Pràctica 5 (2015)

Pràctica Inglés
Universidad Universidad Politécnica de Cataluña (UPC)
Grado Ingeniería Telemática - 2º curso
Asignatura ICOM
Año del apunte 2015
Páginas 10
Fecha de subida 01/04/2016
Descargas 9
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Marc Peig i Jordi Biosca. Grup 21.
Session 5:Inter-Symbol Interference and Baseband Equalization Activity 5.1 Comment the step 6 and step 7 figures Step 6: Matched Filter (WITH noise) Marc Peig i Jordi Biosca. Grup 21.
Step 7: Equalizer (WITH noise) Step 6: Matched Filter (WITHOUT noise) Marc Peig i Jordi Biosca. Grup 21.
Step 6: Equalizer (WITHOUT noise) First of all, observing the constellation of the Matched filter with noise, we can see that there are four red crosses corresponding to the four sent symbols and a continuous blue shape corresponding to the noise. However, if there is no noise in the matched filter, in the Constellation we can distinguish the four symbols and blue crosses corresponding to the ISI, as the channel is not ideal. Secondly, observing the constellation of the equalizer with noise, there is more or less the same shape as we have in the matched filter, with only one difference, now; there is a separation in the decision thresholds that is the effect of the equalizer, so we reduce the error probability. Conversely, in the constellation of the equalizer without noise, we can distinguish the four symbols and some blue crosses overlapping the symbols, this cross corresponds to the terms of ISI that our equalizer is not able to eliminate.
Activity 5.2 Generate and save the QAM simulation Activity 5.3 Measure the symbol rate and the ratio in dB between the principal and the secondary lobe; compare it with the theoretical ones.
Marc Peig i Jordi Biosca. Grup 21.
Conversion from Lavicad to VSA 50 realizations (Video RMS Averaging) of the spectrum (plot A) The rate between principal and secondary lobe is 13,463 dB and it is similar to the obtained in the previous study (10,97 dB). The symbol rate corresponds to the Marc Peig i Jordi Biosca. Grup 21.
expression r = 1/T. We measure this parameter because r corresponds to the frequency value of the first zero of the spectrum. So, it is more or less 1 MHz, so 1 Mbaud.
Activity 5.4 Identify the main differences between the eye diagram you observe now with a rectangular pulse and the one you obtained in Session 4 where a square root raised cosine was used.
Eye Diagram obtained in this session (left) and the one obtained in the session 4 (right) The main difference is that in this session we obtained an eye diagram with opening near to 0, and the one we obtained in the last session has an opening of 79%, approximately.
Activity 5.5 What is the effect of the non--ideal channel on the spectrum? Compare it with the theoretical shape calculated in Question 5.1. Repeat the same tasks done in the Activity 5.4, and compare the results with the ones obtained there. Justify the differences you observe. Measure the MER and compare it with the Eb/No used in the system.
The effect of the non‐ideal channel is seen in the principal lobule, the amplitude of this lobule is cut. This effect is given by the continuous component of the spectral density obtained in the previous study.
Marc Peig i Jordi Biosca. Grup 21.
50 realizations (Video RMS Averaging) of the spectrum (plot A) Observing the spectrum obtained in this activity and the one obtained in the previous one, we can see the effect of the ISI because we cannot distinguish clearly the shape of the signal. The received constellation has the four different tendencies for each sent symbol caused by the ISI. However, in the previous activity, we sent symbols almost equal to the ideal symbols. Comparing now the I‐Eye Diagrams, in this activity this diagram is distorted by ISI and we can observe a cleaner eye diagram. Finally, the Signal-to‐Noise Ration (MER/SNR) obtained in this activity is 14,37 dB and we obtained 28,829 dB. This value is changing while option ‘play’ of the VSA is active, when we pressed ‘pause’ we got a concrete value that there is s low probability that this value would be the same if we repeat this process.
Marc Peig i Jordi Biosca. Grup 21.
Spectrum, Constellation, I--‐Eye Diagram and QPSK Syms/Err of the received signal Before equalization stage The MER value is 11,962 dB, the effect of the noise is reflected in this value.
Marc Peig i Jordi Biosca. Grup 21.
QPSK Syms/Err ansd Spectrum of the signal before stage 5 Activity 5.6 Compare the received constellation and the error probability obtained in this session without an equalizer and with ZF equalizer with 3 taps.
Received constellation without equalizer Marc Peig i Jordi Biosca. Grup 21.
Using an equalizer the received symbols are closer to the sent ones, however, if we don’t use an equalizer, the symbols we receive are more dispersed from the ones we send.
Received constellation with a 3‐taps Zero Forcing Equalizer Marc Peig i Jordi Biosca. Grup 21.
Probability of error in function of Eb/No. it’s the same in both cases.
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