What enables wireless transmission?

Transmitter

(Electronic Equipment)

Sound waves

Microphone

time

current

frequency 4000 Hz

Audio signal

1

What enables wireless transmission? (2)

• The information signal (e.g. audio) is in the form of a current (or voltage) waveform flowing through a conductor

• How do we get this information signal across a medium that employs NO conductors?

– Efficiently?

– Over reasonable distances?

• Answer: Electromagnetic waves!

2

Electromagnetic spectrum

3

Radio spectrum

VHF TV and FM broadcast Mobile radio

Millimeter waves (EHF)

Super high frequency

(SHF)

Ultra high frequency

(UHF)

Very high frequency

(VHF)

High frequency

(HF)

Medium frequency

(MF)

Low frequency

(LF)

Very low frequency

(VLF)

Audio band

Aeronautical Navigation

Radio teletype

AM broadcast

Business Amateur radio

International radio Citizen’s band

Mobile, aeronautical

UHF TV and mobile radio

Experimental

Navigation Satellite to Satellite

Microwave relay Earth-satellite

Radar Mobile Radio

Microwave Radio

Shortwave Radio

Longwave Radio

100 km

10 km

1 km

100 m

10 m

1 m

10 cm

1 cm

1 kHz

10 kHz

100 kHz

1 MHz

10 MHz

100 MHz

1 GHz

10 GHz

100 GHz

Ground wave propagation

Sky wave propagation

Line-of-sight (LOS) propagation

4

Radio Spectrum (2) • Mode of propagation is dependent on frequency

– Ground wave – Sky wave (ionospheric propagation) – Line-of-sight propagation

• Propagation conditions are heavily dependent on frequency – Free space path loss (inverse square law) – Absorption – atmosphere (e.g. water vapour, atmosphere) – Absorption - vegetation – Reflection, refraction, diffraction – Environmental clutter

• Bandwidth

Fading due to multipath

5

Spectrum allocation and assignment

• International Telecommunication Union – Radiocommunication sector (ITU-RS)

– Regional radio conference (RRC)

– World radio conference (WRC)

• Table of Frequency Allocations

• National spectrum management authorities

– Assign spectrum to service providers, network operators

– Police the use of the spectrum

6

RF channels

• An example: Television broadcasting

7

Modulation

• It is the process by which a signal is translated to another part of the spectrum

• As seen before, the actual spectrum location is dependent on – Nature of the application

– Propagation characteristics of that part of the spectrum

– Spectrum allocation/management authorities

– Antenna size

• Analog modulation techniques – Amplitude modulation

– Angle modulation (i.e. frequency modulation (FM), phase modulation (PM)

8

9

Modulation • Information signal

10

Modulation • Example: amplitude modulated signal

Antennas • An alternating current in a conductor produces

– An alternating electric field

– An alternating magnetic field

Carr, Joseph J. 2001. Antenna Toolkit. 2nd ed. Newnes

11

Antennas (2) • The antenna converts electrical energy into electromagnetic energy (

it is a transducer)

• Energy is radiated in all directions – Depending on the antenna design, more energy may be radiated in

some directions than in others

• For efficient radiation antennas should be at least 1/10 of the wavelength of the e.m. wave

• Baseband signals are low frequency (slow varying) signals. They will require very long (impractical) antennas

12

Antennas (3)

13

Antennas (5)

60 cm DirecTV

26 × 24 cm NetGear ANT24D18 ProSafe Wireless LAN Antenna

1.8 m Log Periodic Yagi Antenna,

http://www.zcg.com.au/log-periodic-yagi-base-station-antennas.htm

14

Antennas (6)

http://www.raymaps.com/index.php/antennas-on-samsung-galaxy-s/

•2.6 GHz WiMAX Tx/Rx Antenna •2.6 GHz WiMAX Antenna Rx Only (as a diversity antenna) •WiFi/Bluetooth Tx/Rx Antenna •Cell/PCS CDMA/EVDO Tx/Rx Antenna •Cell/PCS CDMA/EVDO Rx Only (as a diversity antenna) •GPS Antenna Rx Only

Samsung Galaxy S

15

Electromagnetic waves

mAcos

mVcos

max

max

xtHH

xtEE

z

y

z

y

p

H

E

fv1

22

T

Polarization (Vertical, Horizontal)

16

Electromagnetic waves(2)

• Spatial domain • Time domain

17

Propagation

http://www.nonstopsystems.com/radio/hellschreiber-performance.htm 18

Propagation (2)

http://mysite.verizon.net/k3nco/prop.htm 19