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BINARY PHASE SHIFT KEYING (BPSK)
&QUADRI PHASE SHIFT
KEYING (QPSK)
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BINARY PHASE SHIFT KEYING (BPSK)
The BPSK signal is generated as:
The transmitted signals are:
- -
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ILLUSTRATION OF BPSK
Note: Bits 1 and 0 have the same amplitude and frequency but they differ in phase.
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FREQUENCY SPECTRUM OF BPSK SIGNAL
Note : The spectrum of the binary BSK resemblesthat of double sideband suppressed carrier
modulation.
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BPSK DEMODULATOR The detection of BPSK is achieved by:
1. XOR-gate
2. Low – pass filter ( LPF)
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QUADRI - PHASE SHIFT KEYING (QPSK)
In QPSK, the phase of the carrier takes on one of four equally spaced values such as
π/4, 3π/4, 5π/4, 7π/4 or 0,π/2, π , 3π/4.
The transmitted signal is:
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GENERATION OF QPSK SIGNALS
Signal space representation
- si(t) can be expressed as:
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CONSTELLATION DIAGRAM
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ILLUSTRATION OF QPSK Quadri means 4 messages are to be
transmitted. Hence, 2 bits are needed to present each message
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DETECTION OF QPSK
Optimum Receiver:
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EXAMPLES ON M-ARY CONSTELLATION
DIAGRAMS
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M-ARY PSK VERSUS BPSK
M-ary PSK requires more complexity in thedecision-making process.
M-ary PSK requires more transmitted power.