1. Lecture 7:
Noise to ASK, FSK and PSK
2nd semester

2. Outline - Several types of noise.
- Additive white Gaussian noise (AWGN).
- Signal to noise ratio (SNR).

3. Noise
As signal is transmitted through a channel, undesired signal in the form of noise gets mixed up with the signal, along with the distortion introduced by the transmission media.
Noise is any unwanted energy tending to interfere with the signal to be transmitted.

4. Noise The noise either be: External Noise:
This is noise originating from outside the communication system
Internal Noise: This is noise originating from within the communication system.

5. Some Examples of Noise
Thermal Noise: This noise is due to the random and rapid movement of electrons in any resistive component. Electrons “bump” with each other.
Impulse noise:
is irregular pulses or noise spikes of short duration

6. Some Examples of Noise
Cross talk is a result of bunching several conductors together in a single cable. Signal carrying wires generate electromagnetic radiation, which is induced on other conductors because of close proximity of the conductors.

7. Signal-to-Noise Ratio
In the study of noise, it is not important to know the absolute value of noise.
Even if the power of the noise is very small, it may have a significant effect if the power of the signal is also small.
What is important is a comparison between noise and the signal.
The signal-to-noise ratio (SNR) is the ratio of signal power to noise power.

8. Signal-to-Noise Ratio
SNR = Ps / Pn

9. Signal-to-Noise Ratio
Ideally, SNR = ∞ (when Pn = 0). In practice, SNR should be high as possible.
A high SNR ratio means a good-quality signal.
A low SNR ratio means a low-quality signal.
The SNR is normally expressed in decibels, that is:
SNR = 10 log10 (Ps / Pn) dB

10. Figure 3.30 Two cases of SNR: a high SNR and a low SNR

11. Example
The power of a signal is 10 mW and the power of the noise is 1 μW; what are the values of SNR and SNRdB
SNR = 10 × / = 10,000
SNRdB = 10 log10 (10 × 10-3 / 10-6)
= 10 log10 (10,000) = 40 dB

12. Additive White Gaussian Noise (AWGN)
Is a basic noise model used in Information theory to mimic the effect of many random processes that occur in nature.

13. OOK Modulator with noise
Apply a OOK for a random digital signal using the following carrier
3 sin (70πt) , SNRdb = 5
2 sin (2π20t), SNRdb = 10
4 sin (50πt), SNRdb = 15

15. SNR =10
SNR =20

16. FSK Modulator with noise
Implement a BFSK modulation that use the following carriers:
1- fc1 = 2π and fc2 = 2π10 SNRdb = 10
2- fc1 = 100π and fc2 = 50π , SNRdb = 20
3- fc1 = 90π and fc2 = 30π SNRdb = 25

18. SNR =10
SNR = 25

19. PSK Modulator
Implement a BPSK modulation that use the following carriers:
1- f = 2π7 Hz SNRdb = 10
2- f = 2π4 Hz SNRdb = 23
3- f = 2π 5 Hz SNRdb = 18

20. SNR =5
SNR =20

21. Any Questions ?