ECET 380 Midterm Exam
1. (TCO 1) Multipath occurs in a radio channel creating small-scale fading due to the following factor:
2. (TCO 1) Frequency is ________________ proportional to wavelength
3. (TCO 1) Doppler shift is _______________ proportional to velocity
4. (TCO 1) The coherence time of a communication channel is estimated to be 500 µs. Small scale propagation measurements are made in real time from a vehicle moving at 50 m/s. Assuming that samples are taken at intervals of half the Coherence time to ensure correlation of consecutive samples, how many samples are taken over a 10 m travel distance?
5. (TCO 1) Assume a discrete channel impulse response is used to model an urban RF radio channel with excess delays as large as 125 µs. If the number of multipath bins is fixed at 64, what is the maximum RF bandwidth which the model can accurately represent?
6. (TCO 1) A spread spectrum system using sliding correlation has the following properties: Chip Rate = 32 Mbps; Slide factor 10-4; 24 shift registers in the sequence generator. What is the time between maximum correlations (ΔT)?
7. (TCO 1) In small scale fading based on multipath time delay spread, flat fading has the characteristics of:
8. (TCO 2) A spatially diverse system using multiple input and output antennas will ________________ the required transmit power.
9. (TCO 2) A certain transmission channel has a bandwidth of 500 kHz. What is the channel capacity if the SNR is 35 dB?
10. (TCO 2) When using multiple antennas, which technique typically increases signal level?
11. (TCO 3) The most popular Nyquist condition pulse shaping filter used in mobile communications is the __________________ filter
12. (TCO 3) A digital mobile communication system has a maximum channel bandwidth of 15 kHz and a spectral efficiency of 1.5 bps/Hz. If we use a rate ½ FEC coder, what is the upper bound of the transmission bit rate that a speech encoder (vocoder) used in the system should provide?
13. (TCO 3) What is the spread spectrum bandwidth of a channel that has hop bandwidth of 250 kHz and 25 frequency hop slots?
14. (TCO 3) What is the processing gain (in dB) of a direct sequence spread spectrum system that has a spreading bit rate of 100 Mbps and a message data rate of 25 kbps?
15. (TCO 3) Two important properties of a pseudo random sequence are _________________ and __________________.
16. (TCO 3) A correlation function equals ____________ if the two signals are identical.
17. (TCO 3) A wireless communication system that has separate frequencies for uplink and downlink connectivity for each user defines this process as:
18. (TCO 3) A TDMA/FDD system uses 32 MHz which is broken down in to 400 kHz channels. If eight total channels are supported on a single radio channel, with four channels assigned to the uplink and four channels assigned to the downlink, how many simultaneous full duplex users can this system support?
19. (TCO 3) A system has eight trailing bits, eight guard bits, 32 synchronizing bits, and three traffic bursts of 64 bits of data per time slot. What is the efficiency of this system?
20. (TCO 4) In a cellular system, channels are reused within _________________.
21. (TCO 4) 2.5G Mobile Radio Networks support
22. (TCO 4) CDMA systems increase a user’s data throughput by
1. List the important antenna parameters and give the definition of three of the parameters of your choice.
2. What are the main differences between MS antennas and BS antennas? List the antennas used at mobile stations and describe the construction and characteristics of one of them in detail.
3. Describe how spatial diversity can be used to improve system performance in wireless communication systems
4. Compare and contrast transmit and receive diversity. Describe how each diversity type lead to an improvement in system performance.
5. What is beamforming? What are the advantages of beamforming? Describe the differences between DOA based beamforming and Eigen beamforming
6. Describe spatial multiplexing. Do you think spatial multiplexing is important? Justify your response