1 /*
2 * Copyright (c) 2007 - 2015 Joseph Gaeddert
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining a copy
5 * of this software and associated documentation files (the "Software"), to deal
6 * in the Software without restriction, including without limitation the rights
7 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
8 * copies of the Software, and to permit persons to whom the Software is
9 * furnished to do so, subject to the following conditions:
10 *
11 * The above copyright notice and this permission notice shall be included in
12 * all copies or substantial portions of the Software.
13 *
14 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
15 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
16 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
17 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
18 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
19 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
20 * THE SOFTWARE.
21 */
22
23 //
24 // modem_psk.c
25 //
26
27 // create a psk (phase-shift keying) modem object
MODEM(_create_psk)28 MODEM() MODEM(_create_psk)(unsigned int _bits_per_symbol)
29 {
30 MODEM() q = (MODEM()) malloc( sizeof(struct MODEM(_s)) );
31
32 switch (_bits_per_symbol) {
33 case 1: q->scheme = LIQUID_MODEM_PSK2; break;
34 case 2: q->scheme = LIQUID_MODEM_PSK4; break;
35 case 3: q->scheme = LIQUID_MODEM_PSK8; break;
36 case 4: q->scheme = LIQUID_MODEM_PSK16; break;
37 case 5: q->scheme = LIQUID_MODEM_PSK32; break;
38 case 6: q->scheme = LIQUID_MODEM_PSK64; break;
39 case 7: q->scheme = LIQUID_MODEM_PSK128; break;
40 case 8: q->scheme = LIQUID_MODEM_PSK256; break;
41 default:
42 fprintf(stderr,"error: modem_create_psk(), cannot support PSK with m > 8\n");
43 exit(1);
44 }
45
46 // initialize basic modem structure
47 MODEM(_init)(q, _bits_per_symbol);
48
49 // compute alpha
50 q->data.psk.alpha = M_PI/(T)(q->M);
51
52 // initialize demodulation array reference
53 unsigned int k;
54 for (k=0; k<(q->m); k++)
55 q->ref[k] = (1<<k) * q->data.psk.alpha;
56
57 // compute phase offset (half of phase difference between symbols)
58 q->data.psk.d_phi = M_PI*(1.0f - 1.0f/(T)(q->M));
59
60 // set modulation/demodulation functions
61 q->modulate_func = &MODEM(_modulate_psk);
62 q->demodulate_func = &MODEM(_demodulate_psk);
63
64 // initialize symbol map
65 q->symbol_map = (TC*)malloc(q->M*sizeof(TC));
66 MODEM(_init_map)(q);
67 q->modulate_using_map = 1;
68
69 // initialize soft-demodulation look-up table
70 if (q->m >= 3)
71 MODEM(_demodsoft_gentab)(q, 2);
72
73 // reset and return
74 MODEM(_reset)(q);
75 return q;
76 }
77
78 // modulate PSK
MODEM(_modulate_psk)79 void MODEM(_modulate_psk)(MODEM() _q,
80 unsigned int _sym_in,
81 TC * _y)
82 {
83 // 'encode' input symbol (actually gray decoding)
84 _sym_in = gray_decode(_sym_in);
85
86 // compute output sample
87 *_y = liquid_cexpjf(_sym_in * 2 * _q->data.psk.alpha );
88 }
89
90 // demodulate PSK
MODEM(_demodulate_psk)91 void MODEM(_demodulate_psk)(MODEM() _q,
92 TC _x,
93 unsigned int * _sym_out)
94 {
95 // compute angle and subtract phase offset, ensuring phase is in [-pi,pi)
96 T theta = cargf(_x);
97 theta -= _q->data.psk.d_phi;
98 if (theta < -M_PI)
99 theta += 2*M_PI;
100
101 // demodulate on linearly-spaced array
102 unsigned int s; // demodulated symbol
103 T demod_phase_error; // demodulation phase error
104 MODEM(_demodulate_linear_array_ref)(theta, _q->m, _q->ref, &s, &demod_phase_error);
105
106 // 'decode' output symbol (actually gray encoding)
107 *_sym_out = gray_encode(s);
108
109 // re-modulate symbol and store state
110 MODEM(_modulate_psk)(_q, *_sym_out, &_q->x_hat);
111 _q->r = _x;
112 }
113
114