ETN 4086
Mobile and Satellite Communications
Lab Manual
MSC2: Propagation Path Loss Measurement
At Telecommunications Lab AR4022
All students are expected to read through the manual before attending this laboratory session
Name/ID : ______
Group : ______
Majoring : ______
Date : ______
Previous Reviewer: YL Foo /Sep2010. Updated by LCK / Feb2011. Revised by CKTAN/June2014 4/4
ETN4086 Mobile and Satellite Communications MSC2
EXPERIMENT MSC2
PROPAGATION PATH LOSS MEASUREMENT
1. OBJECTIVES
· To acquire the technique of measuring the propagation path loss.
· To estimate the path loss exponent based on the measured power.
2. INTRODUCTION
Path loss in free space plays an important role in wireless communication system design. It is inevitable in link budget calculation, in determining the signal coverage or the required transmit power. In general, the average large-scale power path loss, , is found to follow this power law equation
/ (1)The power received at distant d is (from Eq. (1) Chapter 3 Lecture note)
/ (2)Or, in the logarithmic form,
/ (3)where d is the transmitter-receiver separation, d0 is the close-in reference distance, n is commonly known as the path loss exponent, and is the power level at d0.
Given the following set of equipment, by applying the above knowledge, the students are to conduct an experiment with the purpose of determining the path loss exponent value, n, for the given environment.
3. EQUIPMENT LIST
Equipment required per group of students:
· 1 unit of walkie-talkie (GP300/328)
· 1 unit of spectrum analyzer (IFR2398)
· 1 unit of measuring tape
· 1 unit of telescopic antenna with suitable connector for connection to the spectrum analyzer
4. PREPARATION
· Read the lab sheet and the relevant materials.
· The followings are required when conducting the experiment: a log book for recording observations and results, graph paper, and a scientific calculator.
5. REFERENCES
· T. S. Rappaport, “Wireless Communications: Principles and Practice,” 2nd edition, Prentice-Hall, Section 4.9.1, 4.9.2, 4.11.3, and 5.6.
· S. Y. Seidel, and T. S. Rappaport, “914 MHz Path Loss Prediction Models for Indoor Wireless Communications in Multifloored Buildings,” IEEE Trans. Antenna and Propagation, vol. 40, no. 2, pp. 207-217, Feb 1992.
6. PROCEDURES
CAUTION!
1. The walkie-talkie batteries are pre-charged and have limited operating hour. Save the power by turning the walkie-talkie ON only when carry out the measurement. Turn it OFF otherwise.
2. The walkie-talkie can overheat if it keeps transmitting (when you hold down the ‘push-to-talk’ button). Press the ‘push-to-talk’ button only when measurement is to be taken. Release the button and turn off the walkie-talkie immediately after the reading has been recorded.
a) The walkie-talkie functions as a transmitter in this experiment, while the spectrum analyzer functions as a receiver.
b) On the walkie-talkie, there is a channel selector and a ‘push-to-talk’ button.
c) Once the walkie-talkie is turned on, it can receive signal at the selected channel. When you hold down the ‘push-to-talk’ button, the walkie-talkie stops receiving and starts transmitting. Transmission stops when the button is released.
d) Connect the telescopic antenna to the spectrum analyzer.
e) The Auto Tune function of the spectrum analyzer is useful for scanning the spectrum. ([Freq] > [Auto Tune]). If the spectrum analyzer picks up a signal within its scanning range, it would indicate the signal’s frequency and power. (Use the Marker function to pinpoint the peak received power and the respective frequency.)
f) You can also use the averaging function of the spectrum analyzer to get the average value from a group of measured values. ([Trace] > [Average] – Turn it ON > [Count] – Choose, for example, 10. Use larger number if necessary.)
g) Determine the transmit frequency of the walkie-talkie and its associated power. Demonstrate to the lab instructor how you did it.
h) Calculate the wavelength, .
i) Determine the noise power level.
j) Given these equipment, you are to design an experiment that allows you to determine the path loss exponent of the environment you are situated in. Basically this requires collecting a set of received power values at various distances from the spectrum analyzer, and then relate the collected data to the path loss model introduced at the beginning of this instruction sheet.
For example, you may follow the following steps:
· Choose a close-in reference distance d0. It must be much larger than both the antenna length and .
· Place the walkie-talkie at d0 meter away from the spectrum analyzer. Turn on the walkie-talkie and press the ‘push-to-talk’ button. Record the received signal power measured at the spectrum analyzer, .
· Measure the received signal power for different transmitter-receiver separation distance d.
Choose a space that is free of obstacle for about 1~3m from the spectrum analyzer. Carry the walkie-talkie and walk in that direction in a straight line. Stop at different spots (i.e. different ‘d’) and set the walkie-talkie to transmit. Record the signal power received at the spectrum analyzer at regular interval of 5m.
· Maintain the same height and same pointing direction of the walkie-talkie throughout the experiment.
7. ANALYSIS OF RESULTS
a) Tabulate the measured values with respect to the distances.
b) The change in is closely related to the change in. Explain how they are related.
c) Plot in dB versus . Draw the best-fit line.
d) Relate the plot to the path loss model introduced at the beginning of this instruction sheet.
Illustrate how you determine the path loss exponent, n, from the plot. Find the minimum mean square error (MMSE) estimate for n.
e) Calculate the standard deviation, s (dB) about the mean value.
8. DISCUSSION
a) Based on the path loss model you have just constructed, estimate the received power at d = 180 m.
b) Evaluate the possibility of reducing s by using a greater number of measurements.
9. MARKING SCHEME
Assessment Components / Marks1 / The level of preparation that is done before the experiment / 10
2 / The level of understanding on the concept of path loss and its log-distance model / 10
3 / Ability to explain the meaning of path loss exponent and its significance / 10
4 / Correctness of the measured transmit frequency and power / 10
5 / Ability to relate the measurement results to the theoretical model and explain the relationship between them / 10
6 / Ability to explain how to determine path loss exponent based on the results / 10
7 / Ability to apply knowledge in statistics in estimating the value of path loss exponent / 10
8 / Correctness of the estimated path loss exponent value / 10
9 / Evaluation on the possibility of reducing the standard deviation value by using a larger number of measurements / 10
10 / Effectiveness in working as a team to ensure smooth running of the lab session / 10
Total / 100
Previous Reviewer: YL Foo /Sep2010. Updated by LCK / Feb2011. Revised by CKTAN/June2014 4/4