ASK,FSK,PSK

1. An Najah National University
Telecommunication Engineering Department
comparison of binary shift keying techniques
Prepeared by : Suhad Malayshi
Raghad foqha
Ola mashaqi
submitted to Dr. Allam Mousa

2. What is digital modulation?
The techniques used to modulate digital information so that it can be transmitted
via microwave, satellite or down a cable pair are different to that of Analogue
transmission .

3. Fundamental digital modulation methods:
Binary Amplitude shift keying (on-off keying)
advantage: simplicity
•disadvantage: ASK is very
susceptible to noise interference–
noise usually (only)affects the
amplitude, therefore ASK is the
modulation technique most
affected by noise
•application: ASK is used to
transmit digital data over optical
fiber

4. Frequency Shift Keying
Frequency Shift Keying (FSK) is a frequency modulation scheme (conveys
information over a carrier wave by varying its instantaneous frequency)
in which digital information is transmitted through discrete frequency
changes of a carrier wave .

5. FSK is the most common form of digital modulation in the high frequency radio
spectrum, and has important applications in telephone cct.
 A modem converts the binary data from a computer to FSK for transmission
over telephone lines, cables, or wireless media.
 Shifts are usually in the range of 50 to 1000Hz.
demodulation:
demodulator must be able to determine which of two possible frequencies is
present at a given time
advantage:
FSK is less susceptible to errors than ASK – receiver looks for specific frequency
changes over a number of intervals, so voltage (noise) spikes can be ignored
disadvantage:
FSK spectrum is 2 x ASK spectrum
application:
over voice lines, in high-freq. radio transmission, etc.

6. BFSK ( Binary Frequency Shift Keying )
General form of BFSK is :
0),2cos(
1),2cos(
)(
2
1
binarytfA
binarytfA
ts
Here , in BFSK, the “1” is called the mark frequency and the “0” is called the space
frequency.
The optical field of FSK form is :
The total B.W of FSK is given by :
2Δf + 2B, where B is the bit rate.

8. Multiple FSK ( MFSK) :
 MFSK is a variation of FSK that uses more than 2 frequencies.
MFSK is a form of M-ary orthogonal modulation. MFSK is classed as an M-ary orthogonal
signaling scheme because each of the M tone detection filters at the receiver responds only
to its tone and not at all to the others; this independence provides the orthogonality.
 M, the size of alphabet, is usually a power of 2 , so that, each symbol represent log2M bits.
The required Eb/N0 ratio (energy per bit to noise power spectral density ratio ) for a given
probability of error decreases as M increases.
Eb/N0
 It’s useful when comparing the bit error rate (BER) performance of different digital
modulation schemes without taking bandwidth into account.
Eb/N0 is closely related to the carrier- to- noise ratio (CNR or C/N), i.e. the signal-to-noise-
ratio (SNR) of the received signal, after the receiver filter but before detection:

9. where
fb is the channel data rate
B is the channel bandwidth
 As M approaches infinity the required Eb/N0 ratio decreases asymptotically to
the Shannon limit of -1.6 dB.

10. Audio FSK (AFSK) and it’s applications :
AFSK is a modulation technique by which digital data is represented by changes
in the frequency of an audio tone, yielding an encoded signal suitable for
transmission via radio or telephone.
Normally, the transmitted audio alternates between two tones: one, the "mark",
represents a binary one; the other, the "space", represents a binary zero.
Most early telephone-line modems used audio frequency-shift keying (AFSK) to
send and receive data at rates up to about 1200 bits per second.
Some early microcomputers used a specific form of AFSK modulation, the
Kansas City Standard(Byte standard), to store data on audio cossets.
AFSK is not always used for high-speed data communications, since it is far less
efficient both power and bandwidth than most other modulation modes.

11. • Phase-shift keying (PSK) is a method of digital communication in which
the phase of a transmitted signal is varied to transmit information. There are
several methods that can be used to do PSK.
Phase Shift Keying
•The simplest PSK technique is called binary phase-shift keying (BPSK). It uses two
opposite signal phases (0 and 180 degrees). The digital signal is broken up timewise
into individual bits (binary digits).

12. BPSK QPSK or( 4-PSK

14. `

15. The “PSK” in 8PSK refers to the use of Phased Shift Keying.
Phased Shift Keying : is a form of phase modulation which is
accomplished by the use of a discrete number of states. 8PSK
refers to PSK with 8 sates.
With half that number of states, you will have QPSK. With
twice the number of states as 8PSK, you will have 16PSK

16. Differential phase shift keying is a no coherent form
of phase shift keying ; which avoids the need for a
coherent reference signal at the receiver.
No coherent receivers are easy and cheap to build, and
hence are widely used in wireless communications. In
DPSK system, the input binary sequence is first
differentially encoded and then modulated using a
BPSK modulator.

17.  DPSK → COHERENT
→ NON-COHERENT
 Coherent systems need carrier phase information at
the receiver and they use matched filters (or
correlation receiver) to detect and decide what data
was sent
 while non coherent systems do not need carrier
phase information and use methods like square law
(push detection or energy detection) to recover the
data.

18. coherent vs noncoherent
 In terms of performance coherent systems are much
better than non coherent systems.
 DPSK: non-coherent
QPSK & BPSK & MPSK : coherent
 In coherent phase shift keying different phase
modulation schemes will be covered i.e. binary PSK,
quadrature phase shift keying and M-ary PSK

19. OFF-SET PSK
 At 180 phase-shift, the amplitude of the transmitted
signal changes very rapidly costing amplitude change .
 This signal may be distorted when is passed through
the filter or nonlinear amplifier.
 To solve the amplitude change problem, we propose
the offset QPSK.
 Offset QPSK delay the data in quadrature component
by T/2 seconds (half of symbol).
 In the offset QPSK, the phase of the signal can change
by 90 or 0 degree only ,,, while in the QPSK the phase
of the signal can change by 180; 90 or 0 degree.

20. Applications on PSK
The wireless LAN standard

21.  A wireless local area network (WLAN) links two or
more devices using some wireless distribution
method ,and usually providing a connection through
an access point to the wider Internet. This gives users
the mobility to move around within a local coverage
area and still be connected to the network. Most
modern WLANs are based on IEEE 802.11 standards,
marketed under the Wi-Fi brand name. WLANs were
once called LAWNs (for local area wireless network)
by the Department of Defense.

22.  Wireless LANs have become popular in the home due
to ease of installation, and in commercial complexes
offering wireless access to their customers; often for
free

23. How to choose ??
There are many other types of modulation you could
use and which one would work best would depend
on your project

24. Differences
FSK vs PSK
 less susceptible to interference .
 easier to generate with modern electronics
 BFSK requires twice the bandwidth of BPSK
 power fsk is better compared to psk
but
 it is expensive 
ASK
 Simplicity
 low implementation costs
 conserving power.

25. How to Imagine noise ?
 ф1 and ф 2 are vectors
Each diagram represents the additive noise with a dashed
line circle around the signal.

26. FSK vs PSK noise immunity?
you need to define a quantitative metric that has a level playing
field between the two, such as measuring the systems' bit-error
rate versus the signal to noise ratio ”

27. Error performance

28. Eb/N0 (the energy per bit to noise power spectral density ratio

29. THANK YOU
Questions