| 75 | | } |
| 76 | | |
| 77 | | // Find frame header using Costas loop |
| 78 | | bool FrameSynchronizerDSP::FindFrameHeaderCostasLoop( |
| 79 | | short * I_in, |
| 80 | | short * Q_in, |
| 81 | | unsigned int input_length, |
| 82 | | unsigned int &num_read, |
| 83 | | short * I_out, |
| 84 | | short * Q_out, |
| 85 | | unsigned int output_length, |
| 86 | | unsigned int &num_written) |
| 87 | | { |
| 88 | | alpha_s = 0.027f; |
| 89 | | beta_s = 1.02f; |
| 90 | | |
| 91 | | int i(0); |
| 92 | | short I, Q; |
| 93 | | num_read = 0; |
| 94 | | num_written = 0; |
| 95 | | //printf("nco CV = %f\n", cv/(2*PI)); |
| 96 | | |
| 97 | | while ( i < (signed int) input_length ) { |
| 98 | | v++; |
| 99 | | |
| 100 | | // apply nco to input sample |
| 101 | | ApplyNCO(I_in[i], Q_in[i], I, Q); |
| 102 | | //I = I_in[i]; |
| 103 | | //Q = Q_in[i]; |
| 104 | | i++; |
| 105 | | |
| 106 | | // push samples into buffer |
| 107 | | PushInput(I, Q); |
| 108 | | |
| 109 | | // compute filtered outputs (stored in mf_i, mf_q) |
| 110 | | ComputeFilterBankOutputs(); |
| 111 | | |
| 112 | | // compute costas loop phase error on matched-filter outputs |
| 113 | | ///\todo matched filter output won't work because of delay |
| 114 | | pd2_cl = GenerateCostasLoopPhaseError(I, Q); |
| 115 | | //pd2_cl = GenerateCostasLoopPhaseError(mf_i, mf_q); |
| 116 | | pd2_cl /= Ac; |
| 117 | | |
| 118 | | // advance costas loop filter |
| 119 | | AdvanceCostasLoopFilter(); |
| 120 | | |
| 121 | | // update nco |
| 122 | | UpdateNCO(); |
| 123 | | //I_out[num_written] = mf_i; |
| 124 | | //Q_out[num_written] = mf_q; |
| 125 | | //num_written++; |
| 126 | | |
| 127 | | // decimate |
| 128 | | if ( v >= (signed int) k ) { |
| 129 | | // enable output |
| 130 | | v -= k; |
| 131 | | I_out[num_written] = mf_i; |
| 132 | | Q_out[num_written] = mf_q; |
| 133 | | num_written++; |
| 134 | | //printf("I = %d, Q = %d\n", mf_i, mf_q); |
| 135 | | |
| 136 | | // generate timing error |
| 137 | | GenerateTimingError(); |
| 138 | | |
| 139 | | // advance timing loop filter |
| 140 | | AdvanceTimingLoopFilter(); |
| 141 | | |
| 142 | | // compute filter bank index |
| 143 | | ComputeFilterBankIndex(); |
| 144 | | |
| 145 | | // update v |
| 146 | | switch (lc) { |
| 147 | | case SHIFT: |
| 148 | | // normal operation; do nothing |
| 149 | | break; |
| 150 | | case SKIP: |
| 151 | | v--; |
| 152 | | //printf("skip\n"); |
| 153 | | lc = SHIFT; |
| 154 | | break; |
| 155 | | case STUFF: |
| 156 | | v++; |
| 157 | | //printf("stuff\n"); |
| 158 | | lc = SHIFT; |
| 159 | | break; |
| 160 | | default:; |
| 161 | | } |
| 162 | | |
| 163 | | // push sample into buffer |
| 164 | | inputBuffer.Push(mf_i); |
| 165 | | r = CorrelateSequence( pnFrameSyncCode, 255 ); |
| 166 | | |
| 167 | | if ( abs(r) > int( Ac/2 ) ) { |
| 168 | | r_frame_sync = abs(r); |
| 169 | | std::cout << "PN FRAME SYNC CODE FOUND!!!" << std::endl; |
| 170 | | std::cout << " r = " << r_frame_sync << std::endl; |
| 171 | | |
| 172 | | // check for phase inversion; if so inject pi radians into NCO |
| 173 | | // [not sure how well this will work with band-limited pulse shapes] |
| 174 | | if ( r<0 ) { |
| 175 | | std::cout << " [Frame sync found negative PN code]" << std::endl; |
| 176 | | nco_control += PI; |
| 177 | | } |
| 178 | | |
| 179 | | operationalMode = EXTRACT_CONTROL_CODES; |
| 180 | | inputBuffer.Release(); |
| 181 | | numControlCodesReceived = 0; |
| 182 | | |
| 183 | | //num_read = i+1; |
| 184 | | //return true; |
| 185 | | |
| 186 | | // reduce bandwidth of loop filters for steady tracking mode |
| 187 | | //UpdatePhaseLoopFilterCoefficients(0.0025f); |
| 188 | | //UpdateTimingLoopFilterCoefficients(ALPHA_T_LO, BETA_T_LO); |
| 189 | | |
| 190 | | } |
| 191 | | |
| 192 | | } |
| 193 | | } |
| 194 | | |
| 195 | | num_read = input_length; |
| 196 | | return false; |
