Wireless Communication
CECS 5400
September 19 & 26, 2002
Sharon Smith
Dee Susong
This class is located at
http://courseweb.tac.unt.edu/gjones/fall2002/cecs5400/schedule.html
The class focuses on wireless communications based on modern day communications.
Whatis.com offers the following definition of wireless: Wireless is a term used to
describe telecommunications in which electromagnetic waves (rather than some form of
wire) carry the signal over part or all of the communication path. Some monitoring
devices, such as intrusion alarms, employ acoustic waves at frequencies above the range
of human hearing; these are also sometimes classified as wireless.
http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci213380,00.html
What are some forms of wireless communications?
Common examples of wireless equipment in use today include what?
List five examples.
1.
2.
3.
4.
5.
List a few of the more specialized and exotic examples of wireless communications and
control:
1.
2.
3.
4.
5.
What is frequency? Explain your answer and definition.
http://www.whatis.com
What is 802.11b, 2.4 GHz DSSS (Direct Sequence Spread Spectrum) or DSSS?
http://www.zoom.com/zoomair/index.html
The only thing that changes in frequency is the speed at which it varies.
*** In frequency are we making the waves change or are we changing how often it takes
place?
Check out the following URL’s to find the answer.
Who was the ‘father’ of wireless communication and what did he do to get that
title?
http://www.haarp.alaska.edu/haarp/ion2.html
What is Bluetooth technology and what does it have to do with wireless
communications?
http://www.bluetooth.com/tech/works.asp
Radio Frequencies:
http://courseweb.tac.unt.edu/gknezek/98spring/CECS5400/rf.htm
Radio Frequencies
Class
Abbreviation Range
Applications
1. Extremely low
frequency
ELF
30-300 Hz
110 VAC Power
2. Voice frequency
VF
300-30000
Hz
Telephone Data Modems
3. Very low frequency
VLF
3-30 KHz
Home Security
4. Low frequency
LF
30-300 KHz Cicaria's Experiments
5. Medium freq.
MF
300-3000
KHZ
AM Radio
6. High frequency
HF
3-30 MHz
HF, CB Radio
7. Very high frequency
VHF
30-300 MHz
FM Radio Pecaesat
Experiments, TV
8. Ultra high frequency
UHF
300-3000
MHz
TV
9. Super high frequency
SHF
3-300 GHz
Intel Sat
10. Extremely high
frequency
EHF
30-300 GHz None
The audio/video portion of this class described in detail the many different aspects of this
chart.
Class large group discussion on frequencies: low to
extremely high with examples of each
What can you tell me about radio frequencies? Where does it fall on the chart?
Lower frequencies are called transbound; middle frequencies are normal radio
AM/FM; and high to extremely high frequencies are x-ray and gamma rays.
“Voice frequencies: What are examples of 60 hz? What country?
What do other countries consider standard power supply? Hint: -10 hz. = ?
(example given in video was the song “Hokey Pokey” and it was played in 5
different ways. (no joke) The example was played 5 times to show how a power
supply outlet can super impose information to a source. In this case, the AC power
was the ‘carrier’. (keep thinking frequency…) (wavelengths)
2-way radio: the same; it has 49 mhz- What do we hear from 2-way
communication? (voice)
The ‘carrier’ gets it there and then we don’t need the ‘carrier’ anymore. This is a
VERY SIMPLE form of an explanation for frequencies. He didn’t want to offend
the engineers in the class making it ‘too’ simple but for the novice, he just keeps
saying: DO YOU UNDERSTAND? ARE YOU WITH ME?
Transmitters: example given above in wireless
communication systems; baby monitors; speaker system
with wireless transmitters
What are carrier frequencies?
The _______ carries the signal and the ______________
carries the ‘voice’. (group answer)
When you change the channel on the radio, you are
changing the _(begins with an f)_____________________?
What level do submarines communicate on? (look at the spectrum chart)
High, medium, or low frequencies?
What would the problem be with high frequencies?
Hint: think of the geographical areas
Why is there interference when an airplane flies through
microwaves?
Where are microwaves on the spectrum? What speed does it
take to cook a chicken in the microwave? (ghz)
Globe: A globe was used as an example for sattelittes, the
radio, and transmitters. The transmitters are in the sky and
they are parked in space above the equator because the Earth
spins on it.
Question: What does an amateur radio operator have to do
with atmospheric conditions?
This is the end of the video/audio part I session of the lesson.
This is a link sent by Dr. Jones for us to refer to for more depth
in the area of spread spectrum.
http://www.tapr.org/ss/
Questions:
1. What is Spread Spectrum?
2. List the five different examples of it and briefly explain
each one.
3. What are the advantages and disadvantages to spread
spectrum?
4. Why spread spectrum and list some of the properties of
it?
What are higher frequencies used for?
Links for higher frequency ‘things’:
http://www.gopherlink.com/DeltaXray/
Info on instruments used to measure the The HAARP Ionospheric Observatory uses
numerous scientific instruments to study the earth's geomagnetic environment and
to assess radio propagation conditions. These instruments operate continuously,
monitoring and archiving the naturally occurring variations that take place in
response to the sun's day-to-day and long-term variability.
http://www.haarp.alaska.edu/haarp/data.fcgi
Good resource for pictorial charts on this subject and instruments used.
900mhz telephones: Question: If 10 of your neighbors had the same 900 mhz
telephones, could there be interference with each other?
Cell phones:
World cellular subscribers chart:
http://courseweb.tac.unt.edu/gknezek/telecom/WorldCell.GIF
Most asked TV questions:
Why do I hear a radio station when I watch Channel 13?
I notice in the newspaper TV listings that some shows have a symbol "DVS." What
does "DVS" mean?
Why is it difficult to receive KDTN Channel 2 in some parts of the Metroplex?
What is "High Definition Television (HDTV)?"
Will I need to buy a new television to receive HDTV?
I have heard that the Emergency Broadcast System (EBS) has changed. What is it,
and how will it affect me at home?
Ever wondered how a cellular call works? Look at the anatomy of one:
http://courseweb.tac.unt.edu/gknezek/telecom/CellCall.GIF
Calculating the Frequency of Wavelengths
Wavelength- The distance between successive crest or trough in a wave
Frequency- The number of complete waves passing a point in a given amount of time
Dee will go over this in depth next time we meet. (September 26, 2002)
Consider bits per second to mhz? These are really two different topics. They relate
to each other like a ‘pipe’. MHZ is how WIDE the pipe is and ‘bits per second’ is
‘how fast does the water travel in the pipe’?
Many characteristics of the ‘pipe’.
Standard cable:
See the chart online:
http://courseweb.tac.unt.edu/gknezek/01sum/5400/wavecalculation.html
Audio portion on Radio Frequency Spectrum Part 2 (Real Video 5.0 28.8) is an example
of how long a wavelength is. Explains the calculations.
Standarized cable- tells you how fast it is
but not how it is traveling.
How long does it take to transfer one cd
over a certain type of line?
ISDN- 24 hours
T1- 1 hour (24 phone lines put together)
T3- 2 minutes (these are like long
distance carriers)
“Sneaker net”- 6 seconds - anyone know
what this is??
So to sum it up: use telecommunications
when it is appropriate. Ask yourself the
question: Is it practical?
Last item: look at assignment #3 and how
this class relates to #1 and #2.
Rubric:
Bandwidth of Cable Rates
Service Bandwidth
Approx time to transmit 680MB
ISDN
64Kbps
24 hours, 10 min, 26 sec
T1
1.544Mbps
58 min, 43 sec
T3
44.736
2 min, 2 sec
STS-1
51.840
STS-3
155.240
34.95 sec
STS-12
622.080
8.77 sec
STS-24
1.244360
STS-48
2.488320
TABLE 2-6 Typical Digital Microwave Performance
Band (GHz) Bandwidth (MHz) Data Rate (Mbps)
2
7
12
6
30
90
11
40
90
18
220
274
Source: Stallings, William (1988). Data and Computer Communications, New York:
MacMilliam Publishing Co.