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

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1 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 How to access the portal. Overview of Cellular Evolution and Wireless Technologies Wireless Propagation and Cellular Concepts Cellular System Design, Capacity, Handoff, and Outage Week 4 - Multipath Fading Environment Week 5 - BER Performance in Fading Week 6 - Wide Sense Stationary Uncorrelated Scattering (WSSUS) Channel Model MGF Part II, WSSUS Model WSSUS Part II, Coherence Time, Doppler Spectrum Doppler, Temporal Characteristics of Fading 1) Let the probability of error in AWGN for a particular modulation type be defined as: P e,awgn = 5e -2γ,where γ is the instantaneous SNR What will be the probability of error in Rayleigh fading channel obtained via integration with average SNR (Γ) = 10 db P e,fading = P (γ) (γ)dγ 0 e,awgn f γ 1 Given f γ γ (γ) = Γ e Γ ) Consider a base station and a mobile system with two antennas. The transmission from base station is picked up by both the antennas which experience different channel conditions and hence different values of instantaneous SNR. The SNR for both the antennas is below the threshold at which the signal can be properly detected. Which of the following diversity technique(s) may lead to a proper detection of the signal? Selection diversity 1/5

2 WSSUS Characterization of Time Dispersive Fading WSSUS Classification of Fading Lec24_notes 3) In the previous question, assume that one of the antennas experiences SNR which is above the required threshold while the other antenna does not. Which of the following diversity technique(s) will lead to a proper detection of the signal in this case? Selection diversity Lec25_notes Lec26_notes Lec27_notes Lec28_notes Quiz : Feedback for week 6 Solutions 4) Consider two users U1 and U2. U1 is a pedestrian walking slowly while U2 is travelling in a car at a much higher speed than U1. Which user will experience a more highly correlated channel? (Here we are talking about correlation in time and not in frequency) U1 U2 Both U1 and U2 will experience same channel Week 7 - Computer simulation of Rayleigh fading, Antenna Diversity Week 8 - Fading - Diversity and Capacity U1 5) Which of the following statements is true? In low Doppler condition, frequency hopping gives better performance Large interleaver size is required for channels with low coherence time None of these Week 9 - Capacity and Introduction to CDMA Week 10 - Introduction to CDMA Week 11 - CDMA Receivers Week 12 MATLAB In low Doppler condition, frequency hopping gives better performance 6) For questions 6 to 11 use the following information. Consider a GSM system with channel bandwidth of 200kHz operating across 10 MHz spectrum. Communication is happening using 2 GHz carrier. A vehicle is moving at 100 kmph. Find the approx. coherence time of the channel. 967 microseconds 470 microseconds 500 microseconds 220 microseconds 967 microseconds 7) For the system in question 5, find the approximate spectral widening at the receiver due to Doppler?(Assume single tap rayleigh fading channel) 300 Hz 370 Hz 230 Hz 400 Hz 2/5

3 370 Hz 8) For the system in question 5, it is decided to incorporate Frequency hopping into the system mentioned in the above question. Find the hop rate to avoid fades. (Assume there is at least one good GSM channel at any instant of time) 1034 per second 500 per second 640 per second 700 per second 1034 per second 9) For the system in question 5, find the maximum number of fades per second that can occur using the expression for N v ) For the system in question 5, if V rms is set as the threshold then find the expected fade duration. 3.7 ms 3.7 µs 1.5 ms 1.5 µs 3.7 ms 11) For the system in question 5, if a user is assigned a time slot and V rms is set as the threshold, find the approximate throughput per user kbps 6.23 kbps 1.08 kbps 2.35 kbps 8.41 kbps 12The power-delay profile of a channel is shown below. Delay(µseconds) Power(dB) /5

4 Calculate the mean delay in microseconds ) For the channel described in question 12, calculate the RMS delay spread in microseconds ) For channel described in question 12, calculate the minimum coherence bandwidth in khz ) Consider a channel with RMS delay spread = 7.1 microseconds. For which of the following symbol rates is an equalizer required? 24.3 Ksymbols/sec 35.1 Ksymbols/sec 5.4 Ksymbols/sec 16) What does the term Doubly Selective Channel imply? Time flat, Frequency selective channel Time-varying, Frequency flat channel Time-varying, Dispersive channel Time flat, Frequency flat channel Time-varying, Dispersive channel 4/5

5 17) Consider a channel with coherence time T C = 2.12 milliseconds and coherence bandwidth B C = 50 KHz. How would the channel appear to a signal with bandwidth of 2 KHz and symbol rate = 5 Ksymbols/sec? Frequency flat, slow fading Frequency selective, slow fading Frequency flat, fast fading Frequency selective, fast fading Frequency flat, slow fading 18) GSM is designed for 900 MHz carrier and vehicular speeds of up to 250 Km/hr with an RMS delay spread(στ) = 15 microseconds. The symbol duration is 3.7 microseconds and duration of a time slot is 577 microseconds. Statement 1 : GSM is a fast fading, frequency flat cellular system. Statement 2 : Channel estimation and tracking is essential when the duration of demodulation exceeds coherence time. State whether the above statements are True/False respectively. True, False False, True True, True False, False False, True Previous Page End 2014 NPTEL - Privacy & Terms - Honor Code - FAQs - 5/5

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

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