Final Exam 2012

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University of Toronto, ECE1508 Winter 2012 Page 1 of 11 Name: Student ID: UNIVERSITY OF TORONTO DEPARTMENT OF ELECTRICAL & COMPUTER ENGINEERING ECE 1508 Special Topics in Communications: 4G LTE for Mobile Broadband Date: April 19, 2012 Time: 6 pm – 8:30 pm Examiner: Ivo Maljević Instructions: 1) Only a non-programmable calculator and the provided aid sheet are allowed in the exam. 2) Answer all 7 questions. 3) Write the answer to each question starting on the page of the question and on the following blank page if necessary. 4) Answers must be very clear and show justification. Question 1 2 3 4 5 6 7 Marks

University of Toronto, ECE1508 Winter 2012 Page 2 of 11 1) (6 points ) Answer the following questions: a) Describe the following multiple access schemes: i) FDMA ii) TDMA iii) CDMA iv) OFDMA b) Describe the concept of fractional frequency reuse. c) Describe the concept of soft fractional frequency reuse. d) Determine the sampling rate for the 20 MHz wide LTE channel and the required CPRI interface data rate assuming that each sample is represented by 16 bits and that 2x2 MIMO is used.

University of Toronto, ECE1508 Winter 2012 Page 3 of 11 2) ( 10 points ) Answer the following questions: a) What is the purpose of the RACH channel in LTE? b) What is the purpose of the time gap at the end of the preamble? c) What is the purpose of the repetition of the preamble in RACH formats 2 and 3? d) State one reason why it is a common practice to reserve some of the RACH sequences for non- contention based access. e) Using the table below, determine the time in μ s for the T CP , T SEQ and T GT (hint: find the value for T s first). Enter the calculated values in the table. f) Determine the cell size radius for the preamble formats 2 and 3 using the T GT values determined in e). Enter the calculated values in the table. Preamble format T CP T SEQ T GT Max Cell Radius (km) 2 6240Ts ≈ μ s 2x24576Ts = μ s μ s 3 21024Ts ≈ μ s 2x24576Ts = μ s μ s

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University of Toronto, ECE1508 Winter 2012 Page 4 of 11

University of Toronto, ECE1508 Winter 2012 Page 5 of 11 3) (6 points ) Five hexagonal cells cover a certain geographic area as shown in the figure below. The cell sites are located at the center of each hexagon (black circles), while a single UE is located at the cell edge of the serving cell 1 (white circle). The inter-site distance (distance between the black dots) is 1 km and the pathloss exponent is n = 3.76. Assuming that the thermal noise has a negligible effect, determine the geometry (SINR) at the location where the cell edge UE is. Each cell site transmits with equal power. Cell 1

University of Toronto, ECE1508 Winter 2012 Page 6 of 11

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University of Toronto, ECE1508 Winter 2012 Page 7 of 11 4) (5 points ) Using the tables below (from TS 36.213) select the proper number of resource blocks for the LTE system with the channel bandwidth of 1.4 MHz, and then determine the peak downlink data rates for: a) SISO mode transmission b) MIMO mode transmission Also, using the α -Shannon formula with α =0.75 determine the required SNR for the determined data rates. Assume that the channel bandwidth is equal to the bandwidth determined by the resource blocks. Transport block size table (partial table) TBS I PRB N 1 2 3 4 5 6 7 8 9 10 16 328 632 968 1288 1608 1928 2280 2600 2984 3240 17 336 696 1064 1416 1800 2152 2536 2856 3240 3624 18 376 776 1160 1544 1992 2344 2792 3112 3624 4008 19 408 840 1288 1736 2152 2600 2984 3496 3880 4264 20 440 904 1384 1864 2344 2792 3240 3752 4136 4584 21 488 1000 1480 1992 2472 2984 3496 4008 4584 4968 22 520 1064 1608 2152 2664 3240 3752 4264 4776 5352 23 552 1128 1736 2280 2856 3496 4008 4584 5160 5736 24 584 1192 1800 2408 2984 3624 4264 4968 5544 5992 25 616 1256 1864 2536 3112 3752 4392 5160 5736 6200 26 712 1480 2216 2984 3752 4392 5160 5992 6712 7480 One-layer to two-layer TBS translation table (partial table) TBS_L1 TBS_L2 TBS_L1 TBS_L2 TBS_L1 TBS_L2 TBS_L1 TBS_L2 1544 3112 3752 7480 10296 20616 28336 57336 1608 3240 3880 7736 10680 21384 29296 59256 1672 3368 4008 7992 11064 22152 30576 61664 1736 3496 4136 8248 11448 22920 31704 63776 1800 3624 4264 8504 11832 23688 32856 66592 1864 3752 4392 8760 12216 24496 34008 68808 1928 3880 4584 9144 12576 25456 35160 71112 1992 4008 4776 9528 12960 25456 36696 73712

University of Toronto, ECE1508 Winter 2012 Page 8 of 11

University of Toronto, ECE1508 Winter 2012 Page 9 of 11 5) (5 points ) Using the tables below, determine the peak DL and UL rates for the SS formats 0 and 4, DL/UL configuration 5. Assume that the TDD-LTE system in question uses the system bandwidth of 20 MHz. DL/UL Configuration DL:UL Ratio Subframe number 0 1 2 3 4 5 6 7 8 9 5 9:1 D S U D D D D D D D SS Format DwPTS GP UpPTS 0 3 10 1 4 12 1 1

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University of Toronto, ECE1508 Winter 2012 Page 10 of 11 6) (5 points ) Two eNodeBs are located 1 km from each other. The serving eNodeB is serving 3 users. If each user has a data rate of 1 Mbps, but uses different number of resource blocks, determine: a) Required SINR if user 1 uses 2 RBs, user 2 uses 5 RBs and user 3 uses 12 RBs using the α - Shannon formula with α =0.75. b) Using the SINR values determined in a) determine the distance of each user from the serving eNodeB if the pathloss exponent is n = 3.76 (assume that the thermal noise effect is negligible). c) Determine the distance when the handover will be triggered if user 3 is moving away from the serving cell; the handover trigger condition is when the neighbour’s eNodeB signal is 3 dB stronger t han the serving eNodeB’s signal .

University of Toronto, ECE1508 Winter 2012 Page 11 of 11 7) (5 points ) Answer the following questions: a) What is a soft combining in HARQ? b) Describe UE mobility states. c) What is the purpose of fractional power control in the UL? d) Name two transmission categories in Coordinated Multi Point (CoMP)? e) Determine the receive sensitivity at the UE for a 10 MHz channel if all the resource blocks are allocated to the UE. The noise figure is 7 dB and the required SINR = - 4 dB. f) What is the preferred MIMO mode (open vs. closed loop) in high mobility scenario? g) What are the two main options for voice over LTE?