = [];
- f_log = [];
- EbNodB_log = [];
- rx_bits_log = [];
- rx_bits_sd_log = [];
-
- for f=1:frames
-
- % extract nin samples from input stream
-
- nin = states.nin;
- en = st + states.nin - 1;
- sf = rx(st:en);
- st += nin;
-
- % demodulate to stream of bits
-
- [rx_bits states] = fmfsk_demod(states, sf);
-
- rx_bits_buf(1:nbit) = rx_bits_buf(nbit+1:2*nbit);
- rx_bits_buf(nbit+1:2*nbit) = rx_bits;
- rx_bits_log = [rx_bits_log rx_bits];
-
- end
-
- ber = 1;
- ox = 1;
- rx_bits = rx_bits_log;
- bitcnt = length(tx_bits);
- for offset = (1:100)
- nerr = sum(xor(rx_bits(offset:length(rx_bits)),tx_bits(1:length(rx_bits)+1-offset)));
- bern = nerr/(bitcnt-offset);
- if(bern < ber)
- ox = offset;
- best_nerr = nerr;
- end
- ber = min([ber bern]);
- end
- offset = ox;
- figure(3);
- plot(xor(rx_bits(ox:length(rx_bits)),tx_bits(1:length(rx_bits)+1-ox)))
-
- printf("BER: %f Errors: %d Bits:%d\n",ber,best_nerr,bitcnt-offset);
-
- endfunction
-
-
-% demodulate a file of 8kHz 16bit short samples --------------------------------
-
-
-
-
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