## 12 Jul 2018

### Generation of Binary Phase Shift Keying (BPSK Generation) - Block Diagram of Binary Phase Shift Keying (BPSK)

Here we will understand the generation of BPSK signal. BPSK stands for Binary Phase Shift Keying. With the help of block diagram we will discuss the concept of Binary Phase Shift Keying generation.
But before discussing the generation of Binary Phase Shift Keying, we will first understand what is Phase Shift Keying (PSK).

## Phase Shift Keying (PSK) Introduction

In Phase Shift Keying, the phase of the carrier wave (analog) is switched as per the input digital signal. This is analogous to Phase Modulation (PM).
As we know, in case of phase modulation, phase of the carrier wave is changed according to the instantaneous value of the modulating signal. In the same way, in phase shift keying also, the phase of the sinusoidal carrier wave is changed according to the digital input signal. So the basic difference between analogue modulation and digital modulation is based on the nature of the modulating signal (message signal).

In analogue modulation, the modulating signal is of analogue nature while in case of digital modulation, the modulating signal is digital.

Now to understand the concept of phase shift keying, look at the image shown below - Phase Shift Keying (PSK) Waveform
Here in this image you can see, the digital input signal, sinusoidal carrier wave (in red colour) and PSK signal (in blue colour). Now observe the image carefully. The sinusoidal carrier wave is having constant amplitude, constant frequency and also there is no change in the phase. You can observe here that phase of the sinusoidal carrier wave is changing according to the digital input signal. See here that, phase of the carrier wave changes only when there is a change in the binary symbol. It means that whenever the binary digital input signal change is either from 0 to 1 or from 1 to 0, then the phase of the carrier wave changes by 180 degrees (pi radians).
Hence Information of the message signal is present in the phase changes of the carrier wave.
So now you can understand what is 'binary' in binary phase shift keying. As the phase of the carrier wave is modulated by the binary symbols '1' and '0' in binary phase shift keying. So here we see only two phases 0 degrees and 180 degrees. That's why it is known as binary phase shift keying (BPSK).

The mathematical equation of the binary phase shift keying (BPSK) signal is shown below-

## Binary Phase Shift Keying (BPSK) Equation BPSK Signal Equation

Here b(t) = +1; when transmitting binary '1'
= -1; when binary '0' is to be transmitted.
In this equation, 'P' is the dissipated power.  So to generate BPSK signal first of all we need to produce this b(t) signal.

Now we will understand, how we can produce the b(t) signal-
The diagram below shows the binary sequence and the b(t) signal produced from this binary sequence. NRZ Bipolar b(t) Signal Waveform

From the binary sequence waveform it is clear that, its amplitude (value) is 1 for binary 1 and 0 for Binary 0.

Now according to the waveform of b(t) signal, you can easily observe that for binary input 1, its amplitude is 1 and for binary input 0, it has amplitude of -1.
One thing you need to observe here is; the b(t) signal is NRZ signal. NRZ means Non Returning to Zero. In non returning to zero, the signal does not return to zero, when we have same binary symbols subsequently in the digital input sequence. It is a bipolar signal because, it has +1 and -1 amplitudes (amplitudes having opposite signs or polarities).

Now lets understand the generation of Binary Phase Shift Keying (BPSK) with the help of block diagram.
See the image shown below-

## Generation of Binary Phase Shift Keying (Block Diagram of BPSK) Generation of BPSK Signal (Binary Phase Shift Keying)
Here in the image, you can see that we apply binary data sequence to bipolar NRZ level encoder and at its output we get bipolar NRZ signal b(t). The b(t) signal we have discussed already. This is a bipolar signal because, it has +1 and -1 amplitudes (amplitudes having opposite signs or polarities).
Now this bipolar NRZ b(t) signal is applied to a balanced modulator. This balanced modulator has two inputs, so at it's another input we apply the carrier signal. So at the output, we get Binary Phase Shift Keying (BPSK) signal. So in this way we can generate the BPSK signal.

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