Binary Phase Shift Keying

Communication is the process of transfer of information from one place to another. There are various means of communication being used today. The evolution in the field of communication took up pace during world war. From wired communication methods, we have moved towards wireless communication. From analog communication methods, we have moved towards digital communication methods. As wireless communication was found more effective, various techniques were introduced to make it more reliable and secure. One of such techniques introduced to transfer data over long distances is modulation. The Binary Phase Shift Keying is one of the digital modulation methods.

What is Binary Phase Shift Keying?

In digital modulation instead of the analog waveform, digital data is transferred from one place to another. Here the logic levels high and logic level low are transmitted. The baseband signal used in digital modulation is in the form of 0’s and 1’s. Based on the logic level of the baseband signal the carrier waveform characteristics are varied.

In this Binary Phase Shift Keying, the phase of the carrier waveform is varied according to the digital baseband signal. As the digital baseband signal has only two levels, either 0 or 1, hence the name ‘Binary’.

Binary Phase Shift Keying Modulation

In this modulation, the phase of the carrier is varied. When the baseband signal is at logic -1, the carrier wave phase remains unchanged. When the logic level of the baseband signal is low-0, the phase of the carrier signal is inverted. Thus, in this modulation method, when there is a logic -0 in the baseband signal, the phase of the carrier signal undergoes 180° phaseshift.

Circuit Diagram

Binary-Phase-Shift-Keying-Circuit-Diagram
Binary-Phase-Shift-Keying-Circuit-Diagram

In this digital modulation method, the phase of the carrier signal has to be inverted when the logic level 0 is detected in the baseband signal. This can be achieved simply by multiplying the sinusoidal carrier waveform with -1. This makes the implementation of this modulation very simple.

Waveform

This modulation faces the challenge of High-slope transitions in carrier waveform and these can generate high-frequency energy which can interfere with the other RF signals and distort the system. So, for smooth transitions, the digital bit period should be equal to one complete carrier cycle and synchronization of digital transitions with carrier waveform should be done.

Binary-Phase-Shift-Keying-Waveform
Binary-Phase-Shift-Keying-Waveform

A coherent detector along with the phase lock loop is used at the receiver end for demodulation. Before modulation, the message signal is coded using the NRZ method.

Advantages and Disadvantages

  • The separation of binary 0 and 1 of the baseband with 180° phase shift of carrier makes this modulation more robust allowing data to be transferred to larger distances.
  • The receiver used here is very simple compared to other techniques.
  • Here, per carrier symbol, only one bit is transmitted. Hence, the data rate is less compared to other techniques.
  • This digital modulation technique is not bandwidth efficient compared to other methods.

This modulation method is easy to implement and less cost. This method is used in cellular towers for long-distance transmission of data, channel estimation process. What is the main drawback of Binary Phase Shift Keying?



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