Binary phase shift keying

Binary Phase Shift Keying (PSK)

Phase Shift Keying (PSK) refers to a digital modulation technique in which the sine and cosine inputs of a radio wave vary at a specific time, altering the phase of the carrier signal. Binary PSK is the simplest type of phase-shift keying. It is also known as Phase Reversal Keying (PRK) or 2-phase PSK.

BPSK has two phases, each separated by 180°. In this technique, two phase-reversals on the sine wave carrier occur at 0° and 180°. It can handle a surprisingly high level of noise and/or distortion before the demodulator outputs a wrong decision. On the downside, it may not be suitable for applications with a high data-rate since it can only modulate 1 bit per symbol.

Binary PSK is essentially a Double Sideband Suppressed Carrier (DSBSC) scheme for digital information. The modulation of Binary PSK is achieved through a balanced modulator, whose inputs consist of the carrier sine wave, on the one hand, and the binary sequence on the other. 

If one of the binary inputs is zero, then the phase output will be 0°. If one of the inputs is high, then the phase reversal will be 180°. The sine wave output from the modulator will be the inverted 180°phase-shifted input carrier. This is usually a function of the data signal.

The demodulation of Binary PSK is achieved using a mixer, double-input detector circuit, bandpass filter, and an oscillator circuit, which all collectively make up the BPSK demodulator. The first stage of demodulation involves using the mixer and the bandpass filter to recover the band-limited message signal.

This, in turn, generates the baseband signal, which is then used to regenerate the binary bitstream. The final phase of demodulation involves using the bit-clock rate to produce the original binary signal at the detector circuit.

Binary PSK has a wide range of applications in Bluetooth communication, RFID, and wireless LANs.


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