DCN 1-4 Nyquist Shannon
-
Upload
buihuynhthanhngan -
Category
Documents
-
view
234 -
download
0
description
Transcript of DCN 1-4 Nyquist Shannon
-
Data Communications and
NetworksNetworksChapter 1: Signal impairment
Pham Quang Thai [email protected]
1
-
Signal impairment: received signal is
different than transmitted signal
-
Attenuation: change in power
-
Distortion: change in time domain
-
Noise: addition in power
-
Example
1. A 1mW signal travels through a transmission medium and looses half of its power. Find the total attenuation in dB.
2. The loss in a cable is usually defined in decibels per kilometer (dB/km). If the signal at the beginning of a kilometer (dB/km). If the signal at the beginning of a cable with 0.3 dB/km has a power of 2 mW, what is the power of the signal at 5 km?
3. The power of a signal is 10 mW and the power of the noise is 1 W. The signal to noise ratio is called SNR. What are the values of SNR and SNR in dB ?
-
Bit rate limitation of transmission
medium
How fast we can send data, in bits per second, over a
channel depending on three factors:
The bandwidth available of the channel (B)
The level of the signals we use (L)
The quality of the channel (the level of noise N)
-
The foundation of information
theories
The maximum bit rate (Nyquist bit rate) in noiseless
channel: C = Blog2L
The maximum bit rate (Shannon capacity) in noisy
channel: C = Blog2(1+SNR)channel: C = Blog2(1+SNR)
Harry Nyquist Claude Shannon
-
Examples
4. A noiseless channel with a bandwidth of 3000 Hz transmitting a signal with two signal levels. Find the maximum bit rate
5. The same noiseless channel transmitting a signal with 2 bits per signal level. Find the maximum bit rate
6. We need to send 265 kbps over a noiseless channel with a 6. We need to send 265 kbps over a noiseless channel with a bandwidth of 20 kHz. How many signal levels do we need?
7. A telephone line normally has a bandwidth of 3000 Hz. The signal-to-noise ratio is usually 3162. Find the bit rate
8. A channel has 1-MHz bandwidth and SNR of 63. Find the signal level
-
The Shannon capacity gives us the upper limit;
the Nyquist formula tells us how many signal
levels we need.
-
Optical transmission link simulations
-
Questions for Simulation 1
9. Set the laser source power at 3 dBm. Turn off the fibers dispersion. Set fiber attenuation at 0.2 dB/km. Compare and explain the input/output signals
10. Set the laser source power at 3 dBm. Turn on the fibers dispersion. Set fiber attenuation at 0 dB/km. Compare dispersion. Set fiber attenuation at 0 dB/km. Compare and explain the input/output signals
11. Turn on the fibers dispersion. Set fiber attenuation at 0.2 dB/km. Set the laser source power at -3 dBm and 3 dBm. Compare and explain the input/output signals
12. Calculate the total attenuation and SNR. Why the total attenuation is larger than the fiber attenuation?
-
Optical transmission link simulations