Quadrature Phase Shift Keying (QPSK) Techniques and its Block Diagram

QUADRATURE PHASE SHIFT KEYING (QPSK) TECHNIQUES AND ITS BLOCK DIAGRAM:

Advantages of QPSK

·     Very good noise immunity

·     Effective utilization of available bandwidth

·     Low error probability

Very high bit rate data transmission

This is Synchronous reception. Therefore coherent carrier is to be recovered from the received signal s(t).

Compare binary PSK with QPSK.

BPSK QPSK

1.  One bit forms a symbol. Two bits form a symbol.

2.  Two possible symbols. Four possible symbols.

3.  Minimum bandwidth is twice of fb. Minimum bandwidth is equal to fb.

4.  Symbol duration = Tb. Symbol duration = 2Tb.

9. What are the advantages of M-ary signaling scheme?

1.  M-ary signaling schemes transmit bits at a time.

2.  Bandwidth requirement of M-ary signaling schemes is reduced.

The probability of error in M-Ary FSK as the value of m increases:

As the value of „M‟ increases, the Euclidean distance between the symbols reduces. Hence the symbols come closer to each other. This increases the probability of error in M-ary systems.

Correlative coding allows the signaling rate of 2B0 in the channel of bandwidth B0. This is made physically possible by allowing ISI in the transmitted signal in controlled manner. This ISI is known to the receiver. Hence effects of ISI are eliminated at the receiver. Correlative coding is implemented by duobinary signaling and modified duobinary signaling.