S-72.1140 Transmission Methods in Telecommunication Systems (5 cr)

1. S-72.1140 Transmission Methods in Telecommunication Systems (5 cr) Solutions for lecture assignments

2. Assignment

3. Solution (i) example: IEEE 802 specifies a large number on local area networking standard. Relating technologies include for instance TDMA, FDMA and CDMA and several technologies of integrated circuit are applied in realization of practical devices (as routers and terminals). IETF standardizes Internet. (ii) Standardization refers to recommendations to assure compatibility among manufacturers, regulation is must that need to be followed as in the way how electrical appliances must be constructed for being safe (iii) Effect of market can be quantified (evaluated) for instance in terms of potential or expanding market size, expected revenues and investment costs required to act or even dominate in the market

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7. Assignment solution:

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9. Conclusions: Nonlinearity is reflected as extra harmonics at the output of the circuit

10. Assignment ans: 20 dB

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15. Solution a) b)

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17. Solution u(t) a) u(-t) u(-t+t1) u(t-t1) u(t+t1), t1>0

18. Solution b)

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22. Assignment Solution: FM can utilize bandwidth expansion to increase post detection SNR. Therefore, information transfer capacity of FM accommodates to channel better than in AM.

23. Assignment Solution:

24. Assignment (i) Briefly summarize what is the main difference between FM and PM ? (ii) How would you generate FM by using a PM modulator? Solution (i) In PM instantaneous phase is directly proportional to modulating signal amplitude, in FM instantaneous frequency is directly proportional to modulating signal amplitude. (ii) One need to integrate the modulating signal before applying it to the PM modulator

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26. Example

27. Assignment • Show that for radio transmission following simplification applies:

28. Assignment • Solution:

29. Assignment • How many dB:s channel SNR should be increased in order to accommodate 16-level signaling?Therefore SNR should be increased 6 dB

30. Assignment Solution M(b) is determined from the condition |Jn(b)| > e, therefore the curve on the previous page can be obtained for instance by fixing a value for b and then adjusting n until the condition is met. Note: n = 1 equals the case with two sidebands (magnitude spectra the same as for AM)

31. Assignment Solution Definition of voltage controlled oscillator (VCO) indicates that it is an FM modulator because its instantaneous output frequency is directly proportional to modulating signal amplitude. Therefore, the signal after VCO is an FM wave. The inherent integration of FM in output phase must be cancelled for PM signal, that is then realized by setting the differentiator to the input of VCO.

32. Assignment Consider the following RC-filter transfer function Inspect the relating group delay and state what is a frequency range of low linear distortion

34. Frequency range of low linear distortion?

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37. Assignment (i) How would you know if a channel has in general non-some linear characteristics? (ii) How would you measure a linear channel? (iii) Suggest how to measure a non-linear channel! (i) Channel output has frequency components that can’t be found in its input (ii) For instance by sending a known signal (frequency spectra) to its input and by monitoring the output. Note the frequency range of the input signal. The result is system transfer function. (iii) The same method as in (ii). However, now both frequency and amplitude of the signal should be changed. Often a single sinusoidal is applied. The result is system transfer characteristics. For more discussions about (ii) and (iii) see few slides ahead.

38. Assignment (i) Determine channel input impedance for Vg=1 V, Rg = 50 ohms and Vi=0.5 V (ii) Assume load impedance is Zl= 50+j10 ohms and Zg= 50 ohms. How much is the dissipation angle theta?

39. Solution (i) Voltage divides evenly between the resistive components. Therefore the load equals internal impedance and matching is perfect. (ii) Dissipation angle follows directly from given equations:

40. Assignment • Channel input has two frequency components at f1=1 kHz and f2=2 kHz. The channel frequency response follows H(f)=exp(-jf). How much is the time difference of the frequency components after this channel? Is this a linear or non-linear channel? • Solution: Both frequency components have the same delay after the channel!

41. Assignment • How would you measure in practice 3rd order intercept point? Ans: it would be required to apply two frequencies to the circuit and adjust the other one by simultaneously monitoring the output by a spectrum analyzer

42. Doppler effect [7] Assignment • How the formulas below explain the change of pitch for a train when it passes a station in full speed? ans: the angle of signal source changes

43. Assignment • How would you measure interference level in a channel? Solution: By monitoring channel output by a spectrum analyzer. If the interference results from channel nonlinearity, for instance 3rd order intercept point measurement could be taken to quantify relative magnitude of the interference.

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46. Assignment Solution: The respective probability must be integrated from Gaussian pdf, yielding for instance in terms of Q-function 2Q(VT/s) where s is the square root ofX.

47. Assignment Explain how the results shown connects to the phasor diagram!

48. Assignment Solution M(b) is determined from the condition |Jn(b)| > e, therefore the curve on the previous page can be obtained for instance by fixing a value for b and then adjusting n until the condition is met. Note: n = 1 equals the case with two sidebands (magnitude spectra the same as for AM)

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50. Solution