wireless networking basic Transmission Factors Responsible

phones are also a type of wireless communication and are popular today for people talking to each other worldwide.
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Wireless Basic

Radio Frequency Transmission Factors

Radio frequencies (RF) are generated by antennas that propagate the waves into the air.
Antennas fall under two different categories:

directional and omni-directional.

Directional antennas are commonly used in point-to-point configurations (connecting two distant buildings), and sometimes point-to-multipoint (connecting two WLANs).
An example of a directional antenna is a Yagi antenna: this antenna allows you to adjust the direction and focus of the signal to intensify your range/reach.

Omni-directional antennas are used in point-to-multipoint configurations, where they distribute the wireless signal to other computers or devices in your WLAN. An access point would use an omni-directional antenna. These antennas can also be used for point-to-point connections, but they lack the distance that directional antennas supply

Three main factors influence signal distortion:

• Absorption Objects
  that absorb the RF waves, such as walls, ceilings, and floors
• Scattering Objects 
  that disperse the RF waves, such as rough plaster on a wall, carpet on the floor, or drop-down ceiling tiles
• Reflection Objects 
  that reflect the RF waves, such as metal and glass

Responsible body

The International Telecommunication Union-Radio Communication Sector (ITU-R) is responsible for managing the radio frequency (RF) spectrum and satellite orbits for wireless communications: its main purpose is to provide for cooperation and coexistence of standards and implementations across country boundaries.

Two standards bodies are primarily responsible for implementing WLANs:

• IEEE
  defines the mechanical process of how WLANs are implemented in the 802.11 standards so that vendors can create compatible products.
• The Wi-Fi Alliance
  basically certifies companies by ensuring that their products follow the 802.11 standards, thus allowing customers to buy WLAN products from different vendors without having to be concerned about any compatibility issues.

Frequencies bands:

WLANs use three unlicensed bands:

1. 900 MHz Used by older cordless phones
2. 2.4 GHz Used by newer cordless phones, WLANs, Bluetooth, microwaves, and other devices
3. 5 GHz Used by the newest models of cordless phones and WLAN devices

• 900 MHz and 2.4 GHz frequencies are referred to as the Industrial, Scientific, and Medical (ISM) bands.
• 5 GHz frequency the Unlicensed National Information Infrastructure (UNII) band.
• Unlicensed bands are still regulated by governments, which might define restrictions in their usage.

A hertz (Hz) is a unit of frequency that measures the change in a state or cycle in a wave (sound or radio) or alternating current (electricity) during 1 second.

Transmission Method

Direct Sequence Spread Spectrum (DSSS)
uses one channel to send data across all frequencies within that channel. Complementary Code Keying (CCK) is a method for encoding transmissions for higher data rates, such as 5.5 and 11 Mbps, but it still allows backward compatibility with the original 802.11 standard, which supports only 1 and 2 Mbps speeds. 802.11b and 802.11g support this transmission method.

OFDM (Orthogonal Frequency Division Multiplexing)
increases data rates by using a spread spectrum: modulation. 802.11a and 802.11g support this transmission method.

MIMO (Multiple Input Multiple Output)
transmission, which uses DSSS and/or OFDM by spreading its signal across 14 overlapping channels at 5 MHz intervals. 802.11n uses it. Use of 802.11n requires multiple antennas.

WLAN Standards

Standards	802.11a	802.11b	802.11g	802.11n
Data Rate	54 Mbps	11 Mbps	54 Mbps	248 Mbps (with 2×2 antennas)
Throughput	23 Mbps	4.3 Mbps	19 Mbps	74 Mbps
Frequency	5 GHz	2.4 GHz	2.4 GHz	2.4 and/or 5 GHz
Compatibility	None	With 802.11g and the original 802.11	With 802.11b	802.11a, b, and g
Range (meters)	35–120	38–140	38–140	70–250
Number of Channels	3	Up to 23	3	14
Transmission	OFDM	DSSS	DSSS/OFDM	MIMO