Factors affecting choice of WT for different applications
Maturity of WT
Range of coverage
Frequency band
Sensitivity of application
Security features
Weight
Portability
Cost Related
Cost of equipment
Setup / Installation costs
Recurrent costs
Service and maintenance costs
Upgrading costs
Operational costs
Electromagnetic Waves
Wireless communications sends data signals via EM waves. EM waves travel through space at the speed of light (~ 300,000 km/s)
Created when a changing magnetic field causes a changing electric field, which then causes another changing magnetic field, and so on…
Properties of an EM Wave
Frequency (measured in Hertz, Hz) is the no. of cycles per second
Radio Spectrum
Radio Frequency (RF) Spectrum - 30Hz to 30GHz
Radio Spectrum
Frequency Bands
Very Low Frequencies (VLF)
Frequency (kHz): 3 - 30
Common Usage: Marine shipping
Low Frequencies (LF)
Frequency (kHz): 30 - 300
Common Usage: Cordless telephone
Medium Frequencies (MF)
Frequency (kHz): 300 - 3,000
Common Usage: AM radio
High Frequencies (HF)
Frequency (kHz): 3,000 - 30,000
Common Usage: Short wave radio
Very High Frequencies (VHF)
Frequency (kHz): 30,000 - 300,000
Common Usage: FM radio, TV
Ultra High Frequencies (UHF)
Frequency (kHz): 300,000 - 3,000,000
Common Usage: Cell phones, WLAN 802.11b, Air traffic controller
Super High Frequencies (SHF)
Frequency (kHz): 3,000,000 - 30,000,000
Common Usage: WLAN 802.11a
Extremely High Frequencies (EHF)
Frequency (kHz): > 30,000,000
Common Usage: Radio astronomy
Analog and Digital Signals
Analog Signal
A continuously variable signal that may be represented as a wave
Often a measured response to changes in physical phenomena, such as sound, light, temperature, position or pressure. (e.g. Varying pressure of sound striking a mic)
Digital Signal
A signal that is both discrete and quantised
Digital signals convey information to digital computers to be processed.
How is Data represented?
Data is encoded using coding systems
Examples
ASCII (American Standard Code for Information Interchange)
Max 256 codes using 8 bits (Extended version)
Unicode
Thousands of codes using up to 32 bits
> 90,000 encoded characters
How is Data represented using Signals?
ASCII code for ‘Y’ - 0101 1001
Digital and Analog signals for ASCII
How is Data sent via Radio Waves?
For both analog and digital, data has to be encoded into radio waves before it can be sent. The radio wave acts as a carrier wave.
Modulation
The process of encoding data into the carrier wave
