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Wireless Communication Technologies (Radio Waves (Wavelength (m) - the…
Wireless Communication Technologies
Radio Waves
Wavelength (m)
- the distance between points where the wave pattern repeats itself
Period
- the amount of time it takes a wave to complete one cycle
Frequency (Hz)
- the number of waves that pass a given point in space in one second
Phase (degree of lag or lead)
- measures how much ahead or behind a wave is to a reference frequency of the same wavelength
Amplitude
- the greatest distance from equilibrium. The larger the amplitude, the more energy the wave has
Digital Modulation
Frequency Shift-Keying (FSK)
type of frequency modulation, in which
the frequency of the carrier signals varies according to the digital signal changes
requires a larger bandwidth
Phase Shift-Keying (PSK)
the
phase of the carrier signal is changed by varying the sine and cosine inputs
at a particular time
more complex
robust against interference
Amplitude Shift-Keying (ASK)
a type of amplitude modulation that
represents binary data in the form of variations in the amplitude of a signal
low bandwidth requirements
very susceptible to interference
Analog Modulation
Amplitude Modulation (535 - 1,705 KHz)
the
amplitude of the carrier signal is modified
in order to send the input signal
AM is more vulnerable to interference than FM, better sound quality in FM
Frequency Modulation (88 - 108 MHz)
FM is more
restricted in terms of geographical regions it can cover
FM
equipment
requirements are
more costly
modulates the vibration rate or frequency of a carrier signal
Spread Spectrum
- uses a spreading code that produces a noise like signal that is hard to detect and intercept
Direct-Sequence (DSSS)
uses
amplitude modulation to combine the waveforms
of the data and carrier signals
pseudo-noise
is added to the signal
Frequency-Hopping (FHSS)
constantly
switches the carrier signal between frequency channels
using a sequence known by the transmitter and transceiver
pseudo noise randomly applied
Impairments
Multipath propagation
occurs when obstacles reflect signals so that
multiple copies of a signal with varying delays are received
Reflection, Diffraction & Scattering
Attenuation
the
strength of a signal decreases with distance
over a transmission medium.
its
greater at higher frequencies
, causing distortion
Refraction
a
transition from one medium to another results in the bending of radio waves