Unit 5 - Week 4 - Multipath Fading Environment

Transcription

1 2/29/207 Introduction to ireless and Cellular Communications - - Unit 5 - eek 4 - Multipath Fading Environment X Courses Unit 5 - eek 4 - Multipath Fading Environment Course outline How to access the portal Assignment 4. Overview of Cellular Evolution and ireless Technologies ireless Propagation and Cellular Concepts Cellular System Design, Capacity, Handoff, and Outage eek 4 - Multipath Fading Environment Rayleigh Fading and Statistical Characterization Properties of Rayleigh Distribution BER in Fading, Narrowband vs ideband Channels Characterization of Multipath Fading Channels Choice of Modulation Lec5_notes Lec6_notes Lec7_notes Lec8_notes A user is travelling in a car that is moving towards the base-station to which he point is connected to, at a constant velocity v = 00 kmph. At some point of time the user is nearest to the base-station, and moments later he crosses the BS and starts moving away from his base-station. hich of the following is true about the magnitude of doppler shift? It increases as the user moves towards the BS and keeps increasing as the user crosses the BS with a constant velocity It decreases as the user moves towards the BS and keeps decreasing as the user crosses the BS with a constant velocity It increases first, reaches a maximum value when the user is nearest to his BS and starts falling when the user crosses the BS It decreases first, goes to a zero when the user is nearest to the BS, and keeps increasing once he crosses the BS It decreases first, goes to a zero when the user is nearest to the BS, and keeps increasing once he crosses the BS 2 2. Consider the path-loss model for a log-normal shadowing characterized point statistically by a standard deviation of 5 db. hat should be the margin, if the desired Pr(outage = % You may use Q function table from here : Q function tables 58.5 db.65 db 5.72 db None of these.65 db 3 Consider a multipath channel/system defined by y(t = exp(-at x(t + exp(bt-c point x(t-t0, where x(t is the input to the system and y(t is the corresponding output. a, b, c /6

2 2/29/207 Introduction to ireless and Cellular Communications - - Unit 5 - eek 4 - Multipath Fading Environment Lec9_notes are positive constants. The system is Quiz : Assignment 4 Feedback for week 4 Computer Assignment Quiz : Computer Assignment Questions Assignment 4 Solutions eek 5 - BER Performance in Fading Channels eek 6 - ide Sense Stationary Uncorrelated Scattering (SSUS Channel Model eek 7 - Computer simulation of Rayleigh fading, Antenna Diversity eek 8 - Fading Channels - Diversity and Capacity Linear and Time-Invariant Linear and Time-Variant not linear but Time-Invariant Non-linear and Time-Variant Linear and Time-Variant 4 In which of the following scenarios will the assumption of Rayleigh fading channel be valid? In the absence of Line of Sight component In indoor environments In ultra-wideband systems In the presence of narrow antenna beams In the absence of Line of Sight component 5 Consider a Rayleigh pdf channel type with σ = 3. hat are the mean and RMS values of the distribution respectively? 5.45 and and and and 3.58 point point eek 9 - Capacity and Introduction to CDMA eek 0 - Introduction to CDMA eek - CDMA Receivers eek 2 MATLAB 3.76 and Consider a mobile communication system. hich of the following point characteristic(s should the system possess so that frequency hopping is not required? Signal bandwidth must be sufficiently wide to resolve multipath components Receiver must be able to co-phase and combine the multipath components Both (a and (b None of the above Both (a and (b 7 hich of the following is/are multiplicative impairment(s? point Thermal noise in receiver Rayleigh Fading Both (a and (b None of the above Rayleigh Fading 2/6

3 2/29/207 Introduction to ireless and Cellular Communications - - Unit 5 - eek 4 - Multipath Fading Environment 8 In lecture 9, case 2 of Tse and Viswanath example was discussed where point receiver antenna was moving away from the fixed transmitter. Let the initial distance between the transmitter and the receiver be r 0 = Km. The speed of the receiver is v = 30 meters per second and the transmitting frequency is f c = 800 MHz. hat is the maximum doppler shift (magnitude? 20 Hz 40 Hz 80 Hz 60 Hz 80 Hz 9 In lecture 9, case 3 of Tse and Viswanath example was discussed where point receiver antenna is fixed between the transmitter and a reflecting wall. Let the distance between the transmitter and the reflecting wall be d = 4 Km. The distance between the transmitter and the receiver is r = 3 km. The transmitting frequency is f c = 800 MHz. hat is the coherence distance? Note: The receiver is in between the transmitter antenna and the reflecting wall meters meters meters meters meters 0 In the above question (9., what is the delay spread of the channel? point 6.67 microseconds 3.33 microseconds microseconds.665 microseconds 6.67 microseconds In question(9 what is the coherence bandwidth of the channel? Hint:( Coherence B = /(2*Delay spread point MHz 75 KHz 303 KHz KHz 75 KHz 2 In lecture 9, case 4 of Tse and Viswanath example was discussed where point receiver antenna is moving between the transmitter and a reflecting wall. Let the distance between the transmitter and the reflecting wall be d = 4 Km. The distance between the transmitter and receiver is r = 3 km and the receiver is moving towards the wall with 3/6

4 2/29/207 Introduction to ireless and Cellular Communications - - Unit 5 - eek 4 - Multipath Fading Environment speed v = 60 meters per second. The transmitting frequency is f c = 800 MHz. hat is the range of maximum Doppler Spread? 240 Hz 20 Hz 60 Hz 320 Hz 320 Hz 3 Consider a cellular system designed with omnidirectional cells and with the point farthest point of the cell at a distance R and average signal power received at the cell edge Pr(R= P min, where P min is the receiver sensitivity. Then the Outage Probability P outage will be Insufficient information to make the statement If the log-normal shadowing has a Gaussian distribution with variance σ=8 db, point what should be the margin β at the cell-edge in order to ensure that P outage =0.. Given that Q(.282=0. 8 db 0.8 db 0.3 db Insufficient information to compute the margin β 0.3 db 5 For questions 5 to 9 use the below information. If and are IID Gaussian RVs with zero mean and variance, and and are two RVs satisfying X 2 + Y 2, and =arctan Y/X. Express X and Y in terms of and X=cos ϕ, Y=sin ϕ X=sin ϕ, Y=cos ϕ X= sin ϕ, Y= cos ϕ None of the above point X= sin ϕ, Y= cos ϕ 6 (Continued question.5 rite down the joint pdf f x,y (x, y point 2πσ exp( x 2 + y 2 4/6

5 2/29/207 Introduction to ireless and Cellular Communications - - Unit 5 - eek 4 - Multipath Fading Environment 2πσ 4σ 4 7 (continued question 5 Consider the transformation of variables from (X,Y to (, ϕ The expression for the determinant of Jacobian matrix is point cosϕ sinϕ 2 J = 2 [ sinϕ ] cosϕ cosϕ sinϕ J = [ sinϕ cosϕ ] cosϕ sinϕ J = [ sinϕ cosϕ ] J = 2 2 cosϕ sinϕ 2 2 sinϕ cosϕ cosϕ J = [ sinϕ ] 2 2 sinϕ cosϕ 8 (Continued question. 5 Using transformation of variables, obtain the joint pdf f,φ (w, ϕ point 4πσ 2 2 4πσ 2 2πσ 4πσ 2 9 Assuming that the RV has a uniform distribution i.e., f ( = /2π, obtain the marginal pdf f (w point 5/6

6 2/29/207 Introduction to ireless and Cellular Communications - - Unit 5 - eek 4 - Multipath Fading Environment 4πσ /6