B INARY P HASE S HIFT K EYING (BPSK) & Q UADRI P HASE S HIFT K EYING (QPSK)

B INARY P HASE S HIFT K EYING (BPSK) The BPSK signal is generated as: The transmitted signals are: -

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

F REQUENCY S PECTRUM OF BPSK S IGNAL Note : The spectrum of the binary BSK resembles that of double sideband suppressed carrier modulation.

BPSK D EMODULATOR The detection of BPSK is achieved by: 1. XOR-gate 2. Low – pass filter ( LPF)

Q UADRI - P HASE S HIFT K EYING (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:

G ENERATION OF QPSK S IGNALS Signal space representation - si(t) can be expressed as:

C ONSTELLATION D IAGRAM

I LLUSTRATION OF QPSK Quadri means 4 messages are to be transmitted. Hence, 2 bits are needed to present each message

D ETECTION OF QPSK Optimum Receiver:

E XAMPLES ON M- ARY C ONSTELLATION D IAGRAMS

M- ARY PSK V ERSUS BPSK M-ary PSK requires more complexity in the decision-making process. M-ary PSK requires more transmitted power.