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Code No: R5411907

IV B.Tech I Semester(R05) Supplementary Examinations, May/June 2009 CELLULAR AND MOBILE COMMUNICATIONS (Electronics & Computer Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) Explain the inefficient spectrum utilization based on the existing mobile systems MTS and IMTS (b) Describe the special features in amps and compare these with now a days systems? [8+8] 2. (a) Present the concept frequency reuse channels and frequency reuse distance? (b) Why cell splitting and explain the cell splitting?

[8+8] √

3. (a) Prove that for hexagonal geometry the co channel reuse radio is given byQ = 3N Where N = i2 +ij + j2 . (b) Explain the co channel interference are from the mobile receivers based on test? [8+8] 4. (a) Discuss about the near in distance and long distance propagation? (b) Explain the propagation path loss due to natural and man made structures? [6+10] 5. (a) Discuss the characteristics of cell site antennas? (b) If the antenna heights are varying what are the effects you are getting at the time of operation of mobile system? [8+8] 6. The U.S AMPS system is allocated 50MHz of spectrum in the 800 Mhz range and provides 832 channels. 42 of those channels are control channels. The forward channel frequency is exactly 45MHz greater then the reverse channel frequency. (a) If the AMPS system is simplex, half duplex or full duplex? What is the band width for each channel and how is it distributed between the base station and subscriber? (b) Assume a base station transmits control information on channel 352, operating at 880.560MHz What is the transmission frequency of the subscriber unit on transmitting on channel 352? (c) The A- side and B - Side cellular carriers evenly split the AMPS channels. Find the number of voice channels and the number of control channels for each carrier? (d) let suppose you are chief engineer of a cellular system using seven cell reuse purpose a channel assignment strategy for a uniform distribution of user through out your cellular system specifically , assume that each cell has three control channels (1200 sector is employed)and specify the number of voice channels you would assign to each control in your system? (e) For an ideal hexagonal cellular layout which has an identical cell coverage, what is the distance between the centers of two nearest co channel cells for seven cell reuse? For four cell reuse? [16] 7. (a) Discuss the reasons why hand offs are needed in cellular communication. (b) Determine the probability of requirement for hand offs. 8. Compare the capacity improvement in 120 degree and 60 degree sectoring. ?????

[8+8] [16]

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Code No: R5411907

IV B.Tech I Semester(R05) Supplementary Examinations, May/June 2009 CELLULAR AND MOBILE COMMUNICATIONS (Electronics & Computer Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) Differentiate the generations in the cordless phones and cellular phones? (b) Explain about the dynamic channel assignment?

[10+6]

2. (a) With help of neat diagrams, explain the N cell reuse pattern for four and seven cell reuse? (b) Derive the co channel interference factor for 7 cell reuse pattern?

[9+7]

3. (a) Show that the frequency reuse factor for a cellular system is given by K/S Where K is average number of channels per cell and S is the total number of channels available to the cellular system provider? (b) Explain co channel interference which effects at a cell site?

[8+8]

4. (a) Briefly explain the multiple knife edge diffraction? (b) Explain about the scattering phenomena in mobile system?

[8+8]

5. (a) Describe the effects of the cell site antenna heights and signal coverage cells? (b) Define the following concern to the antennas i. ERP ii. Equivalent aperture iii. Null free pattern iv. 120 o Sector cell.

[6+10]

6. (a) Explain the concept the dynamic channel assignment in detail? (b) Describe the non fixed channel assignment algorithms?

[8+8]

7. (a) How hand offs are prioritized? Explain. (b) Discuss the practical hand off considerations. What is meant by cell dragging? [8+8] 8. (a) Prove that sectoring decreases trunking efficiency with an example. (b) Explain how lowering the threshold level of a received signal increases the coverage area. [8+8] ?????

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Code No: R5411907

IV B.Tech I Semester(R05) Supplementary Examinations, May/June 2009 CELLULAR AND MOBILE COMMUNICATIONS (Electronics & Computer Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) Explain the digital cellular system with TACS (b) Compare and explain the advantages of cellular phones over cordless phones. [8+8] 2. (a) Derive the maximum number calls per hour per cell and the maximum number frequency channels per cell . How are they related? (b) Find the desire co channel interference phenomena in a reuse cellular system that employs omni directional antenna system? [8+8] 3. What is meant by co-channel interference? Derive the expression for Signal to Interference ratio in terms of channel reuse factor considering only the co-channel interference. [16] 4. Explain the terms: delay spread, Coherence bandwidth and confidence interval with a neat figure. [16] 5. (a) Explain in detail importance of consideration of cell site antennas? (b) Assume a receiver is located 10Km from a 50W transmitter. The carrier frequency is 6GHz and free space propagation is assumed Gt =1 and Gr =1W. i. Find the power at the receiver ii. The magnitude of the electric field at the receiving antenna iii. The rms voltage applied to the receiver input assuming that the receiving antenna has purely real importance of 50 ohms and is matched to the receiver. [8+8] 6. (a) Write the procedure to allot the channels for the traveling mobile units? (b) Explain the channel assignment to the cell sites based on the adjacent channels?

[8+8]

7. (a) Discuss the advantages of delayed hand offs. (b) Distinguish between forced hand off and soft hand offs.

[8+8]

8. (a) Briefly explain the diversity in operational techniques. (b) Explain the different co phase techniques. ?????

[9+7]

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Code No: R5411907

IV B.Tech I Semester(R05) Supplementary Examinations, May/June 2009 CELLULAR AND MOBILE COMMUNICATIONS (Electronics & Computer Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) Explain the trunking efficiency? (b) Explain about the mobile fading characteristics?

[8+8]

2. (a) A cellular system uses FDMA with a spectrum allocation of 12.5MHz in each direction a guard band at the edge of the allocated spectrum of 10KHz at channel bandwidth of 30KHz What is the number of the available channels? (b) If 8 Speech channels are provided in a single radio channel and if no guard band is assumed what is the number of simultaneous users that can accommodate in GSM receiver? [8+8] 3. (a) Explain the co channel interference reduction using the directional antenna system? (b) Describe the different type of non co channel interference in the cellular system ? How are they dealt? [8+8] 4. Explain the path loss prediction over hilly terrain with suitable diagrams. 5. (a) Obtain the free space path loss formula from the transmitting antenna end? (b) Obtain the free space path loss formula from the receiving antenna end?

[16] [8+8]

6. The U.S AMPS system is allocated 50MHz of spectrum in the 800 Mhz range and provides 832 channels. 42 of those channels are control channels. The forward channel frequency is exactly 45MHz greater then the reverse channel frequency. (a) If the AMPS system is simplex, half duplex or full duplex? What is the band width for each channel and how is it distributed between the base station and subscriber? (b) Assume a base station transmits control information on channel 352, operating at 880.560MHz What is the transmission frequency of the subscriber unit on transmitting on channel 352? (c) The A- side and B - Side cellular carriers evenly split the AMPS channels. Find the number of voice channels and the number of control channels for each carrier? (d) let suppose you are chief engineer of a cellular system using seven cell reuse purpose a channel assignment strategy for a uniform distribution of user through out your cellular system specifically , assume that each cell has three control channels (1200 sector is employed)and specify the number of voice channels you would assign to each control in your system? (e) For an ideal hexagonal cellular layout which has an identical cell coverage, what is the distance between the centers of two nearest co channel cells for seven cell reuse? For four cell reuse? [16] 7. (a) Explain the queuing handoff mechanism? (b) If the number channels at the cell site N=70 the call holding time is 101S The number of originated calls per hour expressed asλ is 2270. The number of handoff calls attempted per hour is expressed as λ2 is 80. Find the probability of the queuing handoff. calls but not the originated calls . Also find the probability of the queuing the originated calls but not the handoff calls? [8+8] 8. Explain the principle of permanent cell splitting and dynamic splitting techniques. [16] ?????