BINARY PHASE SHIFT KEYING (BPSK)

&QUADRI PHASE SHIFT

KEYING (QPSK)

BINARY PHASE SHIFT KEYING (BPSK)

The BPSK signal is generated as:

The transmitted signals are:

- -

ILLUSTRATION OF BPSK

Note: Bits 1 and 0 have the same amplitude and frequency but they differ in phase.

FREQUENCY SPECTRUM OF BPSK SIGNAL

Note : The spectrum of the binary BSK resemblesthat of double sideband suppressed carrier

modulation.

BPSK DEMODULATOR The detection of BPSK is achieved by:

1. XOR-gate

2. Low – pass filter ( LPF)

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:

GENERATION OF QPSK SIGNALS

Signal space representation

- si(t) can be expressed as:

CONSTELLATION DIAGRAM

ILLUSTRATION OF QPSK Quadri means 4 messages are to be

transmitted. Hence, 2 bits are needed to present each message

DETECTION OF QPSK

Optimum Receiver:

EXAMPLES ON M-ARY CONSTELLATION

DIAGRAMS

M-ARY PSK VERSUS BPSK

M-ary PSK requires more complexity in thedecision-making process.

M-ary PSK requires more transmitted power.