BPSK: Binary Phase Shift Keying Explained

This page describes the Binary Phase Shift Keying (BPSK) technique and BPSK modulation basics. It also provides a link to the difference between BPSK and QPSK and a BPSK MATLAB code link.

BPSK stands for Binary Phase Shift Keying. It’s a digital modulation technique where binary 1 and binary 0 are represented by different carrier phases, each 180 degrees apart. The simplest BPSK scheme uses these two phases to represent the two binary digits.

The resulting transmitted signal for one bit time is:

S(t) = A * cos(2 * pi * fc * t) for binary 1

S(t) = A * cos(2 * pi * fc * t + pi) for binary 0

This is considered a very robust digital modulation technique, often used for long-distance wireless communication. When the Carrier to Interference plus Noise Ratio (CINR) is poor, base stations often choose BPSK in adaptive modulation schemes used in cellular communication. While robust, it’s relatively less immune to interference compared to more complex modulation schemes.

Typically, the modulation constant (KMOD) is 1 for BPSK in the equation relating signal power to symbol energy.

BPSK Figure showing constellation points and encoding rule, adapted from IEEE standard 802.16-2004 to illustrate the BPSK concept.

BPSK Applications

BPSK is a fundamental technique used in various wireless standards, including CDMA, WiMAX (16d, 16e), WLAN 11a, 11b, 11g, 11n, Satellite, DVB, Cable modem, and others.

It’s considered more robust than other modulation types because of the 180-degree separation between its two constellation points. This allows it to withstand significant channel impairments and fading.

It is often used in Orthogonal Frequency Division Multiplexing (OFDM) and OFDMA to modulate the pilot subcarriers used for channel estimation and equalization.

In cellular systems, channels used to transmit essential system-related information are often modulated using BPSK, ensuring reliable delivery of critical data.