CS6895 Assignments Wireless Networking and Mobile Communications

Assignment 1

1. What are the differences between the following types of wireless channel impairments: path

loss, multipath effect, interference from other sources?

2. As a mobile node gets farther and farther away from a base station, what are two actions

that a base station could take to ensure the bit error rate of transmitted data does not

increase?

3. Assume that the magnitude a signal transmitted over a wireless channel follows a Rayleigh

distribution, whose probability density function is given by p(r) =

r

σ2

exp(

−r2

2σ2

). Suppose

that the bit error rate (BER) becomes intolerable if the signal is 10 dB or more below the

root mean square (RMS) value

√

2σ. Find the percentage of time that BER is too high to

be acceptable. (Hint: first find the cumulative probability distribution function of the signal

magnitude.)

4. Given a stationary transmitter is sending at a center frequency of 900 MHz, the receiver is

travelling at speeds of (a) 1 km/hr; (b) 10 km/hr; (c) 100 km/hr; or (d) 500 km/hr. Draw

a graph of four curves that show deviation of spectral frequencies from the center frequency

for the above four scenarios. Use a legend properly to distinguish different scenarios.

5. Suppose that a mobile node is moving at a speed of 150 km/hr in a typical urban environment

(e.g., highway). It transmits a signal to the base station at a center frequency of fc = 1 GHz

using a binary modulation at a data rate R. It is known that the typical RMS delay spread

στ of multipath propagation in this scenario is around 5 µs. For each of the following cases,

decide if the received signal is best described as undergoing fast/slow fading, frequency

selective fading or flat fading.

(a) The mobile node is sending at a data rate of R = 1 Mbps.

(b) The mobile node is sending at a data rate of R = 500 kbps.

(c) The mobile node is sending at a data rate of R = 50 kbps.

Updated on January 16, 2013 1