1. Department of Electrical and Computer Engineering
ECE 4371, Fall, Introduction to Telecommunication Engineering/Telecommunication Laboratory
                                                           
Zhu Han
Department of Electrical and Computer Engineering
Class 13
Oct. 8th, 2014

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

3. 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.

4. Example Duobinary Pulse Interpretation of received signal
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

5. Duobinary signaling
Duobinary signaling (class I partial response)

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

7. 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).

8. 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.

9. Modified duobinary signaling
Spectrum

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

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

12. 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.

13. Exercise What is the differential Duobinary output
What is the modified Duobinary output and decoded signal? Interpretation of receiving 2, 0, and -2?
What is the modified differential Duobinary output

14. Other types of partial response signals
paper
Type r0 r1 r2 r3 r4
p(t)
P(W)
Levels
ideal 1 2 I 3 II 5
III -1 6 IV V

15. 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)

16. 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

17. Implementation of binary ASK

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

19. Pro, Con and Applications
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

20. Example
We have an available bandwidth of 100 kHz which spans from 200 to 300 kHz. What are the carrier frequency and the bit rate if we modulated our data by using ASK with d = 1?
Solution
The middle of the bandwidth is located at 250 kHz. This means that our carrier frequency can be at fc = 250 kHz. We can use the formula for bandwidth to find the bit rate (with d = 1 and r = 1).

21. 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)

22. 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

23. Example
We have an available bandwidth of 100 kHz which spans from 200 to 300 kHz. What should be the carrier frequency and the bit rate if we modulated our data by using FSK with d = 1?
Solution
This problem is similar to Example 5.3, but we are modulating by using FSK. The midpoint of the band is at 250 kHz. We choose 2Δf to be 50 kHz; this means

24. 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

25. Phase Shift Keying
One phase change encodes a 0 while another phase change encodes a 1 (a form of phase modulation)

26. DBPSK, QPSK Differential BPSK Four Level: QPSK
0 = same phase as last signal element
1 = 180º shift from last signal element
Four Level: QPSK

27. QPSK Example

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

29. Concept of a constellation diagram

30. 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 = 2L
L = number of bits per signal element

31. 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)

32. 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

33. 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

34. 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.

35. 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.
ECE Fall 2008

36. 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 2nd generation digital cellular and cordless telephone apps. such as GSM