Autumn Main Exam SEAT NUMBER: STUDENTNUMBER: L--- ~~--~--~--~----~--~--L-~ SURNAME: (FAMILY NAME) OTHER NAMES: LECTURER NAME:

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1 Autumn 216- Main Exam SEAT NUMBER: iuts UNIVERSITY OF TECHNOLOGY SYDNEY STUDENTNUMBER: L--- ~~--~--~--~----~--~--L-~ SURNAME: (FAMILY NAME) OTHER NAMES: LECTURER NAME: This paper and all materials issued must be returned at the end of the examination. They are not to be removed from the exam centre. Examination Conditions: It is your responsibility to fill out and complete your details in the space provided on all the examination material provided to you. Use the time before your examination to do so as you will not be allowed any extra time once the exam has ended. You are not permitted to have on your desk or on your person any unauthorised material. This includes but not limited to: Mobile phones Smart watches and bands Electronic devices Draft paper (unless provided) Textbooks (unless specified) Notes (unless specified) You are not permitted to obtain assistance by improper means or ask for help from or give help to any other person. During the examination you must first seek permission (by raising your hand) from a supervisor before: Leaving early Using the toilet Accessing your bag Disciplinary action will be taken against you if you infringe university rules Mobile Communications Time Allowed: 2 hours and 1 mins Includes 1 minutes of reading time. Reading time is for reading only. You are not permitted to write, calculate or mark your paper in any way during reading time. This is a Restricted Open Book exam Please refer to the permitted materials below: Permitted materials for this exam: Calculators (non-programmable only) Drawing instruments i.e. Rulers, Set Squares and Compasses Two (2) revision sheets (A4 double-sided). They must be handwritten only. Materials provided for this exam: This examination paper One (1) answer booklet (2 pages) Students please note: All Questions must be attempted. Each question carries a total of 25 Marks. The necessary graphs are provided with the paper. No formulas will be provided. Clearly provide your explanation, reasoning and working for each attempted problem. Do not open your exam paper until instructed. Page 1 of 8

2 4878 Mobile Communications - Main Exam Rough work space Do not write your answers on this page. Page 2 of 8

3 Problem One (25 marks) 4878 Mobile Communications- Main Exam A. A total of24mhz of bandwidth is allocated to a particular FDD cellular telephone system that uses two 2 KHz simplex channels to provide full duplex voice and control channels. Assume each cell phone user generates.1 Erlangs oftraffic. Assume Erlang B model is used. [ 15 Marks] i. Find the number of channels in each cell for a four-cell reuse system. ii. If each cell is to offer capacity that is 9% of perfect scheduling, find the blocking probability and maximum number of users that can be supported per cell where omnidirectional antennas are used at each base station. iii. If each cell covers five square kilometres, then how many subscribers could be supported in an urban market that is 5km by 5km for the case of omnidirectional base station antennas? B. What is the coverage of a base station that transmits a signal at 2kW given that the receiver sensitivity is -1dBm, the path loss at the reference distance (do =1m) is 32dB, and the path loss exponent is n = 4. [1 Marks] Problem Two (25 Marks) A. A wireless system employs a vertical, thin 'A/2 dipole as the transmit antenna, and a thin, vertical, A/2 dipole as the receive antenna. 1. What are the radiation resistances oftx and RX antennas? [4 marks] ii. Assuming ohmic losses represented by Rohmic = I n, what are the radiation efficiencies ofboth of these antennas? [3 Marks] B. A Transmitter provides 15W to an antenna having 12dB gain. The receiver antenna has a gain of 3dB and the receiver bandwidth is 3KHz. If the receiver system noise figure is 8dB and the carrier frequency is 18MHz, find the maximum T -R separation that will ensure that a SNR of 2dB is provided for 95% of the time. Assume log-normal shadowing with cr = 8dB, path loss exponent n = 4, and reference distance do= 1km. [ 8 Marks] C. Consider a transmitted signal s (t) which in a multipath channel takes three significant signal paths to reach the receiver. The received signal r (t) is given by r (t) = ao s (t) + a1 s (t -r 1) + a2 s (t -1: 2) + n(t) where 1:~1 = 1:~1 = -5dB, 1:1 =1J..Ls, 't2 = 8J..Ls and n(t) is the additive white Gaussian noise. Thus, the second of the three components received is the strongest, and the other two are each 1 db (in power) smaller. Drawing the schematic of the impulse response and power delay profile, i) Find the difference in length between the longest and shortest paths? [ 2 Marks] ii) Compute the excess mean delay and root mean square (RMS) delay spread for the channel. [4 Marks] iii) Estimate the coherence bandwidth. [4 Marks] Page 3 of 8

4 4878 Mobile Communications - Main Exam Problem Three (25 marks) A. Consider the average bit error rate (BER) for receive diversity system with maximum ratio combining (MRC) and BPSK modulation. Assume that the average signal to noise ratio (SNR) is 2 db. i) Calculate the average BER when only one receive antenna is present i.e., Nr = 1. [3 marks] ii) Calculate the average BER when three receive antennas are employed, i.e, Nr = 3. [4 marks] B. Consider a CDMA system with a target signal-to-noise-plus-interference ratio (SINR) of 6 db. At the cell boundary, the signal to noise ratio (SNR) is 9 db. The spreading factor is 64 and the orthogonality factor is.4. How many users can be served per cell (disregard adjacent cell interference). [8 marks] C. Four received power measurements were taken at distances of loom, 2m, lkm and 2 km from a base station transmitter. The measured received powers at these distances are: - dbm, -25 dbm, -35dBm, and -38dBm, respectively. The reference distance do= I OOm. It is assumed that the path loss for these measurements follow PL(d)dB = PL(d) +Xu= PL(dO) + 1 n log (ddo) +Xu Find the minimum mean square error (MMSE) estimate of the path loss exponent 'n' and calculate the standard deviation of shadowing about the mean value'. [1 marks] Problem Four A. Consider a mobile radio link with a carrier frequency of fc = 1,2 MHz, a data rate of 3 kilobits/s, and a required maximum bit error rate (BER) of 1 4. The modulation format is differentially detected MSK. A maximum transmit power of 1 dbm (EIRP) is used with 5-dB gain antennas both at Tx and Rx. The noise figure of the Rx is 9 db. The heights of base station (BS) and user mobile (MS) antennas are 4 and 3m, respectively. Assuming a flat-rayleigh-fading channel, calculate the achievable cell radius in a suburban environment using the Okumura-Hata empirical path loss model? (Hint: use empirical formulas) [15 Marks] B. Provide short descriptive answers (using equations if required) to the following: [ 1 marks] i) Discuss the spectral and band width efficiencies of digital modulation systems. ii) What do you understand about a Ricean fading channel? iii) What is the difference between coherence bandwidth and coherence time? iv) What is the significance offresnel zones? v) Discuss how signal is spread in a CDMA system. Page 4 of 8

5 ... ~ 4878 Mobile Communications- Main Exam a:! 1 u -. <;I J: '- - ro - c :u... d/km 7~i ~1 l!: -1 (.) HIO woo Effective BS height hb(m) 7. 1 rl/km co 5 E 4., "' 3 4: ttj ttj ttj ttj 1 Q) X 5 UJ H}O Frequency (MHz) Figl and Fig 2: Okumura Model Page 5 of8

6 4878 Mobile Communications - Main Exam ftmhz 2 : 1 (J) N 'i 7 en 4 E:.c,;;,:"<3 (J) 2 E co ~ IOO E t.> :r: 1 c:: co ;:! u. 2 <I) 1. 4()-.,. - c HJOO e ;::; -(J) (.) ~ (.) " E ! MS Antenna height hm (m} Fig 3 : Okumura Model Fig 4: Determination of percentage coverage area Page 6 of 8

7 4878 Mobile Communications- Main Exam 3 s.,_._.....,_ '-o- -~ -' l.-2 ~-- "--3 Fresnel Oiffra<:tkm P;tmnwter ".L - - -"---...,-. - ' Fig 5: Knife-Edge Diffraction Gain Tabulation of the Q-function z Q(z) ~ Q(::) () ( ') ().()139 ().; : G G %67 : ')..,. - I.:147 1.:3.9() o.oom l.g.548 : : :3593 :3.8.7 Ul.2872 :3.9.5 Page 7 of 8

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