 | Practice questions in Stallings: Review : 3.1, 3.2, 3.5, 3.7,
3.8, 3.9. Problems: 3.2, 3.4, 3.5, 3.10, 3.15, 3.16, 3.17, 3.19 (second one) |
| Other practice questions (see appendix 3A for help in using dB):
 | Convert the following linear signal-to-noise ratios to dB: 100, 1423,
89323, 234333, 0.14 |
| Convert the following power levels to Watts: 10 dBm, 43 dBm, -12dBm,
-32dBm |
| The average noise level is observed on an oscilloscope as 1mV (note:
that's a voltage). What is the SNR (for power) in dB if the signal voltage
has the following peak-to-peak levels: 1V, 124mV, 1000V |
|
| Transmission Lines:
| Most of the energy that goes "into" a transmission line is stored in
the line. How is it stored? |
| Compute the characteristic impedance and signal propagation speed of
transmission lines with the following characteristics:
 | Coax, inner core diameter is 1.2mm, shield has inner diameter of
6mm, dielectric is Polyethylene. |
| Coax, inner core diameter is 2.5mm, shield has inner diameter of
1.2cm, dielectric is Teflon. |
| Parallel lines, wire diameter is 1mm, spacing is 1cm, dielectric is
Polyethylene. |
|
| Explain what happens to a signal when the end of a finite transmission
line is open, shorted, or terminated with a resistance equal to the
characteristic impedance. |
| Why are reflections in transmission lines generally considered bad? |
| Describe three different ways a designer can (accidentally) change the
characteristic impedance of a transmission line on a printed circuit
board. |
|
| Practice questions in Stallings:
| A/D: Review: 5.11. Problems: 5.20, 5.21 |
| Band-Limited signals:
| Practice drawing
sample waveforms modulated using AM and FM techniques. |
| What are some benefits of modulating a signal on a carrier frequency? |
| Describe the process of AM modulation and de-modulation (recovery). |
| A signal in the band 0-20KHz is amplitude modulated on a carrier at
1MHz. What frequency band is occupied by the resultant signal using
dual-sideband (classic) AM? What about single sideband? |
| A signal in the band 0-20KHz is frequency modulated on a carrier at
1MHz. What bandwidth does the resultant signal use? Assume the maximum
frequency deviation is 5KHz. |
| What are some benefits of constant power-level transmissions? Is AM or
FM constant power? |
|
| RF/Antennas: Review: 4.9, 4.10, 4.11, 4.12. Problems: 4.5, 4.7,
4.8, 4.14
| A transmission system transmits a signal at 2.4GHz with a power of
250mW using a 6cm dipole antenna system with a gain of 1.8dB over an
isotropic antenna. At what distance can far-field metrics be used? What is
the EIRP (in W and dBm)? If the signal is received with an isotropic
antenna 5km away, what is the power received (in W and dBm). Use a free
space loss model. |
| Repeat the last part of the above problem, but use a Hata loss model
instead. Assume an urban environment, 1.5m mobile height, 10m base height. |
| Compute the sensitivity of a receiver with the following
characteristics: Receiver filter bandwidth: 20KHz, LNA NF = 2dB, Temp =
25C. Minimum SNR required = 25dB.
|
|
|
| Security:
| Get your ports probed! Use the
Shields Up!
web site from Gibson Research to examine
your computer's security. Click on all five of the
buttons (File Sharing to Browser Headers) and read through the reports. You may be asked to give a synopsis of
what you found for your computer. Note: You are encouraged to use your home
computer for this if it has Internet connectivity, but you may use a lab
computer if you like. |
| Describe how packet filtering can protect a system. |
| Describe how a proxy server can protect a system. |
| What are some of the disadvantages of using a firewall? |
| Explain how NAT works and how it protects your computer from intruders.
|
|
| Multiplexing:
| Describe the key characteristics of Frequency-, Time- and Code-Division
multiplexing. |
| Give three examples of systems that use FDM. |
| Compare synchronous and asynchronous TDM. |
| Problems:
8.12, 8.13 (omit the part about limiting TDM utilization to 0.8) |
| Eight channels wish to send the following bits (one bit for each
channel): 0,1,1,0,1,1,0,0. You are using an eight-way Walsh code on a CDMA
channel. Show what is actually sent over the channel during eight chip
times. |
| The following eight chips are seen on an 8-way CDMA channel using
Walsh codes: -4,0,0,4,4,0,0,4. What bit was sent by each of the eight
channels? |
| See Walsh codes in action
for yourself. Download the
Excel file: walsh8.xls. Open this up,
change the input vectors, see how the transmitted chips vary, and confirm
that the received vector is the same. |
| What happens if a CDMA sender is simply not present (sends 0's instead
of 1's of -1's)? Experiment with the walsh8 spreadsheet by zeroing out
rows in "chips to send" matrix and see what happens. |
|
| Cellular: Review: 14.1, 14.2, 14.4, 14.9, 14.10. Problems:
14.4
| A cellular system is allocated enough bandwidth for 200 channels. If
the system has a re-use factor of 7 (each cell surrounded by six others
with different channels), how many channels are allowed per cell? What if
the re-use factor is 4? What if the re-use factor is 12? |
| If a 10km x 10km area is to be covered by hexagonal cells with a
diameter of 1km, how many cells are needed? The area of a hexagon with
side of length t (diameter 2t) is
 |
|
| GSM:
| GSM voice sampling is changed to take 6-bit samples instead of 8-bit
samples. How many bits in a 20ms sample will be class IA, IB, and II. Assume
all portions scale linearly. |
| If the channel coding for GSM was changed so that class IB bits are
treated as class II (unencoded), how many bits will be in the resulting 20ms
sample? Assume that the 4-bit trailer is still included for IA. |
| In a GSM TDMA burst, what percentage of the transmitted data is used for
overhead (things other than actual data produced by the RPE-LPC encoder)? |
|
