Unit 8 - Week 7 - Computer simulation of Rayleigh fading, Antenna Diversity

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1 X Courses» Introduction to Wireless and Cellular Communications Announcements Course Forum Progress Mentor Unit 8 - Week 7 - Computer simulation of Rayleigh fading, Antenna Diversity Course outline How to access the portal Assignment 7. Overview of Cellular Evolution and Wireless Technologies 1) Given channel coherence time and coherence bandwidth are 1 us and 500 khz respectively. 16-QAM modulation is used for communication to achieve 1Mbps throughput. Which of the following is true about the channel? Wireless Propagation and Cellular Concepts Cellular System Design, Capacity, Handoff, and Outage Week 4 - Multipath Fading Environment Week 5 - BER Performance in Fading Channels Week 6 - Wide Sense Stationary Uncorrelated Scattering (WSSUS) Channel Model Week 7 - Computer simulation of Rayleigh fading, Antenna Diversity Practical Channel Models (ITU, COST), Computer generation of Rayleigh fading Slow fading, Frequency selective Fast fading, frequency selective Slow fading, Frequency flat Fast fading, Frequency flat Fast fading, Frequency flat 2) How would the above answer change if BPSK is used instead of 16-QAM. (consider 1Mbps throughput) Slow fading, Frequency selective Fast fading, frequency selective Slow fading, Frequency flat Fast fading, Frequency flat Fast fading, frequency selective 3) Which of the following spectral density plots refer to spectrum with an LOS component? 1/6

Rayleigh Fading simulation - Clark and Gans Method, Jakes Method Jakes Method properties Introduction to Diversity, Antenna selection diversity Statistical Characterization of Antenna Diversity,

2 Rayleigh Fading simulation - Clark and Gans Method, Jakes Method Jakes Method properties Introduction to Diversity, Antenna selection diversity Statistical Characterization of Antenna Diversity, Optimal Diversity Combining Feedback for week 7 lec29_notes lec30_notes lec31_notes lec32_notes lec33_notes Quiz : Assignment 7 Assignment 7 Solutions Week 8 - Fading Channels - Diversity and Capacity Week 9 - Capacity and Introduction to CDMA Week 10 - Introduction to CDMA Week 11 - CDMA Receivers 4) You are asked to generate a rayleigh fading channel and are aware of a method to generate a rayleigh random variables and many independent random variables can be generated following that procedure. If so, what is the need to resort to methods such as Smith method or Clarke and Gans method. Independent random variables do not model the time correlation. To reduce the computational complexity Both (a) and (b) None of these Week 12 MATLAB Independent random variables do not model the time correlation. 5) Given the maximum doppler shift in a channel is 100 Hz. It is required to simulate the channel using Jakes model with 20 oscillators. Which of the following is not an oscillator frequency? 100 Hz 0 Hz Hz Hz 2/6

3 0 Hz 6) Which of the following is true about the Walsh hadamard matrices? Symmetric matrix Orthogonal matrix Anti symmetric matrix None of the above Orthogonal matrix 7) Which of the following is true w.r.t Smith method and Clarke and Gans? Smith method requires less number of computations Clarke and gans method has less computational complexity Both have same complexity None of the above Smith method requires less number of computations 8) Selection diversity is not useful in which of the following scenarios. Few of the antennas are weak Antennas are correlated The antennas are very close to each other All of the above All of the above 9) The probability of bit error for coherent BPSK in AWGN channel is given by P e, BPSK = Q( (2γ) ) where γ is the SNR. Estimate the outage probability for BPSK at a performance level P e = 10-3 in a Rayleigh fading channel with antenna selection diversity using M = 3 antennas. Assume that the average SNR of each antenna is the same and is given by = 12 db. Given that Q(3.1) = Γ ) The probability of bit error for differential BPSK in AWGN channel is given by P e, DBPSK = 12e - γ where is the SNR. Estimate the outage probability for differential BPSK at 3/6

4 a performance level P e = in a Rayleigh fading channel with antenna selection diversity using M = 2 antennas. Assume that the average SNR of each antenna is the same and is given by = 15 db Γ ) In a noise limited system, which of the following diversity methods will be effective. Selection diversity Optimal diversity Co phasing Both (b) and (c) Both (b) and (c) 12) Co phasing was discussed in the lecture. Consider the case where cophasing is implemented using 3 receiver antennas. There are three signals r1(t), r2(t) and r3(t) that will be combined here. Assume that the average SNR of each antenna is the same and is given by. What is the average SNR ie.,e[ co-phasing ] for the combination of the 3 antennas Γ in cophasing? γ Γ(1 + π/4) Γ(1 + π/3) Γ(1 + π/2) Γ(1 + π/6) Γ(1 + π/2) 13) In MRC for Optimal Combining diversity: Statement 1: The scaling constant G k is chosen such that the weightage is lower weightage for weak antennas Statement 2: The scaling constant G k is chosen such that the phase dependence on SNR is eliminated Which of the following is correct? Statement 1 is False; Statement 2 is True Statement 1 is True; Statement 2 is True Statement 1 is False; Statement 2 is False Statement 1 is True; Statement 2 is False 4/6

5 Statement 1 is True; Statement 2 is True 14) Which selection diversity will you implement in a high noise system and why? Choose the option with the most appropriate reason. Post Detection Selection Diversity, because all the SNRs are present and we can select the maximum Pre Detection Selection Diversity, because only one Receiver is required compared to Post Detection Selection Diversity where many Receivers are required Post Detection Selection Diversity, because even though more receivers are required we can be sure about the SNR value. RSSI is not a good measure of SNR in high noise system Both Post Detection and Pre Detection Selection Diversity can be implemented as there is no difference between the two in a high noise system. Post Detection Selection Diversity, because even though more receivers are required we can be sure about the SNR value. RSSI is not a good measure of SNR in high noise system 15) For the different diversity schemes MRC : Average SNR for MRC with diversity 2 Cophasing: Average SNR for Cophasing with diversity 2 SC : Average SNR for Selection diversity with diversity 3 Arrange MRC, Cophasing and SC assuming the average SNR of each antenna is same and is given by. MRC > Cophasing > SC SC > MRC > Cophasing MRC > SC > Cophasing Cophasing > SC > MRC MRC > SC > Cophasing A project of 2014 NPTEL - Privacy & Terms - Honor Code - FAQs - In association with Funded by 5/6

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Unit 7 - Week 6 - Wide Sense Stationary Uncorrelated Scattering (WSSUS) Channel Model

X Courses» Introduction to Wireless and Cellular Communications Announcements Course Forum Progress Mentor Unit 7 - Week 6 - Wide Sense Stationary Uncorrelated Scattering (WSSUS) Channel Model Course outline