ADVANTAGES OF QPSK
With fourphases, QPSK can encode two bits per symbol, to minimize the BER —
twice the rate of BPSK. Analysis shows that this may be used either to double the
data rate compared to a BPSK system while maintaining the bandwidth of the signal
or to maintain the data-rate of BPSK but halve the bandwidth needed.
As with BPSK, there are phase ambiguity problems at the receiver and differentially
encoded QPSK is more normally used in practice.
One of the advantages of qpsk is its use of Differential QPSK (DQPSK). Here the
phase shift is not relative to a reference signal but relative to the phase of previous
two bits. The receiver does not need the reference signal but only compares two
signal to reconstruct data.
The phase shift can always be relative to a reference signal. If this scheme is used,
phases shift of 0 means that the signal is in phase with the reference signal. A QPSK
signal will then exhibit a phase shift of 450 for the data II, 135° for 10, 225° for 00,
and 3150 for 01, with all phase shifts being relative of the reference signal. This is
one of the advantages of qpsk.
DISADVANTAGES OF QPSK:
Interchannelinterference is signiﬁcantly large in QPSK.
To avoid ICI QPSK requires ﬁltering, can change amplitude and phase of
QPSK requires around 8 times its bandwidth to transmit the same power.
The disadvantage of QPSK relative to BPSK is that it is more sensitive to
Transmitter and receiver have to be synchronized very often, eg. by using special
synchronization patterns before user data arrives or via a plot frequency as
ADVANTAGES OF ASK
ASK is heavily effected by noise and interference and can be easily demodulated.
FSK is insensitive to channel fluctuations and not easily effected by noise.
Reduction in the amount of energy required to transmit informations.
It has good bandwidth efficiency
DISADVANTAGES OF ASK
Easily influenced to noise interference - refer to unintentional voltage probably
affected by heat or electromagnetic induction created by other source.
It has low power efficiency.
The system is simplest and has more power efficiency.
It has low bandwidth efficiency.
It is used in low speed communications.
DPSK has some advantages over BPSK, but at the same time it has some drawbacks.
ADVANTAGES OF DPSK:
1) DPSK does not need carrier at its receiver. Hence the complicated circuitry for
generation of local carrier is avoided.
2) The bandwidth requirement of DPSK is reduced compared to that of BPSK.
1) The probability of error or bit error rate of DPSK is higher than that of BPSK.
2) Since DPSK uses two successive bits for its reception, error in the first bit
creates error in the second bit. Hence error propagation in DPSK is more.
Whereas in PSK single bit can go in error since detection of each bit is
3) Noise interference in DPSK is more.
In DPSK, previous bit is used to detect next bit. Therefore if error is present in
previous bit, detection of next bit can also go wrong. Thus error is created in bit
also. Thus there is tendency of appearing errors in pairs in DPSK.
Power efficiency. System is
Low bandwidth efficiency
Low speed communication
DRAWBACKS OF BPSK: AMBIGUITY IN OUTPUT SIGNAL: