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Characteristics of Wireless Transmission

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Derek Hink

on 6 April 2014

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Transcript of Characteristics of Wireless Transmission

Characteristics of Wireless Transmission
Julian Sarabia
Derek Hink
Signal Degradation
No matter what what type of signal data is transferred, it has to deal with degradation

Fading is a form of degradation. This may weaken the signal and require a repeater (digital) or amplified (Analog)

The type of antenna is determined by the type of wireless service.

This service specifies:
(1) the antenna's power output
(2) frequency
(3) radiation pattern

Wireless signals are still affected by attenuation

Attenuation is not the major flaw in wireless. Noise or (EMI) is. In the context of wireless it is named interference.

(1) Directional Antennas - issue wireless signals along a single direction.

(2) Omnidirectional Antennas issue and receive wireless signals with equal strength and clarity in all directions.
The geographical area an antenna cover is it's

Receivers must be inside it's range to receive signals accurately.
Antennas are responsible for both receiving and transmitting.
Frequency Ranges
From Bird's Eye View, the omnidirectional provides 360 degree coverage.
Vertical coverage is limited.
Mostly relied on the 2.4-2.4835 GHz frequency range which was fine when it was first introduced

Newer ranges started to appear to combat the flaws that the 2.4 frequency band had.

Wireless LAN's now use the 5-GHz band which is then split into four other bands. 5.1,5.2,5.3,5.4 and 5.8 GHz

The newer WLAN uses military radar communication which requires the WLAN to be able to change channels automatically.
Signal Propagation
Propagation refers to how the signal spreads, or travels to it's destination.
Narrow Band, Broadband and Spread Spectrum
Typically, a transmission would follow
Line of Sight (LOS)
(a) LOS uses the least amount of energy
(b) results in the clearest reception
In reality, the signal faces obstacles in it's path.

The signal will either:
1. Pass through the obstacle.
2. Be absorbed by the obstacle.
3. Be reflected
4. Be diffracted.
5. Be scattered.
Reflection is the simplest of the 3 phenomenon.
Narrowband works within a narrow range of frequency bands or even one band.

Broadband, in the other hand, offers a wide range of frequencies that allow the throughput to be even faster then narrowband.
The signal hits the obstacle and bounces back towards the source.
Happens when the obstacle is large in comparison with the signal's average wavelength.
The spread spectrum is another wireless technology that allows the signal to spread around to other frequencies.

There are different types of spread spectrum but are very similar in how data is moved.

FHSS moves data around frequencies within the band in a synched pattern

DSSS is similar to FHSS but the signals bits are distributed over the entire frequency instead of the bands and the entire signal.
The signal strikes a corner and splits. The signal appears to "bend" around corner.

Strength is minimally diminished.
Happens when the obstacle is sharp-angled. Like the edge of a desk or table.
Strength is heavily diminished.
Happens when the obstacle has rough texture or is small compared to the size of the signal's wavelength.
Signal encounters obstacle and reflects in many different directions.

Signal "washes" over the object.
Fixed and Mobile
each type of wireless communications falls into either fixed or mobile categories.

In fixed, the transmitting antenna is at a fixed location.

In mobile, the transmitting antenna is moving around and is usually using omnidirectional antenna to get the best signal
Like wired transmission, wireless relies on Layer 3 and up (Data Link and Physical)

Wireless mainly differs in physical. The lack of a fixed signal path requires the use of an antenna.
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