In PSK modulation, the amplitude and frequency remain constant and the only difference is to the phase of carrier .
The general analytical expression for PSK is
Where the phase term will have M discrete values ,typically given by
MiM
ii ,.....3,2,1,
*2
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will
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will
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( - 1)
We use MC1496 for balance PSK modulation .
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circuit diagram of 1-bit PSK which the carrier signal and data signal are single-ended input.
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data signal is passed through the unipolar to bipolar converter which is comprise by 74HCU04, 74HC126, 3904, 3906, D1, D2, D3 and R1 t0 R8.
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Pin 10 is the carrier input
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unbuffered inverter
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unbuffered inverter
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74HC126 provides provides four independent buffer
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The converted bipolar signal will be sent to pin 1
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R22 determines the gain of the circuit
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R23 determines the bias voltage of the circuit.
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If we adjust VR1 or change the amplitude of the data signal, then we can prevent the PSK modulation signal from distortion.
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This signal will be sent to the filter, which is comprised by µA741, C4, C6, R26, R27 and R28. Then the high frequency signals, which are produced by the balanced modulator will be filtered and a better PSK signal will be performed.
The basic diagram of PSK Demodulation
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Finally the output from the analog switch will be sent to the rectifier and the comparator for data signal recovery .
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This square wave will be sent to the phase shifter to adjust the phase in order to control the analog switch.
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By using PLL ,the double frequency signal converted to square wave , then the frequency divider will reduce the frequency of this square wave.
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using squaring loop detector
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filter to block the DC signal
If PSK signal is
The output of signal squarer is
The output of high pass filter is
By using PLL ,the double frequency signal converted to square wave , then the frequency divider will reduce the frequency of this square wave.
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The first term is the DC signal. Second term is the 2nd harmonic output (2w) of the carrier signal.
This square wave will be sent to the phase shifter to adjust the phase in order to control the analog switch.
Finally the output from the analog switch will be sent to the rectifier and the comparator for data signal recovery .
Probability bit error for BPSK:
Probability of symbol error for MPSK (M>2)
As M increase ,the data rate increase and for a given Eb/N0 the Pe increase with constant bandwidth.
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MPSK
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MPSK
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Es=Eb*K
As M increase the minimum distance between symbols decrease because the number of basis function is the same number for all M>2 .
Advantage: PSK is less susceptible to errors than ASK, while it requires/occupies the same bandwidth as ASK more efficient use of bandwidth are possible, compared to FSK .
Disadvantage: more complex signal detection / recovery process, than in ASK and FSK
Practical Parts :
1. Use DCS-6000-08 module to modulate Data signal 100 Hz TTL and sine wave carrier 20KHz.
2. To demodulate the modulated output signal of the first part use the PSK demodulation.
