Binary Phase Shift Keying (BPSK) & Quadri Phase Shift Keying (QPSK)

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 resembles that of double sideband suppressed carrier modulation.

BPSK Demodulator • The detection of BPSK is achieved by: • XOR-gate • 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-aryPSK requires more complexity in the decision-making process. • M-ary PSK requires more transmitted power.

Binary Phase Shift Keying (BPSK) & Quadri Phase Shift Keying (QPSK)