Wireless Glossary: Radio Frequency Terms
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- Antenna
- Antenna (a.k.a. radio antenna, or aerial) is a component designed to transmit and receive radio (and other electromagnetic) waves. An antenna is typically an arrangement of conductors (conducting elements) designed to radiate (transmit) an electromagnetic field in response to being applied with an alternating (AC) voltage/current, or to produce an electrical signal (an alternating voltage or a induced potential difference) between it's two terminals upon being subjected to an electromagnetic field.
- Dipole
- Dipoles are typically low-gain (2.2 dBi) antennas consisting of two (hence the term "Di") antenna elements (or "poles").
- Directional Antenna
- An antenna designed to concentrate transmission power into a direction so as to possibly increase it's coverage distance (range) at the expense of coverage angle. Directional antennas are designed to focus (transmit or receive) maximum power in a certain direction. In reality, however, all practical antennas are (somewhat) directional –at least (omnidirectional) in the plane parallel to the earth. Examples of directional antennas include Yagi, patch, log-parabolic dish antennas, the corner reflector (residential TV antennas), and Cellular repeater antennas.
- Diversity Antenna
- A Diversity Antenna System makes use of a pair of antennas and an intelligent radio that continually senses the success rate of incoming (our transmitted) radio signals and automatically selects the antenna best situated for receiving or transmitting data at a given moment.
- Isotropic Antenna
- Isotropic Antennas denote a rather theoretical/conceptual construct of an (ideal) antenna that radiates its signal through out a perfect sphere -i.e. provides a 360 degrees coverage not only vertically, but also horizontally.
- Parabolic Antenna
- As the name suggests Parabolic Antennas (a.k.a. dish antennas) are constructed using a concave or a dish-shaped object. Parabolic dish antennas are typically suited for point-to-point transmissions (requiring high gain and the narrow beamwidth) for long distance RF links.
- Patch Antenna
- As the name suggests, a Patch Antenna looks like a "flat panel" and is ideally suitable flush wall mounting. It is designed to provide a hemispherical radiation coverage area.
- Yagi
- Yagi-Uda Antennas (commonly known as Yagi Antennas) are a type of midrange-gain, directional antennas constructed using an array of a dipole and a set of parasitic elements.
- dB
- dB stands for: Decibel. It is a unit for measuring relative power ratio and is expressed in Watts. dB denotes gain or loss ratios expressed using the logarithm scale to base 10 of a ratio. It is not an absolute value; but a relative measure of change in signal power level (loss or gain) between two devices.
- Fresnel Effect
- Fresnel Effect (a.k.a. Fresnel diffraction) denotes a phenomenon whereby a transmitted radio signal is degraded by interference by obstacles (i.e. by physical objects) surrounding the path (a.k.a. the line of sight) of a radio beam.
- Gain
- Gain (or Antenna Gain) is computed as the ratio of the output amplitude of a RF signal to the input amplitude of a RF signal, typically expressed in decibels (dB).
- LoS
- LoS is an abbreviation for: Line of Sight. LOS denotes an unobstructed straight line between two radio (transmitting and/or receiving) devices. Line of sight calculations are particularly important for (directional) radio links that need to carry data over longer distances, and must allow for not only the curvature of the earth, but also the Fresnel Effects. In other words, even though theoretical RF Line of Sight (RF LoS) is simply a straight line between the transmitting and receiving antennas, antenna/radio mounting heights must be adjusted so as to accommodate the Fresnel zone. Typically LoS for radio devices not mounted on towers is less than 6 miles (9.65 km).
- Microcell
- The term Microcell describes a bounded physical space designed to accommodate wireless communications among numerous wireless devices. Boundaries of (Isolated or Overlapping) Microcells are established by a set of predefined rules.
- Modulation
- The term Modulation denotes any of many techniques (such as Amplitude Modulation, Freqnency Modulation, etc.) for combining user information (data) with a transmitter (carrier) signal.
- CCK
- CCK is an abbreviation of: Complementary Code Keying. CCK (a modulation technique) allows IEEE 802.11–compliant wireless devices (WLANs) to transmit at data transmission rates reaching 5.5 and 11 Mbps.
- DBPSK
- DBPSK stands for: Differential Binary Phase Shift Keying. DBPSK modulation technique allows IEEE 802.11–compliant wireless LANs to transmit at 1 Mbps.
- DQPSK
- DQPSK stands for: Differential Quadrature Phase Shift Keying. Being a step up from DBPSK (Differential Binary Phase Shift Keying) modulation technique, it allows IEEE 802.11–compliant wireless LANs to transmit at 2 Mbps.
- DSSS
- DSSS stands for: Direct Sequence Spread Spectrum. It is a modulation technique that spreads its signal continuously over a wide frequency band. It is called "Spread Spectrum" because the transmitted signal takes up more bandwidth (hence the work "spread") than the actual information signal that is to be modulated. DSSS phase-modulates a sine wave pseudorandomly using a continuous (of durations smaller than a bit) string of pseudonoise code symbols, and transmits the modulated information bits as a pseudorandom sequence of chips. DSSS is used for many 2.4 and 5.8 GHz cordless phones, and 802.11b and 802.11g based wireless networking devices.
- FHSS
- FHSS is an acronym for: Frequency Hopping Spread Spectrum. It is a method of modulation in which both the transmitter as well as the receiver simultaneously hop (i.e. rapidly switch the carrier among many frequency channels) from one frequency to another according to a prearranged (a pseudorandom sequence) pattern known only to the participating transmitters and receivers.
- OFDM
- OFDM is an abbreviation for: Orthogonal Frequency Division Multiplexing. A variation of OFDM is called Coded OFDM abbreviated or COFDM. OFDM is a signal modulation technique that allows for data transfer speeds of up to 54 Mbps in the 5 GHz RF band. OFDM is also known as Discrete Multitone Modulation or DMT. In order to eliminate/minimize the interference between channels, the frequencies and modulation of FDM are arranged to be orthogonal in OFDM. In doing so, OFDM provides better Multipath resistance.
- Multipath
- The term Multipath describes the propagation of radio signals that are echoed/bounced-off of physical objects along (or near) the intended LoS.
- Range
- Range of a radio transmitter is a linear measure of the distance that it can send a signal to without causing excessive signal degradation.
- Receiver Sensitivity
- Receiver Sensitivity is a measurement of the weakest RF signal that a receiver can receive and still correctly interpret/translate it into data.
- RF
- RF is an abbreviation for: Radio Frequency. The international unit (SI Unit) for measuring frequency is Hertz (Hz), which is equivalent to cycles per second. Frequency of Radio Waves (RF) is usually expressed in terms of: Hz, kHz (One Thousand Cycles/Sec) MHz (One Million Cycles/Sec), or GHz (One Billion Cycles/Sec.)
- Roaming
- The term Roaming describes movement of a wireless node across two Microcell boundaries. Roaming usually occurs in infrastructure networks built around multiple access points arranged so as to provide overlapping Microcells.
- Spread Spectrum
- Spread Spectrum denotes a radio transmission (modulation) technology that Spreads the data being sent over a much wider bandwidth than what would have been required otherwise.