The introduction to Telecomunication engineering

Telecommunication

1. ECE 4371, Fall, 2017
Introduction to Telecommunication
Engineering/Telecommunication Laboratory
Zhu Han
Department of Electrical and Computer Engineering
Class 11
Oct. 11
th
, 2017

2. Outline
Eye Diagram
Partial Response
Carrier systems
–ASK, OOK, MASK
–FSK, MFSK
–BPSK, DBPSK, MPSK
–MQAM, MQPR
–OQPSK,
–Continuous phase modulation (CPM): MSK, GMSK

3. Eye Diagram Setup
Eye diagram is a retrace display of
data waveform
–Data waveform is applied to
input channel
–Scope is triggered by data
clock
–Horizontal span is set to cover
2-3 symbol intervals
Measurement of eye opening is
performed to estimate BER
–BER is reduced because of
additive interference and noise
–Sampling also impacted by
jitter

4. Eye Diagram
Eye diagram is a means of evaluating the quality of a received
“digital waveform”
–By quality is meant the ability to correctly recover symbols and
timing
–The received signal could be examined at the input to a digital
receiver or at some stage within the receiver before the decision
stage
Eye diagrams reveal the impact of ISI and noise
Two major issues are 1) sample value variation, and 2) jitter and
sensitivity of sampling instant
Eye diagram reveals issues of both
Eye diagram can also give an estimate of achievable BER
Check eye diagrams at the end of class for participation

5. Vertical and Horizontal Eye Openings
The vertical eye opening or noise
margin is related to the SNR, and
thus the BER
–A large eye opening corresponds
to a low BER
The horizontal eye opening relates
the jitter and the sensitivity of the
sampling instant to jitter
–The red brace indicates the range
of sample instants with good eye
opening
–At other sample instants, the eye
opening is greatly reduced, as
governed by the indicated slope

6. Interpretation of Eye Diagram

7. Cosine rolloff filter: Eye pattern
2nd Nyquist
1st Nyquist


2nd Nyquist:
1st Nyquist:


2nd Nyquist:
1st Nyquist: 

2nd Nyquist:
1st Nyquist:


2nd Nyquist:
1st Nyquist:

8. Eye Diagram
The eye diagram is created by taking the time domain signal and
overlapping the traces for a certain number of symbols.
The open part of the signal represents the time that we can
safely sample the signal with fidelity

9. Figure 4.34 (a) Eye diagram for noiseless quaternary system. (b) Eye diagram for quaternary system
with SNR 20 dB. (c) Eye diagram for quaternary system with SNR 10 dB.

10. Figure 4.35 (a) Eye diagram for noiseless band-limited quaternary system:
cutoff frequency fo 0.975 Hz.(b) Eye diagram for noiseless band-limited
quaternary system: cutoff frequency fo 0.5 Hz.

11. Jitter in Circuit design
Circuit design

12. Eye Diagram In Phase

13. Linear Modulation with Nyquist Impulse Shaping
QPSK diagram under limited bandwidth conditions
if system (tx andrx filter) meets 1st Nyquist : 4 sharp signal points (right diagram)

14. Partial Response Signals
Previous classes: Sy(w)=|P(w)|^2 Sx(w)
–Control signal generation methods to reduce Sx(w)
–Raise Cosine function for better |P(w)|^2
This class: improve the bandwidth efficiency
–Widen the pulse, the smaller the bandwidth.
–But there is ISI. For binary case with two symbols, there is only
few possible interference patterns.
–By adding ISI in a controlled manner, it is possible to achieve a
signaling rate equal to the Nyquist rate (2W symbols/sec) in a
channel of bandwidth W Hertz.

15. Example
Duobinary Pulse
–p(nTb)=1, n=0,1
–p(nTb)=1, otherwise
Interpretation of received signal
–2: 11
–-2: 00
–0: 01 or 10 depends on the previous transmission

16. Duobinary signaling
Duobinary signaling (class I partial response)

17. Duobinary signal and Nyguist Criteria
Nyguist second criteria: but twice the bandwidth

18. Differential Coding
The response of a pulse is spread over more than one signaling
interval.
The response is partial in any signaling interval.
Detection :
–Major drawback : error propagation.
To avoid error propagation, need deferential coding (precoding).

19. Modified duobinary signaling
Modified duobinary signaling
–In duobinary signaling, H(f) is nonzero at the origin.
–We can correct this deficiency by using the class IV partial
response.

20. Modified duobinary signaling
Spectrum

21. Modified duobinary signaling
Time Sequency: interpretation of receiving 2, 0, and -2?

22. Pulse Generation
Generalized form of
correlative-level
coding
(partial response signaling)

23. Tradeoffs
Binary data transmission over a physical baseband channel can
be accomplished at a rate close to the Nyquist rate, using
realizable filters with gradual cutoff characteristics.
Different spectral shapes can be produced, appropriate for the
application at hand.
However, these desirable characteristics are achieved at a price :
–A large SNR is required to yield the same average probability of
symbol error in the presence of noise.

24. Other types of partial response signals
Typer0r1r2r3r4p(t) P(W) Levels
ideal1 2
I 11 3
II 121 5
III21-1 6
IV 10-1 3
V -1020-1 5
paper

25. ASK, OOK, MASK
The amplitude (or height) of the sine wave varies to transmit the
ones and zeros
One amplitude encodes a 0 while another amplitude encodes a 1
(a form of amplitude modulation)

26. Binary amplitude shift keying, Bandwidth
d ≥ 0 related to the condition of the line
B = (1+d) x S = (1+d) x N x 1/r

27. Implementation of binary ASK

28. OOK and MASK
OOK (On-OFF Key)
–0 silence.
–Sensor networks: battery life, simple implementation
MASK: multiple amplitude levels

29. Pro, Con and Applications
Pro
–Simple implementation
Con
–Major disadvantage is that telephone lines are very susceptible to
variations in transmission quality that can affect amplitude
–Susceptible to sudden gain changes
–Inefficient modulation technique for data
Applications
–On voice-grade lines, used up to 1200 bps
–Used to transmit digital data over optical fiber
–Morse code
–Laser transmitters

30. Frequency Shift Keying
One frequency encodes a 0 while another frequency encodes a 1
(a form of frequency modulation)
Represent each logical value with another frequency (like FM)





ts tfA
12cos tfA
22cos 1binary 0binary

31. FSK Bandwidth
Limiting factor: Physical capabilities of the carrier
Not susceptible to noise as much as ASK
Applications
–On voice-grade lines, used up to 1200bps
–Used for high-frequency (3 to 30 MHz) radio transmission
–used at higher frequencies on LANs that use coaxial cable

32. Multiple Frequency-Shift Keying (MFSK)
More than two frequencies are used
More bandwidth efficient but more susceptible to error
f
i= f
c+ (2i –1 –M)f
d
f
c= the carrier frequency
f
d= the difference frequency
M = number of different signal elements = 2
L
L = number of bits per signal element tfAts
ii 2cos Mi1

33. Phase Shift Keying
One phase change encodes a 0 while another phase change
encodes a 1 (a form of phase modulation)





ts tfA
c2cos  tfA
c2cos 1binary 0binary

34. DBPSK, QPSK
Differential BPSK
–0 = same phase as last signal element
–1 = 180º shift from last signal element
Four Level: QPSK






ts 






4
2cos

tfA
c 11 






4
3
2cos

tfA
c 






4
3
2cos

tfA
c 






4
2cos

tfA
c 01 00 10

35. QPSK Example

36. Bandwidth
Min. BW requirement: same as ASK!
Self clocking (most cases)

37. Concept of a constellation diagram

38. MPSK
Using multiple phase angles with each angle having more than
one amplitude, multiple signals elements can be achieved
–D= modulation rate, baud
–R= data rate, bps
–M= number of different signal elements = 2
L
–L= number of bits per signal elementM
R
L
R
D
2log


39. QAM –Quadrature Amplitude Modulation
Modulation technique used in the cable/video networking world
Instead of a single signal change representing only 1 bps –
multiple bits can be represented buy a single signal change
Combination of phase shifting and amplitude shifting (8 phases, 2
amplitudes)

40. QAM
QAM
–As an example of QAM, 12
different phases are combined
with two different amplitudes
–Since only 4 phase angles have 2
different amplitudes, there are a
total of 16 combinations
–With 16 signal combinations, each
baud equals 4 bits of information
(2 ^ 4 = 16)
–Combine ASK and PSK such that
each signal corresponds to
multiple bits
–More phases than amplitudes
–Minimum bandwidth requirement
same as ASK or PSK

41. QAM and QPR
QAM is a combination of ASK and PSK
–Two different signals sent simultaneously on the same carrier frequency
–M=4, 16, 32, 64, 128, 256
Quadrature Partial Response (QPR)
–3 levels (+1, 0, -1), so 9QPR, 49QPR  tftdtftdts
cc  2sin2cos
21 

42. Offset quadrature phase-shift keying (OQPSK)
QPSK can have 180 degree jump, amplitude fluctuation
By offsetting the timing of the odd and even bits by one bit-period, or half a
symbol-period, the in-phase and quadrature components will never change at
the same time.

43. ECE 4371 Fall 2008
Continuous phase modulation (CPM)
CPM the carrier phase is modulated in a continuous manner
constant-envelope waveform
yields excellent power efficiency
high implementation complexity required for an optimal
receiver
minimum shift keying (MSK)
–Similarly to OQPSK, MSK is encoded with bits alternating between
quarternary components, with the Q component delayed by half a bit
period. However, instead of square pulses as OQPSK uses, MSK encodes
each bit as a half sinusoid. This results in a constant-modulus signal,
which reduces problems caused by non-linear distortion.

44. Gaussian minimum shift keying
GMSK is similar to MSK except it incorporates a premodulation Gaussian
LPF
Achieves smooth phase transitions between signal states which can
significantly reduce bandwidth requirements
There are no well-defined phase transitions to detect for bit synchronization
at the receiving end.
With smoother phase transitions, there is an increased chance in intersymbol
interference which increases the complexity of the receiver.
Used extensively in 2
nd
generation digital cellular and cordless telephone
apps. such as GSM