16-07-2013, 03:20 PM
cdma systems model questions 2012
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PART A
1. What is the concept of spread spectrum modulation?
2. What are the limitations of DS CDMA?
3. Explain the properties of codes to be used in multiple access schemes.
4. Compare fast and slow frequency hopped spread spectrum.
5. Differentiate between DS SS and FH SS systems.
6. Compare soft and hard hand off strategies.
7. What do you understood by synchronization?
8. Differentiate PIC and SIC receivers.
9. What is MUD?
10. Explain the needs of power control.
11. Define spreading factor in a DS-CDMA system.
12. Draw any three pulse waveforms used in PPH-CDMA system.
13. Explain minimum distance decoding rule.
14. List the randomness properties of maximal length sequences.
15. What are the advantages of using gold codes?
16. Define Shannon capacity of a discrete time Gaussian memory less channel
17. What are the two models that help to determine probability of lost calls?
18. Explain SIC with a neat diagram.
19. Explain the role of decorrelating detector in multiuser detection schemes
20. Define erlang capacity of a CDMA system
Module 1
1. Derive the expression for channel capacity of DS CDMA system.
2. Explain TH SS system with block diagrams.
3. Explain the generation of FH SS signals with the help of diagrams.
4. Explain the uplink and downlink model of a DS CDMA system
5. Find the normalized autocorrelation function and power spectral density of a Manchester pulse used in PPH-CDMA system.
6. Explain BFSK FH spread spectrum non-coherent receiver.
Module 2
1. Consider a DS CDMA system with BPSK, where the spreading sequence is generated by MLSR of length 7. The Channel is undergoing Rayleigh fading. Determining the minimum time to acquisition if K=100, N=Np , Tc=0.5 micro sec, γ=1.2 ,ρB= 8dB.
2. Explain the generation and acquisition of pseudo random signals with help of diagrams.
3. Explain Shannon channel capacity of DS CDMA system.
4. Compare convolutional encoding used in DS CDMA systems with orthogonal convolutional codes.
5. Consider the maximal length sequence generated by the primitive polynomial G(D)=1+D+D3+D4+D6.Verify the balance property, run-length property and delay-add property.
6. Find the total Shannon capacity of a single cell DS CDMA system using omni directional antennas and no voice activity detection(γa=1,γv=1).Assume that channel bandwidth goes to infinity and all users transmit at the same rate R.
Module 3
1. What is the necessity of the power control in CDMA? Explain different methods of power control in CDMA systems.
2. With the help of diagrams the working of optimum receiver.
3. Explain with the help of diagrams, working of a decorrelator detector.
4. Explain decorrelating detectors used in synchronous and asynchronous channels.
5. Explain the different interference cancellation techniques used in CDMA networks
6. Explain MMSE linear multiuser detection technique.