1. CS 590/490 Wireless Networks Baseband Transmissions (1)
A type of signal transmissions in which signals are directly
inserted onto a signal transmission medium
Transmission Medium
Sender
Receiver
Transmission
Data
Digital Signals 1 1
Signals all same shape
Wireless_01/001

2. CS 590/490 Wireless Networks Baseband Transmissions (1)
A type of signal transmissions in which signals are directly
inserted onto a signal transmission medium
Sender
Receiver
Transmission
Analog Signals
Transmission Medium
Signals all same shape
Fundamentals/002

3. CS 590/490 Wireless Networks Baseband Transmissions (2)
A type of signal transmissions in which signals are directly
inserted onto a signal transmission medium
(the shape of the signals are same at the sender, in the transmission
medium and even at the receiver)
A type of signal transmissions that can transmit a signal from single
sender at a time
Host A
Host B
Host C
(Transmission Medium)
Fundamentals/003

4. CS 590/490 Wireless Networks Baseband Transmissions (2)
A type of signal transmissions in which signals are directly
inserted onto a signal transmission medium
(the shape of the signals are same at the sender, in the transmission
medium and even at the receiver)
A type of signal transmissions that can transmit a signal from single
sender at a time 1
(Signals merged)
(Transmission Medium)
Host A
Host B
Host C 1
The receiver receives “ ”,
but can’t tell who sent which signals 1
Fundamentals/004

5. CS 590/490 Wireless Networks + Baseband Transmissions (2)
A type of signal transmissions in which signals are directly
inserted onto a signal transmission medium
(the shape of the signals are same at the sender, in the transmission
medium and even at the receiver)
A type of signal transmissions that can transmit a signal from single
sender at a time
Host A
(Signals merged)
Host C +
Host B
The receiver will receive merged analog
signals, which will sound like gibberish
(Transmission Medium)
Fundamentals/005

6. CS 590/490 Wireless Networks Baseband Transmissions (3)
Two major problems in baseband transmissions
 Only one signal transmitter at a time
 Can’t achieve (high-speed)  (long distance) transmission
Fundamentals/006

7. CS 590/490 Wireless Networks Baseband Transmissions (3)
Two major problems in baseband transmissions
 Only one signal transmitter at a time
Wired networks
= “transmission medium” is “cable”
What if we need to support multiple
simultaneous communication using
the baseband transmission? A B C D E F G
Cable A-F
Cable B-C
Install more cables!
Cable E-F
Cable A-D
(not efficient, but
it would work)
Cable B-G
Fundamentals/007

8. CS 590/490 Wireless Networks Baseband Transmissions (3)
Two major problems in baseband transmissions
 Only one signal transmitter at a time
Wireless networks
= “transmission medium” is “open air”
If we have to use the baseband
transmission, only one user can
use the cell phone at a time
We can’t install another
transmission medium for this
cell.
Your cell phone company may have
To build a tower for each active customer
Fundamentals/008

9. CS 590/490 Wireless Networks ? Baseband Transmissions (3)
We sacrifice
long-distance
signal transmissions
Two major problems in baseband transmissions
 Can’t achieve (high-speed)  (long distance) transmission
Input
(Sender)
Output
(Receiver)
Transmission
Shorter Cable Length
skew & distortion
Digital Signals ?
Transmission Medium
Cable Length
Fundamentals/009

10. Time for one signal cycle
CS 590/490 Wireless Networks
Baseband Transmissions (3)
We sacrifice
Signal frequency
(transmission speed)
Two major problems in baseband transmissions
 Can’t achieve (high-speed)  (long distance) transmission 1
skew & distortion ?
Transmission Medium 1
The minimum signal
pattern possible
Time for one signal cycle
= signal cycle time
Signal cycle 2
# of signal cycles
in one second
Signal frequency
(in Hz)
Fundamentals/010

11. Baseband Transmissions (4)
Summary of baseband transmissions

12. CS 590/490 Wireless Networks Broadband Transmissions (1)
A type of signal transmissions in which signals are first modulated onto
“carrier signals” and then modulated signals are inserted onto a signal
transmission medium
Data 1
Digital Signals
Modulator
Carrier Signal
Carrier Signal De
Modulator
Modulated
Signals
Modulated
Signals
Transmission Medium
Fundamentals/012

13. CS 590/490 Wireless Networks Broadband Transmissions (2)
Carrier signal
= sin curve analog signal defined by three parameters
 A (Amplitude)
Time +v -v
Amplitude (volt or power) t
 F (Frequency) = 1 second / t
Fundamentals/013

14. CS 590/490 Wireless Networks Broadband Transmissions (2)
Carrier signal
= sin curve analog signal defined by three parameters 0
90
180
270 +v
t/4
2t/4
3t/4
Amplitude (volt or power)
 P (Phase) in degree (0  P  360 )
Time t -v
Fundamentals/014

15. CS 590/490 Wireless Networks Broadband Transmissions (3)
Why “carrier signal”?
 Sin carrier signals are known to have no skew or distortion on
the signal-shape (even for long distance transmission)
 Each sin carrier signal has a specific frequency and two carriers
with different frequency can be separated at a receiver
Fundamentals/015

16. CS 590/490 Wireless Networks Broadband Transmissions (3)
Why “carrier signal”?
 Sin carrier signals are known to have no skew even for long
distance transmission
Input
(Sender)
Output
(Receiver)
Transmission
Carrier signals with
a specific frequency
If there is no
“noise”
Distance =  P F A
= decrease
The only limiting factor for transmission
distance = Transmission Power (W)
= not affected
= not affected
Fundamentals/016

17. CS 590/490 Wireless Networks Broadband Transmissions (3)
No “phase”, not “amplitude
but “frequency”
Why “carrier signal”?
 Each sin carrier signal has a specific frequency and two carriers
with different frequency can be separated at a receiver
Senders
Receivers 1
FDM
De-Multiplexer
FDM
Multiplexer
Transmission Medium 2
1  2
Fundamentals/017

18. CS 590/490 Wireless Networks Broadband Transmissions (4)
Called “modulation”
Why “carrier signal”?
Sin analog carrier signal itself does not have any meaning
We override our payload signals on top of the carrier signal
Senders
Receivers
payload
signals
payload
signals
FDM
Multiplexer
De-Multiplexer
Tx Medium
carrier
carrier
modulated
carrier
DeModulator
Modulator
modulated
carrier
carrier
payload
signals
Fundamentals/018

19. Host A
Host C
Host B
Computer D
Computer B
Computer F
Computer A
Computer E
Computer G
Computer C