Hello Everyone I was dealing with a problem for the past 2 years with the GNURadio, i made a very simple loopback flowgraph which consists into something like this
Wav File Source --> Rational resampler --> multiply const --> float to char --> GFSK mod --> GFSK demod --> Char to float --> multiply const ---> Audio sink I made the following assumptions to desing my digital communication system Audio_rate: 32 KHz Audio_bit_depth: 8 bits Bits_per_symbol: 1 bit. Samples_per_symbol: 8 sps And made the following calculations: Bit_rate(Audio): Audio_rate * Audio_bit_depth = 8 * 32e3 = 256 Kbps Baud_rate(Symbols): Bit_rate * Bits_per_symbol = 256e3 * 1 = 256 KSyps Sample_rate (modulated samples): Baud_Rate * Sample_per_symbol = 256e3 * 8 = 2.048 MSps I did this calculations thanks to the Wikipedia and GNURADIO wiki Frequency_deviation = Bit_rate/2 = 256e3/2 =128 KHz Modulation_index = Frequency_deviation /(baud_rate/2) = 128e3 / (256e3 / 2) = 1 Sensitivity = (math.pi* Modulation_index )/( Samples_per_symbol ) = (3.1416..* 1)/8 = 392.699e-3 In the transmitter side: Wav File source: An audio file sampled at 44100 KHz Rational resampler: Interpolation 320 Decimation 441 con resample to 32 KHz Multiply Const: 0.5x to avoid clipping Float to char: scale of 256 levels In the Receiver side: Char to float: scale of 256 levels Multiply Const: 2x to restore level Audio sink: to play the wav file at 32000 KHz I tested it without the GFSK blocks, and works awesome without errors, the main problem is at conecting the GFSK blocks which produce bit errors, i made the followind configurations. GFSK mod: Samples/Symbol: 8 Sensitivity: 392.699e-3 BT: 350e-3 GFSK demod: Samples/Symbol: 8 Sensitivity: 392.699e-3 BT: 350e-3 Gain Mu: 175e-3 Mu: 500e-3 Omega relative frequency: 5e-3 Freq error: 0 But looks like im doing something wrong in the GFSK blocks, can you help me experts to debug it im attaching my flowgraph. -- Con la mejor de las intenciones Atte. Giancarlo Freddy Murillo Arenas Bachiller de Ingeniería Electrónica y de telecomunicaciones Universidad Católica San Pablo
fsk_nohier.grc
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