Wi-Fi Wireless Networks Transmission Methods
Bluetooth Bluetooth is a wireless technology for connecting mobile devices, operating at the 2.45 GHz frequency spectrum. This spectrum allows smooth operation for interconnected devices anywhere on the planet. To overcome interference from related devices, Bluetooth uses frequency hopping (up to 1600 hops per second) and full-duplex communication. However, a drawback is that, due to using the free 2.45 GHz frequency band, devices cannot use many IEEE 802.11 protocols simultaneously without experiencing significant interference issues.
Infrared Radiation Infrared rays have the following characteristics:
- Cannot bypass potential obstacles (e.g., walls)
- High data transmission rate and wide range due to high frequency
- Wide coverage within a space due to ceiling reflections
- Optical contact is necessary with an access point due to their high directivity, which should be located on the ceiling
- The above limitation minimizes signal mobility
- Emitted freely without the need for a license
- Economical equipment, high protection due to short range
Microwaves Unlike infrared, microwaves possess telecommunication properties where their range is not affected by obstacles (e.g., walls) and can exceed 30 to 50 meters, hence differing applications. In the case of WLAN spread spectrum, there are two modes of operation: peer-to-peer, where there is no central base station/access point, nodes are equal, and access to the common medium is regulated by a distributed protocol like CSMA (as in ad hoc WLANs), and with an access point, a central node of the local network -usually connected to a wired trunk network (e.g., the Internet or a large Ethernet LAN)- which controls access to the common medium and acts as a bidirectional repeater.
WLANs with an access point are called infrastructure or structured networks. The usual model describing such networks is as follows: there is a wired trunk network (Distribution System, DS) to which access points (AP) are connected. A group of common nodes (STA) that wirelessly communicate with a specific AP at a specific frequency is called a Basic Service Set (BSS).
The BSS are interconnected via the DS. The STAs of a BSS might not all be within the range of all others, but all must be within the range of the access point.
Wireless Transmission Radio waves are the low frequencies of the electromagnetic spectrum, ranging from about 3 KHz to 300 GHz. Wireless telecommunications typically occur with wide-band radio waves (from 30 MHz to 1 GHz) or microwaves (from 2 GHz to 40 GHz). Lower frequency radio waves generally attenuate relatively quickly as they carry less energy but can penetrate physical barriers. Higher frequency waves propagate over longer distances but are more easily reflected by natural obstacles. Also, the higher the frequency of a wave, the greater its directivity (i.e., it can be emitted in a relatively narrow beam instead of in all directions). Thus, generally speaking, microwaves are directional while wide-band radio waves are not.
Antenna for Point-to-Point WiFi Transmission There are four basic wave propagation methods for wireless telecommunications:
- Ground-Wave Propagation: Low frequencies (up to 2 MHz) that follow the Earth’s curved surface due to atmospheric refraction, covering satisfactory distances. They have the disadvantage of rapid attenuation.
- Sky-Wave Propagation: High frequencies, their power does not easily attenuate, transmitted over long distances through successive reflections from the ionosphere to the ground and vice versa – until they reach the receiver.
- Line-Of-Sight Propagation: Very high frequencies, not reflected by surfaces. The antennas are in visual contact, and the wave is emitted directed from one to the other. Atmospheric refraction must be considered, so this method works better for communications away from the Earth’s surface.
- Two-Ray Ground Reflection