1% fsk_lib_demo.m
2% Uncoded FSK modem demo
3
4fsk_lib;
5
6% set up waveform
7function [states M bits_per_frame] = modem_init(Rs,Fs,df)
8  M  = 4;
9  states = fsk_init(Fs,Rs,M,P=8,nsym=100);
10  bits_per_frame = 512;
11  states.tx_real = 0; % complex signal
12  states.tx_tone_separation = 250;
13  states.ftx = -2.5*states.tx_tone_separation + states.tx_tone_separation*(1:M);
14  states.fest_fmin = -Fs/2;
15  states.fest_fmax = +Fs/2;
16  states.fest_min_spacing = Rs/2;
17  states.df = df;
18
19  states.ber_valid_thresh = 0.1;
20  states.ber_invalid_thresh = 0.2;
21end
22
23% Run a complete modem (freq and timing estimators running) at a
24% single Eb/No point.  At low Eb/No the estimators occasionally fall
25% over so we get complete junk, we consider that case a packet error
26% and exclude it from the BER estimation.
27
28function [states ber per] = modem_run_test(EbNodB = 10, num_frames=10, Fs=8000, Rs=100, df=0, plots=0)
29  randn('state',1); rand('state',1);
30  [states M bits_per_frame] = modem_init(Rs, Fs, df);
31  N = states.N;
32  if plots; states.verbose = 0x4; end
33  EbNo = 10^(EbNodB/10);
34  variance = states.Fs/(states.Rs*EbNo*states.bitspersymbol);
35
36  nbits = bits_per_frame*num_frames;
37  test_frame = round(rand(1,bits_per_frame)); tx_bits = [];
38  for f=1:num_frames
39    tx_bits = [tx_bits test_frame];
40  end
41
42  tx = fsk_mod(states, tx_bits);
43  noise = sqrt(variance/2)*randn(length(tx),1) + j*sqrt(variance/2)*randn(length(tx),1);
44  rx = tx + noise;
45
46  run_frames = floor(length(rx)/N)-1;
47  st = 1; f_log = []; f_log2 = []; rx_bits = []; rx_bits2 = [];
48  for f=1:run_frames
49
50    % extract nin samples from input stream
51    nin = states.nin;
52    en = st + states.nin - 1;
53
54    % due to nin variations it's possible to overrun buffer
55    if en < length(rx)
56      sf = rx(st:en);
57      states = est_freq(states, sf, states.M);  states.f = states.f2;
58      [arx_bits states] = fsk_demod(states, sf);
59      rx_bits = [rx_bits arx_bits];
60      f_log = [f_log; states.f];
61      st += nin;
62    end
63  end
64
65  num_frames=floor(length(rx_bits)/bits_per_frame);
66  log_nerrs = []; num_frames_rx = 0;
67  for f=1:num_frames-1
68    st = (f-1)*bits_per_frame + 1; en = (f+1)*bits_per_frame;
69    states = ber_counter(states, test_frame, rx_bits(st:en));
70    log_nerrs = [log_nerrs states.nerr];
71    if states.ber_state; num_frames_rx++; end
72  end
73  if states.Terrs
74    printf("Fs: %d Rs: %d df % 3.2f EbNo: %4.2f ftx: %3d frx: %3d nbits: %4d nerrs: %3d ber: %4.3f\n",
75            Fs, Rs, df, EbNodB, num_frames, num_frames_rx, states.Tbits, states.Terrs, states.Terrs/states.Tbits);
76    ber = states.Terrs/states.Tbits;
77  else
78    ber = 0.5;
79  end
80
81  if plots
82    figure(1); clf;
83    ideal=ones(length(f_log),1)*states.ftx;
84    plot((1:length(f_log)),ideal(:,1),'bk;ideal;')
85    hold on; plot((1:length(f_log)),ideal(:,2:states.M),'bk'); hold off;
86    hold on;
87    plot(f_log(:,1), 'linewidth', 2, 'b;peak;');
88    plot(f_log(:,2:states.M), 'linewidth', 2, 'b');
89    hold off;
90    xlabel('Time (frames)'); ylabel('Frequency (Hz)');
91    figure(2); clf; plot(log_nerrs); title('Errors per frame');
92  end
93
94  per = 1 - num_frames_rx/num_frames;
95end
96
97[states ber per] = modem_run_test(EbNodB=6);
98BER_theory=0.01579; % for Eb/No = 6dB
99if ber < 1.5*BER_theory
100  printf("PASS\n");
101end
102